EP0663968B1 - Plasma treatment process of antiballistic materials - Google Patents

Abstract

A plasma treatment process in two steps is disclosed for antiballistic materials, such as aromatic polyamides. In the first step, a plasma treatment is applied with at least 50 % inorganic gas or a mixture of inorganic gasses and in the second step a plasma treatment is applied with a water-proofing organic gas or with mixtures of such gasses from the group of the saturated hydrocarbons, unsaturated hydrocarbons, saturated fluorohydrocarbons, unsaturated fluorohydrocarbons, siloxanes or vinyl compounds. In the second step a mixture of one or several inorganic gasses with one or several water-proofing organic gasses may also be used. This process improves the antiballistic properties.

Description

The invention relates to a continuous or discontinuous process for the plasma treatment of antiballistically active materials.

Plasma treatments have been described several times for different polymers, with a number of very different plasmas being proposed. Plasmas of noble gases are often mentioned, but oxygen and nitrogen plasmas are also used. The goal of plasma treatment is usually to change the surfaces of the polymers with the task of achieving better adhesion of coating or finishing agents. Another treatment goal frequently described is an improvement in dye affinity.

The polymers to be treated also include those which can be used for antiballistically active materials, such as aromatic polyamide fibers or polyethylene fibers spun by the gel spinning process. Also with the plasma treatment of these fibers always stand Property changes as mentioned above are the focus of interest.

Combined treatments are also sometimes proposed for this, which consist of a pretreatment in a plasma and a subsequent wet treatment by immersion impregnation with different finishing agents.

For example, JP-A 63-223 043 describes a treatment of aromatic polyamide fibers in an argon, oxygen or nitrogen plasma. This is followed by treatment with a gaseous or liquid mixture of compounds and dienes containing glycidyl groups. This is intended to improve the dyeing behavior of the fiber and the adhesion of finishing agents to the fiber surface.

Further two-stage processes with a plasma pretreatment of aromatic polyamide fibers and a wet aftertreatment by immersion impregnation, for example with polymerizable substances, are described in EP-A 191 680, EP-A 192 510 and CA-A 1 122 566. In all of these processes, the aim is to improve the adhesion of coating or finishing agents by changing the surface during the plasma treatment.

While these methods allow good adhesion between the aromatic polyamide fiber base material and the finishing or coating agent, they are very great because of the need for treatment in two very different devices (plasma device for the first stage and dipping or coating device for the second stage) inexpensive. Furthermore, they are Wet process of the second stage is also of concern for ecological reasons.

A plasma treatment for a number of very different fiber materials is described in EP-A 492 649. Here treatment takes place in a plasma of polymerizable gases, among which alkenes and fluorinated alkenes are also mentioned. These gases can possibly be "diluted" with noble gases. The aim of the treatment is to improve the dyeing properties and to have a positive influence on the processing properties of sewing threads.

A combined plasma treatment of polyethylene with noble gases and fluorocarbons is described in US 3,740,325. An attempt is being made here to improve the corrosion resistance by means of the plasma treatment.

All of these methods do not provide any clues as to how plasma treatment of antiballistically active materials must take place.

The improvement of the antiballistic effect is a permanent task for the manufacturers of protective clothing against bullets and against splinters as well as for the suppliers of the materials to be used for this. It should be noted that an improvement in the antiballistic effect must not only be sought in the dry state, but that this effect, particularly in accordance with the requirements for protective clothing for the military sector, must also be continuously improved in the wet state.

In order to meet the demands for a good antiballistic effectiveness when wet, Up to now, fabrics made from aromatic polyamide fibers have frequently been subjected to a bath treatment with hydrophobizing agents, for which fluorocarbon compounds in particular have been used. In addition to the cost involved in the bath treatment and subsequent drying, wet treatment with such compounds is also of concern for ecological reasons.

Therefore, the task was to develop a cost-effective method that once improves the antiballistic effectiveness in the dry and especially in the wet state and which offers the possibility of being able to do without the previous wet treatment.

Surprisingly, it has now been found that this problem can be solved if a plasma treatment of the antiballistically active materials is carried out in a two-stage process. In the first stage, treatment is carried out in a plasma consisting of at least 50% of an inorganic gas or a mixture of inorganic gases. In the second stage, treatment takes place in a plasma of hydrophobic organic gases or mixtures of such gases from the group consisting of saturated hydrocarbons, unsaturated hydrocarbons, saturated fluorocarbons, unsaturated fluorocarbons, siloxanes or vinyl compounds. The treatment in the second stage can also be carried out with a mixture of organic gases having a hydrophobic effect and inorganic gases.

Oxygen, nitrogen, hydrogen and noble gases such as argon, helium, xenon and. Come as inorganic gases for the plasma treatment according to the inventive method Krypton in question. Argon and helium are preferred among the noble gases. Treatment in an argon plasma is particularly preferred. Mixtures of the inorganic gases can also be used. Mixtures of inorganic gases with organic gases can also be used, but the proportion of inorganic gases in each case must be at least 50%. Among the organic gases, the hydrophobicizing gases also provided for the second treatment stage are preferred.

The gas flow amounts of the inorganic gas or the gas mixtures introduced into the plasma chamber are, depending on the desired effect, between 1 ml / min and 500 ml / min, preferably between 5 ml / min and 200 ml / min, particularly preferably between 10 ml / min and 50 ml / min. This information relates to a volume of the plasma chamber of 20 1. With other chamber sizes, the gas flow quantities can be converted accordingly. If the chamber geometry is very different, the gas flow quantities may have to be re-determined experimentally.

The plasma treatment with an inorganic gas or a gas mixture with at least 50% of an inorganic gas in the first treatment stage activates the surface of the polymer and thus prepares it for the subsequent treatment with a hydrophobic organic gas.

Saturated hydrocarbon compounds, unsaturated hydrocarbon compounds, saturated fluorocarbon compounds, unsaturated fluorocarbon compounds, are found as organic gases having a hydrophobic effect for the plasma treatment by the process according to the invention in the second treatment stage, Siloxanes or vinyl compounds or mixtures of the compounds mentioned application.

Compounds from the groups of alkanes, alkenes, alkynes, dienes, trienes and cumulenes are used as saturated and unsaturated hydrocarbon compounds. The process according to the invention can be carried out either with hydrocarbon compounds of the groups mentioned or with corresponding compounds in which one or more hydrogen atoms are substituted by fluorine atoms. Unsaturated compounds are preferred for carrying out the method according to the invention.

Examples of gases from the alkane series are compounds of the general formula C _n H _2n + ₂ with n = 1-10.

Ethene, propene, butene, hexene or heptene can be used as gases from the alkene series. Examples of suitable alkynes are acetylene and diacetylene. Butadiene can preferably be used among the dienes. Other suitable compounds are pentadiene and hexadiene. An example of gases from the Triene class is hexatriene.

Suitable saturated fluorocarbon compounds are, for example, tetrafluoromethane and hexafluoroethane. For the unsaturated fluorocarbons, for example, tetrafluoroethylene and hexafluorobutadiene are well suited.

Examples of siloxanes are tetramethyldisiloxane and hexamethyldisiloxane.

Examples of the vinyl compounds include styrene, divinylbenzene and hydrophobic acrylic compounds will. The latter can be methyl, ethyl or butyl acrylate.

The naming of suitable compounds should not be interpreted as restrictive, but merely as an enumeration of examples.

It is obvious that those hydrophobicizing compounds which are gaseous at room temperature are particularly preferred. However, it is also possible to use compounds with a hydrophobic effect which are not gaseous at room temperature if they have a sufficiently high vapor pressure. For example, hydrophobic liquids, if they have the necessary conditions with regard to the vapor pressure, can be connected to the vacuum of the plasma reactor, as a result of which the liquid evaporates and is then present in the plasma reactor as a gas having a hydrophobic effect.

Another possibility of introducing hydrophobic compounds which are liquid at room temperature into the plasma reactor is to pass a gas, for example an inorganic gas, through the liquid, the gas being saturated with molecules of the liquid. When the gas is introduced into the plasma reactor, the entrained molecules of the liquid are exposed to the plasma there.

In the second treatment stage, the treatment can also be carried out with a mixture of organic gases and inorganic gases having a hydrophobic effect, the proportion of organic gases preferably being more than 50%. The gases mentioned above are also used here. Such mixtures can be used in a suitable manner if the organic compound with a hydrophobic effect is present as a liquid at room temperature.

When working with mixtures of hydrophobic organic gases in the second stage, there are no restrictions with regard to the mixing ratios. The type of mixtures and the proportions of the individual gases depend on the desired effect.

The amounts of gas introduced into the plasma chamber in the second treatment stage are in the same ranges as in the first treatment stage. The quantities mentioned there can also be used here.

The reactions taking place in plasma treatment with a hydrophobic organic gas or with mixtures of such gases have not yet been sufficiently clarified. Polymerization of these gases is probably triggered on the surface of the polymer activated by the treatment with a noble gas plasma. This polymerization takes place in the known manner for monomers with double bonds, for example unsaturated hydrocarbons such as alkenes or dienes. There is still insufficient clarity about the processes of polymerization in saturated hydrocarbons. Here, partial cracking is likely to generate radicals with double bonds that are capable of polymerization.

In addition to the polymerization reaction, an exchange of atoms between plasma gas and the substrate to be treated is also possible. Thus, when using a plasma of fluorine-containing gases, H atoms of the benzene nucleus of an aromatic polyamide can be exchanged for F atoms.

Furthermore, it has not yet been sufficiently clarified whether the observed positive effect on the antiballistic properties is solely due to the formation of a polymer film produced on the surface of the antiballistically active materials or whether other processes, such as, for example, changing the surface of the antiballistically active materials, play a role here.

The treatment to be carried out in two stages can take place, for example, in two plasma chambers connected in series, which can be accommodated in a reactor. It is also possible to work in one reactor in two reactors connected in series. Finally, it is also possible to work in the same chamber by direct succession of processes, i.e. without venting the chamber to perform the two-stage plasma treatment.

The antiballistically effective materials can be treated in different forms. In the interest of a continuous driving style, web-like presentations in the form of flat structures such as foils, fabrics, knitwear or nonwovens are best suited. In the same way you can also work with thread coulters. The latter can be used, for example, for plasma treatment of the freshly spun fiber, which means that the method according to the invention can also be combined with a fiber production method. In the same way, combinations of the method according to the invention with other treatment steps can also be carried out with other forms of presentation of the material to be treated, such as foils, fabrics, knitted fabrics or nonwovens.

In addition, it is also possible to subject individual threads or yarns as well as fiber tapes to plasma treatment. The latter can be card or drawstring belts, ridges or flyers. Fiber cables can also be treated. These forms of presentation can also be used to integrate the plasma treatment into various manufacturing processes such as fiber production. For this purpose, for example, the freshly spun aromatic polyamide fiber, after passing through the washing passages and drying, can be subjected to a plasma treatment continuously using the method according to the invention.

The previously mentioned sheet-like or thread-like materials are suitable for the continuous treatment, which is preferred when carrying out the method according to the invention. In contrast, the method according to the invention can also be carried out discontinuously, the two treatment stages being carried out in the same treatment chamber or in two different treatment chambers. Any form of presentation can be used for the discontinuous treatment. It is particularly suitable for the treatment of blanks for the antiballistic protective layers of bulletproof or splinterproof vests.

The antiballistically effective materials include, above all, aromatic polyamide fibers, which are also known as aramid fibers. Such fibers are commercially available, for example, under brand names such as Twaron. In addition, aromatic polyamides can also be non-fibrous, for example as films. Aromatic polyamides include polymers which are obtained by polycondensation of aromatic diamines with aromatic dicarboxylic acids arise. Aromatic polyamides are also to be understood as meaning the polymers which, in addition to aromatic compounds, also contain portions of aliphatic compounds.

The antiballistically active materials also include polyolefin fibers, especially polyethylene fibers spun using the gel spinning process. Aromatic polyamides are particularly suitable for carrying out the process according to the invention.

Aromatic polyamides are preferably used in the form of fibers in very different areas of clothing and technology. They are used, among other things, for the manufacture of ball and splinter-resistant clothing, in which the actual protective layer forms a so-called antiballistic package consisting of several superimposed layers of, for example, fabrics made from aromatic polyamide fibers. In addition to fabrics, other flat structures such as nonwovens, knitwear or foils can also be used here.

When aromatic polyamide fibers are used in such protective clothing, it is known that the antiballistic effectiveness suffers when the protective clothing gets wet. For this reason, it is common to provide fabrics made of aromatic polyamide fibers with water-repellent materials before they are further processed into protective clothing with fluorocarbon resins, and thus to have the antiballistic effect of the spherical or. to improve splinter-resistant layers in protective clothing during wet bombardment. This is a wet process to be carried out at a high cost, which is also not harmless for ecological reasons.

In a particularly advantageous manner, the process according to the invention offers the possibility of circumventing this wet process and of carrying out the inexpensive and environmentally friendly finishing of the aromatic polyamide fibers. Fabrics made from aromatic polyamide fibers treated by the process according to the invention result in a significant improvement in the antiballistic effect compared to untreated materials. This improvement is not only found in wet bombardment, since it has surprisingly been found that fabrics made from aromatic polyamide fibers treated in the dry state by the process according to the invention also give improved antiballistic activity. The values listed below clearly show this.

To test the antiballistic effectiveness, a splinter bombardment can be carried out, for example. This test method is particularly useful when it comes to protective clothing that should preferably be used in the military sector, since the antiballistic effectiveness in wet condition is of much greater importance than, for example, protective clothing for police use.

To test the effect against the splintering, a total of 14 blanks for the west are put together in a package and sewn together along the edges for the attempted bombardment. The antiballistic package produced in this way is subjected to a splinter bombardment in accordance with the conditions of STANAG 2920. The bombardment is carried out with 1.1 g fragments. The protective effect is expressed by the V50 value and given in speeds of m / sec. The V50 value means that the determined Speed there is a penetration probability of 50%.

To test the antiballistic effectiveness when wet, the test material in the form of the prepared antiballistic package is placed in water for one hour. The bombardment occurs after three minutes of dripping.

The clear progress in the antiballistic effectiveness when using the method according to the invention is evident from the V50 values listed below. Here, a comparison was made between an untreated fabric, a fabric hydrophobized in a conventional manner in a wet process with a fluorocarbon resin, and a fabric treated by the process according to the invention. A first treatment stage in an argon plasma was used for the plasma treatment. In the second stage, a mixture of 80% butadiene and 20% argon was used in a plasma. The items to be treated were fabrics made from aromatic polyamide fibers. The yarn titer of the filament yarns used for the fabric production was 1,100 dtex, the fabrics made in plain weave had a basis weight of 187 g / m ² in the raw material. V50 value dry wet Untreated 344 205 Conventionally hydrophobic 345 361 Plasma treated 370 365

This table, which is an average of 6 bombardment tests, shows that the conventional wet hydrophobization process with fluorocarbon resins during dry bombardment shows no improvement in the antiballistic effectiveness compared to the untreated material, which also corresponds to the experience of the manufacturers of such splinter protection vests. In practice, a decline in antiballistic effectiveness in dry bombardment after wet treatment with fluorocarbon resins is even observed in some cases. In contrast, when using the method according to the invention, surprisingly, an improvement in the antiballistic effectiveness as a result of the plasma treatment can also be found with dry bombardment.

In the case of wet bombardment, the material treated by the process according to the invention exhibits approximately the same antiballistic activity as that which has been rendered hydrophobic by the conventional process.

The conditions for the plasma treatment when carrying out the method according to the invention depend very much on the material to be treated, on the desired effect and on any additional pretreatment or aftertreatment and must be coordinated with this. Other factors that influence the definition of the treatment conditions are the type of plasma, i.e. a direct current plasma, low- or high-frequency alternating current plasma, the type of coupling of the plasma into the reaction zone (capacitive or inductive), the reactor size and reactor geometry Geometry of the electrodes, the area of material to be treated per unit of time and the position of the material in the reactor.

A temperature range of 10-90 ° C. has proven to be suitable for the plasma treatment according to the method according to the invention. A temperature range between 20 and 50 ° C. is preferred. However, the treatment according to the method according to the invention should not be restricted to the low-temperature plasma mentioned here. Treatment in the high-temperature plasma, also called corona plasma, can also be carried out by the method according to the invention. This works in a pressure range between 100 Pa and 100,000 Pa, whereby higher temperatures are reached.

5 to 1,000 W are selected as power. A range between 20 and 600 W is preferred. The treatment can take place both in direct current and in alternating current plasma. AC plasmas are preferred. In the latter case, high-frequency and low-frequency plasmas are equally suitable. Ranges between 0.1 and 100 Pa have proven to be favorable as pressures; a range between 1 and 10 Pa is preferred. These pressures apply to treatment in low-temperature plasma. Suitable pressures for corona plasma are values between 100 and 100,000 Pa.

There are no restrictions with regard to the inflow of the gas forming the plasma. In this way, the gas can be routed parallel or perpendicular or at an angle to the web. In the case of continuous driving, the direction of flow can be both rectified and opposite to that of the material to be treated.

The residence time in the plasma chamber, which is essentially determined by the speed of the goods in the continuous process, depends very much on the material to be treated and the desired effect, according to the type of plasma (direct current, low-frequency or high-frequency alternating current plasma), according to the type of coupling (inductive or capacitive), according to the reactor size and geometry, according to the geometry of the electrodes, according to the pro Unit of time to be treated and according to the position of the material to be treated in the reactor. The residence time is also influenced by the ion density in the treatment chamber. If the ion density is high, the residence time can be reduced with the same effect. Normally, a shorter residence time is required for the activating treatment in the first treatment stage in the plasma of an inorganic gas than for the treatment in the second stage in a plasma of a hydrophobizing organic gas or in a mixture of hydrophobizing organic gas and inorganic gas.

The method according to the invention offers a particularly advantageous possibility for the plasma treatment of antiballistically active materials, the most important advantage being the achievement of improved antiballistic properties. This advantage is particularly evident in dry bombardment compared to conventional finishing with fluorocarbon resins in a wet process. In addition to the improvement of the antiballistic properties, the method according to the invention results in a considerable simplification of the process, an improved economy and, above all, a significantly lower environmental impact compared to the previously used wet method.

Claims (14)

1. Continuous or discontinuous method of plasma-treating antiballistically active materials, characterised in that the plasma treatment is in two stages, whereby in the first stage a plasma consisting of at least 50% of an inorganic gas or a mixture of inorganic gases is used, and in the second stage treatment takes place in organic gases or mixtures of such gases, selected from the group of hydrophobically acting saturated hydrocarbons, unsaturated hydrocarbons, saturated fluorohydrocarbons, unsaturated fluoro-hydrocarbons, siloxanes or vinyl compounds or in a plasma composed of mixtures of one or more of these gases with one or more inorganic gases.
2. Method according to claim 1, characterised in that the inorganic gases are oxygen, nitrogen, hydrogen or nobles gases such as argon or helium or mixtures of these gases.
3. Method according to claim 1, characterised in that the inorganic gas is argon.
4. Method according to claim 1, characterised in that the hydrophobically acting organic gases are alkanes, alkenes, alkines, dienes, trienes, cumulenes or the corresponding fluorine-containing compounds, in which case one or more hydrogen atoms are substituted by fluorine atoms.
5. Method according to claim 1, characterised in that the hydrophobically acting organic gases are siloxanes or vinyl compounds.
6. Method according to claim 1, characterised in that the first treatment stage takes place in a plasma consisting of at least 50% of one or more inorganic gases and in that the remaining quantity of gas consists of hydrophobically acting organic gases.
7. Method according to claim 1, characterised in that in the first stage treatment takes place in a plasma of an inorganic gas or a mixture of inorganic gases, and in the second stage treatment takes place in a plasma consisting of a hydrophobically acting organic gas or gas mixture from the group of saturated hydrocarbons, unsaturated hydrocarbons, saturated fluorohydrocarbons, unsaturated fluorohydrocarbons, siloxanes or vinyl compounds.
8. Method according to claim 1, characterised in that in the first stage, treatment takes place in a plasma of an inorganic gas or a mixture of inorganic gases, and in the second stage treatment takes place in a plasma consisting of a mixture of one or more inorganic gases comprising a hydrophobically acting organic gas or gas mixture from the group of saturated hydrocarbons, unsaturated hydrocarbons, saturated fluorohydrocarbons, unsaturated fluorohydrocarbons, siloxanes or vinyl compounds.
9. Method according to at least one of claims 1-8, characterised in that the antiballistic materials to be treated are aromatic polyamides and these are in the form of yarns, yarn sheets, fibre bands, sheets or flat textile structures such as wovens, knitwear, non-wovens or thread composites.
10. Method according to at least one of claims 1-8, characterised in that the antiballistic materials to be treated are in the form of wovens of aromatic polyamide fibres.
11. Method according to at least one of claims 1-8, characterised in that the antiballistic materials to be treated are polyethylene fibres spun according to the gel spinning process or yarns, yarn sheets, fibre bands, wovens, knitwear, non-wovens or thread composites from these fibres.
12. Flat textile structure composed of aromatic polyamide fibres or polyethylene fibres spun according to the gel spinning process treated according to at least one of claims 1-8.
13. Use of flat structures of antiballistically active materials, treated acccording to at least one of claims 1-8 for the manufacture of protective clothing, particularly protective clothing with bullet and splinter protection properties.
14. Protective clothing, in particular protective clothing with bullet and splinter inhibiting properties, manufactured with the use of a flat structure of antiballistically active materials treated according to at least one of claims 1-8.