JP2019002780A - Evaluation method of interfacial adhesion force - Google Patents

Abstract

To provide a method capable of easily evaluating deterioration in interfacial adhesion force of a tire cord rubber composite.SOLUTION: An evaluation method of interfacial adhesion force of a tire cord rubber composite includes: a frist step of measuring drawing adhesion force of a tire cord rubber composite on which a specific amount of vulcanization is performed; a second step of performing a larger amount of vulcanization than in the first step on the same tire cord rubber composite used in the first step, so as to measure the drawing adhesion force of the tire cord rubber composite; and a third step of calculating a rate of change in the drawing adhesion force calculated in the first and second steps.SELECTED DRAWING: None

Description

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

  If the adhesion between the members constituting the tire is poor, there is a risk that a serious accident will occur during traveling. Therefore, the tire needs to have high durability during traveling. The tire has a tire and a tire cord that reinforces the rubber as a constitution, and development of an inexpensive and highly durable tire has been actively promoted by improving the bonding technique thereof.

  It is known that the adhesive strength varies depending on the method of fracture, and evaluation of the degradation of the adhesion force according to the deterioration condition and the fracture condition of the tire and the mechanism analysis thereof are also important issues. Under these circumstances, a method that easily reproduces the failure mode of a tire on a laboratory scale and easily determines and evaluates the decrease in interfacial adhesion is strongly sought after to promote the development of a tire with improved adhesion durability. It has been.

  Patent Document 1 discloses a method for evaluating an adhesive force by measuring an adhesive force after a mechanical fatigue test. However, since this method is a method of giving fatigue by an external force, the deterioration of the cord is remarkable, the adhesive force of the adhesive interface (interface adhesive force) cannot be accurately evaluated, and the appearance of the tire is It is thought that the destruction form cannot be reproduced sufficiently.

International Publication No. 2013/118785

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

  As a result of intensive studies for solving the above problems, the present inventors have found that the failure mode of a tire can be reproduced on a laboratory scale by performing a pull-out test after overvulcanization. Furthermore, the correlation between the equivalent vulcanization amount (ECU) and the decrease in the interfacial adhesive strength can be easily evaluated by calculating the rate of change of the adhesive strength at the initial stage of vulcanization and the adhesive strength after overvulcanization. The present invention was completed.

That is, the present invention
[1] A method for evaluating the interfacial adhesive strength of a tire cord rubber composite,
A first step of measuring the pull-out adhesion of a tire cord rubber composite having a specific vulcanization amount;
For the same tire cord rubber composite as used in the first step, the second step of measuring the pulling adhesion force of the tire cord rubber composite when a higher vulcanization amount is given than in the first step, and The evaluation method including the 3rd process of calculating the change rate of the drawing adhesive force calculated by the 1st process and the 2nd process.
[2] The evaluation method according to [1], wherein the vulcanization amount in the first step is less than 100 ECU.
[3] The evaluation method according to [1] or [2], wherein the vulcanization amount in the second step is 200 ECU or more.
[4] The evaluation method according to [1] or [2], wherein the vulcanization amount 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 drawing adhesion strength-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 drawing adhesion strength 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 cord is a fiber cord.
About.

  According to the present invention, the fracture mode actually occurring in the tire can be reproduced on a lab scale, and a large number of samples are prepared for tire cord rubber composites having different vulcanization conditions, and the adhesion between the ECU and the interface is reduced. Can be simply and appropriately evaluated. Therefore, the present invention can be a very useful technique for promoting the development of tires with improved adhesion durability.

4 is a photograph of the surface of a tire after a tire destruction experiment in Reference Example 1. 2 is a surface photograph of a PET cord after a tire breaking experiment of Reference Example 1. It is the photograph which image | photographed the rubber surface after the tire destruction experiment of the reference example 1 from the top. It is the photograph which image | photographed the rubber surface after the tire destruction experiment of the reference example 1 from the side. It is the result of having plotted the change of ECU and the change of drawing adhesion power about a test piece to tire cord rubber composites 1-3, and creating the drawing adhesion power-vulcanization amount curve. For the test pieces on the tire cord rubber composites 1 to 3, the change in the ECU and the change in the pull-out adhesion force when the pull-out adhesion force when the ECU is 50 are plotted as 100, and the pull-out adhesion force-vulcanization amount This is the result of creating a curve. 2 is a surface photograph on the PET 2 side after a pull-out test was conducted after vulcanization deterioration in Example 1. FIG. 2 is a rubber-side surface photograph after a pull-out test after vulcanization deterioration of Example 1. FIG. It is the surface photograph by the side of PET2 after performing a drawing test after the wet heat deterioration of the comparative example 1. 2 is a rubber-side surface photograph after a pull-out test after vulcanization deterioration of Comparative Example 1. FIG.

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

  According to the present invention, destruction of the adhesion interface actually occurring in a tire can be easily reproduced on a lab scale under overvulcanization conditions.

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

t ₀ : Reference time (minutes)
t: Vulcanization time (min)
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; the reference time is 1 minute.

  The evaluation method of the present invention is based on the first step of measuring the pullout adhesion of a tire cord rubber composite having a specific vulcanization amount, and the same tire cord rubber composite as that used in the first step. The second step of measuring the pulling adhesive strength of the tire cord rubber composite when a vulcanization amount greater than the step is given, and the change rate of the pulling adhesive force calculated in the first step and the second step are calculated. The third process is included as a configuration.

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

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

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

  ADVANTAGE OF THE INVENTION According to this invention, correlation with ECU and the fall of interface adhesive force can be easily evaluated about a tire cord rubber composite. Further, different vulcanization amounts can be given to one tire cord rubber composite, the relationship between the ECU and the pull-out adhesion force can be plotted, and a pull-out adhesion force-vulcanization amount curve can be created. If the ECU equation is used, the vulcanization temperature and vulcanization time can be changed even with the same amount of heat.

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

  The tire cord rubber composite that can be applied 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, it is possible to improve durability, breaking strength, and peel resistance after wet heat deterioration (wet heat peel resistance).

  Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. Examples of the modified natural rubber include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Moreover, what is generally used in the field of tire manufacture can be used as NR and IR. 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, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. is there.

  Examples of the rubber component used in addition to the isoprene rubber in the present embodiment include diene 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 as a vulcanization acceleration aid by adding zinc oxide cannot be obtained sufficiently, and durability, breaking strength, and peeling resistance after wet heat degradation (wet heat peeling resistance) tend to be reduced. . Further, the content of zinc oxide 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 resistance to flex crack growth will decrease, and the durability, breaking strength, and peel resistance after wet heat degradation (wet heat peel resistance) will tend to decrease.

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

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

  Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited thereto. 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 / g or less. When it exceeds 200 m ² / g, the Mooney viscosity increases and the processability tends to decrease. In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

  Although content of carbon black is not specifically limited, Preferably it is 40 mass parts or more with respect to 100 mass parts of rubber components, More preferably, it is 50 mass parts or more.

  The dibutyl phthalate oil absorption (DBP) of carbon black is not particularly limited, but is preferably 50 mL / 100 g or more, 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 still more preferably 80 mL / 100 g or less. In addition, DBP of carbon black is calculated | required by the measuring method of JISK6217-4.

<Manufacture of rubber composition>
In the production of the rubber composition used in the present embodiment, sulfur is suitably used as a vulcanizing agent. As 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 still more preferably 4.5 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 10.0 mass parts or less, More preferably, it is 6.0 mass parts or less. In addition, content of sulfur means content of sulfur content, and in the case of insoluble sulfur, it is content of the sulfur content contained in insoluble sulfur. Moreover, a vulcanization accelerator etc. can be suitably mix | blended with said vulcanizing agent.

  In addition to the above components, the rubber composition produced in the present embodiment includes a compounding agent generally used in the production of a rubber composition, for example, a reinforcing filler such as silica, a silane coupling agent, stearic acid, Organic acid cobalt, an antioxidant, a processing aid, oil, wax, and the like can be appropriately blended.

  Examples of the oil include process oil, vegetable oil and fat, and mixtures thereof. Examples of the process oil include paraffinic process oil, naphthenic process oil, aromatic process oil (aromatic oil), and the like. As vegetable oils and fats, castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut hot water, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil.

  Although content of oil is not specifically limited, Preferably it is 0.5 mass part or more with respect to 100 mass parts of rubber components, More preferably, it is 1.0 mass part or more. The oil content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, and still more preferably 3.0 parts by mass or less.

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

<Production of tire cord rubber composite>
The rubber composition used in the present embodiment is used as a rubber composition for covering a tire cord. Examples of tire cords include fiber cords and steel cords. Examples of fiber cords 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, and the like (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 the rubber exhibit an adhesive force through a dip liquid existing between them, and the typical dip prescription varies depending on the tire cord. For example, nylon 66, which is a representative polyamide cord, uses RFL (resorcin-formalin-latex). In polyethylene terephthalate (PET), which is a typical polyester cord, an epoxy / block isocyanate mixture is used for the first layer, and RFL is used for the second layer.

  The tire cord rubber composite test piece used in the evaluation method of the present invention is, for example, after impregnating and adhering the above dip solution to the tire cord, and then heat-treating, and then embedding the tire cord in unvulcanized rubber, Next, the unvulcanized rubber is vulcanized to produce a tire cord and rubber integrated together. The heat treatment temperature after impregnating and attaching the dip liquid to the tire cord is preferably 230 to 255 ° C, more preferably 235 to 250 ° C. Further, the amount of the dip liquid attached to the tire cord (the increased mass by 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 The content 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.

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

The various chemicals used in the examples and comparative examples are collectively shown below. Various chemicals were purified according to conventional methods as necessary.
NR: TSR20
SBR: JSR 1502 made by JSR
Carbon black: Dia Black LH (N326, N2SA: 84 m ² / g, DBP: 74 mL / 100 g) 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 Shinsei Chemical Industry Co., Ltd.
Zinc oxide: Fine zinc oxide (average primary particle size: 65 nm)
Sulfur: Kristex HSOT20 (insoluble sulfur containing 80% by mass of sulfur and 20% by mass of oil) manufactured by Flexis
Vulcanization accelerator: Noxeller DZ made by Ouchi Shinsei Chemical Co., Ltd.
Cobalt stearate: cost-F (cobalt content: 9.5% by mass) manufactured by Dainippon Ink & Chemicals, Inc.
Nylon: 940 dtex / 2 nylon cord PET manufactured by Ayaha Kogyo Co., Ltd. PET1: 1100 dtex / 2 polyester cord manufactured by Comet Co., Ltd. (DIP1)
PET2: 1100 dtex / 2 polyester cord (DIP2) manufactured by Comet Co., Ltd.

Production Example <Production of Unvulcanized Rubber Composition>
According to the composition shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. 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 kneaded for 5 minutes under a condition of 80 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition. The amount of sulfur in Table 1 indicates the amount of insoluble sulfur (sulfur content + oil content).

<Preparation of tire cord rubber composite specimen>
The unvulcanized rubber composition in which the cord shown in Table 1 was embedded was molded to prepare tire cord rubber composite test pieces of Examples 1 to 3.

Reference Example: Tire Destruction Test Using a test 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 cord surface was exposed in the PET part (FIG. 1), whereas it was in a state as it was. This suggested that the layer interface of the PET cord or the layer itself was destroyed. Furthermore, when the surface image and 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 the PET and the epoxy / block isocyanate mixture of the first dip layer was weak.

Example: Over cure and pull-out test For the test pieces of Examples 1 to 3, the test piece was vulcanized by a press vulcanizer according to JIS G 3510 "Rubber adhesion test method" and given a vulcanization amount. Each was subjected to a pull-out test. The pull-out test is carried out using Autograph AGS-5kNX or AGS-10kNX (manufactured by Shimadzu Corporation) according to JIS L 1017 “Test method for chemical fiber tire cords”, and pulls out the maximum force required for pull-out. The adhesive strength (N) was evaluated (Table 2, FIG. 5, FIG. 6). In addition, it shows that it is hard to peel and the adhesiveness is excellent, so that drawing-out adhesive force is large.

  From this result, when the ECU is in the range of 350 to 500, the difference in the rate of change in the pulling adhesive force between the nylon rubber composite 1 and the PET rubber composites 2 and 3 is particularly large, which is suitable for evaluating the difference in deterioration. It became clear that it was a condition. Further, regarding the composite 1 to which the vulcanization amount 430 ECU was given, the surface of the PET cord and the rubber after the pull-out test was observed. (FIGS. 7 and 8). Therefore, this method was considered to be a test method consistent with the actual fracture conditions of the tire.

Comparative example: wet heat deterioration and pull-out test In accordance with JIS K 7277 "wet heat test method", the pull-out test was similarly performed on the test piece of Example 3 that had been heat-heat deteriorated for 6 days under conditions of temperature 80 ° C and humidity 95%. When the surface of the later PET cord and rubber was observed, rubber and a dip layer were adhered to the surface of the PET filament, which was different from the destruction mode in the tire (FIGS. 9 and 10). Therefore, this method was not considered to be a test method that appropriately reflected the failure conditions of the tire.

  According to the present invention, destruction of the adhesion interface actually occurring in a tire can be easily reproduced on a lab scale under overvulcanization conditions. In addition, a large number of samples can be prepared for tire cord rubber composites having different vulcanization conditions, and the correlation between the ECU and the decrease in the interfacial adhesive force can be evaluated simply and appropriately. Therefore, the present invention can be a very useful technique for promoting the development of tires with improved adhesion durability.

Claims (7)

A method for evaluating the interfacial adhesion of a tire cord rubber composite,
A first step of measuring the pull-out adhesion of a tire cord rubber composite having a specific vulcanization amount;
For the same tire cord rubber composite as used in the first step, the second step of measuring the pulling adhesion force of the tire cord rubber composite when a higher vulcanization amount is given than in the first step, and The evaluation method including the 3rd process of calculating the change rate of the drawing adhesive force calculated by the 1st process and the 2nd process.   The evaluation method according to claim 1, wherein the vulcanization amount in the first step is less than 100 ECU.   The evaluation method according to claim 1 or 2, wherein the vulcanization amount in the second step is 200 ECU or more.   The evaluation method according to claim 1 or 2, wherein the vulcanization amount in the second step is 350 to 500 ECU.   The evaluation method as described in any one of Claims 1-4 whose ratio of ECU of a 1st process and a 2nd process is the range of 2-20.   A step of creating a drawing adhesion force-vulcanization amount curve for a plurality of tire cord rubber composites and identifying a range of vulcanization amounts in which a difference in the rate of change of the drawing adhesion strength between the tire cord rubber composites is increased; The evaluation method according to claim 1 comprising:   The evaluation method according to any one of claims 1 to 6, wherein the tire cord is a fiber cord.