阅读说明：本技术 一种低硬度、低粘性的胎面橡胶组合物及其混炼方法和轮胎 (Low-hardness and low-viscosity tread rubber composition, mixing method thereof and tire ) 是由 任福君 黄大业 王丹灵 王菲菲 任会明 熊能 陈波宇 于 2021-07-27 设计创作，主要内容包括：本发明属于橡胶轮胎制造新材料技术领域,尤其涉及一种低硬度、低粘性的胎面橡胶组合物及其混炼方法和轮胎。本发明为了减少生胶体系对终炼胶门尼粘度的影响,应用了门尼较高的低Tg溶聚丁苯橡胶。辅以吸附型强的新型硅化合物,以此材料在保证低模量的同时,吸附一定的小分子物质,减少小分子的迁出。外加的防粘润滑助剂可以减少胎胚与金属模具的亲和力,降低粘模风险。从而使得胎面橡胶组合的门尼粘度较高、与金属的亲和力较低,不会发生终炼胶粘结成坨、硫化过程胎胚粘模具等问题。(The invention belongs to the technical field of new materials for manufacturing rubber tires, and particularly relates to a low-hardness and low-viscosity tread rubber composition, a mixing method thereof and a tire. In order to reduce the influence of a crude rubber system on the Mooney viscosity of final rubber, the invention applies the low-Tg solution-polymerized styrene-butadiene rubber with higher Mooney. The material is assisted with a novel silicon compound with strong adsorption, and can adsorb certain micromolecular substances and reduce the emigration of the micromolecules while ensuring low modulus. The added anti-sticking lubricating additive can reduce the affinity between the tire blank and a metal mold and reduce the risk of mold sticking. Therefore, the Mooney viscosity of the tread rubber composition is high, the affinity with metal is low, and the problems of final rubber compound bonding to lump, tire blank bonding to a mold in the vulcanization process and the like can be avoided.)

1. The tread rubber composition with low hardness and low viscosity is characterized by being prepared by mixing the following raw materials in parts by weight based on 100 parts by weight of pure rubber:

30-70 parts of natural rubber

10-40 parts of butadiene rubber

10-50 parts of solution polymerized styrene-butadiene rubber

40-70 parts of white carbon black

0-30 parts of carbon black

4.0 to 20 portions of nano amorphous silicon dioxide

0.5-5.0 parts of anti-sticking lubricating additive;

the solution polymerized styrene-butadiene rubber has the vinyl content of less than 10 percent in the polymer, the styrene content of less than 20 percent in the polymer, the glass transition temperature of less than-65 ℃ and the Mooney viscosity (ML1+4) of more than 70.

2. The low-hardness and low-viscosity tread rubber composition according to claim 1, wherein the composition is prepared by mixing the following raw materials, based on 100 parts by weight of pure rubber:

40-60 parts of natural rubber

20-30 parts of butadiene rubber

20-40 parts of solution polymerized styrene-butadiene rubber

45-55 parts of white carbon black

10-25 parts of carbon black

5.0-15 parts of nano amorphous silica

1.5-3.0 parts of anti-sticking lubricating additive.

3. The low-hardness low-viscosity tread rubber composition according to claim 1 or 2, wherein the solution-polymerized styrene-butadiene rubber has a vinyl content of 9% in the polymer, a styrene content of 18.7% in the polymer, a glass transition temperature of-73 ℃ and a Mooney viscosity (ML1+4) of 72.

4. The low-hardness low-viscosity tread rubber composition according to claim 1 or 2, wherein the anti-sticking lubrication auxiliary agent is obtained by compounding or reacting one or more of fatty acid calcium, fatty acid amide, fatty acid ester and monoglyceride.

5. The low-hardness low-viscosity tread rubber composition according to claim 1 or 2, wherein the amorphous silica is produced by silica powder TSI, Haerbin silica New materials Ltd.

6. The low-hardness low-viscosity tread rubber composition according to claim 1 or 2, wherein the raw materials of the composition further comprise an activator, a plasticizer, an anti-aging agent, an accelerator and a vulcanizing agent.

7. The low-hardness and low-viscosity tread rubber composition as claimed in claim 6, wherein the raw materials of the composition further comprise 20.0-25 parts of environmentally-friendly aromatic oil, 3.0-4.0 parts of silane coupling agent, 5.0-7.0 parts of alpha-methylstyrene resin, 1.0-2.0 parts of white carbon black dispersant, 1.5-3.0 parts of zinc oxide, 1.0-2.0 parts of stearic acid, 1.0-2.0 parts of antioxidant TMQ, 1.0-2.0 parts of antioxidant 6PPD, 1.0-2.0 parts of microcrystalline wax, 1.0-2.0 parts of accelerator NS, and 1.0-2.5 parts of sulfur.

8. The method for mixing a tread rubber composition having a low hardness and a low viscosity as claimed in claim 7, wherein the mixing is carried out by using an internal mixer of a tandem one-shot type, and the rotor speed of the internal mixer is controlled to be 30 to 55rpm, and the upper plug pressure is controlled to be 50 to 60N/cm²The temperature of the cooling water of the internal mixer is 25-35 ℃; the method comprises the following steps:

firstly, an upper auxiliary machine process:

adding rubber, carbon black, white carbon black, a silane coupling agent, a rubber active agent, a rubber anti-aging agent, a plasticizer, alpha-methylstyrene resin and nano amorphous silica, and pressing a top bolt to heat the rubber material to 105 ℃;

secondly, lifting the top plug to the proper position, adding environment-friendly aromatic oil, and keeping for 8 seconds;

thirdly, pressing a top bolt to heat the rubber material to 125 ℃;

lifting the top bolt to the proper position, and keeping for 5 seconds;

pressing the top bolt to heat the rubber material to 140 ℃;

pressing a top plug to mix the rubber material for 80 seconds at the constant temperature of 140-145 ℃;

seventhly, discharging the rubber material to a lower auxiliary machine;

II, auxiliary machine process:

firstly, heating the sizing material to 140 ℃;

② mixing at 140-145 ℃ for 150 seconds;

thirdly, discharging the glue to an extruder for sheet discharging;

vulcanizing by adopting a tangent internal mixer; controlling the rotor speed of the internal mixer to be 10-25rpm, the upper ram pressure to be 4.2 +/-0.2 bar and the cooling water temperature of the internal mixer to be 25-35 ℃;

thirdly, a vulcanization process:

adding master batch, vulcanized rubber, a rubber accelerator and an anti-sticking lubricating auxiliary agent, and pressing a top bolt to heat the rubber material to 75 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

thirdly, pressing a top bolt to heat the rubber material to 95 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

pressing the top bolt to heat the rubber material to 102 ℃;

lifting the top bolt to the proper position, and discharging the glue until the sheet is discharged from the extruder.

9. Use of the tread rubber composition of any of claims 1 to 7 for the preparation of a winter tyre.

10. A tire for winter use, characterized in that a tread rubber of the tire is obtained by vulcanizing the tread rubber composition of any one of claims 1 to 7.

Technical Field

The invention belongs to the technical field of new materials for manufacturing rubber tires, and particularly relates to a low-hardness and low-viscosity tread rubber composition, a mixing method thereof and a tire.

Background

In winter in cold regions, the temperature drops suddenly and the road surface has ice, snow and ice-snow mixture, which deteriorates the adhesion effect of the tire to the road surface, reduces the microcosmic contact area, and lowers the grip performance of the tire. Meanwhile, the glass transition temperature (Tg) of the tread of a common summer tire is higher, so that the tread is hardened under a low-temperature condition, the hysteresis effect of the tread is poor, the adhesion effect is reduced, the microcosmic contact area of the tire and the road surface is reduced, and the braking distance is further prolonged. Therefore, the common summer tire used in winter in cold areas can bring great potential safety hazards.

In order to solve and improve the above problems, tire companies are developing low hardness, low modulus, low Tg winter tires. The low Tg ensures that the hardness rise amplitude of the tread under the low-temperature condition is small, and reduces the influence of low temperature on hysteresis loss and microcosmic contact area. The microcosmic contact area is increased by low hardness and low modulus, and the ground gripping performance is improved.

At the present stage, it is a common practice for tire enterprises to fill a large amount of environment-friendly oil, resin, liquid rubber, etc. to ensure low hardness and low modulus. This design leads to better low temperature performance but typically results in very low mooney viscosity of the final mix, resulting in a cohesive mass of final mix that cannot be extruded, and problems with vulcanization sticking of the mold.

Disclosure of Invention

In order to solve the technical problems, the invention develops a low-hardness and low-viscosity tread rubber composition, and a winter tire produced by using the rubber composition has extremely high low-temperature ice and snow ground gripping performance, and simultaneously has no production problems of final rubber adhesion, vulcanization adhesion of a mold and the like.

In order to achieve the purpose, the invention adopts the following technical scheme:

the tread rubber composition with low hardness and low viscosity is prepared by mixing the following raw materials in parts by weight based on 100 parts by weight of pure rubber:

the solution polymerized styrene-butadiene rubber has the vinyl content of less than 10 percent in the polymer, the styrene content of less than 20 percent in the polymer, the glass transition temperature of less than-65 ℃ and the Mooney viscosity (ML1+4) of more than 70.

Preferably, the composition is prepared by mixing the following raw materials in parts by weight based on 100 parts by weight of pure rubber:

preferably, the solution-polymerized styrene-butadiene rubber has a vinyl group content of 9% in the polymer, a styrene content of 18.7% in the polymer, a glass transition temperature of-73 ℃ and a Mooney viscosity (ML1+4) of 72.

Preferably, the anti-sticking lubricating aid is obtained by compounding or reacting one or more of fatty acid calcium, fatty acid amide, fatty acid ester and monoglyceride.

Preferably, amorphous silica is produced by using silica powder TSI, harbin silica new material, ltd.

Preferably, the raw materials of the composition also comprise an active agent, a plasticizer, an anti-aging agent, a promoter and a vulcanizing agent.

Preferably, the raw materials of the composition also comprise 20.0-25 parts of environment-friendly aromatic oil, 3.0-4.0 parts of silane coupling agent, 5.0-7.0 parts of alpha-methyl styrene resin, 1.0-2.0 parts of white carbon black dispersing agent, 1.5-3.0 parts of zinc oxide, 1.0-2.0 parts of stearic acid, 1.0-2.0 parts of anti-aging agent TMQ, 1.0-2.0 parts of anti-aging agent 6PPD, 1.0-2.0 parts of microcrystalline wax, 1.0-2.0 parts of NS accelerator and 1.0-2.5 parts of sulfur.

Further, the invention also discloses a mixing method of the tread rubber composition, the method adopts a series one-time method internal mixer to mix rubber, the rotor speed of the internal mixer is controlled to be 30-55rpm, the upper top bolt pressure is controlled to be 50-60N/cm²The temperature of the cooling water of the internal mixer is 25-35 ℃; the method comprises the following steps:

firstly, an upper auxiliary machine process:

adding rubber, carbon black, white carbon black, a silane coupling agent, a rubber active agent, a rubber anti-aging agent, a plasticizer, alpha-methylstyrene resin and nano amorphous silica, and pressing a top bolt to heat the rubber material to 105 ℃;

secondly, lifting the top plug to the proper position, adding environment-friendly aromatic oil, and keeping for 8 seconds;

thirdly, pressing a top bolt to heat the rubber material to 125 ℃;

lifting the top bolt to the proper position, and keeping for 5 seconds;

pressing the top bolt to heat the rubber material to 140 ℃;

pressing a top plug to mix the rubber material for 80 seconds at the constant temperature of 140-145 ℃;

seventhly, discharging the rubber material to a lower auxiliary machine;

II, auxiliary machine process:

firstly, heating the sizing material to 140 ℃;

② mixing at 140-145 ℃ for 150 seconds;

thirdly, discharging the glue to an extruder for sheet discharging.

Vulcanizing by adopting a tangent internal mixer; controlling the rotor speed of the internal mixer to be 10-25rpm, the upper ram pressure to be 4.2 +/-0.2 bar and the cooling water temperature of the internal mixer to be 25-35 ℃;

thirdly, a vulcanization process:

adding master batch, vulcanized rubber, a rubber accelerator and an anti-sticking lubricating auxiliary agent, and pressing a top bolt to heat the rubber material to 75 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

thirdly, pressing a top bolt to heat the rubber material to 95 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

pressing the top bolt to heat the rubber material to 102 ℃;

lifting the top bolt to the proper position, and discharging the glue until the sheet is discharged from the extruder.

Further, the invention also discloses application of the tread rubber composition in preparing winter tires.

Furthermore, the invention also discloses a winter tire, and the tread rubber of the tire is prepared by vulcanizing the tread rubber composition.

The beneficial effects of adopting the technical scheme are that: in order to reduce the influence of a crude rubber system on the Mooney viscosity of final rubber, the invention applies the low-Tg solution-polymerized styrene-butadiene rubber with higher Mooney. The material is supplemented with strong adsorption type nano amorphous silica, so that a certain small molecular substance is adsorbed while the low modulus is ensured, and the emigration of the small molecules is reduced. The added anti-sticking lubricating additive can reduce the affinity between the tire blank and a metal mold and reduce the risk of mold sticking. Therefore, the Mooney viscosity of the tread rubber composition is high, the affinity with metal is low, and the problems of final rubber compound bonding to lump, tire blank bonding to a mold in the vulcanization process and the like can be avoided.

Detailed Description

The technical solutions in the embodiments of the present invention will be described in detail and fully below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. Given the embodiments of the present invention, all other embodiments that can be obtained by a person of ordinary skill in the art without any inventive step are within the scope of the present invention.

Reference ratio

The raw materials comprise: 55.0 parts of natural rubber, 30.0 parts of butadiene rubber, 15.0 parts of emulsion polymerized styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS and 1.7 parts of sulfur.

Wherein the emulsion polymerized styrene butadiene rubber is SBR 1500; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

Comparative example 1

The raw materials comprise: 55.0 parts of natural rubber, 30.0 parts of butadiene rubber, 15.0 parts of emulsion styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS, 1.7 parts of sulfur and 5.0 parts of nano amorphous silica.

Wherein, the nano amorphous silicon dioxide is sold as silicon lattice powder TSI and produced by Harbin silicon lattice new material company Limited; the emulsion polymerized styrene butadiene rubber is SBR 1500; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

Comparative example 2

The raw materials comprise: 55.0 parts of natural rubber, 30.0 parts of butadiene rubber, 15.0 parts of emulsion polymerized styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS, 1.7 parts of sulfur and 2.5 parts of anti-sticking lubricating auxiliary agent.

Wherein, the anti-sticking lubricating additive is obtained by the reaction of fatty acid calcium and fatty acid amide under the high-temperature condition; the emulsion polymerized styrene butadiene rubber is SBR 1500; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

Comparative example 3

The raw materials comprise: 55.0 parts of natural rubber, 25.0 parts of butadiene rubber, 22.99 parts of solution polymerized styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS and 1.7 parts of sulfur.

Wherein the solution polymerized styrene-butadiene rubber contains 9 percent of vinyl, 18.7 percent of styrene, 72 percent of Mooney viscosity (ML1+4) and 13 percent of oil; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

Example 1

The raw materials comprise: 55.0 parts of natural rubber, 25.0 parts of butadiene rubber, 22.99 parts of solution polymerized styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS, 1.7 parts of sulfur, 5.0 parts of nano amorphous silicon dioxide and 2.5 parts of anti-sticking lubricating auxiliary agent.

Wherein the solution polymerized styrene-butadiene rubber contains 9 percent of vinyl, 18.7 percent of styrene, 72 percent of Mooney viscosity (ML1+4) and 13 percent of oil; nano amorphous silica with the trade name of silica powder TSI, produced by Harbin silica New Material Co., Ltd; the anti-sticking lubricating additive is obtained by reacting fatty acid calcium and fatty acid amide at high temperature; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

Example 2

The raw materials comprise: 55.0 parts of natural rubber, 20.0 parts of butadiene rubber, 28.74 parts of solution polymerized styrene-butadiene rubber, 18.0 parts of carbon black, 50.0 parts of white carbon black, 22.0 parts of environment-friendly aromatic oil, 3.6 parts of silane coupling agent, 6.0 parts of alpha-methylstyrene resin, 1.5 parts of white carbon black dispersing agent, 2.0 parts of zinc oxide, 1.5 parts of stearic acid, 1.5 parts of anti-aging agent TMQ, 1.5 parts of anti-aging agent 6PPD, 1.5 parts of microcrystalline wax, 1.6 parts of accelerator NS, 1.7 parts of sulfur, 5.0 parts of nano amorphous silicon dioxide and 2.5 parts of anti-sticking lubricating auxiliary agent.

Wherein the solution polymerized styrene-butadiene rubber contains 9 percent of vinyl, 18.7 percent of styrene, 72 percent of Mooney viscosity (ML1+4) and 13 percent of oil; nano amorphous silica with the trade name of silica powder TSI, produced by Harbin silica New Material Co., Ltd; the anti-sticking lubricating additive is obtained by reacting fatty acid calcium and fatty acid amide at high temperature; the silane coupling agent is one of TESPD and TESPT; the remaining products are all commercially available.

The rubber material mixing method of the reference proportion, the comparative proportion and the embodiment adopts a series one-step internal mixer for mixing rubber, the rotor speed of the internal mixer is controlled to be 30-55rpm, and the upper ram pressure is controlled to be 50-60N/cm²The temperature of the cooling water of the internal mixer is 25-35 ℃; the method comprises the following steps:

firstly, an upper auxiliary machine process:

adding rubber, carbon black, white carbon black, a silane coupling agent, a rubber active agent, a rubber anti-aging agent, a plasticizer, alpha-methylstyrene resin and nano amorphous silica (if any), and pressing a top bolt to heat the rubber material to 105 ℃;

secondly, lifting the top plug to the proper position, adding environment-friendly aromatic oil, and keeping for 8 seconds;

thirdly, pressing a top bolt to heat the rubber material to 125 ℃;

lifting the top bolt to the proper position, and keeping for 5 seconds;

pressing the top bolt to heat the rubber material to 140 ℃;

pressing a top plug to mix the rubber material for 80 seconds at the constant temperature of 140-145 ℃;

seventhly, discharging the rubber material to a lower auxiliary machine;

II, auxiliary machine process:

firstly, heating the sizing material to 140 ℃;

② mixing at 140-145 ℃ for 150 seconds;

thirdly, discharging the glue to an extruder for sheet discharging.

Vulcanizing by adopting a tangent internal mixer; controlling the rotor speed of the internal mixer to be 10-25rpm, the upper ram pressure to be 4.2 +/-0.2 bar and the cooling water temperature of the internal mixer to be 25-35 ℃;

thirdly, a vulcanization process:

adding master batch, vulcanized rubber, rubber accelerator and anti-sticking lubricating additive (if any), and pressing a top bolt to heat the rubber material to 75 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

thirdly, pressing a top bolt to heat the rubber material to 95 ℃;

lifting the top bolt to the proper position, and keeping for 10 seconds;

pressing the top bolt to heat the rubber material to 102 ℃;

lifting the top bolt to the proper position, and discharging the glue until the sheet is discharged from the extruder.

The relevant performance parameters of the rubber compositions obtained from the reference proportions and examples are shown in Table 1. In Table 1, the data of the examples are processed with the properties of the reference example as 100%, except for the Mooney viscosity and hardness results.

The dynamic viscoelastic property of the rubber composition is represented by adopting a DMA (direct memory access) test method, the wet grip performance of the rubber composition is represented by tan delta at 0 ℃, and the higher the numerical value is, the better the wet grip performance is; the heat buildup of the rubber composition is characterized by tan delta at 60 ℃, with higher values giving lower heat buildup; the low temperature properties of the rubber compositions are characterized by E' at-30 ℃, the higher the number the better.

Table 1 reference proportions and example compound related performance parameters

The tire is trial-manufactured for the reference example and the example VI with the best performance, the adhesion of the final rubber compound and the vulcanization sticking condition are verified, the wet grip, the rolling resistance and the low-temperature performance of the tire are tested, and the evaluation result is shown in the table 2. Except for the conditions of final rubber mixing adhesion and vulcanization die adhesion, the evaluation results of the other examples are that the performance of the reference example is 100 percent, and the higher the value is, the better the performance is.

TABLE 2 reference proportions and final rubber in examples and evaluation results of tires (tire specification 205/55R16)

	Reference ratio	Example VI
			Wet land braking/%)	100	100.9
Iced land braking/%)	100	139.2
			Snow brake/%)	100	108.7
Rolling resistance/%)	100	100.7

The results of the above tests on compounds show that a tread rubber composition with low hardness and low viscosity has a higher Mooney viscosity, a lower hardness, a smaller change in hardness at low temperatures and a lower modulus at low temperatures. The DMA predicted wetland performance, low-temperature performance and rolling resistance performance are excellent, and the Tg meets the design requirement. The rubber composition has no problems of final rubber compound adhesion and mold vulcanization adhesion. The winter tyre trial-manufactured by using the rubber composition is slightly superior to reference ratio in wet performance and rolling resistance performance, and has obvious performance improvement on low-temperature performance.

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-mentioned 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.