SE413416B - PUT TO CLEAN POLLUTED FORMAL AND DEVICE THEREOF - Google Patents

Description

72124Ûh-3 agents and flux residues. Azcotropic mixtures of alcohols with the primary solvent are often used (Swedish patent 332 409) (often in the boiling state), but such mixtures may not contain sufficient alcohol to effectively remove the fluxes.

Consequently, the use of such azeotropic mixtures is by no means a complete solution to the problem. Attempts have been made to solve the problem simply by immersing the contaminated object in mixtures of the primary solvent with much higher concentrations of alcohols than those present in the azeotropic mixture, and said mixture has been used at relatively low temperatures, ie near room temperature e.g. . 20 ° C or lower. If desired, such treatment may be followed by contacting the article with a pure cold mixture of the primary solvent and alcohol in a separate tank or with a cold liquid obtained by evaporation from a liquid mixture followed by condensation. while the object is in the vapor zone, after which the liquid is allowed to drain from the object. In such methods, severe solvent losses may occur due to an adhesive film of cold solvent on the object, which is removed from the plant and / or by in some cases not removing the flux sufficiently from the contaminated object.

Treatment plants for the treatment of contaminated objects may contain a liquid tank, in which the object is immersed, the liquid tank being provided with an overflow drain to a container. The latter contains a relatively small amount of liquid, which is kept boiling, and the purpose of the container is not to bring the dry matter into contact with the liquid, but to take advantage of the soiled solvent which collects in the container. Steam above the liquid level is condensed and returned to the liquid tank, thus ensuring the presence of a clean solvent in the liquid tank, while dirty solvent flows over to the container. The objects are taken out of the liquid tank, passed through the steam zone and finally out through the plant. The use of boiling solvent mixtures containing high concentrations of alcohol in the tanks of such a plant is not effective, since there is a depletion of the alcohol from the liquid tank and an increase in the alcohol in the container. The system is therefore not stable and does not provide the cleaning required.

According to the present invention, there is now provided a method for cleaning contaminated articles, which method is completely different from previously used methods. The procedure allows efficient cleaning of contaminated objects at high temperatures. Procedures 721240¿r- ~ 3 it is stable and the disadvantages of the previous procedures are avoided.

According to the present invention there is provided a process for the purification of a contaminated article, which process is characterized in that the article is brought into contact with a first azeotroping-forming mixture of 1,1,2,2-trichlonryl, 2,2-trifluoroethane and an organic co-solvent, which together may form an azeotrope, the concentration of the co-solvent in the mixture being greater than the concentration in the azeotrope itself, and the mixture being heated to a temperature of between 30 ° C and the boiling point of the mixture, and by subsequently cleaning the object with a second liquid mixture containing 1,2,2-trichloro-1,2,2-trifluoroethane and a proportion of the organic co-solvent, which proportion is less than in the first liquid mixture but at least as large as the proportion of organic co-solvent in the azeotrope.

Preferably, a substantially azeotropic mixture of 1,1,2,2-triclone, 2,2-trifluoroethane and the co-solvent, or appropriate proportions of said solvent corresponding to the main solvent, are introduced into the system, continuously or intermittently from an external source - actually the azeotropic mixture. According to a preferred method of carrying out the process according to the invention, the object is immersed in said first heated liquid mixture, and said mixture is stored in a container part in a purification system, and then the object is transferred to the second liquid mixture in a rinsing part in said system, the first and the second liquid mixture has a common vapor zone. Preferably, the other liquid mixture is also heated. The second liquid mixture is in equilibrium with (ie its mixture is substantially constant with respect to) the steam in the steam zone over the container and the rinsing part and with said mixture in the container part. Several rinsing parts can be used, if desired.

The substantially azeotropic mixture or appropriate proportions of 1,2,2-trichloro-1,2,2-trifluoroethane and the co-solvent corresponding to the substantially azeotropic mixture are suitably introduced continuously or intermittently into the container and / or the rinse aid. part of the purification system.

According to said, preferably selected methods of carrying out the method according to the invention, at least a part of and preferably all the liquid obtained by condensation of the vapors is returned, from the common vapor zone, to the rinsing part. It is also convenient to ensure that liquid mixture flows from the rinsing part to the container. The first azeotroping mixture in the container portion preferably contains at least 5 parts by weight (and preferably at least 10 parts by weight) of the co-solvent per 100 parts by weight of the total mixture more than the proportions in the corresponding azeotrope.

Examples of co-solvents which can be used in conjunction with 1,1,1 Z-trichloromethyl, 2,2-trifluoroethane to prepare an azeotroping mixture include methyl acetate, nitroparaffins (eg nitromethane) and alcohols which likewise form an azeotrope. with said trichlorotrifluoroethane. Thus, alcohols containing one to four carbon atoms can be used, e.g. methyl alcohol, ethyl alcohol, tert-butanol and isopropyl alcohol. The latter alcohol is especially useful.

The concentration of the alcohol in the halogenated hydrocarbon used in the container and the rinsing part may vary depending on the particular alcohol used. When e.g. isopropanol is used in the container, it is advantageous that the concentration of isopropanol is lower than 70% by weight.

The liquid in the rinsing tank has a different composition than that in the container. When stable conditions occur, the solvent mixture in the rinsing part has in practice a concentration of the second solvent generally between that present in the azeotrope and up to more than 11% by weight and preferably not more than 5% by weight more than the concentration in the azeotrope. This method of immersing the contaminated liquid in said heated liquid mixture in the container part alone or followed by further immersion in said heated solvent mixture in the rinsing part is in itself an unusual feature according to the present method. With concentrations of isopropanol between 10% and 70% in the container part, concentrations up to 14% by weight of isopropanol can be used in the rinsing part. In general, concentrations of isopropanol between 10 and 40% by weight are used in the container, and concentrations in the range between 22 and 27% by weight give particularly good results. With these lower values in the container part, up to 4% more is preferably used in the rinsing part than in the azeotropic mixtures. As a particular example, it has been found that a solvent mixture in the rinsing tank containing 5.5% isopropanol becomes substantially constant in relation to the steam in the steam zone over the rinsing part and the container part, and with a solvent mixture in the latter part with a mixture containing 25% isopropanol, boil both mixtures.

Preferably, ethyl alcohol concentrations between J25% and 30% by weight of the solvent mixture in the container part are used, while with methyl alcohol concentrations between 17 and 22% by weight are preferably used. With these concentrations in the container mixtures, the rinsing part preferably contains an ethyl alcohol concentration between 6 and 8% and a methyl alcohol concentration between 8 and 10% by weight. The substantially azeotropic mixture introduced into the system may contain a concentration of the second solvent up to that present in the rinsing tank. Good results can be obtained with solvent mixtures boiling between 1 ° C and 200 from the boiling point of the azeotrope. Very good results have been obtained with the azeotropic mixture itself, e.g. the azeotropic mixture, which consists of 97.1% by weight of 1,1,2-trichloro-1,2,2-trifluoroethane and 2.9% by weight of isopropanol. The azeotropic mixture itself is most conveniently introduced as it is into the system. However, if desired, appropriate proportions of the first and second solvents may e.g. 1,2,2-Trichloro-1,2,2-trifluoroethane and isopropanol, which correspond to the mainly azeotropic mixture, are introduced separately into the container and / or the rinsing part. The amount of the substantially azeotropic mixture introduced into the system is preferably that required to maintain constant levels in the container and rinse portion.

The solvent mixtures in the container and rinsing parts are kept at a temperature above room temperature. Usually the mixtures have a temperature of at least 30 ° C and preferably at least 40 ° C. The temperature of the solvents is preferably maintained at the boiling point, which in the case of mixtures of 1,2,2-trichloro-1,2,2-trifluoroethane is often between 45 and 50 ° C. If desired, other solvents or additives may be added to the solvent mixture used in the present process to modify its cleaning and dissolving power. Suitable additives include cationic, anionic and non-ionic detergents. Water can also be added in some cases, especially when the mixtures contain a detergent, but this is not necessary.

Generally, it is not necessary to use stabilizers in the solvent mixtures. However, it is possible that stabilizers may be desirable under corrosive conditions, e.g. the conditions under which the solvent mixtures are brought into contact with light metals, e.g. zinc and aluminum.

Another advantageous feature of the process according to the present invention is that the system is very stable, ie the concentrations of the second solvent e.g. isopropanol can be effectively maintained in the various parts throughout the time the solvent is used. An evenly high rate of removal of the contaminants is also obtained. The procedure has e.g. run around the clock with intermittent cleaning of contaminated objects for a period of 220 hours. After this time, the weight percent of isopropanol in the container portion was essentially the same as at the start of the operation, i.e. the isopropanol content was * initially 23.6% and during the operation between the limits 23.3 and 23.9%.

In the rinsing part, the amounts also remained constant. The isopropanol content was initially 5.4% and remained within the limits of 5.3 to 5.6%.

The present process also has the advantage that flammable mixtures are avoided.

The present method is useful in a wide variety of applications, including the removal of tough solder fluxes from electrical equipment. It is particularly useful for removing fluxes from equipment containing a plastic or resin substrate, as the base plates and components are not destroyed.

According to another embodiment of the method according to the invention, the contaminated object is brought into contact with the first heated liquid mixture in a cleaning system, consisting of a part (container part) and the object is moved to the vapor zone over this part and rinsed there with the second liquid mixture. According to a modified procedure, the contaminated object is moved, after immersion in said first heated liquid mixture, through and out of the steam zone, allowed to cool and then returned to the steam zone, where it is rinsed with the second liquid mixture, obtained by direct condensation of the vapors from the vapor zone of the cooled object.

According to another variant of the process, the first and second liquid mixtures are present in separate parts and do not have a common vapor zone, whereby condensed liquid from steam over said first hot mixture is returned to the second hot mixture.

A suitable device which can be used in the present method is shown in the drawing (Fig. 1), which represents a schematic view in vertical cross-section and is not scalable. In the drawing, a vessel (1) is divided into a container part (2) and a rinsing part (4) separated by a wall (3). The container part 2 contains the first azeotroping-forming mixture, as previously described, in sufficient quantity so that the contaminated object can be immersed therein, and is provided with a heating device 5. The rinsing part 4 next to the container part 2 is equipped with a heating device 6 and contains the second liquid, 7212404-3 as mentioned earlier, with a composition different from that in the container part 2. The steam zone 7 is in communication with the container and rinsing parts 2 and_4. The steam zone 7 is equipped with a cooling coil 8 for condensing steam together with a chute 9. The latter is for collecting condensed liquid, and the line 10 is for refluxing the condensate to the rinsing part 4. A cooling device 11 is attached to the outside of the vessel, and through this a coolant can be passed for extra cooling. The equipment can be provided with an inlet 12 for supplying a mainly azeotropic mixture, as mentioned earlier. In the drawing, this leads to the container part 2, but it can be placed for supply to the system in any suitable place; Equipment (not detailed) for transporting the contaminated objects through the device is also available. The path of the objects is represented by the line which begins at the inlet 13 and leads through the container part 2, the steam zone 7 and the rinsing part 4 and ends at the end point 14.

When the equipment is used, the solvent mixtures in the two parts 2 and 4 are heated, and the vapors from these are mixed in the steam zone 7, condense on the cooling coil 8 and flow back as liquid into the rinsing part 4, from which the excess liquid flows over the Wall 3 into container part 2. The continuous flow of liquid and steam maintains a clean rinse aid in part 4 and ensures that dirt and contaminants accumulate in part 2, from which they can be removed in a suitable way, e.g. by periodic recovery, in whole or in part, of the dirty liquid. Liquid levels are maintained by adding a new solvent to compensate for losses.

The present invention relates to an apparatus containing a vessel (1) with a container (2) equipped with a heating device and an amount of the first azeotroping mixture described, with sufficient depth for immersing the contaminated objects, a rinsing part (4) (or parts) adjacent to the container part and equipped (e) with a heating device (or devices) and containing an amount of the second liquid mixture, and which differs from that in the container part, the rinsing part (4) being adapted to enable liquid to flow over to the container part (2), and a steam zone (7), which communicates with both the container part (2) and the rinsing part (4), cooling coils (8) adapted for condensation of steam over the container part ( 2) and the rinsing part (4) in such a way that condensed liquid is returned to the rinsing part (4) (or the parts).

The following examples illustrate but do not limit the invention: 7212404-3 - Example 1 The material to be cleaned consists of printed circuits on fiberboard of resin-bonded paper, contaminated with a flux.

The flux coating is prepared by stroking a brush over the disc, then drying at 70 ° C for 2 minutes and soldering at 25,000 for 5 seconds, after which a 15 minute pause is made. The fluxes are activated with rosin-based fluxes, which are supplied commercially as Trade Marks Zeva C4, Fry's R8, Fry's S64, Multicore PC25, Alpha 711, Alpha 809 and Alpha 862.

This is followed by the cleaning method previously described, which involves immersing the contaminated objects in the container part of a cleaning chamber for a period of 1 minute, after which it is immersed in an adjacent rinsing chamber for 10 seconds. The solution mixture in the container part consists of 1,2,2-trichloro-1,2,2-trifluoroethane, containing 23 to 24% by weight of isopropanol. The mixture in the rinsing tank consists of 94.6% by weight of said trichlorotrifluoroethane and of 5.4% by weight of isopropanol. Both liquids are kept boiling. The steam above-mentioned liquid level is condensed with cooling coils, and the condensate is returned to the rinsing tank. An azeotropic mixture of said trichlorotrifluoroethane and said alcohol is fed to the container at a rate which maintains the liquid level in the container.

All traces of flux are removed with this treatment, without damaging the boards.

Example 2 The material to be cleaned and the method of cleaning are as described in Example 1 except that: (i) the solvent mixture in the container consists of 1,1,1,2-trichloro-1,2,2- trifluoroethane, containing 24 to 25.5% by weight of denatured alcohol (96% by weight of ethyl alcohol, 4% by weight of methyl alcohol), '(ii) the mixture in the rinsing part consists of 94.6% by weight of said trichlorotrifluoroethane and 5.4% by weight of denatured alcohol (iii) the azeotropic mixture fed into the container contains 96.2% by weight of said trichlorotrifluoroethane and 3.8% by weight of denatured alcohol. U All traces of flux are removed with this method without damaging the boards. Example 3 The material to be cleaned and the methods of cleaning are as described in Example 1 except that: (1) the solvent mixture in the container consists of 1,1,2-trichloro-1,2,2- trifluoroethane, containing 22.5 to 23% by weight of isopropanol, (ii) two rinsing tanks were used, one adjacent to the container containing 5.4% by weight of isopropanol and the other spaced from the container containing 4.7% by weight of isopropanol.

All traces of flux are removed with this treatment without damaging the boards.

Claims (23)

Claim 1. A method of purifying a contaminated article, characterized in that the article is brought into contact with an azeotroping mixture of 1,2,2-trichloro [1,2,2-trifluoroethane]. and an organic co-solvent, which together may form an azeotrope, wherein the concentration of the co-solvent in the mixture is greater than the concentration in the azeotrope itself, and the mixture is heated to a temperature of between 30 ° C and the boiling point of the mixture, and by subsequently cleaning the object with a modified liquid mixture containing 1,2,1-trichlonr1, 2,24trifluoroethane and a proportion of the organic co-solvent, which proportion is less than in the first liquid mixture but at least as large as the proportion of organic co-solvent in the azeotrope. _ 2. A method according to claim 1, characterized in that in a system continuously or intermittently introduced from an external source a supply of a substantially azeotropic mixture of 1,1,2,2-trichlanol, 22-trifluoroethane and the co-solvent, or suitable proportions of said solvent, which essentially ß corresponds to the azeotropic mixture. 3. A method according to claim 1, characterized in that the second liquid mixture is also heated. - HRS. 4. A method according to claim 3, characterized in that the substantially azeotropic mixture, or suitable amounts of 1,2,1-trichynxryl, 2,2-trifluoroethane and of the co-solvent corresponding to the substantially azeotropic mixture are introduced continuously or intermittently into a container where the article is contacted with the first mixture, and / or a rinsing member, wherein the article is contacted with the second liquid composition. 5. A method according to claim 1, characterized in that the first azeotroping mixture contains at least 10 parts by weight of the co-solvent per 100 parts by weight of the total mixture more than the corresponding amount in the azeotrope itself. 6. A process according to any one of the preceding claims, characterized in that the co-solvent is an alcohol containing 1 to H carbon atoms. 7. A method according to claim 6, characterized in that the alcohol is ethyl alcohol. 8. A method according to claim 6, characterized in that the alcohol is methyl alcohol. ~ 72124fl il-3 11 9. A method according to claim 6, characterized in that the alcohol is isopropyl alcohol. 10. A method according to claim 9, characterized in that the concentration of ieopropyl alcohol in the azeotroping mixture is 10 to RO weight percent of the mixture. 11. ll. A method according to claim 10, characterized in that the concentration of isopropyl alcohol in the azeotroping mixture is 22 to 27% by weight of the mixture. 12. A method according to one or more of the preceding claims, characterized in that the second liquid mixture in the cooling part has a concentration of the co-solvent from that in the azeotrope up to not more than 5% by weight above that in the azeotropic mixture. A method according to any one of the preceding claims 4-6,9 and 12, characterized in that the concentration of isopropanol in the first liquid in the container part is between 10 and 70% by weight and that the concentration of isopropanol in the second liquid in the rinsing part is between the azeotrope concentration and up to 1% by weight ieopropanol. leeward. A method according to any one of the preceding claims H to 6 and 9 to 13, characterized in that the concentration of iopropanol in the first liquid in the container part is 22 to 27% by weight of the mixture, and that the concentration of isopropanol in the second liquid in the the rinsing part is between the azeotrope concentration and up to 7% by weight of isopropanol. 15. A method according to any one of the preceding claims M-7 and 12, characterized in that the concentration of ethyl alcohol in the liquid carried out in the container part is 25 to 30% by weight. 16. A method according to claim 15, characterized in that the concentration of ethyl alcohol in the second liquid in the slurrying part is 5 to 8% by weight. 17. A method according to any one of the preceding claims N to 7 and 12, characterized in that the concentration of methyl alcohol in the first liquid in the container part is 17 to 22% by weight. 18. l8. A method according to claim 17, characterized in that the concentration of methyl alcohol in the second liquid in the rinsing part is 8 to 10% by weight. _ 19. A method according to any one of the preceding claims 2-6, and 9-lä, characterized in that the azeotropic mixture introduced into the system consists essentially of 97.1% by weight, 'ÛTZÅÛÄ-Z 3- 12 l, 1, 2-Trichloro-1,2,2-trifluoroethane and 2.9% by weight of isopropanol. 20. A method according to claim 1, characterized in that the temperature of the liquid mixture in the container part and the rinsing part is at least 40 ° C and up to the boiling point of the mixture. 21. A method according to claim 20, characterized in that the liquid mixture contains 1,1,2-trichloro-1,2,2-trifluoroethane and isopropanol, and that the temperature of the mixture is between 45 and 50 ° C. 2 22. A method according to any one of the preceding claims 1 to 21, characterized in that the object to be cleaned is a printed circuit or a component thereof, contaminated with flux residues. An apparatus for cleaning contaminated articles according to claim 1, wherein the article is contacted with a first azeotroping mixture of 1,1,2,2-trichynxyl, 2,2-trifluoroethane and an organic co-solvent which together may form an azeotrope. wherein the concentration of the co-solvent in the mixture is greater than the concentration in the azeotrope itself, and the mixture is heated to a temperature of between 30 ° C and the boiling point of the mixture, and the object is then cleaned with a second liquid mixture containing 1,1,2 «trichloro-1,2 , 2-trifluoroethane and a proportion of the organic co-solvent, which proportion is less than in the first liquid mixture but at least as large as the proportion of organic co-solvent in the azeotrope, characterized in that it comprises a vessel (1) with a container part (2) equipped with a heating device and an amount of the first azeotroping mixture and with a sufficient depth for immersion of contaminated objects, a rinse part (4) (or parts) adjacent to the container part and equipped with a heating device (or devices) and containing an amount of the second liquid mixture, which mixture differs from that in the container part, said rinsing (U) part being adapted to enable the overflow of liquid to the container part (2), a vapor zone (7), which communicates with the hide container part (2) and the rinsing part (4), cooling coils (8) adapted for condensation of vapors above the container part (2) and the rinsing part (4), and equipment adapted for returning condensed liquid to the rinsing part (H) (or parts). MENTIONED PUBLICATIONS: