Field of the Invention

The present invention relates to a method for producing monofilament yarns in order to be used in cord fabric production wherein polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) materials are processed by mixing and using a copolymer produced in this way. Background of the Invention

Mechanical properties and heat resistance of the textile cord fabric reinforcements used in automotive tires determine the maximum speed, road holding, noise level, wearing and rolling resistance of tires. Polyethylene naphthalate (PEN) has smaller shrinkage, higher stiffness, toughness and strength, furthermore better resistance against high temperature, chemicals and UV light compared with polyethylene terephthalate (PET) which is frequently used as cord fabric material. Due to these features, PEN has started to be preferred in new generation high performance tires. However, due to the high cost of PEN, producing new generation mixture yarns commercially by mixing low cost PET with PEN has recently become appealing.

Since the PEN raw material is 5 times more expensive than PET, working on PEN-PET mixtures has gained great importance lately. Commercializing pure PEN has been realized almost 30 years ago, and several studies has been made about examining structures and features of both pure PEN and PET-PEN fibers until today.

In the studies that have been performed until today, in obtaining a homogenous mixture from PET-PEN chips and transforming into yarn, the optimization of PEN/PET ratio, melting temperature during extrusion, and residence time of polymer in the extrusion have not been optimized. However, the mixing ratio of these two polymers and formation of copolymer structure in the mixture directly influence the quality of monofilament product which is obtained. Similarly, unless the applied temperatures are not kept in certain intervals, it would not be possible to produce a material with improved strength and physical properties compared with PET; and in this case it would be pointless to prepare the said PET-PEN mixtures and use them in monofilament production.

Summary of the Invention

The objective of the present invention is to provide a method for monofilament yarn production wherein a mixture comprised of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) polymers are used.

Another objective of the present invention is to develop method for monofilament yarn production wherein formation of a copolymer in the structure of the mixture is achieved.

A further objective of the present invention is to provide a production method for monofilament yarn having higher dimensional stability compared with PET monofilament yam due to the rigid structure of PEN in PET-PEN mixture.

Detailed Description of the Invention

A method for monofilament yarn production developed to fulfill the objective of the present invention is illustrated in the accompanying figure, in which; Figure 1 is the view of the flowchart of the inventive method for monofilament yarn production.

A method for monofilament yarn production (10) developed to fulfill the objective of the present invention comprises the steps of

Mixing of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) polymers (1 1 ), Melting the mixture in the extruder and then passing it through the water bath . (12),

Transferring the raw material passed through the extruder and the water bath to the godet no 1 (13),

- transferring the material coming out of the godet no 1 to godet no 2 (14), transferring the material coming out of the godet no 2 to convective furnace no 1 (15),

transferring the material coming out of the convective furnace no 1 to convective furnace no 2 (16),

- transferring the material coming out of the convective furnace no 2 to the godet no 3 (17),

- transferring the yarn coming out of the godet no 3 to the winder (18).

In the inventive method (10), first of all two different polymers, namely PET and PEN, mixing is achieved (11). In this step, the ratio of PEN added to the mixture varies between 5-50%.

The analyses performed about the PEN ratio in the mixture have shown that this ratio directly influences the transesterification degree achieved between the PEN and PET. As a result of DMA tests, it was deteraiined that the storage modulus of monofilament yams obtained from mixtures comprising 10% and 20% PEN is higher than the pure PET monofilament yam; and this value is lower in yarn mixtures comprising 30% and 40% PEN. This shows that the storage energy increases as the amount of PEN increases; however storage energy decreases due to the different crystallization mechanism of the yam after a certain point.

XRD analyses have shown that as a result of using PEN material in PET-PEN mixtures below a certain ratio, PEN material behaves like impurity, and negatively affects the dimensional stability of the monofilament yam obtained from the said mixture. Additionally, it was also seen that the crystallinity of the mixture decreases with the increase in amount of PEN in the mixture. For this reason, copolymer formation should be provided by using PEN in optimum ratio in the mixture.

Using excess PEN is a disadvantage in terms of cost, therefore it is significantly important to optimize this ratio.

With another analysis, the dimensional stabilities of monofilament yams obtained from PET-PEN mixtures comprising PEN in different amounts and pure PET monofilament yarn were compared. It was seen that the best dimensional stability is obtained with mixture comprising 40% PEN. The dimensional stability was calculated by adding % shrinkage and elongation values in 0.5kg. This value is desired to be as low as possible in a monofilament yarn used in cord fabric production. As a result of all these analyses, it was determined that optimum PEN ratio is 40%, and this ratio is preferred to be used in mixing step of PET an PEN polymers (11) in the inventive method, and PET-PEN copolymer formation is enabled. After the mixture is composed, the said PET-PEN mixture is first passed through extruder and then water bath (12). The exit temperature of the mixture from the extruder is 290-300°C. The water bath temperature is preferably between 55-80°C.

PET-PEN raw material mixture coming out of water bath is then sent to the godet no 1 (13). The material is passed through this double godet heated to 100-120 °C by being wound at speed of 30-300 m/min. After leaving here, it is sent to the second double godet heated to 120-180°C and having a speed of 50-500 m/min (14). The material coming out of the second godet is then sent to the first convective furnace (15) and it is heated here between 250-300°C. The material heated in the first furnace is then sent to a second convective furnace at the same temperature range (16). In one embodiment of the invention, there may be a godet heated to 120-18()°C between these two furnaces optionally. The material coming out of the second furnace is sent to the double godet no 3 which is the last godet, and moves here at speed of 100-1000 m/min (17). Differently from the previous godets, the said godet operates without heating. Finally, the obtained monofilament yarn is sent to the winder in order to be wound (18). The winding rate in here is in the range of 200-1000 m/min, and the diameter of the monofilament obtained is nearly 150-200 μιη. The efficiency of the monofilament yam production with this inventive method is 10-20 g/min.

Due to the different glass transition temperatures and melting temperatures of PET and PEN materials, homogenous mixing can be realized in molten phase. Therefore, the residence time of these two materials and the temperatures in the extruder are quite critical for homogenous mixing.

Considering the NMR results, consistently with the literature, degree of randomness decreases in the mixture as % PEN concentration increases, which shows that a homogenous mixture is obtained and thus copolymer formation is realized. On the other hand, PEN block length increases, whereas the PET's decreases.

Concerning the dimensional stability of the PET-PEN monofilament yarn produced with the inventive method, it is seen that there is an improvement when pure PET monofilament yarn is taken as reference. In the preierred embodiment of the invention, dimensional stability of PET-PEN monofilament yarn comprising 40% PEN has shown 40% improvement compared to pure PET yarn. Furthermore, the ratios and production steps which are used have great importance in terms of enabling copolymer formation in PET-PEN mixture.