Patent Grant
7744984
1. Field of the Invention
One aspect of the present invention relates to a method for treating a substrate prior to bonding. Another aspect of the present invention relates to a method for bonding substrates.
2. Background Art
In the automotive industry, substantial resources are expended in developing effective windshield bonding processes to account for the typical contamination present under manufacturing conditions. Once a windshield is formed and before the windshield is bonded to the vehicle frame, contaminants may collect and/or settle on the windshield, thereby dirtying the windshield. The existence of contaminants on windshields was documented as an “Industry Update” in the March/April 2003 issue of AutoGlass magazine, available at http://www.glass.org/autoglass/maraprnews.htm. This article proposes the application of a solvent cleaning solution followed by manual scrubbing for cleaning and prepping the dirty windshield before bonding.
According to another proposal, the process of bonding automotive glass, e.g. windshields, side windows, and rear windows, includes the duplicate application of a primer for cleaning and priming the glass substrate, followed by a second primer step, followed by adhesively joining the glass substrate to a vehicle frame with an adhesive.
The first priming step includes priming the glass substrate with a red primer, for example, Betaseal 43519, available from Dow Chemical of Midland, Mich. The red primer contains a coupling agent to chemically modify the substrate surface. The red primer is highly diluted in a solvent blend that is similar to that typically used for other generic cleaning applications carried out at an automotive manufacturing facility, e.g. the cleaning of body surfaces before painting and the cleaning of body side moldings before adhesive bonding. Non-limiting examples of suitable solvents include any of a variety of aprotic solvents, such as toluene and xylene.
The second priming step includes priming the glass substrate with a black primer, for example Betaseal 43520A, available from Dow Chemical. The black primer is typically a thicker paint-like layer that chemically bonds to the coupling agent imparted by the first red primer layer, and adds bonding functionality to adhere to the subsequently applied adhesive material.
Problematically, the red and black primers cannot be consistently and reliably applied in an assembly plant environment. In general, both primers are commonly applied by hand, which may involve human error. For instance, in automotive manufacturing facilities, the red primer is commonly referred to by name as a “cleaner”. If the red primer is mistakenly identified as simply a cleaning solvent, the red primer may be applied as if it were a cleaning solvent. Since a solvent cleaning step does not require as much precision as a primer priming step, this mistake may detrimentally affect the effectiveness of the red primer application. If the glass is perceived already as a clean surface, the step may be mistakenly viewed as unnecessary, instead of being viewed properly as applying a coupling agent for the black primer. This mistake may lead to the omission of the red primer application step.
Moreover, the red primer is invisible to the human eye once applied to the glass surface. Yet, the black primer must be applied exactly over the area of application of the “invisible” red primer. If the application does not match, the resulting adhesive bond between the glass and the frame may be compromised. Further, the black primer only adheres to a glass substrate that has been modified by the coupling agent of the red primer, and does not directly adhere to a fritted glass. Thus, if the black primer is not applied correctly, adhesion to the fritted glass may not occur.
If the adhesion is unacceptable, the windshield may be scrapped, or used for other purposes, at a cost to the manufacturer. Additionally, environmental concerns exist regarding the solvent cleaner, and the red and black primers, as these compounds may contain volatile components that result in the necessity of venting solvent fumes.
In light of the foregoing, a method of treating substrates for bonding that increases reliability of the resulting substrate bond is needed. What is also needed is a method that simplifies and/or automates the bonding process.
One aspect of the present invention relates to a method and system of treating substrates for bonding that increases the reliability of the resulting substrate bond. Examples of suitable substrates include, without limitation, glass and coated glass. One example of a coating is a ceramic frit. Another aspect of the present invention is a method and system that simplifies and/or automates a glass bonding process. Advantageously, certain aspects of the present invention include treating substrates for bonding without the use of solvent-based primers.
According to a first embodiment of the present invention, a method of treating a glass substrate for bonding is disclosed. The method includes providing a glass substrate having a fritted portion of a ceramic frit material and a non-fritted portion. At least a portion of the fritted portion comprises a bondable surface. The method further includes cleaning the bondable surface for subsequent bonding and activating the bondable surface for subsequent bonding. The cleaning and activating steps are carried out by applying air plasma to the bondable surface.
According to another embodiment of the present invention, a pretreated fritted glass substrate for use in subsequent bonding is disclosed. The substrate includes a substrate having a fritted portion. The fritted portion includes a bondable surface portion. The substrate also includes a contaminant layer at least partially contacting the bondable surface portion of the substrate. The contaminant layer has an atomic concentration percentage of Si as silicone of less than 5.0 percent.
According to yet another embodiment of the present invention, a method of providing a glass substrate for bonding to a frame is disclosed. The method includes providing a glass substrate having a fritted portion of a ceramic frit material and a non-fritted portion, directing an air plasma onto the surface of the fritted portion, and applying an adhesive to the fritted portion for subsequent bonding to the frame.
a and 4b depict fragmented, cross-sectional, schematic views of a windshield pretreatment step and windshield bonding step according to one embodiment of the present invention;
a, 5b and 5c depict the results of lapshear failure tests on bonded coupons prepared using one or more embodiments of the present invention;
a and 11b show the results of QKA tests performed on a treated and untreated glass according to one embodiment of the present invention.
Except where expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the present invention. Practice within the numerical limits stated is generally preferred.
The description of a single material, compound or constituent or a group or class of materials, compounds or constituents as suitable for a given purpose in connection with the present invention implies that mixtures of any two or more single materials, compounds or constituents and/or groups or classes of materials, compounds or constituents are also suitable. Also, unless expressly stated to the contrary, percent, “parts of,” and ratio values are by weight. Description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among constituents of the mixture once mixed. The first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
The APAP device 10 includes a voltage supply 18 for supplying voltage to electrode 20 and ground 22 for grounding the APAP device 10. Ionizing gas, e.g. air, is fed into a first chamber 24 through inlet 26. Other ionizing gases can be used to generate plasma streams. Non-limiting examples of ionizing gases for the plasma stream include oxygen, and oxygen diluted in an inert gas, e.g. nitrogen, argon or helium. The ionizing gas exits the first chamber 24 into electrode 20, which is situated within discharge area 28.
Electrode 20 generates a plasma beam 30 that is projected downward through plasma nozzle 32 and exits through outlet 34. The plasma beam 30 contacts bonding surface 14, and in so doing, cleans the bonding surface 14 and activates it for bonding.
The plasma beam 30 can travel along the bonding surface at a velocity in the range of 16 to 840 mm/s according to certain embodiments of the present invention. In other embodiments, the velocity can be in the range of 150 to 450 mm/s. It should be appreciated that the delivery of the plasma beam 30 to the bonding surface 14 can be discontinued and/or continued several times during application. For example, raster patterns with spacings can be used as an application strategy, wherein the beam 30 is discontinued and continued to achieve the desired pattern.
In another embodiment, as depicted schematically in cross-section in
In another embodiment, as depicted schematically in cross section in
According to at least one embodiment, the APAP device can be a device manufactured by PlasmaTreat of PlasmaTreat North America, Inc. of Mississauga, Ontario. According to other embodiments, an APAP device disclosed in U.S. patent application Ser. No. 11/162,741, filed Sep. 21, 2005, can be utilized in accordance with the present invention. The '741 application is herein incorporated by reference in its entirety.
According to at least one embodiment, the present invention includes applying an air plasma to the substrate surface for cleaning and activating the surface prior to bonding. This step can be utilized to pretreat windshield glass prior to bonding. In certain embodiments, the windshield can be at least partially coated with a ceramic frit material. The air plasma pretreatment is especially useful for activating the fritted surface. While not wanting to be bound to any particular theory, the air plasma pretreatment activates the fritted surface by adding hydroxyl groups that can form relative strong covalent bonds with the adhesive.
a depicts a fragmented, cross-sectional view of a windshield 50 receiving an air plasma pretreatment 51. Windshield 50 includes a fritted portion 53, which may be covered with contaminants resulting from exposure to a manufacturing environment and/or a slip coat that is typically applied to the edge of the windshield adjacent to the fritted portion to facilitate attachment of a protective molding. The slip coat is typically a silicone based material. APAP device 10 applies an air plasma to clean and activate the bonding surface 54 of windshield 50 prior to bonding. After this step, an adhesive 56, in certain embodiments, a moisture-cured urethane adhesive, is applied to at least a portion of the pretreated area. Other non-limiting examples of adhesives include moisture-cured silicone adhesives, 1-part and 2-part urethane, silicone and epoxy adhesives, butyls, acrylics and cyanic-acrylics, and hot-melt thermoplastic adhesives. Then, the windshield 50 is bonded to frame 52 through adhesive 56, as depicted in
The air plasma cleaning and activating step can be accomplished manually or robotically, with the air plasma treatment being performed just prior to dispensing a urethane windshield adhesive in a sequential one pass treatment and application. Alternatively, a double pass can be utilized, wherein the first pass is the air plasma treatment and activation step, and the second pass is the application of an adhesive under a similar robot or manual path.
It should be appreciated that glass substrates can be fritted with a ceramic frit compound. According to one embodiment, the adhesive can be selected based on the ceramic frit compound. The following non-limiting parameters that can be considered in selecting the adhesive and glass substrate pair: (1) ceramic frit chemistry; (2) chemistry of the adjoining substrate and/or (3) processing adhesives dictated by the manufacturing plant conditions and production cycle times. According to one embodiment, Dow 15626 urethane adhesive is selected for a Ferro 24-8708 Bi-based fritted glass.
The following non-limiting examples demonstrate the use of the air plasma cleaning and activation process according to certain embodiments of the present invention.
Durability tests were conducted on bonded substrates prepared according to one embodiment of the present invention. The preparation of the bonded substrates was conducted under laboratory conditions. A Ferro 24-8708 bismuth-based enamel coated glass tab, available from Ferro Corp. of Washington, Pa. was used as a first substrate. The dimensions of the glass tab were 1×4 inch width by 5.6 mm thickness. A 1×4 inch DuPont Cormax 6 electro-plate immersion de-ionized water coated unpolished cold-rolled steel panel (CRS), available from ACT Laboratories, Inc., was used as a second substrate. The bonding surface of the first substrate was cleaned and activated by the application of an air plasma via the APAP device 10 as shown in
Three bonded samples 60, 62 and 64 were prepared using this process, as shown in
Each of the samples was exposed for 2 weeks of 95% relative humidity (R.H.) at 38° C. After the exposure period, each sample 60, 62 and 64 was subjected to a lapshear pull to failure test.
In each test, the bond between the adhesive 72 and the enamel-coated glass substrate 68, did not fail. Instead, failure occurred cohesively, either within the adhesive 72 or the enamel-coated glass substrate 68. While not wanting to be bound to any particular theory or principle, the results of this test reveal that, under laboratory conditions, good adhesive-to-glass bonding can be achieved directly.
Turning to
Turning to
Turning to
The dirty surface was assessed for adhesion enhancement by applying adhesive beads 156, 158, 160 and 162 that were air-dried for three (3) days. EFTEC EF7010 urethane adhesive, available from EFTEC North America, L.L.C., Madison Heights, Mich., was used to prepare the adhesive beads. A quick knife adhesion (QKA) test was utilized, wherein the cured adhesive beads were sliced diagonally with a razor blade and then twisted and pulled with pliers until the bead either de-adhered from the glass, or was ripped cohesively in the process.
According to conventional adhesive-to-glass bonding methods, the fritted glass is typically treated with one or more primers to clean the contaminants and activate the fritted glass for the adhesive bonding step.
According to Example 5, a primerless pretreatment process was employed. The surface of the glass 200 of
Glass sample 200 was cleaned and activated using air plasma, and then tested for adhesion. The results of this test are depicted in
A measure of the cleaning ability of the air plasma pretreatment can be demonstrated through surface chemical analysis using X-ray photoelectron spectroscopy (XPS). In this example, a fritted glass with a Zn-based ceramic frit was tested. An air plasma stream rotating at 2000 rpm was passed twice over the fritted glass and adjacent glass surface at a speed of 33 mm/s and distance of 8 mm. The differences in surface chemistry of zinc-based ceramic fritted glass before and after treatment with atmospheric pressure air plasma are shown in Table 1.
For these treatments, XPS surface analysis revealed that 32.5% of the contaminant carbon layer was removed from the fritted surface, and 57.3% of the carbon layer was removed from the glass surface.
Another example of an air plasma cleaning and activation process was demonstrated on a slip coat film contaminated windshield. A slip coat can refer to a silicone-based rubbery material that is used to improve sealing and reduce noise, vibration and harshness (NVH) of a thermoplastic elastomer (TPE) windshield molding.
For this experiment, and according to
The QKA test was performed on the adhesive beads 252 and 256.
A measure of the cleaning ability of the air plasma pretreatment when a slip coat contaminant is present can be demonstrated through surface chemical analysis using X-ray photoelectron spectroscopy (XPS). In this example, a fritted glass with a Bi-based ceramic frit was tested. An air plasma stream was applied in a raster pattern over the fritted glass and adjacent glass surface at a spacing of 3 mm at a speed of 300 mm/s and distance of 6 mm. The differences in surface chemistry of bismuth-based ceramic fritted glass before and after treatment with atmospheric pressure air plasma are shown in Table 2.
For these treatments, XPS surface analysis revealed that 57.8% of the contaminant silicone layer was removed from the fritted surface, and 72.0% of the silicone layer was removed from the glass surface.
The XPS surface analysis also revealed that the hydroxyl content of the bismuth-based ceramic fritted glass increases from 8.9 weight percent before air plasma treatment to 15.0 weight percent after air plasma treatment.
While not wanting to be bound by any theory or principle, these results demonstrate that the fritted-glass surface was effectively cleaned from the contaminant layer and activated chemically for adhesive bonding.
As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of an invention that may be embodied in various and alternative forms. While embodiments of the have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
In accordance with the provisions of the patent statute, the principle and mode of operation of this invention have been explained and illustrated in its various embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
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