Method for the carbonization of an at least inherently stable two-dimensional textile structure

Abstract

The invention relates to a method for the carbonization of an at least inherently stable two-dimensional textile structure, according to which preoxidized fibers or a mixture of preoxidized and non-oxidized fibers is combined to give a two-dimensional structure and is solidified. Said two-dimensional structure is heated up to temperatures ranging from 600° C. to 900° C. line by line or column by column by means of a laser beam and while supplying air, and the temperature increases as the process output increases.

Description

[0001] The present invention is directed to a method for carbonizing an at least inherently stable textile fabric, in which preoxidized or a mixture of preoxidized and non-oxidized fibers are combined to form a fabric, and are stiffened.

[0002] From the Japanese Patents JP 1077624 and JP 1077625, methods are known for fabricating porous material from carbon fibers. In this context, self-binding, carbonizable short fibers, such as pitch fibers, cellulose fibers or acrylic fibers are blended and molded into paper, sheets or boards, and carbonized in an inert gas atmosphere under the action of heat.

[0003] From the document DE 19 45 154, a method for carbonizing and graphitizing fibers is known where precursor fibers, such as polyacrylonitrile polymers or aromatic polyamides, are preoxidized by heating to a temperature of 180° C. to 550° C. in an oxygen-containing atmosphere, and are subsequently heated by a laser beam in a non-oxidized atmosphere to a temperature of between 700° C. and approximately 1,200° C., and are carbonized. For this, the yarn or non-woven fabric to be carbonized is introduced into an inert gas atmosphere. Measures of this kind make the production process more expensive and also slow it down.

[0004] The object of the present invention is to devise a simplified method for carbonizing at least inherently stable textile fabrics.

[0005] The objective is achieved in accordance with the present invention in that at least inherently stable textile fabric, in which preoxidized or a mixture of preoxidized and non-oxidized fibers are combined to form a fabric, and are stiffened, are heated under the admission of air, by a laser beam, in rows or columns, to temperatures of between 600° C. and 900° C., the heating taking place with increasing process power.

[0006] Surprisingly, it was found that the heating may be carried out using a laser beam and in the presence of air, without the fabric being destroyed, i.e., the fibers being burned. As a result, the method is greatly simplified, since the need is eliminated for devices for supplying inert gas, so that the method may be continuously implemented in a simple way.

[0007] Preferably, the process power introduced by laser is between 0.01 und 0.5 watt-seconds g−1. The process power employed ensures a conversion of the output fibers into carbonized fibers without burning the same.

[0008] The heating is preferably effected using a CO2 laser.

[0009] The present invention is also directed to a device for implementing the method according to the present invention, where the laser beam is moved by motor and is directed along adjoining paths in such a way over the surface of the fabric that the fabric is irradiated in all surface zones substantially consistently. A homogeneously carbonized fabric is obtained by using the device according to the present invention.

[0010] The present invention is also directed to a carbonized nonwoven fabric, which is produced in accordance with the method of the present invention and has a flexural rigidity of about 8 Taber to about 1 Taber, a tensile strength (machine running direction) of 0.4 to 4 N/mm2 and a tensile strength (transversely to the machine running direction) of 0.7 to 4 N/mm2, an elongation property (machine running direction) of 0.12 to 14%, an elongation property (transversely to the machine running direction) of 0.15 to 19%, as well as an air permeability at 200 Pa pressure difference of 200 to 1600 l(m2*s), products having a greater flexural rigidity, greater tensile strength, less elongation representing relatively rigid products having less air permeability, and the opposite limiting values of the mentioned parameters leading to products having a substantial air permeability. The carbonized fabric in accordance with the present invention has sufficient mechanical strength, so that the handling characteristics of the carbonized fabric are ensured. In comparison to conventional methods, the rigidity of the fabric carbonized using a CO2 laser may be clearly increased, without the material becoming brittle.

[0011] The present invention is elucidated in the following on the basis of an example.

EXAMPLE 1

[0012] A mechanically stiffened nonwoven fabric having a mass per unit area of 120 g/m2 undergoes treatment, as indicated in Table 1. The laser power is successively increased in ten steps, the treatment being repeated many times, in particular at the beginning of the process at low power stages. The maximum laser power was 1000 W. The laser beam having a diameter of 14 mm was directed with a lateral scan velocity (in the crosswise direction—CD) of 4 m/s and an advance (in the machine direction—MD) of 2 mm over the nonwoven fabric. The weight loss in response to the carbonization using the CO2 laser was about 50% by weight. This corresponds to the weight reduction occurring during carbonization in the high-temperature oven. 1 Laser Laser Laser process Number of power power power CD Step treatments [%] [kW] [kW s g−1] 1 4× 25 0.480 0.14 2 3× 30 0.550 0.16 3 3× 35 0.630 0.19 4 1× 40 0.680 0.20 5 1× 45 0.740 0.22 6 1× 50 0.790 0.24 7 1× 55 0.830 0.25 8 1× 60 0.880 0.26 9 1× 65 0.910 0.27 10 1× 77 1.000 0.30

Claims

1. A method for carbonizing an at least inherently stable textile fabric, in which preoxidized or a mixture of preoxidized and non-oxidized fibers are combined to form a fabric, and are stiffened,

wherein the textile fabric is heated under the admission of air, by a laser beam, by lines or columns, to temperatures of between 600° C. and 900° C., the heating taking place with increasing process power.

2. The method as recited in claim 1,

wherein the process power is varied in steps between 0.01 und 0.5 watt-seconds g−1.

3. The method as recited in claim 1 or 2,

wherein the low process powers are input repeatedly.

4. The method as recited in one of claims 1 through 3,

wherein the heating is effected using a CO2 laser.

5. The device as recited in one of claims 1 through 4,

wherein the laser beam is moved by motor and is directed along adjoining paths in such a way over the surface of the fabric that the fabric is irradiated in all surface zones substantially consistently.

6. A carbonized nonwoven fabric produced in accordance with one or more of the claims 1 through 4,

wherein it has a flexural rigidity of about 8 Taber to about 1 Taber, a tensile strength (machine running direction) of 0.4 to 4 N/mm2 and a tensile strength (transversely to the machine running direction) of 0.7 to 4 N/mm2, an elongation property of 0.12 to 14 (flexible) %, an elongation property (transverse) of 0.15 (rigid) to 19%, as well as an air permeability at 200 Pa pressure difference of 200 to 1600 l(m2*s).