ARAMID PULP AND METHOD FOR MANUFACTURING THE SAME

Abstract

According the present disclosure, there is provided an aramid pulp and a method for manufacturing the same, in which a completely dried, oilless aramid yarn that has not been applied with a general spinning oil agent is used, and thus the water dispersion and swelling time of the fiber can be reduced as compared with a conventional case, thereby providing an aramid pulp that is improved in productivity and pulp properties and excellent in interfacial adhesion force with different materials.

Claims

1. An aramid pulp characterized in that it is formed from an oilless aramid staple fiber of dried multifilaments that are not coated with a spinning oil agent.

2. The aramid pulp of claim 1, wherein freeness is 500 ml or less.

3. The aramid pulp of claim 1, wherein freeness is 100 to 500 ml, and a fiber length (length-weighted average fiber length) is 0.3 to 1.5 mm.

4. The aramid pulp of claim 1, wherein a specific surface area is 10 m.sup.2/g or more.

5. The aramid pulp of claim 1, wherein a specific surface area is 10 to 20 m.sup.2/g.

6. The aramid pulp of claim 1, wherein a residual oil content in the pulp of the final product is 0.1% or less.

7. A method for manufacturing the aramid pulp of claim 1, the method comprising the steps of: providing an oilless aramid staple fiber; preparing a water dispersion slurry of the oilless aramid staple fiber; and refining the water dispersion slurry, wherein the oilless aramid staple fiber is produced by a method which comprises spinning and coagulating a spinning dope using an aromatic polyamide polymer to produce a multifilament, and drying and cutting the multifilament, so that the fiber does not contain a spinning oil agent and water.

8. The method for manufacturing the aramid pulp of claim 7, wherein the step of preparing a water dispersion slurry comprises a step of dissociating the aramid staple fiber in water for 10 minutes or more and 120 minutes or less at room temperature to swell the aramid staple fiber.

9. The method for manufacturing the aramid pulp of claim 7, wherein the aramid staple fiber swollen in the water dispersion slurry has a swelling degree of 102% or more relative to the aramid staple fiber before swelling.

10. The method for manufacturing the aramid pulp of claim 7, which further comprises a step of washing the aramid staple fiber with a surfactant-containing washing solution, before the step of preparing a water dispersion slurry.

11. The method for manufacturing the aramid pulp of claim 7, which further comprises a sheet making step, a sheet drying step, and a sheet crushing step, after the refining step.

12. The method for manufacturing the aramid pulp of claim 7, wherein freeness is 500 ml or less, a specific surface area is 10 m.sup.2/g or more, and a residual oil content in the pulp of the final product is 0.1% or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] FIG. 1 is a process diagram which briefly shows the process of producing an aramid filament according to an embodiment of the present disclosure.

[0076] FIG. 2 is a process diagram which briefly shows the process of manufacturing an aramid pulp according to another embodiment of the present disclosure.

[0077] FIG. 3 is a result of visually observing the water dispersibility of Example 1 and Comparative Example 1.

[0078] FIGS. 4a and 4b are the results of observing the fiber swelling degree of Example 1 and Comparative Example 1 with an optical microscope.

[0079] FIG. 5 is a refining degree evaluation result with respect to Example 1 and Comparative Example 2.

[0080] FIG. 6 is an orientation evaluation result with respect to Example 1 and Comparative Example 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0081] Hereinafter, the actions and effects of the invention will be described more specifically with reference to specific examples of the present disclosure. However, the examples are for illustrative purposes only, and are not intended to limit the scope of rights of the invention in any sense.

Example 1

[0082] 1) Production of Aramid Staple Fiber

[0083] CaCl.sub.2) was added to N-methyl-2-pyrrolidone (NMP) to prepare a polymerization solvent, and then para-phenylenediamine was dissolved in the polymerization solvent to prepare a mixed solution.

[0084] Then, while stirring the mixed solution, the same number of moles of terephthaloyl dichloride as para-phenylenediamine was added to the mixed solution in two divided portions to produce a poly(paraphenylene terephthalamide) polymer. Water and NaOH were then added to the polymerization solution containing the polymer to neutralize acid. Then, the polymer was pulverized, and the polymerization solvent contained in the aromatic polyamide polymer was extracted using water, and subjected to dehydration and drying steps to finally obtain an aromatic polyamide polymer.

[0085] Then, the obtained aromatic polyamide polymer was dissolved in 99% concentrated sulfuic acid to prepare a spinning dope. The polymer concentration in the spinning dope was set to 20 wt %.

[0086] The spinning dope was spun through a spinneret, and solidified in a coagulation tank containing a 13% aqueous sulfuric acid solution through a 7 mm air gap. Thereby, an aramid multifilament composed of 1000 monofilaments were produced.

[0087] The produced multifilament was washed with water, dried, and wound to produce an aramid fiber having a linear density of 1500 denier. At this time, the drying was performed by hot air drying at 100° C.

[0088] Then, the aramid fiber to which the oil agent was not applied was cut using a rotary cutter to make an aramid staple fiber (oilless aramid raw yarn).

[0089] 2) Manufacture of Aramid Pulp

[0090] The oilless aramid staple fiber (aramid yarn) was put in water, circulated for 10 minutes, and dispersed, and the refining was performed immediately for 60 minutes using a valley beater, which is a laboratory beater. The aramid staple fiber swollen in this process could be obtained.

[0091] That is, the oilless yarn was beaten using the valley beater, which is a laboratory beater. The refining conditions were a 0.6% concentration, 1 hour, and a load of 10 kg.

[0092] After input to the refining section, it was beaten for 60 minutes to produce fibrillated aramid staple fibers 2 having an average length of 1 mm.

[0093] After the refining, dehydration was performed using a centrifugal dehydrator, and dried for about half a day (12 hours) at 100° C. in a hot air dryer to manufacture an aramid pulp.

Comparative Example 1

[0094] The process was performed in the same manner as in Example 1, except that during the production of the aramid staple fiber, a spinning oil agent was applied to the multifilament having a linear density of 1500 denier.

[0095] That is, a first oil agent containing ester oil and a second oil agent containing phosphate ether oil were sequentially passed through the multifilament, and then crimped so that the average number of crimps was 3 crimps/cm.

Comparative Example 2

[0096] Aramid pulp was manufactured in the same manner as in Example 1, except that during the production of the aramid staple fiber, drying (heat treatment) was not performed.

Experimental Example 1

[0097] The physical properties of Example 1 and Comparative Example 1 were evaluated by the following methods.

[0098] That is, in order to compare the effects of aramid staple fibers on the presence or absence of the oil agent, it is a comparison of the results using a laboratory beater (valley beater) at room temperature for 10 minutes.

[0099] (1) Evaluation of Fiber Water Dispersion

[0100] The water dispersion evaluation during the production of the aramid staple fiber water dispersion slurry of Example 1 and Comparative Example 1 was observed with the naked eye, and the results are shown in FIG. 3.

[0101] As shown in FIG. 3, it can be confirmed that Example 1 using the oilless aramid raw yarn of the present disclosure was very excellent in dispersibility as compared with Comparative Example 1 using the conventional yarn containing an oil agent.

[0102] That is, the result of observation with the naked eye after the water dispersion of the raw yarn showed that in Example 1, the raw yarn was smoothly dispersed without floating due to the oilless.

[0103] On the other hand, the existing raw yarn of Comparative Example 1 floated due to the oil agent, and the fiber floc was not broken.

[0104] (2) Fiber Swelling Degree

[0105] The oilless raw yarn of Example 1 and the oil agent-applied raw yarn of Comparative Example 1 were immersed in water, then the diameter was measured through an optical microscope, and a difference in swelling degree (increase in diameter) was confirmed. The results are shown in FIGS. 4a and 4b. In FIGS. 4a and 4b, a to e indicate the fiber length of the indicated section.

[0106] The oilless raw yarn of Example 1 of FIG. 4a was immersed in water and observed through an optical microscope. As a result, the swelling degree after 60 minutes of immersion was 105.0% relative to before immersion.

[0107] However, the conventional raw yarn of Comparative Example 1 of FIG. 4b showed a swelling degree of 101.7% after 60 minutes of immersion, which was inferior to that of Example 1.

[0108] (3) Canadian Standard Freeness (CSF: ml)

[0109] After refining, the pulp made from the oilless yarn/oil agent-applied yarn of Example 1 and Comparative Example 1 was completely dried and then dissociated using a standard dissociator, and then the freeness was measured. The freeness evaluates the dehydration of pulp, and generally, it is evaluated as an excellent pulp if the dehydration is poor (the freeness value is low). The results are shown in Table 1.

[0110] That is, in accordance with the TAPPI 227 evaluation regulations, 3 g/L of pulp was dissociated for a certain period of time using a standard dissociator, then put into the freedom tester specified in the above regulations, and then the amount of overflowing water was measured to qualitatively evaluate the degree of fibrillation of the pulp.

[0111] (4) Fiber Length (Fiber Weighted Average Fiber Length)

[0112] After refining, the pulp made form oilless yarn/oil agent-applied yarn was measured with a Valmet FS300, which is a fiber length measuring machine.

[0113] (5) Filler Retention. F/R

[0114] F/R is a method of evaluating the fibrils of pulp. The pulp and the filler were mixed and sieved, and the degree to which the pulp holds the filler was evaluated. In general, it was judged that the higher the value, the better the pulp with well-developed fibrils.

[0115] (6) Temporary Molding/Bending Strength

[0116] Temporary molding/bending strength is a method of evaluating the reinforcing performance of pulp. The pulp and the filler were mixed, and then temporarily molded using a press facility to produce a pad.

[0117] The bending strength of the produced pad was measured to evaluate the reinforcing performance of the pulp. At this time, the bending strength was evaluated by measuring the force (resistance force) of resisting bending by modifying the plastic-bending measurement standard according to KS M ISO 178 (unit: kgf)

[0118] As a result of the temporary molding/bending strength evaluation, it was found that the pulp using the oilless raw yarn was about 58% higher (excellent).

[0119] (7) Specific Surface Area (m.sup.2/g)

[0120] The specific surface area of the sample was quantitatively measured according to a well-known BET evaluation method.

TABLE-US-00001 TABLE 1 Remarks (Example 1/ Comparative Comparative Example 1 Example 1 Example 1) Water dispersion Poor Excellent — (naked eye) Swelling (%) 101.7 105.0  3% Freeness (ml) 704 665 −6% Fiber length (mm) 0.96 0.90 −7% F/R (%) 15.2 15.7  3% Bending strength (kgf) 0.36 0.57 58% Specific surface area 7 12 71% (m.sup.2/g)

[0121] Looking at Table 1, it was confirmed that the pulp using the oilless aramid staple fiber (yarn) of Example 1 is excellent in pulping as compared with Comparative Example 1, and is excellent in interfacial adhesion force with dissimilar materials in the final product.

[0122] That is, as described above, it was shown that Example 1 is excellent in water dispersibility and swelling degree as compared with Comparative Example 1, and the specific surface area is high at about 12 m.sup.2/g.

[0123] The fiber length results also showed that Example 1 is about 7% shorter than Comparative Example 1. The fiber length being short can be interpreted as causing a lot of refining. Therefore, in the case of the present disclosure, the refining can be easily performed, and pulp performance can be improved.

[0124] The freeness evaluation results showed that the freeness of the pulp using the oilless aramid staple fiber (yam) of Example 1 is about 6% lower (excellent) than Comparative Example 1. The freeness evaluates the dehydration properties of the pulp, and generally, it can be evaluated as an excellent pulp if the dehydration property is poor (the freeness value is low).

[0125] The F/R evaluation result showed that the F/R of the pulp using the oilless aramid staple fibers (raw yarn) of Example 1 was about 3% higher (excellent) than that of Comparative Example 1.

[0126] The temporary molding/bending strength evaluation result showed that the pulp using the oilless aramid staple fiber (raw yarn) of Example 1 is about 58% higher (excellent) than that of Comparative Example 1.

[0127] Further, the above evaluation result is the result of using a laboratory beater (valley beater), and the freeness of the pulp using a general factory beater may be 500 ml or less or 100 to 500 ml.

[0128] On the other hand, Comparative Example 1 has no peculiarities observed with the naked eye in the refining as compared with Example 1, but the fiber length was long, the freeness was high, and the F/R value was low as compared with the oilless aramid staple fiber (raw yarn) of Example 1. This means that Comparative Example 1 is deficient in the degree of pulping as compared with Example 1. Further, the temporary molding/bending strength value of Comparative Example 1 is lower than that of Example 1. In Comparative Example 1, the oil agent of the pulp interferes with the adsorption of N.sub.2 when the specific surface area is evaluated, and the evaluation result is decreased to about 7 m.sup.2/cm (decreased in interfacial adhesion force). This can be judged that the pulp oil agent lowers the interfacial adhesion force with different materials, and ultimately adversely affects the physical properties of the finished product.

[0129] Therefore, it was confirmed that the oil agent coated on the aramid yarn interferes with the pulping, and finally remains in the pulp to lower the interfacial adhesion force with the dissimilar materials.

Experimental Example 2

[0130] At the time of providing the aramid staple fibers (aramid raw yarns) used in Example 1 and Comparative Example 2, the refining evaluation was performed according to the presence or absence of drying, and the results are shown in FIGS. 5 and 6.

[0131] FIG. 5 is a refining degree evaluation result with respect to Example 1 and Comparative Example 2. FIG. 6 is an orientation evaluation with respect to Example 1 and Comparative Example 2.

[0132] Further, Comparative Example 2 in FIGS. 5 and 6 is a result of using a fiber in a state in which the aramid staple fibers are in a wet state of not being dried. Further, Example 1 is the result of using the fiber after the aramid fiber is completely dried through normal drying.

[0133] The refining degree evaluation is the result after 1.5 h at pH7 and pH12, respectively, after the refining step with a valley beater for each aramid staple fiber, and the structure of the fibers was measured by optical electron microscopy.

[0134] Further, when evaluating the fiber structure, general XRD was used to measure the orientation angle, crystallinity, size, and the like of the fiber.

[0135] Looking at FIGS. 5 and 6, in the case of Comparative Example 1, as an aramid raw yarn that was not dried (heat treated) after spinning was used, there was a significant difference from Example 1 in the fibril expression level before and after refining.

[0136] That is, Comparative Example 2 using the aramid fibers that have been subjected to abnormal drying in FIG. 5 showed weak fibril expression after refining. As a result, as shown in FIG. 6, in Comparative Example 2, the fibers were in a wet state before refining, and thus, after the refining step, the fibril expression was very weak, and even if it showed a fibrous structure with a diameter of 85 μm, XRD could not be measured.

[0137] Therefore, Comparative Example 2 is significantly inferior in the refining performance due to low orientation, crystallinity, and structure after refining, as compared with Example 1 using the dried (heat-treated) oilless aramid yarn.

[0138] On the other hand, in the case of Example 1, the aramid fibers were completely dried and then used in an oilless state to form a fibrous structure in which fibril expression was very strong after the refining step. Thereby, in the case of the present disclosure, it exhibits a fibrous structure in which the fiber orientation angle measured by XRD is 7 to 12°, the crystallinity is as high as 75%, and the diameter is 12 μm.

[0139] Therefore, when using fibers that have not been dried (heat treated) during the production of aramid pulp, the fiber structure (skin-core) is incomplete, and fibrils are not easily generated at the time of refining under the same conditions due to a low degree of orientation/crystallization. From these results, it was confirmed that as the present disclosure uses an oilless aramid yarn that has been completely dried through heat treatment as compared with the conventional case, it exhibits excellent orientation/crystallinity without the problems such as incomplete fiber structure, so that high quality aramid pulp having improved fibrillation can be produced.

DESCRIPTION OF REFERENCE NUMERALS

[0140] 1: aramid staple fiber [0141] 2: fibrillated aramid staple fiber [0142] 3: sheet [0143] 4: dehydrated sheet [0144] 5: dried sheet [0145] 6: aramid pulp [0146] 110: dissociation unit [0147] 120: refining unit [0148] 130: sheet forming unit [0149] 140: press unit [0150] 150: drying unit [0151] 160: crushing unit [0152] 170: packaging unit [0153] 10: spinneret [0154] 20: coagulation bath [0155] 30: washing tank [0156] 31: multifilament [0157] 50: drying unit [0158] 51: drying roll [0159] 60: winder