METHOD FOR PRODUCING A REINFORCING MATERIAL AND REINFORCING MATERIAL

Abstract

The invention relates to a method for producing a reinforcement material in the form of a core-shell structure, in particular of a tyre cord, wherein there is provided in a step a core having linear arrangements, in particular a cord-like core, wherein the linear arrangements have segments that are coupled to one another in a linear way by means of strength-increasing segment couplings, and wherein in a further step the core is provided with a shell by forming a core-shell coupling that increases adhesion, wherein segment couplings that are near to the surface are converted for the core-shell coupling.

Claims

1. A method for producing a reinforcement material for a rubber product in the form of a core-shell structure, in particular of a tyre cord, wherein the method comprises the following steps: a) providing a cord-like core having linear arrangements, wherein the linear arrangements have segments that are coupled to one another in a linear way by means of strength-increasing segment couplings, b) enzymatically converting the core, wherein segment couplings that are near to the core surface are cleaved at least in part, c) applying a shell onto the core, wherein the core obtained in step b) is equipped with a shell.

2. A method according to claim 1, wherein the segment couplings are ester bonds.

3. A method according to claim 2, wherein the linear arrangements comprise a polyester.

4. A method according to claim 1, wherein in step b) the temperature of the enzymatic treatment is higher than 18° C., preferably higher than 30° C., especially preferably higher than 44° C. and preferably lower than 80° C., especially preferably lower than 70° C., most preferably lower than 66° C.

5. A method according to claim 1, wherein in step b) the segment couplings that are near to the core surface are hydrolytically cleaved.

6. A method according to claim 1, wherein in step c) the core obtained in step b) is equipped with a shell material in a bath, preferably wherein there is applied a shell material comprising rubber.

7. A core for a reinforcement for a rubber product, wherein the core comprises linear arrangements, which comprise in particular at least one polyester multi-filament, and wherein the linear arrangements have segments that are coupled to one another in a linear way by means of strength-increasing segment couplings and wherein the segment couplings are ester bonds, characterized in that the ester bonds that are near to the surface are cleaved at least in part.

8. A core for a reinforcement according to claim 7, wherein the ester bonds that are cleaved in part and near to the surface are hydrolytically cleaved.

9. A core for a reinforcement according to claim 7, wherein the portion of the cleaved ester bonds is quantified by the level of carboxylation of the core and wherein said level of carboxylation is >0.08 nmol/mm.sup.2, preferably >0.10 nmol/mm.sup.2, especially preferably >0.12 nmol/mm.sup.2.

10. A core according to claim 7, wherein the core has a relative strength of more than 95%, preferably more than 97%, especially preferably more than 98%, and wherein the relative strength is determined as ratio of the strength of the core to the strength of a reference core, wherein the reference core is a core without cleaved ester bonds and that has been formed otherwise in the same way, and wherein the strengths are determined respectively as tenacity greige cord according to ASTM D76/D2256.

11. A reinforcement material in the form of a core-shell structure having a core according to claim 7, with a shell having a rubber material, which surrounds the core by a core-shell coupling that increases adhesion.

12. A reinforcement material according to claim 11, wherein the reinforcement material has a relative coverage improvement of at least 20%, preferably at least 50%, especially preferably at least 100%, wherein the relative coverage improvement C is determined by
C=(CT−CR)/CR, wherein CT is the coverage for the reinforcement material and CR is the coverage of a reference reinforcement material, wherein the reference reinforcement material is formed in the same way, apart from a core without cleaved ester bonds, and wherein the coverage is respectively determined according to ASTM D4393.

13. A reinforcement material according to claim 11, wherein the reinforcement material has a relative pull improvement of at least 100%, preferably at least 200%, wherein the relative pull improvement C is determined by
P=(PT−PR)/PR, wherein PT is the pull for the reinforcement material and PR is the pull of a reference reinforcement material, wherein the reference reinforcement material is formed in the same way, apart from a core without cleaved ester bonds, and wherein the pull is respectively determined according to ASTM D4393.

14. A method according to claim 2, wherein the linear arrangements comprise dicarboxylic acids and di-alcohols as segments that are coupled to one another in a linear way, which form a polyester.

15. A method according to claim 14, wherein the dicarboxylic acid segments are selected from 1,4-benzene dicarboxylic acid and 2,5-furan dicarboxylic acid and wherein the di-alcohol segments are 1,2-ethanediol.

16. A method according claim 2, wherein the linear arrangements comprise at least one polyester multi-filament.

17. A method according to claim 16, wherein the polyester multi-filament is a twisted cord, in particular a cord from polyethylene terephthalate (PET), preferably from HMLS-PET.

18. The core according to claim 7 incorporated as a reinforcement of rubber products, in particular as a carcass and belt bandage material or for conveyor belts or hoses.

19. A rubber product, in particular tyres, reinforced by a reinforcement material according to claim 11.

Description

[0017] In an especially preferred embodiment of the method, the linear arrangements that are adjacent to one another have transverse couplings acting transversely to the linear extension thereof and obtained by stretching the linear arrangements upon the spinning thereof, which also promote strength (non-covalent interaction within a linear arrangement). In the experiments, there has been shown that with the fibres tested, the highly relevant characteristic of strength in a reinforcement material remains more or less unaffected by the fracture of the segment couplings. There is believed that this observation is based on the fact that in this embodiment, the transverse couplings are essentially less affected than the segment couplings cleaved for conversion. Hence, the method preferably provides a mild effect on the core in this regard. This mild effect is especially preferably obtained by the segment couplings being selectively cleaved, as the cleavage/conversion process is realized enzymatically. Herein it is relevant that enzymatic catalysts are highly specific for selected reactions and may thus selectively address the segment couplings to be cleaved. In this way, “harsh” (unspecific) effects may be prevented, which would also affect the transverse couplings to the same extent, which would, for example, occur by way of a brine attack such as caustic soda.

[0018] In an especially preferred embodiment of the method, the segment couplings are ester bonds.

[0019] In a preferred embodiment of the method, enzymatic cleaving is realized by way of hydrolytic cleavage. The enzymatic treatment is performed preferably by means of enzymes from the group of hydrolases. Hydrolases are assigned to the EC3 (enzyme class 3) according to the established enzyme classification system. In particular preferred are (EC3.1-) hydrolases.

[0020] In an especially preferred embodiment of the method, at least a portion of the docking positions is formed by respectively one carboxylic group. In this connection, in particular cutinases (E.C.3.1.1.74 carboxylic ester hydrolases) could be used for the enzymatic treatment. The invention, however, is not limited to this special form of enzymes. There may rather be used hydrolytic enzymes selected from the group consisting of proteases, lipases, cutinases, esterases or a combination of the same. A portion of the docking positions may also be formed by respectively one hydroxyl group.

[0021] In a preferred embodiment, the preferably hydrolytic cleavage of the segment couplings is accelerated by accelerating agents that are added, preferably by hydrophobins.

[0022] In regard to the segment couplings there is further preferred that at least one diol is selected from the group consisting of 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, ethylene glycol, di(ethylene) glycol, tri(ethylene) glycol, poly(alkylene ether) glycol, poly(propylene ether) glycols and mixtures thereof.

[0023] There is further provided that at least one aromatic dicarboxylic acid or ester is selected from the group consisting of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, 2,6-naphthaline decarboxylic acid, dimethyl-2,6-dicarboxylic acid, dimethyl-2,6-naphthalate and mixtures thereof.

[0024] The linear arrangements thus comprise in a preferred embodiment a polyester, and the linear arrangement may, for example, comprise a polyester multi-filament. At least one polyester multi-filament may preferably be a twisted cord, in particular a cord made from polyethylene terephthalate (PET), preferably from HMLS-PET.

[0025] It will be appreciated that for the linear arrangements there are valid special requirements regarding material properties, as the reinforcement materials produced according to the inventive method are intended for rubber products under high stress. Accordingly, the materials provided for the core are different, for example, from fibres, which are intended for use in textiles. Hence, there is provided that the core has preferably at least one polyester multi-filament, the titre of which is preferably higher than 240 dtex, in particular higher than 400 dtex, and which has a breaking strength of more than 55 cN/tex, preferably more than 65 cN/tex.

[0026] While there is commonly aimed at a possibly low number of carboxyl groups as chain ends before the provision of the linear arrangement for the production of a reinforcement material, e.g., in the procedural production of polyester yarns, as these will lead to a thermally induced degradation reaction and, hence, in trend to a shortening of the polymer chain causing a deterioration of mechanical properties, in the method according to the invention there is aimed at increasing the carboxyl concentration in the region near to the core surface. In this regard, it is preferred that the carboxyl concentration (measured according to the Toluidine Blue O Method (TBO), described as in S. Rodiger et al, Analytische Chemie, 2011, 83, 3379-3385) compared with an untreated reference is higher by at least 0.03 nmol/mm.sup.2, further preferred at least 0.04 nmol/mm.sup.2, in particular at least 0.05 nmol/mm.sup.2, even at least 0.6 nmol/mm.sup.2. Furthermore there is preferred that the absolute carboxyl concentration of the enzymatically treated core is higher than 0.08 nmol/mm.sup.2, further preferably higher than 0.1 nmol/mm.sup.2, in particular than 0.12 nmol/mm.sup.2, on the other side, however, lower than 3.5 nmol/mm.sup.2, preferably lower than 3.0 nmol/mm.sup.2, in particular lower than 2.5 nmol/mm.sup.2. In this way there is achieved that the strength characteristics of the core will only be reduced in a practically hardly noticeable way.

[0027] In this connection there is alternatively or additionally provided that the weight loss involved with the enzymatic treatment (the cleavage of the segment couplings) of the core is merely insubstantial and in any case lower than 4% w/w, in particular lower than 3% w/w, even lower than 2.0% w/w.

[0028] Increasing adhesion of the core-shell coupling is thus realized by means of the increase of covalent bonds with the shell material achieved via the cleavage of the segment couplings, which is, for example, present in the form of the RFL dip or any other convenient shell material, i.e. that is accessible for such covalent bonds, which is in particular suitable for the vulcanization with the rubber products of the area of application selected.

[0029] Hence, it is conceivable to keep the residence time comparably long and to use suitably lower enzyme activities; but the residence time should preferably not exceed 72 h, preferably not exceed 48 h, and in particular not exceed 24 h. Especially preferred are, however, in particular rather short residence times of preferably less than one hour, in particular less than 30 min and also in the range of 5 min or less.

[0030] In this regard, there are preferably used process conditions, wherein the temperature of the enzymatic treatment is higher than 18°, preferably higher than 30° C., in particular preferably higher than 44° C. and preferably lower than 80° C., in particular preferably lower than 70° C., most preferably lower than 66° C. These will lead to a good balance between adhesion and strength.

[0031] In regard to the device, the invention provides a core for the reinforcement for a rubber product, wherein the core comprises linear arrangements, and the linear arrangements have segments that are coupled to one another in a linear way via strength-increasing segment couplings and the segment couplings are ester bonds, characterized in that the ester bonds that are near to the surface are cleaved at least in part, preferably hydrolysed.

[0032] In a further aspect the invention relates to a reinforcement material for a rubber product in the form of a core-shell structure having an in particular cord-like core having linear arrangements, which form in particular at least one polyester multi-filament, wherein the linear arrangements have segments that are coupled to one another in a linear way via strength-increasing segment couplings, with a shell having in particular a rubber material, which shell surrounds the core by an adhesion increasing core-shell coupling. The reinforcement material may have converted parts of segment couplings that are near the core surface and that are already contained during the provision of the core, such as carboxyl groups in order to form the core-shell coupling. The converted parts such as carboxyl groups are involved in the formation of the core-shell coupling, thus no longer detectable as such.

[0033] The advantages of the inventive core and the inventive reinforcement material are essentially the result of the above facts explained by way of the inventive method. This will also lead to preferred embodiments for the core and the reinforcement material from the embodiments preferred for the method.

[0034] In particular the core is obtained by a method comprising the following steps:

a) provision of an in particular cord-like core having linear arrangements, which comprise in particular at least one polyester multi-filament, wherein the linear arrangements have ester bonds as strength-increasing segment couplings of the segment that are coupled to one another in a linear way, and
b) enzymatic conversion of the core, wherein ester bonds that are near the core surface are cleaved at least in part.

[0035] There is further achieved a markedly improved adhesion behaviour by the reinforcement material in comparison to a reference material that is formed in the same way, apart from the treatment for conversion of the segment couplings that is not performed. In coverage percentage as determined according to ASTM D4393, this improvement amounts to at least 20%, preferably at least 50%, especially preferably even more than 100% and most preferably more than 300 or even 400%.

[0036] The reinforcement material according to the invention is also improved in regard to the “pull” determined according to ASTM D4393 in N/cm compared to the above defined reference material, wherein herein the improvement, measured in percent, is at least 10%, wherein also improvements of 20% are achieved, even improvements of 40% and higher.

[0037] These improvements are obtained, even though the strength of the core according to ASTM D76/D2256, greige cord deviates in relation to the reference material mentioned above by less than 5%, in particular less than 3% and even less than 2%. The strength properties of the core or the respectively formed reinforcement material, thus de facto remain at the respective values of the starting material for the core, when used in its initial construction, wherein, as usual, the absolute strength values depend greatly on the cord construction selected.

[0038] As already mentioned, the core of the reinforcement material has preferably at least one twisted polyester multi-filament.

[0039] The core may, however, also have further fibre ingredients, and it may, for example, be a hybrid cord, wherein the polyester multi-filament is combined with other filaments, which may be pre-immersed or not. There may be preferably used high-strength cellulose yarns as partners, for example having a strength oven-dried of higher than 35 cN/tex, preferably higher than 40 cN/tex; there may, however, also be used further polymer yarns, in particular further polyester multi-filaments from various polyesters as hybrid partners. There is preferably used for the contained polyester multi-filament a polyethylene terephthalate multi-filament, but also other polyester materials (PEN, PAN, PEE, PEF, PBO) are contemplated as well as contemplated as hybrid partners.

[0040] The polyester multi-filament may be combined, for example, also with a hybrid partner in the form of fibre material from polyketones, glass, steel, basalt or carbon. In an embodiment the core or the reinforcement material has a further fibre material with a material different from the linear arrangements and/or with a different structure.

[0041] The core in its shape is also not limited to a linear structure, for example a twisted cord. There is also provided that the core may be present in the form of a flat structure, for example of a fabric. For the formation of such a fabric, there may preferably be used a construction of a polyester cord and a different polymer cord or also cellulose cord, e.g., in a construction of 1×1. In one embodiment, the core or the core of the reinforcement material is a flat structure having the linear arrangements, in particular a fabric.

[0042] The invention further claims the use of such a core with segment couplings cleaved for conversion and a reinforcement material according to the aspects mentioned above for the reinforcement of rubber products (products having rubber structures), as well as such reinforced rubber products, which are not especially limited in their type and which may comprise, for example, carcass and belt bandage material, conveyor belts, hoses or even complete tyres.

[0043] The invention is explained in greater detail in the following by way of exemplary embodiments.

[0044] In the following exemplary embodiments (in the first step) for the provision of the core there is used a twisted cord of two polyethylene terephthalate multi-fibres. The carboxyl concentration of the untreated cord maximally detectable using the TBO method amounts to 0.07 nmol/mm.sup.2.

[0045] In an intermediate step before the application of the dip forming the shell, the core is subjected to an enzymatic hydrolysis. For this purpose, there were used as enzyme in a first example cutinase 1 of Thermobifida cellulosilytica (native), in the following Thc_Cut1 (E. Herrero Acero et al. Macromolecules 2011, 44, 4632-4640), and in a second example the cutinase, also of Thermobifida cellulosilytica, but modified, namely a triple-mutant variant of Thc_Cut 2, in the following Thc_Cut2TM, with the mutations Arg19Ser, Arg29Asn and Ala30Val (E. Herrero Acero et al, Biotechnol. Bioeng. 2013, 2581-2590). The exact process in the intermediate step was as follows:

Enzyme-Catalysed Hydrolysis with Thc_Cut1

[0046] 10 m of a 1670×2 PET cord (Durafiber 50×1, 360 tpm) were fixed on a bobbin, washed with Triton X-100 (5 g L.sup.−1), Na.sub.2CO.sub.3 (100 mM) and distilled water, and subsequently incubated in 400 ml phosphate buffer (100 mM, pH 7), containing 0.5 μM of Thc_Cut1, at 60° C. for 24 h. Following incubation, the cord was again washed with Triton X-100 (5 g L.sup.−1), Na.sub.2CO.sub.3 (100 mM) and distilled water. According to EDA (energy-dispersive X-ray analysis), no more enzyme was detectable on the surface.

Enzyme-Catalysed Hydrolysis with Thc_Cut2TM

[0047] 10 m of a 1670×2 PET cord (Durafiber 50×1, 360 tpm) were fixed on a bobbin, washed with Triton X-100 (5 g L.sup.−1), Na.sub.2CO.sub.3 (100 mM) and distilled water and then incubated in 400 ml phosphate buffer (100 mM, pH 7), containing 0.5 μM of Thc_Cut2TM, at 60° C. for 24 h. Following incubation, the cord was again washed with Triton X-100 (5 g L.sup.−1), Na.sub.2CO.sub.3 (100 mM) and distilled water. According to EDA, no more enzyme was detectable on the surface.

[0048] The application of the shell in the further step was carried out by dipping into an RFL dip, for the first as well as for the second embodiment. More particularly, the core in the form of the cord resulting from the enzyme treatment in the intermediate step was dipped into a single-bath RFL dip having a total solid content of 22% that is common for rayon cord for at 18/min in a Labour-Single-End-Cord plant by C.A. Litzler Co., Inc. (Cleveland, Ohio) and crimped at 180° in the first oven and 230° in the second oven.

[0049] For the first and the second embodiment example, the coverage and the pull were determined according to ASTM D4393 for testing the adhesion strength. The results are presented in the following table 1 in relation to a zero reference, wherein the zero reference is a comparison example, wherein there has not been performed an enzymatic treatment but the core has only been exposed to the enzyme-free buffer solution for two hours.

TABLE-US-00001 TABLE 1 Coverage, related to the Pull, related to the zero Sample zero reference reference Zero reference 1 1 Embodiment 1 2.5 (+150%) 1.32 (+32%) Embodiment 2 4.5 (+350%) 1.53 (+53%)

[0050] These significant improvements in adhesion are obtained by conversion of the segment couplings for the core-shell coupling, herein the PET-cord-dip coupling. This may also be verified in experiments in that the number of available docking points in the form of carboxyl groups is determined for the core of the zero reference and of the first and second embodiments. The determination of the level of carboxylation by means of the TBO method is used as a suitable measure for this purpose, and the level of carboxylation [nmol/mm.sup.2] (DoC) is determined, with details being given in the following:

Determination of DoC by Means of TBO Method

[0051] The sample to be tested (approx. 1 g) was incubated in a 0.1% TBO solution in Tris/HCl buffer (100 mM, pH 8.6) for 15 min at 50° C. and 130 rpm (6 ml), then removed from the TBO solution and washed with Tris/HCl (100 mM, pH 8.6) until the wash solution was clear. The sample containing TBO was stirred with 20% SDS for 30 min at 50° C. and 130 rpm in order to release the TBO adhering to the carboxyls. The extinction at 625 n and 23° C. was measured in this solution. The carboxyl concentration (DoC) was calculated using the formula

DoC=(A*V)/(As*d*E)

A: absorption at 625 nm;
V: volume of the desorption solution [L];
As: PET surface [mm.sup.2] (in the case of cords, the area of the circular cylinder defining the cord
with the diameter of the cord was used).
d: optical path [cm];
ε: extinction coefficient of TBO [=54800 L mol.sup.−1 cm.sup.−1];
DoC: level of carboxylation [nmol/mm.sup.2]

[0052] The results are given in the following table 2.

TABLE-US-00002 TABLE 2 Sample DoC (nMol/mm.sup.2), TBO method Zero reference <0.07 Embodiment 1 0.17 Embodiment 2 0.29

[0053] By converting only segment couplings that are near to the surface into the core-shell coupling, no reduction in strength can be detected. For the zero reference as well as for the first and the second embodiment examples, the tenacity [N] greige cord according to ASTM D76/D2256 was determined and, as visible from the following table 3, there could not be detected any noticeable deterioration within the frame of measurement accuracy.

TABLE-US-00003 TABLE 3 Tenacity [N] greige cord (ASTM Sample D76/D2256) Zero reference 174.5 ± 2.97  Embodiment 1  176 ± 0.96 Embodiment 2 175 ± 0.8

[0054] Maintaining the mechanical properties is achieved in that in the intermediate step the segment coupling are selectively cleaved, while the structural integrity of the strength structure formed by the linear arrangements is largely unaffected. Thus, as to this aspect, there is applied a mild treatment in the intermediate step. If one attempted to perform a treatment using caustic soda (e.g., treatment with a 400 ml 0.5 NaOH solution for two hours at 50° C.) in the intermediate step, one would be able to reach a DoC in the range of the first or second embodiment, but rather with substantial loss in strength, which would be seen, on the one side, in a reduction of the tenacity within a relevant percentage range and, on the other side, in an impairment of the yarn structure of the core (pitting) that is detectable by means of SEM or AFM technology.

[0055] The invention is not limited to the features individually shown in the embodiments. The features of the subsequent claims and the preceding description may rather be relevant, individually or in combination, for the realization of the invention in the various embodiments thereof.