Method for prolonging scorching time of natural rubber
By using the rare earth element lanthanum chloride (La³⁺) to form coordination bonds in natural rubber, the toxicity and pollution problems of traditional additives are solved, the scorch time is extended, the processing safety and mechanical properties are improved, and the quality of vulcanized rubber is enhanced.
Patent Information
- Application Number
- CN202511683738.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-01-20
AI Technical Summary
Existing technologies for extending the scorch time of natural rubber have problems such as toxicity, environmental pollution, and impact on rubber compound performance. Traditional additives such as Bedford accelerator M and CTP have carcinogenic risks or toxicity.
Lanthanum chloride (La³⁺), a rare earth element, is used as an additive. It forms coordination bonds with natural rubber to block free radical migration and prolong scorch time. Specific process steps, such as dilution, stabilization, and solidification control, ensure its uniform distribution and effect.
This achieves a non-toxic and environmentally friendly extended scorch time, improves processing safety and mechanical properties, reduces bubbles and surface roughness defects, and enhances the quality and dimensional accuracy of vulcanized rubber.
Smart Images
Figure CN121362352A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of rubber processing, in particular to a method for prolonging the scorch time of natural rubber. BACKGROUND
[0002] Natural rubber (NR) as an important strategic material, has irreplaceable role in the field of national defense, aerospace, transportation and other fields. The rubber vulcanization invented by Goodyear accidentally has been an important step in the processing of natural rubber, which has a direct impact on the performance of rubber products. The length of the scorch time t10 determines the degree of interaction of various additives, the dispersion of the additives in the rubber compound, whether the rubber compound can completely fill the vulcanization mold cavity to eliminate bubbles and defects, and is closely related to the quality of the rubber products. How to prolong the scorch time t10 and make it in the appropriate range is a problem to be solved in the process of substituting high-performance natural rubber at home.
[0003] At present, the main methods to adjust the scorch time t10 of natural rubber are accelerators, anti-scorching agents, plasticizers, anti-aging agents and other systems. Bedford found that the accelerator M (2-mercaptobenzothiazole) and its derivative sulfenamide can prolong the scorch time of rubber and have good comprehensive performance, but it was listed as a 2A carcinogen in 2017; Anti-scorching agent CTP (N-cyclohexyl thio phthalimide) can effectively prevent the rubber compound from scorching during processing, but it is toxic and causes slight discoloration of the product; Plasticizers generally increase the flowability of the rubber compound during the vulcanization induction period and prolong the scorch time; Anti-aging agents D, RD and 4010NA can prolong the scorch time of the rubber compound, but they will affect the vulcanization properties of the rubber compound. As can be seen, the traditional methods for improving the scorch time of the rubber compound generally have the problems of toxicity, environmental pollution and affecting the performance of the rubber compound. Therefore, a method for adding separated rare earth element lanthanum (La3+) to improve the scorch time is proposed. SUMMARY
[0004] In view of the deficiencies of the prior art, the present application provides a method for prolonging the scorch time of natural rubber, which solves the problems raised in the background art.
[0005] To achieve the above purpose, the present application is realized by the following technical scheme: a method for prolonging the scorch time of natural rubber, comprising the following steps: Step 1, raw material preparation: select natural rubber fresh latex with a Mooney viscosity of 60-80 as the raw material, and detect the purity of lanthanum chloride reagent and remove impurities through a 100 mesh sieve; Step 2, lanthanum chloride pretreatment: dissolve the lanthanum chloride in deionized water to prepare an aqueous solution at a dosage of 0.1-0.7 phr (based on every hundred parts of dry rubber); Step three, fresh latex dilution: dilute the natural rubber fresh latex with deionized water to a solid content of 18%-28%, stir uniformly and stand for 30 minutes; Step four, latex stabilization treatment: add potassium laurate to the diluted latex and stir for 30-60 minutes; Step five, lanthanum chloride addition: slowly add the pretreated lanthanum chloride solution to the diluted fresh latex under stirring, and continue stirring to disperse uniformly; Step six, acid coagulation control: add coagulant to the mixture, and the amount is adjusted to control the pH of the system to 4.5-5.0; Step seven, rubber block curing: wash the coagulated rubber block with clean water to remove surface acid liquid and impurities, then press it into a rubber sheet with a thickness of ≤3mm by a tablet press, and then let the rubber sheet stand for 24-48 hours.
[0006] According to the above technical scheme, the solid content of the fresh latex in step one is not less than 30%, and the purity of the lanthanum chloride (LaCl3·nH2O) is ≥99.0%.
[0007] According to the above technical scheme, the dissolution temperature in step two is controlled at 40-50°C, the stirring speed is 200-300rpm, and the time is ≥15 minutes to be clear and transparent.
[0008] According to the above technical scheme, the stabilization environment temperature in step four is maintained at 25-30°C, and the rotation speed is 100-200rpm.
[0009] According to the above technical scheme, the stirring speed in step five is 200-300rpm, and lasts at least 15 minutes.
[0010] According to the above technical scheme, the coagulation temperature in step six is controlled at 25-40°C, and the water bath heating is used to maintain the constant temperature, and the coagulation time is controlled at 1-2 hours until the latex is completely coagulated into a block.
[0011] According to the above technical scheme, the coagulant in step six is selected from formic acid or acetic acid with a concentration of 10-15%.
[0012] According to the above technical scheme, the number of times of washing with clean water in step seven is not less than 3 times, and the rubber sheet standing environment temperature is ≤25°C and the humidity is ≤60%, which ensures that the lanthanum chloride fully acts on the rubber.
[0013] The present application provides a method for prolonging the scorch time of natural rubber. It has the following beneficial effects: (1) The method, unlike the accelerator M and the scorch retardant CTP used in the traditional process, uses lanthanum chloride as an additive, which is non-toxic and does not harm the processing personnel, and the acetone solubles content is ≤2.34%, which meets the environmental protection standard, solving the problem of "toxicity and environmental pollution" of traditional methods.
[0014] (2) The method, by forming a coordination bond between lanthanum chloride and the polar groups of natural rubber, blocking the migration of free radicals, effectively extending the scorching time and the vulcanization time, providing a more sufficient operation window for mixing, extrusion and other processing procedures, and avoiding the material from scorching in advance.
[0015] (3) The method, the rare earth element lanthanum (La3+) in the vulcanization process improves the uniformity of the crosslinked network better than the traditional ZnO system, and at the same time improves the modulus, realizing the double effect of "processing safety + mechanical properties".
[0016] (4) The method, the rare earth element lanthanum (La3+) and the -COOH, -NH2 in the natural rubber form an octahedral coordination structure, effectively optimizing the uniformity of the vulcanization crosslinked network, and compared with the traditional process, the microstructure of the vulcanized rubber is more regular, reducing the defects such as bubbles and surface roughness caused by uneven vulcanization of the product, and improving the dimensional accuracy and performance stability. BRIEF DESCRIPTION OF DRAWINGS
[0017] Fig. 1 The flowchart of the present application is made; Fig. 2 The influence of lanthanum element on the components and vulcanization characteristics of natural rubber is shown in the following table; Fig. 3 The influence of lanthanum element on the physical and mechanical properties of natural rubber is shown in the following table. DETAILED DESCRIPTION
[0018] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.
[0019] Please refer to Figs. 1-3 An embodiment of the present application is: a method for extending the scorching time of natural rubber, comprising the following steps: Step 1, raw material preparation: select natural rubber fresh latex with a Mooney viscosity of 60-80 as raw material, and detect the purity of lanthanum chloride reagent and remove impurities through a 100 mesh sieve; Step two, lanthanum chloride pretreatment: dissolve lanthanum chloride in deionized water to prepare an aqueous solution according to the amount of 0.1-0.7 phr (per hundred dry rubber); Step three, fresh latex dilution: dilute the natural rubber fresh latex with deionized water to a solid content of 18%-28%, stir uniformly and stand for 30 minutes; Step four, latex stabilization treatment: add potassium laurate to the diluted latex and stir for 30-60 minutes; Step five, lanthanum chloride addition: slowly add the pretreated lanthanum chloride solution to the diluted fresh latex under stirring to ensure uniform dispersion; Step six, acid coagulation control: add coagulant to the mixture, and the amount should be adjusted to control the pH of the system to 4.5-5.0; Step seven, rubber block curing: wash the coagulated rubber block with clean water to remove surface acid and impurities, then press it into a rubber sheet with a thickness of ≤3mm using a tablet press, and then let the rubber sheet stand for 24-48 hours.
[0020] Through the whole process of "raw material selection → lanthanum chloride treatment → latex dilution → coagulation control → post-treatment", the scorch time t10 of natural rubber is extended from 2.068 minutes in the prior art to more than 2.797 minutes, and the crosslinking network uniformity is better than that of the ZnO system, achieving "processing safety + mechanical properties" double improvement.
[0021] The fresh latex solid content in step one is not less than 30%, and the purity of lanthanum chloride (LaCl3·nH2O) is ≥99.0%, which avoids the deterioration of mechanical properties of the coagulated rubber block due to low concentration, ensures the formation of coordination bonds between La³⁺ and rubber polar groups, and maximizes the scorch time extension effect.
[0022] In step two, the dissolution temperature is controlled at 40-50℃, the stirring speed is 200-300rpm, and the time is ≥15 minutes to clarify and transparent, which avoids uneven La³⁺ concentration in the latex due to undissolved crystals; lays a foundation for uniform dispersion in the latex, and prevents abnormal crosslinking caused by excessive local La³⁺ concentration.
[0023] In step four, the stabilization environment temperature is maintained at 25-30℃, and the speed is 100-200rpm, which can form a stable emulsion system after latex dilution, prevent coagulation or demulsification of rubber particles, avoid uneven dispersion of lanthanum chloride due to unstable latex, and ensure uniform distribution of La³⁺ ions, so that the scorch time extension effect has repeatability.
[0024] In step five, the stirring speed is 200-300rpm and lasts at least 15 minutes, which makes La³⁺ ions fully contact with the polar groups on the molecular chain of natural rubber, forms an octahedral coordination structure, and effectively blocks the migration of free radicals.
[0025] The temperature in the coagulation process in step six is controlled at 25-40°C, and a water bath is used for heating to maintain constant temperature. The coagulation time is controlled at 1-2 hours until the latex is completely coagulated into a block to avoid the premature activation of the accelerator caused by high temperature (>50°C) in the traditional process, while ensuring the slow and uniform coagulation of the latex and reducing the risk of scorching during processing.
[0026] Formic acid or acetic acid is selected as the coagulant in step six, and the concentration is 10-15%. Compared with traditional inorganic acid (such as hydrochloric acid), it can reduce the oxidative damage to the rubber molecular chain, avoid the problem of accelerated aging of the vulcanized rubber caused by residual acid in the prior art, and at the same time meet the environmental protection standard and have no toxicity residue.
[0027] The number of water washing times in step seven is not less than 3 times, and the rubber sheet is placed in an environment with a temperature ≤25°C and a humidity ≤60%, which ensures the full action of lanthanum chloride and rubber, prevents the acid liquid from catalyzing the premature decomposition of the accelerator during subsequent vulcanization, prolongs the scorching time, and keeps the effect stable (t10 decay ≤5% within 72 hours), ensuring the consistency of the rubber properties during the production cycle.
[0028] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.
Claims
1. A method of extending the scorch time of natural rubber, characterized in that, It comprises the following steps: Step one, raw material preparation: select the fresh natural rubber latex with the Mooney viscosity of 60-80 as the raw material, and detect the purity of the lanthanum chloride reagent, and remove impurities through a 100 mesh sieve; Step two, lanthanum chloride pretreatment: dissolve the lanthanum chloride in deionized water to prepare an aqueous solution according to the dosage of 0.1-0.7 phr (based on every hundred parts of dry rubber); Step three, fresh latex dilution: dilute the fresh natural rubber latex with deionized water to a solid content of 18%-28%, and stir uniformly and then stand for 30 minutes; Step four, latex stabilization treatment: add potassium laurate to the diluted latex, and stir for 30-60 minutes; Step five, lanthanum chloride addition: slowly add the pretreated lanthanum chloride solution to the diluted fresh latex under stirring, and continuously stir to disperse uniformly; Step six, acid coagulation control: add a coagulant to the mixture, and the dosage is adjusted to the pH of 4.5-5.0; Step seven, rubber block curing: wash the coagulated rubber block with clean water to remove surface acid liquid and impurities, then press it into a rubber sheet with a thickness of ≤3 mm through a tablet press, and then stand the rubber sheet for 24-48 hours.
2. A method of extending the scorch time of natural rubber according to claim 1, characterized in that: The solid content of the fresh latex in step one is not less than 30%, and the purity of the lanthanum chloride (LaCl3·nH2O) is ≥99.0%.
3. A method of extending the scorch time of natural rubber according to claim 2, characterized in that: The stirring speed in step two is 200-300 rpm, and the time is ≥15 minutes to be clear and transparent.
4. A method of extending the scorch time of natural rubber according to claim 3, characterized in that: The stabilization environment temperature in step four is maintained at 25-30℃, and the rotating speed is 100-200 rpm.
5. A method of extending the scorch time of natural rubber according to claim 4, characterized in that: The stirring rotating speed in step five is 200-300 rpm, and the stirring is continued for at least 15 minutes.
6. A method of extending the scorch time of natural rubber according to claim 5, characterized in that: The coagulation temperature in step six is controlled at 25-40℃, and the water bath heating is used to maintain the constant temperature, and the coagulation time is controlled at 1-2 hours until the latex is completely coagulated into a block.
7. A method of extending the scorch time of natural rubber according to claim 6, characterized in that: The coagulant in step six is selected from formic acid or acetic acid, and the concentration is 10-15%.
8. A method of extending the scorch time of natural rubber according to claim 7, characterized in that: The number of times of washing with clean water in step seven is not less than 3 times, and the rubber sheet is placed in an environment with a temperature of ≤25℃ and a humidity of ≤60%, to ensure that the lanthanum chloride fully reacts with the rubber.