2. Description of the Prior Art Waste tires, which are now generated in large quantities, have been used as a source from which a variety of goods can be molded. Conventionally, adhesives have been used in manufacturing waste tires into goods. However, they are insufficiently competitive in terms of production cost because the, adhesives added to vulcanized waste tire powder are expensive. Much effort has been made to avoid the problems. For example, reference may be made to the patents which have been made by the applicant of the present invention, Korean Pat. Laid-Open Publication No. 97-027524, which discloses the manufacture of rubber blocks from waste tires by use of latex, and Korean Pat. Appl'n No. 98-63410,

which introduces the use of DEG in molding waste tires with the aim of improving commercial values of the goods.

However, physical properties of the molded goods made by use of latex or DEG are poorer than those of the molded goods using the adhesive, as shown in Fig. l. Therefore, there remains a need for improving physical properties of the goods molded from waste tires with maintenance of a low production cost.

SUMMARY OF THE INVENTION The present inventors have conducted extensive studies into the treatment and uses of scrap rubber produced by the rubber industry, reaching the conclusion that a combination of additives, including process oil, a vulcanizing accelerant, and a vulcanizing agent, can bring about an improvement in physical properties of the goods molded from waste tires.

Therefore, it is an object of the present invention to provide goods molded from waste tires, which can be produced at a low production cost with high physical properties.

It is another object of the present invention to provide a method for manufacturing such goods recycled from waste tires.

In accordance with an aspect of the present invention,

there is provided a method for manufacturing rubber goods from waste rubber powder, comprising the steps of: admixing 10-20 ml of a process oil, 2-3 parts by weight of a vulcanizing accelerant, 5-10 parts by weight of a vulcanizing agent, 0-15 parts by weight of a pine resin with 100 parts by weight of a waste rubber powder; uniformly homogenizing the admixture ; melting the admixture at 150 to 170°C in a mold ; and molding the melt into goods.

In accordance with another aspect of the present invention, there is provided a composition of recycled goods, comprising 100 parts by weight of waste rubber powder, 10 to 20 ml of a process oil, 2 to 3 parts by weight of a vulcanizing accelerant, 5 to 10 parts by weight of a vulcanizing agent, and 0 to 15 parts by weight of a pine resin.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a histogram illustrating physical properties of waste tire-recycled goods according to kinds of additives.

Figs. 2 and 3 are histograms illustrating physical

properties of waste rubber-recycled goods according to kinds of waste rubbers and process oils.

Figs. 4 and 5 are curves illustrating the change of physical properties of waste rubber-recycled goods with amounts of pine resin added to the goods.

DETAILED DESCRIPTION OF THE INVENTION The present invention pertains to recycling of waste rubber, which is generated in a large quantity in the rubber industry. Useful in the present invention are rubber powders which comprises 0.1% or less of iron content, 0.1% or less of fiber powder content, 10% or less of ash content, 1. 0% or less of moisture content, meeting the criteria of KSM 6710 rubber powder of the waste tire, Korean Industry Standard.

Compositions of the waste tire powder used in the invention are as described in the following Table 1: TABLE 1 Composition Content (PHR) Powder A Powder B Polymer base (NR/SBR/BR) 100 100 100 Carbon black 78.3 45.6 47.3 Additive Oil 18.4 21.0 47.1 Sulfur 3 14.9 22.4 Antiaging agent6C 1.8 0.1 0.4 Stearic acid 0.7 1.6 2.0 Wax 0.6 1.0 1.1 Inorganics 6.1 3.9 2.8 Total organics 39.1 72.9

The advantages of the invention will be apparent with reference to the accompanying drawings The present invention is characterized in that a combination of additives, including process oil, a vulcanizing accelerant, a vulcanizing agent, and optionally pine resin depending on necessary physical properties, is used, instead of adhesives, in molding goods from waste rubber powder.

Exemplified by sulfur in the present invention, the vulcanizing agent is preferably used in the amount of 5 to 10 parts by weight based on 100 parts by weight of the waste rubber powder. The amount of vulcanizing agent may affect physical properties of the formed goods. For example, adding less than 5 parts by weight may give rise to no or poor vulcanization, whereas adding more than 10 parts by weight may give rise to excessive vulcanization.

In the invention, it is preferred that TMTD (Tetramethyl Thiuram Disulfide) as the vulcanizing accelerant is used in the amount of 2 to 3 parts by weight based on 100 parts by weight of the waste rubber powder.

For example, when the vulcanizing accelerant is used in the amount less than 2 parts by weight, the vulcanizing time may be lengthened. On the other hand, more than 3 parts by weight of the vulcanizing accelerant may cause an increase in the risk of scotching.

As for the process oil, its use also characterizes the present invention. With reference to Fig. 1, there are compared physical properties of goods which are recycled from waste tires by use of urethane adhesive, SBR latex, DEG and process oil. As shown in the histogram, the recycled goods by use of process oil are poorer in elongation, but better in tensile strength, compared to those using the other additives. Furthermore, process oil has an economic advantage over the other additives. The process oil can be selected from naphthanic and aromatic oils, depending on kinds of recycled rubber, as shown in Figs. 2 and 3.

Preferably, the amount of the process oil may be 5 to 20 parts by weight based on 100 parts by weight of the used waste rubber powder. When the amount is not within this range, the resulting rubber goods have poor physical properties since mixing and forming cannot be easily accomplished.

Optionally, pine resin may be used to improve the physical properties of the recycled goods, such as tensile strength, elongation at break, hardness, and tear strength.

With reference to Figs. 4 and 5, these physical properties are plotted versus contents of pine resin. As apparent from the curves, the amount of the pine resin is determined depending on necessary physical properties and preferably falls within the range of 0 to 10 parts by weight based on 100 parts by weight of the waste rubber powder. Greater than 10 parts by weight of the pine resin makes the recycled goods poor in physical properties.

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE 1 10-20 ml of a process oil, 2-3 parts by weight of a vulcanizing accelerant, and 5-10 parts by weight of a vulcanizing agent were admixed with 100 parts by weight of a waste rubber powder, followed by uniformly homogenizing the admixture. After being melted at 150 to 170 °C in a mold, the mixture was molded to goods with the aid of an ordinary process and apparatus.

EXAMPLE 2

10-20 ml of a process oil, 2-3 parts by weight of a vulcanizing accelerant, 5-10 parts by weight of a vulcanizing agent, and 5-15 parts by weight of a pine resin were admixed with 100 parts by weight of a waste rubber powder, followed by uniformly homogenizing the admixture.

After being melted at 150 to 170 °C in a mold, the mixture was molded to goods with the aid of an ordinary process and apparatus.

A measurement was made of physical properties of goods (dumbbell type 3) manufactured from waste tire powder (particle size 900 pm) by the molding process. The goods of the present invention were found to have a tensile strength of 44 kgf/cm2, an elongation at break of about 110%, and a hardness of 84 of hardness. Low as they are in elongation at break, the recycled goods of the present invention are better in terms of tensile strength than those using DEG.

In addition, recycled goods of the present invention were measured to be generally superior in physical properties compared to those using latex (tensile strength 32kgf/cm2, elongation at break 180%, hardness 80). Over the recycled rubber goods using urethane adhesive, the rubber goods of the present invention have economic advantages, even though being poor in physical properties in comparison with the conventional goods (tensile strength 70 kgf/cm, elongation

at break 200%, and hardness 76). Whereas materials for conventional rubber goods are limited to waste tires, the present invention is applicable to waste rubber as well as waste tires. Moreover, the improved physical properties make the recycled goods have applications in a broad spectrum of fields. Furthermore, the present invention saves production expenses by 7/20-9/20 of expenses of conventional adhesive case.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.