Methods for cleaning industrial equipment with pre-treatment

[0001] The present invention relates to the cleaning of industrial devices such as evaporators, heat exchangers and other devices of this type that are conventionally cleaned in a CIP (in-place cleaning) process.

[0002] In many industrial applications, such as the production of food and beverages, hard surfaces usually become contaminated with carbohydrate, protein, hard dirt and other soils. These types of impurities can appear as a result of the production of both liquid and solid food. Carbohydrate impurities, such as those derived from cellulose, monosaccharides, disaccharides, oligosaccharides, starches, gums and other complex materials, after drying they can form hard, hard to remove impurities, in particular when combined with other solid components such as proteins, enzymes , fats and more. Removing such carbohydrate contaminants can be a serious problem. Similarly, other materials such as proteins, enzymes, fats and oils can also form stubborn dirt and residues.

[0003] On-site cleaning techniques are a specific cleaning procedure adapted to remove dirt from internal parts of tanks, lines, pumps or other process equipment used in the treatment of typical liquid products such as drinks, milk, juices, etc. On-site cleaning involves passing cleaning solutions through the system without taking apart any system components. The minimum on-site cleaning technique involves passing the cleaning solution through the equipment and then taking normal action. Any product contaminated by a cleaner residue may be discarded. Often, on-site cleaning methods include first rinsing, use of cleaning solutions, second rinsing with drinking water followed by resumption of surgery. The method may also include any other contacting step in which the washing agent, acidic or alkaline fluid, solvent or other cleaning component such as hot water, cold water etc. may be contacted with the devices at any stage of the method. Often, the final stage of rinsing with drinking water is omitted to prevent bacterial contamination after cleaning with disinfectants.

[0004] On-site cleaning requires the equipment to be turned off completely, resulting in a loss of production time. In many cases, the devices are not thoroughly cleaned due to the long shutdown period required. An improved way of cleaning this type of equipment is needed, using an in-house cleaning process that requires less time to thoroughly remove dirt.

[0005] Patent EP 0 751 211 A1 describes a cleaning composition for cleaning dairy equipment in a CIP process. The composition includes an alkaline and acidic solution and compounds with active oxygen. US Patent 5,993,562 describes a method and composition for abrasive cleaning of fluid delivery systems. The composition includes a liquid carrier with abrasive particles that is used for cleaning.

[0006] The invention relates to methods for cleaning devices such as heat exchangers, evaporators, tanks and other industrial devices, using on-site cleaning procedures. The way is

EP 1 781 763 B1 suitable for removing organic soil or, more particularly, removing contaminants from food. In addition, the method relates to cleaning methods that allow the removal of carbohydrate and protein impurities from beverage production sites using the on-site cleaning method. The method includes applying a pre-cleaning or pre-cleaning step prior to the conventional cleaning process.

[0007] The invention relates to a method for cleaning impurities, including sintered and burnt carbohydrate and protein impurities on industrial equipment using a CIP process, the method comprising:

(a) the use of a solution for the initial cleaning of impurities, the solution containing at least 0.25% by weight of active ingredients, active ingredients include 0.5 to 1.5% w / w or 2 to 5% w / w of the alkaline agent contained in the solution, a penetrating agent that increases degree of softening of impurities, thereby accelerating the removal of impurities, oxidant and 0.5 to 2.5% w / w of the active filler contained in the solution;

(b) recirculating the first CIP solution in the devices after the pre-cleaning solution, the CIP solution comprising a diluted detergent; followed by a device rinse.

[0008] Figure 1 is a schematic diagram of an industrial process that includes cleaned devices, CIP devices and pre-cleaned devices.

[0009] The present invention is directed to the cleaning of industrial equipment using a pre-cleaning step in combination with an in-place cleaning procedure. The use of a pre-cleaning step, in combination with conventional methods and on-site cleaning solutions, provides improved impurity removal compared to the conventional method itself. In addition, the use of a pre-cleaning step followed by rinsing with water ensures that unexpected amounts of contaminants are removed. The use of a pre-cleaning stage allows the use of traditional incompatible chemicals.

[0010] As used herein, the terms "weight percent", "% w / w", "weight%" and variations thereof refer to the concentration of the substance calculated as the mass of that substance divided by the total mass of the composition and multiplied by 100. It is understood that here the terms "percentage" and "%" are by default synonymous with "weight percent", "% w / w".

[0011] The method of the present invention is generally used to clean devices using an in-place cleaning procedure (i.e. CIP). Examples of this type of equipment include evaporators, heat exchangers (including two-pipe exchangers and plate-frame heat exchangers), heating coils (including systems with liquid, steam or flame heating), recrystallizers, pan crystallizers, spray dryers, tumble driers and tanks. This method can generally be used in any application where it is necessary to remove sintered or burnt impurities such as carbohydrate or protein; applications include the food (in particular dairy), brewing, oil processing, industrial agriculture and ethanol processing.

EP 1 781 763 B1 [0012] CIP treatment is generally known. The method involves applying a diluted solution (usually about 0.5-3%) to the surface being cleaned. The solution cascades down the surface (usually downwards), slowly removing impurities. The surface can be reapplied with either a new solution or the same solution is recirculated and reapplied to the surface.

[0013] A typical CIP process for removing impurities (including organic, inorganic or a mixture of ingredients) involves at least three steps: washing with an alkaline solution, washing with an acid solution, and then washing with water. Alkaline solution softens impurities and removes organic soluble pollutants. The acid solution then removes the mineral impurities left after the alkali cleaning step. The concentration of alkaline and acid solutions and the time of the cleaning steps usually depend on the resistance of the impurities. Rinsing with water removes any residues of solutions and impurities, and cleans the surface before returning to service. The present invention describes a pre-cleaning step, prior to the CIP process, which ensures penetration of contaminants. Penetrating material softens the impurities as a catalyst or enhances the activity of a conventional CIP solution when it is in contact with the impurities. Thus, pre-cleaning speeds up the removal of dirt.

[0014] Referring to figure 1, it shows a schematic diagram of the process device illustrated at number 10. The process device 10 comprises a tank 20, which is the device to be cleaned. The feed line 25 supplies various cleaning solutions to the tank 20, while the drain line 27 removes the solution from the tank 20. The equipment for the CIP process, marked with number 30, is properly connected through pipes, valves, pumps, etc. The CIP process device 30 includes a tank 35 for retaining diluted chemicals from the CIP process. The drain line 27 from the tank 20 is used to recirculate the solution from the tank 20 back to the CIP process device 30 and tank 35. The process device 10 also includes pre-cleaning devices marked with number 40. Pre-cleaning devices 40 include a first tank 42 and a second tank 44. In the case where two tanks are used, usually one tank, e.g. tank 42, contains an alkaline pre-cleaning solution, while the other tank, e.g. tank 44, contains an acid pre-cleaning solution. Corresponding pipes, valves, pumps etc. are in the place connecting the tanks 42, 44 with the supply line 25 to the tank 20. This arrangement of the device 10 allows the use of pre-cleaning in the tank 20 without the use of significant amounts of additional devices such as pipes. Additional details on how to clean tank 20 are described below.

Pre-cleaning solution [0015] As described above, the pre-cleaning solution or pre-cleaning step is applied to the impurities prior to the introduction of conventional CIP chemicals. The pre-cleaning solution chemicals are selected to increase the efficiency of removing contaminants from the surfaces being cleaned. The pre-cleaning solution first covers and penetrates the dirt, softening it. The specific chemicals used can be selected based on the nature of the impurities to be removed. The chemicals used can be compatible with

EP 1 781 763 B1 chemicals used in the CIP process. In some embodiments, it is desirable that the pre-treatment be incompatible with the chemistry of the CIP process; in such cases, the pre-cleaning chemicals react with the chemicals from the CIP process. It has been found that the use of incompatible chemicals further increases the efficiency of removing impurities.

[0016] The pre-cleaning solution contains at least 0.25% active ingredients, usually at least 0.5%, preferably at least 2%, and most preferably at least 40%. By the term "active ingredients" is meant non-inert ingredients that increase the effectiveness of softening, dissolving and removing impurities. Such active ingredients include an alkaline / acid penetrant, builder and oxidant.

[0017] In most embodiments, the water is a solution builder. Typically, the solution contains no more than 15% active ingredients, preferably no more than about 10%. In most applications, the preferred concentration is about 1-10%; a suitable concentration for most applications is 2-5%.

Alkaline components [0018] The pre-cleaning solution contains alkaline components. Examples of suitable alkaline substances include basic salts, amines, morpholine, carbonates and silicates. Particularly preferred alkaline substances include NaOH (sodium hydroxide), KOH (potassium hydroxide), TEA (triethanolamine), DEA (diethanolamine) and MEA (monoethanolamine), sodium metasilicate and potassium silicate.

[0019] Typical concentrations of alkaline substances are from 2 to 5% w / w and 0.5 to 1.5% w / w.

Penetrating agents [0020] Penetrating agent is present in the pre-cleaning. The penetrating agent combines with the alkaline substance in solution or can be used without alkaline or acidic substances. Preferably, the piercing agent is water soluble.

[0021] Examples of suitable penetrants include alcohols, short chain ethoxylated alcohols and phenol (having from 1-6 ethoxylate groups). Organic solvents are also suitable penetrating agents. Examples of suitable organic solvents for use as a penetrant include esters, ethers, ketones, amines, and nitrated and chlorinated hydrocarbons.

[0022] Another preferred class of penetrating agents are ethoxylated alcohols. Examples of ethoxylated alcohols include alkyl, aryl and alkylaryl alkoxylates. Such alkoxylates can be further modified by introducing the terminal chloro, bromo, benzyl, methyl, ethyl, propyl, butyl and alkyl group. The preferred concentration of ethoxylated alcohols in the solution is from 1 to 20% w / w.

[0023] Another class of preferred solvents used as penetrating agents are glycol ethers, which are water soluble. Examples of glycol ethers include dipropylene glycol methyl ether (available from Dow Chemical Co. under the trade name DOWANOL

DPM), and diethylene glycol methyl ether (available from Dow Chemical Co. under the trade name)

DOWANOL DM), and propylene glycol methyl ether (available from Dow Chemical Co. under

EP 1 781 763 B1 with the trade name DOWANOL PM). The preferred concentration of glycol ether in the solution is from 0.5 to 20% w / w.

[0024] Surfactants are also suitable penetrants for use in pre-cleaning solutions. Examples of suitable surfactants include nonionic, cationic and anionic surfactants. Nonionic surfactants are preferred. Nonionic surfactants improve the efficiency of removing impurities and can reduce the contact angle with the solution to be cleaned. Examples of suitable nonionic surfactants include alkyl, aryl and arylalkyl, alkoxylates, alkylpolyglycosides and their derivatives, amines and their derivatives and amides and their derivatives. Additionally preferred nonionic surfactants include those having a polyoxyalkene polymer as part of the surfactant molecule. Such nonionic surfactants include, for example, chloro, benzyl, methyl, ethyl, propyl, butyl and other terminally terminated compounds such as polyoxyethylene and / or polyoxypropylene glycol, fatty alcohol ethers; non-ionic compounds free from polyalkylene oxides such as alkyl polyglycosides; sorbitan and sucrose esters and their ethoxylated derivatives, alkoxylated ethylenediamine; carboxylic acid esters such as glycerol esters, polyoxyethylene esters, ethoxylated and glycol fatty acid esters, carboxylic acid amides such as diethanolamine condensation products, monoalkanolamine condensation products, polyoxyethylene fatty acid amides and the like; and ethoxylated amines and amine ethers and other similar nonionic compounds. Silicone surfactants can also be used.

[0025] Additionally, suitable nonionic surfactants having a polyalkylene oxide polymer fragment include nonionic surfactants of C6-C24 ethoxylated alcohols having from 1 to about 20 ethylene oxide groups; C6-C24 alkyl phenol ethoxylates having from 1 to about 100 ethylene oxide groups; C6-C24 alkylpolyglycosides having from 1 to about 20 glycosidic groups; ethoxylated, propoxylated or glycerin C6-C24 fatty acid esters; and C4C24 mono or dialkanolamides.

[0026] If a surfactant is used as a penetrating agent, the amount of surfactant in the pre-cleaning solution is usually at least 0.25% and not more than 10% w / w. Typical surfactant content is from 0.4 to 8% w / w and 1 to 4% w / w.

[0027] When an alkaline compound is present, the total amount of penetrant in the pre-treatment solution is usually at least 0.2% w / w and not more than 2.5% w / w. A typical penetrating agent content, when an alkaline compound is present, is from 0.4-2% w / w, preferably 1-2% w / w. The amount of penetrant relative to any alkali is generally from 1: 1 to 1: 5.

[0028] Typical content of penetration is 0.5 to 10% w / w and 1 to 5% w / w.

Oxidizers [0029] The reaction of these oxygen compounds with impurities, especially when they are combined with alkaline substances, causes a rapid mechanical action outside and inside the impurities, which increases the efficiency of removing impurities compared to chemical based methods.

[0030] Suitable components are oxidants such as chlorites, bromine, bromate, bromine monochloride, iodine, iodine monochloride, iodates, permanganates, nitrates, borates, perborates and gaseous oxidants such as ozone, oxygen, chlorine dioxide , chlorine, sulfur dioxide. Peroxygen compounds that include peroxides and various percarboxylic acids, including percarbonates, are suitable. Typical peroxygen compounds include hydrogen peroxide (H2O3), peracetic acid, persulfate, or percarbonate.

[0031] The amount of oxidant in the pre-treatment solution is usually at least 0.01% w / w and not more than 1% w / w. Typical oxidant concentration is 0.01 to 0.25% w / w; with 0.05% w / w being particularly convenient and typical concentration.

Active fillers [0032] The pre-cleaning solution contains an active filler. Active fillers include chelating agents (chelates), masking agents (sequestrants), active detergent builders. The builder often stabilizes the composition or solution. Examples of active fillers include phosphonic acids and phosphonates, phosphates, aminocarboxylates and their derivatives, pyrophosphates, polyphosphates, ethylenediamine and ethylenetriamine derivatives, hydroxy acids and mono-, dioras, tricarboxylates and their corresponding acids. Other active fillers include aluminosilicates, nitrile acetates and their derivatives and mixtures thereof. Still other active fillers include aminocarboxylates, including ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetetraacetic acid (HEDTA) and diethylenetriaminepentaacetic acid salts. Preferred builders are water-soluble.

[0033] Particularly preferred builders include EDTA (including the tetra-sodium EDTA salt), TKPP (tripotassium potassium phosphate), PAA (polyacrylic acid) and their salts, phosphonobutane carboxylic acid and sodium gluconate.

[0034] The amount of builder in the pre-cleaning solution is 0.5% w / w to 2.5% w / w. Typical content of active filler is 0.5 to 1.0% w / w and 1% w / w to 2.5% w / w.

Pre-cleaning methods [0035] The method of the present invention consists in applying a pre-cleaning solution to the surface being cleaned, prior to a conventional CIP process. As a result, the CIP process requires fewer stages and / or less time for each stage. For example, the conventional CIP method includes five steps after the initial washing with water: rinsing with a conventional alkaline agent (NaOH) to remove impurities, intermediate rinsing, rinsing with a conventional acid agent to remove mineral impurities and scale, rinsing with water and a conventional decontamination step. This process can be replaced by a three-step method carried out after the initial rinsing with water: the pre-acid cleaning stage, conventional alkali rinsing and water rinsing. Alternatively, the three step method may include: an alkaline pre-cleaning step, conventional acid scrubbing, and water scrubbing. Using this method, transient washing is not necessary because the reaction between acid and base is desired in separate steps.

[0036] Using each of the two pre-cleaning methods described above, the amount of water used in the entire pre-cleaning process is reduced by 30% compared to a conventional five-step process. The amount of time needed to complete the process

EP 1 781 763 B1 with pre-cleaning is reduced by 30% compared to a conventional five-step process. The reduction of the detailed number of stages, water consumption, or treatment time depends on the concentration and chemical action of the pre-cleaning solution.

[0037] Referring again to Figure 1, the pre-cleaning solution is stored in the device designated 40. In the process device 10, the tank 42 contains an alkaline pre-cleaning solution and the tank 44 contains an acid pre-cleaning solution that includes peroxide.

[0038] To clean the device 20, the tank 20 and its connections are dried from any products that may be present. Water flushing can be used to remove any residue. In one embodiment, the alkaline pre-cleaning solution from tank 42 is pumped through pipes and a supply line 25 into tank 20. A conventional CIP device, such as a spray head, applies the pre-cleaning solution to the inner surface of the tank 20. The pre-cleaning solution flows down in a cascade or otherwise across the surface of the tank 20 softening the contaminants. It is possible to re-apply the pre-cleaning solution, but this is generally not needed.

[0039] After the pre-cleaning solution has been applied and drained, conventional CIP cleaning is performed using the detergent from the process device 30 and tank 35. The CIP detergent may be acidic or alkaline. The detergent from tank 35 is recirculated through tank 20 through supply line 25, return line 27 and other suitable pipes.

[0040] In a further embodiment, the hydrogen peroxide pre-cleaning solution from the tank 44 is pumped through the pipes and the supply line 25 into the tank 20. After the peroxide pre-cleaning solution has been applied and drained, conventional CIP cleaning is performed using an alkaline detergent such as sodium hydroxide from process device 30 and tank 35. Sodium hydroxide activates any residual peroxide on the walls of the tank 20.

Examples [0041] All pre-cleaning solutions are outside the claimed range and therefore all examples are comparative examples.

Example 1

Test procedure [0042] Milk powder lozenges were prepared by mixing 3 grams of dry milk powder and 3 grams of impurities. The resulting mixture was pressed in the matrix for 30 seconds at 4.54% (10,000 lb), then pressurized and applied again 4.54% (10,000 lb) for an additional 30 seconds. The pellets were placed in sieves and immersed in the pre-cleaning solutions described below for 5 minutes, removed and then dried. The strainer and dried pellets were placed in a beaker with 0.5% w / w NaOH at 48.8 ⁰C (120 ⁰F). (No pre-cleaning was used in the test marked "None"; pre-cleaning was not used in the test marked "None *" and 3.0% NaOH at 48.8 was used⁰C (120 ⁰F) instead of 0.5%

EP 1 781 763 B1

NaOH). The beakers were placed on hotplates set at 49⁰C (about 120 ⁰F) and large mixing elements rotating at 350 rpm were inserted. After 30 minutes, the sieves and pellets were removed from the cleaning solution and gently immersed and removed from deionized water five times, then dried overnight in an oven at 50⁰C. The results of the tests are presented below.

Pre-cleaning 1 [0043] A 10% w / w solution of active NaOH was prepared and used for pre-cleaning. The pre-cleaning solution contained 100,000 ppm sodium hydroxide (alkaline cleaner).

Pre-cleaning 2 [0044] A pre-cleaning solution was prepared containing 1360 ppm EDTA (active filler and / or chelate), sodium gluconate (active filler and / or chelate), 2400 ppm potassium silicate (alkaline cleaner), 7000 ppm polyglycoside alkyl (surfactant), and 4200 ppm potassium hydroxide (alkaline cleaner). Pre-cleaning solution 2 contained 0.66% alkaline, 0.43% active filler / chelate, and 0.7% surfactant, giving 4.79% active ingredients.

Pre-cleaning 3 [0045] A pre-cleaning solution was prepared containing 41550 ppm polycarboxylated ethoxylated alcohol (surfactant), 9540 ppm octylamine oxide (surfactant), 25,500 ppm alkyl polyglycoside (surfactant), and 4,150 ppm ethoxylated 220 ethylhexanol (penetrating agent). Pre-cleaning solution 3 contained 0.4% penetration and 7.6% surfactant, giving 8% active ingredients.

Pre-cleaning 4 [0046] A pre-cleaning solution was prepared containing 1600 ppm potassium hydroxide (alkaline cleaner, 9455 ppm sodium hydroxide (alkaline cleaner), 18500 ppm polyacrylic acid (active filler and / or chelate), and 4625 ppm phosphonobutane tricarboxylic acid ( builder and / or chelate). Pre-cleaning solution 4 contained 1.10% alkaline, 2.3% active filler / chelate, giving 2.9% active ingredients.

<td>Solution for initial cleaning</td><td>The weight of the strainer (G)</td><td>Weight strainer + tablet before cleaning (g)</td><td>Weight strainer + tablet after cleaning (g)</td><td>Mass pills in front of cleaning (g)</td><td>Mass pastilles after cleaning (g)</td><td>Loss weight pills%</td>

<td> 1</td><td> 18.23</td><td> 23.93</td><td> 22.59</td><td> 5.70</td><td> 4.36</td><td> 23.51%</td>

<td> 1</td><td> 18.20</td><td> 23.86</td><td> 22.52</td><td> 5.66</td><td> 4.32</td><td> 23.67%</td>

<td> 2</td><td> 18.23</td><td> 23.91</td><td> 22.54</td><td> 5.68</td><td> 4.31</td><td> 24.12%</td>

<td> 2</td><td> 18.02</td><td> 23.34</td><td> 22.08</td><td> 5.32</td><td> 4.06</td><td> 23.68%</td>

<td> 3</td><td> 19.24</td><td> 24.70</td><td> 22.14</td><td> 5.46</td><td> 2.90</td><td> 46.89%</td>

EP 1 781 763 B1

<td> 3</td><td> 18.06</td><td> 23.67</td><td> 21.19</td><td> 5.61</td><td> 3.13</td><td> 44.21%</td>

<td> 4</td><td> 17.95</td><td> 23.50</td><td> 20.09</td><td> 5.55</td><td> 2.14</td><td> 61.44%</td>

<td> 4</td><td> 18.22</td><td> 23.90</td><td> 21.69</td><td> 5.68</td><td> 3.47</td><td> 38.91%</td>

<td>Lack</td><td> 19.16</td><td> 24.81</td><td> 23.22</td><td> 5.65</td><td> 4.06</td><td> 28.14%</td>

<td>Lack</td><td> 13.47</td><td> 18.76</td><td> 17.22</td><td> 5.29</td><td> 3.75</td><td> 29.11%</td>

<td>Lack*</td><td> 19.27</td><td> 25.01</td><td> 24.14</td><td> 5.74</td><td> 4.87</td><td> 15.16%</td>

<td>Lack*</td><td> 18.15</td><td> 23.82</td><td> 23.02</td><td> 5.67</td><td> 4.87</td><td> 14.11%</td>

[0047] The results show both the regularity of cleaning and the differences in compared methods. The results indicate that lower NaOH concentrations are better than high concentrations, and pre-cleaning solutions 3 and 4 show an advantage over pre-cleaning solutions 1 and

2. However, this difference may be due to the test procedure used. Tests 1 and 2 were carried out on one hob, while tests 3 and 4 were carried out on another hob. It is possible that the two back plates used are not equal in temperature 48.8⁰C (120 ⁰F).

[0048] A dramatic difference was observed between the duplicate tests (i.e. 61% and 39% for 10 solutions 4); it is possible that one of the lozenges had a crack causing the lozenge to be more prone to breaking at this point. A significant area of ​​exposed surface could increase the rate of disintegration.

[0049] The tests were repeated on the same hob to determine if there was any inconsistency between temperature control in the hobs. The results are presented in the table below in the column marked "weight loss pellets with pre-cleaning% w / w".

[0050] As an alternative and comparative method, 1 gram of pre-cleaning solution was added to 315 grams of 0.5% NaOH cleaning solution. So instead of using pre-cleaning in a separate step, they were combined with the cleaning solution. The results are presented in the table below in the column labeled "weight loss of the pellet without initial cleaning% w / w".

<td>Initial Cleaning</td><td>weight loss pellets with pre-cleaning% in / in</td><td>lozenge weight loss without pre-cleaning% w / w</td>

<td> 1</td><td> 22.16%</td><td> 36.92%</td>

<td> 2</td><td> 23.90%</td><td> 37.39%</td>

<td> 3</td><td> 41.96%</td><td> 34.01%</td>

<td> 4</td><td> 50.17%</td><td> 31.95%</td>

[0051] The results indicate that the elimination of a separate pre-cleaning step and the addition of chemicals directly to the cleaning solution increases the efficiency of two less effective solutions (1-10% NaOH; 2-10% KX-3108) and reduces the efficiency of two more effective

EP 1 781 763 B1 solutions (3-10% Quadexx 400; 4-10% Quadexx 500). All of these results were better than in the absence of pre-cleaning (which resulted in a weight loss of approximately 29%)

Example 2

Test procedure [0052] Contaminated stainless steel test panels with impurities on one side, prepared by drying the mashed corn mixture on one side of the panel in an oven at 120 ⁰C for 4 hours. The contaminated panels were then cleaned as described below.

[0053] In test (I), with the pre-cleaning step, 800 grams of the pre-cleaning solution was placed in a 1000 ml beaker. About 1 gram of pre-cleaning solution was found to be in contact and remaining on the dirty panel. After brief immersion in the pre-cleaning solution, the panels were hung for 5 minutes under ambient conditions. The dried panels were then placed in 1000 ml beakers, which contained 750 g of water at 40⁰C, contaminated side down. After 30 minutes, the panels were gently immersed and removed from deionized water five times, after which the panels were dried. Test results are shown below.

[0054] In test (II), the test panels were not subjected to preliminary cleaning, but were cleaned in 750 g of water at a temperature of 40 ⁰C with 1 g of pre-cleaning solution added 5.

[0055] In test (III), the test panels were not subjected to preliminary cleaning, but were cleaned in 750 g of water at a temperature of 40 ⁰C.

Pre-cleaning [0056] A pre-cleaning solution containing 400 ppm EDTA tetra-sodium salt (active filler / chelate), 4500 ppm tripotassium potassium phosphate (active filler / chelate), 3852 ppm potassium hydroxide (alkaline cleaner), 3000 ppm polyethylene phenol phosphate ether was prepared (surfactant), 1000 ppm sodium metasilicate (alkaline cleaner), 9000 ppm ethylene glycol monobutyl ether (penetrating agent), and 2400 ppm sodium xylene sulfonate. The pre-cleaning solution contained 0.5% alkaline, 0.5% active filler / chelate, and 0.5% surfactant, and 0.9% penetrant, giving 2.4% active ingredients.

<td>Test method</td><td>average amount of impurities removed</td>

<td>AND</td><td>99.12% (average of three tests)</td>

<td>II</td><td>14.14% (average of three tests)</td>

<td>III</td><td>14.12% (average of two tests)</td>

[0057] The above results show that by simply adding pre-cleaning chemicals to the cleaning solution, the removal efficiency of the impurities from the test panels is not improved. Rather, the separate and gradual application of the pre-cleaning solution and the cleaning solution provides improved dirt removal efficiency.

EP 1 781 763 B1