WO2020130952A1

WO2020130952A1 - Elastomer mixture and method of its preparation

Info

Publication number: WO2020130952A1
Application number: PCT/SK2019/050015
Authority: WO
Inventors: Darina ONDRUŠOVÁ; Ivan LABAJ; Mariana PAJTÁŠOVÁ
Original assignee: Trenčianska univerzita Alexandra Dubčeka v Trenčíne
Priority date: 2018-12-19
Filing date: 2019-12-11
Publication date: 2020-06-25
Also published as: EP3898821A1; SK289160B6; SK500732018A3

Abstract

Elastomer mixture intended for production of rubber and rubber-metallic products, mainly for solid wheels of different types and sizes for transportation equipment containing 100 parts by weigh of natural rubber per 20 to 40 parts by weigh of carbon black, 40 to 60 parts by weigh of gypsum, 3 to 6 parts by weigh of zinc oxide, 1 to 4 parts by weigh of stearic acid, 1 to 5 parts by weigh of sulfur and 1 to 4 parts by weigh of vulcanization accelerator, wherein the gypsum is energo-gypsum. Method of preparation of elastomer mixture according to this invention by two- stage mixing, wherein individual ingredients are added to the rubber in stepwise manner, while mixing at 90 °C to 120 °C and 50 to 80 rpm.

Description

Elastomer mixture and method of its preparation

Technical field

This invention relates to an elastomer mixture for production of rubber and rubber-metallic products, mainly for various types and sizes of solid wheels for transportation equipment, and belongs to the field of material engineering. It relates to polymers and composites, more specifically production of rubber and rubber-metallic products.

Background Art

The elastomer mixture according to this invention is primarily intended for products produced by rubber industry that has recently used, almost exclusively, rubber mixtures with carbon black-based fillers, wherein parameters of the final product should meet criteria such as low rolling resistance, high rebound elasticity, required hardness, etc.

Considering the use of rubber and rubber-metallic products in automotive industry and other fields, it is demanded that production of rubber and rubber-metallic products uses elastomer mixtures that would be as inexpensive as possible, environment-friendly and retain the required properties of vulcanizates according to their intended function. Several patent documents have addressed this problem by using various types of natural and synthetic rubber and substitution of the carbon black as the filler.

Patent document CN104629107 discloses an elastomer mixture for production of antiskid tires, which contains rubber, butyl rubber, epoxy resin, carbon black, methacrylate, paraffin wax, polyethylene glycol and additives and agents.

Patent document CN104327431 discloses an elastomer mixture containing polymeric compounds, protein mixture, cellulose compounds, phosphate, tartaric acid as a cellulose compound filler, polymers, sulfonate, carbon black, magnesium oxide, vulcanizing agent and propenyl ether.

Document CN104327431 discloses an elastomer material in which a matrix is a synthetic mixed elastomer based on fluorocarbons (fluorobutadiene rubber) to which is added lots of additives. One of them is calcium sulfate dihydrate, but clearly as a pure substance. The material is characterized by high resistance to aging, radiation and it has high purity. The main disadvantage is a complicated recipe with a combination of many different types of fillers (cellulose compounds, carbon black, magnesium oxide, calcium sulfate dihydrate...). Quantity of used fillers increases the difficulty of preparation of the mixture and the fact that they are pure substances increases a price of the final product.

Patent document CN104031298 discloses an elastomer mixture for production of a flame- retardant rubber containing several rubber types, fatty acids, zinc oxide, aromatic oil, carbon black, white carbon black, PEG, agents, antioxidants, sulfate, sulfur and microcrystalline wax.

Gypsum (calcium sulfate dihydrate CaSCE^EhO) or silica has proven to be a suitable substitute or partial substitute of the filler. Silica is an industrially used light active filler, which is manufactured and has a high price.

Patent document CN102234387 discloses an elastomer mixture containing several types of rubber, zinc oxide, stearic acid, paraffin as a softener, sulfur, vulcanization accelerator, carbon black and calcium sulfate as a filler. The disadvantage of the present invention is the quite complicated recipe, as it contains three types of rubber and two types of carbon black. The calcium sulphate filler is used as a partial substitute for carbon black, however, the elastomer mixture according to the present invention contains a relatively high content of ecologically harmful carbon black and also the total fillers content is relatively high. The use of environmentally harmful softener is also a disadvantage.

Although the use of filler substitute can cut the price of elastomer mixture, other solutions have to be researched that use environment-friendly materials that retain the requested qualitative parameters of final products, yet reduce the final costs as much as possible. The required qualitative parameters of these products mainly include low values of rolling resistance combined with high rebound elasticity while maintaining the required hardness of the vulcanizates.

The required values of such combination of parameters depend on activity and composition of the vulcanization system, composition of the actual elastomer mixture and its mixing conditions. Physical and mechanical parameters of resulting vulcanizates are determined by type and amount of the filler used (carbon black or silica) in suitable mixing ratio and addition of softener (high- or low-aromatic oils). Nature of Invention

The role of this invention is to design elastomer mixture for production of rubber and rubber- metallic products, mainly for solid wheels of different types and sizes for transportation equipment, and method of its preparation that would be environmentally and economically beneficial, while retaining or improving required parameters of the final products. Main required qualitative parameters of these products include low values of rolling resistance combined with high rebound elasticity, while retaining the required vulcanizate hardness.

This can be achieved by substitution of carbon black in the role of filler as well as by substitution or omission of the commonly used low- or high-aromatic oil softeners that adversely affect the environment.

While the parameters of final products are affected by the actual vulcanization system and by mixing conditions of the elastomer mixture, the solution of the elastomer mixture design according to this invention includes a proposal of production conditions that vary, due to the required properties of vulcanizates, depending on composition of each mixture.

The nature of this invention is elastomer mixture recipe that includes partial substitution of nonecological carbon black with gypsum obtained as byproduct from power engineering. At the same time, substitution of carbon black with the alternative filler - energo-gypsum facilitates simplification of elastomer mixture composition, which therefore does not require use of softeners, thereby reducing the negative impact of aromatic oils on environment.

The elastomer mixture according to this invention contains rubber, carbon black and gypsum as fillers, zinc oxide, stearic acid, sulfur, vulcanization accelerator and the nature composition of the elastomer mixture contains 100 parts by weight of natural rubber per 20 to 40 parts by weight of carbon black, 40 to 60 parts by weight of gypsum (calcium sulfate dihydrate CaSCri 2H2O), 3 to 6 parts by weight of zinc oxide, 1 to 4 parts by weight of stearic acid, 1 to 5 parts by weight of sulfur and 1 to 4 parts by weight of vulcanization accelerator. The gypsum is energo-gypsum, a byproduct of flue gas desulfurization process in thermal power stations.

The recipe is simple and the simple nature of the elastomer mixture recipe according to this invention is based on use of single type of rubber and single type of carbon black. The carbon black and the energo-gypsum are used as fillers. The overall content of fillers in the elastomer mixture according to this invention is lower than that of the currently known elastomer mixtures intended for use in similar products whereas the content of the alternative filler - energo-gypsum prevails over the content of the standard filler - carbon black, unlike the currently known solutions, where carbon black is prevalent.

The more carbon black is replaced by energo-gypsum, the more the process is beneficial for the environment. Besides the actual replacement of nonecological carbon black with the alternative filler - gypsum, another environmental benefit is the use of energo-gypsum in place of gypsum. This material does not come from natural source but originates as byproduct of flue gas desulfurization process in thermal power stations, is produced in large amounts, which mostly accumulate as waste. A major advantage of the invention is the completely new way of re-using the energo-gypsum production that has been previously used only in civil engineering.

It has been generally known that softeners, high- or low-aromatic oils, have adverse impact on the environment. Another advantage is that no softeners are used in the elastomer mixture according to this invention.

Environmental benefits of the elastomer mixture according to this invention include mainly:

- substitution of nonecological carbon black,

- protection of natural mineral resources,

- use of energo-gypsum,

- making softeners unnecessary.

Elastomer mixture according to this invention is more economical as previously known elastomer mixtures, which also reduces the price of final products made of the elastomer mixture according to this invention.

Besides environmental and economic benefits, the elastomer mixture according to this invention also shows improvement of important properties, such as low rolling resistance, high rebound elasticity, while maintaining the optimum hardness. The elastomer mixture can be prepared from any natural rubber classified as TSR (technically specified rubber), such as SMR-10, SIR-20 and SVR-CV60.

To prepare the elastomer mixture, the following carbon black types can be used: N339, N330, N326, N351. Any accelerator from the following group can be used to accelerate the vulcanization: N-tert-butyl-2-benzothiazolesulfenamide (TBBS), N-cyclohexyl-2- benzothiazolesulfenamide (CBS), 2-(4-morpholinothio)benzothiazole (MBS), mercaptobenzothiazole disulfide (MBTS).

Preparation of the elastomer mixture according to this invention is carried out as two-stage mixing, i.e. it is performed in two stages. Individual ingredients of the elastomer mixture are added to the rubber in stepwise manner, while mixing at 90 to 120 °C and 50 to 80 revolutions per min, as follows:

Stage I of mixing includes the following steps:

- rubber is mixed 180 to 600 seconds, then another component is added - zinc oxide;

- rubber with zinc oxide are mixed 45 to 60 seconds, then other two components are added - carbon black and gypsum as the filler;

- rubber with zinc oxide and with carbon black and gypsum are mixed 180 to 300 seconds, then stearic acid is added;

- rubber with zinc oxide, carbon black and gypsum and stearic acid are mixed 30 to 60 seconds.

After the stage I of mixing, additional homogenization is performed on twin cylinder, then the mixture is let stand for 24 to 48 hours. After standing, the mixture is mixed for 180 to 300 seconds for additional blending (plastification), followed by the stage II of mixing.

Stage of mixing includes the following step:

- two additional components are added to the mixture obtained from the stage I of mixing, standing and plastification: sulfur and vulcanization accelerator; the mixture is then mixed 90 to 300 seconds.

After the stage II of mixing the elastomer mixture, additional homogenization is performed on twin cylinder and the elastomer mixture is let stand for 24 hours to 1 month (expiry period). Description of Figures

Fig. 1. Vulcanization curve of the prepared elastomer mixture with alternative energo-gypsum filler

Examples of Embodiments

Example 1

Elastomer mixture with alternative energo-gypsum filler, which is a power generation byproduct (PGBP) is prepared according to the recipe shown in Table 1 using the laboratory blender Plastograf Bradender with chamber volume 80 cm³. The elastomer mixture is prepared by two-stage mixing. Mixing is performed at 90 °C and 50 rpm. Mixing times of respective ingredients and sequence of their addition are specified in Table 2. Individual ingredients are added in the sequence shown and each ingredient is only added after mixing of the previous one (column 3). For the fillers energo-gypsum + carbon black N339, the time is measured only after mixing in the whole filler volume from the loading funnel of the blender.

After mixing of the first stage of elastomer mixture, additional homogenization is performed on twin cylinder and the mixture is let stand for 24 hours. After standing, the first stage mixture is added into blender chamber at 90 °C and 50 rpm for 3 minutes for additional blending of the mixture (plastification) and the second stage raw materials are added to the mixture. Mixing of the second stage is followed by additional homogenization on twin cylinder and the mixture is let stand for 24 hours.

Table 1. Elastomer mixture recipe

dsk = number of parts of additive per 100 parts of rubber Table 2. Feeding sequence of the additives into the mixture and the respective mixing time

Determination of vulcanization characteristics of elastomer mixture

Using the PRPA 2000 apparatus, the following vulcanization characteristics were determined:

- Time@2 dNm scorch S' - processing safety of the mixture - is important quality, mainly for molding of products of complex shapes. Safety value of the mixture expresses time, during which mixture warmed up to the vulcanization temperature does not vulcanize and is plastic - i.e. it retains fluid properties so it can fill even forms of complex shapes. Safety value of the mixture is also important in molding of products using an injection molding machine, which aspirates mixture into the reservoir of the injection molding machine and then warms it up. For mixture with low value of processing safety, undesirable premature vulcanization may occur during its storage in the injection molding machine’s reservoir. Vulcanization of the mixture is mainly observed inside injection nozzles and as impaired product quality. Particles (aggregates) of vulcanized mixture appear that are carried out of the injection nozzles by mixture during injection. On the other hand, too high safety value of the mixture causes elongation of the vulcanization process and increased costs of the process.

- Time@90% cure S' - optimum vulcanization time - Expresses the time at which 90 % of cross-linking reactions have taken place in the mixture. This value is important for achieving optimum properties of the final vulcanizate as well as for recalculation of the vulcanization time for products with higher thickness of rubber mixture. Higher value of optimum vulcanization time will cause longer vulcanization process and increased costs of the process.

Table 3 shows the measured vulcanization characteristics of the prepared elastomer mixture with alternative energo-gypsum filler (PGBP) compared to the vulcanization characteristics of the other two industrially used rubber mixtures (designated X, Y). Table 3. Vulcanization characteristics of the prepared elastomer mixture with alternative energo-gypsum filler (PGBP) and two industrially used rubber mixtures

The above results indicate that the processing safety value of the elastomer mixture prepared according to this embodiment with the alternative energo-gypsum filler is in the range between the values shown by the industrially used mixtures X and Y. From the comparison, it can be concluded that the elastomer mixture prepared according to this embodiment achieved a slight increase in time of the processing safety of the mixture compared to the X mixture. It can be stated that the elastomer mixture containing energo-gypsum is also more suitable for molding of products of complex shapes. At the same time, it has lower safety value compared to the Y mixture, which eliminates the risk of prolonging the vulcanization process and the associated cost increase.

In view of the optimum vulcanization time, the elastomer energo-gypsum mixture prepared according to this embodiment achieved the lowest value compared to the industrially used X and Y mixtures. Again, it can be pointed out that costs associated with the vulcanization process will be lower in the case of the elastomer energo-gypsum mixture compared to the X and Y mixtures. Alternative filler energo-gypsum likely affects and accelerates the vulcanization process by its ions content (S04² ).

Vulcanization curve of the prepared elastomer mixture with alternative energo-gypsum filler is shown in Fig. 1.

Determination of tensile properties

Table 4 shows the measured tensile strength and elongation values of the prepared mixture with alternative energo-gypsum filler, as well as the mixture commonly used to produce solid wheels in industry. Comparison of the data in Table 4 shows that the mixture with the alternative energo-gypsum filler achieves higher tensile strength values than the traditionally used mixture. The higher tensile strength with the alternative filler allows its application in the production of tensile products.

Comparison of elongation values of mixtures in the Table 4 shows that the elastomer mixture according to this invention reached up to 123.96 % higher value compared to the mixture commonly used in the industry. This result corresponds with the increased value of rebound elasticity of this elastomer mixture containing the alternative energo-gypsum filler.

Table 4. Measured tensile properties of elastomer mixture with alternative energo-gypsum filler according to this invention and industrially used mixtures

Determination of hardness and rebound elasticity hardness - rebound elasticity relationship In industrial use of elastomer mixtures in the form of final vulcanizates, it is necessary to maintain the hardness values required by technical documentation of the product, intended for the specific product type. The Table 5 shows measured hardness values of the prepared vulcanizate with alternative energo-gypsum filler according to this invention as well as that of the vulcanizate used in the industry (X) for the given product type - solid wheels. Lower hardness of the vulcanizate with alternative energo-gypsum filler can be attributed to the partial replacement of the commonly used carbon black filler with the alternative energo- gypsum filler. Carbon black belongs to active, toughening fillers and their increasing content also increases hardness value of the vulcanizate. On the contrary, alternative energo-gypsum filler is a semi-toughening filler (hardness only increases up to certain limit of filler content within the mixture).

Table 5. Comparison of the values of the vulcanizate hardness with the alternative energo- gypsum filler according to this invention and the industrially used vulcanizate (X)

Vulcanizate with alternative energo-gypsum filler achieves lower hardness level compared to mixture commonly used in the industry. The value, however, lies within the hardness range required for the application in question - production of solid wheels. Hardness of vulcanizate for this application is important to maintain the shape of the product (solid wheels) upon its loading during operation. Low hardness of elastomer vulcanizate could imply higher product deformation during operation and, therefore, change of its shape and dimensions, which would negatively impact performance of the product.

Another important property of vulcanizates for their application - production of solid wheels is the rebound elasticity value, which is related to the rolling resistance. Rebound elasticity can be defined as the ratio of returned energy to energy spent for deformation of testing body during impact of pendulum ply.

The involvement of rolling resistance can be described as decrease of rolling resistance value with increasing rebound elasticity value - less energy is spent for movement. Operation of solid wheel-like product type requires less energy for movement of the transportation equipment, even with higher loads.

Table 6. Comparison of the rebound elasticity of the vulcanizate with the alternative PGBP filler and industrially used vulcanizate

The values of hardness and rebound elasticity are closely interrelated and with use of common fillers such as carbon black, the rebound elasticity drops with increasing hardness values. Therefore, when using of carbon black, the rebound elasticity values must be increased by softening the mixture by addition of softener or by reducing the carbon black content. This brings about increased rubber content in the mixture, leading to increased prices of both the mixture and the final product.

The higher price of the mixture currently used in the industry is also related, besides the price of the softener, to its incorporation during mixing as well as ensuring good manipulation (most softeners require warming to required temperatures in order to achieve lower viscosity and, thereby, improved manipulation in the weighing process).

Elastomer mixture with alternative energo-gypsum filler according to this invention does not require addition of softeners, which eliminates all the negative effects mentioned above.

Example 2

Elastomer mixture with alternative energo-gypsum filler as the power generation byproduct (PGBP) is prepared as in Example 1 except that are used: natural rubber SIR-20, carbon black type N330 and vulcanization accelerator CBS and composition of the mixture is following:

The preparation method is identical to the preparation method as in Example 1 except that the mixing is performed at 100 °C and 70 rpm. and mixing time is shown in the following table:

Example 3

Elastomer mixture with alternative energo-gypsum filler as the power generation byproduct (PGBP) is prepared as in Example 1 except that are used: natural rubber SVR-CV60, carbon black type N326 and vulcanization accelerator MBS and composition of the mixture is following:

The preparation method is identical to the preparation method as in Example 1 except that mixing is performed at 105 °C and 60 rpm. and mixing time is shown in the following table:

Example 4

Elastomer mixture with alternative energo-gypsum filler as the power generation byproduct (PGBP) is prepared as in Example 1 except that are used: carbon black type N351 and vulcanization accelerator MBTS and composition of the mixture is following:

The preparation method is identical to the preparation method as in Example 1 except that mixing is performed at 115 °C and 75 rpm. and mixing time is shown in the following table:

Claims

1. An elastomer mixture intended for production of rubber and rubber-metallic products, mainly for solid wheels of different types and sizes for transportation equipment containing a rubber, a carbon black and a gypsum as fillers, a zinc oxide, a stearic acid, a sulfur and a vulcanization accelerator, characterized in that it contains 100 parts by weigh of natural rubber per 20 to 40 parts by weigh of carbon black, 40 to 60 parts by weigh of gypsum, 3 to 6 parts by weigh of zinc oxide, 1 to 4 parts by weigh of stearic acid, 1 to 5 parts by weigh of sulfur and 1 to 4 parts by weigh of vulcanization accelerator, wherein the gypsum is energo-gypsum.

2. The elastomer mixture according to claim 1, characterized in that the natural rubber is technically specified rubber.

3. The elastomer mixture according to claim 2, characterized in that the technically specified rubber is selected from the group consisting of SMR-10, SIR-20 and SVR- CV60.

4. The elastomer mixture according to any one of claims 1 to 3, characterized in that the carbon black is from the group of types: N339, N330, N326, N351.

5. The elastomer mixture according to any one of claims 1 to 4, characterized in that the vulcanization accelerator is from the group consisting of N-tert-butyl-2- benzothiazolesulfenamide, N-cyclohexyl-2-benzothiazolesulfenamide, 2-(4- morpholinothio) benzothi azole, 2,2 -dibenzothiazyl disulfide.

6. A method of preparation of elastomer mixture according to any one of claims 1 to 5, characterized in that is carried out as two-stage mixing, wherein individual ingredients are added to the rubber in stepwise manner, while mixing at 90 °C to 120 °C and 50 to 80 revolutions per min, as follows:

in the stage of mixing:

- the rubber is mixed 180 to 600 seconds, then another component is added - zinc oxide, the rubber with zinc oxide are mixed 45 to 60 seconds, then other two components are added - carbon black and gypsum as the filler,

- the rubber with zinc oxide and with carbon black and gypsum are mixed 180 to 300 seconds, then stearic acid is added,

- the rubber with zinc oxide, carbon black and gypsum and stearic acid are mixed 30 to 60 seconds; after the stage I of mixing, additional homogenization is performed on twin cylinder, then the mixture is let stand for 24 to 48 hours, after standing, the mixture is mixed for 180 to 300 seconds for additional blending (plastification), followed by the stage II of mixing.

in the stage of mixing:

- two additional components are added to the mixture obtained from the stage I of mixing and that sulfur and vulcanization accelerator and the elastomer mixture is mixed 90 to 300 seconds. after the stage II of mixing the elastomer mixture, additional homogenization is performed on twin cylinder and the elastomer mixture is let stand at least for 24 hours.