KR20150077070A - Meta aramid paper with low density and enhanced Tear strength and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a meta-aramid paper having an excellent intensity, which enables to provide an excellent elongation and cutting load. Furthermore, since the meta-aramid paper having an excellent intensity and a meta-aramid sheet, manufactured by the meta-aramid paper, have high bulk and excellent oil absorptiveness, the present invention enables to be used in a product requiring oil immersion, etc. and to provide a meta-aramid paper having the excellent tearing strength as well as the excellent elongation and the cutting load at the same time rather than meta-aramid manufactured by an existing technology. The low density and high strength meta-aramid paper requires: (1) less than or equal to 0.4 g/cm^3 of the density; (2) greater than or equal to 25 N/cm of the tensile strength in an MD direction when the thickness is 0.14 mm; (3) greater than or equal to 5.0% of an elongation rate in the MD direction when the thickness is 0.14 mm; and (4) 0.95 N of the tearing strength in the MD direction when the thickness is 0.14 mm.

Description

TECHNICAL FIELD The present invention relates to a low-density high-strength meta-aramid paper and a method of manufacturing the same,

The present invention relates to a low-density high-strength meta-aramid paper and a method for producing the same. More particularly, the present invention relates to a low-density high-strength meta-aramid paper excellent in both tensile strength, tear strength, non-tear strength and elongation.

Generally, polyamide-based synthetic resins are classified into aliphatic polyamides and aromatic polyamides. Aliphatic polyamides are generally known under the trade name Nylon, and aromatic polyamides are known under the trade name Aramid. Among the aliphatic polyamides, nylon 6 and nylon 6,6 are the most common thermoplastic engineering plastics, and they are used not only as fibers but also as molding materials in various fields. The nylon resin used in the molding industry is made of reinforced plastics which is reinforced with mineral or glass fiber to improve mechanical properties such as elasticity and lowering the price to have improved flame retardancy and impact resistance.

Aromatic polyamides, developed in the 1960s, were developed to improve the heat resistance of nylon, an aliphatic polyamide. Aromatic polyamides, well known for their trade names such as Nomex and Kevlar, And has excellent heat resistance and high tensile strength which can be used for fibers such as cord. A typical aliphatic polyamide is a synthetic resin having an aliphatic hydrocarbon bonded between amide groups, and an aramid is a synthetic resin having an amide bond having 85% of benzene groups bonded to two aromatic rings between amide groups. The aliphatic hydrocarbon of the aliphatic polyamide easily undergoes molecular motion when heat is applied, whereas the benzene ring of the aromatic polyamide is stable to heat and has high elasticity because the molecule chains are rigid and the molecules do not easily move even when heat is applied. And there are many differences in characteristics.

The aromatic polyamides are classified into para-aramid and meta-aramid. The para-aramid is represented by Kevlar developed by DuPont. The para-aramid is the benzene ring bound to the amide group at the para position. Since the molecular chain is very stiff and has a linear structure, it has a very high strength and a particularly high elasticity, so that it has excellent shock absorbing performance. It is used for armor, bulletproof helmet, safety gloves, boots and fire extinguisher. It is used for sports equipment such as sticks, fishing rods and golf clubs, and also for industrial use such as FRP (Fiber Reinforced Plastic) and asbestos replacement fibers. The meta-aramid is a combination of benzene ring and amide group at the meta position. Its strength and elongation are similar to ordinary nylon, but it has very good heat stability. It is light and sweat-absorbing compared to other heat-resistant materials. have. In the early days, the color was limited to a few, but recently it has been made in various colors including fluorescent colors. It is used as fire-resistant clothing, uniforms for racing motorists, astronaut uniforms, work clothes, etc., and for industrial use, it is used for high-temperature filters.

Generally, meta-aramid paper is produced by mixing meta-aramid flock with meta-aramid fibrid at a certain ratio. The produced meta-aramid paper is classified into low-density paper and high-density paper depending on the presence or absence of the subsequent calendering process, and the high-density meta-aramid paper is used for insulation of electrical / electronic devices driven at high temperatures, such as dry type transformers, motors, and generators Mainly used and low density meta aramid paper is mainly used for iron core, phase insulation and winding of wet type transformer which needs oil absorption property.

On the other hand, such a low-density meta-aramid paper has a disadvantage in that the tensile strength, tear strength, non-drawn strength and elongation are remarkably lowered as compared with a high-density meta-aramid paper due to the bulkiness of the structure itself. Specifically, U.S. Patent No. 3756908 discloses a meta-aramid paper having improved flexibility of paper by using a low initial modulus (80 gm / denier) meta-aramid floc and high elongation without calendering. In this case, however, there is a problem that the tensile strength, the tear strength, the non-inhomogeneity and the elongation are as low as one-half of that of the calendering treated product.

It is an object of the present invention to provide a low-density high-strength meta-aramid paper having excellent tensile strength, tear strength, non-in-tear strength and elongation, and a method of manufacturing the same.

In order to solve the above-described problems, the present invention provides a low-density high-strength meta-aramid paper satisfying all of the following conditions (1) to (4).

(1) an apparent density of 0.4 g / cm 3 or less,

(2) a tensile strength in the MD direction of not less than 25 N / cm when the thickness is 0.14 mm,

(3) When the thickness is 0.14 mm, the elongation in the MD direction is 5.0% or more,

(4) When the thickness is 0.14 mm, the tear strength in the MD direction is 0.95 N or more

According to a preferred embodiment of the present invention, the apparent density may be 0.25 to 0.35 g / cm < 3 >.

According to another preferred embodiment of the present invention, the low density high strength meta aramid paper may further satisfy the following condition (5).

(5) When the thickness is 0.14 mm, the tensile strength in the MD direction is not less than 23 Nm 2 / ㎏

According to another preferred embodiment of the present invention, the basis weight of the meta-aramid paper may be 35 to 50 g / m 2.

According to another preferred embodiment of the present invention, the meta-aramid paper comprises meta-aramid floc and meta-amide fibrids, and the floc and fibrids may have an intrinsic viscosity (IV) of 1.5 to 2.0.

According to another preferred embodiment of the present invention, the condition (2) is 30 N / cm or more, the condition (3) is 7% or more, and the condition (4) is 1.1N or more.

According to another preferred embodiment of the present invention, the condition (5) may be 27 Nm2 / kg or more.

According to another preferred embodiment of the present invention, the thickness of the meta-aramid paper may be 0.13 to 0.16 mm.

According to another preferred embodiment of the present invention, there is provided a method for producing a low density meta-aramid paper which does not include a calendering process, comprising the steps of: (1) adding a meta- aramid floc and meta- producing a wet-web; (3) drying the dehydrated wet paper by primary hot air drying; (4) second drying the dried wet paper; And (5) drying the dried paper at a temperature of 250 to 320 DEG C .

According to another preferred embodiment of the present invention, the floc and fibrids may have an intrinsic viscosity (IV) of 1.5 to 2.0.

According to another preferred embodiment of the present invention, the primary drying may be performed by hot air drying at 195 to 250 ° C, and the secondary drying may be performed at 100 to 150 ° C.

According to another preferred embodiment of the present invention, the tertiary drying may be performed for 10 to 80 seconds.

According to another preferred embodiment of the present invention, the method may further comprise compressing and dewatering the wet paper between the steps (2) and (3) or between the steps (3) and (4).

According to another preferred embodiment of the present invention, there is provided an insulating paper comprising the meta-aramid paper of the present invention.

Hereinafter, terms used in the present invention will be defined.

"Flock" refers to fibers of shorter length than staple fibers. The length of the flocs is from about 0.5 to about 15 mm and the diameter is from 4 to 50 micrometers, preferably from 1 to 12 mm in length and from 8 to 40 micrometers in diameter. Aramid floc can be produced by cutting aramid fibers to short lengths without significant or optional fibrillization, such as those produced by the methods described in U.S. Patent Nos. 3,063,966, 3,133,138, 3,767,756 and 3,869,430 .

The term "fibrids" refers to non-granular pulp or film-like particles. Preferably, the melting point or decomposition point thereof may exceed 320 ° C. The fibrids have an average length of 0.5 to 2 mm and an aspect ratio of 15: 1 to 50: 1. Including the use of a fibridation apparatus of the type disclosed in U.S. Patent No. 3,018,091, and any method in which the polymer solution is precipitated and sheared in a single step.

The low density high strength meta aramid paper of the present invention has excellent tensile strength, tear strength, non-inhomogeneity, and elongation.

1 is a process diagram for a method for producing a meta-aramid paper according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings.

As described above, the low-density meta-aramid paper which is not subjected to the calendering process has a disadvantage in that tensile strength, tear strength, non-drawn strength and elongation are remarkably lowered compared with high-density meta-aramid paper due to the bulkiness of the structure itself.

Accordingly, the present invention provides a low-density, high-strength meta-aramid paper satisfying all of the following conditions (1) to (4) As a result, the low density high strength meta aramid paper of the present invention has excellent tensile strength, tear strength, non-tear strength and elongation.

(1) an apparent density of 0.4 g / cm 3 or less,

(2) a tensile strength in the MD direction of not less than 25 N / cm when the thickness is 0.14 mm,

(3) When the thickness is 0.14 mm, the elongation in the MD direction is 5.0% or more,

(4) When the thickness is 0.14 mm, the tear strength in the MD direction is 0.95 N or more

More specifically, FIG. 1 is a process diagram for a method for producing a meta-aramid paper according to an embodiment of the present invention. The method comprises the steps of (1) loading a meta-aramid flock and a meta- Producing; (3) drying the dehydrated wet paper by primary hot air drying; (4) second drying the dried wet paper; And (5) drying the dried paper at a temperature of 250 to 320 DEG C .

First, as a step (1), a step of adding a material containing meta-aramid floc and meta-amide fibrids to produce a wet-web will be described. The meta-aramid floc and meta-aramid fibrids used in the present invention can be used without limitation as long as they are conventionally used in meta-aramid paper. In the present invention, 80 to 200 parts by weight of meta-aramid fibrids are mixed with 100 parts by weight of meta- Can be used.

Meta-aramid polymers suitable for use in meta-aramid fibrids and meta-aramid flocs may be polyamides in which at least 85% of the amide (-CO-NH-) linkages are attached directly to the two aromatic rings, , Up to 10% by weight of many other polymeric materials can be blended with the meta-aramid. Copolymers having as many as 10% of other diamines replacing the diamine of the aramid or as many as 10% other diacids replacing the diacid chlorides of the aramid may be used. The meta-aramid may be poly (metaphenylene isophthalamide), 4,4-diaminodiphenylsulfone, 3,3-diaminodiphenylsulfone, but is not limited thereto. In some of the most preferred embodiments, the meta-aramid polymer may be a poly (metaphenylene isophthalamide).

The intrinsic viscosity (IV) of the meta-aramid contained in the meta-aramid fibrids and meta-aramid flocs is preferably in the range of 1.5 to 2.0, It is very advantageous to improve. If the intrinsic viscosity is less than 1.5 or more than 2.0, the degree of improvement of the physical properties is remarkably deteriorated.

On the other hand, in step (1), meta-aramid floc and meta-aramid fibrids are mixed with water using a refiner (100) to prepare a paper stock. The meta-aramid floc and fibrids may be present in an amount ranging from 1 to 10% by weight, based on the total composition, but are not limited thereto. And is transferred to the wire part 210 through the head box 120 passing through the defuzzifier 100. The gold net 210 is formed by a fourdrinier machine formed in endless form, a cylinder machine having a large cylindrical shape, an inclinable machine, and a net net formed up and down. And a gap former, which can be used without limitation in the present invention. Specifically, the material discharged from the head box 120 forms a wet web through the forming board 211 of the gold net.

In the next step (2), the produced wet paper is dehydrated. The wet paper is conveyed by a plurality of rollers provided in the gold net 210. At this time, a dehydration process is performed while passing through the dehydrating unit 212. [ The dewatering unit may be achieved through a suction box, and the suction box may include a plurality of suction boxes. The suction box is installed in contact with the bottom of the net, and the dehydrated water is discharged outside the net.

In the next step (3), the dehydrated wet paper is subjected to a primary hot air drying in a hot air drying unit 220. The step (3) is performed to increase the removal of moisture from the wet paper web and to minimize the thickness reduction of the wet paper web structure. As a result, the physical properties such as bulk, air permeability, . Meanwhile, the step (3) is preferably carried out at a temperature of 195 to 250 ° C (see Table 1). If the hot air drying is performed outside the temperature range, there is a possibility that the degree of property improvement becomes insignificant. Also, the step (3) must be accomplished through hot air drying. Examples of the hot air dryer include a through air dryer, a spooner, and the like. If you use a dryer other than hot air drying (eg, Cylinder Dryer, Yankee Dryer, Lab, etc.), the moisture in the paper will remain in the form of pockets and the drying will be poor. And a problem that the thickness of the wet paper is decreased due to the drying of the wet paper by the dry felt may occur. Even if the temperature condition is satisfied, it is difficult to achieve the object of the present invention (see Table 1).

The paper is then conveyed out of the paper machine and the lumber is cleaned with the washer 213.

According to another preferred embodiment of the present invention, the step of compressing and dewatering the wet paper web between the step (2) and step (3) or step (3) and step (4) . In this case as well, the compression dehydration can be selectively carried out in the case where the density of the meta-aramid paper satisfies the low density range.

Next, in step (4), the hot-air dried wet paper is subjected to secondary drying in the secondary drying unit 240 to produce paper. This is to effectively remove moisture from wet paper pellets, and the drying temperature may be from 100 to 150 ° C. If the drying temperature is less than 100 ° C, drying may not be performed as desired, and drying problems may occur. If the drying temperature exceeds 150 ° C, the moisture inside the wet paper filter may remain in the form of a pocket due to rapid drying. The drying time may be from 30 seconds to 600 seconds.

Next, in step (5), the hot air-dried paper is thirdly dried at a temperature of 250 to 320 ° C in a tertiary drying unit 250. Conventional low-density meta-aramid paper did not undergo steps (3) and (5) but merely obtained a methaaded paper through a drying process at 100 to 150 ° C of step (4). As a result, it was confirmed that extensibility, tear strength and the like were remarkably improved compared to high density meta aramid paper while maintaining low density because no calendering was performed. Specifically, the tertiary drying is carried out at 250 to 320 ° C, which is very advantageous in improving the physical properties. If the tertiary drying temperature is lower than 250 ° C or higher than 320 ° C, it is difficult to satisfy the desired properties (see Table 1). On the other hand, the tertiary drying can be performed for 10 to 80 seconds. If it is less than 10 seconds, it is difficult to achieve the desired purpose, and if it exceeds 80 seconds, the flexibility of the paper is decreased, which may cause problems in workability of the product.

The low-density high-strength meta-aramid paper produced through such a manufacturing process satisfies all of the following conditions (1) to (4), and more preferably satisfies the following condition (5). On the other hand, since the strength and elongation ratio are functions that are proportional to the thickness, accurate physical properties can be prepared by measuring the strength and elongation while maintaining the thickness constant.

(1) an apparent density of 0.4 g / cm 3 or less,

(2) a tensile strength in the MD direction of not less than 25 N / cm when the thickness is 0.14 mm,

(3) When the thickness is 0.14 mm, the elongation in the MD direction is 5.0% or more,

(4) When the thickness is 0.14 mm, the tear strength in the MD direction is 0.95 N or more

(5) When the thickness is 0.14 mm, the tensile strength in the MD direction is not less than 23 Nm 2 / ㎏

 The apparent density may be from 0.25 to 0.35 g / cm < 3 >.

On the other hand, the thickness of the meta-aramid paper may be 0.13 to 0.16 mm. If it is less than 0.13 mm, there may arise a problem that the absorbency is lowered due to the increase in density.

According to another preferred embodiment of the present invention, the basis weight of the meta-aramid paper may be 35 to 50 g / m ² . If the basis weight is less than 35 g / m ^{2, the} strength may be lowered. If the basis weight is more than 50 g / m ² , the efficiency of the hot air dryer may be lowered and the density may increase.

According to another preferred embodiment of the present invention, the meta-aramid paper comprises meta-aramid floc and meta-amide fibrids, and the floc and fibrids may have an intrinsic viscosity (IV) of 1.5 to 2.0. In this case, the meta-aramid paper satisfying both the first hot air drying temperature condition, the secondary drying condition and the tertiary drying condition satisfies the condition (2) of 30 N / cm or more, the condition (3) (4) can have the best physical properties of 1.1 N or more, and further, the above condition (5), which is the non-inhomogeneity, can have 27 Nm 2 / kg or more.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

≪ Example 1 >

A meta-aramid (polymetaphenylene isophthalamide) dope (mA Dope) having an intrinsic viscosity of 1.8 was prepared and a meta-aramid fibrid having a Canadian Standard Freeness of 150 ml was manufactured using a fibril production apparatus Respectively. The prepared fibrids were adjusted to 0.8% concentration using a double disk refiner to improve the processability of the wet nonwoven fabric and to improve the physical properties of the final separator, thereby adjusting the freeness of the fibrids to 80 ml.

On the other hand, a 2.0 denier fiber was produced by using the same polymer, and the fiber length was 7 mm to make a floc. The strength of the floc was 5.3 g / de and elongation was 35%.

Thereafter, the fibrids and flocs were mixed in water at a weight ratio of 6: 4, and the resultant mixture was added to water in an amount of 0.5% by weight to prepare a ground.

The above-mentioned materials were put into the paper manufacturing apparatus of Fig. 1 to prepare wet paper pills. After that, primary hot air drying was performed at 200 ° C for 30 seconds in the hot air dryer, and secondary drying was performed at 120 ° C for 60 seconds. Then, the paper was subjected to tertiary drying at 300 ° C for 20 seconds in a cylinder dryer, .

≪ Example 2 >

A metha aramid paper was prepared in the same manner as in Example 1 except that the temperature of the hot air dryer was 235 ° C.

≪ Example 3 >

A meta-aramid paper was prepared in the same manner as in Example 1, except that a meta-aramid having an intrinsic viscosity of 1.2 was used.

<Example 4>

A meta-aramid paper was prepared in the same manner as in Example 1, except that a meta-aramid having an intrinsic viscosity of 2.2 was used.

&Lt; Example 5 >

A metha aramid paper was prepared in the same manner as in Example 1, except that the temperature of the hot air dryer was 190 ° C.

&Lt; Example 6 >

A metha aramid paper was prepared in the same manner as in Example 1, except that the temperature of the hot air dryer was 260 ° C.

&Lt; Comparative Example 1 &

A meta-aramid paper was prepared in the same manner as in Example 1, except that the third drying was not performed.

&Lt; Comparative Example 2 &

A metha aramid paper was prepared in the same manner as in Example 1, except that a primary hot air dryer was used.

<Experimental Example>

The following properties of the meta-aramid paper of the Examples and Comparative Examples were evaluated, and the results are shown in Table 1.

1. Tensile strength (N / cm) and elongation (%)

The tensile strength and elongation were measured according to ASTM D-828 for 24 hours under constant temperature and humidity conditions, and then the specimens were cut in the machine direction and subjected to MD (machine direction) load in a horizontal tensile strength meter. , And elongation was measured at the elongation ratio of the specimen until the tensile break.

2. Tear strength (N)

The tear strength was measured according to TAPPI T414 for 24 hours under constant temperature and humidity conditions. The sample was cut in the width direction and the tear strength in MD (machine direction) was measured in an Elmendorf tear strength tester.

3. Intrinsic strength (Nm ² / kg)

The non - inhomogeneity was calculated from the measured basis weight and tear strength by the following equation.

(Nm ² / kg) = Tear strength (N) * 1000 / gram (g / m ² )

4. Absorbed amount

The amount of water absorption was measured by a Cobb tester having an area of 100 cm ² in accordance with TAPPI T441, and after weighing the sample, the sample was poured in 100 ml of water. After 60 seconds, the unabsorbed water was discarded. After the water was removed, weighing was carried out and the amount of water absorption was calculated by the following equation.

(G / m ² ) = (weight of final specimen (g) - weight of specimen subjected to constant temperature and humidity treatment (g)) * 100

One) 2) 3) 4) 5) 6) 7) 8) Example 1 41.4 0.142 0.28 32.72 7.36 1.15 27.8 13.7 Example 2 42.0 0.151 0.28 31.03 7.14 1.13 26.9 14.1 Example 3 41.2 0.145 0.28 29.25 6.57 1.04 25.2 13.1 Example 4 41.3 0.143 0.29 29.45 6.79 1.08 26.2 13.5 Example 5 41.6 0.139 0.30 29.59 7.26 1.07 25.8 13.5 Example 6 41.8 0.151 0.28 30.12 6.92 1.08 25.8 13.0 Comparative Example 1 41.6 0.145 0.29 9.27 1.61 0.79 19.0 13.6 Comparative Example 2 41.7 0.139 0.32 30.3 7.16 1.01 24.2 12.4
1) Basis weight (g / ㎡)
2) Thickness (mm)
3) Apparent density (g / cm3)
4) MD tensile strength (N / cm)
5) MD elongation rate (%)
6) MD tear strength (N)
7) MD Non-inhaled strength (Nm 2 / kg)
8) Water absorption (g / ㎡)

As can be seen from Table 1, the papers of Examples 1 to 6 of the present invention showed excellent mechanical strength as compared with Comparative Example 1 in which the third drying was not carried out. In addition, it was confirmed that Example 1 using a hot-air dryer was superior in bulkiness and water absorption to Comparative Example 2 in which it was not used. Further, Examples 1 and 2 which satisfied the temperature condition of the hot air drying exhibited excellent physical properties as compared with Example 5 which had a low hot air temperature and showed similar physical properties to those of Example 6 which had a high hot air temperature, It was confirmed that the efficiency was excellent. In addition, the paper of Examples 1 and 2 satisfying the range of the intrinsic viscosity exhibited excellent physical properties as compared with the paper of Examples 3 and 4 in which the paper of Examples 1 and 2 deviates from the paper of Examples 1 and 2.

Claims (14)

A low-density high-strength meta-aramid paper satisfying all of the following conditions (1) to (4).
(1) an apparent density of 0.4 g / cm 3 or less,
(2) a tensile strength in the MD direction of not less than 25 N / cm when the thickness is 0.14 mm,
(3) When the thickness is 0.14 mm, the elongation in the MD direction is 5.0% or more,
(4) When the thickness is 0.14 mm, the tear strength in the MD direction is 0.95 N The method according to claim 1,
Wherein the apparent density is 0.25 to 0.35 g / cm &lt; 3 &gt;. The method according to claim 1,
Wherein the low-density high-strength meta-aramid paper further satisfies the following condition (5).
(5) When the thickness is 0.14 mm, the tensile strength in the MD direction is not less than 23 Nm 2 / ㎏ The method according to claim 1,
Wherein the meta-aramid paper has a basis weight of 35 to 50 g / m &lt; 2 &gt;. The method according to claim 1,
Wherein the meta-aramid paper comprises meta-aramid floc and meta-amide fibrids, and the floc and fibrids have an intrinsic viscosity (IV) of 1.5 to 2.0. The method of claim 3,
The condition (2) is 30 N / cm or more, the condition (3) is 7% or more, the condition (4) is 1.1 N &lt; / RTI &gt; or higher. The method according to claim 6,
Wherein the condition (5) is 27 Nm &lt; 2 &gt; / kg or more. The method according to claim 1,
Wherein the meta-aramid paper has a thickness of 0.13 to 0.16 mm. A method of producing a low-density meta-aramid paper that does not include a calendering step,
(1) preparing a wet-web by charging a stock containing meta-aramid floc and meta-amide fibrids;
(2) dewatering the wet paper;
(3) drying the dehydrated wet paper by primary hot air drying;
(4) drying the dried wet paper by a second drying process to produce paper paper; And
(5) A third step of drying the dried paper at a temperature of 250 to 320 DEG C to form a low density high strength meta-aramid paper. 10. The method of claim 9,
Wherein the first hot air drying is a hot air drying at 195 to 250 ° C. 10. The method of claim 9,
Wherein the secondary drying is performed at 100 to 150 &lt; 0 &gt; C. 10. The method of claim 9,
Wherein the third drying is performed for 10 to 80 seconds. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 10. The method of claim 9,
The method of claim 1, further comprising compressing and dewatering the wet paper between steps (2) and (3) or between steps (3) and (4). An insulating paper comprising the meta-aramid paper of any one of claims 1 to 8.

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