JP2021501263A - Processes and compositions for treating metal surfaces using trivalent chromium compounds - Google Patents

Abstract

An aqueous composition useful as a pretreatment before painting to reduce rust formation in the uncoated state. The composition is essentially from water, a trivalent chromium compound having the formula Cr (HxPO4) 3 (where x can be 1.5 or 2), a silica compound, and optionally hydrogen peroxide. become. The pH of the composition can be between about pH 1 and about pH 4. The process for treating the metal surface comprises contacting the surface with such an aqueous composition. The composition and the process have advantages over metal pretreatment with zinc phosphate, which is considered the industry standard.

Description

Related Application This application claims the priority benefit of US Provisional Patent Application No. 62 / 578,787 filed October 30, 2017, the contents of which are incorporated herein by reference.

Technical Fields The present invention generally relates to compositions for passivation of metal surfaces and improvement of paint adhesions and the use of such compositions. More specifically, the present invention relates to aqueous compositions suitable for use as dried-in-place coatings for metals and methods of using the aforementioned compositions.

Background of the Invention Known methods of treating metal surfaces to improve paint adhesion and corrosion resistance of painted metal surfaces include two common chemical classes. The first class is based on traditional chemical coating type chemicals (zinc phosphate, iron phosphate, chromium chromate, chromium phosphate, etc.). The second class is based on recent developments in the metal pretreatment industry, which features what is now called "stationary drying" technology. Traditional chemical coating chemicals require the metal substrate to be rinsed to remove the applied pretreatment solution. For stationary drying chemicals, the applied solution is dried on the metal substrate to which the solution is applied and is not rinsed prior to application of the paint.

For stationary drying processes, metal surfaces such as iron, zinc, cadmium, aluminum, or alloys thereof are treated with an aqueous hexavalent chromium solution containing a chemical that dissolves the metal surface and an insoluble thin film known as "chromate chemical coating". Is generally known to form. These coatings, including hexavalent chromium, exhibit corrosion resistance and protect the metal from various corroding elements. In addition, hexavalent chromate chemical coatings are generally known to have good paint binding properties and therefore provide an excellent base for paints or other finish coatings.

Although the aforementioned coating enhances corrosion resistance and paint bondability, this coating has major drawbacks. Hexavalent chromium has a toxic effect and is considered an environmental risk by the US Environmental Protection Agency and a health risk by the US Occupational Safety and Health Administration. In addition, hexavalent chromium-based chemicals are classified as carcinogens by these institutions.

Over the last decade, various compositions and processes for hexavalent chromium-independent metal surface treatments have been described and used. One such example is Rausch et al. US Pat. No. 4,169,741 describes a stationary drying method using a composition containing trivalent chromium, phosphate ions, and dispersed silica, among other elements. doing.
It is possible to provide coatings and processes that do not contain hexavalent chromium but are still capable of improving paint adhesion and corrosion resistance on metal surfaces (such as aluminum), comparable to traditional hexavalent chromium-based coatings. Very desirable. Further, it is necessary to provide a protective coating agent having excellent corrosion resistance having a low resistivity and an appropriate coating weight.

U.S. Pat. No. 4,169,741

Brief Abstracts of the Invention The present invention relates to compositions for treating metal surfaces to improve paint adhesion and corrosion resistance and / or maintain low electrical contact resistance. The composition can be used as a pre-painting treatment to treat a range of metals, including copper, brass, magnesium, aluminum, iron, zinc, cadmium, or alloys thereof. Intended to be used for. In one embodiment, the composition is water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and if desired. Contains hydrogen peroxide accordingly.

In another embodiment, the composition is water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and hydrogen peroxide. Essentially from hydrogen.

In another embodiment, the composition is water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and hydrogen peroxide. Consists of hydrogen.

In one embodiment, the trivalent chromium compound is: about 10% wt. % ~ About 5% wt. %; Approximately 10% wt. % ~ Approximately 2.5% wt. %, About 10% wt. % ~ Approximately 1% wt. %, Or about 10% wt. % ~ Approximately 0.5% wt. Present in% amount.

In another embodiment of the invention, silica is 2% wt. Less than%; 1.75% wt. Less than%; or 1.5% wt. It is present in an amount less than%.

In yet another embodiment, the invention is a process of treating a metal surface. This process involves removing the metal surface to water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and optionally. Including the step of contacting with a composition containing hydrogen peroxide.

In one further embodiment, the invention is a process of treating a metal surface, (1) a step of cleaning the metal surface to form a cleaned metal surface, a cleaning step; (2) said cleaning. The step of rinsing the rinsed metal surface with water to form the rinsed metal surface; and (3) the rinsed metal surface is water, formula Cr (H _x PO ₄ ) ₃ (formula). Medium, x is a process comprising contacting with a composition comprising a trivalent chromium compound, a silica compound, and hydrogen peroxide having (which can be 1.5 or 2).

In one still further embodiment, the process further comprises contacting the rinsed metal surface with the composition, then rinsing the metal surface again with water and then sealing the metal surface.

The process may further include cleaning and rinsing the metal surface with an alkaline cleaner prior to the first contact step. The process may further include contacting the metal surface with the pretreatment composition, then rinsing the metal surface with water, and then painting the metal surface. PH of an aqueous pretreatment composition containing water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and hydrogen peroxide. Is preferably acidic, more preferably between about pH 1 and about pH 4.

It should be understood that both the general description above and the detailed description below are exemplary and do not limit the invention.

The present invention can be most understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized by convention that the various features of the drawings are not on scale. In contrast, various features are arbitrarily enlarged or reduced for clarity. The drawings include the following figures:

FIG. 1 is a photographic comparison of the results from Composition 1 when lined according to ASTM B117 and compared to a control composition for panels exposed to neutral salt spray for 250 hours.

FIG. 2 is a parallel photographic comparison of the results from Composition 1 when a panel drawn according to ASTM B117 and exposed to a neutral salt spray for 250 hours was compared to a control composition.

FIG. 3 is a parallel photographic comparison of the results from Composition 1 and Composition 2 when lined according to ASTM B117 and compared to the control composition for panels exposed to neutral salt spray for 500 hours.

FIG. 4 is a parallel photograph of the results from Composition 2 for a panel drawn according to ASTM B117 and exposed to a neutral salt spray for 250 hours.

FIG. 5 is a side-by-side photograph of the results from Composition 1 when lined according to ASTM B117 and compared to the composition of Example 1 disclosed in Rausch's patent for panels exposed to neutral salt spray for 250 hours. It is a comparison.

FIG. 6 is a side-by-side photograph of the results from Composition 1 when lined according to ASTM B117 and compared to the composition of Example 1 disclosed in Rausch's patent for panels exposed to neutral salt spray for 250 hours. It is a comparison.

Detailed Description of the Invention The present invention relates to compositions and processes for treating metal surfaces. The compositions of the present invention are water, trivalent chromium compounds having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), silica compounds, and optionally hydrogen peroxide. It contains hydrogen peroxide, preferably consists essentially of these, or most preferably consists of these. In the process of the present invention, the metal surface is made of water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and if necessary. Including a step of contacting with the above composition comprising hydrogen peroxide accordingly.

After cleaning, but before applying some finish coating to the metal surface, applying the aqueous composition of the invention to the metal surface helps at least one of the following: (1) To improve paint adhesion; (2) to improve the corrosion resistance of metal surfaces; and (3) to maintain or reduce the resistivity of metal surfaces. The compositions of the present invention include compositions that significantly improve one or two of these characteristics, but one of the other is less aggravated. The improvement may be due to the composition alone or in combination with other process steps. Such compositions are referred to herein or in the metal processing industry as pretreatment compositions, chemical coatings, or processed compositions. "Resistivity" is defined as resistance per unit surface area; a typical unit of resistivity is μΩ / square inch.

As used herein, the term "hexavalent chromium compound" means a chromium compound, or salt, in which the valence of chromium is +6. A wide range of anions can be used, and more than one hexavalent chromium compound can be used. Preferably, the hexavalent chromium compound is chromic anhydride (CrO ₃ ), chromic acid (H ₂ CrO ₄ ), or chromium chromate (Cr ₅ O ₁₂ ).

As used herein, for example, the term "metal" as used in the phrase "metal surface" includes copper, brass, magnesium, aluminum, iron, zinc, cadmium, or alloys thereof. Each of the listed metals includes both elemental metals and their alloys; for example, the term "aluminum" means aluminum and aluminum alloys. The term "alloy" is a metal in which the content of the main element is higher than any other element or equal to the highest content of any other element (for example, in aluminum alloys, aluminum is optional). A metal that is present in an amount that is at least equal to the amount of the elements in.) Ferroalloys include cold-rolled steel, electrogalvanized steel, and hot-dip galvanized steel. Preferably, the compositions of the present invention are used to treat a range of metals, including alloys of copper, brass, magnesium, aluminum, and iron.

As used herein, the term "pretreatment composition" means any composition that improves paint adhesion on metal surfaces, reduces electrical contact resistance, and improves corrosion resistance. The aqueous pretreatment composition can be used as a pretreatment for coating and as a passivation treatment to reduce corrosion formation under uncoated (unpainted) conditions. Thus, for convenience, the composition can be referred to as a pretreatment composition, which is a composition used to improve the adhesion of subsequently applied paints and resist corrosion of unpainted surfaces. is there.

As used herein, the term "treatment" means the application of treatment, or the application of cleaning, rinsing, and pretreatment. The pretreatment also acts as a sealant to seal the metal surface, so the term "treatment" shall optionally include the step of sealing the metal surface. Further, the "treatment" may optionally include a process step up to painting and a process step including painting. For example, the treatment step may also include the step of applying a cosmetic coating agent (such as a paint). After applying the pretreatment agent, the pretreatment agent can be rinsed first or allowed to stand dry before applying the paint. Each of these steps affects the ability of the final product to resist corrosion and minimize paint loss. As described above, the treatment composition can be used as a coating pretreatment agent.

As used herein, the term "trivalent chromium compound" means a chromium compound, or salt, in which the valence of chromium is +3. Hexavalent chromium is absent in such compounds (or contains at least a very small, insignificant amount of hexavalent chromium). A wide range of anions can be used, and more than one trivalent chromium compound can be used. Preferably, the trivalent chromium compound is a compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2).

In one other embodiment, the compositions of the invention are water, a compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound, and. Essentially from hydrogen peroxide if needed. Such compositions can include additives while eliminating halide ions that promote undercutting. If undercutting occurs, it can be accompanied by performance degradation.

The appropriate concentration range for the various components depends on their solubility. If the concentration is too low, the amount of constituents will coat the metal surface and be insufficient to perform its function. If the dissolution limit is exceeded, solutes may begin to precipitate from the solution. In one embodiment of the invention, the trivalent chromium compound is about 10% wt. % ~ About 5% wt. %; Approximately 10% wt. % ~ Approximately 2.5% wt. %, About 10% wt. % ~ Approximately 1% wt. %, Or about 10% wt. % ~ Approximately 0.5% wt. Present in% amount. In one embodiment of the invention, the silica is 2% wt. Less than%; 1.75% wt. Less than%; or 1.5% wt. It is present in an amount less than%.

In one embodiment of the invention where the precursor hexavalent chromium compound is chromic anhydride (CrO ₃ ), the chromium acid is first reduced in the presence of phosphoric acid to the trivalent chromium compound: chromium dihydrogen phosphate (chromic dihydrogen phosphate). Cr (H ₂ PO ₄ ) ₃ ) is produced. Hydrogen peroxide is a reducing agent. After the chrome is reduced, silica is added. Considering certain other conditions, the following pH range was found to be preferred: pH 1-4.

The above composition is a composition for a working bath. Of course, it is desirable to transport the product in the form of a concentrate (ie, a concentration up to 10 to 100 times the concentration for the working bath). The upper limit of such concentration is the dissolution limit of the first component that meets or exceeds the dissolution limit of the first component.

The pH of the composition is preferably pH 1-4 when the composition is used to process cold rolled steel. More preferably, the pH is about 1.75.

The compositions of the present invention can be made by mixing the ingredients in any of several orders. In a non-limiting embodiment in which the hexavalent chromium compound is the precursor, the hexavalent chromium compound is first reduced in the presence of phosphoric acid to the trivalent chromium compound: chromium dihydrogen phosphate (Cr (H _2). PO ₄ ) ₃ ) is produced. Hydrogen peroxide is a reducing agent. After the chrome is reduced, silica is added. In a non-limiting embodiment in which the hexavalent chromium compound is a precursor, the hexavalent chromium compound is measured in a solution containing phosphoric acid and hydrogen peroxide until the hexavalent chromium compound is completely reduced. After the chrome is reduced, silica is added.

In one non-limiting embodiment, by mixing a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x is between 1.5 and 2) with water. Make a concentrate (ie, masterbatch). The silica compound can then be added to the solution. The concentrate can then be diluted with deionized water at the metal treatment site prior to use to obtain the desired concentration.

In one non-limiting embodiment, some hydrogen peroxide may remain upon completion of the reaction. Conversely, in another non-limiting embodiment, hydrogen peroxide is fully utilized. Preferably, upon completion of the reaction, the hydrogen peroxide concentration is in the following range: 0 to about 0.85 grams H ₂ O ₂ (35%) per 1 gram of Cr (H ₂ PO ₄ ) 3.

Additional components well known in the art can be included in the compositions of the present invention. For example, wetting can be improved by including a wetting agent such as a fluorosurfactant. In some cases, thickeners can also be included if higher viscosity is required at the time of application.

In one process of the invention, the metal surface is coated with the pretreatment composition of the invention. In this coating step, the composition can be contacted with the metal surface by any number of techniques known in the art. One such method is a dip coating that impregnates the metal into the pretreatment bath. Other techniques known in the art include spraying, roll coating, or reverse roll coating, and manual coating (eg, brush coating). The coating process is carried out over a period of time sufficient to obtain the desired coating weight on the metal surface, which time can be determined empirically. This desired coating weight will depend on several factors well known in the art. In one embodiment, the coverage is sufficient to leave about 0.1 to about 30 milligrams of chromium and phosphate per square foot of each dry metal surface as determined by the weight strip weight method. The amount. In another embodiment, the coverage is about 1 to about 10 milligrams of chromium per square foot of each dry metal surface, as determined by X-ray fluorescence, most preferably each dry metal as determined by X-ray fluorescence. Enough to leave about 2.5 to about 3.5 milligrams of chromium per square foot of surface. By using a solution with a higher concentration of contained elements, it is possible to leave the desired dry coating amount with a shorter waiting time.

The process of treating metal surfaces to improve corrosion resistance, improve paint adhesion, and / or maintain low electrical contact resistance is as follows: (1) Clean the metal surface to form a clean metal surface. And (3) Rinse the cleaned metal surface with water to form a rinsed metal surface; and (3) Rinse the rinsed metal surface with water. , Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), comprising contacting with a composition comprising a trivalent chromium compound, a silica compound, and hydrogen peroxide. ..

The cleaning step can be performed in any manner known in the art. The type of detergent suitable for use in the present invention will vary depending on several factors, including the metal being treated, the desired application, and the amount and type of impurities and solids on the metal surface. .. As such, the preferred detergent can be empirically determined based on these factors. In one non-limiting embodiment, an alkaline detergent is used. An exemplary alkaline cleaning agent that can be used in conjunction with the present invention is a Bulk Kleen® 841MC cleaning agent (an alkaline liquid cleaning agent sold by Bulk Chemicals, Inc., Inc. of Reading, Pa.). In another non-limiting embodiment, a phosphoric acid detergent is used. Generally, the cleaning step can be carried out by contacting the metal surface with an alkaline cleaning solution bath to form a cleaned metal surface. The alkaline cleaning solution can be an aqueous solution of an alkaline cleaning agent. The cleaning bath cleans the metal surface by removing oil and other contaminants from the metal surface. The cleaning bath is effective in removing non-stick impurities and surface solids. Therefore, the cleaning bath removes solids and certain impurities from the metal surface. If the metal surface is excessively soiled, cleaning aids for cleaning agents can be included in the cleaning process.

The metal surface in contact with the alkaline cleaning solution is referred to herein as the "cleaned metal surface". It is cleaned in the sense that it is exposed to a cleaning bath. However, it may not be completely cleaned in the sense that substantially all impurities have been removed so that it is ready for exposure to the pretreatment composition. In some cases the metal surface may have been properly cleaned, but in other cases it should first be rinsed with water before contact with the pretreatment composition (ie). Removes virtually all impurities before contact).

The rinsing process is well known in the art and it is preferable to use deionized water. The use of deionized water prevents any harmful ions, such as chlorine ions, from being mixed into the system. The rinsing step can be two steps (the first rinsing step is performed using tap water and then the rinsing is performed using deionized water).

After the above step (3) of bringing the metal surface into contact with the composition, the metal surface can be rerinsed with water, as is well known in the art. The rinsed metal surface can then be sealed. Any chemical sealing composition well known in the industry can be used. In one preferred embodiment, the pretreatment composition includes water, a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2), a silica compound. , And only compositions containing hydrogen peroxide are included. When a sealing composition is used, it is preferable to intervene a rinsing step.

After step (3) or any subsequent sealing step, the metal surface may be dried or rinsed to dry, and then a decorative coating may be applied to the metal surface. For example, the metal surface may be painted or lacquered, or may be first primed and then painted. Such steps (undercoating and coating) are known in the art as "finish coating steps", and any known and appropriate finish coating process can be used. Suitable paints include, among other things, acrylic paints and fluorocarbon paints.

As can be inferred, after the above step (3) or any subsequent sealing step, the metal surface can be dried and then the decorative coating (painting layer) is rinsed between these steps. Is applied without intervening. This alternative process is known as a "stationary drying" pretreatment. Regardless of whether the pretreatment is "stationary drying", a rinsing step is involved and any known drying method can be used. The coating can be dried using, for example, an oven, forced ventilation, and the like.

Determining the treatment time of metal surfaces using baths of various steps is well known in the art. The treatment time only needs to be long enough to provide sufficient time for cleaning (in the case of a cleaning step) or reaction (in the case of a pretreatment step or sealing step). The treatment time is very short or about 30 minutes, and the treatment time depends on the treatment stage, the type of application (eg impregnation, spraying), the type of metal surface, and the desired coating weight, among other factors. Can depend on it. The impregnation time of the substrate into the composition solution will vary from step to step and will generally vary from approximately 1 minute to approximately 10 minutes. The impregnation time is typically longer than when spraying is used as the contact method. Rinse time can generally be fairly short (eg, 30 seconds to 1 minute). The specific processing time may vary over a wide range and can be easily determined by those skilled in the art.

The desired performance characteristics of the present invention can be achieved by the above processing steps, thereby producing a pretreated metal surface with good paint adhesion and corrosion resistance. These properties can be obtained on a metal surface without the use of a decorative coating. Therefore, the treated metal surface can be used as an unpainted product, which will exhibit corrosion resistance even if there is a delay between the treatment process and any subsequent coating.

The compositions and processes of the invention provide the benefits of description without the use of additional components that affect the basic and novel features of the invention. Other components can affect new features when added in sufficient amounts to the composition. For example, certain components can destabilize the composition. Such components can affect the life of the process. Other components can reduce the performance of the compositions and processes of the invention.

Taken together, the present invention provides compositions and processes for metal treatments that are environmentally friendly while still maintaining excellent paint adhesion and corrosion resistance. More specifically, the present invention avoids the use of hexavalent chromium and its associated health hazards and disposal problems.

The following examples are included to more clearly demonstrate the overall nature of the invention. FIGS. 1 to 4 show the improvement results obtained by using the aqueous composition of the present invention. These examples are exemplary of the invention and do not limit the invention.

In the experiments below, batches of Cr (H ₂ PO ₄ ) ₃ were first synthesized in combination with the raw materials identified in Table 1 below.

A total of 87.1 grams of chromium dihydrogen phosphate (Cr (H ₂ PO ₄ ) ₃ ) was synthesized. Further water was added to the solution and the final concentration of the masterbatch was 39.2% wt. Was determined to be%. The masterbatch was further diluted with water to make two separate compositions identified in Table 2 below.

Test Panel Preparation-Composition 1

Cold rolled steel panels were treated by the following spraying process. First, the panel was cleaned with 3% v / v Bulk Kleen® 841MC solution at 165 ° F for 5 seconds. Bulk Kleen® 841MC is an alkaline cleaner designed to clean steel, zinc, and aluminum components. Second, the panel was rinsed at ambient temperature for 30 seconds. Third, the panel was recleaned with 3% v / v Bulk Kleen® 841MC at 165 ° F for 5 seconds. Fourth, the panel was rinsed with deionized water at ambient temperature for 30 seconds. Fifth, composition 1 was applied to the panel using a roll coater. Sixth, the panel was dried with hot air. Seventh, all panels were painted to a dry coating thickness of 0.7-0.8 mils using a high reflectance white single coated polyester.

Test Panel Preparation-Composition 2

Cold rolled steel panels were treated by the following spraying process. First, the panel was cleaned with 3% v / v Bulk Kleen® 841MC solution at 165 ° F for 5 seconds. Second, the panel was rinsed at ambient temperature for 30 seconds. Third, the panel was recleaned with 3% v / v Bulk Kleen® 841MC at 165 ° F for 5 seconds. Fourth, the panel was rinsed with deionized water at ambient temperature for 30 seconds. Fifth, the composition 2 was applied to the panel using a roll coater. Sixth, the panel was dried with hot air. Seventh, all panels were painted to a dry coating thickness of 0.7-0.8 mils using a high reflectance white single coated polyester.

Test panel preparation-control formulation

Cold rolled steel panels were treated by the following spraying process. First, the panel was cleaned with 3% v / v Bulk Kleen® 841MC solution at 165 ° F for 5 seconds. Second, the panel was rinsed at ambient temperature for 30 seconds. Third, the panel was recleaned with 3% v / v Bulk Kleen® 841MC at 165 ° F for 5 seconds. Fourth, the panel was rinsed with deionized water at ambient temperature for 30 seconds. Fifth, Bulk Bond® 780 12% v / v was applied in a spray washer at 165 ° F for 8 seconds. Bulk Bond® 780 is a liquid chemical used in the coil coating process to impart corrosion-resistant, paint-bonding phosphate ion coatings to steel. After that, the panel was rinsed with deionized water. Sixth, the panel was dried with hot air. Seventh, the control panel was then sealed with a Bulk Bond® NP250 35% v / v using a roll coater. Bulk Bond® NP250 is a liquid chromium / silica product designed to be rolled in as a passivation / pretreatment for multi-metal surfaces. Eighth, all panels were dried and coated with a high reflectance white single coated polyester to a dry coating thickness of 0.7-0.8 mil.

Test panel preparation-Rasch formulation

Cold rolled steel panels were treated by the following spraying process. First, the panel was cleaned with 3% v / v Bulk Kleen® 841MC solution at 165 ° F for 5 seconds. Second, the panel was rinsed at ambient temperature for 30 seconds. Third, the panel was recleaned with 3% v / v Bulk Kleen® 841MC at 165 ° F for 5 seconds. Fourth, the panel was rinsed with deionized water at ambient temperature for 30 seconds. Fifth, Rasch et al. The composition outlined in Example 1 of the patent was applied to the panel using a roll coater. Sixth, the panel was dried with hot air. Seventh, all panels were painted to a dry coating thickness of 0.7-0.8 mils using a high reflectance white single coated polyester.

All test panels were then exposed to neutral salt spray for 250 or 500 hours according to ASTM B117. Photographic comparisons of the results obtained are shown in FIGS. 1-6. As can be seen, Compositions 1 and 2 show protection comparable to the control formulation (ie, Bulk Bond® 780), and Rasch et al. Was superior to the formulation of. Specifically, Composition 1 and Composition 2 exhibited corrosion and pitting corrosion similar to the control formulation, whereas Rasch et al. The formulation of was increased in corrosion and pitting corrosion.

Without being bound by any particular theory, Rasch et al. Since additional ions are present in the formulation of, in addition to chromium, phosphate, and silica, Composition 1 and Composition 2 are described in Rausch et al. It is considered that it was superior to the formulation of.

Although illustrated and described above with reference to certain embodiments and examples, the invention is never intended to be limited to the details presented. Rather, various modifications can be made to the details within the equivalent of the claims without departing from the spirit of the invention. For example, all ranges broadly enumerated in this document are expressly intended to include all narrower ranges contained within this broader range. It is also expressly intended that the steps of the methods of use of the various compositions disclosed above are not restricted to any particular order.

Claims (18)

An aqueous pretreatment composition for treating metal surfaces.
water;
silica;
An aqueous pretreatment composition comprising a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2). The aqueous pretreatment composition according to claim 1, which is acidic. The aqueous pretreatment composition according to claim 1, which is between about pH 1 and about pH 4. The aqueous pretreatment composition according to claim 1, further comprising hydrogen peroxide. The trivalent chromium compound is about 10% wt. % ~ Approximately 0.5% wt. The aqueous pretreatment composition according to claim 1, which is present in an amount of%. The aqueous pretreatment composition according to claim 1, wherein x is 1.5. The aqueous pretreatment composition according to claim 1, wherein x is 2. An aqueous pretreatment composition for treating metal surfaces.
water;
silica;
An aqueous pretreatment composition comprising a trivalent chromium compound having the formula Cr (H _x PO ₄ ) ₃ (where x can be 1.5 or 2). The aqueous pretreatment composition according to claim 8, which is acidic. The aqueous pretreatment composition according to claim 8, which is between about pH 1 and about pH 4. The aqueous pretreatment composition according to claim 8, which is acidic. The trivalent chromium compound is about 10% wt. % ~ About 5% wt. The aqueous pretreatment composition according to claim 8, which is present in an amount of%. The aqueous pretreatment composition according to claim 8, wherein x is 1.5. The aqueous pretreatment composition according to claim 8, wherein x is 2. A method of preparing a metal pretreatment composition,
A step of reducing a hexavalent chromium compound with hydrogen peroxide in the presence of phosphoric acid, in which the pH is between about pH 1 and about pH 4, and the formula Cr (H _x PO ₄ ) ₃ (where x is in the formula). A method comprising the steps of making a trivalent chromium compound having (which can be 1.5 or 2); and adding silica after the hexavalent chromium compound has been completely reduced. 15. The method of claim 15, wherein the silica is Aerodisp W7512S. A method of coating a metal surface
A step of roll-coating the metal surface with the composition according to claim 1.
The step of spraying the composition according to claim 1 on the metal surface for a period of up to about 300 seconds; or the step of immersing the metal surface in the composition according to claim 1 for a period of up to about 300 seconds. Including methods. 17. The method of claim 17, wherein the metal surface is selected from the group consisting of zinc, zinc alloys, aluminum, aluminum alloys, steels, zinc plated steels, and zinc having an aluminum alloy.

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