Bimodal distribution PS tackifying resin, preparation method thereof and rubber composition

Abstract

The invention relates to the technical field of tackifying resin, in particular to bimodal distribution PS tackifying resin, a preparation method thereof and a rubber composition. The bimodal distribution PS tackifying resin is prepared by adopting a mode that two reaction kettles are connected in series for reaction: in a first reaction kettle, a low-molecular-weight PS component with the number-average molecular weight of 1100-1300 g / mol is synthesized through specific control conditions; and in a second reaction kettle, a specific initiator inhibitor is added, so that the activity of the initiator is reduced, and a part of polymer active chains are continuously subjected to a chain propagation reaction under low activity to generate a high-molecular-weight PS component with the number-average molecular weight of 18000-22000 g / mol. The bimodal distribution PS tackifying resin additive can be used for plasticizing and tackifying modification of rubber, adhesives and other materials, and the actual use effect is excellent.

Description

Technical Field

[0001] This invention relates to the field of tackifying resin technology, specifically to a bimodal PS tackifying resin, its preparation method, and a rubber composition thereof. Background Technology

[0002] In the field of polymer processing, adding functional additives is an important way to optimize the performance of rubber, adhesives, and plastic products. Among them, plasticizers and tackifiers are the core components for adjusting the processing characteristics and performance of the matrix material. The core function of these additives is to reduce melt viscosity to improve processing fluidity without damaging the basic structure of the matrix material, while enhancing the surface adhesion and intercomponent compatibility of the material. They also need to consider key indicators such as the mechanical strength and weather resistance of the finished product. PS (polystyrene) materials have become one of the mainstream choices for plasticizers and tackifiers due to their excellent compatibility with various polymer matrices such as natural rubber and styrene-butadiene rubber, as well as controllable raw material costs and mature preparation processes. They are widely used in industrial fields such as tires, seals, and construction adhesives.

[0003] However, traditional single-molecular-weight PS tackifying resins have significant performance shortcomings, making it difficult to meet the composite performance requirements of high-end products. While low molecular weight polystyrene (PS) with a number-average molecular weight (Mn) < 2000 g / mol can effectively reduce the Mooney viscosity of the rubber matrix and significantly improve the processing efficiency of compounding, extrusion, and other processes, and can penetrate into the gaps between rubber molecular chains to enhance the surface adhesion and interfacial bonding of the material, thus exhibiting excellent plasticizing and tackifying effects, this type of component lacks mechanical support. Excessive addition can lead to a significant decrease in key mechanical properties of rubber products, such as tensile strength and tear strength, and can also significantly reduce the anti-aging properties and solvent resistance of the products, making it unsuitable for applications with stringent mechanical performance requirements, such as automotive tires and engineering machinery seals. On the other hand, high molecular weight polystyrene (Polystyrene) with a number-average molecular weight (Mn) > 15000 g / mol can improve the mechanical strength and anti-aging stability of rubber products through molecular chain entanglement, its long molecular chains and high melt viscosity not only make it difficult to exert a plasticizing effect, but also increase the processing difficulty of the matrix material, reduce production efficiency, and have a very limited effect on improving the adhesion of the material, thus failing to meet the core requirements for adhesion in adhesives and pressure-sensitive tapes.

[0004] To address the performance contradictions of polystyrene with different molecular weights, the industry has commonly employed physical blending, mixing low-molecular-weight and high-molecular-weight polystyrene in specific proportions to create composite additives. This aims to achieve a balance between plasticizing and tackifying properties and mechanical enhancement. However, physical blending only achieves macroscopic component mixing and cannot achieve uniform dispersion at the molecular level. During storage or processing, component stratification and agglomeration are prone to occur, leading to uneven distribution of the additive within the matrix material. This not only fails to fully leverage the synergistic effect of the two molecular weight components but also causes fluctuations in the performance of rubber products, severely impacting product quality stability. Therefore, developing a styrene-based additive that can achieve molecular-level blending and possesses both excellent plasticizing and tackifying effects and improved mechanical properties has become a pressing technical challenge in the modification of rubber and other polymer materials. Summary of the Invention

[0005] The purpose of this invention is to provide a bimodal distribution PS tackifying resin, its preparation method, and a rubber composition containing the same, so as to solve the problems in the prior art where single molecular weight PS tackifying resins cannot simultaneously achieve plasticizing and tackifying effects and mechanical property improvement, and where it is difficult to achieve molecular-level dispersion and poor performance stability in the preparation of composite additives by physical blending.

[0006] To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing a bimodal PS tackifying resin, comprising the following steps: S1. Connect the first and second reactors in series; S2. Styrene monomer and initiator are added to the first reactor to carry out the first polymerization reaction, and a first component containing low molecular weight PS is obtained. S3. The first component containing low molecular weight PS in the first reactor is transferred to the second reactor. An initiator inhibitor is added to allow some of the low molecular weight PS to undergo a second polymerization reaction to generate high molecular weight PS. After the reaction is completed, a product containing both low molecular weight PS and high molecular weight PS is obtained, which is a bimodal PS tackifying resin. Among them, the number average molecular weight (Mn) of low molecular weight PS is 1100~1300 g / mol, and the number average molecular weight (Mn) of high molecular weight PS is 18000~22000 g / mol.

[0007] As an feasible example, the number average molecular weight (Mn) of the low molecular weight PS is 1200 g / mol; the number average molecular weight (Mn) of the high molecular weight PS is 20000 g / mol; this molecular weight range can more accurately match the plasticizing and tackifying requirements of the rubber matrix with the balance requirements of mechanical properties.

[0008] As an feasible example, the reaction temperature of the first polymerization reaction is 20~40℃, the reaction time is 1~2.5 h, and the initiator is 0.8~1.2% of the mass of styrene monomer.

[0009] As an feasible example, the reaction temperature of the second polymerization reaction is -40 to -20°C, the reaction time is 2 to 3.5 h, and the molar ratio of initiator inhibitor to initiator is (0.6 to 1): 1.

[0010] Furthermore, the initiator inhibitor includes dimethylacetamide (DMA).

[0011] In this invention, the first reactor rapidly generates low molecular weight PS components through a high initiator concentration and a high temperature; in the second reactor, the chain growth rate is controlled by inhibiting the initiator and lowering the temperature, ensuring the orderly generation of high molecular weight PS components.

[0012] As an feasible example, in the second reactor, the PS polymer molecules continuing the chain growth reaction account for 10-25% of the total PS polymer molecules delivered from the first reactor. This proportion range allows the low molecular weight plasticizing and tackifying components to achieve the best synergistic effect with the high molecular weight reinforcing components. Furthermore, the initiator used in both the first and second reactors is a Lewis acid initiator, preferably AlCl3. AlCl3 has the characteristics of high activity and strong reaction controllability, enabling precise control of the PS polymer molecular weight distribution.

[0013] The initiator selected in this invention is Lewis acid AlCl3. The activity of AlCl3 initiator originates from its empty orbitals accepting electron pairs to activate styrene monomers. Dimethylacetamide, as a nucleophile, has a strong electron-donating ability in its amide bond, which can form a stable complex with AlCl3, thereby occupying the active site of the initiator, reducing its activity, and achieving precise control of the polymerization rate. However, it does not completely terminate the polymerization reaction, but only weakens the initiator activity, satisfying the requirement for the slow chain growth of some low molecular weight PS polymer active chains in the second reactor to generate high molecular weight PS components, thus avoiding the problem of not being able to form a bimodal molecular weight distribution due to complete initiator deactivation.

[0014] The second aspect of the present invention provides a bimodal PS tackifying resin prepared by the above-described method for preparing bimodal PS tackifying resin. The bimodal PS tackifying resin additive achieves molecular-level blending, and the low molecular weight and high molecular weight PS components are uniformly dispersed, thus simultaneously playing the roles of plasticizing and tackifying as well as mechanical reinforcement.

[0015] The third aspect of the present invention provides a rubber composition, the raw materials for which, by mass parts, comprise: 100 parts of rubber matrix, 8-35 parts of bimodal PS tackifying resin, 1-3 parts of vulcanizing agent, 0.5-2 parts of accelerator and 20-50 parts of reinforcing agent.

[0016] As an feasible example, the rubber matrix is ​​one or more of natural rubber, styrene-butadiene rubber, or cis-butadiene rubber. This type of rubber matrix is ​​widely used in tires, seals, hoses and other fields. It has good compatibility with the bimodal distribution PS tackifying resin additive of the present invention and has a significant performance improvement effect.

[0017] As an feasible example, the vulcanizing agent includes sulfur, the accelerator includes N-cyclohexyl-2-benzothiazole sulfenamide (CBS), and the reinforcing agent includes carbon black N330. The synergistic effect of these components can further optimize the performance of rubber products.

[0018] As an implementable example, the method for preparing the rubber composition includes the following steps: The rubber matrix, bimodal PS tackifying resin, and reinforcing agent are mixed in a two-roll mill or internal mixer at 80-110°C for 10-20 min to achieve initial dispersion of the components. Then, the vulcanizing agent and accelerator are added, and the mixture is further mixed at 60-80°C for 5-10 min to avoid premature reaction of the vulcanizing agent due to high temperature. Finally, the compound is vulcanized at 150-170°C and 10-15 MPa for 15-30 min to obtain a stable rubber composition.

[0019] Beneficial effects (i) The use of a dual-reactor series process, instead of traditional physical blending, allows low molecular weight (Mn≈1200 g / mol) and high molecular weight (Mn≈20000 g / mol) PS components to be uniformly dispersed at the molecular level, avoiding the layering and agglomeration problems that are easy to occur in physical blending. This allows the plasticizing and thickening effect of the low molecular weight component to fully synergize with the mechanical strengthening effect of the high molecular weight component, maximizing the performance advantages of the two components.

[0020] (ii) Compared with single molecular weight additives, the bimodal PS tackifying resin provided by the present invention can reduce the Mooney viscosity of the rubber matrix and improve the processing fluidity and adhesion through low molecular weight components, while maintaining or even improving the tensile strength, tear strength and other mechanical properties of rubber products by high molecular weight components, while ensuring anti-aging and solvent resistance, thus solving the technical contradiction in the industry that plasticization inevitably reduces strength.

[0021] (III) The temperature, initiator concentration, inhibitor ratio and other parameters of the preparation process in this invention have clear and stable control ranges. The first reaction vessel can quickly synthesize low molecular weight components, and the second reaction vessel can accurately control the chain growth rate to generate high molecular weight components. The whole process is controllable and repeatable, does not require complex special equipment, and has the conditions for large-scale industrial production.

[0022] (iv) The bimodal PS tackifying resin provided by the present invention has excellent compatibility with mainstream rubber matrices such as natural rubber, styrene-butadiene rubber, and cis-butadiene rubber. It can be widely used in many fields such as tires, seals, hoses, and adhesives. At the same time, it can also be adapted to plasticizing and tackifying modification of other polymer materials such as plastics, providing a new technical solution for polymer modification.

[0023] (v) Rubber compositions containing bimodal PS tackifying resins not only have a smooth processing after mixing and vulcanization, but also achieve balanced and stable performance in terms of Mooney viscosity, tensile strength, elongation at break, hardness, and other indicators of the finished product. Compared with rubber products with single molecular weight or physical blending additives, the performance fluctuations are smaller, and the quality requirements of industrial products can be better met. Attached Figure Description

[0024] Figure 1 This is a GPC (gel permeation chromatography) spectrum of bimodal PS tackifying resin, where the sharp peak on the left represents high molecular weight PS and the broad peak on the right represents low molecular weight PS. Detailed Implementation

[0025] Examples 1-5 Examples 1-5: The first aspect provides a method for preparing a bimodal PS tackifying resin, comprising the following steps: S1. Connect the first and second reactors in series; S2. Styrene monomer and AlCl3 are added to the first reactor to carry out the first polymerization reaction, and a first component containing low molecular weight PS with a number average molecular weight (Mn) of 1200 g / mol is obtained. S3. The first component containing low molecular weight PS with a number average molecular weight (Mn) of 1200 g / mol in the first reactor is transferred to the second reactor. DMA is added to carry out the second polymerization reaction to obtain a product containing low molecular weight PS and high molecular weight PS with a number average molecular weight (Mn) of 20000 g / mol, namely bimodal PS tackifying resin, which is denoted as BPS-1 to BPS-5.

[0026] The GPC (gel permeation chromatography) spectra of BPS-1 to BPS-5 are as follows: Figure 1 As shown.

[0027] The dosage and parameters of the components involved in the preparation process of Examples 1-5 are detailed in Table 1.

[0028] Table 1

[0029] The second aspect of Examples 1-5 provides bimodal PS tackifying resins BPS-1 to BPS-5 prepared by the above-described method for preparing bimodal PS tackifying resins. The specific physical properties of the products are detailed in Table 2.

[0030] Table 2

[0031] Where D (molecular weight distribution index) = Mw / Mn.

[0032] The third aspect of Examples 1-5 provides a rubber composition, the raw materials of which, by mass parts, include: 100 parts of natural rubber, 20 parts of bimodal PS tackifying resin (i.e., BPS-1 to BPS-5), 2 parts of sulfur, 1 part of CBS and 40 parts of carbon black N330.

[0033] The method for preparing the rubber composition includes the following steps: Natural rubber, bimodal PS tackifying resin, and 40 parts of carbon black N330 were mixed in a two-roll mill or internal mixer at 100°C for 10 min to achieve initial dispersion of the components. Then, sulfur and CBS were added, and the mixture was further mixed at 70°C for 10 min to avoid premature reaction of the vulcanizing agent due to high temperature, thus obtaining a compound. Finally, the compound was vulcanized at 160°C and 12 MPa for 30 min to obtain a stable rubber composition.

[0034] Comparative Example 1 This example provides a single low molecular weight PS tackifying resin additive, including the following steps: Styrene monomer and AlCl3 were added in a single reactor. The reaction temperature was controlled at 15℃, and the amount of AlCl3 added was 1% of the amount of styrene monomer. The reaction was carried out for 1.5 hours to prepare a low molecular weight PS tackifying resin with a number average molecular weight (Mn) of 1200 g / mol. This resin was used as a comparative additive and was designated as PS-1.

[0035] Comparative Example 2 This example provides a single high molecular weight PS tackifying resin additive, including the following steps: Styrene monomer and n-butyllithium were added in a single reactor. The reaction temperature was controlled at 65°C. The amount of n-butyllithium added was 1% of the amount of styrene monomer. The reaction was carried out for 2.5 hours to prepare a high molecular weight PS tackifying resin with a number average molecular weight (Mn) of 20,000 g / mol. This resin was used as a comparative additive and was designated as PS-2.

[0036] Comparative Example 3 This example provides a physically blended bimodal distribution PS tackifying resin additive, including the following steps: The two components, PS-1 and PS-2, were added to a high-speed mixer at a mass ratio of 7:3 and mixed at 220°C for 30 minutes to obtain a physically blended bimodal distribution PS tackifying resin additive, which was used as a control additive and designated as PS-3.

[0037] Rubber compositions were prepared for PS-1, PS-2, and PS-3 according to the method in Example 1. The performance test results of the rubber compositions are detailed in Table 3; sample number 1 is the blank control group, i.e., no tackifying resin additive was added.

[0038] Table 3

[0039] 1. Processing fluidity analysis The Mooney viscosity of the blank control group was 82, the highest among all groups, indicating that the rubber matrix had the worst processing fluidity without the addition of tackifying resin. The group with added PS-1 had the lowest Mooney viscosity. Low molecular weight components can effectively reduce the intermolecular forces of rubber molecules and improve fluidity, but this also confirms that while low molecular weight components improve processability, they also have shortcomings in mechanical properties. In contrast, the groups with the bimodal distribution tackifying resins BPS-1 to BPS-5 of this invention had Mooney viscosities between 73 and 75, which were significantly lower than the blank control group and slightly higher than PS-1, and slightly lower than PS-2 and the physically blended additive PS-3. This indicates that the bimodal distribution resin can ensure processing fluidity while avoiding subsequent performance loss due to over-plasticization, achieving a preliminary balance between processability and mechanical properties.

[0040] 2. Mechanical property analysis Tensile strength: The tensile strength of the blank group was 19.8 MPa; the tensile strength of the group with added PS-1 decreased to 18.4 MPa, indicating the weakening effect of low molecular weight components on mechanical strength; the group with added PS-2 had the highest tensile strength, but poor flowability; while the groups with added BPS series resins had tensile strengths between 18.7 and 20.1 MPa, with BPS-4 reaching 20.1 MPa, close to the level of PS-2 and much higher than PS-1, while the tensile strength of BPS-3 was the same as that of the blank group, indicating that the high molecular weight components in the bimodal distribution PS tackifying resin can effectively compensate for the strength shortcomings of the low molecular weight components, achieving plasticization without "reducing strength"; the tensile strength of the physically blended PS-3 group was 19.7 MPa, which was close to that of the blank group, but the improvement in flowability was not as great as that of the BPS series.

[0041] Elongation at break: The elongation at break of the blank group was 265%; the elongation at break of the groups with added BPS series resins ranged from 278% to 294%, which was generally higher than that of the blank group, PS-2 and PS-3. Among them, the elongation at break of BPS-2 was slightly higher than that of PS-1, indicating that the bimodal resin retained the toughening advantage of the low molecular weight component while not reducing the flexibility of the rubber due to the addition of the high molecular weight component, and the overall toughness performance was excellent.

[0042] 3. Hardness Analysis The hardness of the blank control group rubber was 81 Shore A; the hardness of the groups with added BPS series resins was between 82-86 Shore A, slightly higher than that of the blank control group; and the hardness of PS-1 was the same as or slightly higher than that of PS-2 and PS-3. This indicates that the bimodal distribution PS tackifying resin can maintain or even moderately increase the hardness of rubber while improving the processability and mechanical properties of rubber, which can meet the application requirements of rubber products with specific hardness requirements.

[0043] In summary, compared with single-molecular-weight PS tackifying resin additives and physically blended PS tackifying resin additives, the bimodal distribution PS tackifying resin of the present invention can improve the processing fluidity of rubber while taking into account tensile strength and elongation at break, thus achieving a balanced optimization of processing performance and mechanical properties, and has a better overall performance.

Claims

1. A method for preparing a bimodal PS tackifying resin, characterized in that, Includes the following steps: S1. Connect the first and second reactors in series; S2. Styrene monomer and initiator are added to the first reactor to carry out the first polymerization reaction, and a first component containing low molecular weight PS is obtained. S3. The first component containing low molecular weight PS in the first reactor is transferred to the second reactor. An initiator inhibitor is added to allow some of the low molecular weight PS to undergo a second polymerization reaction to generate high molecular weight PS. After the reaction is completed, a product containing both low molecular weight PS and high molecular weight PS is obtained, which is a bimodal PS tackifying resin. Among them, the number average molecular weight of low molecular weight PS is 1100~1300 g / mol, and the number average molecular weight of high molecular weight PS is 18000~22000 g / mol.

2. The method for preparing bimodal PS tackifying resin according to claim 1, characterized in that, The reaction temperature of the first polymerization reaction is 20~40℃, the reaction time is 1~2.5 h, and the initiator is 0.8~1.2% of the mass of styrene monomer.

3. The method for preparing the bimodal PS tackifying resin according to claim 1, characterized in that, The initiator is Lewis acid.

4. The method for preparing the bimodal PS tackifying resin according to claim 3, characterized in that, The Lewis acid includes AlCl3.

5. The method for preparing the bimodal PS tackifying resin according to claim 1, characterized in that, The reaction temperature of the second polymerization reaction is -40 ~ -20℃, the reaction time is 2 ~ 3.5h, and the molar ratio of initiator inhibitor to initiator is (0.6 ~ 1):

1.

6. The method for preparing the bimodal PS tackifying resin according to claim 5, characterized in that, The initiator inhibitors include dimethylacetamide.

7. A bimodal PS tackifying resin prepared by the method of any one of claims 1-6.

8. A rubber composition, characterized in that, The raw materials for preparation, by mass parts, include: 100 parts rubber matrix; 8-35 parts of the bimodal PS tackifying resin as described in claim 7; 1-3 parts vulcanizing agent; 0.5 to 2 parts accelerator; 20-50 parts of reinforcing agent.

9. The rubber composition according to claim 8, characterized in that, The rubber matrix is ​​one or more of natural rubber, styrene-butadiene rubber, or cis-butadiene rubber.

10. The rubber composition according to claim 8, characterized in that, The vulcanizing agent includes sulfur, the accelerator includes N-cyclohexyl-2-benzothiazole sulfenamide, and the reinforcing agent includes carbon black N330.

Images