JPS6140706B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a molding rubber composition containing vulcanized scrap rubber, and its purpose is to use natural rubber, SBR, and BR, which account for most of the vulcanized scrap rubber that has traditionally been discarded or incinerated. The aim is to reuse vulcanized scrap rubber, which uses petroleum process oils such as , IR, IIR, and EPDM as compounding agents, as a useful compounding agent. The problem of reusing vulcanized scrap rubber is a major issue in the rubber industry, and engineers in the rubber industry are most interested in how to utilize it to improve the performance of the resulting rubber. Therefore, many technologies have been provided to the world so far. The main methods include (1) a method of desulfurizing recycled rubber, and (2) a method of regenerating oil and carbon by thermal decomposition, which has recently been attracting attention.However, as a conventional technique close to the present invention, , (3) A method of using scrap rubber powder as it is as a compounding agent,
(4) There is a method of completely depolymerizing and dissolving rubber powder in high boiling point oil at a high temperature of 200°C or higher and blending it as a process oil. However, in method (3), in which scrap rubber powder is blended as is, the physical properties deteriorate significantly as the blending ratio increases, so the blending ratio is limited to approximately 10 parts by weight or less. Furthermore, the drawback of this method is that
The problems include poor dispersibility, large mold shrinkage, and when extrusion molding is performed, the surface condition of the molded product is poor, making it impractical. Recently, there has been a proposal (Japanese Patent Application Laid-Open No. 1983-6535) that it is possible to blend up to 50 parts by weight if the powder is pulverized to 70 mesh passes or less by deep cold pulverization, but this has the drawback that the pulverization cost is extremely high. . The method (4) of dissolving in high boiling point oil is useful as a substitute for process oil, and it is also proposed that up to 50 parts by weight of this type of dissolved product can be used as a compounding agent ( JP 50-109979) has also been made, but when the amount is increased to nearly 50 parts by weight, the physical properties of the obtained rubber inevitably deteriorate, and moreover, the tackiness increases, making rolling work extremely difficult. Therefore, it was not possible to expect a large increase in the blending ratio. Furthermore, the depolymerized melt increases in viscosity during dissolution due to its rapid rate of viscosity, requiring a powerful mixer such as a kneader, and handling of the product is also extremely difficult. In the present invention, the method shown in (3), which uses scrap rubber powder as it is as a compounding agent, has poor dispersion and weak bonding force at the rubber interface between the mixed scrap rubber powder and raw rubber, and the scrap rubber powder has a large reinforcing property. It seems that it only exists as an unexpected filler, and the methods shown in (1) and (4) involve depolymerization, so it is difficult to maintain the previous crosslinked state even if recrosslinked. Focusing on this, we investigated a method that would allow scrap rubber to be used in as large a quantity as possible without impairing its original performance, and at the same time would have sufficient bonding strength with the raw rubber, and as a result we have finally completed this process. That is, the above purpose is achieved by swelling and partially dissolving the particle surface of vulcanized scrap rubber with petroleum-based process oil, which has a weak action as a regenerating agent but is generally used as a rubber compounding agent. We were able to achieve this. Moreover, the effect was unexpected, as will be discussed later. Specifically, 100 parts by weight of pulverized vulcanized scrap rubber (the particle size does not need to be very small and may be about 5 mesh or less) and 50 to 50 parts by weight of petroleum-based process oil.
Mix 200 parts by weight of powdered scrap rubber and swell it at a temperature of 100 to 200°C to create a special vulcanized rubber composition (hereinafter simply referred to as a partially melted product) in which only the surface is partially dissolved. A partially dissolved product is blended with raw rubber and used. Furthermore, a vulcanizing agent,
It is the same as before that vulcanization accelerators, reinforcing agents, fillers, etc. are appropriately blended depending on the purpose. The production of the above partially melted product is extremely simple and can be carried out efficiently using a conventional mixer equipped with a heat source and stirring function. Furthermore, when the partially dissolved material is taken out of the mixer, it can be quickly cooled by putting it into water or by showering it with a large amount of water, which will eliminate the stickiness on the surface and make it easier to handle. The physical properties of the material are further improved. Vulcanized scrap rubber that can be used here is generally natural rubber, SBR.BR, which has weak oil resistance and can use petroleum process oil as a compounding agent.
It is a vulcanized rubber made from IR, IIR, EPDM, etc., and can be used, for example, from old tires, processing waste from rubber factories, etc. The method for pulverizing these vulcanized scrap rubbers does not need to be deep-cold pulverization or other special pulverization methods; rather, normal-temperature pulverization using a pulverizer such as a crusher roll or a disc grinder is sufficient. If the particle size of the powdered rubber is uniform to some extent below the mesh, it is suitable for partial melting of only a uniform surface. The petroleum-based process oil can be arbitrarily selected from common rubber compounding agents such as naphthenic, aromatic, and paraffinic compounds, and it is desirable to use one that is suitable for the raw material rubber to be compounded. The amount of process oil blended is 50 to 200 parts per 100 parts by weight of powdered rubber.
The parts by weight should be appropriate; if it is less than 50 parts by weight, sufficient swelling cannot be expected, and if it is more than 200 parts by weight, more process oil than necessary will be added. This is not preferable because it goes against the intention of blending as much as possible. The suitable temperature for heating the mixture of vulcanized scrap rubber and the above process oil is 100-200℃.
At temperatures above 200°C, the particles not only partially dissolve on the surface, but also depolymerize to the inside, causing excessive plasticization, or recombination and regelation between particles, resulting in a decrease in physical properties.
If the temperature is below 100℃, it will take a long time and is not practical. Therefore, the most suitable heating temperature is 150-190°C. Partial dissolution of vulcanized scrap rubber can be determined by confirming the presence of internal solid rubber by applying mechanical pressing force, but it can also be conveniently done by simply crushing it with your fingers and checking whether a core remains. As shown in the examples, it has not yet been completely elucidated why physical properties do not deteriorate even when a large amount of vulcanized scrap rubber is blended according to the present invention. However, based on the knowledge obtained from various experimental results, it has been found that by swelling the scrap rubber and partially dissolving only the surface, the inside of the scrap rubber retains the function of the original vulcanized rubber; It is thought that only the surface layer that has been dissolved or depolymerized is re-crosslinked at the same time as the unvulcanized rubber that is the raw material rubber, and that the scrap rubber and the raw rubber are firmly bonded. This means that when manufacturing a molding composition using EPDM as a raw material, (1) only a process oil is mixed with the raw material EPDM, and (2) a part of the above process oil is mixed with the raw material EPDM. The above raw material EPDM
Although the surface of vulcanized EPDM powder, which has a higher tensile strength than the vulcanized product of (1), was partially dissolved, and the process oil was adjusted to the same amount as (1),
This is evidenced by the fact that when comparing (1) and (2), the tensile strength of both after molding is higher for (2), which contains partially dissolved vulcanized EPDM powder. . As mentioned above, by rapidly cooling the partially melted material in water, the physical properties of the molded product subsequently obtained are significantly improved. There are various possible reasons for this, but the most important factor is believed to be improved dispersibility due to increased viscosity of the partially melted material.Furthermore, proper water content optimizes the crosslinking reaction with the raw rubber. considered to be a thing. The present invention is also effective for natural rubber such as old tires, but it is difficult to recycle them using conventional techniques.
Furthermore, SBR and EPDM contain large amounts of process oil.
It is noteworthy that it is effective for systems.
In addition, when mixing vulcanized scrap rubber powder and process oil, it is also possible to simultaneously mix carbon black and other compounding agents, or to use a partially melted material mixed with a raw material rubber with good compatibility in advance. It has become a useful method that is fully possible and has a wide range of applications. This will be explained in detail below using examples. Example 1 Crushed tire material that is thought to contain mostly natural rubber
After adding 200 parts by weight of naphthenic process oil (Flex 1400N, manufactured by Fuji Kosan Co., Ltd.) to 100 parts by weight of powdered rubber (manufactured by Hayakawa Rubber Co., Ltd.) of 30 meshes and stirring, steam heating can be performed from the outer periphery. When placed in a container and heated at 170°C for 24 hours, a partially dissolved product was obtained in which only the surface was partially dissolved. and (1) unvulcanized rubber only, (2) the above partially dissolved material,
(3) The above tire pulverized product and (4) commercially available recycled tire rubber (RS-0 manufactured by Hayakawa Rubber) were mixed with various compounding agents as shown in the upper column of Table 1, and then heated to 170°C.
Table 1 shows the physical properties of the products cured for 10 minutes. As is clear from Table 1, scrap rubber powder was blended as is (3) and commercially available recycled rubber was blended.
Comparison (2) according to the method of the present invention compared to case (4)
Not only is the product obtained by this process very good, but its physical properties are comparable to those of the case (1) in which no scrap rubber or the like is added. Furthermore, in the case of (3) and (4), the upper limit is 20 parts by weight, and adding more than this leads to further deterioration of physical properties, whereas in the method of the present invention shown in (2), 60 parts by weight is the upper limit. The fact that the above-mentioned results were obtained even with the addition of even parts by weight shows how superior the present invention is.

【table】

[Table] Example 2 The EPDM molding rubber composition shown in the formulation in Table 2 was vulcanized and then crushed in a disc grinder (manufactured by Kobe Kikai Co., Ltd.), and 100 parts by weight of 20 meshes were mixed with paraffin. 50 parts by weight of process oil (Samper 2280 manufactured by Sunoil Co., Ltd.) and 1 part by weight of pentachlorothiophenol (Pepta S manufactured by Kawaguchi Chemical Co., Ltd.)
After adding parts by weight, put it in a super mixer and heat it at 180℃ for 2 hours while stirring to dissolve the partially dissolved material.
(a). At the same time, this product was taken out of the mixer and rapidly cooled in a water tank to prepare a partially dissolved product (b). Table 2 shows the physical properties of molding rubber compositions using varying amounts of these partially dissolved vulcanized rubber compositions, which were vulcanized at 170°C for 20 minutes. As is clear from Table 2 below, even in the EPDM system, there is no decrease in physical properties up to 100 parts by weight (blended) in terms of powder rubber, and up to 200 parts by weight (blended)
However, it exhibited excellent effects with almost no deterioration in physical properties. Furthermore, it was found that the material that was rapidly cooled with water after being taken out of the mixer (formulation) had the same composition as the composition, but the physical properties were further improved. Example 3 Table 3 shows the formulation and physical properties of an EPDM vulcanized rubber composition for grinding.

[Table] Paraffinic process oil (Thumper 2280) was added to 100 parts by weight of this vulcanized rubber composition, which was pulverized with a disk blower and passed through 20 meshes.
Add 200 parts by weight and 1 part by weight of a pentachlorothiophenol mixture (Renasid 7 manufactured by Bayer),
When the mixture is placed in a separable flask and heated at 190° C. for 1 hour with stirring, a vulcanized rubber composition with only the surface partially dissolved is obtained. In addition, for comparison, the mixture was heated in the same manner at 250℃ for 2 hours with stirring.
A paste-like material in which the powdered rubber was completely melted was obtained. Table 4 shows the results of physical properties and mold shrinkage of formulation examples in which these recycled vulcanized rubber compositions were applied to the formulation of Example 2, and of those vulcanized at 170°C for 10 minutes. As is clear from Table 4 below, the products containing the partially melted product of the present invention exhibit much better physical properties than those containing the completely melted product or untreated powdered rubber. Furthermore, mold shrinkage, which is a drawback of untreated powdered rubber, has been improved. Further, from the physical property values in Tables 3 and 4, the physical properties are improved when a partially dissolved vulcanized rubber composition made from a vulcanized rubber with better physical properties is mixed. That is, the present invention is characterized by the unexpected effect that additivity is substantially established between the unvulcanized rubber and the partially dissolved vulcanized rubber composition. In addition, the unvulcanized rubber of the blend A of the present invention and the blend C of the untreated powder rubber was extruded using a test extruder with a diameter of 35 m/m.
Comparing the surface textures, it was found that Blend C had a rough surface due to the powdered rubber, while Blend A had a smooth surface texture and could be used practically as an extrusion molding composition.

【table】

【table】

【table】

Claims (1)

[Claims] 1. 100 parts by weight of pulverized vulcanized scrap rubber is mixed with 50 to 200 parts by weight of petroleum-based process oil,
The partially dissolved material obtained by swelling the pulverized product at a temperature of 200°C and partially dissolving its surface is blended into raw rubber, and a vulcanizing agent, a vulcanization accelerator, a reinforcing agent, a filler, etc. are appropriately blended. A method for producing a molding rubber composition containing vulcanized scrap rubber, characterized in that: 2. A method for producing a molding rubber composition containing vulcanized scrap rubber according to claim 1, wherein the partially dissolved material is rapidly cooled with water and then blended into the raw rubber.