Process for the fluorination of a surface layer of shaped bodies made of plastics.

The invention relates to a method according to the preamble of claim 1.

From SU-PS 330 177 (referenced in DE-AS 23 28 037) is known to treat the surface of rubber moldings by immersing them in a bath of liquid antimony pentafluoride as the fluorinating. The treatment is followed by three washes, one with a 5-20% aqueous solution of alkali metal carbonate. A disadvantage of this method is a very large consumption of antimony pentafluoride in the lifting out of the moldings. A draining of the liquid leads to uneven fluorination, and even the destruction of the molding. A large-scale application of the known method is referred to as unprofitable.

By contrast, the object of providing a process for the fluorination of a surface layer of moldings, in which in a bathroom or other exposure to a fluorine-donating fluid (eg by charging and swinging in a vessel) a controlled, cost-effective and reproducible fluorination can be carried out.

This object is achieved in a method of the aforementioned type characterized in that the liquid consists of a solvent or solvent mixture with ingested or dissolved elemental fluorine, wherein the solvent or solvent mixture reacts even only slightly or not with fluoride, the surface of the molding substantially unaffected leaves and a liquid phase comprising at least within a temperature range in which a fluorination reaction proceeds controllable, wherein responding during the action of the liquid has substantially elemental fluorine with the material of the surface layer.

This method using a liquid containing elemental fluorine, ie, for example dissolved or dispersed fine bubbles, is substantially different from a process reacts with the fluorine in the gas phase. Here is a very extensive state of the art (see. U.S. Patents 3,862,284, .3 988,491, 4,020,223, magazine "plastic u. Rubber", 24 (1977) 617, and therefrom removable further notes). The treatment in the gas phase is a high security risk, since the heat of reaction is significant and can be removed only with great effort. If one wants to take any impractical exposure times or decomposition of the plastic in purchasing, so the variations of temperature and fluorine concentration are limited. Are generally required in the gas-phase fluorination because of the relatively low fluorine content in the fluorine / inert gas mixture long action to achieve the desired change of the plastic surface. Nevertheless, it is not possible due to the unavoidable local overheating, fluorinate surface layers reproducibly uniform. These methods for continuous fluorination of individual moldings are less suitable. Moreover, the disposal is problematic, and it is the provisions of immission relatively difficult to meet.

The inventive method avoids the disadvantages mentioned of the gas-phase. With it is possible to dip molding in a pool with a elemental fluorine-containing liquid or this liquid to fill (pipes, containers and the like), the Einwirkungszeitesehr can be accurately measured.

Suitable solvents are especially liquid halocarbons (low molecular weight, aliphatic and cycloaliphatic hydrocarbon compounds, the most complete, are substituted by chlorine and / or fluorine). Such halocarbons are listed and classified, for example, in DIN 8962nd The selection of these halocarbons as suitable solvent, essentially according to their value for money and by the criterion of whether they are liquid within the temperature range -30 ° C ... +10 ° C. From this viewpoint, in particular trichlorofluoromethane, dibromodifluoromethane, 1,1,2-trichlorotrifluoroethane, 1,2-dibromotetrafluoroethane or 1,₁-Dichlordifluorethylen Or mixtures thereof suitable. It is particularly advantageous that it can be worked in such solvents at temperatures in the range of about -20 ° C. The resultant in the fluorination reaction is dissipated readily through the frozen liquid.

Surprisingly, in the fluorination process according to the invention that with the aid of the solvents used to swell the plastic surface is achieved by the penetration of fluorine is promoted. The surface of the moldings can thus be significantly more intense than ennoble fluorination in the gas phase. At the same time, the moldings are gently treated '.

Even water can be used as solvents. Although water reacts even at low temperatures with fluorine to various compounds, but in turn partly act itself fluorinating action. However, the fluorination in water as a solvent should be restricted to special plastics.

By continuous, controlled compliance with fluorine gas, preferably in admixture with a suitable fluorinerten gas such as nitrogen or helium, at a ratio of 1:. 5-1: 100, preferably 1:, are mixed for 10, the fluorine content in is the liquid standardized. The gas mixture can also be pre-cooled.

It has been shown that some physical properties of the plastic moldings can be further improved if in the solvent or the solvent mixture in addition to fluorine or other gases such as sulfur dioxide, oxygen, carbon monoxide, carbon dioxide, chlorine; Bromine or mixtures of these gases dissolves and treats the plastic molded body with or in these solutions.

The three parameters concentration, temperature and exposure time can be varied as follows:

fluorine concentration

The fluorine concentration in the liquid may be in a range of 1 x 10^-5 mol / 1 up to the maximum saturation value, preferably in the range between 0.5 x 10^-3 to 1 x 10^-2 mol /. 1

temperature

The fluorination reaction may proceed at temperatures between -70⁰ C and held the boiling point of the solvent or solvent mixture, preferably in the range from -30 ° C to O ° C.

exposure

The reaction time can be between 1 are s and 10 days, preferably s 20 to 30 min.

It can be seen that outside these limits quite reactions can be carried out, if this practical appears selected according to professional discretion without the scope of the invention.

Examples and reaction processes are described below to illustrate the invention:

example 1

In a closed, fluorine-resistant reaction vessel with about 10 1 content by the introduction of inert gas with a diluted pre-cooled fluorine has a fluorine concentration of 10^-2 mol / 1 maintained. The vessel is equipped with trichlorofluoromethane (CCI₃F) filled. Polyethylene pipes with an outer diameter of 18 mm and a wall thickness of 2 mm<ul><li>a) from the inside and</li><li>b) from the outside during 15 min at -20 ° C with said liquid</li><li>a) flushes or</li><li>b) treated in a bath.</li></ul>

Subsequently, the tubes with sodium hydroxide solution (concentration c # 1 mol / l) and with water to be rinsed.

Untreated and treated tubes are then checked with respect to gas permeability, heat resistance, stress cracking resistance and heat aging. The oxygen permeation rate under. Alike is reduced to less than 0.5% of the original value. Heat resistance, stress cracking resistance and heat aging, as measured by standardized methods, provide significantly improved values.

The resistance to chemical attack and to solvents (eg., N-pentane, gasoline, alkalis and acids) is substantially increased.

example 2

A cylindrical molded body made of vulcanized natural rubber is used in a bathroom with about 5 x 10^-3mol / l fluoride in 1,1,2-trichlorotrifluoroethane at -5 ° C submerged (by dry ice cooling) over 15 min and fluorinated therewith. After washing and drying is obtained on the fluorinated surface of a coefficient of sliding friction, which is significantly lower than in untreated rubber.

Similarly, other vulcanized rubbers can (stereoregular butadiene and isoprene rubbers, butadiene-styrene, chloroprene rubber, ethylene propylene rubber and copolymers of fluorine-containing monomers) and butadiene-acrylonitrile fluoridate. Corresponding variation of the treatment parameters here results in a more or less strong fluorination or depth of penetration.

example 3

A bottle (volume 1 1) of polyvinyl chloride is from the outside in a bath of dibromodifluoromethane with a fluorine concentration of about 10^-2 mol / 1 at 0 ° C for 60 min.

Compared to an untreated bottle the resistance to chemicals (eg acids, alkalis, oxidizing agents such.) And solvents (eg., N-pentane, gasoline, diesel fuel) is substantially increased. Next, the gas permeability is almost completely suppressed.

example 4

A polypropylene film (thickness 0, .1 mm) is stoaf in a bath of carbon tetrachloride coals. dipped whose fluorine concentration using a pre-cooled F₂/ N₂Gas mixture (volume ratio 1: 50) to about 10^-3_{mol / 1} is maintained. After the treatment, the film is washed with water and then dried in warm air stream.

can be measured a reduced water vapor and oxygen permeability after only one Fluorierungsdauer 15 min.

example 5

Several 1.5. mm thick polyethylene plates in a perfluorobutanesulphonyl fluoride-Bad (C₄F₉SO₂F) immersed by one F_{2 /}He gas mixture (1: 20) is passed.

The bath temperature is set to -5 ° C. After regular intervals samples taken show a continuous decrease in the coefficient of friction and increase the decomposition temperature.

example 6

Instead of the above in Example 5 bath liquid is Dibromdifluarmethan at 0 ° C until saturation with a gas flow F₂/ N₂ (1: 10) passes through. The fluorination of polyethylene sheets as in Example 5 for about 20 minutes and results in improved friction coefficients as in Example 5. FIG.

example 7

In place of that in Example 5 bath liquid ₁, 2-dibromotetrafluoroethane in _-20 ° C with a F_{2 /}N₂Gas mixture (1: 50) 1 h flows through long. be Fluorinated PE plates 5. pay as Example The friction improve.

example 8

An injection-molded part made of polyamide (PA 6.6) is immersed in a water-filled bath, by stirring one _{F2 /}N₂Mixture (1: 10) about 6 hours bubbled. The bath temperature is 0 ° C.

The molding thus treated has a considerably improved abrasion resistance.

example 9

A polyethylene canister (volume 5 1), which is cooled to -20 ° C, with CC1₃F, in which about 10^-2 mol / 1 F₂ is dissolved, filled. The filled to 80 to 90% of its volume canister is sealed and shaken for 10 minutes at -20 ° C.

The vessel thus treated, the transmittance for n-pentane is lowered by a multiple.

example 10

In the procedure according to Example 1, the bath is photoactivated by means of a UV fluorescent lamp during the application to the mold body. The exposure time can be shortened under otherwise identical test parameters.

example 11

In the procedure according to Example 1 is treated during the application to the mold body, the bath with the aid of an ultrasound source, wherein the energy density is adjusted so that a degassing of the liquid is not observed. Also by this treatment, the exposure time can be shortened under otherwise identical test parameters.

sample 12

A bath liquid of 1,1,2-trichlorotrifluoroethane is saturated at room temperature with a gas mixture of 5 Vol .-% fluorine, 5 vol .-% sulfur dioxide and 90 vol .-% nitrogen. A polyethylene bottle is treated with this solution inside and out. The retention capacity of the solvent is more than 10% better than in the treatment with only fluorine enthaltehder solution after this treatment. Similarly, additives have 2-25 vol .-% of oxygen, up to 25 Vol .-% sulfur dioxide or carbon monoxide, up to 50 vol .-% of carbon dioxide and / or up to 50 Vol .-% chlorine or bromine, or mixtures thereof , together with an inert carrier gas and the reactive gas fluorine. ,