JP6946766B2 - Evaluation method of interfacial adhesive strength - Google Patents

Description

The present invention relates to a novel method for evaluating a decrease in interfacial adhesive force due to thermal deterioration of a tire cord rubber composite.

Poor adhesion between the members constituting the tire may lead to a serious accident during running, so the tire is required to have high durability during running. Tires have rubber and tire cords that reinforce rubber, and the development of inexpensive and highly durable tires is being actively promoted by improving their bonding technology.

It is known that the adhesive strength differs depending on the method of fracture, and evaluation of the decrease in adhesive strength according to the deterioration condition and the fracture condition of the tire and its mechanism analysis are also important issues. Under these circumstances, a method that easily reproduces the fractured form of a tire on a laboratory scale and easily determines and evaluates a decrease in interfacial adhesive strength is strongly sought in order to promote the development of tires with improved adhesive durability. Has been done.

Patent Document 1 discloses a method of evaluating an adhesive force by measuring an adhesive force after a mechanical fatigue test. However, since this method is a method of applying stress by an external force, the deterioration of the cord is remarkable, the adhesive force of the adhesive interface (interface adhesive force) cannot be evaluated accurately, and the appearance of the tire is It is considered that the destroyed form has not been sufficiently reproduced.

International Publication No. 2013/118785

The present invention provides a method capable of reproducing the fracture mode actually occurring in a tire on a lab scale and easily evaluating a decrease in the interfacial adhesive force of the tire cord rubber composite.

As a result of diligent studies to solve the above problems, the present inventors have found that the fracture morphology of a tire can be reproduced on a laboratory scale by performing a pull-out test after supervulcanization. Furthermore, by calculating the rate of change between the adhesive strength at the initial stage of vulcanization and the adhesive strength after supervulcanization, the correlation between the equivalent vulcanization amount (ECU) and the decrease in interfacial adhesive strength can be easily evaluated. And completed the present invention.

That is, the present invention
[1] A method for evaluating the interfacial adhesive force of a tire cord rubber composite.
The first step of measuring the pull-out adhesive strength of a tire cord rubber composite given a specific amount of vulcanization,
For the same tire cord rubber composite used in the first step, the second step of measuring the pull-out adhesive force of the tire cord rubber composite when a larger amount of vulcanization is given than in the first step, and the above-mentioned An evaluation method including a third step of calculating the rate of change of the pull-out adhesive force calculated in the first step and the second step.
[2] The evaluation method according to [1], wherein the amount of vulcanization in the first step is less than 100 ECUs.
[3] pressurized硫量the second step Ru der least 200ECU, evaluation method of [1] or [2].
[4] The evaluation method according to [1] or [2], wherein the amount of vulcanization in the second step is 350 to 500 ECU.
[5] The evaluation method according to any one of [1] to [4], wherein the ratio of the ECUs in the first step and the second step is in the range of 2 to 20.
[6] A pull-out adhesive force-vulcanization amount curve is created for a plurality of tire cord rubber composites, and a range of vulcanization amounts in which the difference in the rate of change in the pull-out adhesive force between the tire cord rubber composites is large is specified. The evaluation method according to [1], further comprising a step.
[7] The evaluation method according to any one of [1] to [6], wherein the tire code is a fiber code.
Regarding.

According to the present invention, it is possible to reproduce the fracture mode actually occurring in the tire on a lab scale, prepare a large number of samples for the tire cord rubber composites having different vulcanization conditions, and reduce the interfacial adhesive force with the ECU. The correlation with and can be evaluated easily and appropriately. Therefore, the present invention can be a very useful method for promoting the development of a tire having improved adhesive durability.

It is a surface photograph of a tire after the tire destruction experiment of Reference Example 1. It is a surface photograph of the PET code after the tire destruction experiment of Reference Example 1. It is a photograph of the rubber surface after the tire destruction experiment of Reference Example 1 taken from above. It is a photograph taken from the side of the rubber surface after the tire destruction experiment of Reference Example 1. This is the result of plotting the changes in the ECU and the changes in the pull-out adhesive force of the test pieces on the tire cord rubber composites 1 to 3 to create a pull-out adhesive force-vulcanization amount curve. For the test pieces on the tire cord rubber composites 1 to 3, the changes in the ECU and the changes in the pull-out adhesive force when the pull-out adhesive force is 100 when the ECU is 50 are plotted, and the pull-out adhesive force-vulcanization amount is plotted. This is the result of creating a curve. It is a surface photograph of the PET2 side after performing a pull-out test after vulcanization deterioration of Example 1. It is a surface photograph of the rubber side after the drawing test was performed after the vulcanization deterioration of Example 1. It is a surface photograph of the PET2 side after performing a pull-out test after the deterioration of wet heat of Comparative Example 1. It is a surface photograph of the rubber side after the drawing test was performed after the vulcanization deterioration of Comparative Example 1.

Hereinafter, the configuration of the present invention will be described in detail.

According to the present invention, the fracture of the adhesive interface that actually occurs in a tire can be easily reproduced on a laboratory scale under supervulcanization conditions.

An equivalent vulcanization amount (ECU) can be mentioned as an index that is considered to reflect the amount of heat received by the vulcanized rubber during vulcanization. The ECU is defined as the amount of vulcanization at a certain vulcanization temperature and vulcanization time when the degree of vulcanization (vulcanization amount) at the reference temperature and the reference time is 1. Specifically, it is calculated by the following equation derived from the Arrhenius reaction rate equation.

ｔ₀：基準時間（分）
ｔ：加硫時間（分）
Ｅ：活性化エネルギー（ｋｃａｌ／ｍｏｌ）
Ｒ：気体定数（１．９８７×１０^-3ｋｃａｌ／ｍｏｌ／ｄｅｇ）
Ｔ₀：基準温度（Ｋ）
Ｔ：加硫中の加硫ゴムの測定温度（Ｋ）
ただし、活性化エネルギーは２０ｋｃａｌ／ｍｏｌ；基準温度は４１４．８５Ｋ；基準時間は１分とする。

t ₀ : Reference time (minutes)
t: Vulcanization time (minutes)
E: Activation energy (kcal / mol)
R: Gas constant (1.987 × 10 ^-3 kcal / mol / deg)
T ₀ : Reference temperature (K)
T: Measurement temperature (K) of vulcanized rubber during vulcanization
However, the activation energy is 20 kcal / mol; the reference temperature is 414.85 K; and the reference time is 1 minute.

The evaluation method of the present invention is the first step of measuring the pull-out adhesive force of the tire cord rubber composite given a specific amount of sulfide, and the first step for the same tire cord rubber composite used in the first step. The second step of measuring the pull-out adhesive force of the tire cord rubber composite when a brewing amount larger than that of the step is given, and the rate of change of the pull-out adhesive force calculated in the first step and the second step are calculated. The third step is included as a configuration.

The amount of vulcanization in the first step is not particularly limited, but is preferably less than 100 ECUs, more preferably 20 to 80 ECUs, still more preferably 40 to 60 ECUs, and particularly preferably 50 ECUs.

The amount of vulcanization in the second step is not particularly limited, but is preferably 200 ECU or more, more preferably 200 to 600 ECU, and further preferably 350 to 500 ECU.

The ratio of the ECUs in the first step and the second step is not particularly limited, but is preferably in the range of 2 to 20, more preferably in the range of 5 to 15, and even more preferably in the range of 7 to 10.

According to the present invention, it is possible to easily evaluate the correlation between the ECU and the decrease in the interfacial adhesive force of the tire cord rubber composite. It is also possible to give different vulcanization amounts to one tire cord rubber composite, plot the relationship between the ECU and the pull-out adhesive force, and create a pull-out adhesive force-vulcanization amount curve. By using the formula of the ECU, it is possible to change the vulcanization temperature and the vulcanization time even if the amount of heat is the same.

Further, according to the present invention, a pull-out adhesive force-vulcanization amount curve is created for a plurality of different tire cord rubber composites, and the vulcanization amount in which the difference in the rate of change of the pull-out adhesive force between the composites is large is specified. can do. That is, it is possible to easily find vulcanization conditions suitable for easily determining and evaluating a decrease in interfacial adhesive force, which has a particularly large difference in deterioration as compared with the existing tire cord rubber composite (Example 1, Example 1). (See FIGS. 5 and 6). Therefore, the present invention can be a very useful method for promoting the development of a tire having improved adhesive durability.

The tire cord rubber composite applicable to the evaluation method of the present invention is not particularly limited, but is suitably used for evaluating the adhesive strength of the fiber cord rubber composite.

<Rubber component>
As the rubber component used in this embodiment, isoprene-based rubber is preferably used. By blending isoprene-based rubber, durability, breaking strength, and peel resistance after moist heat deterioration (wet heat peel resistance) can be improved.

Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), modified natural rubber and the like. Examples of the modified natural rubber include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber and the like. Further, as NR and IR, those widely used in the field of tire manufacturing can be used. These rubbers may be used alone or in combination of two or more.

The content of the isoprene-based rubber in 100% by mass of the rubber component is not particularly limited, but is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more. be.

Examples of the rubber component used in addition to the isoprene-based rubber in the present embodiment include diene-based rubbers such as butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and chloroprene rubber (CR). Can be mentioned. These rubbers may be used alone or in combination of two or more.

The rubber composition produced in this embodiment may contain zinc oxide. The content of zinc oxide is not particularly limited, but is preferably 4 parts by mass or more, more preferably 6 parts by mass or more, and further preferably 7 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 4 parts by mass, the effect of zinc oxide as a vulcanization accelerator is not sufficiently obtained, and the durability, breaking strength, and peeling resistance after moist heat deterioration (wet heat peeling resistance) tend to decrease. .. The zinc oxide content is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 9 parts by mass or less. If it exceeds 12 parts by mass, the bending crack growth resistance tends to decrease, and the durability, breaking strength, and peeling resistance after moist heat deterioration (wet heat peeling resistance) tend to decrease.

The average primary particle size of zinc oxide is not particularly limited, but is preferably 200 nm or less, more preferably 150 nm or less, still more preferably 120 nm or less, and particularly preferably 90 nm or less.

The average primary particle size of zinc oxide is not particularly limited, but is preferably 20 nm or more, more preferably 50 nm or more. The average primary particle size of zinc oxide represents the average particle size (average primary particle size) converted from the specific surface area measured by the BET method by adsorption of nitrogen.

The rubber composition produced in this embodiment may contain carbon black. Thereby, the reinforcing property can be improved, and the durability and the breaking strength can be improved.

Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, SAF and the like. The carbon black may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is not particularly limited, but is preferably 50 m ² / g or more, more preferably 70 m ² / g or more, from the viewpoint of durability. Further, the nitrogen-adsorbing specific surface area of carbon black, from the viewpoint of processability, preferably 200 meters ² / g or less, more preferably 150 meters ² / g or less, more preferably 120 m ² / g or less, particularly preferably 100 m ² / It is less than or equal to g. If it exceeds 200 m ² / g, the Mooney viscosity tends to increase and the workability tends to decrease. The nitrogen adsorption specific surface area of carbon black is determined by the method A of JIS K 6217.

The content of carbon black is not particularly limited, but is preferably 40 parts by mass or more, and more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component.

The amount of dibutyl phthalate oil absorbed (DBP) of carbon black is not particularly limited, but is preferably 50 mL / 100 g or more, and more preferably 60 mL / 100 g or more. The DBP of carbon black is preferably 100 mL / 100 g or less, more preferably 90 mL / 100 g or less, and further preferably 80 mL / 100 g or less. The carbon black DBP is determined by the measuring method of JIS K 6217-4.

<Manufacturing of rubber composition>
Sulfur is preferably used as the vulcanizing agent in the production of the rubber composition used in the present embodiment. As the sulfur, powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and the like can be used.

The sulfur content is preferably 3.5 parts by mass or more, more preferably 4.0 parts by mass or more, and further preferably 4.5 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less. The sulfur content means the content of sulfur, and in the case of insoluble sulfur, it is the content of sulfur contained in the insoluble sulfur. In addition, a vulcanization accelerator or the like can be appropriately blended together with the above vulcanization agent.

In addition to the above-mentioned components, the rubber composition produced in the present embodiment includes a compounding agent generally used for producing the rubber composition, for example, a reinforcing filler such as silica, a silane coupling agent, stearic acid, and the like. Cobalt organic acid, anti-aging agent, processing aid, oil, wax and the like can be appropriately blended.

Examples of the oil include process oils, vegetable oils and fats, and mixtures thereof. Examples of the process oil include paraffin-based process oils, naphthen-based process oils, aromatic process oils (aromatic oils) and the like. Vegetable oils and fats include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, rosin, pine oil, pineapple, tall oil, corn oil, rice oil, beni flower oil, sesame oil, Examples thereof include olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil.

The content of the oil is not particularly limited, but is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more with respect to 100 parts by mass of the rubber component. The oil content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, and further preferably 3.0 parts by mass or less.

The rubber composition used in this embodiment is produced by a general method. That is, it can be produced by a method of kneading each of the above components with a Banbury mixer, a kneader, an open roll, or the like, and then vulcanizing.

<Manufacturing of tire cord rubber complex>
The rubber composition used in this embodiment is used as a rubber composition for coating a tire cord. Examples of the tire cord include a fiber cord and a steel cord. Examples of the fiber cord include cords obtained from raw materials such as polyamide, rayon, and polyester. Examples of the steel cord include a single-stranded steel cord having a 1 × n configuration, a layer-twisted steel cord having a k + m configuration (n is an integer of 1 to 27, k is an integer of 1 to 10, and m is an integer of 1 to 3). Such).

The tire cord and rubber exert an adhesive force through a dip liquid existing in the middle, and the typical dip prescription differs depending on the tire cord. For example, RFL (resorcin-formalin-latex) is used for nylon 66, which is a representative of polyamide cords. Further, in polyethylene terephthalate (PET) which is a representative of polyester cord, a mixture of epoxy / blocked isocyanate is used in the first layer, and RFL is used in the second layer.

The tire cord rubber composite test piece used in the evaluation method of the present invention is obtained by, for example, impregnating and adhering the dip liquid to the tire cord, heat-treating the tire cord, and then embedding the tire cord in unvulcanized rubber. Next, the unvulcanized rubber is vulcanized to integrate the tire cord and the rubber. The heat treatment temperature after impregnating and adhering the dip liquid to the tire cord is preferably 230 to 255 ° C, more preferably 235 to 250 ° C. The amount of the dip liquid adhering to the tire cord (increased mass due to the dip liquid based on the mass of the impregnated cord after drying) is preferably 2.0 to 7.0% by mass, preferably 2.0 to 7.0% by mass. It is more preferably 6.0% by mass, and particularly preferably 3.0 to 6.0% by mass. Further, the unvulcanized rubber is appropriately selected according to the use of the obtained rubber product.

Although the present invention will be described based on examples, the present invention is not limited to the examples.

The various chemicals used in Examples and Comparative Examples are shown below. Various chemicals were purified according to a conventional method as needed.
NR: TSR20
SBR: JSR1502 made by JSR
Carbon Black: Dia Black LH (N326, N2SA: 84m ² / g, DBP: 74mL / 100g) manufactured by Mitsubishi Chemical Corporation.
Oil: Diana process oil PS323 (mineral oil) manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent: Nocrack FR manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Zinc oxide: Fine particle zinc oxide (average primary particle size: 65 nm)
Sulfur: Cristex HSOT20 manufactured by Flexis (insoluble sulfur containing 80% by mass of sulfur and 20% by mass of oil)
Vulcanization accelerator: Noxeller DZ manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Cobalt stearate: cost-F (cobalt content 9.5% by mass) manufactured by Dainippon Ink and Chemicals Co., Ltd.
Nylon: 940dtex / 2 nylon cord manufactured by Ayaha Industries Co., Ltd. PET1: 1100dtex / 2 polyester cord manufactured by Hyosung Co., Ltd. (DIP1)
PET2: 1100dtex / 2 polyester cord (DIP2) manufactured by Hyosung Co., Ltd.

Production example <Production of unvulcanized rubber composition>
According to the formulation shown in Table 1, the materials other than sulfur and the vulcanization accelerator were kneaded under the condition of 150 ° C. for 5 minutes using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded for 5 minutes under the condition of 80 ° C. using a twin-screw open roll to obtain an unvulcanized rubber composition. The amount of sulfur compounded in Table 1 indicates the amount of insoluble sulfur (sulfur content + oil content).

<Preparation of tire cord rubber complex test piece>
The above-mentioned unvulcanized rubber composition in which the cords shown in Table 1 were embedded was molded to prepare tire cord rubber composite test pieces of Examples 1 to 3.

Reference example: Tire fracture test test Using the tire size (205 / 55R16), a machine durability test was conducted according to JIS D 4230 "Durability performance test method", and when the fracture surface was observed, the nylon part was covered with rubber. The surface of the cord was exposed in the PET portion, while it was in the same state as it was (Fig. 1). This suggests that the layer interface of the PET cord or the layer itself is destroyed. Further, when the surface image and the cross-sectional image of the tire fracture surface were analyzed, it was confirmed that the PET filament was detached from the dip layer and the dip layer was attached to the rubber side (FIGS. 2 to 4). From the above results, it was suggested that the adhesive force between PET and the epoxy / blocked isocyanate mixture in the first dip layer was weak.

Example: Overcure and pull-out test The test pieces of Examples 1 to 3 were vulcanized with a press vulcanizer according to JIS G 3510 "Rubber Adhesion Test Method" to give a vulcanized amount. Each of the above was subjected to a withdrawal test. The pull-out test was carried out using Autograph AGS-5kNX or AGS-10kNX (manufactured by Shimadzu Corporation) in accordance with JIS L 1017 "Chemical Fiber Tire Cord Test Method", and the maximum force required for pulling out was pulled out. The adhesive strength (N) was evaluated (Table 2, FIG. 5, FIG. 6). It should be noted that the greater the pull-out adhesive force, the more difficult it is to peel off, indicating that the adhesiveness is excellent.

From this result, when the ECU is in the range of 350 to 500, the difference in the rate of change in the pull-out adhesive force between the nylon rubber complex 1 and the PET rubber complexes 2 and 3 becomes particularly large, which is suitable for evaluating the difference in deterioration. It became clear that the conditions were met. Further, when the PET cord and the surface of the rubber after the withdrawal test were observed for the complex 1 to which the vulcanization amount of 430 ECU was given, a dip layer was attached to the rubber side, which was close to the fracture form in the tire. It was confirmed (FIGS. 7 and 8). Therefore, this method was considered to be a test method that matched the actual fracture conditions of the tire.

Comparative Example: Wet Heat Deterioration and Pull-out Test According to JIS K 7277 "Moist heat test method", the test piece of Example 3 which was moist heat-deteriorated for 6 days under the conditions of a temperature of 80 ° C. and a humidity of 95% was similarly pulled out. When the surface of the PET cord and the rubber was observed later, the rubber and the dip layer were attached to the surface of the PET filament, which was different from the fractured form in the tire (FIGS. 9 and 10). Therefore, it was considered that this method cannot be said to be a test method that appropriately reflects the tire fracture conditions.

According to the present invention, the fracture of the adhesive interface that actually occurs in a tire can be easily reproduced on a laboratory scale under supervulcanization conditions. In addition, a large number of samples can be prepared for tire cord rubber complexes having different vulcanization conditions, and the correlation between the ECU and the decrease in interfacial adhesive force can be easily and appropriately evaluated. Therefore, the present invention can be a very useful method for promoting the development of a tire having improved adhesive durability.

Claims (5)

This is a method for evaluating the interfacial adhesive strength of tire cord rubber complexes.
The first step of measuring the pull-out adhesive strength of a tire cord rubber composite given a specific amount of vulcanization,
The second step of measuring the pull-out adhesive force of the tire cord rubber composite when a vulcanization amount larger than that of the first step is applied to the same tire cord rubber composite used in the first step .
A third step of calculating a pre-Symbol first step and the rate of change of pull-out adhesion calculated in the second step, and
Includes a step of creating a pull-out adhesive force-vulcanization amount curve for a plurality of tire cord rubber composites and specifying a range of the vulcanization amount in which the difference in the rate of change in the pull-out adhesive force between the tire cord rubber composites becomes large. ,
An evaluation method in which the tire code is a fiber code. The evaluation method according to claim 1, wherein the amount of vulcanization in the first step is less than 100 ECUs. Ru der pressurized硫量or more 200ECU the second step, the evaluation method according to claim 1 or 2. The evaluation method according to claim 1 or 2, wherein the amount of vulcanization in the second step is 350 to 500 ECU. The evaluation method according to any one of claims 1 to 4, wherein the ratio of the ECUs in the first step and the second step is in the range of 2 to 20.

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