CN112129808A

CN112129808A - Method for evaluating heat stability of insoluble sulfur in unvulcanized rubber

Info

Publication number: CN112129808A
Application number: CN202011112370.6A
Authority: CN
Inventors: 高杨; 李梁; 张进; 唐志民
Original assignee: Sennics Co ltd
Current assignee: Sennics Co ltd
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2020-12-25

Abstract

The invention provides a method for evaluating the thermal stability of insoluble sulfur in an uncured rubber, which is characterized by comprising the step of obtaining the vulcanization reaction activation energy of the uncured rubber containing the insoluble sulfur, wherein the lower the vulcanization reaction activation energy is, the higher the thermal stability of the insoluble sulfur in the uncured rubber is. The method comprises the following steps: (1) measuring the vulcanization time T90 of the uncured rubber containing the insoluble sulfur at different temperatures; (2) the activation energy of the vulcanization reaction was calculated from the vulcanization time T90 at different temperatures. The method of the invention can accurately and directly evaluate, compare and judge the thermal stability of the insoluble sulfur in the rubber material in actual production.

Description

Method for evaluating heat stability of insoluble sulfur in unvulcanized rubber

Technical Field

The invention belongs to the field of rubber vulcanizing agents, and particularly relates to a method for evaluating the thermal stability of insoluble sulfur in unvulcanized rubber.

Background

Insoluble sulfur (IS, insoluble sulfur) IS a linear macromolecular polymer of common sulfur, has good compatibility with olefin elastomers, and can greatly reduce the blooming phenomenon in the processing process of rubber products. However, the insoluble sulfur is irreversibly reduced to normal sulfur with the increase of external storage time and temperature, thereby causing blooming phenomenon. Therefore, the thermal stability of insoluble sulfur becomes one of its key properties. The evaluation method of the thermal stability of the insoluble sulfur is mainly characterized by the change of the mass percent of the insoluble sulfur before and after the insoluble sulfur is heated under the specific temperature and time.

Methods for evaluating the thermal stability of insoluble sulfur are classified into an oven method, an oil bath method, and a Differential Scanning Calorimeter (DSC) method, depending on the heat-receiving conductive medium and the method. The three methods are methods for directly judging the thermal stability of insoluble sulfur products, and the oven method and the oil bath method adopt a mode of heating, cooling and then washing, so that the risk that the soluble sulfur in a sample cannot be completely washed out exists, and the result difference is caused. In addition, the above methods are all used for characterizing the change of the stability of the insoluble sulfur under the condition that the insoluble sulfur is not influenced by other materials and is only subjected to a single condition of heat temperature change. The method is not in accordance with the application conditions of the actual insoluble sulfur in the refining and processing of the sizing material, and the thermal stability of the insoluble sulfur in the actual application can not be accurately represented.

Because various auxiliary agents are added into a rubber formula, including an anti-aging agent, an accelerator, an activator, a scorch retarder and the like, the auxiliary agents, particularly the auxiliary agents containing amine substances, influence the vulcanization process of rubber materials and the properties of insoluble sulfur, and are influenced by a plurality of factors in the rubber processing process, the thermal stability of the insoluble sulfur in the rubber may show results inconsistent with the thermal stability test of raw materials, and therefore, a method for more directly representing the thermal stability of the insoluble sulfur in the rubber is needed in practical use.

Disclosure of Invention

In order to solve the above problems, the present invention provides a method for evaluating the thermal stability of insoluble sulfur in an unvulcanized rubber, the method comprising obtaining a vulcanization reaction activation energy of an unvulcanized rubber containing insoluble sulfur, the lower the activation energy of the vulcanization reaction, the higher the thermal stability of the insoluble sulfur in the unvulcanized rubber.

In one or more embodiments, the method comprises the steps of:

(1) measuring the vulcanization time T90 of the uncured rubber containing the insoluble sulfur at different temperatures;

(2) the activation energy of the vulcanization reaction was calculated from the vulcanization time T90 at different temperatures.

In one or more embodiments, in step (1), the cure time T90 at various temperatures is determined for the uncured rubber containing the insoluble sulfur using a vulcameter.

In one or more embodiments, in step (1), the test temperature for cure time T90 is between 135 ℃ and 185 ℃, and/or cure times T90 of 3 temperatures or more are determined.

In one or more embodiments, in step (1), the cure times T90 are determined at 140. + -. 2 ℃, 150. + -. 2 ℃, 160. + -. 2 ℃, 170. + -. 2 ℃ and 180. + -. 2 ℃.

In one or more embodiments, in step (2), the Aloneius equation is replaced with the reciprocal 1/T90 of the cure time T90

And (3) fitting ln (T90) and the reciprocal 1/T of the test temperature to a straight line, and calculating the activation energy E of the vulcanization reaction according to the slope of the straight line.

In one or more embodiments, the uncured rubber comprises the following components in parts by weight: 100 parts by weight of diene elastomer, 30-70 parts by weight of reinforcing filler, 1-10 parts by weight of insoluble sulfur, 0-10 parts by weight of active agent, 0-20 parts by weight of softener, 0-2 parts by weight of accelerator and 0-10 parts by weight of anti-aging agent.

In one or more embodiments, the uncured rubber is prepared by the following method:

(1) mixing unvulcanized rubber components except for insoluble sulfur and an accelerator in a thermomechanical mixer to obtain a master batch;

(2) and (2) mixing the master batch obtained in the step (1), insoluble sulfur and an accelerator in a thermomechanical mixer to obtain an unvulcanized rubber.

In one or more embodiments, in the step (1), the rubber is discharged when the total mixing time reaches 300-; and/or in the step (2), discharging the glue when the temperature reaches 60-150 ℃.

In another aspect of the present invention, there is provided a method for screening unvulcanized rubber with high heat stability of insoluble sulfur, the method comprising obtaining vulcanization reaction activation energy of unvulcanized rubber containing different insoluble sulfur, the unvulcanized rubber with lower vulcanization reaction activation energy having higher heat stability of insoluble sulfur.

In one or more embodiments, the method comprises the steps of:

Drawings

FIG. 1 is a graph of the vulcameter of example 1 at various temperatures.

FIG. 2 is a straight line fit for calculation of activation energy by plotting Ln (T90) against 1/T in example 1.

FIG. 3 is a graph of the free sulfur content of the compound of example 1 as a function of standing time.

FIG. 4 is a graph of the surface tack of the compound of example 1 as a function of standing time.

FIG. 5 is a graph of free sulfur content as a function of parking time for the compound of example 2.

FIG. 6 is the surface tack of the compound of example 2 as a function of standing time.

Detailed Description

To make the features and effects of the present invention obvious to those skilled in the art, the terms and words used in the specification and claims are generally described and defined below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.

The terms "comprising," including, "" containing, "and the like, herein, encompass the meanings of" consisting essentially of … … "and" consisting of … …, "e.g., when" A comprises B and C, "A consists of B and C" is disclosed herein is to be considered disclosed by the text.

All features defined herein as numerical ranges or percentage ranges, such as numbers, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.

In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.

The vulcanization performance of the rubber added with the insoluble sulfur is closely related to the thermal stability of the insoluble sulfur and the performance of other raw materials in the formula. The invention characterizes the thermal stability of insoluble sulfur in the application process of the actual rubber formula and under the influence of other application auxiliary agents by calculating the activation energy of the vulcanization reaction. The method of the present invention uses unvulcanized rubber containing insoluble sulfur to be evaluated as a test object; the vulcanization characteristic of an unvulcanized rubber material is tested by using a vulcanizer, the vulcanization kinetic rule of the rubber material can be obtained by selecting different test temperatures to test the vulcanization characteristic of the rubber, and the vulcanization reaction activation energy is calculated by model establishment and curve fitting of an Arrhenius equation; the error generated by the test of the vulcanizing instrument at a certain specific temperature can be eliminated by calculating the activation energy through different temperature points, so that a more accurate result is obtained; the activation energy value can visually represent the vulcanization characteristic of the rubber; by testing the vulcanization reaction activation energy of the unvulcanized rubber prepared by a formula containing different insoluble sulfur but the same other raw materials under a certain mixing process, the thermal stability difference of different insoluble sulfur in the rubber compound is evaluated according to the lower the vulcanization reaction activation energy and the higher the thermal stability of the insoluble sulfur in the rubber compound.

The method for evaluating the heat stability of the insoluble sulfur in the unvulcanized rubber comprises the steps of obtaining the vulcanization reaction activation energy of the unvulcanized rubber containing the insoluble sulfur, evaluating the heat stability of the insoluble sulfur in the unvulcanized rubber according to the level of the vulcanization reaction activation energy, and obtaining the higher heat stability of the insoluble sulfur in the unvulcanized rubber according to the lower vulcanization reaction activation energy.

It is understood that it is preferable to obtain the vulcanization reaction activation energy of the same type of unvulcanized rubber containing different insoluble sulfur, which means unvulcanized rubber having the same material formulation and preparation process except for different insoluble sulfur, and the different insoluble sulfur is evaluated for the thermal stability in the type of unvulcanized rubber according to the level of the vulcanization reaction activation energy, and the lower the vulcanization reaction activation energy, the higher the thermal stability of the insoluble sulfur in the type of unvulcanized rubber.

In some embodiments, the method of the present invention for evaluating the thermal stability of insoluble sulfur in uncured rubber comprises the steps of:

In the present invention, the cure time T90 has the meaning conventional in the art and refers to the time corresponding to the torque reaching the torque minimum + (torque maximum-torque minimum) × 90% in the vulkameter curve (torque-cure time relationship curve). The vulcameter curves can be obtained, for example, by carrying out the vulcameter test on unvulcanized rubber in accordance with the standard GB/T16584-1996. In some embodiments, the cure time T90 is measured using a vulcameter, preferably according to the standard GB/T16584-. It is known in the art that the cure time T90 is related to the cure temperature, and that cure times T90 at different temperatures can be obtained by subjecting unvulcanized rubber to a vulcameter test at different temperatures.

In the present invention, the vulcanization time T90 of an unvulcanized rubber containing insoluble sulfur is measured at 2 or more, preferably 3 or more (e.g., 3 or 4), and more preferably 5 or more (e.g., 5, 6, 7, 8, 9, 10). Preferably, the vulcanization time T90 is determined for the uncured rubber containing insoluble sulfur at a plurality of temperatures within the temperature range of 120-. Preferably, the temperatures of two adjacent measured vulcanisation times T90 differ by more than 5 deg.C, for example by 5 deg.C-20 deg.C, by 10 + -5 deg.C and by 10 + -2 deg.C. The temperature difference between the temperatures of each adjacent two of the measured curing times T90 may be the same or different. In a preferred embodiment, the present invention measures the curing time T90 of an uncured rubber containing insoluble sulfur at 140. + -. 2 ℃, 150. + -. 2 ℃, 160. + -. 2 ℃, 170. + -. 2 ℃ and 180. + -. 2 ℃.

The activation energy E of the vulcanization reaction can be calculated by the following method: the inverse 1/T90 of the vulcanization time T90 measured at different temperatures T is used instead of the Arrhenius equation

And (3) fitting ln (T90) and the reciprocal 1/T of the test temperature T to a straight line, and calculating the activation energy E of the vulcanization reaction according to the slope of the straight line.

Suitable unvulcanized rubbers for use in the present invention may be unvulcanized rubbers prepared from various rubber formulations containing insoluble sulfur. The unvulcanized rubber generally comprises a diene elastomer, a reinforcing filler and a crosslinking agent. The reinforcing filler is generally used in an amount of 30 to 70 parts by weight and the crosslinking agent is generally used in an amount of 1 to 10 parts by weight, based on 100 parts by weight of the diene elastomer, in the unvulcanized rubber. Herein, unless otherwise specified, the parts by weight of each component contained in the unvulcanized rubber are based on 100 parts by weight of the diene elastomer contained in the unvulcanized rubber.

By diene elastomer is meant herein an elastomer in which the monomers comprise dienes (e.g. butadiene, isoprene). The diene elastomer suitable for use in the present invention may be various diene elastomers known in the art, including, but not limited to, one or more selected from Natural Rubber (NR), Butadiene Rubber (BR), isoprene rubber, styrene-butadiene rubber (SBR), Chloroprene Rubber (CR), nitrile-butadiene rubber (NBR), isoprene/butadiene copolymer, isoprene/styrene copolymer, and isoprene/butadiene/styrene copolymer. In some embodiments, the diene elastomer included in the uncured rubber comprises, or consists of, natural rubber. Examples of natural rubber include SCR 5.

The reinforcing filler suitable for use in the present invention may be a reinforcing filler conventionally used in rubber compositions, including but not limited to one or more selected from carbon black, titanium oxide, magnesium oxide, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, clay and talc. In some embodiments, the reinforcing filler is carbon black in the uncured rubber. The unvulcanized rubber usually contains 30 to 70 parts by weight, preferably 40 to 60 parts by mass, more preferably 45 to 55 parts by weight of a reinforcing filler. In some embodiments, the uncured rubber comprises 30 to 70 parts by weight, preferably 40 to 60 parts by weight, more preferably 45 to 60 parts by weight (e.g., 45 to 55 parts by weight, 50 to 60 parts by weight, 50 to 55 parts by weight) of carbon black.

The cross-linking agent is typically sulphur. The crosslinking agent suitable for use in the uncured rubber of the present invention is insoluble sulfur. The uncured rubber typically comprises from 1 to 10 parts by weight, preferably from 1 to 8 parts by weight, more preferably from 1 to 5 parts by weight, for example from 4 to 5 parts by weight, of crosslinking agent. In some embodiments, the uncured rubber comprises from 1 to 10 parts by weight, preferably from 1 to 8 parts by weight, more preferably from 1 to 6 parts by weight, e.g., from 3 to 6 parts by weight, from 4 to 5 parts by weight of insoluble sulfur.

The uncured rubber suitable for use in the present invention optionally or preferably further comprises one or more or all of an active agent, a softening agent, an accelerator and an anti-aging agent. When included, the amount of the activator is usually not more than 10 parts by weight, the amount of the softener is usually not more than 20 parts by weight, the amount of the accelerator is usually not more than 2 parts by weight, and the amount of the antioxidant is usually not more than 10 parts by weight, based on 100 parts by weight of the diene elastomer. In some embodiments, the uncured gum includes an active agent, a softening agent, and an accelerator. In other embodiments, the uncured rubber includes an active agent, a softening agent, an accelerator, and an anti-aging agent.

The activator has the functions of accelerating the vulcanization speed, improving the heat conductivity, the wear resistance, the tearing resistance and the like of the rubber. Exemplary active agents include zinc oxide. The uncured rubber may contain 0 to 10 parts by weight, preferably 2 to 8 parts by weight, more preferably 3 to 6 parts by weight, for example 4 to 5 parts by weight, of an active agent (e.g. zinc oxide).

The softener is used for improving the properties such as processability. The softening agent may include petroleum type softening agents such as naphthenic oil, aromatic oil, process oil, lubricating oil, paraffin wax, microcrystalline wax, liquid paraffin wax, petroleum asphalt, vaseline and the like, and may also include fatty oil type softening agents such as stearic acid, castor oil, linseed oil, rapeseed oil, coconut oil, waxes (such as beeswax, carnauba wax and lanolin), tall oil, linoleic acid, palmitic acid, lauric acid and the like. Generally, the softener is used in a total amount of not more than 20 parts by weight (e.g., 1 to 20 parts by weight, 5 to 20 parts by weight), preferably not more than 10 parts by weight (e.g., 1 to 10 parts by weight, 5 to 10 parts by weight, 7 to 10 parts by weight, 8 to 9.5 parts by weight) per 100 parts by weight of the diene elastomer. In some embodiments, the uncured gum includes petroleum-based softeners, such as aromatic oils and/or microcrystalline waxes. The unvulcanized rubber may contain 0 to 10 parts by weight, preferably 1 to 10 parts by weight, more preferably 5 to 10 parts by weight (e.g., 5 to 8 parts by weight, 6 to 7.5 parts by weight) of a petroleum-based softening agent (e.g., aromatic oil and/or microcrystalline wax). The unvulcanized rubber may contain the aromatic oil in an amount of 0 to 10 parts by weight, preferably 1 to 10 parts by weight, more preferably 2 to 8 parts by weight (e.g., 3 to 7 parts by weight, 4 to 6 parts by weight). The unvulcanized rubber may contain 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight (e.g., 2 ± 0.5 parts by weight) of the microcrystalline wax. In some embodiments, the uncured gum includes a fatty oil softener, such as stearic acid. The unvulcanized rubber may contain 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight (e.g., 2 ± 0.5 parts by weight) of a fatty oil type softener (e.g., stearic acid).

The accelerator is usually a vulcanization accelerator, and may be one or more selected from the group consisting of sulfonamide vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, thiourea vulcanization accelerators, guanidine vulcanization accelerators, dithiocarbamate vulcanization accelerators, aldehyde amine vulcanization accelerators, aldehyde ammonia vulcanization accelerators, imidazoline vulcanization accelerators and xanthate vulcanization accelerators. For example, the accelerator may be accelerator NS (N-tert-butyl-2-benzothiazolesulfenamide). In some embodiments, the uncured rubber includes an accelerator (e.g., accelerator NS). The unvulcanized rubber may comprise an accelerator (e.g., accelerator NS) in an amount of 0 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight, e.g., 0.8 ± 0.2 parts by weight, 0.8 ± 0.1 parts by weight.

The anti-aging agent is used for delaying rubber aging and prolonging the service life of rubber. The uncured rubber may include one or more antioxidants known in the art. Suitable antioxidants include, but are not limited to, amine antioxidants, phenolic antioxidants, heterocyclic antioxidants, and non-migratory antioxidants. Examples of amine antioxidants include antioxidant 6PPD (N- (1, 3-dimethylbutyl) -N ' -phenyl-p-phenylenediamine), antioxidant IPPD (N-isopropyl-N ' -phenyl-p-phenylenediamine), antioxidant 77PD (N, N ' -bis (1, 4-dimethylpentyl) p-phenylenediamine), and antioxidant DTPD (a mixture of diphenyl-p-phenylenediamine, di (tolyl) p-phenylenediamine, and phenyl-tolyl-p-phenylenediamine). Examples of phenolic antioxidants include antioxidant 264(2, 6-di-tert-butyl-4-methylphenol), antioxidant 2246S and antioxidant DOD. Examples of heterocyclic antioxidants include antioxidant MB (2-mercaptobenzimidazole) and antioxidant MBZ (zinc salt of 2-mercaptobenzimidazole). The total amount of the antioxidant to be used in the unvulcanized rubber is usually not more than 10 parts by weight (e.g., 0.5 to 10 parts by weight, 1 to 10 parts by weight), preferably not more than 5 parts by weight (e.g., 0.5 to 5 parts by weight, 1 to 5 parts by weight, 2 to 4 parts by weight). In some embodiments, the uncured rubber includes an amine-based antioxidant and/or a heterocyclic antioxidant. The unvulcanized rubber may contain 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight (e.g., 2 ± 0.5 parts by weight) of an amine-based antioxidant (e.g., antioxidant 6 PPD). The unvulcanized rubber may contain 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight (e.g., 2. + -. 0.5 parts by weight) of a heterocyclic antioxidant (e.g., antioxidant MBZ).

In addition, the unvulcanized rubber may contain other additives useful for the rubber composition, such as a plasticizer, if necessary. Examples of plasticizers include, but are not limited to, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (diisodecyl phthalate), BBP (butyl benzyl phthalate), DWP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), and the like. The amount of plasticizer used may be that conventionally used in the art.

In some preferred embodiments, the uncured rubber comprises a diene elastomer, a reinforcing filler, a crosslinking agent, an active agent, a softening agent, and an accelerator; the diene elastomer preferably comprises natural rubber; the reinforcing filler preferably comprises carbon black; the cross-linking agent is insoluble sulfur; the active agent preferably comprises zinc oxide; the softening agent preferably includes petroleum-based softening agents and fatty oil-based softening agents, more preferably includes stearic acid, aromatic oil, and microcrystalline wax; the accelerator preferably comprises accelerator NS; the amount of reinforcing filler in the unvulcanized rubber is preferably 45 to 60 parts by weight, the amount of crosslinking agent is preferably 3 to 6 parts by weight, the amount of active agent is preferably 3 to 6 parts by weight, the amount of softening agent is preferably 7 to 10 parts by weight, and the amount of accelerator is preferably 0.5 to 1.2 parts by weight, based on 100 parts by weight of the diene elastomer.

In some preferred embodiments, the uncured rubber comprises a diene elastomer, a reinforcing filler, a crosslinking agent, an active agent, a softening agent, an accelerator, and an anti-aging agent; the diene elastomer preferably comprises natural rubber; the reinforcing filler preferably comprises carbon black; the cross-linking agent is insoluble sulfur; the active agent preferably comprises zinc oxide; the softening agent includes petroleum type softening agent and fatty oil type softening agent, more preferably stearic acid, aromatic oil and microcrystalline wax; the accelerator preferably comprises accelerator NS; the anti-aging agent preferably comprises an amine anti-aging agent and a heterocyclic anti-aging agent, and more preferably comprises an anti-aging agent 6PPD and an anti-aging agent TMQ; the amount of the reinforcing filler in the unvulcanized rubber is preferably 45 to 60 parts by weight, the amount of the crosslinking agent is preferably 3 to 6 parts by weight, the amount of the activating agent is preferably 3 to 6 parts by weight, the amount of the softening agent is preferably 7 to 10 parts by weight, the amount of the accelerator is preferably 0.5 to 1.2 parts by weight, and the amount of the anti-aging agent is preferably 1 to 5 parts by weight, based on 100 parts by weight of the diene elastomer.

The unvulcanized rubber may be prepared by a conventional rubber mixing method, for example, by a two-stage mixing method: mixing the diene elastomer and unvulcanized rubber components (such as a reinforcing filler, an activator, a softener, an antioxidant and the like) except for a crosslinking agent and an accelerator in a first mixing step, and discharging the rubber at a temperature of preferably more than 110 ℃ to obtain a master batch; and (3) two-stage mixing, namely mixing the master batch with a cross-linking agent and an accelerant to obtain the unvulcanized rubber.

In some embodiments, the uncured rubber is prepared by:

(1) first-stage mixing: firstly adding diene elastomer into a thermomechanical mixer (such as an internal mixer), mixing for a certain time (such as 30-120s, preferably 80 +/-20 s), adding reinforcing filler and auxiliary agent, continuing mixing, and discharging when the total mixing time reaches 300-600s, preferably 450 +/-50 s or the temperature reaches 120-160 ℃, preferably 145 +/-5 ℃ to obtain master batch;

(2) and (3) second-stage mixing: adding the master batch into a two-stage thermomechanical mixer (such as an internal mixer), mixing for a certain time (such as 30-120s, preferably 70 +/-20 s), adding a crosslinking agent and an accelerator, continuing mixing, and discharging when the temperature reaches 60-150 ℃ and preferably 100-150 ℃ (such as 105 +/-5 ℃ and 125 +/-5 ℃) to obtain the unvulcanized rubber.

The unvulcanized rubber obtained by the two-stage mixing can be discharged from the extruder. The thickness of the unvulcanized rubber sheet is preferably 2. + -. 0.5 mm.

In step (1), the mixing is preferably carried out in an internal mixer. The thermomechanical mixer (e.g.internal mixer) is preferably set to an initial temperature of 60. + -.10 ℃ and an initial speed of 50. + -.5 rpm. The reinforcing filler and various auxiliaries may be added in portions. For example, after the diene elastomer is added for the time required for mixing, the reinforcing filler is added, preferably at a speed of 60. + -.5 rpm, and when the temperature reaches preferably 120. + -.10 ℃ the mixing is continued with the addition of the other auxiliary agents. Preferably, other auxiliary agents are added to the mixture, the mixing temperature is up to 135 +/-5 ℃, cleaning is carried out, then mixing is continued, and rubber is discharged when the required total mixing time or temperature is reached.

In step (2), the mixing is preferably carried out in an internal mixer. The thermomechanical mixer (e.g.internal mixer) is preferably at an initial temperature of 50. + -.10 ℃ and a rotation speed of 50. + -.5 rpm. After the master batch is added and mixed for the required time, the crosslinking agent and the accelerator are preferably added and mixed for 120 +/-20 seconds, then sweeping is carried out, and then mixing is continued until the rubber is discharged when the required temperature is reached.

The method for evaluating the heat stability of the insoluble sulfur in the unvulcanized rubber can be used for screening the unvulcanized rubber with high heat stability of the insoluble sulfur, and the unvulcanized rubber with lower activation energy of the vulcanization reaction has higher heat stability of the insoluble sulfur.

The method has the advantage that the thermal stability of the insoluble sulfur in the rubber material actually produced can be accurately and directly evaluated, compared and judged. The method can be used for judging the thermal stability of the insoluble sulfur in the rubber, and compared with a method for directly testing the thermal stability of the insoluble sulfur, the method can be used for judging the thermal stability of the insoluble sulfur in the rubber material during actual application, and has important practical guiding significance.

The present invention will be illustrated below by way of specific examples. It should be understood that these examples are illustrative only and are not intended to limit the scope of the present invention. The methods, reagents and materials used in the examples are, unless otherwise indicated, conventional in the art. The starting compounds in the preparation examples are all commercially available.

Example 1

1) This example uses a practical production recipe for rubbers comprising different varieties of IS, consisting of the following components in parts by mass:

raw rubber, the brand SCR5, product of Xishuangbanna Zhonghua rubber Limited company, 100 parts;

carbon black N330, Shanghai Kabot carbon black Limited product, 50 parts;

5 parts of zinc oxide, product of Yonghua chemical technology (Jiangsu) limited company;

stearic acid, product of Yonghua chemical technology (Jiangsu) limited company, 2 parts;

insoluble sulfur, products of Saint chemical science and technology limited, IS-A, IS-B or IS-C, 4 parts;

accelerator NS, Saint Olympic chemical science and technology Limited, 0.8 part;

aromatic oil, TDAE, a product of petrochemical engineering Limited in Shanghai Beilan Xin, 6 parts;

microcrystalline wax, available from highland barley science and technology (Shanghai) Co., Ltd., 1.5 parts.

The thermal stability of 3 different batches of IS was tested using an oil bath method according to standard GB/T18592-.

Table 1: thermal stability of 3 IS

Different batches IS	IS-A	IS-B	IS-C
				105 ℃ IS based on the total sulfur content%	85.66	81.07	75.6
120 ℃ IS on total sulfur content%	55.81	51.46	44.76

2) Mixing process

The rubber material mixing is carried out in two sections.

The first-stage master batch is carried out in an internal mixer, and the mixing process comprises the following steps: the internal mixer has an initial temperature of 60 ℃ and an initial rotor speed of 50 rpm. Adding raw rubber, mixing for 80s, adding carbon black, increasing the rotating speed to 60rpm, adding other small materials when the temperature reaches 120 ℃, continuously mixing, cleaning when the temperature reaches 135 ℃, and continuously mixing for 450s or 145 ℃ to discharge rubber.

And carrying out two-stage final rubber mixing in an internal mixer, and discharging sheets by an open mill. The mixing process comprises the following steps: the initial temperature of the internal mixer IS 50 ℃, the rotating speed of the internal mixer IS 50rpm, a section of master batch IS added for mixing for 70s, then sulfur and an accelerant are added for mixing for 120s, cleaning IS carried out, mixing IS continued to 105 ℃, rubber discharging IS carried out, the sheet of the rubber material IS obtained, the thickness of the sheet IS controlled to be about 2.5mm, and three types of unvulcanized rubber (respectively containing IS-A, IS-B and IS-C) are obtained.

3) Test of the vulcanizers

The unvulcanized rubber was subjected to A vulcameter test according to the standard GB/T16584-.

Table 2: t90 data for compounds containing different IS at different temperatures

According to the Arrhenius equation

Taking logarithm on two sides to obtain

By substituting 1/T90 for k in the above formula, a curve can be obtained by plotting ln (T90) against 1/T, and fitting the curve to obtain a straight line. In the case of the IS-A containing compound, the fitting result IS shown in fig. 2, where the slope b IS E/R, so that E ═ b · R. The activation energy E of the various insoluble sulfur obtained was finally calculated and the results are shown in Table 3.

Table 3: activation energy of sizing materials containing different IS

Different batches IS	IS-A	IS-B	IS-C
				Activation energy E/(kJ/mol)	92.41	93.00	93.94

4) Variation of free sulfur content in unvulcanized rubber

According to the determination of free sulfur in rubber A by the copper spiral method in GB/T15251-2008, unvulcanized rubber materials with different parking times are tested, and the results are shown in FIG. 3.

The content of free sulphur in the initial state of the size, i.e. the ordinary sulphur content in IS, and the worse the thermal stability of IS, the higher the content of free sulphur. From the test results, it IS clear that the tendency of the free sulfur content in the group 3 IS containing compounds to vary with the standing time IS consistent, while the free sulfur content increases the fastest with increasing standing time for the compounds containing IS-C, which IS the least thermally stable compound.

5) Surface tackiness Change of uncured rubber

The adhesion test was performed on the unvulcanized rubber stock surface for different parking times according to the standard GB/T4852-2002 rolling method, and the results are shown in FIG. 4.

The sulfur content of the surface of the rubber material affects the viscosity of the surface of the rubber material, and the higher the sulfur content of the surface, the worse the viscosity of the rubber material, and the lower the viscous force. From the test results it IS clear that the poorer the thermal stability of IS, the higher the sulphur content occurring at the surface, ultimately resulting in a lower stickiness of the gum surface. The tendency of the viscous force between the 3 groups of IS-containing compounds with the standing time was consistent. Wherein the IS-A compound having the highest thermal stability exhibits the least reduction in tack with extended standing time.

By comparison, the data in table 1, fig. 3, and fig. 4 are consistent and all show the thermal stability differences of the three groups of IS. By correlating the thermal stability data of Table 1 with the activation energy data of the different insoluble sulfur in Table 3, it can be seen that the higher the thermal stability, the lower the activation energy of the vulcanization reaction, since the activation energy reflects the energy required for the vulcanization reaction, and the higher the thermal stability, the higher the content of insoluble sulfur in the rubber, the lower the content of elemental sulfur, and the faster the vulcanization speed of the insoluble sulfur than elemental sulfur, the lower the corresponding required activation energy of vulcanization.

Example 2

carbon black N330, Shanghai Kabot carbon black Limited product, 55 parts;

zinc oxide, product of Yonghua chemical technology (Jiangsu) limited company, 4 parts;

insoluble sulfur, products of Saint chemical science and technology limited, IS-D, IS-E or IS-F, 5 parts;

2 parts of microcrystalline wax, a product of highland barley New science and technology (Shanghai) limited company;

antioxidant 6PPD, Saint Olympic chemical technology products, 2;

1.5 parts of an anti-aging agent TMQ, a product of Shengao chemical science and technology Limited company;

aromatic oil, TDAE, a product of petrochemical engineering Limited in Shanghai Beilan Xin, 4 parts.

The thermal stability of 3 different batches of IS was tested using an oil bath according to standard GB/T18592-.

Table 4: thermal stability of 3 IS

Different batches IS	IS-D	IS-E	IS-F
				105 ℃ IS based on the total sulfur content%	84.36	82.03	77.82
120 ℃ IS on total sulfur content%	53.93	51.05	43.21

2) Mixing process

The rubber material mixing is carried out in two sections.

And carrying out two-stage final rubber mixing in an internal mixer, and discharging sheets by an open mill. The mixing process comprises the following steps: the initial temperature of the internal mixer IS 50 ℃, the rotating speed of the internal mixer IS 50rpm, a section of master batch IS added for mixing for 70s, then sulfur and an accelerant are added for mixing for 120s, cleaning IS carried out, mixing IS continued to 125 ℃ for rubber discharge, the rubber material IS obtained, the sheet IS discharged from the rubber material open mill, the thickness IS controlled to be about 2.5mm, and three types of unvulcanized rubber (respectively containing IS-D, IS-E and IS-F) are obtained.

3) Test of the vulcanizers

According to the standard GB/T16584-.

Table 5: t90 data for compounds containing different IS at different temperatures

According to the Arrhenius equation

Taking logarithm on two sides to obtain

The activation energy E of different insoluble sulfur was finally calculated by plotting 1/T90 instead of k in the above formula against 1/T to obtain a curve, fitting the curve to obtain a straight line with the slope b being E/R, so that E ═ b · R, and the results are shown in table 6.

Table 6: activation energy of sizing materials containing different IS

Due to the fact that the rubber discharge temperature IS increased, the properties of insoluble sulfur are changed in the rubber mixing process, and the reaction activation energy of rubber materials containing different IS in example 2 IS inconsistent with the thermal stability test result rule of the IS.

4) Variation of free sulfur content in unvulcanized rubber

The unvulcanized rubber stocks for different parking times were tested according to the determination of free sulfur in the standard GB/T15251-2008 rubber, and the results are shown in FIG. 5.

From the results, the least thermally stable IS increases the most rapidly with longer dwell time, but the most thermally stable IS-D free sulfur content IS not the lowest, indicating that the conversion of IS-D insoluble sulfur to ordinary sulfur IS greater than that of IS-E, which IS inconsistent with the thermal stability results, but IS consistent with the activation energy test results. Therefore, the thermal stability of the insoluble sulfur in the rubber material prepared by the rubber mixing process at the higher rubber discharge temperature cannot be accurately evaluated according to the thermal stability test result of the IS, and the thermal stability of the insoluble sulfur in the rubber material prepared by the rubber mixing process at the higher rubber discharge temperature can be accurately evaluated according to the activation energy test result obtained by the method.

5) Surface tackiness Change of uncured rubber

The adhesion test was performed on the unvulcanized rubber stock surface for different parking times according to the standard GB/T4852-2002 rolling method, and the results are shown in FIG. 6.

The poorer the thermal stability of IS, the higher the amount of sulfur present at the surface, ultimately resulting in a lower tack at the surface of the compound, although the thermal stability values of the IS-D test are the highest, but the tack drop of the compound IS not minimal with longer standing times, and IS-E drops more slowly at the surface, indicating that IS-E IS more stable during standing and the lowest amount of ordinary sulfur, consistent with the activation energy test results. The results also prove that the thermal stability of the insoluble sulfur in the rubber material prepared by the rubber mixing process at the higher rubber discharge temperature can not be accurately evaluated according to the thermal stability test result of the IS, and the thermal stability of the insoluble sulfur in the rubber material prepared by the rubber mixing process at the higher rubber discharge temperature can be accurately evaluated according to the activation energy test result obtained by the method.

From the above data, it can be seen that the actual stability of the insoluble sulfur in the rubber is inconsistent with the thermal stability data of the raw material directly tested due to the variations in the materials in the formulation and the differences in the rubber mixing process. The result obtained by the activation energy testing method is consistent with the actual free sulfur content and the rubber material surface viscosity result, and the thermal stability of the insoluble sulfur in the rubber can be truly reflected.

Claims

1. A method for evaluating the thermal stability of insoluble sulfur in an uncured rubber, said method comprising obtaining a curing reaction activation energy of an uncured rubber containing insoluble sulfur, the lower the curing reaction activation energy, the higher the thermal stability of the insoluble sulfur in the uncured rubber.

2. A method for screening unvulcanized rubber with high heat stability of insoluble sulfur, which is characterized in that the method comprises the step of obtaining the vulcanization reaction activation energy of the unvulcanized rubber containing different insoluble sulfur, and the unvulcanized rubber with lower vulcanization reaction activation energy has higher heat stability of the insoluble sulfur.

3. A method according to claim 1 or 2, characterized in that the method comprises the steps of:

4. The method of claim 3, wherein in step (1), the vulcanization time T90 of the uncured rubber containing insoluble sulfur at different temperatures is measured using a vulcameter.

5. The method according to claim 3, wherein in step (1), the test temperature for the vulcanization time T90 is between 135 ℃ and 185 ℃, and/or the vulcanization time T90 is determined for more than 3 temperatures.

6. The method of claim 3, wherein in step (1), the curing times T90 are measured at 140. + -. 2 ℃, 150. + -. 2 ℃, 160. + -. 2 ℃, 170. + -. 2 ℃ and 180. + -. 2 ℃.

7. The method of claim 3, wherein in step (2), the Aloneius equation is replaced with the reciprocal 1/T90 of the cure time T90

8. The method of claim 1 or 2, wherein the uncured rubber comprises the following components in parts by weight: 100 parts by weight of diene elastomer, 30-70 parts by weight of reinforcing filler, 1-10 parts by weight of insoluble sulfur, 0-10 parts by weight of active agent, 0-20 parts by weight of softener, 0-2 parts by weight of accelerator and 0-10 parts by weight of anti-aging agent.

9. The method of claim 1 or 2, wherein the uncured rubber is prepared by:

10. The method as claimed in claim 9, wherein in the step (1), the rubber is removed when the total mixing time reaches 300-; and/or in the step (2), discharging the glue when the temperature reaches 60-150 ℃.