Heatable windshield notch sealant

2~2~172 -- 1 - HEATABLE WINDSHIELD NOTCH SEALA~T BackRround of the Invention l.

Field of the Invention This lnvention relates to sealing edge portions of a laminated transparency and in particular to sealing the notch area of a heatable, laminated windshield to prevent air from diffusing into the interior of the windshield during lamination.

2a.

Technical Considerations It has been known to pass electric current through a transparent conductive coating on a transparency in order to raise its temperature.

Generally, the transparency includes a spaced pair of bus bars electrically interconnected by a conductive coating.

The bus bars are usually connected by leads to a power source to 15 distribute current from the power source through the coating. Where the transparency is a laminated windshield, passing current through the coating elevates the temperature of the laminate sufficient to melt snow or ice that has accumulated on an exposed surface of the wlndshield.

A heatable windshield usually includes a cut-out section, or notch area, along an edge of one of the plies of the windshield that exposes a lead portion of the bus bars and provides a location at which the power source can be connected to the windshield.

During lamlnation, the wind3hield components are exposed to elevated 25 temperatures and pressures. After lamination, air bubbles have been observed wlthin the wlndshleld in the vicinlty of the notch area. It 18 believed that this defect 18 the result of air diffusing through the bus bar leads into the lnterior of the windshield during lamination, Not only ie the bubbling a visible and ob~ectionable 30 defect but excessive bubbling within the windshield may reduce the windshielt strength in this area.

It would be advantageou~ to prevent diffusion of air into the interior of the windshield, and in particular at the notch area, during lamination.

202~172 -- 2 - - 2b.

Patents of Interest U.S.

Patent Nos. 3,789,191 and 3,789,192 to Spindler teach a heated window with a temperature sensing device, wherein the electrical leads to the temperature sensor are embedded within the 5 plastic interlayer of the window.

U.S.

Patent No. 3,790,752 to Boaz et al. teaches a heatable, laminated windshield in which an electrical connection i8 made within the windshield to a transparent interlayer which has a conductive coating thereon. The connection is sealed 80 that moisture cannot 10 penetrate the laminate.

U.S.

Patent No~. 3,794,809 to Beck; 4,543,466 to Ramus; and 4,789,784 to NiXodem et al. teach an electrically heatable wind~hield with opposing bus bars that are electrically interconnected by an electroconductive coating on an interior surface of the windshield.

15 In Beck, the leads to the bus bars extend outside of the windshield aesembly.

In Ramus and Nikodem et al., the leads extend into a cut-out portion, or terminal area, along an edge of the windshield.

Electrical power is provided to the leads at the terminal area.

U.S.

Patent No. 4,593,175 to Bowser et al. teaches a coating 20 compositlon to prevent moieture from penetrating along a power cable oS an electrically heated architectural glazing unit.

Summary of the Inventl~a The ~reeent invention teaches a laminate wherein an exposed surface of a gas permeable material which ex~ends beyond one of the 25 plies of the laminate i8 sealed prior to bonding the plies together to form a unitary a~sembly. In one particular embodiment of the invention, a surface of a first ply of the laminate includes a pair of opposing bus bars interconnected by an electroconductive coating.

The bus bars are made of a gas permeable material and are bonded to 30 the firet ply's surface.

The bus bare extend to an electrical connection area along a peripheral edge of the laminate. A second ply overlaye the firet ply and includes a cut-out section at the connection area that exposee a portion of the bus bars. The exposed portlons of the bue bars are eealed prior to bonding the plies 35 together to prevent gae from entering the interior of the laminate through the bus bare.

_ 3 _ 2 ~ 2 ~ 1 7 2 In an additional embodiment of the invention, the laminate i9 a heatable windshield. The bus bars are a conductive ceramic enamel bonded to an interior surface of one of the glass plles of the windshield. The entire electrical connection area is ~ealed with a 5 sealant, such as a butyl-based sealant or a silicone elastomer sealant.

Brief Dçscriptlon of the DrawinQs Figure l is a plan view of a heatable wind~hield incorporating features of the present invention, with portions lO removed for clarity.

Figure 2 i~ an enlarged view of the notch area of the windshield shown in Figure l, with portions removed for clarity.

Figure 3 is a view taken along line 3-3 of Figure 2 showing a sealant in the notch area of the windshield.

Figure 4 is a view taken along line 4-4 of Figure 2 showing a sealant in the notch area of the windshield.

Detailed DescriDtion of ~he Invention The description of the invention is taught in connection with a heatable, laminated transparency comprised of two glass plies 20 bonded together by a thermoplastic interlayer and an electroconductive coating positioned between the plies.

The preceding construction represents a typical heatable windshield construction, but it is understood that the invention can be practiced to make any construction of heatable transparencie~ having two or more plies of 25 glass or plastic or any combination thereof. Furthermore, the lnventlon 18 not llmlted to fabrlcating an automotive windshield but may be practlced ln the fabrlcation of any transparency where there 18 a problem Of 8as dlffuslng lnto the lnterior of a laminated transparency.

Referrlng to Figures l, 3, and 4, the transparency 10 is a heatable windshield which includes an outboard glass ply 12, i.e. the ply furthe~t from the vehicle interior, a plastic interlayer 14, which may be polyvlnylbutyral as is commonly used for laminated windshleld~, and an lnboard glass ply 16.

Although not llmlting in 3S the present lnvention, ln the preferred embodlment of the inventlon, the wlndshleld lO has a the heatlng arrangement including an 2~2~72 . .

-- 4 - electroconductive coating 18 preferably positioned on the inside surface 20 of the outboard glass ply 12. Various coatlngs may exhibit the necessary combination of transparency and electroconductivity required to serve as the heating element for the 5 transparency 10. A preferred coating is similar to that disclosed in U.S.

Patent No. 4,610,771 to Gillery. These coatings generally include one or more silver films between pairs of zinc stannate films, each of which may be applied sequentially by magnetron sputtering. In one particular embodiment of the invention) the coating taught in U.S.

10 Patent No~ 4,610,771 exhibits an approximate resistlvity of about 7 to 8 ohms per square with a single silver film layer having a thickness of about 110 Angstroms.

Electrical power from a power supply 22 passes to the electroconductive coating 18 through a bu~ bar and lead arrangement 15 which, although not limiting in thé present invention, is similar to the double feed buq bar arrangement disclosed in U.S.

Patent No. 4,820,902 to Gillery. Referring to Figure l, a bottom bus bar 24 and top bus bar 26 are positioned on surface 20 of the gla9s ply 12 in contact with the coating 18. The electrical connection to the upper bus bar 20 26 ig made by a pair of extensions of the bus bar 26, i.e. leads 28 and 30, each extending along opposing side portions and bottom edge of the windshield 10 to a terminal area 32. Electrical access to the bottom bus bar 24 is had by a lead 34 which extends from the bus bar 24 to the terminal area 32. Although not limiting in the present 25 lnvention, the electrical connections to the bottom bus bar 24 and to the top bus bar 26 via leads 28 and 30 are preferably made along the bottom edge of the windshield lO at the terminal 32 as illustrated in Figure 1, but it should be appreciated that the connections may be made to the windshield lO at any convenient location.

With continued reference to Figure 1, wire 36 connects the bottom bus b~r 24 to one pole of an electrical power source 22.

Leads 28 and 30 leading to the top bus bar 26 are connected in common to the opposlte pole of power 90urce 22 by means of wires 38 and 40 and ~umper wlre 42.

,t~l 2~2~ ~ 72 -- 5 - ~ eferring also to Figure 2, the leads 28 and 30 are electrically insulated from the coating 18 and bottom bus bar 24 in any convenient manner known in the art to ensure that the power to the coating 18 is delivered through the bus bars 24 and 26.

Although 5 not limiting in the present invention, the edge of the coating 18 is spaced from edge of the transparency 10, a~ indicated by line 44 in Figures 1 and 2 and the leads 28 and 30 are positioned within this uncoated, marginal area.

The bus bars and leads are preferably made of a æilver 10 containing ceramic frit material, as is well known in the art, and may be applied in any convenient manner, e.g. screen printing onto the glass surface 20 of the glass ply 12.

After printing, the frit material is heated, or "fired", to melt the frit material and fuse it onto the glass surface.

An opaque ceramic enamel border (not shown) 15 may optionally be applied on surface 20 of the glass ply 12 to hide the bus bars 24 and 26 and leads 28 and 30.

After the bus bars and leads are fired onto the glass ply 12 and the coating 18 is applied to surface 20, the interlayer 14 is positioned between the glass sheets 12 and 16 and the entire assembly 20 is laminated in any convenient manner available in the art, to form a unitary structure, i.e. a laminated windshield.

With reference to Figures 2, 3, and 4, lnner ply 16 includes a cut-out or notch area 46 to expose portion 48 of lead 34 and portions 50 and 52 of leads 28 and 30, respectively, and provide access for electrical connection to 25 the bus bar~ 24 and 26 from the power source 22 ~shown only in Figure 1).

In partlcular, referring to Figure 2, wires 54, 56, and 58 are electrically interconnected to lead portions 48, 50, and 52, respectively, in any convenient manner known in the art, e.g.

soldering.

Bubble~ have been observed on the inner surface 60 of the 30 inner gla~s ply 16 along the leads 28, 30 and 34 and along bottom bus bar 24 in the vicinity of the notch area 46.

It is believed that these bubbles are caused by air diffusing through the exposed portions 48, 50, and 52 of the silver ceramic leads 28, 30, and 34, respectlvely, and into the lnterior of the windshield 10 during 35 lamlnation.

The bubbles detract from the aesthetlcs of the wlndshleld and excesslve bubbling may reduce the strength of the windshield 10 in the notch area 46.

2020172 -- 6 - To protect against this condition and with continued reference to Figures 2 through 4, an air impervious sealant 62 fills the notch area 46 to prevent air from diffusing through the lead portions and into the interior of the windshield 10. ~he sealant 52 5 must be able to survive the elevated temperatures and pressures of a laminating cycle, which for automotive windshields are typically on the order of about 275~ (135C) and 200 psi (1.38 x 106 Pa). In addition, the sealant material preferably should not give off toxic fumes or other gases during lamination. Furthermore, the sealant 10 material should not adversely affect the silver lead portions 48, 50, and 52, or any exposed coating 18 in the notch area 46. In particular, sulfur containing sealant materials should be avoided because the sulfur or sulfur compounds may react with the silver, forming silver sulfides which will reduce the 15 electroconductivity of the leads and/or coating in the notch area 46. Since electrical power to the windshield 10 will be provided through the notch area 46, the sealant materials should also be non-electroconductive to prevent shorting of the windshield circuitry by electrically interconnecting the lead portion 48 with the ad~acent 20 lead portions 50 and 52. Lastly, the sealant material must be sufficiently resilient 80 as to not induce any undue stresses on the windshield in the notch area 46.

Sealants that have been used in the practice of the invention include silicone elastomers, and in particular, elastomer 25 materials available from Dow Corning Corp., Michigan, under the trade marks DOW CORNING 732TM multi-purpose sealant and DOW CORNING~3 982 silicone lnsulating glass sealant. DOW CORNING 732~ sealant i8 a one-component material that dries tack free in about 20 minutes and forms a tough, rubbery solid. Material data sheets for this sealant 30 indicate that this material will corrode copper and copper containing alloys, magnesium, and zinc and zinc containing alloys. ~herefore the u8e of DOW CORNING 732~ sealant with these metals should be avoided. Although the DOW CORNING 732~ sealant satlsfactorily seals the notch area 46, during lamination of the windshield components, it 35 ha8 been observed to bubble, resulting in a less than desirable a~pearance. DOW CORNING~ 982 sealant is a two-part, variable cure rate, high modulus~ elastomeric sealant that provides good adhesion 2~2017~ -- 7 - to uncoated and coated glass and wlll not bubble as severely as the DOW CORNING 732~ sealant during lamination. This sealant will cure within 15 to 60 minute3, depending on the ratio between the base and curing components of the sealant.

In addition, it was found that 5 increasing the amount of the curing component relative to the amount of the ba~e component will reduce the amount of bubbling and reduce the curing time. Both the DOW CORNING 732 and 982 sealants will not flow under their own weight so that a thick layer of sealant can be used to fill the notch area 46 without the sealant flowing out of the 10 notch area 46.

These sealants are applied to the notch area 46 in any convenient manner and although not limiting to the present invention, the sealants are preferably applied using a caulking gun. A putty knife is used to smooth the surface of the sealant before it begin~ to cure.

Butyl based coating compositions similar to those disclosed in U.S.

Patent No. 4,593,175 to Bowser et al. have been used as sealants.

In particular, the butyl based composition as described hereinbelow in Table 1 is based on the teachings of the patent and has been u~ed to ~eal the notch area 46 in windshield 10.

TABLE 1 MaterialsAmount (Parts bY Wei~ht~ 1. BUTYL 165 100 2. VISTANEX LM, MS 30 3. STATEX N-550 110 25 4.

ZnO xx4 6 5. HI SIL EP 10 6. UNION CARBIDE A-174 silane 10 7. ESCOREZ 1315 60 8. VM&P NAPHTHA 712 _ _ 2~2~:~72 -- 8 - (1) BUTYL 165 is the registered trademark of Exxon Chemical Co. for an isobutylene-isoprene elastomer (llR).

(2) VISTANEX LM, MS is the registered trademark of Exxon Chemical Company for a hlgh molecular weight polyisobutylene resin.

5 (3) STATEX N-550 is the registered trademark of Columbian Chemical Co. for a general purpose amorphous furnace black.

(4) Zinc oxide xx4 grade i8 manufactured by New Jersey Zinc Co.

(5) HI SIL EP is the registered trademark of PPG Industries, Inc. for a hydrated amorphous silica.

10 (6) UNION CARBIDE A-174 is the registered trademark of Union Carbide Corp. for a silane coupling agent; gamma- methacryoxpropyltrimethoxy silane.

(7) ESCOREZ 1315 is the registered trademark of Exxon Chemical Co.

for a saturated hydrocarbon resin.

15 (8) VM~P NAPHTHA is varnish makers' naphtha; a solvent with a narrow boiling point.

This sealant dries in approximately 5 minutes but still remains tacky. Additional carbon black and/or iller material, such 20 as e.g. hydrated silica, can be added to the formulation to reduce tack. The coating may be applied ln any convenient manner known in the art, e.g. brush, dauber, or rollers. Although not limiting in the invention, the thickness of this sealant i9 preferably about 1 mil (0.025 mm). Since the butyl coating does not fill the notch area 25 46, additional fillers must be used if it is required that the windshield 10 have a flush notch area 46.

Although the sealant 62 has been shown to be a silicone elastomer or butyl based composition, it is expected that other materials may also be used to seal the lead portions 48, 50, and 52 30 in the notch area 46 such as, but not limited to soldering flux and epoxy materials.

In operation, after the windshield assembly 10 is prepressed ~rior to lamination, the interlayer 14 i8 removed from the notch area 46 and the electrical connectore 54, 56, and 58 or any other type of 35 well known connector, are connected in any convenient manner to lead portions 48, 50, and 52, respectively. As an alternative, the 2~172 interlayer 14 can be precut 80 that it does not extend into the notch area 46. The sealant 62 i8 then applied in the notch area 46 and allowed to dry or cure. The assembly 10 is then laminated.

Although the embodiment of the invention illustrated in 5 Figures 1 through 4 show the entire notch area 46 completely filled by the sealant 62, it should be appreciated that only the exposed surface of the lead portions 48, 50, and 52 have to be coated with sealant 62.

Furthermore, it i8 obvious that as more of the exposed surface of the leads 48, 50, and 52 is covered with the sealant 62, 10 the more effective the seal because of the reduced surface area that is available through which the air can enter the windshield 10 via the leads.

Based on the teachings of this disclosure, it should be apparent that the amount of exposed lead area and the lead material 15 porosity, as well as the type of sealant and the temperature/pressure conditions during lamination each contribute to the effectiveness of the sealing arrangement.

In particular, for example, if the laminate is fabricated under lower temperature and/or pressure conditions than those discuss earlier, the sealant material can be less sensitive to 20 these factors and still provide adequate sealing of the notch area.

Furthermore, if the exposed lead area is reduced and/or the porosity of the lead material is reduced, a less effective sealant material can be used to adequately seal the notch area.

The forms of the invention shown and described in this 25 specification represents illustrative preferred embodiments and it is understood that various changes may be made without departing from the spirit of the invention as defined in the following claimed sub~ect matter.