Patent Application
20070251624
The lyocell dipped cord according to the present invention is characterized in that it is prepared by dipping a lyocell raw cord comprising at least 2-ply lyocell multifilament in RFL and curing the dipped cord, and it gives a stress-strain curve exhibiting that (a) the lyocell dipped cord has an elongation of 1.2% or less at an initial stress of 1.0 g/d, and an initial modulus value of 80 to 200 g/d; (b) has an elongation of 6% or less in a stress region of 1.0 g/d to 4.0 g/d; and (c) has an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point, as measured in the dried state.
Further, the lyocell dipped cord preferably has a reduction ratio of the degree of polymerization (DP) of 3.0% or less.
Further, the lyocell dipped cord preferably has a twist number of 250 to 550 TPM (turns per meter).
Further, the lyocell dipped cord preferably has the strength of 16.0 to 30.0 kgf.
Further, the lyocell dipped cord is characterized in that it has a density of 1.48 to 1.52 g/cm3.
Further, the lyocell multifilament is characterized in that it has a degree of crystalline orientation of 0.80 or more.
Further, the lyocell dipped cord preferably has a coefficient of dynamic friction of 0.2 to 0.6.
Further, the lyocell dipped cord is prepared by the raw cord which is prepared by twisting 2- or 3-ply lyocell multifilaments.
Further, a tire is provided, which comprises the lyocell dipped cord.
In order to provide a high tenacity fiber for industrial use, in particular, a lyocell dipped cord for a tire cord, of the present invention, with high dimensional stability, it is important to control the stress-strain curve of the lyocell dipped cord. At this time, the lyocell dipped cord preferably gives a stress-strain curve exhibiting that the lyocell dipped cord has an elongation of 1.2% or less at an initial stress of 1.0 g/d, and an initial modulus value of 80 to 200 g/d; an elongation of 6% or less in a stress region of from 1.0 g/d to 4.0 g/d; and an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point, as measured in the dry state.
In the preparation of a tire, in order to maintain high dimensional stability in the vulcanization process, the lyocell dipped cord is required to have high initial modulus. For this reason, the lyocell dipped cord of the present invention preferably has an elongation of 1.2% or less at an initial stress of 1.0 g/d, and an initial modulus value of 80 to 200 g/d. If the dipped cord has an elongation of more than 1% at an initial stress of 1.0 g/d, the dimensional stability after the preparation of a tire is lowered, and the resistance due to external deformation is also lowered, which leads to dramatic deformation of the tire, and thus to lowered ride comfort and driving performance.
Further, the lyocell dipped cord of the present invention preferably has an elongation of 6% or less in a stress region of 1.0 g/d to 4.0 g/d. If it has an elongation of more than 6%, the dimensional stability is lowered, which leads to lowered resistance due to the external deformation, thus it being possible to cause deformation of the tire.
Further, in order to design a high energy-efficiency car, it is preferable that the weight of the tire is minimized. Thus, for achieving this, a high tenacity tire cord is required. The lyocell dipped cord of the present invention preferably gives a stress-strain curve exhibiting that the lyocell dipped cord has an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point. This is because, when the lyocell dipped cord has an elongation of less than 1% at a tensile strength of 4.0 g/d to the breaking point of the dipped cord, the maximum load-absorbing ability is insufficient, and thus, it becomes difficult to reduce the weight of the cord per a tire and the fatigue resistance is drastically lowered.
Hereinbelow, the present invention will be described in detail.
In order to prepare the lyocell filament as defined in the present invention, a high purity cellulose pulp should be used, and in order to prepare a high-quality cellulose fiber, a pulp having a high content of a-cellulose is preferably used. This is because the use of the cellulose molecule with a high degree of polymerization allows high orientation structure and high crystallization, thereby high tenacity and high initial modulus being possibly expected. Accordingly, the cellulose used in the present invention is a soft wood pulp with a DP of 1,200 and a content of α-cellulose of 93% or more.
NMMO is known as a solvent having excellent solubility of cellulose and having no toxicity. The NMMO used in the present invention is the form of a hydrate controlled to about 87% concentration, since the presence of water is essential for providing the solubility of cellulose by opening the pores of the high crystalline cellulose. In order to suppress the thermal decomposition of the NMMO hydrate and provide stability of the cellulose solution, a small amount of 3,4,5-trihydroxybezoic acid propyl ester (hereinafter, referred to as propyl gallate) was added.
In order to dissolve cellulose in NMMO, physical forces such as a shear force is required, and in the present invention, a twin screw extruder was used to dissolve cellulose in NMMO. Thus obtained cellulose solution was spun through a nozzle with an orifice diameter of 100 to 200 μm and an orifice length of 200 to 1,600 μm such that the ratio of the orifice diameter to the orifice length is about 2 to 8, and then subjected to the process as depicted in
The solution extruded from the spinning nozzle 1 passes through an air gap in the vertical direction and is solidified in a coagulation bath 2. The air gap suitably has a length of 10 to 300 mm to obtain a dense and uniform fiber and provide a good cooling effect.
The filament which passed through the coagulation bath 2 then passes through a washing bath 3. The temperatures of the coagulation bath 2 and the washing bath 3 are preferably controlled to about 10 to 25° C. in order to prevent the dropping of the physical properties caused by the formation of the pores due to rapid diffusion of solvent.
The fiber which passed through the washing bath 3 passes through a squeezing roller 4 to remove water, and then passes through a first finishing oil treatment unit 5.
Thereafter, the filament which passed through the first finishing oil treatment unit 5 is dried over a dryer 6. At this time, the drying temperature, the drying method, the drying tension, and the like largely affect the post-processes and the physical properties of the filament. In the present invention, the drying temperature was controlled for a moisture regain in the process of 7 to 13%.
The filament which passed through the dryer 6 passed through a secondary finishing oil treatment unit 7 and is finally wound in a winder 8.
The denier of the lyocell filament wound in the winder 8 is not particularly limited, but the denier of a mono-filament is preferably 0.01 to 10 deniers. For the purpose of maintaining the high tenacity characteristics of the lyocell filament, the denier of a monofilament may be preferably 0.5 to 10 deniers, more preferably 0.7 to 3 deniers, and most preferably 0.7 to 2 deniers. Further, the total denier is not particularly limited, but it is usually 50 to 10000 deniers, and in the case of the use for the industrial materials, it would be preferably 100 to 5000 deniers.
The yarn of the prepared filament was twisted using a direct twister to prepare a raw cord, and the raw cord was dipped in a conventional resorcinol-formalin-latex (RFL) solution, and then subjected to heat treatment to prepare a ‘dipped cord’.
The industrial high tenacity cord, in particular, the lyocell dipped cord used for a tire cord, of the present invention, imparts high dimensional stability by controlling the stress-strain curve of the lyocell dipped cord. The stress-strain curve of the lyocell dipped cord of the present invention preferably exhibits that the lyocell dipped cord has an elongation of 1.2% or less at an initial stress of 1.0 g/d, and an initial modulus value of 80 to 200 g/d; an elongation of 6% or less in a stress region of 1.0 g/d to 4.0 g/d; and an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point.
The first factor which affects the stress-strain curve of the present invention includes a reduction ratio (%) in the degree of polymerization (DP) of the dipped cord. The reduction ratio (%) in the degree of polymerization (DP) of the dipped cord is determined by measuring the DP (D0) of the raw cord before heat treatment and then the DP (D1) of the dipped cord after heat treatment, and using the obtained values, the reduction ratio was calculated according to the following equation:
DP reduction ratio (%)=(D0−D1)/D0×100
The reduction ratio in the degree of polymerization (DP) of the dipped cord in the present invention is preferably 3% or less. If the reduction ratio in the degree of polymerization exceeds 3%, the mechanical physical properties of the dipped cord are considerably deteriorated, thus it being not possible to obtain a stress-strain curve for the dipped cord suitable for a tire cord intended by the present invention. There are various factors which affect the reduction ratio (%) in the DP of the dipped cord. The time and the temperature for heat treatment in the dipping process can be suitably controlled to minimize the reduction ratio in DP.
The second factor which affects the stress-strain curve includes a coefficient of dynamic friction between the lyocell filament-filament. The values of the coefficient of dynamic friction are preferably 0.01 to 3.0, more preferably 0.1 to 2.5, and even more preferably 0.2 to 0.6. If the value of the coefficient of dynamic friction is less than 0.01, slip is generated in the twisting process, whereas if the value of the coefficient of dynamic friction is more than 3.0, damage is caused to the cord in the twisting process, thereby lowering the tenacity and the fatigue resistance. For the purpose of controlling the above-described coefficient of dynamic friction, the finishing oil can be applied to the surface of the filament. The amount of the finishing oil to be applied is preferably 0.1 to 7% by weight, more preferably 0.2 to 4% by weight, and even more preferably 0.4 to 1.5% by weight, relative to the weight of the fiber. If the amount of the finishing oil to be applied is less than 0.1% by weight, the cord damage is occurred in the twisting process, thereby lowering the tenacity and the fatigue resistance, whereas if the amount of the finishing oil to be applied is more than 7% by weight, the adhesion among filaments is occurred.
The finishing oil used in the present invention is not particularly limited, but preferably, the finishing oil agent contains at least one compound selected from the group consisting of the following compounds (1) to (3) as essential components, and the summed amount of the essential components is 30 to 100% by weight, relative to the total weight of the oiling agent.
(1) Ester compound with molecular weight of 300 to 2000
(2) Minerals
(3) Copolymer of ethylene oxide and propylene oxide, with molecular weight of 300 to 2000
Another factor which affects the stress-strain curve of the present invention includes the degree of crystalline orientation of the lyocell multifilament. The degree of crystalline orientation is preferably 0.80 or more, and more preferably 0.90 or more. If the degree of crystalline orientation is less than 0.80, the orientation of the molecular chains is insufficient, and thus, due to the lowered tenacity of the lyocell multifilament, it is impossible to give a stress-strain curve exhibiting that the dipped cord has an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point. The process factors which affect the degree of crystalline orientation include the concentration of the cellulose in the NMMO solvent, the ratio of the length/diameter of the orifice, the quenching condition, the temperature of the coagulation bath, and the like. By suitably controlling various process factors as described above, the degree of crystalline orientation of the cord can be controlled to 0.80 or more.
The Other factor which affects the stress-strain curve of the present invention includes the density of the cord. The density of the dipped cord having RFL removed is preferably 1.48 to 1.54 g/cm3, and more preferably 1.50 to 1.52 g/cm3. If there are many voids in the dipped cord, or the filament develops in a skin core structure too much, the density of the cord becomes less than 1.48 g/cm3, and thus it is impossible to obtain a stress-strain curve according to the present invention due to the deficient compactness and tenacity. If the density of the cord is more than 1.54 g/cm3, the elongation of the cord is too reduced, and thus the stress-strain curve exhibits that the cord has an elongation of less than 1% at a tensile strength of 4.0 g/d to the breaking point, thereby causing the fatigue resistance to be lowered.
Hereinbelow, the twisting, weaving and heat treatment processes of the present invention will be described in detail.
To specifically describe the twisting process of the present invention, the lyocell multifilaments are prepared by the above-described process are twisted using a direct twister, in which two wound yarns are false-twisted and ply-twisted at one time, to prepare a ‘raw cord’ for a tire cord. The raw cord is prepared by applying a ply twist and then a cable twist and ply-twisting the lyocell multifilaments, and generally the ply twist and the cable twist thus have the numbers of twist which are the same or different from each other if necessary.
Generally, the physical properties such as the strength and the elongation at break, the elongation at specific load, the fatigue resistance, and the like vary depending on the level of the twist (number of twist) given to the multifilament. Generally, in the case of high twisting, there is tendency that the tenacity is reduced and the elongation at specific load and elongation at break are increased. The fatigue resistance tends to be improved by the increase of the twist. The lyocell tire cord as prepared in the present invention has the number of twist of 250/250 TPM to 550/550 TPM in both of the ply twist, and the cable twist. Providing the same value of the number of the ply twist and the cable twist to each other does not exhibit rotation, twisting, or the like of the prepared tire cord and facilitates the maintenance of the linear form, thus to maximize the physical properties. Here, in the case of less than 250/250 TPM, the elongation at break of the cord is decreased, thus the fatigue resistance being likely to be lowered, whereas in the case of more than 550/550 TPM, the reduction in tenacity is large, thus it being not suitable for a tire cord.
The prepared raw cord is woven using a weaving machine, and the obtained fabric is dipped in a dipping solution, and then cured to prepare a ‘dipped cord’ for a tire cord having a resin layer attached on the surface of the raw cord.
To specifically describe the dipping process of the present invention, dipping comprises a process of impregnating a resin layer called as an RFL (Resorcinol-Formaline-Latex) on the surface of the fiber originally, dipping is carried out in order to improve the drawbacks of the fiber for a tire cord having the adhesiveness with a rubber deteriorated. A conventional rayon fiber or a nylon is commonly subject to one-bath dipping, and in the case of using a PET fiber, the number of the reactive groups on the surface of the PET fiber is smaller than that of the rayon fiber or the nylon fiber, thus firstly the surface of the PET is activated and then adhesive treatment is performed (two-bath dipping).
The lyocell multifilament according to the present invention was prepared by one-bath dipping. As the dipping bath, a dipping bath known for a tire cord is used.
Hereinbelow, the constitution and the effects of the present invention will be described in detail with reference to specific Examples and Comparative Examples, but these Examples are presented only for the purpose of facilitating the understanding of the present invention, and not intended to restrict the scope of the present invention.
In the Examples and Comparative Examples, the characteristics such as the physical properties of the cellulose solution, the filament, and the like were evaluated in the following analysis methods.
(a) Strength (kgf), Tenacity (g/d) and Initial Modulus (g/d) of Tire Cord
A lyocell dipped cord having the surface coated with an RFL solution was dried at 107° C. for 2 hours, and then the strength and initial modulus were measured using a low-speed elongation type tensile test machine (manufactured by Instron) with a gauge length of 250 mm at a test speed of 300 m/min. The initial load applied at an initial stage in the tensile test was applied on the basis of 0.05 g/d, and the particulars of the test were conducted according to ASTM D885. The initial modulus indicates the gradient of the stress-strain curve before the yield point. The denier of lyocell dipped cord is measured with a gauge length of 600 mm at a initial load of 0.05 g/d.
(b) DPU (Dipping Pick-Up)
3 g of the dipped cord was dissolved in 71±1% sulfuric acid which had been maintained at 30±5° C., filtered through a glass filter, and then dried to measure the weight.
DPU(%)=Weight of dried residue/(Weight of dried sample−Weight of dried residue)×100
(c) Method for Measurement of Coefficient of Dynamic Friction
For measurement of the coefficient of friction, used was an apparatus for measuring the coefficient of friction (manufactured by Northchild (Swiss)), which uses a theory that when a fiber passes through a pulley (device for converting a linear motion to a rotary motion), a tension enough to overcome the friction generated between the surface of the pullery and the fiber is increased. While moving the fiber at 200 m/min, the values of the let off tension and the take up tension were measured using a tensiometer, and the resultant values were applied in the following equation to calculate the coefficient of friction.
μ(Coefficient of friction)=ln (Take up tension/Let off tension)/θ(contact angle)
(d) Method for Measurement of Degree of Crystalline Orientation (WAXD)
For measurement of the crystallinity of the multifilament, a wide angle X-ray diffraction was used as follows. Apparatus for generation of X-ray: Product manufactured by Rigaku, X-ray source: CuKα (Use of Ni filter), Output power: 50 KV 200 mA, Range for measurement: 2θ=5 to 45°
(e) Method for Measurement of Density
Under the same conditions for heat treatment, a dipped cord which had not been dipped in the RFL solution, was wound, and the specimen was cut to a size of 2 to 3 mm and taken out in an amount of about 0.01 g. The specimen was introduced to a density gradient column which had been prepared according to ASTM D1505, left to stand for about 24 hours and then stabilized to measure a density value.
(f) Dry Heat Shrinkage (%, Shrinkage)
After being left to stand at 25° C. and 65% RH for 24 hours, the ratio of the length (L0) as measured at a static load of 0.05 g/d, and the length (L1) as measured after treatment at a static load of 0.05 g/d at 150° C. for 30 minutes is used to indicate a dry heat shrinkage.
S(%)=(L0−L1)/L0×100
(g) Reduction Ratio of Degree of Polymerization (DP) of Dipped Cord (%)
The intrinsic viscosity [IV] of the dissolved cellulose was measured using an Ubbelohde viscometer with a 0.5 M cupriethylenediamine hydroxide solution prepared according to ASTM D539-51T at 25±0.01° C. in a concentration in the range of 0.1 to 0.6 g/dl. The intrinsic viscosity was determined by extrapolation of the specific viscosity according to the concentration, and was applied in the following a Mark-Hauwink equation, to determine the degree of polymerization.
[IV]=0.98×10−2DPw0.9
Firstly, a DP (D0) of the raw cord before heat treatment and then a DP (D1) of the dipped cord after heat treatment were measured, and then the reduction ratio was calculated according to the following equation:
DP reduction ratio (%)=(D0−D1)/D0×100
(h) Method for Measurement of the Oil Pick-Up (OPU, %)
A specimen of the raw cord was cut to a size of 10 to 15 m, taken out in an amount of about 5.0 g, and then dried in a dryer at 107° C. for 2 hours, and the resultant was weighed (W0), dipped in CCl4 for 2 hours to remove the finishing oil. The resultant was dried under the above-described drying condition and weighed (W1), to calculate the oil pick-up.
Oil pick-up (OPU, %)=(W0−W1)/W1×100
A cellulose solution prepared from a V-81 pulp with a degree of polymerization (DPw) of 1200 (α-cellulose content: 97%) manufactured by Buckeye Technology Inc., NMMO·1H2O, and propyl gallate at a concentration of 0.045 wt % relative to the solution, was used. At this time, the settings were as follows: the concentration of cellulose was 9 to 14%, the number of the orifices was 1,000, the diameter of the orifice varied in the range of 120 to 200 μm. The solution discharged from a spinning nozzle with a ratio of the diameter and the length of the orifice (L/D) of 4 to 8, and an outer diameter of 100 mmφ was cooled through an air gap with a length of 30 to 100 mm, the spinning speed varied in the range of 90 to 150 m/min, and the final filament fineness was 1,500 deniers. The temperature of the coagulation solution is from 10 to 25° C., and the concentration was set at water 80% and NMMO 20%. The temperature and the concentration of the coagulation solution were continuously monitored using a refractometer. The residual NMMO was removed from the filament leaving from the coagulation bath through a washing process. It was subject to a first finishing oil treatment, and then dried. Thereafter, it was subject to a second finishing oil treatment, and then wound. The OPU of the wound yarn filament was adjusted to 0.1 to 0.6%. The spinning conditions and parameters were shown in Table 1. The obtained filament as described above was twisted using a direct twister at a twist number (turns per meter) of 350 to 470 TPM in both of the ply twist and the cable twist, thus to prepare a 2-ply raw cord (Examples 1 to 6). Further, the filament was twisted at a twist number of 260 to 400 TPM in both of the ply twist and the cable twist, thus to prepare a 3-ply raw cord (Examples 7 to 12). Thereafter, the tensile of the whole heat treatment process was applied at 1.0 to 3.0% to prepare a dipped cord having a DPU set at 3.0 to 6.0%. At this time, the raw cord was dried to remove moisture at a temperature of 100 to 120° C., and then dipped in an RFL solution. The heat treatment temperature and the residence time after dipping affect the reduction of the DP of the cellulose. In the present Example, the treatment temperature after the dipping in an RFL solution was 140 to 200° C., and the residence time in the treatment process after the dipping was 50 to 200 seconds.
As a result, the physical properties of the dipped cord were shown in Table 2.
Super-III, a dipped cord which is at present commercially available for use as a rayon tire cord, was used under the conditions other than those as presented above to prepare a lyocell, which was evaluated in the same analysis method as in Examples. The results thereof were also shown in Tables 1 and 2.
The lyocell dipped cord prepared in the present invention, as described in Examples 1 to 12 in Table 2, has an initial modulus value of 80 to 200 g/d, and a high strength of 16 kgf or more, and thus solves the problems of a conventional viscose rayon such as low tenacity and low initial modulus to provide a lyocell tire cord with excellent dimensional stability and heat resistance.
As such, the present invention solves the problems of a conventional viscose rayon such as low tenacity and low initial modulus by providing a lyocell dipped cord, which gives a stress-strain curve exhibiting that (a) the lyocell dipped cord has an elongation of 1.2% or less at an initial stress of 1.0 g/d, and an initial modulus value of 80 to 200 g/d; (b) has an elongation of 6% or less in a stress region of 1.0 g/d to 4.0 g/d; and (c) has an elongation of 1% or more at a tensile strength of 4.0 g/d to the breaking point, as measured in the dried state. Therefore, the present invention has an effect to provide a lyocell tire cord with excellent dimensional stability and heat resistance.
As described above, the present invention is described only with reference to specific examples, but a skilled person in the art will easily appreciate that various modifications and changes can be made without departing from the spirit of the present invention, and the modifications and changes will be apparently within the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0038086 | Apr 2006 | KR | national |
