DE1646769A1 - Process for the production of carbon threads - Google Patents

Description

National Research Development Corporation, London ¥ .1.

Process for the production of carbon thread

The invention relates to the production of coal and. Carbon fiber or thread.

In general, carbon fibers or filaments belong to a class of non-metallic fibers that have been proposed as reinforcing or stiffening elements or elements of high strength for composite materials, the matrix material of which can optionally be metal.

It can be shown that such fibers or threads, especially carbon threads, usually have the highest specificity Have strength when their diameter is smallest. The manufacture of non-metallic fibers or. Threads, in particular of such fibers of very small diameter and very high strength, for the carbon Example is there are numerous ^ problems on * one of these

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Problems are found in finding means and processes for the production and obtaining of fibers or threads of sufficient length so that they have a load-bearing effect in the composite material and enable them to withstand loads or stresses that are comparable to their intrinsic strength.

The production of carbon fibers or threads has been to me so far the charring or coking of organic Mate-P Materials such as cotton and fiber or threads of synthetic resin materials have been proposed. In particular polyacrylonitrile fibers were recommended for investigations, but only limited success could be achieved.

At this point it should be noted that the expression "Polyacrylonitrile fibers" as used by experts is also copolymers or terpolymers of acrylonitrile with other monomers such as methyl methacrylate or Vinylaeek did that are either used alone or with polymers compatible with them, such as phenolic resins or Friedel Grafts condensates are added. In the same sense, the term "polyacrylonitrile fibers" used in this description.

According to the invention, a method for producing carbon fibers comprises heating polyacrylic fibers

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to relatively high carbonization temperatures under non-oxidizing conditions, keeping them under tension will.

The method also according to the invention comprises one preceding oxidation process or a heat treatment in oxygen-containing atmosphere at low temperature, the is carried out, for example, by heating in air.

The charring or coking .at high temperature is under vacuum or in a non-oxidizing atmosphere, as in Hydrogen.

If the previous oxidation process at lower Temperature which "may form part of the process, If the duration is too short, the fibers retain a soft core and in the subsequent heat treatment at a higher level Temperature, holes are created in the resulting fiber or cavities formed.

In a further embodiment of the invention, the method for producing carbon fibers or filaments, an initial heating up, maintained at train or voltage polyacrylonitrile in an oxidizing atmosphere at 200 to 25O ⁰ C for times for substantially

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complete permeation of oxygen through the individual fibers or threads are sufficient; and a subsequent further heating of the fibers thus formed to a charring temperature of at least 100O ⁰ G under non-oxidizing conditions.

The time required for the initial heat-up process depends to a large extent on the diameter of the respective fibers or threads; at a temperature of 220 C, however, becomes a complete penetration of the fibers with oxygen after heating for about 24 hours with 2 1/2 denier fibers and after about 50 hours of heating on 4 1/2 denier fibers achieved.

The bevels or threads are stretched or stretched to the extent that that that normally occurs during this initial heating up any longitudinal shrinkage that occurs is reduced or eliminated or that even the fibers are elongated.

Further improvements in the properties of the fibers produced are achieved if the fibers are further ^{heat-treated after the carbonization at about 1000 G up to temperatures above 2000 0} O in a non-oxidizing atmosphere »

The tension of the fibers or threads can also be applied during

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subsequent charring and / or heat treatment.

The following are for illustration purposes only some examples of the invention are described. In these examples, a multi-filament yarn was used as the starting material made of polyacrylonitrile with continuous single threads used.

example 1

A 4 1/2 denier bundle of around 500 polyacrylonitrile fibers or threads, each about 27 / u in diameter and about 12.8 cm in length, was hung as the starting material in a vertical stovepipe with attached weights totaling 10 g, so that the Fibers were under tension. The furnace chamber was evacuated and the vacuum pumping process was then maintained throughout the heat treatment. The heat treatment consisted in an increase oven temperature to 1000 ⁰ G at a rate of 15 ⁰ O per hour. After this treatment, the charred or coked fibers had the following properties:

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Density after coking} 1.6 g / cm. Diameter of the carbon thread obtained 11 to 13 / U.

Tensile strength of the individual strands 7.72 χ 10 ⁵ kg / cm ² (110 χ

p.s.i.)

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Young module 1.16 χ TO ⁶ kg / cm ² (16.5 x 10 ⁶ psi) Failing strain 0.7%

In a further treatment stage, the carbon fibers have been or yarns to a temperature of 250o ⁰ G "for one hour under argon of 1 atm pressure heated. After this treatment," in which a shrinkage of the fibers in the diameter direction, but not in fiber longitudinal direction occurred, a change in the density of 1.7 g / cm to 1.9 g / om ^'5 was observed. After this treatment, the Young's modulus of the lasers had changed from 1.16 10 kg / cm (16.5 x 10 psi) * to a mean value of 2.46 10 kg / cm (35 x 10 psi). The mean tensile strength after this high temperature treatment was 14.1 x 10 ⁵ kg / cm ² (200 χ 10 ^ psi).

"■■ ■, -Example-2.-,

Material and heat treatment were the same as in Example 1, except that in the charring of the filaments instead of the Vacuum a hydrogen atmosphere of 50 mmHg pressure in the furnace was maintained. After the treatment, the charred or coked loads had the following properties:

Density of the charred threads 1.6 g / cm

Final carbon filament diameter 11-14 yu Tensile strength 9.5 χ 10 ⁵ kg / cm ² (135 x TO ^ psi) Young's modulus 0.91 x 10 ⁶ kg / cm ² (12.9 _v x 10 ⁶ ρ. si) Failing strain $ 1

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In the examples described above, a Shrinkage of each load observed while the original Obtain circular shape of the cross-section remained * The experimental data given show that the diameter has decreased to about half.

In the following Examples 3, 4, 5 and 6, the use of the carbon fibers produced according to Examples 1 and 2 ' described as reinforcement elements in composite materials »

Example 3

The following components were mixed in a rubber kneader or - Rolling mill (calender) brought together:

Fluoroelastomer oil from vinylidine

fluoride and hexafluoropropylene

(Viton B) 100 g

Magnesium oxide 15g

Dicinnamyl! Den-hexamethylene-

diamine (hardener) 3g

Carbon threads, produced according to Example 1, 20 g

The fibers, or threads, became the material used added at the infeed angle of the rollers, where they are briefly

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3) 2 m in length and then distributed uniformly over the material by mixing. The mixed or matched material was molded by a molding operation · and cured in the mold by heating to 16o ° C over an hour and further heat treatment at 250 ⁰ C for 24 hours. The end product is a dense composite rubber of great toughness that retains good strength properties at elevated temperatures.

Example 4

A bundle of unbroken carbon fibers produced according to Example 2 and about 10 cm in length was placed in a test tube of 9) 5 mm (3/8 ") inside diameter tightly packed and a catalytically cold-curing polyester resin was poured over it. The resin consisted of Bakelite 17 449 »a polyester resin mixed with methyl ethyl ketone peroxide and an oily solution of cobalt naphtnenate in a clear volatile solvent (white spirit) in the following proportions «100 parts resin to three Parts by weight of each of the other two ingredients. The fibers were soaked evenly with the resin mixture and formed a longitudinal reinforcement in the by hardening and solidification of the resin at room temperature Resin / fiber of high strength.

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The procedure of Example "4 was followed using an epoxy resin mixture of the following composition: ■

Shell Epikote Resin 815: 60 parts by weight. -

Polyamide hardener (Versamid 125): 40 parts by weight

repeated. The hardening treatment at room temperature resulted to the formation of a product with similar properties, as in example 4 »

Example 6.

A bundle of carbon fibers made according to Example 1 was with a solution of a resin of the ffriedel-Craft type, in particular a resin based on diphenyloxide obtained by reacting the constituents in the following proportions became: . ·

1 mole of diphenyl oxide

1.2 moles of p-xylylene chloride

impregnated in a dichloroethane solution with a solids content of 40% of the resin mixture. After evaporation of the Diohlorethans was \

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the impregnated fiber mass formed and at 180 ⁰ G for two hours

■ ρ

long under a pressure of 35.2 kg / cm (500 p.s.i.) cures to form a hard and rigid composite article reinforced with high strength fibers.

Among those given by the method according to the invention The advantages are the higher tenacity of the charred threads compared to that obtained by regenerated cellulose fibers is achieved, since the latter are generally only a tensile strength of about 3.52 10 kg / cm (50 χ 10 p.s.i.); and also that the fibers have a have a particularly smooth surface, which makes them more suitable as reinforcement in composite materials than those that do made from regenerated cellulose.

Example 7

2 1/2 denier polyacrylonitrile fibers were heated for 24 hours at 22O ⁰ G in air, to ensure complete permeation of oxygen to reach through the fibers and then charred 1000 ⁰ G in a non-oxidizing atmosphere Ms and heat-treated to 250o ⁰ O; fibers with a tensile

3 2 3 strength of 17.6 χ 10 'kg / cm (250 χ 10 psi), while with an initial heating to 220 0 for only two hours, fiber strengths of only 7.04 χ 10 ^ kg / cm (100 χ 10 ⁵ psi).

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For the treatment in the above manner shrank lase during anfängliehen heat treatment at 22O ⁰ C in air for "up to $ 40, while those obtained by subsequent carbonization and heat treatment Ms 250o ⁰ O carbon fibers have a tensile strength which may be sufficient under certain circumstances, Young's modulus is relatively low, but if the fibers are ^{subjected to tensile stress to 220 0} G during the initial heat treatment, both tensile strength and Young's modulus can be increased, as the following table shows: ·

Burden one
Yarn of 100
Threads of
2 1/2 denier
Polyacrylonitrile fibers
220 ⁰ G over ■
24 hours

Length change währ'end treatment at 220 C ^u

Properties of the fibers after coking treatment up to 1000 C in inert the atmosphere

Properties of the fibers after heat treatment up to 2500 C in inert the atmosphere

Tensile strength 2 kg / cm

Young module
axial to
Fiber ^
kg / cm

Train-,
strength ρ
kg / cm

Young's modulus axially to the fiber ₂ cm

0 g
10
20th
30th
40

- $ 40
- $ 12
+ $ 2
+ $ 15
+ $ 36

7.04 x 1Ö ^? 7.04 χ 10 ⁵ 8.44 x 10 ⁵ 14.1 xi O ³ 14.1 x 10 ⁵

0.92 χ 10
1.13 "x
1.41 x 10
1.48 χ 10
1.48 χ 10

5.62x10
7.04x10
8.44XfOYp
14.1x1O ³
14,

2.11 χ 2.67 x, 3 x 10

5.73 x.

Φ, -22

10

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_ ₁₂ _ 184 67S9

Example 8.:. _::

'Polyacrylonitrile or -or- to a carbon-forming bobbin yarns were wound up under a slight train and to 220 ⁰ G for 22 hours in luft'aufgeheizt. The strands were in the form of a yarn of 100 threads of 2 1/2 denier polyacrylonitrile with 20 yarns per side of the form or bobbin, and these were attached to the bobbin in such a way that P the tension was maintained. After this initial heat treatment, the yarns were cut up to 12.7 cm lengths. charred by AujTheizen with a linear temperature increase from 200 to 1000 C in 24 hours in a hydrogen atmosphere of 150 mmHg pressure.

The properties of some fibers were then measured, and the remaining heated in a carbon tube furnace under argon of one atmosphere at 25OO ⁰ C.

>; _ ■ ■■ ■ .. ■

Bine further refinements of the obtained fibers was examined, and the rest under the same conditions of one atmosphere of argon at 290O ⁰ C heated. The properties of the fibers obtained by this final treatment were determined. The results are summarized in the following table: «

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treatment Properties of the resulting
- the fibers Young module 1 . Fibers in air for 22 hours
to 220 ⁰ C under tension
on the bobbin
heated / tensile strenght 2. Heating up the lasers
after 1. from 200 C.
100O ⁰ C for 24 hours in
Hydrogen atmosphere
of 150 mmHg • 1.41 x 10 ⁶ kg / cm ²
20 χ 10 psi 3 · Heating up the fibers
after 2. to 2500 C
for 2 hours in argon
at 1 at pressure 18.3 x 10 \ g / cm ²
260 χ 10 ⁵ psi 3.52 ^ x ^ ro ⁶ kg / cm ²
50 x 10 psi 4. Heating the fibers
after 3rd to 2900 ⁰ O
at 1 under argon
Pressure for 1/4 hour 18.3 x 10 ³ kg / cm ²
260 χ TO ⁵ psi 4.22 χ 10 ⁶ kg / cm ²
60 χ 10 psi 18.3 x 40 ³ kg / cm ²
260 χ 1Cr psi

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Claims (1)

- ^u ■ .- T64676B ■■ '. ■' "claims 1. Process for the production of carbon fibers or threads, characterized in that polyacrylic fibers heated under non-oxidizing conditions to a charring or coking temperature and during held under tension for part of the charring treatment will. 2. The method according to claim 1, characterized by a preceding Oxidation process. 3. The method according to claim 2, characterized in that the preceding oxidation process involves heating in air; on .200 "to 250 ° 0. Λ ' Ί- · Method according to one of the preceding claims, characterized characterized as charring at high temperature is carried out under vacuum. - b> Method according to claim 1 "to ■■ 3, characterized in that the charring is carried out in an open atmosphere". - b. Method according to one of claims 2 to 5, characterized in that, indicates that the preceding oxidation process is a 10938 5/0 332
BATH ORIGINAL The fibers are heated to 200 to 20 ° 0 for a period of time which is sufficient for an essentially complete permeation ν of oxygen through the individual lasers. Y. The method according to any one of claims 2 Ms 6, characterized by a tensile load on the fibers, whereby the otherwise occurring longitudinal shrinkage of the fibers is reduced or is switched off or the fibers are even elongated. ö. Method according to one of the preceding claims, characterized by a further process of heat treatment of the fibers to over 2000 ° 0 in a non-oxidizing one The atmosphere. 9 · The method according to claim 8, characterized in that the tension on the fibers throughout the process is applied. ... 10. Composite material characterized by a matrix syn-hetic fluoroelastomer, a metal oxide, a hardening agent and a reinforcement made of carbon fibers, which through a method according to any one of the preceding claims has been produced. 11. Composite material characterized by a matrix 10988570332 a catalytically cold-curing polyester resin and a reinforcement of carbon fibers obtained by a process according to any one of claims 1 "to 9. 12. Composite material characterized by a matrix an epoxy resin mixture of epoxy resin and hardener with a Reinforcement made of carbon fibers obtained by a process according to any one of Claims 1 to 9. 13. Composite material characterized by a matrix a Friedel-Craft type resin and a reinforcement Carbon fibers obtained by a method according to any one of claims 1 to 9. 109885/0332