CN111189748A

CN111189748A - Method for evaluating white carbon black dispersion degree based on torque continuous rising index

Info

Publication number: CN111189748A
Application number: CN202010090738.7A
Authority: CN
Inventors: 王丹灵; 左敏
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-02-13
Filing date: 2020-02-13
Publication date: 2020-05-22
Anticipated expiration: 2040-02-13
Also published as: CN111189748B

Abstract

The invention discloses an evaluation method of the dispersion degree of white carbon black in a white carbon black reinforced rubber material, which comprises the following steps: firstly, putting unvulcanized white carbon black reinforcing rubber material into a rotor-free vulcanizing instrument for vulcanizing for more than 30 minutes, and recording torques at different moments in the vulcanizing process, wherein the vulcanizing temperature is 140-190 ℃; then, a continuous torque rise index is calculated according to the torque at different moments, and the continuous torque rise index is equal to (T)_t2‑T_t2)/(t2‑t1)，T_t2Torque at time T2, T_t1Torque at time t 1; t2 > t1 > 3 min; and finally, judging the dispersion degree of the white carbon black in the white carbon black reinforcing rubber material according to the continuous torque rising index, wherein the smaller the continuous torque rising index is, the higher the dispersion degree of the white carbon black is. The evaluation method disclosed by the invention has the advantages of strong reproducibility and accurate judgment, and can directionally optimize the formula of the white carbon black reinforced rubber material and the preparation process of the white carbon black reinforced rubber material.

Description

Method for evaluating white carbon black dispersion degree based on torque continuous rising index

Technical Field

The invention relates to the technical field of reinforced rubber, in particular to a method for evaluating the dispersion degree of white carbon black in a white carbon black reinforced rubber material.

Background

In the tire industry, two main types of reinforcing materials (fillers) of rubber are carbon black and white carbon black. Carbon black has good compatibility with olefin rubbers such as natural rubber, styrene butadiene rubber and butadiene rubber due to its oleophylic property, so that the carbon black has good reinforcing effect on the rubbers, and vulcanized rubber of the carbon black often has high strength and elongation at break.

White carbon black is widely used in the tire field due to its low rolling resistance and high wet grip, compared to conventional carbon black. However, white carbon black is hydrophilic and has poor compatibility with olefin rubber, and is difficult to disperse in rubber. Even if the white carbon black particles are dispersed by strong shearing in the mixing process, the dispersed white carbon black particles can be flocculated together again in the subsequent vulcanization process. And the flocculation of the white carbon black can influence the performance of the final product.

The silane coupling agent is often used for reacting with silicon hydroxyl on the surface of the white carbon black, so that the lipophilicity of the white carbon black is improved, and the dispersing capacity of the white carbon black in rubber is improved. One end group (such as triethoxy, silyl and the like) of the silane coupling agent and the silicon hydroxyl on the surface of the white carbon black are subjected to chemical reaction in the mixing stage, and ethanol is removed. The other end can react with the rubber (such as tetrasulfanyl, thiocyanato and the like) to form a rubber-filler network with the rubber in the vulcanization stage, and then the rubber and the white carbon black are indirectly chemically grafted together, so that the aims of reducing the rolling resistance and improving the wetland holding capacity are fulfilled.

Any filler-reinforced rubber needs to be vulcanized to obtain further higher physical properties such as physical torque, and is therefore useful.

The torque (or modulus) of the filler reinforced compound is derived primarily from rubber-to-rubber forces, filler-to-filler forces, and filler-to-rubber forces. "vulcanization starts, shear modulus of the sample increases, and when recorded torque (force) rises to a stable value or a maximum value, a curve of the torque (force) versus time, namely a vulcanization curve, is obtained. The shape of the curve is related to the test temperature and the gum characteristics ". The cure curves for the carbon black reinforced compounds are shown in FIG. 1, where compound A and compound B are cured at different times but at the same torque in FIG. 1.

However, in the case of the silica-reinforced compound, the shear modulus of the sample increased during vulcanization, but the torque did not reach a steady value or a maximum value as vulcanization proceeded, but continued to increase. The vulcanization curves reported in the literature (of the amount of the alkali of the two and polymeric rubbers on the cross sizing of silica filled rubber compound. Kautschuk und Gummi Kunststoffe,2002,55(5): 236) 243) with the addition of 80phr of N234 carbon black and 80phr of white carbon black respectively are shown in FIG. 2, and it can be seen from FIG. 2 that, unlike carbon black compounds, the torque of compounds with the addition of white carbon black shows a continuous rise with the increase of the vulcanization time. However, there is currently no uniform parametric characterization and study of this phenomenon.

Disclosure of Invention

The invention provides a method for evaluating the dispersion degree of white carbon black based on a continuous torque rise index, which is used for calculating the continuous torque rise index according to torques at different moments so as to judge the dispersion degree of white carbon black in a white carbon black reinforced rubber material. The evaluation method has the advantages of strong reproducibility, accurate judgment and wide application.

The technical scheme provided by the invention for solving the technical problems is as follows:

a method for evaluating the dispersion degree of white carbon black in a white carbon black reinforcing sizing material comprises the following steps:

step 1: putting unvulcanized white carbon black reinforcing rubber material into a rotor-free vulcanizing instrument for vulcanizing for more than 30min and recording torques at different moments in the vulcanizing process, wherein the vulcanizing temperature is 140-190 ℃;

step 2: and calculating a torque continuous rising index according to the torque at different moments according to the following formula:

torque continuous rise index ═ T_t2-T_t1)/(t2-t1)；

The T is_t2Torque at time T2, said T_t1Torque at time t 1;

t2 is more than t1 is more than 3 min;

and step 3: and judging the dispersion degree of the white carbon black in the white carbon black reinforcing sizing material according to the continuous torque rising index, wherein the smaller the continuous torque rising index is, the higher the dispersion degree of the white carbon black is.

For the white carbon black reinforced rubber material, the vulcanization is generally carried out at the temperature of 140-190 ℃ for 30-60 min, and the rubber material basically finishes the vulcanization reaction. Therefore, the torque difference between t2 and t1 was divided by the time difference to obtain an index of the torque continuous increase, and the degree of white carbon black dispersion was evaluated.

The magnitude of the torque continuous rising index is closely related to the dispersion degree of the white carbon black, the physical property and the dynamic property of the sizing material and the fluctuation among batches. The torque of the white carbon black reinforced rubber is mainly derived from the white carbon black-white carbon black effect, the white carbon black-rubber effect and the rubber-rubber effect in the rubber material. After the rubber-rubber crosslinking with sulfur and accelerant is finished, the continuous increase of the rubber material torque mainly comes from the white carbon black-white carbon black effect, namely the flocculation phenomenon of the white carbon black at high temperature. If the white carbon black is well dispersed, the flocculation phenomenon at the later stage is also slow, and the relative continuous torque rise index is small. Therefore, the torque continuously rising index can be used to judge the degree of dispersion of white carbon black.

In addition, it is known that white carbon black is well dispersed, and can bring favorable influence on the physical properties and dynamic properties of vulcanized rubber. Meanwhile, if the continuous torque rise index is small, the difference of the torque of the rubber materials in different batches is small under the same vulcanization time, which means that the fluctuation between the batches is small.

The t1 is more than 30min and less than 60 min. The t2-t1 is more than 0min and less than or equal to 30 min.

The white carbon black reinforcing sizing material is prepared from solution polymerized styrene-butadiene rubber, emulsion polymerized styrene-butadiene rubber, natural rubber, polyisoprene rubber and the like, and the types are not limited.

The preparation method of the unvulcanized white carbon black reinforcing rubber material comprises the following steps of:

setting the rotor rotating speed of an internal mixer to be 20-40 rpm; the initial temperature is 30-60 ℃; the filling coefficient is 0.6-0.8;

adding rubber in 0 second; adding fine materials, a silane coupling agent and white carbon black accounting for 40-60% of the total amount in about 30 seconds; adding the rest white carbon black when the time is 100-300 seconds; the fine materials are zinc oxide, stearic acid, an anti-aging agent or protective wax;

adding softening oil when the temperature in the internal mixer rises to 80-110 ℃;

when the temperature in the internal mixer rises to the preset silanization reaction temperature, adjusting the rotating speed of the rotor to keep the temperature at the preset silanization reaction temperature, and carrying out silanization reaction;

and (e) finally mixing the rubber material obtained after the reaction in the step (e) on an open mill, adding sulfur and an accelerator, uniformly mixing and then discharging the mixture into a sheet.

The rubber is one or a mixture of at least two of solution polymerized styrene-butadiene rubber, cis-butadiene rubber, emulsion polymerized styrene-butadiene rubber, natural rubber, polyisoprene rubber and the like, preferably, the rubber is a mixture of solution polymerized styrene-butadiene rubber and cis-butadiene rubber, and the mixture ratio is not limited.

The white carbon black is precipitated silica, fumed silica, superfine silica gel, powdery synthetic aluminum silicate or calcium silicate. The white carbon black is common white carbon black or high-dispersion white carbon black produced by processes such as a precipitation method, a gas phase method and the like.

The silane coupling agent of the present invention is a silane containing a polysulfide bond, such as Si69 and Si 75; also mercapto group-containing silanes such as Si363 and NXT silane; it may also be a silane without any sulphur.

The preset silanization reaction temperature in the step (d) is 135-160 ℃; the preset reaction time is 40-200 seconds. The invention has the following beneficial effects:

(1) the method for evaluating the dispersion degree of the white carbon black based on the continuous torque rise index is simple and convenient to operate, high in reproducibility, accurate in judgment and wide in application.

(2) According to the invention, the dispersion performance of the white carbon black and the performance stability of the sizing material in the later vulcanization period are judged through the continuous torque rising index, the formula of the white carbon black reinforced sizing material and the preparation process of the white carbon black reinforced sizing material can be directionally optimized, and the method can also be used for judging the advantages and disadvantages of different types and grades of white carbon black.

Drawings

FIG. 1 is a vulcanization curve of a carbon black reinforced rubber.

FIG. 2 is a graph showing the curing curves and curing rate curves (curing temperature 165 ℃ C.) for carbon black and white carbon black.

FIG. 3 is a cure curve for case 1 of example 1.

Detailed Description

Example 1 torque continuous rise indexes of white carbon black reinforced rubber materials prepared by different formulas and different mixing processes are calculated.

Schemes 1-6, the formulation and mixing process of comparative example 1 are described in table 1:

table 1:

formulation (phr parts)	Scheme 1	Scheme 2	Scheme 3	Scheme 4	Scheme 5	Comparative example 1	Comparative example 2
								Solution polymerized styrene-butadiene rubber	75	75	75	75	75	75	75
Cis-butadiene rubber	25	25	25	25	25	25	25
								White carbon black	80	80	80	80	80	0	0
Carbon black	0	0	0	0	0	80	80
								Silane coupling agent Si69	6.4	6.4	6.4	6.4	6.4	6.4	0
Silane coupling agent Si75	0	0	0	0	0	0	6.4
								Softening oil	32.5	32.5	32.5	32.5	32.5	32.5	32.5
Others	10.7	10.7	10.7	10.7	10.7	10.7	10.7
								Total parts of	229.6	229.6	229.6	229.6	229.6	229.6	229.6
Silanization holding temperature/. degree.C	150	150	150	140	140	150	150
								Silanization retention time/s	60	120	180	120	180	120	120

The raw materials used in the formula are detailed:

solution polymerized styrene butadiene rubber, 4526-2HM, langsheng chemical product;

cis-butadiene rubber, BR9000, a product of the daqing petrochemical division of medium petroleum;

white carbon black, 1165MP, solvay chemical products;

carbon black, N234, cabot product;

silane coupling agent, Si69, conifer chemical;

silane coupling agent, Si75, conifer chemical;

softening oil, TDAE, hansheng chemical products; the rest raw materials are commercial industrial products.

The 7 formulas are respectively put into an internal mixer for mixing, the schemes 1-5 and the comparative examples 1-2 use the same process for mixing, and the concrete steps are as follows:

(a) setting the rotating speed of a rotor of the internal mixer to be 40 rpm; the initial temperature is 60 ℃; the filling factor is 0.7;

(b) all rubber was added at 0 second; adding 1/2 total amount of white carbon black, zinc oxide, stearic acid, anti-aging agent and protective wax at 30 s, and adding the rest white carbon black at 60 s;

(c) adding softening oil when the temperature of the internal mixer rises to 95 ℃;

(d) when the temperature of the internal mixer rises to the temperature of the silylation reaction corresponding to the scheme, the rotating speed of the rotor is adjusted to keep the temperature at the temperature of the silylation reaction corresponding to the scheme for the silylation reaction, and the reaction time is the silylation reaction time preset in the scheme 1-6 respectively;

example 1 used silane Si69, the silylation reaction temperature was 150 ℃, and the preset reaction time was 60 s; .

Example 2 used silane Si69, the silylation reaction temperature was 150 ℃, and the preset reaction time was 120 s;

example 3 used silane Si69, the silylation reaction temperature was 150 ℃, and the preset reaction time was 180 s;

example 4 used silane Si69, the silylation reaction temperature was 140 ℃, and the preset reaction time was 120 s;

example 5 used silane Si69, the silylation reaction temperature was 140 ℃, and the preset reaction time was 180 s;

example 6 used silane Si75, the silylation reaction temperature was 150 ℃, and the preset reaction time was 120 s;

in comparative examples 1 to 2, carbon black was used instead of silica, although the silylation reaction between silica and silane did not occur. But by contrast, still at a temperature of 150 ℃, for 120 s;

(e) after the reaction is finished, rubber is discharged, the rubber material is finally refined on an open mill, sulfur (10 percent of oil-filled sulfur powder, a tin-free lush product) and an accelerator (an accelerator CZ, a Shandong Shunhui product) are added, the mixture is uniformly mixed and then is discharged, and the mixture is kept stand for 8 hours.

The test was carried out in a rotorless vulcameter for 60 min. Taking T2-20 min, T1-40 min, schemes 1-5, and T of comparative example 1_40minAnd T_20minAs shown in table 2. Wherein the cure profile for scheme 1 is shown in figure 3.

TABLE 2

Scheme(s)	Scheme 1	Scheme 2	Scheme 3	Scheme 4	Square case 5	Comparative example 1	Comparative example 2
								T_40min/dNm	28.31	27.43	27.02	30.5	30.04	30.80	25.01
T_20min/dNm	25.32	24.97	24.93	25.98	25.74	30.80	24.33

The torque continuation increase indexes of the schemes 1 to 5 and the comparative examples 1 to 2 were calculated from the data in Table 2. The calculation results are shown in table 3.

TABLE 3

Performance testing

Vulcanizing unvulcanized white carbon black reinforced rubber material in a flat vulcanizing instrument under the vulcanizing condition of 160 ℃ for 15min to obtain vulcanized rubber, and then testing physical properties (tensile strength and elongation at break) and dynamic properties. The test results are shown in table 4.

And (3) representing the dispersion condition of the white carbon black in the vulcanized rubber by using a Payne effect. The Payne effect is tested in a rubber processing analyzer (RPA2000) under the conditions of 60 ℃, the testing frequency of 12Hz and the strain scanning range of 0-42%. The final Payne effect is the difference between the elastic modulus at 0% strain and the elastic modulus at 42% strain. The lower the Payne effect, the better the dispersion of the white carbon black.

The dynamic hysteresis loss of the compound, tan δ, was measured using a Dynamic Mechanical Analyzer (DMA). The test condition is 60 ℃, the test frequency is 12Hz, the static strain is 7 percent, the dynamic strain is +/-0.25 percent, and the temperature scanning range is-50-80 ℃. The wet grip of the tread rubber of the tire is generally characterized by the tan delta at 0 ℃, and the rolling resistance of the tread rubber is generally characterized by the tan delta at 60 ℃. And under the condition of better dispersion of the white carbon black, the tan delta at 60 ℃ is lower.

The test results of tensile strength, elongation at break, Payne effect, tan delta (0 ℃ C.) and tan delta (60 ℃ C.) are shown in Table 4.

TABLE 4

As can be seen by comparing schemes 1-5 in Table 4, the smaller the continuous torque rise index is, the lower the Payne effect is, the high dispersion degree of white carbon black is, the high stability of the rubber material is, and various performances of vulcanized rubber are obviously improved.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention, including any reference to the above-described embodiments. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. an evaluation method of silica dispersion degree in a silica reinforcing compound, is characterized in that, comprises the following steps:

Step 1: Put the unvulcanized silica reinforcing compound in a rotorless vulcanizer for more than 30 minutes and record the torque at different times during the vulcanization process. The vulcanization temperature is 140-190°C;

Step 2: Calculate the torque continuous increase index according to the torque at different times according to the following formula:

Torque continuous rising index=(T _t2 -T _t1 )/(t2-t1);

The T _t2 is the torque at the time t2, and the T _t1 is the torque at the time t1;

The t2>t1>3min;

Step 3: Judging the dispersion degree of silica in the silica reinforcing compound according to the torque continuous increase index, the smaller the torque continuous increase index, the higher the silica dispersion degree.

2 . The evaluation method according to claim 1 , wherein the t1 is greater than or equal to 30 minutes and less than or equal to 60 minutes. 3 .

3. The evaluation method according to claim 1, wherein the t2-t1 is greater than 0min and less than or equal to 30min.

4. evaluation method according to claim 1, is characterized in that, the preparation method of described unvulcanized white carbon black reinforcement compound comprises the following steps:

In step (a), the rotor speed of the internal mixer is set to be 20-40 rpm; the initial temperature is 30-60° C.; the filling factor is 0.6-0.8;

Step (b) adding rubber at 0 seconds; adding fines, silane coupling agent and 40% to 60% white carbon black in total at about 30 seconds; adding remaining white carbon black at 100 to 300 seconds; the fines Zinc oxide, stearic acid, antioxidant or protective wax;

Step (c) adding softening oil when the temperature in the internal mixer rises to 80-110°C;

In step (d), when the temperature in the internal mixer rises to the preset silylation reaction temperature, adjust the rotational speed of the rotor to keep the temperature at the preset silylation reaction temperature, and carry out the silylation reaction;

The sizing material obtained after the reaction in step (e) is finalized on an open mill, adding sulfur and an accelerator, and uniformly kneading to produce a sheet.

5 . The evaluation method according to claim 4 , wherein the rubber is a mixture of solution-polymerized styrene-butadiene rubber and cis-butadiene rubber. 6 .

6. evaluation method according to claim 1 or 4 is characterized in that, described white carbon black is precipitated silica, fumed silica, ultrafine silica gel, powdery synthetic aluminum silicate or calcium silicate.

7 . The evaluation method according to claim 4 , wherein the silane coupling agent is Si69, Si75, Si363 or NXT silane. 8 .

8 . The evaluation method according to claim 4 , wherein the preset silanization reaction temperature is 135-160° C.; and the silanization reaction time is 40-200 seconds. 9 .