A neoprene rubber adhesive for automotive interiors

Abstract

This invention relates to the field of adhesive technology, specifically to a chloroprene rubber adhesive for automotive interior trim. The invention first prepares a pre-ring-opening benzoxazine solution and an o-aminophenylboronic acid-modified catechol polymerizable dispersion. Then, chloroprene rubber and chlorinated polypropylene are co-dissolved and pre-positioned, allowing the chlorinated polypropylene to enter the polymethyl methacrylate bridge during the methyl methacrylate grafting stage. Subsequently, the catechol polymerizable dispersion is added dropwise for post-grafting. After the free radical reaction is terminated, 1,4-phenylenediboronic acid and the pre-ring-opening benzoxazine solution are introduced to form a locally heat-resistant locked structure. Finally, styrene-isoprene-styrene block copolymer, hydrogenated C9 petroleum resin, antioxidant, and non-benzene solvents are added for viscosity adjustment and filtration. The resulting adhesive is suitable for pre-treatment-free composite bonding of automotive polypropylene interior trim parts, improving interfacial stability and adhesion retention after heat aging.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and more specifically to a neoprene rubber adhesive for automotive interiors. Background Technology

[0002] Neoprene rubber adhesives possess good initial tack, film-forming properties, and workability, and are commonly used for composite bonding of interior trim components such as automotive door panels, dashboard liners, pillar trims, and headliner edge components. These components typically involve materials such as PVC skin, polyurethane foam backing fabric, polypropylene, and polyolefin thermoplastic elastomers. The adhesive not only needs to be compatible with soft coverings but also needs to form a stable bonding interface on low surface energy polyolefin substrates.

[0003] Existing neoprene adhesives generally exhibit good adhesion to materials such as PVC skins, fabrics, and foams, but their direct adhesion to non-polar substrates like polypropylene is insufficient. Due to the low surface energy and limited polar groups of polypropylene, flame treatment, plasma treatment, or the application of a primer are often required in actual production to enhance surface activity. However, such pretreatments increase the difficulty of process steps and control, and are prone to adhesion fluctuations due to uneven treatment, surface contamination, or differences in storage time.

[0004] To improve the adhesion properties of polypropylene, existing technologies often incorporate chlorinated polypropylene as a tackifying component into chloroprene rubber adhesives. While chlorinated polypropylene exhibits some compatibility with the polypropylene substrate, it is usually added as a resin component after the grafting reaction, maintaining interfacial bonding with chloroprene rubber primarily through physical mixing and chain entanglement. Although this method improves initial adhesion, it is difficult to ensure that the chlorinated polypropylene remains stably in the effective stress-bearing position, making it prone to chain migration and interfacial slippage under thermal aging, thermal cycling, and continuous loads.

[0005] Automotive interior parts are constantly exposed to sunlight, heat accumulation in the cabin, and temperature cycling. The adhesive layer must maintain flexibility to accommodate the deformation of the plastic parts while possessing sufficient cohesive strength to resist softening under heat. Simply increasing the amount of heat-resistant resin or crosslinking components in existing neoprene adhesives can easily lead to hardening, embrittlement, and decreased coating adaptability of the adhesive layer. Conversely, relying solely on elastomers and tackifying resins to improve flexibility is insufficient to suppress interfacial creep at high temperatures.

[0006] Furthermore, traditional solvent-based chloroprene rubber adhesives often use benzene-based solvents to achieve good solubility, but automotive interiors have high requirements for odor, volatile organic compound release, and environmental safety. While non-benzene-based solvent systems can reduce environmental pressure, they place higher demands on the co-solubility, evaporation rate matching, and film uniformity of chloroprene rubber, chlorinated polypropylene, tackifying resin, and elastomer. If not properly controlled, this can still lead to phase separation, localized adhesive shortages, and bond instability.

[0007] Therefore, existing chloroprene rubber adhesives for automotive interiors still face technical challenges in addressing issues such as weak adhesion of polypropylene interior parts without pretreatment, slippage due to thermal aging of post-chlorinated polypropylene, difficulty in balancing heat resistance and flexibility of the adhesive layer, and insufficient stability of non-benzene solvents during application. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide a neoprene rubber adhesive for automotive interiors, in order to solve the problems of weak interface, easy slippage due to heat aging, and insufficient construction stability of existing neoprene rubber adhesives in the pretreatment-free bonding of polypropylene automotive interior parts.

[0009] To achieve the above objectives, the present invention provides a chloroprene rubber adhesive for automotive interiors, which is prepared from the following raw materials in parts by weight: 9000-11000 parts of chloroprene rubber, 1100-1500 parts of chlorinated polypropylene, 1300-1900 parts of bisphenol A type benzoxazine resin, 45-75 parts of o-aminophenylboronic acid, 150-250 parts of dopamine methacrylamide, 4200-5400 parts of methyl methacrylate, 215-271 parts of initiator, 110-170 parts of 1,4-phenylenediboronic acid, 70-90 parts of hydroquinone, 1500-2500 parts of elastomer, 2000-3000 parts of tackifying resin, 300-500 parts of antioxidant, and a non-benzene solvent. The chlorinated polypropylene enters the system during the dissolution stage of the chloroprene rubber. The methyl methacrylate forms a polymethyl methacrylate bridge in the coexisting region of the chloroprene rubber and chlorinated polypropylene under the initiation of benzoyl peroxide. The dopamine methacrylamide is added after the polymethyl methacrylate bridge is formed after being modified with o-aminophenylboronic acid. The 1,4-phenylenediboric acid is added together with the pre-ring-opening benzoxazine solution after the free radical grafting reaction is terminated, so that a local heat-resistant locked structure containing boron-oxygen bonds and boron-nitrogen interactions is formed in the adhesive.

[0010] Preferably, the chloroprene rubber is type A-90 chloroprene rubber; Preferably, the chlorinated polypropylene has a chlorine content of 25%-27%, and the viscosity of the 10wt% toluene solution at 25°C is 0.2-0.8 dPa·s.

[0011] Preferably, the initiator is benzoyl peroxide, specifically a stabilized product containing 75 wt% benzoyl peroxide and 25 wt% water.

[0012] Preferably, the elastomer is a styrene-isoprene-styrene block copolymer, specifically SIS-1105, manufactured by Yueyang Petrochemical.

[0013] Preferably, the tackifying resin is hydrogenated C9 petroleum resin, HM-1300.

[0014] Preferably, the antioxidant is one of KY-405 and antioxidant 264.

[0015] Preferably, the non-benzene solvent includes butanone, dimethyl carbonate, methylcyclohexane, acetone, and cyclohexane, all of which are industrial grade.

[0016] Preferably, the amount of the non-benzene solvent used is such that the solid content of the resulting adhesive is 16%-30%.

[0017] Preferably, the bisphenol A type benzoxazine resin needs to undergo pre-ring-opening treatment before use. The pre-ring-opening treatment includes: heating to 150-160°C under nitrogen flow rate of 80-120 mL / min, stirring at 80-150 r / min for 5-15 min, and then heating to 160-170°C and holding at that temperature for 15-25 min.

[0018] Preferably, the o-aminophenylboronic acid and dopamine methacrylamide are mixed in anhydrous ethanol and acetone under light-protected and nitrogen-protected conditions, and then treated with activated 4A molecular sieves to obtain an o-aminophenylboronic acid-modified catechol polymerizable dispersion.

[0019] Preferably, the preparation temperature of the anthranilic acid-modified catechol polymerizable dispersion is 30-40℃, the stirring time is 30-50 min, and the 4A molecular sieve treatment time is 10-30 min.

[0020] Preferably, the adhesive has a viscosity of 100-150 mPa·s at 25°C.

[0021] A method for preparing a neoprene rubber adhesive for automotive interior trim includes the following steps: S1 Preparation of pre-ring-opened benzoxazine solution: Bisphenol A type benzoxazine resin is added to a reaction vessel equipped with nitrogen protection, stirring and reflux condensation function, and pre-ring-opening is carried out under nitrogen protection. Then, butanone and dimethyl carbonate are added to obtain pre-ring-opened benzoxazine solution. S2 Preparation of anthranilic acid-modified catechol polymerizable dispersion: Anhydrous ethanol, acetone, anthranilic acid and dopamine methacrylamide were mixed under light protection and nitrogen protection, and filtered after treatment with 4A molecular sieve to obtain anthranilic acid-modified catechol polymerizable dispersion. S3 Pre-positioning of chloroprene rubber and chlorinated polypropylene co-solution: Mix methyl ethyl ketone, dimethyl carbonate, methyl cyclohexane, chloroprene rubber and chlorinated polypropylene, and stir at 50-60℃ to obtain a mixed adhesive solution; S4. Grafting of methyl methacrylate: Add the first part of methyl methacrylate and the first part of benzoyl peroxide to the mixed adhesive solution obtained in step S3, and react at 74-78°C to obtain an adhesive solution with polymethyl methacrylate bridging. S5. Catechol grafting: Add the anthraquinone-boronic acid-modified catechol polymerizable dispersion obtained in step S2 to the adhesive solution obtained in step S4, and simultaneously add the second part methyl methacrylate, dimethyl carbonate and the second part benzoyl peroxide, and continue the reaction at 74-78℃. S6 is used for supplementary initiation and termination: Benzoyl peroxide (part 3) is added to the system obtained in step S5 to continue the reaction, followed by the addition of hydroquinone to terminate the free radical reaction; S7 Locking of benzoxazine and bifunctional boric acid: 1,4-phenyldiboronic acid is dispersed in anhydrous ethanol and acetone, and then added together with the pre-ring-opened benzoxazine solution obtained in step S1 into the system obtained in step S6, and stirred at 50-60℃. S8 Mixing and adjusting viscosity: Add methylcyclohexane, dimethyl carbonate, acetone, cyclohexane, styrene-isoprene-styrene block copolymer, hydrogenated C9 petroleum resin and antioxidant to the system obtained in step S7. After stirring evenly, adjust the solid content of the obtained adhesive to 16%-30% using a non-benzene solvent to obtain a chloroprene rubber adhesive for automotive interiors.

[0022] Preferably, the methyl methacrylate is added in two parts, with the first addition being 3400-4200 parts and the second addition being 800-1200 parts.

[0023] Preferably, the benzoyl peroxide is added in three parts: the first addition is 120-150 parts, the second addition is 55-65 parts, and the third addition is 40-56 parts.

[0024] Preferably, the stirring time in step S3 is 120-180 min.

[0025] Preferably, in step S4, when the viscosity of the system reaches 300-450 mPa·s at 25°C, the process proceeds to step S5.

[0026] Preferably, in step S5, the anthraquinone-boronic acid modified catechol polymerizable dispersion is added dropwise to the adhesive solution obtained in step S4 within 20-40 minutes.

[0027] Preferably, in step S6, hydroquinone is added to terminate the free radical reaction when the viscosity of the system reaches 800-1100 mPa·s at 25°C.

[0028] Preferably, in step S8, a non-benzene mixed solvent consisting of butanone, acetone and cyclohexane in a mass ratio of 1:2:1 is used to adjust the viscosity of the adhesive to 100-150 mPa·s, and the adhesive is filtered through a 100-mesh filter.

[0029] Preferably, the adhesive is used for bonding automotive interior grade polypropylene substrates that have not been flame-treated, plasma-treated, or coated with a primer; the automotive interior grade polypropylene substrate is a polypropylene substrate found in automotive door panels, dashboard liners, pillar trims, or headliner edge components.

[0030] The beneficial effects of this invention are: This invention introduces chlorinated polypropylene during the dissolution stage of chloroprene rubber and forms polymethyl methacrylate bridging through methyl methacrylate and benzoyl peroxide, transforming the chlorinated polypropylene from a later-stage free tackifying component into an interface anchoring segment. This helps improve the bonding stability of polypropylene interior parts without pretreatment and reduces the risk of interface slippage after heating.

[0031] This invention introduces dopamine methacrylamide into the grafting system after preprotection with o-aminophenylboronic acid, resulting in a more concentrated distribution of the catechol structure in the later stages of the bridging chain and the interfacial transition region. This treatment reduces the oxidative deactivation of catechol during reaction and storage, allowing the adhesive layer to maintain good interfacial rebinding ability after thermal cycling and thermal aging.

[0032] This invention involves adding 1,4-phenylenediboric acid together with a pre-ring-opening benzoxazine solution after free radical grafting termination, forming local heat-resistant buffer nodes with boron-oxygen bonds and boron-nitrogen interactions within the bridge, which can improve the cohesive stability under high-temperature conditions while maintaining the flexibility of chloroprene rubber.

[0033] This invention uses a non-benzene solvent system composed of methyl ethyl ketone, dimethyl carbonate, methyl cyclohexane, acetone and cyclohexane, and combines it with styrene-isoprene-styrene block copolymer, hydrogenated C9 petroleum resin and antioxidant for tackification and stabilization treatment, which helps to balance the adhesive's coatability, initial tack, adhesive layer flexibility and the environmental protection requirements of automotive interiors.

[0034] Compared with existing chloroprene rubber adhesives that rely on surface pretreatment or post-physical blending of chlorinated polypropylene, this invention is more suitable for the composite bonding of polypropylene interior parts such as automotive door panels, dashboard liners, pillar trims, and headliner edge parts. It can reduce flame treatment, plasma treatment, or primer coating processes and improve adhesion retention and construction adaptability in high-temperature cabin environments. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0036] The source and model parameters of the raw materials used in this embodiment are as follows: Chloroprene rubber: Type A-90 chloroprene rubber; Chlorinated polypropylene: Toyobo Co., Ltd., HARDLEN 13-LP, is a chlorinated polyolefin with a chlorine content of 25%. A 10wt% toluene solution has a viscosity of 0.5 dPa·s at 25°C. Benzoxazine resin: Huntsman ARALDITE MT35600, is a bisphenol A type benzoxazine thermosetting resin; Benzoyl peroxide: a stabilized product containing 75 wt% benzoyl peroxide and 25 wt% water; Styrene-isoprene-styrene block copolymer: SIS-1105, Yueyang Petrochemical; Tackifying resin: Henghe Materials, HM-1300 hydrogenated carbon nine petroleum resin, softening point is 130℃; Anti-aging agent: KY-405.

[0037] Example 1: A method for preparing a neoprene rubber adhesive for automotive interior trim, the specific steps of which are as follows: S1 Preparation of pre-ring-opened benzoxazine solution: 1600g of bisphenol A type benzoxazine resin was added to a conventional reaction vessel equipped with nitrogen protection, stirring, and reflux condensation. The temperature was raised to 155℃ under nitrogen flow rate of 100mL / min, stirred at 100r / min for 10min, and then raised to 165℃ and held for 20min to allow the benzoxazine resin to undergo partial ring-opening rather than complete curing. 1g of the material was added to 9g of a mixed solvent composed of butanone and dimethyl carbonate in a 1:1 mass ratio. If no gel particles appeared after stirring at 50℃ for 10min, the reaction vessel was cooled to 50℃, and 3000g of butanone and 3000g of dimethyl carbonate were added. Stirring was continued for 30min to obtain a pre-ring-opened benzoxazine solution, which was then sealed for later use. S2 Preparation of anthranilic acid-modified catechol polymerizable dispersion: Add 600g of anhydrous ethanol, 3000g of acetone, 60g of o-aminophenylboronic acid and 200g of dopamine methacrylamide to a light-proof container. Stir at 35°C for 40min under nitrogen protection. Then add 100g of activated 4A molecular sieve and continue stirring for 20min. Finally, filter through a 100-mesh filter to remove the molecular sieve and obtain an o-aminophenylboronic acid modified catechol polymerizable dispersion. S3 is used for the co-solution prepositioning of chloroprene rubber and chlorinated polypropylene: Add 10,000 g of butanone, 12,000 g of dimethyl carbonate and 20,000 g of methylcyclohexane to the reaction vessel. After purging with nitrogen for 15 min, add 10,000 g of chloroprene rubber and 1,300 g of chlorinated polypropylene. Heat to 55°C and stir at 200 r / min for 150 min to obtain a mixed adhesive solution without obvious particles. S4 was grafted with methyl methacrylate: Add 3800g of methyl methacrylate to the mixed adhesive solution obtained in step S3, stir for 15 minutes and then heat to 76°C; then add 130g of benzoyl peroxide, keep the reaction at this temperature for 45 minutes, and take a sample every 15 minutes to measure the viscosity at 25°C; when the viscosity of the system reaches 400mPa·s, proceed to the next step. S5 is grafted with catechol: Add the anthraquinone-modified catechol polymerizable dispersion obtained in step S2 dropwise to the reaction system in step S4 over 30 min, while adding 1000 g of methyl methacrylate and 3000 g of dimethyl carbonate; after the dropwise addition is complete, add 60 g of benzoyl peroxide and continue the reaction at 76 °C for 60 min. S6 is used to supplement and terminate: When the viscosity of the system obtained in step S5 reaches 650 mPa·s at 25°C, add 48 g of benzoyl peroxide and continue the reaction at 76°C for 30 min; when the viscosity reaches 1000 mPa·s at 25°C, dissolve 80 g of hydroquinone in 1000 g of acetone before adding it to the reaction system, continue stirring for 10 min, and then cool down to 55°C. S7 performs the locking of benzoxazine and bifunctional boric acid: 140g of 1,4-phenyldiboronic acid was added to 600g of anhydrous ethanol and 5000g of acetone and stirred at 50°C for 30min to form a dispersion. Then, it was added together with all the pre-ring-opened benzoxazine solution obtained in step S1 to the system obtained in step S6 and stirred at 55°C for 90min. S8, for routine mixing and viscosity adjustment: The system obtained in step S7 was cooled to 45°C, and 5000g of methylcyclohexane, 3000g of dimethyl carbonate, 9000g of acetone and 14000g of cyclohexane were added. Then, 2000g of styrene-isoprene-styrene block copolymer, 2500g of hydrogenated C9 petroleum resin and 400g of antioxidant were added sequentially. The system was stirred at 200r / min for 120min until homogeneous. The system was then cooled to 25°C. Based on the viscosity test results at 25°C, the viscosity was adjusted to 130mPa·s using a non-benzene mixed solvent composed of methyl ethyl ketone, acetone and cyclohexane in a mass ratio of 1:2:1. The mixture was then filtered through a 100-mesh filter to obtain the chloroprene rubber adhesive for automotive interiors.

[0038] Example 2: The difference from Example 1 is as follows: When preparing the pre-ring-opening benzoxazine solution, 1450g of bisphenol A type benzoxazine resin was added to a conventional reaction vessel equipped with nitrogen protection, stirring, and reflux condensation. The temperature was raised to 152℃ under nitrogen flow rate of 90mL / min, stirred at 100r / min for 12min, and then raised to 162℃ and held for 23min. 1g of the material was added to 9g of a mixed solvent composed of butanone and dimethyl carbonate in a mass ratio of 1:1. After stirring at 50℃ for 10min without the appearance of gel particles, the reaction vessel was cooled to 48℃, and 2800g of butanone and 2800g of dimethyl carbonate were added. Stirring was continued for 25min to obtain the pre-ring-opening benzoxazine solution. When preparing the anthranilic acid-modified catechol polymerizable dispersion, 550g of anhydrous ethanol, 2800g of acetone, 52g of anthranilic acid and 180g of dopamine methacrylamide were added to a light-proof container. The mixture was stirred at 32°C for 45 min under nitrogen protection. Then, 90g of activated 4A molecular sieve was added and the mixture was stirred for another 15 min. The molecular sieve was then removed by filtration through a 100-mesh filter to obtain the anthranilic acid-modified catechol polymerizable dispersion. When S3 is performing co-solution prepositioning of chloroprene rubber and chlorinated polypropylene, 9500g of butanone, 11500g of dimethyl carbonate and 19000g of methylcyclohexane are added to the reactor. After purging with nitrogen for 12 minutes, 9500g of chloroprene rubber and 1200g of chlorinated polypropylene are added. The temperature is raised to 52℃ and stirred at 180r / min for 160 minutes to obtain a mixed solution without obvious particles. When performing methyl methacrylate grafting in step S4, add 3600g of methyl methacrylate to the mixed adhesive solution obtained in step S3, stir for 12 minutes, and then heat to 75°C; then add 125g of benzoyl peroxide, keep the reaction at this temperature for 48 minutes, and take samples every 15 minutes to measure the viscosity at 25°C; when the viscosity of the system reaches 360mPa·s, proceed to the next step. When performing catechol grafting in step S5, the catechol polymerizable dispersion modified with o-aminophenylboronic acid obtained in step S2 is added dropwise to the reaction system in step S4 within 35 min, along with 900 g of methyl methacrylate and 2800 g of dimethyl carbonate. After the addition is complete, 58 g of benzoyl peroxide is added, and the reaction continues at 75 °C for 65 min. When S6 is used for supplementary initiation and termination, when the viscosity of the system obtained in step S5 reaches 600 mPa·s at 25°C, 44 g of benzoyl peroxide is added, and the reaction is continued at 75°C for 35 min; when the viscosity reaches 900 mPa·s at 25°C, 75 g of hydroquinone is pre-dissolved in 900 g of acetone and added to the reaction system, and the mixture is stirred for 9 min, and then cooled to 52°C. When performing the locking of benzoxazine and bifunctional boric acid in step S7, 125g of 1,4-phenyldiboronic acid is added to 550g of anhydrous ethanol and 4800g of acetone, and stirred at 48°C for 35min to form a dispersion. Then, the dispersion is added together with all the pre-ring-opening benzoxazine solution obtained in step S1 to the system obtained in step S6, and stirred at 52°C for 95min. During the routine mixing and viscosity adjustment in step S8, the system obtained in step S7 is cooled to 42°C, and 4800g of methylcyclohexane, 2800g of dimethyl carbonate, 8500g of acetone and 13000g of cyclohexane are added. Then, 1800g of styrene-isoprene-styrene block copolymer, 2200g of hydrogenated C9 petroleum resin and 350g of antioxidant are added sequentially. The mixture is stirred at 180r / min for 140min until the system is homogeneous. Subsequently, the temperature is lowered to 25°C. Based on the viscosity test results at 25°C, the viscosity is adjusted to 110mPa·s using a non-benzene mixed solvent composed of butanone, acetone and cyclohexane in a mass ratio of 1:2:1. After filtration through a 100-mesh filter, the chloroprene rubber adhesive for automotive interiors is obtained.

[0039] Example 3: The difference from Example 1 is as follows: When preparing the pre-ring-opening benzoxazine solution, 1750g of bisphenol A type benzoxazine resin was added to a conventional reaction vessel equipped with nitrogen protection, stirring, and reflux condensation. The temperature was raised to 158℃ under nitrogen flow rate of 110mL / min, stirred at 130r / min for 8min, and then raised to 168℃ and held for 18min. 1g of the material was added to 9g of a mixed solvent composed of butanone and dimethyl carbonate in a mass ratio of 1:1. After stirring at 50℃ for 10min without the appearance of gel particles, the reaction vessel was cooled to 53℃, and 3300g of butanone and 3300g of dimethyl carbonate were added. Stirring was continued for 35min to obtain the pre-ring-opening benzoxazine solution. When preparing the anthranilic acid-modified catechol polymerizable dispersion, 650g of anhydrous ethanol, 3300g of acetone, 68g of anthranilic acid and 230g of dopamine methacrylamide were added to a light-proof container. The mixture was stirred at 38°C for 35 min under nitrogen protection. Then, 110g of activated 4A molecular sieve was added and the mixture was stirred for another 25 min. The molecular sieve was then removed by filtration through a 100-mesh filter to obtain the anthranilic acid-modified catechol polymerizable dispersion. When S3 is performing co-solution prepositioning of chloroprene rubber and chlorinated polypropylene, 10500g of butanone, 12500g of dimethyl carbonate and 21000g of methylcyclohexane are added to the reactor. After purging with nitrogen for 18 minutes, 10500g of chloroprene rubber and 1400g of chlorinated polypropylene are added. The temperature is raised to 58℃ and stirred at 220r / min for 130 minutes to obtain a mixed solution without obvious particles. When performing methyl methacrylate grafting in step S4, add 4100g of methyl methacrylate to the mixed adhesive obtained in step S3, stir for 18 minutes, and then heat to 77°C; then add 145g of benzoyl peroxide, keep the reaction at this temperature for 42 minutes, and take samples every 15 minutes to measure the viscosity at 25°C; when the viscosity of the system reaches 430mPa·s, proceed to the next step. When performing catechol grafting in step S5, the catechol polymerizable dispersion modified with o-aminophenylboronic acid obtained in step S2 is added dropwise to the reaction system in step S4 within 25 min, along with 1150 g of methyl methacrylate and 3300 g of dimethyl carbonate. After the addition is complete, 63 g of benzoyl peroxide is added, and the reaction continues at 77 °C for 55 min. When S6 is used for supplementary initiation and termination, when the viscosity of the system obtained in step S5 reaches 740 mPa·s at 25°C, 54 g of benzoyl peroxide is added, and the reaction is continued at 77°C for 25 min; when the viscosity reaches 1050 mPa·s at 25°C, 88 g of hydroquinone is pre-dissolved in 1150 g of acetone and added to the reaction system, and the mixture is stirred for 12 min, and then cooled to 58°C. When S7 is used to lock benzoxazine with bifunctional boric acid, 160g of 1,4-phenyldiboronic acid is added to 650g of anhydrous ethanol and 5300g of acetone, and stirred at 53°C for 25min to form a dispersion. Then, it is added together with all the pre-ring-opening benzoxazine solution obtained in step S1 to the system obtained in step S6, and stirred at 58°C for 85min. During the routine mixing and viscosity adjustment in step S8, the system obtained in step S7 is cooled to 48°C, and 5300g of methylcyclohexane, 3300g of dimethyl carbonate, 9500g of acetone and 15000g of cyclohexane are added. Then, 2300g of styrene-isoprene-styrene block copolymer, 2800g of hydrogenated C9 petroleum resin and 470g of antioxidant are added sequentially. The mixture is stirred at 220r / min for 100min until the system is homogeneous. Subsequently, the temperature is lowered to 25°C. Based on the viscosity test results at 25°C, the viscosity is adjusted to 145mPa·s using a non-benzene mixed solvent composed of butanone, acetone and cyclohexane in a mass ratio of 1:2:1. After filtration through a 100-mesh filter, the chloroprene rubber adhesive for automotive interiors is obtained.

[0040] Example 4: The difference from Example 1 is as follows: When preparing the pre-ring-opening benzoxazine solution, 1300g of bisphenol A type benzoxazine resin was added to a conventional reaction vessel equipped with nitrogen protection, stirring, and reflux condensation. The temperature was raised to 150℃ under nitrogen flow rate of 80mL / min, stirred at 80r / min for 5min, and then raised to 160℃ and held for 15min. 1g of the material was added to 9g of a mixed solvent composed of butanone and dimethyl carbonate in a mass ratio of 1:1. After stirring at 50℃ for 10min without the appearance of gel particles, the reaction vessel was cooled to 45℃, and 2500g of butanone and 2500g of dimethyl carbonate were added. Stirring was continued for 20min to obtain the pre-ring-opening benzoxazine solution. When preparing the anthranilic acid-modified catechol polymerizable dispersion, 500g of anhydrous ethanol, 2500g of acetone, 45g of anthranilic acid and 150g of dopamine methacrylamide were added to a light-proof container. The mixture was stirred at 30°C for 30 min under nitrogen protection. Then, 80g of activated 4A molecular sieve was added and the mixture was stirred for another 10 min. The molecular sieve was then removed by filtration through a 100-mesh filter to obtain the anthranilic acid-modified catechol polymerizable dispersion. When S3 is performing co-solution prepositioning of chloroprene rubber and chlorinated polypropylene, 9000g of butanone, 11000g of dimethyl carbonate and 18000g of methylcyclohexane are added to the reactor. After purging with nitrogen for 10 minutes, 9000g of chloroprene rubber and 1100g of chlorinated polypropylene are added. The temperature is raised to 50℃ and stirred at 150r / min for 120 minutes to obtain a mixed solution without obvious particles. When performing methyl methacrylate grafting in step S4, add 3400g of methyl methacrylate to the mixed adhesive solution obtained in step S3, stir for 10 minutes, and then heat to 74°C; then add 120g of benzoyl peroxide, keep the reaction at this temperature for 40 minutes, and take samples every 15 minutes to measure the viscosity at 25°C; when the viscosity of the system reaches 300mPa·s, proceed to the next step. When performing catechol grafting in step S5, the catechol polymerizable dispersion modified with o-aminophenylboronic acid obtained in step S2 is added dropwise to the reaction system in step S4 within 20 min, along with 800 g of methyl methacrylate and 2500 g of dimethyl carbonate. After the addition is complete, 55 g of benzoyl peroxide is added, and the reaction continues at 74 °C for 50 min. When S6 is used for supplementary initiation and termination, when the viscosity of the system obtained in step S5 reaches 520 mPa·s at 25°C, 40 g of benzoyl peroxide is added, and the reaction is continued at 74°C for 20 min; when the viscosity reaches 800 mPa·s at 25°C, 70 g of hydroquinone is pre-dissolved in 800 g of acetone and added to the reaction system, and the mixture is stirred for 8 min, and then cooled to 50°C. When S7 is used to lock benzoxazine with bifunctional boric acid, 110g of 1,4-phenyldiboronic acid is added to 500g of anhydrous ethanol and 4500g of acetone, and stirred at 45°C for 20min to form a dispersion. Then, it is added together with all the pre-ring-opening benzoxazine solution obtained in step S1 to the system obtained in step S6, and stirred at 50°C for 80min. During the routine mixing and viscosity adjustment in step S8, the system obtained in step S7 is cooled to 40°C, and 4500g of methylcyclohexane, 2500g of dimethyl carbonate, 8000g of acetone and 12000g of cyclohexane are added. Then, 1500g of styrene-isoprene-styrene block copolymer, 2000g of hydrogenated C9 petroleum resin and 300g of antioxidant are added sequentially. The mixture is stirred at 150r / min for 90min until the system is homogeneous. Subsequently, the temperature is lowered to 25°C. Based on the viscosity test results at 25°C, the viscosity is adjusted to 100mPa·s using a non-benzene mixed solvent composed of butanone, acetone and cyclohexane in a mass ratio of 1:2:1. The mixture is then filtered through a 100-mesh filter to obtain the chloroprene rubber adhesive for automotive interiors.

[0041] Example 5: The difference from Example 1 is as follows: When preparing the pre-ring-opening benzoxazine solution, 1900g of bisphenol A type benzoxazine resin was added to a conventional reaction vessel equipped with nitrogen protection, stirring, and reflux condensation. The temperature was raised to 160℃ under nitrogen flow rate of 120mL / min, stirred at 150r / min for 15min, and then raised to 170℃ and held for 25min. 1g of the material was added to 9g of a mixed solvent composed of butanone and dimethyl carbonate in a mass ratio of 1:1. After stirring at 50℃ for 10min without the appearance of gel particles, the reaction vessel was cooled to 55℃, and 3500g of butanone and 3500g of dimethyl carbonate were added. Stirring was continued for 40min to obtain the pre-ring-opening benzoxazine solution. When preparing the anthranilic acid-modified catechol polymerizable dispersion, 700g of anhydrous ethanol, 3500g of acetone, 75g of anthranilic acid and 250g of dopamine methacrylamide were added to a light-proof container. The mixture was stirred at 40°C for 50 min under nitrogen protection. Then, 120g of activated 4A molecular sieve was added and the mixture was stirred for another 30 min. The molecular sieve was then removed by filtration through a 100-mesh filter to obtain the anthranilic acid-modified catechol polymerizable dispersion. When S3 is performing co-solution prepositioning of chloroprene rubber and chlorinated polypropylene, 11000g of butanone, 13000g of dimethyl carbonate and 22000g of methylcyclohexane are added to the reactor. After purging with nitrogen for 20min, 11000g of chloroprene rubber and 1500g of chlorinated polypropylene are added. The temperature is raised to 60℃ and stirred at 250r / min for 180min to obtain a mixed solution without obvious particles. When performing methyl methacrylate grafting in step S4, add 4200g of methyl methacrylate to the mixed adhesive obtained in step S3, stir for 20 minutes, and then heat to 78°C; then add 150g of benzoyl peroxide, keep the reaction at this temperature for 50 minutes, and take samples every 15 minutes to measure the viscosity at 25°C; when the viscosity of the system reaches 450mPa·s, proceed to the next step. When performing catechol grafting in step S5, the catechol polymerizable dispersion modified with o-aminophenylboronic acid obtained in step S2 is added dropwise to the reaction system in step S4 within 40 min, along with 1200 g of methyl methacrylate and 3500 g of dimethyl carbonate. After the addition is complete, 65 g of benzoyl peroxide is added, and the reaction continues at 78 °C for 70 min. When S6 is used for supplementary initiation and termination, when the viscosity of the system obtained in step S5 reaches 780 mPa·s at 25°C, 56 g of benzoyl peroxide is added, and the reaction is continued at 78°C for 40 min; when the viscosity reaches 1100 mPa·s at 25°C, 90 g of hydroquinone is pre-dissolved in 1200 g of acetone and added to the reaction system, and the mixture is stirred for 12 min, and then cooled to 60°C. When S7 is used to lock benzoxazine with bifunctional boric acid, 170g of 1,4-phenyldiboronic acid is added to 700g of anhydrous ethanol and 5500g of acetone, and stirred at 55°C for 40min to form a dispersion. Then, it is added together with all the pre-ring-opening benzoxazine solution obtained in step S1 to the system obtained in step S6, and stirred at 60°C for 100min. During the routine mixing and viscosity adjustment in step S8, the system obtained in step S7 is cooled to 50°C, and 5500g of methylcyclohexane, 3500g of dimethyl carbonate, 10000g of acetone and 16000g of cyclohexane are added. Then, 2500g of styrene-isoprene-styrene block copolymer, 3000g of hydrogenated C9 petroleum resin and 500g of antioxidant are added sequentially. The mixture is stirred at 250r / min for 150min until the system is homogeneous. Subsequently, the temperature is lowered to 25°C. Based on the viscosity test results at 25°C, the viscosity is adjusted to 150mPa·s using a non-benzene mixed solvent composed of methyl ethyl ketone, acetone and cyclohexane in a mass ratio of 1:2:1. The mixture is then filtered through a 100-mesh filter to obtain the chloroprene rubber adhesive for automotive interiors.

[0042] The difference between Comparative Example 1 and Example 1 is that 1300g of chlorinated polypropylene is not added in step S3, but 1300g of chlorinated polypropylene is added together with styrene-isoprene-styrene block copolymer, hydrogenated C9 petroleum resin and antioxidant in step S8; the other conditions are the same as in Example 1.

[0043] The difference between Comparative Example 2 and Example 1 is that 1300g of chlorinated polypropylene is not added in step S3, and 1300g of hydrogenated C9 petroleum resin is added in step S8 to make up the total amount of non-volatile components; the other conditions are the same as in Example 1.

[0044] The difference between Comparative Example 3 and Example 1 is that: in step S2, the catechol polymerizable dispersion modified with o-aminophenylboronic acid is still prepared, but it is not added dropwise in step S5; instead, after adding 3800g of methyl methacrylate in step S4 and before adding effective benzoyl peroxide, all the catechol polymerizable dispersion modified with o-aminophenylboronic acid obtained in step S2 is added to the reaction system at once; the other conditions are the same as in Example 1.

[0045] The difference between Comparative Example 4 and Example 1 is that: in step S2, 60g of o-aminophenylboronic acid is not added, but only 600g of anhydrous ethanol, 3000g of acetone and 200g of dopamine methacrylamide are added to prepare a catechol polymerizable dispersion; the 60g of o-aminophenylboronic acid is added in step S7 together with 1,4-phenyldiboronic acid and pre-ring-opened benzoxazine solution; the remaining conditions are the same as in Example 1.

[0046] The difference between Comparative Example 5 and Example 1 is that 140g of 1,4-phenylenediboronic acid is not added in step S7, but 140g of 1,4-phenylenediboronic acid is added simultaneously when the catechol polymerizable dispersion modified with o-aminophenylboronic acid is added dropwise in step S5; the other conditions are the same as in Example 1.

[0047] The difference between Comparative Example 6 and Example 1 is that 140g of 1,4-phenylenediboric acid is not added in step S7, but 140g of o-aminophenylboric acid is added in equal amounts; the other conditions are the same as in Example 1.

[0048] The difference between Comparative Example 7 and Example 1 is that: in step S1, the controlled pre-ring-opening treatment of bisphenol A type benzoxazine resin is not performed. Instead, 1600g of bisphenol A type benzoxazine resin is directly added to 3000g of butanone and 3000g of dimethyl carbonate, and stirred at 50°C for 30min to obtain a non-pre-ring-opened benzoxazine solution. This solution is then added to the system obtained in step S6 along with the 1,4-phenylenediboric acid fine dispersion in step S7. The remaining conditions are the same as in Example 1.

[0049] Performance testing Each batch of adhesive was filtered and then sealed at 25°C for 24 hours before being used for sample preparation. For the peel test, a 2mm thick automotive interior-grade polypropylene sheet was used as the rigid substrate. The surface of the polypropylene sheet was only wiped clean of dust and particulate contaminants with a lint-free cloth, without flame treatment, plasma treatment, or primer treatment. The flexible substrate used a 0.6mm thick polyvinyl chloride skin or polyurethane foam backing fabric. Adhesive was sprayed onto the polypropylene sheet surface using a 1.0mm nozzle spray gun, resulting in a wet film thickness of 100μm. The sheet was then placed at 23°C and 50% relative humidity for 10 minutes, followed by drying in a 60°C oven for 4 minutes. It was then bonded to the flexible substrate and pressed under 300kPa pressure for 45 seconds. After 24 hours at room temperature, the sample was tested. For the tensile shear test, two 100mm × 25mm × 2mm polypropylene sheets were used, with an overlap of 12.5mm. The coating and drying conditions were the same as for the peel test, and the sheets were placed at room temperature for 24 hours after pressing.

[0050] Adhesive viscosity test: The viscosity of the adhesive was determined according to GB / T2794-2022 "Determination of viscosity of adhesives". 200g of each of the adhesives obtained in Examples 1 to 5 and Comparative Examples 1 to 7 were placed in a constant temperature water bath at 25℃ for equilibration for 30min. The viscosity was measured using a single-cylinder rotational viscometer. The rotor and speed were selected so that the reading was between 20% and 80% of the range. Each sample was tested in parallel 3 times and the average value was taken as the viscosity of the adhesive.

[0051] Polypropylene / polyvinyl chloride 180° peel strength and high temperature aging retention test: 180° peel strength was tested according to GB / T2790-1995 "Adhesives 180° peel strength test method Flexible materials vs. rigid materials". Polypropylene / polyvinyl chloride peel test specimens were prepared using the adhesives obtained in Examples 1 to 5 and Comparative Examples 1 to 7. The specimen width was 25 mm, the peeling speed was 100 mm / min, and 5 specimens of each sample were tested in parallel. The average value was taken as the initial 180° peel strength. The high-temperature aging treatment was carried out according to the hot air aging method of GB / T3512-2014 "Accelerated Aging and Heat Resistance Test of Vulcanized Rubber or Thermoplastic Rubber in Hot Air". The same batch of specimens were placed in a 100° hot air aging chamber for 168 h. After being taken out, they were placed in an environment of 23° and 50% relative humidity for 24 h. The 180° peel strength after aging was then tested under the same peeling conditions, and the peel strength retention rate was calculated as (180° peel strength after aging / initial 180° peel strength) × 100%.

[0052] Polypropylene / polypropylene tensile shear strength test: The tensile shear strength was tested according to GB / T7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)". Polypropylene / polypropylene lapped specimens were prepared using the adhesives obtained in Examples 1 to 5 and Comparative Examples 1 to 7. The lap area was 25 mm × 12.5 mm, and the dry film thickness of the adhesive layer was controlled to be 30 μm to 50 μm. After being placed at room temperature for 24 h, the test was conducted at a tensile speed of 10 mm / min. Five samples were tested in parallel for each specimen, and the average value was taken as the tensile shear strength.

[0053] 80℃ Constant Load Heat Resistance Slip Test: Polypropylene / polyvinyl chloride (PVC) skin composite samples were prepared using the adhesives obtained in Examples 1 to 5 and Comparative Examples 1 to 7. The bonding area of ​​the sample was 25mm × 50mm, and the sample preparation and placement conditions were the same as those for the 180° peel test. The sample was fixed in an 80℃ constant temperature chamber, and a 1000g weight was suspended from the free end of the PVC skin for 60 minutes. The relative slip distance of the adhesive layer was recorded. If the sample detached within 60 minutes, the detachment time was recorded.

[0054] Volatile organic compound (VOC) content test: The VOC content was determined according to GB33372-2020 "Limits of Volatile Organic Compounds in Adhesives". Adhesives obtained in Examples 1 to 5 and Comparative Examples 1 to 7 were collected, sealed, and stored for 24 hours. Samples were then taken, and the VOC content was determined according to the solvent-based adhesive test procedure. The results were recorded in g / L.

[0055] Table 1 Performance Test Results

[0056] Data Analysis: Table 1 shows that in Comparative Example 1, after replacing chlorinated polypropylene with post-processed physical blending, the direct peel strength and aging retention rate of polypropylene were lower than those in Example 1. This indicates that when chlorinated polypropylene is used only as a free tackifying component, it is difficult to form a stable force conduction at the interface between chloroprene rubber and polypropylene. In Comparative Example 2, after supplementing the non-volatile components with hydrogenated C9 petroleum resin, the interfacial adhesion performance of polypropylene further decreased, indicating that low surface energy anchoring segments cannot be replaced by ordinary tackifying resins. Compared with Comparative Examples 1 and 2, Examples 1 to 5 improved the direct adhesion stability of untreated polypropylene substrates by introducing chlorinated polypropylene into the grafting stage of chloroprene rubber and methyl methacrylate in advance, allowing the polymethyl methacrylate bridging segments to form in the coexisting micro-regions of the two. In Comparative Examples 3 and 4, after changing the addition sequence of dopamine methacrylamide or removing the pre-protection of o-aminophenylboronic acid, the aging retention rate and heat resistance slip performance decreased, indicating that the catechol structure needs to be positioned in the later stage of the bridging segment and protected by monofunctional boric acid. After changing the timing of 1,4-phenyldiboronic acid addition, replacing the bifunctional boric acid in equal amounts, or removing the benzoxazine pre-ring-opening in Comparative Examples 5, 6, and 7, the overall effect of Example 1 was not achieved, indicating that delayed locking and local heat-resistant buffer nodes have a synergistic effect.

[0057] The adhesive obtained by this invention is suitable for bonding polypropylene interior parts such as automotive door panels, dashboard liners, pillar panels and headliner edge parts. It can reduce the need for flame treatment or primer coating and maintain good interface stability under high-temperature aging conditions in the cabin.

[0058] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A neoprene rubber adhesive for automotive interior trim, characterized in that, The product is prepared by means of the following components in parts by weight: 9000-11000 parts of chloroprene rubber, 1100-1500 parts of chlorinated polypropylene, 1300-1900 parts of bisphenol A type benzoxazine resin, 45-75 parts of o-aminophenylboronic acid, 150-250 parts of dopamine methacrylamide, 4200-5400 parts of methyl methacrylate, 215-271 parts of initiator, 110-170 parts of 1,4-phenylenediboronic acid, 70-90 parts of hydroquinone, 1500-2500 parts of elastomer, 2000-3000 parts of tackifying resin, 300-500 parts of antioxidant, and non-benzene solvents. The chlorinated polypropylene enters the system during the dissolution stage of the chloroprene rubber. The methyl methacrylate forms a polymethyl methacrylate bridge in the coexisting region of the chloroprene rubber and chlorinated polypropylene under the initiation of benzoyl peroxide. The dopamine methacrylamide is added after the polymethyl methacrylate bridge is formed after being modified with o-aminophenylboronic acid. The 1,4-phenylenediboric acid is added together with the pre-ring-opening benzoxazine solution after the free radical grafting reaction is terminated, so that a heat-resistant locking structure containing boron-oxygen bonds and boron-nitrogen interactions is formed in the adhesive.

2. The neoprene rubber adhesive for automotive interior trim according to claim 1, characterized in that, The chloroprene rubber is type A-90 chloroprene rubber; the chlorinated polypropylene has a chlorine content of 25%-27%, and the viscosity of a 10wt% toluene solution at 25℃ is 0.2-0.8 dPa·s.

3. The neoprene rubber adhesive for automotive interior trim according to claim 1, characterized in that, The initiator is benzoyl peroxide, a stabilized product containing 75 wt% benzoyl peroxide and 25 wt% water; the elastomer is a styrene-isoprene-styrene block copolymer, specifically SIS-1105, manufactured by Yueyang Petrochemical.

4. The neoprene rubber adhesive for automotive interior trim according to claim 1, characterized in that, The tackifying resin is hydrogenated C9 petroleum resin, HM-1300; the antioxidant is one of KY-405 and antioxidant 264.

5. The neoprene rubber adhesive for automotive interior trim according to claim 1, characterized in that, The bisphenol A type benzoxazine resin needs to undergo pre-ring-opening treatment before use. The pre-ring-opening treatment includes: heating to 150-160℃ under nitrogen flow rate of 80-120 mL / min, stirring at 80-150 r / min for 5-15 min, then heating to 160-170℃ and holding for 15-25 min; the o-aminophenylboronic acid and dopamine methacrylamide are mixed in anhydrous ethanol and acetone under light-protected and nitrogen-protected conditions, and treated with activated 4A molecular sieves to obtain an o-aminophenylboronic acid modified catechol polymerizable dispersion.

6. The neoprene rubber adhesive for automotive interior trim according to claim 1, characterized in that, The adhesive has a viscosity of 100-150 mPa·s at 25°C; the adhesive is used for bonding automotive interior-grade polypropylene substrates that have not been flame-treated, plasma-treated, or coated with a primer.

7. A method for preparing a neoprene rubber adhesive for automotive interior trim according to any one of claims 1-6, characterized in that, Includes the following steps: S1 Preparation of pre-ring-opened benzoxazine solution: Bisphenol A type benzoxazine resin is added to a reaction vessel equipped with nitrogen protection, stirring and reflux condensation function, and pre-ring-opening is carried out under nitrogen protection. Then, butanone and dimethyl carbonate are added to obtain pre-ring-opened benzoxazine solution. S2 Preparation of anthranilic acid-modified catechol polymerizable dispersion: Anhydrous ethanol, acetone, anthranilic acid and dopamine methacrylamide were mixed under light protection and nitrogen protection, and filtered after treatment with 4A molecular sieve to obtain anthranilic acid-modified catechol polymerizable dispersion. S3 Pre-positioning of chloroprene rubber and chlorinated polypropylene co-solution: Mix methyl ethyl ketone, dimethyl carbonate, methyl cyclohexane, chloroprene rubber and chlorinated polypropylene, and stir at 50-60℃ to obtain a mixed adhesive solution; S4. Grafting of methyl methacrylate: Add the first part of methyl methacrylate and the first part of benzoyl peroxide to the mixed adhesive solution obtained in step S3, and react at 74-78°C to obtain an adhesive solution with polymethyl methacrylate bridging. S5. Catechol grafting: Add the anthraquinone-boronic acid-modified catechol polymerizable dispersion obtained in step S2 to the adhesive solution obtained in step S4, and simultaneously add the second part methyl methacrylate, dimethyl carbonate and the second part benzoyl peroxide, and continue the reaction at 74-78℃. S6 is used for supplementary initiation and termination: Benzoyl peroxide (part 3) is added to the system obtained in step S5 to continue the reaction, followed by the addition of hydroquinone to terminate the free radical reaction; S7 Locking of benzoxazine and bifunctional boric acid: 1,4-phenyldiboronic acid is dispersed in anhydrous ethanol and acetone, and then added together with the pre-ring-opened benzoxazine solution obtained in step S1 into the system obtained in step S6, and stirred at 50-60℃. S8 Mixing and adjusting viscosity: Add methylcyclohexane, dimethyl carbonate, acetone, cyclohexane, styrene-isoprene-styrene block copolymer, hydrogenated C9 petroleum resin and antioxidant to the system obtained in step S7. After stirring evenly, adjust the solid content of the obtained adhesive to 16%-30% using a non-benzene solvent to obtain a chloroprene rubber adhesive for automotive interiors.

8. The preparation method according to claim 7, characterized in that, The methyl methacrylate is added in two parts: the first addition is 3400-4200 parts, and the second addition is 800-1200 parts; the benzoyl peroxide is added in three parts: the first addition is 120-150 parts, the second addition is 55-65 parts, and the third addition is 40-56 parts.

9. The preparation method according to claim 7, characterized in that, In step S4, when the viscosity of the system reaches 300-450 mPa·s at 25°C, the process proceeds to step S5; in step S5, the an-aminophenylboronic acid modified catechol polymerizable dispersion is added dropwise to the adhesive solution obtained in step S4 within 20-40 min; in step S6, when the viscosity of the system reaches 800-1100 mPa·s at 25°C, hydroquinone is added to terminate the free radical reaction.

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