Patent Grant
7101832
Pulp used to form paper contains a number of impurities which tend to deposit on the paper making equipment. One such impurity is “pitch” which refers to deposits originating from natural resins and their salts. Stickies is a term that refers to hydrophobic components used in the manufacture of a paper product. Stickies arise from residues of polymers that are used in retention aids, drainage aids, adhesives, ink resins and coatings used in various processes of making paper. The term “stickies” has increasingly been used to describe deposits that occur in systems using recycled fiber.
Although paper manufacturers go to great lengths to prevent pitch and sticky deposits on the paper making equipment as well as the deposition of other unwanted material such as dirt, grime and the like, eventually the equipment must be cleaned.
Current commercial cleaners generally are very alkaline and/or chlorine-containing (i.e., chlorine bleaches) chemical compositions. They can be used in a variety of different manners including a boil-out procedure where the hot cleaning solution is circulated through the paper making equipment, or can be sprayed directly onto equipment.
With either type of solution, worker safety is an issue. Further, waste disposal is a problem. The highly caustic material must be neutralized prior to disposal. This requires highly acidic mineral acids and presents additional safety concerns. Chlorine-containing compositions present additional environmental concerns.
The present invention is premised on the realization that a non-chlorinated cleaning composition can effectively clean paper making equipment and coating systems. More particularly, an aqueous composition which contains a stabilized hydrogen peroxide, glycol ether solvent in combination with a non-ionic surfactant, acts to effectively clean paper making equipment using a boil-out procedure. More particularly, the present invention is premised on the realization that the combination of hydrogen peroxide, a phosphonate, a glycol ether solvent and an ethoxylated alcohol non-ionic surfactant effectively cleans paper making equipment. The objects and advantages of the present invention will be further appreciated in light of the following detailed description.
The cleaning solution of the present invention is effective to clean paper making equipment and coating systems. The cleaning solution of the present invention is an aqueous based solution which includes a stabilized peroxide solution in combination with a glycol ether solvent and an non-ionic surfactant.
The peroxide source can be either an aqueous solution of hydrogen peroxide or peroxygen salts or organic peroxide salt. Generally a hydrogen peroxide solution is employed. This can be used in commercially available concentrations of about 35%. The solution should contain 3% to 4% hydrogen peroxide active component which is from about one to about ten percent of a commercial hydrogen peroxide solution (35% H2O2). The use concentration of peroxide should be at least about 50 ppm or higher.
The peroxide is stabilized by the addition of a phosphonate. A wide variety of phosphonates can be employed. These are derivatives of phosphonic acid such as 1-hydroxyethylidene-1-diphosphonic acid, aminotrimethylene phosphonic acid, as well as others. One preferred diphosphonate is HEDP sold as Dequest 2010. The phosphonate should be present in an amount of from about 1% to about 10% on a solids basis. Preferably about 5% of the Dequest 2010 is employed which is 58% to 62% actives which provides about 3% active. The use concentration should be about 1.5 ppm to 150 ppm.
The composition further includes a glycol ether solvent system. This should be in an amount effective to basically dissolve the pitch and stickies present on the equipment. A wide variety of different glycol ethers can be employed including propylene glycol methylether, dipropylene glycol methylether, tripropylene glycol methylether, propylene glycol methylether acetate, dipropylene glycol methylether acetate, propylene glycol n-butylether, dipropylene glycol n-butyl ether, propylene glycol n-propylether, dipropylene glycol n-propylether, tripropylene glycol n-butylether, ethylene glycol n-butylether, diethylene glycol butylether, trimethylene glycol n-butylether, and higher homologues, diethylene glycol methylether, trimethylene glycol methylether, and higher homologues, as well as combinations of these. A combination can be employed to provide better solvency. One combination which is particularly effective is the combination of dipropylene glycol methylether and tripropylene glycol methylether. Basically, these should be present in an amount from about 1 to 20% combined by weight. A preferred formulation includes 1% dipropylene glycol methyether and 1% tripropylene glycol methylether. A preferred source for this is the Dowanol series of glycol ethers. The use concentration of the glycol ether solution should be about 0.5 ppm to about 50 ppm.
In addition to the above, the present formulation further includes an effective amount of a non-ionic surfactant. Preferably the non-ionic surfactant is an alcohol ethoxylate or an alkylphenol ethoxylate. The alcohol ethoxylates are the condensation products of aliphatic alcohols with ethylene oxide. The alcohol chain of the aliphatic alcohol may be either straight or branched and generally contains 8 to 22 carbon atoms. Linear primary alcohol ethoxylates are particularly useful in the present invention and contain an alcohol chain length of C6–C18 with 2.5 to 15 ethylene oxide groups per molecule. One preferred non-ionic is Neodol 91-8 which has a C9–C11 primary alcohol chain with approximately 8 moles of ethylene oxide per mole of C9-11 alcohol. A preferred alkylphenol ethoxylate is nonylphenol ethoxylate The primary limitation on the non-ionic surfactant is that is must be water dispersible and preferably water soluble. This will be present in an amount of from about 1% up to about 10%, with about 2% being preferred. At this amount the nonionic surfactant effectively assists in wetting, cleaning and emulsification of typical soils encountered in a paper mill.
In addition to the above, the formulation will include an effective amount of a base to establish the desired pH range. The desired pH range will be from about 4 to about 12. The phosphonate is generally acidic. Adequate base, such as sodium hydroxide or potassium hydroxide is added to the composition to modify the acidity. The acidity would be maintained in the acid range where the papermaking equipment was experiencing calcium carbonate build up. The acidity would effectively dissolve the calcium carbonate. However, where the paper making equipment is subjected to build up of polymers such as polyvinyl acetate, a more basic pH would be employed and thus more base would be added.
The composition should start out with the desired amount of water which will form from about 50 to about 80% of the composition. The remaining components can be added in any particular order with the peroxide preferably added last.
To use the formulation of the present invention this would be diluted to use concentrations, generally 0.5 to 50% by weight and introduced to paper making machinery during a shut down period. The formulation then would be circulated through the system at a temperature of from about room temperature, i.e., about 20° C., up to about 60° C. This is continued for the required period of time and the solution is then removed and either discarded or returned to a holding tank for subsequent use. The formulation can also be used at 100% concentration and applied directly to the machinery.
The invention will be further appreciated in light of the following detailed example.
The following cleaning formulation was prepared:
Steel panels were coated with the sample of a coating blend provided by the mill. The coated panels were air dried for 24 hours followed by baking in an oven at 100 C/212 F for 24 hrs.
They were soaked in the cleaning solution at 40 C/104 F for 20–25 minutes and rinsed with cold tap water.
Panels soaked in a 5% solution of the above cleaning formulation, in combination with 0.5% of liquid caustic removed approximately 60% of the coated material. Panels soaked in 2% of the above material with 0.5% of liquid caustic removed approximately 50% of the coating, and panels soaked in 2% of the above cleaning formulation without caustic removed approximately 4% of the coating.
Steel panels were coated with residues of various samples of a coating blends provided by different mills. The panels were air dried for 24 hours followed by baking in an oven at 100 C/212 F for one month.
They were soaked in the cleaning solution at 40 C/104 F for 30 minutes and rinsed with cold tap water.
The coating blend was primarily formed from polymer impurities such as polyvinyl alcohol and polyvinyl acetate. Accordingly, this demonstrates the benefit of utilizing a basic cleaning solution.
Panels soaked in 5% of the above cleaning formulation with 0.5% of liquid caustic removed approximately 95% of the material.
Panels coated with residues from a paper mill were baked to dry the residues on the panels. The panels were then soaked in 5% solution of the above cleaning formulation. The pH of this wash solution was between 4–5. The residue which was supplied by the mill, contained a significant amount of calcium carbonate. The mildly acidic cleaning solution was effective in cleaning the panels that were soaked in this solution. Approximately 95–100% of the coating was removed as determined by the loss in weight of the coating before and after soaking in the test solution.
As shown from the above, the formulation of the present invention effectively cleans paper making equipment without reliance on chlorinated chemicals. Further, it permits the pH of the solution to be modified to effectively treat a variety of different conditions.
This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims wherein we claim:
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