Protective barrier for safety glazing

Abstract

A protective barrier adhered to a curved substrate includes a stack of two or more lenses, each of the two or more lenses including a polyethylene terephthalate (PET) film, a hard coat on a first side of the PET film, and an adhesive layer on a second side of the PET film opposite the first side. The stack of two or more lenses can have a modulation transfer function exhibiting a contrast value greater than 75% for a spatial resolution of 1 line pair per 0.0003 radians at a 65-degree angle of incidence. Heat and pressure can be applied to conform the stack of two or more lenses to the shape of the curved substrate.

Description

Technical Field

[0001] The present disclosure generally relates to safety glazing, and more particularly to a protective barrier applied to the exterior of a vehicle's windshield.

Background Art

[0002] Currently, vehicle windshields are manufactured to include optoelectronic devices such as cameras, rain sensors, proximity sensors, head-up display devices, defrosters, and antennas. This has increased the cost of replacing a cracked windshield by a factor of 10. In addition, after a new windshield is installed, costly calibration procedures must be performed, further increasing the cost associated with replacing the windshield.

[0003] The American National Standards Institute (ANSI) Z26.1-1996 standard, titled "Safety Glazing Materials for Glazing Motor Vehicles and Motor Vehicle Equipment Operating on Land Highways," is a standard that specifies the durability and safety requirements for qualifying materials for vehicle glazing. Among the various tests specified by this standard are transmittance, humidity, heat, impact, fragmentation, penetration, distortion, weathering, haze, and abrasion resistance. Applicable standards such as the Z26.1-1996 standard currently specify the structures of 16 categories of acceptable safety glazing for various locations on a vehicle. The most stringent category is for windshields because visual accuracy, impact resistance, and abrasion resistance from pitting and wiper blades are required, and it is necessary to contain glass fragments to prevent injury to passengers.

[0004] The two basic groups of structural materials for windshields are glass and plastic. According to applicable standards, plastic is only used in vehicles such as motorcycles, and its windshield is only permitted to be 38.1 cm (15 inches) higher than the seat so that the driver can see through it. This is because the plastics available today are soft and wear down easily, reducing the visual accuracy of the windshield after a short service life. Considering these limited uses, abrasion tests for plastic (e.g., test 5.17 as specified in the ANSI Z26.1-1996 standard) require only 100 cycles of Taber wear, which is one-tenth the requirement for glass, which is 1000 cycles of Taber wear. On the other hand, plastic can be a preferred material because it does not produce the sharp shards that glass produces upon impact, and it weighs half as much. Glass is hard and abrasion resistant, but its low tensile strength makes it susceptible to pitting corrosion. In addition, upon impact, glass produces dangerous sharp shards that can injure occupants. To mitigate this safety issue, glass windshields can be laminated with a soft plastic core to hold fragments together and improve penetration resistance.

[0005] As shown in the table below, there are no commercially available safety barrier films for windshields that meet the applicable requirements for one year of weathering (e.g., test 5.16 as specified in the ANSI Z26.1-1996 standard), plastic abrasion (e.g., test 5.17 as specified in the ANSI Z26.1-1996 standard), and glass abrasion (e.g., test 5.18 as specified in the ANSI Z26.1-1996 standard).

[0006] [Table 1] In today's market, existing polymer safety films for protecting glass windows are installed inside buildings or vehicles. When installed externally, these commercially available products do not last more than a few months due to the embrittlement of the polyester substrate. This causes the hard coating on the surface to break and thus the film to break. The durability of safety films installed internally on windows is specified in ANSI Z97.1-2015, entitled "American National Standard for Safety Glazing Materials Used in Buildings - Safety Performance Specifications and Methods of Test". An example of such an internally mounted safety film is the 3M Scotch-shield safety and security window film Ultra Series, which has a thickness of 0.2 mm (8 mil), a peel strength of 2,000 g / 2.54 cm (1 inch), a light transmittance of over 88%, virtually no distortion at a 45-degree incident angle, and abrasion resistance of 5% haze after 100 Taber cycles. Such a film can have a service life of 10 years, but it is not manufactured for external use, and its abrasion resistance does not meet the ANSI Z26 standards for windshield applications (e.g., less than 2% haze after 1,000 Taber cycles).

[0007] In the case of internal mounting of safety films such as the 3M film mentioned above, the glass window itself can provide protection from the UV and IR spectrum. Adding UV inhibitors mixed into the mounting adhesive can be sufficient to provide a long service life for the film (e.g., 10 years) and a hard, coated surface facing the interior. However, the external glass surface will still be susceptible to pitting corrosion due to the low tensile strength of the glass.

[0008] The only commercially available safety film for external use on vehicles traveling on land roads is manufactured by Clear-Plex. According to the commercial specifications published by Clear-Plex and related Patent Documents 1 and 2, the Clear-Plex safety film comprises a 0.1 mm (4 mil) thick PET layer with a hard coating and pressure-sensitive adhesive for attachment, has a peel strength of 1,800 g / 2.54 cm (1 inch), a transmittance of over 87%, virtually no distortion at a 40-degree incident angle, and abrasion resistance of 0.5% haze after 100 cycles before weathering. Clear-Plex makes no assertions regarding tests performed against the ANSI Z26 standard. While this haze value may be acceptable for plastics, the commercial specifications do not include a Taber test after one year of weathering.

[0009] Other products exist that can be mounted on the outside of the windshield of vehicles that do not travel on roads, such as racing vehicles or military vehicles. One such product by Optics, Inc. is a 4-layer × 0.1 mm (4 mil) safety film (hereafter "RO4×4"), which has a thickness of 0.45 mm (18 mil) (four layers of 0.1 mm (4 mil) thick PET with a hard coat and pressure-sensitive adhesive on each layer), a peel strength of 100 g / 2.54 cm (1 inch) for the top layer and 400 g / 2.54 cm (1 inch) for the base layer, a transmittance of over 88%, the result of the Z26 haze test #5.17 being less than 1.5% haze before weathering, the result of the Z26 abrasion test #5.16 being less than 5% haze after 100 Taber cycles, and the result of the Z26 weathering test #5.15 being less than 4 months per layer (for example, transmittance is significantly reduced after 3-4 months of weathering, resulting in haze of approximately 20-50% without Taber testing). RO4x4 products are designed for a short service life (each layer is replaced when it peels off during use) and therefore do not possess the weather durability or abrasion resistance required to meet the Z26 standard for windshields of vehicles traveling on land roads. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 7,992,917 [Patent Document 2] U.S. Patent No. 9,023,162 [Overview of the project] [Means for solving the problem]

[0011] This disclosure envisions various systems and methods for overcoming the aforementioned shortcomings associated with the relevant technologies. According to one or more aspects of this disclosure, an external barrier can be added to both glass and plastic windshields to improve abrasion resistance, pitting corrosion, and impact cracking. The external barrier not only enhances occupant safety while reducing the carbon footprint of replacing glass windshields, but can also reduce the biggest insurance cost for domestic fleet vehicles, namely windshield damage.

[0012] One embodiment of the embodiments of the present disclosure is a protective barrier that can be fixed to a curved substrate. The protective barrier may comprise a laminate of two or more lenses, each of which comprises a polyethylene terephthalate (PET) film, a hard coating on a first side of the PET film, and an adhesive layer on a second side of the PET film opposite to the first side. The laminate of two or more lenses may have a modulation transfer function that exhibits a contrast value greater than 75% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees.

[0013] The modulation transfer function of a stack of two or more lenses can exhibit a contrast value exceeding 70% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 70 degrees. The modulation transfer function of a stack of two or more lenses can exhibit a contrast value exceeding 85% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 55 degrees. The modulation transfer function of a stack of two or more lenses can exhibit a contrast value exceeding 90% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 45 degrees.

[0014] Each PET film of two or more lenses can have a modulation transfer function that exhibits a contrast value of more than 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees.

[0015] Each of the two or more lenses may have a thickness of 0.05 to 0.1 mm (2 to 4 mils). Each PET film of two or more lenses may contain a UV stabilizer. Each hard coating and adhesive layer of two or more lenses may also contain a UV stabilizer.

[0016] Each PET film of two or more lenses may have a longitudinal shrinkage of 0.6% to 1.8% and a transverse shrinkage of 0.3% to 1.1% at 150°C. Another embodiment of the embodiments of the present disclosure is a method. The method may comprise the steps of laminating two or more lenses, each of which comprises a polyethylene terephthalate (PET) film, a hard coating on a first side of the PET film, and an adhesive layer on a second side of the PET film opposite to the first side. The laminate of the two or more lenses may have a modulation transfer function that exhibits a contrast value greater than 75% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees. The method may comprise the steps of placing the laminate of the two or more lenses on a curved substrate while bringing the adhesive of the first lens of the laminate into contact with the curved substrate, and applying heat and pressure to conform the laminate of the two or more lenses to the shape of the curved substrate.

[0017] The process of applying heat and pressure may be performed at least partially before each adhesive layer of two or more lenses is completely cured. The process of applying heat and pressure may be performed at least partially before each adhesive layer of two or more lenses exceeds a peel strength of 25 grams per 2.54 cm (1 inch), which is determined as a specific load per unit width required for peeling.

[0018] The method may include a step of peeling off the outermost lens of a laminate of two or more lenses after a step of applying heat and pressure. The adhesive between the first lens of a laminate of two or more lenses may be stronger than the adhesive between the outermost lens of the laminate of two or more lenses.

[0019] The modulation transfer function of a stack of two or more lenses can exhibit a contrast value exceeding 70% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 70 degrees.

[0020] Each PET film of two or more lenses can have a modulation transfer function that exhibits a contrast value of more than 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees.

[0021] Each of the two or more lenses may have a thickness of 0.05 to 0.1 mm (2 to 4 mils). Each of the PET films of the two or more lenses can contain a UV stabilizer. Each of the hard coat and adhesive layers of the two or more lenses can contain a UV stabilizer.

[0022] Each of the PET films of the two or more lenses can have a longitudinal shrinkage of 0.6% to 1.8% and a transverse shrinkage of 0.3% to 1.1% at 150 °C. These and other features and advantages of the various embodiments disclosed in the present disclosure will be better understood with reference to the following description and drawings, in which like numbers refer to like parts throughout the figures.

Brief Description of the Drawings

[0023] [Figure 1] Cross-sectional view of a protective barrier according to an embodiment of the present disclosure. [Figure 2] Images and graphs representing visual distortion in a safety film. [Figure 3] Graph representing modulation transfer function (MTF) data for five samples at different angles of incidence. [Figure 4] Graph representing the windshield damage rate for different film thicknesses. [Figure 5] Diagram showing a protective barrier placed on a vehicle windshield at the start of a process of applying heat and pressure to mold the protective barrier to the shape of the windshield. [Figure 6] Diagram showing the protective barrier on the windshield at the end of the process of applying heat and pressure. [Figure 7] Diagram showing the protective barrier after being trimmed to fit the windshield. [Figure 8] Exemplary operation flow according to an embodiment of the present disclosure.

Modes for Carrying Out the Invention

[0024] This disclosure encompasses various embodiments of protective barriers that can be fixed to curved substrates, as well as methods for manufacturing, installing, and using them. The detailed description below, in relation to the accompanying figures, is intended to describe some currently conceivable embodiments and is not intended to represent the only form in which this disclosure may be developed or utilized. This description describes the functions and features related to the illustrated embodiments. However, it should be understood that the same or equivalent functions may be achieved by different embodiments, which are also intended to be covered within the scope of this disclosure. Furthermore, it should be understood that correlational terms such as first and second are used solely to distinguish such entities from one another, without necessarily requiring or implying an actual relationship in order between the entities.

[0025] Figure 1 is a cross-sectional view of a protective barrier 100 according to one embodiment of the present disclosure. The protective barrier 100 may be fixed to a curved substrate 10, such as a car windshield, and may comprise a laminate of two or more lenses 110, such as lenses 110a, 110b, and 110c shown in Figure 1. Each lens 110 may include a polyethylene terephthalate (PET) film 112, a hard coating 114 on a first side of the PET film 112, and an adhesive layer 116 on a second side of the PET film 112 opposite the first side for bonding the lenses 110 to each other and to the curved substrate 10. The laminate of lenses 110 may have a modulation transfer function at an incident angle of 65 degrees that exhibits a contrast value of more than 75% for spatial resolution of one line pair per 0.0003 radians, which is the approximate resolution of the human eye. By controlling the modulation transfer function of the lens 110 laminate in this way, a protective barrier 100 can be created that is substantially distortion-free (e.g., displacement of less than 0.00045 radians) when viewed at a typical incident angle of an automobile windshield (e.g., 60-70 degrees), and furthermore, the total thickness of this protective barrier 100 is sufficient to withstand impact damage at automobile speeds. In this way, the protective barrier 100 can prevent cracking and pitting corrosion of the windshield 10 beneath it while meeting the durability requirements for use of windshields on the road.

[0026] Distortion is a visual accuracy error caused by displaced objects within a distant field of view (e.g., 12.2 meters to 304.8 meters (40 feet to 1000 feet)). Safety glazing may have localized zones that cause object displacement perceived as distortion, where objects may appear to jump from one position to another when viewed from slightly different positions or angles. Conventionally, distortion is determined only qualitatively, for example, by test 5.15 specified in the ANSI Z26.1-1996 standard. This test uses a shadow graph in a long tunnel with a collimated light source and a white screen. The technician places the sample 38.1 cm (15 inches) from the screen in the optical path at a normal incidence angle. The technician then looks for artifacts in dark and bright areas caused by distortion. The test does not have a quantitative criterion and does not address distortion at high incidence angles (e.g., 60-70 degrees) used in modern car windshields.

[0027] Ideally, distortion should be minimized to match the resolution of the human eye with 20 / 20 vision, which is approximately one line pair per 0.0003 radians. For example, if an object is displaced by 0.0006 radians, the eye perceives the change in its location as distortion. For distortion to be considered virtually distortion-free, any object displacement must be reduced to a level below the resolution capability of the human eye. On the other hand, when safety glazing is viewed at high angles of incidence (e.g., 60-70 degrees), the optical thickness increases as a cosine function of the angle according to Snell's law. This can amplify the distortion effect, especially in the case of safety film thicknesses exceeding approximately 0.1 mm (4 mils), which may be required to withstand impact damage at automotive speeds.

[0028] Figure 2 shows images and graphs representing visual distortion in the safety film 210. To quantitatively measure the distortion, it is assumed that the modulation transfer function of a test material such as the safety film 210 can be evaluated at a fixed spatial frequency of 0.0003 radians, corresponding to the resolution of the eye of a person with 20 / 20 vision. To achieve this, as shown in the upper part of Figure 2, an image of a test pattern 220, such as a checkerboard pattern or target line pairs spaced 0.0003 radians apart, can be captured through the film 210 at a desired angle of incidence (e.g., 65 degrees in Figure 2). The lower part of Figure 2 shows the corresponding modulation transfer function data, which represents contrast as a function of the horizontal position of the data relative to a given cross-section, representing a single horizontal slice of the image. As can be seen in the figure, the modulation transfer function data exhibits reduced contrast, corresponding to distorted line pairs, within the area of ​​the test pattern 220 viewed through the film 210. In some places, the modulation transfer function data exhibits low contrast, comparable to the complete loss of the image.

[0029] A test setup like that shown in Figure 2 may be used to evaluate material and process parameters for manufacturing the protective barrier 100 described herein. In particular, by using such a test setup and / or test results deriveable therefrom, appropriate material and process parameters may be selected and / or adjusted to control the modulation transfer function of the lens 110 laminate at one or more desired incidence angles. In this regard, it is assumed that the modulation transfer function of the lens 110 laminate may be controlled in accordance with the methodology described in U.S. Provisional Patent Application No. 62 / 942,943, filed December 3, 2019, entitled “Method and Apparatus for Reducing Non-Normal Incidence Distortion in Glazing Films,” held by the present applicant, the entirety of which is expressly incorporated herein.

[0030] For example, at any or all stages of producing the lens 110 laminate (e.g., during the formation of the PET film 112 by melting the resin, extruding the molten resin through a die to produce a film, and cooling the film, during the application of the hard coat 114, during the application of the adhesive layer 116, etc.), one or more images of the test pattern 220 may be captured through the lens 110 or the resulting lens 110 laminate. The images may be captured, for example, by orienting an image capture device through the lens 110 or a roll-to-roll processing web containing the lens 110 laminate at one or more desired incident angles. Based on such images, the computer can calculate MTF data and generate an output that can be used to adjust process parameters found to affect the modulation transfer function of the lens 110 or the lens 110 laminate, such as the temperature setting of the heater used to melt the resin (e.g., the absolute or relative temperature of the gradient or profile of multiple heated areas of the extruder assembly), the rotation speed of the extruder screw (which can determine the melting time and the degree of resin mixing), the rotation speed of one or more rollers (which can determine the cooling time and / or the degree of force acting on the polymer film during cooling), the flow rate, the deposition rate, or other application speed of the hard coat 114 or adhesive layer 116, and / or the rate at which the lens 110 is laminated. For example, it is assumed that in some cases the PET film 112 may be prefabricated and selected to match its known MTF data, while the modulation transfer function of the lens 110 laminate may be actively controlled during the application of the hard coat 114 and / or adhesive layer 116 and the lamination of the lens 110. In other cases, the PET film 112 may also be manufactured while actively controlling its modulation transfer function. The computer output may include, for example, feedback signals to automatically adjust relevant process parameters without user input in a continuous or batch-to-batch process.As another example, the output may include a visual representation of the data to be interpreted by the operator, who will then manually make any necessary adjustments.

[0031] Figure 3 is a graph showing the modulation transfer function data for five samples at different incidence angles. To produce the exemplary data in Figure 3, the modulation transfer function data described in Figure 2 can be taken in increments of 10 degrees from the normal (zero degrees) up to an incidence angle of 70 degrees. It is assumed that the data can be normalized to the modulation transfer function value representing a windshield without any protective barrier. Since many car windshields are installed at a 65-degree slope, additional data can be captured at 65 degrees, or similarly at any other angle of particular interest. As shown in Figure 3 by the solid line with triangular data points, the T-ll 3×3 labeled sample can serve as a laminate of the lens 110 of the protective barrier 100 described herein, having a modulation transfer function that exhibits a contrast value of more than 75% for a spatial resolution of one line pair per 0.0003 radians at an incidence angle of 65 degrees. As noted above, 65 degrees is the slope of a typical windshield. However, since drivers must observe objects both above and below eye level, minimizing distortion at larger or smaller incident angles can also be advantageous. To achieve this, as shown in the example of a T-ll 3×3 labeled sample, the modulation transfer function of the lens 110 laminate can further exhibit contrast values ​​exceeding 70% at an incident angle of 70 degrees, exceeding 85% at an incident angle of 55 degrees, and / or exceeding 90% at an incident angle of 45 degrees, for the same spatial resolution of one line pair per 0.0003 radians. A protective barrier 100 having such a controlled modulation transfer function can be applied to a normal automobile windshield without distorting the position of objects seen by the driver.

[0032] An example of a prefabricated PET film 112 that can be selected to match the MTF known for use in the lens 110 laminate is a PET film 112 having a modulation transfer function that itself exhibits a contrast value of over 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees. One such material is a film sold by DuPont Teijin Films under the name "MELINEX® 454," represented in Figure 3 by a solid line with circular data points. A dotted line with diamond data points represents a sample of a lens 110 fabricated using this film as the PET film 112, with its hard coat 114 and adhesive layer 116 applied under MTF control as described above. That is, during the process of applying the hard coat 114 and adhesive layer 116, one or more process parameters were selected or adjusted (continuously or batch-to-batch) to control the modulation transfer function at one or more incident angles, for example, to maintain a contrast value greater than 75% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees. As can be seen in the figure, the MTF data of this sample representing only a single lens 110 according to the disclosed subject is substantially similar to that of the T-ll 3×3 labeled sample representing the entire protective barrier 100 including the laminate of such lens 110, despite the increasing thickness of the laminate. This can be achieved by laminating the lens 110 under MTF control as described above.

[0033] In contrast, the T-8 3×3 labeled sample, represented by a dashed line with square data points in Figure 3, was produced without MTF control. Despite being a three-layer laminate with a similar structure, its optical properties are clearly inferior at the high incidence angles typically used in car windshields. For example, as shown in Figure 3, the contrast value at an incidence angle of 65 degrees is less than 60%. Such a product can only be used in applications with incidence angles less than 60 degrees, where the contrast value remains above 75%. The RO4×4 labeled sample, represented by a solid line with circular data points and corresponding to the RO4×4 product described above, is a four-layer laminate similarly produced without MTF control. This product exhibits even worse MTF data at the relevant incidence angles and can practically only be used in applications with incidence angles less than 50 degrees, beyond which the contrast value drops below 75%. Distortion has been found to become significant below a contrast value of 75%.

[0034] Figure 4 is a graph showing windshield damage rates for different film thicknesses. The exemplary data in Figure 4 is based on the results of a glass shattering study conducted by O'Gara-Hess Armor Company for the U.S. military. Layers of PET were mounted on ballistic glass, increasing in thickness, and 1.905 cm (3 / 4 inch) steel balls were fired at the glass at different speeds. The data shows the minimum speed at which the glass cracked for each PET film thickness. In light of the data shown in Figure 4, it is assumed that the protective barrier 100 described herein must be 0.2 mm (8 mils) or thicker, for example, 0.2 mm (8 mils) to 0.4 mm (16 mils), preferably 0.25 mm (10 mils) to 0.4 mm (16 mils), to protect a glass windshield at a common driving speed of 72.4 to 104.6 km / h (45 to 65 miles). For example, the protective barrier 100 may include two to four lenses 110 (for example, lenses 110a, 110b, and 110c as shown in Figure 1), each of which has a thickness of 0.1 mm (4 mil).

[0035] Typically, increasing the thickness required to protect a glass windshield imposes several challenges in creating the protective barrier 100. As described above, for example, increasing the thickness can amplify distortion at high angles of incidence (e.g., 60-70 degrees). This challenge can be overcome by controlling the modulation transfer function of the protective barrier 100 as described above, thereby creating a laminate of lenses 110 having a modulation transfer function that exhibits a contrast value of more than 75% for a spatial resolution of one line pair per 0.0003 radians at an angle of incidence, for example, 65 degrees. Additional challenges imposed by the thickness of the protective barrier 100 include producing a product that can be successfully molded to a curved substrate 10 (e.g., an automobile windshield), achieving a high degree of weather resistance and abrasion resistance as well as reduced haze, and maintaining a reasonable service life. Each of these challenges can be overcome by the disclosed protective barrier 100, as described in more detail below.

[0036] Figure 5 shows the protective barrier 100 placed on the windshield 10 of the car 20 at the start of the process of applying heat and pressure to mold the protective barrier 10 to the shape of the windshield 10 (the windshield 10 which serves as the substrate 10 shown in Figure 1). The protective barrier 100 can be bonded to the windshield 10 by placing the adhesive layer 116 of the first (bottommost) lens 110a of the laminate into contact with the windshield 10 (see Figure 1). The adhesive layer 116 of the first lens 110a may be a dry mount adhesive, for example, as disclosed in Wilson's U.S. Patent No. 9,295,297, published March 29, 2016, entitled “Adhesive Mountable Stack of Removable Layers,” the entire contents of which are expressly incorporated herein. Alternatively, a wet-mount adhesive may be used, for example, as disclosed in Wilson's U.S. Patent No. 9,128,545, issued on September 8, 2015, entitled “Touch Screen Shield,” the entire contents of which are expressly incorporated herein by reference. The adhesive may be an acrylic adhesive, such as an acrylic pressure-sensitive adhesive (PSA).

[0037] Because most car windshields exhibit a composite curvature, the protective barrier 100 must be compressed within the upper and lower corners to conform to the windshield 10. Since the protective barrier 100 can be flat (for example, manufactured in a roll-to-roll process), a laminate of two or more lenses 110 will not initially conform to the curved shape of the windshield 10, resulting in areas of stronger or weaker adhesion and potentially creating air pockets / bubbles between the lens 110 laminate and the windshield. Therefore, heat and pressure may be applied using a heater 30, such as a high-temperature air source (e.g., a heat gun or blow dryer) or an infrared heater, to conform the lens 110 laminate to the shape of the windshield 10. Simultaneously, pressure may be applied to the lens 110 laminate using a card or squeegee. In some cases, the protective barrier 100 can be applied using a sacrificial layer that acts as a female mold cavity, sandwiching the lens 110 laminate between the sacrificial layer and the windshield 10, as described in U.S. Patent Application No. 16 / 778,928, filed on 31 January 2020 and titled “THERMOFORM WINDSHIELD STACK WITH INTEGRATED FORMABLE MOLD,” held by the present patent holder, the entire contents of which are expressly incorporated herein by reference.

[0038] When the installer heats and presses down on the lens 110 laminate, the lens 110 laminate can shrink and expand to follow the contour of the curved substrate 10 (windshield). For commercially available films with a thickness of only 0.05 mm (2 mils), achieving the required shrinkage can be relatively easy. On the other hand, monolithic films thicker than 0.2 mm (8 mils) wrinkle and become unusable before they can conform to the windshield. In light of this challenge, the protective barrier 100 described herein uses multiple thin lenses 110 (for example, each with a thickness of 0.05–0.1 mm (2–4 mils)) that shrink well individually. The adhesive layer 116 between the lenses 110 of the laminate, which may be the same acrylic adhesive, can be partially cured to produce extremely low peel strength (for example, 15–25 g / 2.54 cm (1 inch)) and high elasticity. Therefore, each individual lens 110 of the laminate can be in a "floating" relationship with one another, thereby allowing shrinkage to occur without wrinkles in any of the lenses 110. When the protective barrier 100 is installed and, for example, exposed to sunlight, the adhesive layer 116 hardens, increasing the peel and bond strength (for example, by 3 to 5 times) and promoting a long service life. The peel strength after initial weathering may be, for example, 100-150 g / 2.54 cm (1 inch).

[0039] Figure 6 shows the protective barrier 100 of the windshield 10 at the end of the process of applying heat and pressure. At this stage, the desired shrinkage has occurred, and the lens 110 laminate of the protective barrier 100 is molded to the curved shape of the windshield 10 without air pockets / bubbles. The technical specifications of the PET film include two shrinkage axes with different values, designated as longitudinal ("MD") and transverse ("TD"). The longitudinal direction refers to the direction of the roll stock in the roll-to-roll process used to produce the PET film, and the transverse direction refers to the direction transverse to the roll direction. It is assumed that the PET film 112 of the protective barrier 100 laminate may have a longitudinal shrinkage of 0.6% to 1.8% (preferably 0.8% to 1.0%) and a transverse shrinkage of 0.3% to 1.1% (preferably 0.5% to 0.6%) at 150°C. PET films with a longitudinal shrinkage of less than 0.6% or a transverse shrinkage of less than 0.3% do not shrink enough to fit a windshield. On the other hand, if the shrinkage is too large, for example, more than 1.8% in the longitudinal direction or more than 1.1% in the transverse direction, it becomes extremely difficult for the installer to control the shrinkage in a manually operated procedure (for example, using the heater 30 as described above).

[0040] Figure 7 shows a protective barrier 100 containing the laminate of lens 110 after the laminate of transparent lens 110 has been trimmed to fit the windshield 10. The laminate of lens 110 can be trimmed using a utility knife or box cutter, etc., with a stainless steel blade (a carbon blade may damage the windshield 10). The resulting trimmed laminate of lens 110 may be virtually invisible because it conforms to the shape of the windshield 10 below it (although the tinting of the windshield may be altered, as in the case of window tinting).

[0041] In addition to improving moldability as described above, using multiple thin lenses 110 (e.g., 0.05–0.1 mm (2–4 mil) thick) instead of a single monolithic film can enable sufficiently reduced haze suitable for use in automotive windshields. Typically, the haze of a PET film has two components: scattering of incident light at the surface and dispersion of incident light within the bulk material. The latter bulk component increases with the thickness of the PET film, for example, as shown in the table below.

[0042] [Table 2] However, when multiple PET films are laminated, the effect is not additive, and the three layers add only about 0.1-0.2% haze in total. On the other hand, the surface components of the haze are mitigated by the addition of a hard coat or adhesive. By structuring the protective barrier 100 as a laminate of lenses 110 containing relatively thin PET films 112 rather than a single large PET film, it becomes possible to achieve reduced haze while the protective barrier 100 can be thick enough (e.g., 0.2 mm (8 mil) or more) to withstand impacts at automotive speeds as described above. In particular, the protective barrier 100 described herein, comprising a laminate of two or more lenses 110 each containing a PET film 112 having a hard coat 114 and an adhesive layer 116, can achieve an initial haze (pre-weathering) of less than 1% (preferably less than 0.6%), making it suitable for use on automotive windshields.

[0043] Weathering is approximately 300 MJ / m 2 Ultraviolet radiation (for example, 301 MJ / m³ according to applicable standards) 2 Alternatively, 306 MJ / m 2 , or 70 MJ / m³ per 3-month period 2 Estimated from 280 MJ / m 2The requirements for one year of exposure in the Arizona climate may be specified according to standards such as ANSI Z26.1-1996. To simulate one year of exposure in the Arizona climate outdoors (Arizona is chosen as a weathering benchmark due to its high temperatures and high-intensity sunlight), a natural light concentrator may be used, such as one conforming to the American Society for Testing and Materials (ASTM) G90 standard, entitled "Standard Practice for Performing Accelerated Outdoor Weathering of Materials Using Concentrated Natural Sunlight". The haze and abrasion resistance of protective barrier 100 may be measured before and after the exposure cycle.

[0044] In the comparative example of the RO4x4 product described above, UV stabilizers such as UV-absorbing compounds are mixed into the hard coat and adhesive of each of the four layers. After 6 months of Arizona exposure, the outermost layer becomes unusable due to loss of transmittance, increased haze, and loss of hardness. Because the hard coat contains many UV inhibitors, the hard coat loses hardness and crumbles, thereby yellowing and brittle the PET core beneath the outermost layer. The resulting haze can exceed 20%.

[0045] In contrast to RO4×4 products, the protective barrier 100 described herein can be produced by each PET film 112 of two or more lenses 110 containing a UV stabilizer, such as a hydroxyphenyl-benzotriazole or hydroxyphenyl-triazine UV absorber. The hard coat 114 and / or adhesive layer 116 of each lens 110 may also contain a UV stabilizer. Since the UV stabilizer is mixed within the PET film 112, a reduced amount of UV stabilizer can be used in the hard coat 114 and adhesive layer 116, thereby allowing the hard coat 114 to maintain its hardness without sacrificing UV stability. Dispersing the UV stabilizer throughout all components makes for an extremely weather-resistant assembly, thereby allowing the protective barrier 100 to withstand more than one year of exposure to the Arizona sun at ANSI G90 and appear very good, with reduced haze and minimal yellowing after weathering. The protective barrier 100 can have abrasion resistance over 1,000 Taber cycles with, for example, less than 1% haze before weathering and less than 4% haze (preferably less than 2%) after weathering.

[0046] While the protective barrier 100 may have sufficient weather resistance, eventually the outermost lens 110 (for example, lens 110c in the three-layer example in Figure 1) may become damaged. If the outermost lens 110 deteriorates to an unacceptable degree over time (e.g., due to chipping, oxidation, etc.) during the lifespan of the vehicle's windshield or other window, the outermost lens 110 can be easily peeled off and removed to expose a new lens 110 underneath. To achieve this, the adhesive layer 116 of the innermost lens 110a (see Figure 1) may be stronger than the adhesive layer 116 used for the other lenses 110 (in some cases, the strength of the adhesive layer 116 may decrease further with each additional lens 110). In this way, the innermost lens 110a can remain adhered to the windshield or other curved substrate 10 while another lens 110 is being peeled off. For example, the innermost lens 110a may be intended to remain on the curved substrate 10 for the lifespan of the protective barrier 100, in which case it is assumed that the additional lenses 110 can be removed if necessary. Accordingly, each such additional lens 110 other than the first one 110a may be provided with a tab or other means for easy removal during the lifespan of the protective barrier 100. By enabling the removal of the outermost lens 110 of the lens 110 laminate in this manner, the practical lifespan of the protective barrier 100 can be extended.

[0047] Figure 8 is an exemplary operational flow according to one embodiment of the present disclosure. The operational flow in Figure 8 can serve as an exemplary method for manufacturing, installing, and using a protective barrier 100 including a laminate of lenses 110 shown in Figure 1. The operational flow can begin with a step of providing PET films 112 to be used as the core of two or more lenses 110 (step 810). As described above, each PET film 112 of the lenses 110 may be selected to match specific MTF data, such as a contrast value greater than 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees, and may be, for example, a film sold by DuPont Teijin Films under the name "MELINEX® 454". Alternatively, each PET film 112 of the lenses 110 may be manufactured in a continuous or batch-to-batch process with active monitoring of MTF data as described above. In this regard, the process of providing the PET film 112 may include, for example, melting a resin, extruding the molten resin through a die to produce a polymer film, and cooling the polymer film. A hard coat 114 may be deposited on a first side of the PET film 112 (step 820), preferably by wet deposition, but may be applied according to any suitable method including spin coating, dip coating, or vacuum deposition. Before and after the application of the hard coat 114, the PET film 112 may be coated on its opposite side with adhesive 116 (step 830). These three elements of the PET film 112, the hard coat 114, and the adhesive 116 may constitute one of the lenses 110 described herein, which can be laminated to produce a protective barrier 100 (step 840).

[0048] During any or all of steps 810-840, the operational flow may include a step (step 850) to control the MTF of the lens 110 laminate. The MTF of the lens 110 laminate may be controlled, for example, to exhibit a contrast value greater than 75% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees. As described above, such control may be achieved by selecting a suitable prefabricated PET film 112 in step 810. Alternatively, or additionally, MTF control may be achieved by actively monitoring and adjusting process parameters (e.g., roller speed in a roll-to-roll process) while fabricating the PET film 112 in step 810, depositing the hard coat 114 in step 820, applying the adhesive layer 116 in step 830, and / or laminating two or more lenses 110 in step 840. Such active monitoring and adjustment of process parameters may include continuous processes involving a feedback loop of monitored MTF data, and / or batch-to-batch processes with MTF measurements manually or automatically fed back from preceding batches.

[0049] Once the protective barrier 100 comprising the lens 110 laminate is assembled, the operation flow may proceed to the step of installing the protective barrier 100 onto a curved substrate 10, such as the windshield of a car 20, as shown in Figures 5-7. As described above, in order to avoid wrinkling, the installation step may be performed while the adhesive layer 116 is only partially cured, allowing the lens 110 to "float" on the adhesive and mold to the shape of the substrate 10 individually rather than as a single integrated structure. Referring to the operation flow in Figure 8, the protective barrier 100 including the lens 110 laminate may be placed on the windshield or other curved substrate 10, with the adhesive layer 116 of the lowest lens 110a (see Figure 1) in contact with the curved substrate 10 (step 860). To facilitate installation, the protective barrier 100 may be roughly cut (for example, using an electric film cutter) so as not to extend too far outside the windshield 10. The operation flow may follow a step (step 870) of applying heat and pressure to conform the laminate of two or more lenses 110 to the shape of the curved substrate 10, as described in relation to Figures 5 and 6. In particular, the step of applying heat and pressure may be performed at least partially before each adhesive layer 116 of the two or more lenses 110 is fully cured, for example, before the adhesive layer 116 exceeds a peel strength of 25 grams per 2.54 cm (1 inch), which is determined as a specific load per unit width required for peeling. The protective barrier 100 may be fully conformed to the shape of the curved substrate 10 before the adhesive layer 116 is fully cured.

[0050] After the protective barrier 100 has cooled, the installation is completed in a step of performing a final trim, as described in relation to Figure 7. The protective barrier 100, including the laminate of lens 110, is then uniformly formed and fixed to the windshield surface. By installing the protective barrier 100 in this manner, it is possible to reduce cracking and abrasion damage to the windshield 10 caused by stone impacts, while complying with applicable standards for light transmission, abrasion resistance, haze, and distortion of the windshield of a vehicle operating on land roads.

[0051] As described above, it is conceivable that a protective barrier 100 having two or more lenses 110 may allow the outermost lens 110 to be peeled off and removed, exposing the unused surface of the lens 110 below. In this regard, the operation flow in Figure 8 can be continued for the lifespan of the protective barrier 100 installed on the vehicle 20. When the outermost lens 110 deteriorates to an unacceptable degree over time (for example, after 6 months, 1 year, or after scratches from the wiper blade have begun), this lens can be peeled off to expose the next lens 110 underneath (step 880). The timing of peeling off the outermost lens 110 can be determined by the specific climate in which the protective barrier 100 is used, for example, some climates involve more exposure to sunlight, while others require more frequent use of the wiper blade.

[0052] The above description is given as an example, not as an limitation. With regard to the above disclosure, those skilled in the art can devise variations that fall within the scope and spirit of the invention disclosed herein. Furthermore, the various features of the embodiments disclosed herein can be used individually or in variable combinations of each other, and are not intended to be limited to the specific combinations described herein. Accordingly, the claims are not limited by the illustrated embodiments.

Claims

1. A protective barrier that can be fixed to a curved substrate, the protective barrier comprising a laminate of two or more lenses, each of the two or more lenses comprising a polyethylene terephthalate (PET) film, a hard coating on a first side of the PET film, and an adhesive layer on a second side of the PET film opposite to the first side, wherein the PET film of each of the two or more lenses has a modulation transfer function that exhibits a contrast value greater than 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees.

2. The protective barrier according to claim 1, wherein each of the two or more lenses has a thickness of 0.05 to 0.1 mm (2 to 4 mils).

3. The protective barrier according to claim 1, wherein each of the two or more lenses' PET films contains a UV stabilizer.

4. The protective barrier according to claim 2, wherein the hard coating and adhesive layer of each of the two or more lenses contains a UV stabilizer.

5. The protective barrier according to claim 1, wherein each of the two or more lenses' PET films has a longitudinal shrinkage of 0.6% to 1.8% and a transverse shrinkage of 0.3% to 1.1% at 150°C.

6. A step of laminating two or more lenses, wherein each of the two or more lenses comprises a polyethylene terephthalate (PET) film, a hard coating on a first side of the PET film, and an adhesive layer on a second side of the PET film opposite to the first side, and the PET film of each of the two or more lenses has a modulation transfer function that exhibits a contrast value greater than 80% for a spatial resolution of one line pair per 0.0003 radians at an incident angle of 65 degrees. The steps include placing the laminate of two or more lenses on the curved substrate while bringing the adhesive of the first lens of the laminate into contact with the curved substrate, A method comprising the steps of applying heat and pressure to conform the laminate of the two or more lenses to the shape of the curved substrate.

7. The method according to claim 6, wherein the step of applying heat and pressure is performed at least partially before the adhesive layer of each of the two or more lenses is completely cured.

8. The method according to claim 7, wherein the step of applying heat and pressure is performed at least partially before the adhesive layer of each of the two or more lenses exceeds a peel strength of 25 grams per 2.54 cm (1 inch), which is determined as a specific load per unit width required for peeling.

9. The method according to claim 6, further comprising the step of peeling off the outermost lens of the laminate of the two or more lenses after the step of applying heat and pressure.

10. The method according to claim 6, wherein the adhesive of the first lens in the laminate of the two or more lenses is stronger than the adhesive of the outermost lens in the laminate of the two or more lenses.

11. The method according to claim 6, wherein each of the two or more lenses has a thickness of 0.05 to 0.1 mm (2 to 4 mils).

12. The method according to claim 6, wherein each of the two or more lenses' PET films contains a UV stabilizer.

13. The method according to claim 12, wherein the hard coating and adhesive layer of each of the two or more lenses contain a UV stabilizer.

14. The method according to claim 6, wherein each of the two or more lenses has a longitudinal shrinkage of 0.6% to 1.8% and a transverse shrinkage of 0.3% to 1.1% at 150°C.

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