Parchmentized fibrous support containing parchmentizable synthetic fibers and method of manufacturing the same

Abstract

The present invention relates to a parchmentized fibrous support containing parchmentizable synthetic fibers parchmentized with sulfuric acid, the process for making such a support and the use thereof.

Claims

1. A process of making a parchmentized fibrous support comprising the steps of: (a) forming a fibrous support comprised of parchmentizable synthetic aramid fibers and parchmentizable synthetic aramid fibrids; and (b) parchmentizing the parchmentizable synthetic aramid fibers and fibrids of the fibrous support by treating the fibrous support with H.sub.2SO.sub.4 at a concentration from about 50% to about 100% and at a temperature from about −20° C. to about +50° C. for between about 5 to about 60 seconds sufficient to obtain a parchmentized fibrous support having an increased strength of at least 30% as compared to the strength of the fibrous support formed according to step (a).

2. The process of claim 1, wherein step (a) is practiced by hydroentangling the parchmentizable synthetic aramid fibers and parchmentizable synthetic aramid fibrids to form the fibrous support.

3. The process of claim 1, comprising forming two fibrous supports and thereafter together parchmentizing the two fibrous supports.

4. The process of claim 1, wherein step (b) is practiced by treating the fibrous support with H.sub.2SO.sub.4 at a concentration of from 72% to 90% for between about 10 to about 20 seconds.

5. The process of claim 4, wherein the fibrous support comprises about 60 wt. % of the parchmentizable synthetic aramid fibers and about 40 wt. % of the parchmentizable synthetic aramid fibrids.

6. The process of claim 1, wherein step (a) comprises including in the fibrous support synthetic fibers selected from the group consisting of polyamide-based fibrous materials; polyester-based fibrous materials; carbon fibers; glass fibers; and mixtures thereof.

7. The process of claim 1, wherein step (a) comprises including natural fibers in the fibrous support.

8. The process of claim 7, wherein the natural fibers comprise cellulose fibers.

9. The process of claim 8, wherein the cellulose fibers comprise regenerated cellulose fibers.

10. The process of claim 1, wherein step (a) comprises including in the fibrous support at least one non-fibrous material selected from the group consisting of titanium dioxide, mica, talc, clay, and organic non-fibrous fillers.

11. The process of claim 1, wherein the parchmentizable synthetic aramid fibers and the parchmentizable aramid fibrids comprise 100 wt. % of the fibrous support formed according to step (a).

12. The process of claim 1, which further comprises the step of: (e) calendering the parchmentized fibrous support.

13. The process of claim 12, wherein step (e) comprises calendering the parchmentized fibrous support at a temperature from about 80° C. to about 350° C.

14. The process of claim 13, wherein parchmentized fibrous support is calendered at a temperature from about 120° C. to about 320° C.

Description

EXAMPLES—DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(1) The invention and its advantages will become more apparent to one skilled in the art from the following examples.

(2) In the following examples, the temperature of parchmentizing is 20° C.

Example 1

(3) A support containing 40% of meta-aramid fibrids and 60% of meta-aramid fibers (6 mm, 2 dTex) was made on an inclined wire pilot machine. One part of the support was then parchmentized during different durations and at different sulfuric acid concentrations.

(4) The characteristics of the supports were as follows (the strength is defined as the square root of the burst index multiplied by tear index of the support): Acid concentration=72% Standard (non parchmentized): Strength=4.68 N.Math.m/g (Tear index=14.6 mN.Math.m.sup.2/g and burst index=1.5 kPa.Math.m.sup.2/g) Sample 1 (parchmentized during 10 s): Strength=6.3 N.Math.m/g Sample 2 (parchmentized during 20 s): Strength=6.9 N.Math.m/g Acid concentration=85% Standard (non parchmentized): Strength=4.68 N.Math.m/g Sample 3 (parchmentized during 10 s): Strength=16.27 N.Math.m/g Sample 4 (parchmentized during 20 s): Strength=15.45 N.Math.m/g

(5) This example clearly shows that parchmentizing increases dramatically the strength of the meta-aramid supports. The optimization of the physical characteristics will be obtained by adjusting the sulfuric acid concentration and by varying the reaction time of the parchmentizing.

Example 2

(6) A support containing 40% of para-aramid fibrids and 60% of para-aramid fibers (6 mm, 2 dTex) was made on an inclined wire pilot machine. One part of the support was then parchmentized at different sulfuric acid concentrations.

(7) The characteristics of the supports were as follows (the strength is defined as the square root of the burst index multiplied by tear index of the support): Acid concentration=85% Standard (non parchmentized): Strength=5.18 N.Math.m/g Sample (parchmentized during 20 s): Strength=6.38 N.Math.m/g Acid concentration=90% Standard (non parchmentized): Strength=5.18 N.Math.m/g Sample (parchmentized during 20 s): Strength=16.1 N.Math.m/g

(8) Para-aramid supports need an acid treatment at higher concentration than meta-aramid ones to achieve high strength characteristics

Example 3

(9) A support containing 40% of meta-aramid fibrids and 60% of meta-aramid fibers (6 mm, 2 dTex) was made on an inclined wire pilot machine. The support was then consolidated according to the previous art (heated at 280° C. or calendared at high temperature: pressure=280 N/mm and temperature=300° C.). One part of the non-consolidated support was parchmentized (sulfuric acid concentration=85%, time=20 s) on a pilot parchmentizer and the characteristics of the support obtained with this process were compared to those obtained with the previous art (see table 1)

(10) TABLE-US-00001 TABLE 1 Bendtsen For a 64 gsm Tensile Wet Tensile Tear index Burst Index Strength porosity Rigidity Cobb support km km mN .Math. m.sup.2/g kPa .Math. m.sup.2/g N .Math. m/g ml/min mN 60 g/m.sup.2 Meta -aramid 0.9 0.3 14.6 1.5 4.68 1700 130 260 raw support Meta-aramid 2.9 1.1 32.6 2.4 8.85 2500 230 70 support heated Meta-aramid 4.7 3.3 23.9 7 12.93 40 80 27 support heated + calendered Meta-aramid 3.1 2.6 44.7 5.8 16.10 1600 315 180 raw support parchmentized

(11) By parchmentizing meta-aramid supports it is possible to reach high physical characteristics and stiffnesses for the end products while keeping a high porosity and an excellent wettability (see the Cobb values)

Example 4

(12) A support containing 40% of para-aramid fibrids and 60% of para-aramid fibers (6 mm, 2 dTex) was made on an inclined wire pilot machine. The support was then consolidated according to the previous art (calendered at high temperature: pressure=280 N/mm and temperature=300° C.). One part of the non-consolidated support was parchmentized (sulfuric acid concentration=90%, time=10 s) on a pilot parchmentizer and the characteristics of the support obtained after the process were compared to those of the previous art (see table 2). Table 2 shows that the parchmentizing process increases the strength of the para-aramid supports while keeping a high porosity that were not achievable by using the previous art (hot calendering)

(13) TABLE-US-00002 TABLE 2 Burst Bendtsen For a 62 gsm Tensile Tear index Index Strength porosity support km mN .Math. m.sup.2/g kPa .Math. m.sup.2/g N .Math. m/g ml/min Para-aramid raw 3.4 15.8 1.7 5.18 2700 support (fibers/fibrids = 60/40) Para-aramid 4.3 21.2 2.6 7.42 45 support (fibers/fibrids = 60/40) heated + calendered = previous art Para-aramid raw 10.3 31.3 8.4 16.1 2200 support (fibers/fibrids = 60/40) parchmentized

Example 5

(14) A support containing 25% of para-aramid fibrids, 25% of para-aramid fibers (6 mm, 2 dTex) and 50% of glass fibers (6 mm, 2.2 dTex) was made on an inclined wire pilot machine. One part of the non-consolidated support was parchmentized (sulfuric acid concentration=90%, time=10 s) and the characteristics of the support obtained after the process were compared to those of the non consolidated support (see table 3)

(15) TABLE-US-00003 TABLE 3 Burst Bendtsen For a 57 gsm Tensile Tear index Index Strength porosity support km mN .Math. m.sup.2/g kPa .Math. m.sup.2/g N .Math. m/g ml/min Para-aramid/ 1.2 6.7 0.8 2.4 7800 glass raw support (fibers/fibrids/ glass = 25/25/50) Para-aramid/ 3.4 13.2 2.7 6.0 8800 glass raw support (fibers/fibrids/ glass = 25/25/50) parchmentized

(16) Parchmentizing allows to produce supports containing glass fibers and presenting high physical characteristics combined with high porosities.

Example 6

(17) Two types of aramid supports were produced on an inclined wire machine: Support 1 is made of 40% of para-aramid fibrids and 60% para-aramid fibers (6 mm, 2 dTex) Support 2 is a 90% para-aramid fibrids/10% para-aramid fibers (6 mm, 2 dTex) support
a multilayer structure comprising one support 2 between two supports 1 is parchmentized at a sulfuric acid concentration of 90% and a duration of 30 seconds. The resulting product shows a high cohesion between the 3 layers and can be used as if it was a mono layer one.

Example 7

(18) A para aramid support was produced, as already described (see example 4) on an inclined wire machine. Before being dried, this support was hydroentangled by using water jets at high pressure. One part of the support was then parchmentized (sulfuric acid concentration=90%, time=10 s): the parchmentized hydroentangled support presents a stiffness that is the double of the one measured on the aramid support that was only hydroentangled.