Textured midlayer

Abstract

In certain embodiments, the present invention provides a PVB interlayer sheet having a surface topography on at least one surface characterized by a relatively low profile and a controlled, collapsible surface roughness profile (on exposure to heat) with a total number of surface peaks significantly greater than negative peaks (valleys) and with peak spacing slightly more distant than typically found in embossed PVB interlayers.Thus, the PVB interlayer sheet of the present invention provides extremely good initial contact and adhesion of the PVB to the glass surface when compared to other surface designs, while leaving virtually no residual air after the first nip in conventional glass lamination processes.The PVB interlayer sheet of the present invention also exhibits a wide degassing window, which allows it to better withstand temperature and process changes.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This invention is in the field of polymer interlayers useful in safety glass applications. [Background technology]

[0002]

[0002] Poly(vinyl butyral) (PVB) is a poly(vinyl acetal) commonly used in the manufacture of light-transmitting laminates, such as safety glass or architectural glass, or polymer sheets that can be used as interlayers in polymer laminates. Safety glass typically refers to a transparent laminate comprising a poly(vinyl butyral) sheet placed between two panes of glass. Safety glass is often used to provide a transparent barrier in architectural and automotive openings. Its primary function is to absorb energy caused by, for example, an impact from an object without penetrating through the opening.

[0003]

[0003] Safety glass can be formed by assembling two layers of glass and a plastic interlayer, such as poly(vinyl butyral), into a pre-press, bonding them into a pre-laminate, and finishing them into an optically clear laminate. The assembly steps can include placing a piece of glass, laminating a poly(vinyl butyral) sheet onto the glass, placing a second piece of glass onto the poly(vinyl butyral) sheet, and trimming the excess poly(vinyl butyral) to the periphery of the glass layers.

[0004]

[0004] PVB interlayers can be laminated between glass using techniques known in the art. A typical glass lamination process includes the following steps: (1) assembling two substrates (e.g., glass) and an interlayer; (2) heating the assembly by short-term infrared (IR) radiation or convection; (3) passing the assembly through pressure nip rolls during a first degassing step; (4) heating the assembly a second time to about 50°C to about 120°C to provide a temporary bond to the assembly sufficient to seal the edges of the interlayer; (5) passing the assembly through a second pressure nip roll to further seal the edges of the interlayer and make it more manageable; and (6) autoclaving the assembly for about 30 to 90 minutes at a temperature between 135°C and 150°C and a pressure between 1034 kPag (150 psig) and 1378 kPag (200 psig). Other means known in the art and commercially practiced for degassing the interlayer-glass interface (steps 2-5) include vacuum bagging and vacuum ring methods, in which a vacuum is applied to remove the air. Alternative lamination methods include the use of a vacuum laminator, which first degasses the assembly and then finishes the laminate at a sufficiently high temperature and vacuum.

[0005] Lamination systems that utilize only relatively short nip (or squeeze) roll processes without vacuum can sometimes result in significant defects that are visible in the final laminated glass product. One of these undesirable defects, called "ice flowers," which nucleate and expand at high temperatures, is formed by trapped air. Therefore, there is a need for improved materials and methods that reduce or eliminate trapped air in these shortened processes, and thus reduce or eliminate the occurrence of such defects.

[0006]

[0006] Ice flower defects are rare, but they are costly defects to laminators and automotive OEMs because they are usually not discovered until after the windshield is installed in the vehicle, where it is part of a much more valuable structure. Ice flower defects are observed in multilayer (coextruded or laminated) PVB sheets. They are thought to result from poor degassing, exacerbated by the stresses of misaligned bending gaps between two aligned windshield safety glass sheets, although other causes or factors may also contribute to their formation. Summary of the Invention [Means for solving the problem]

[0007]

[0007] In certain embodiments, the present invention provides a PVB interlayer sheet having a surface topography on at least one surface characterized by a relatively low profile and a controlled, collapsible surface roughness profile (with exposure to heat) with a significantly greater total number of surface peaks than negative peaks (valleys), with peak spacing slightly more distant than typically found in embossed PVB interlayers. Thus, the PVB interlayer sheet of the present invention provides exceptionally good initial contact and adhesion of the PVB to the glass surface when compared to other surface designs, while leaving virtually no residual air after the first nip in conventional glass lamination processes. The PVB interlayer sheet of the present invention also allows for a wide degassing window when used in laminating glass, better able to withstand temperature and process variations. [Brief explanation of the drawings]

[0008] [Figure 1]

[0008] FIG. 1 is a depiction of a defect known as an "ice flower" that forms on a fitted windshield. [Figure 2]

[0009] FIG. 1 shows the material curve output of an Abbott-Firestone curve analysis according to ISO 13565-2 for a poly(vinyl acetal) sheet of the present invention having a textured surface. [Figure 3]

[0010] Figure 1 shows comparative material curve outputs from an Abbott-Firestone curve analysis according to ISO 13565-2 for a poly(vinyl acetal) sheet with a randomly roughened surface formed by melt fracture of the polymer melt at the die lip during the extrusion process. [Figure 4]

[0011] FIG. 3 shows a best-fit line depiction of the curves of FIG. 2. [Figure 5]

[0012] FIG. 4 shows a best-fit line depiction of the curves of FIG. 3. [Figure 6]

[0013] FIG. 3 shows a depiction of the roughness profile of the sheet of FIG. 2. [Figure 7]

[0014] FIG. 4 shows a depiction of the roughness profile of the sheet of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0009]

[0015] There are a variety of surface metrology parameters that can describe the various characteristics of a textured surface. Raw profiles can be generated for a surface by contact or non-contact means. The profiles are then typically filtered to remove noise and define roughness and waviness regions for further analysis. These profiles are then analyzed and grouped into smaller subgroups with defined parameters for surface roughness, core roughness, waviness, or motif type for comparative characterization.

[0010]

[0016] Some important surface roughness parameters include, inter alia, the roughness height (Rz) and the roughness mean spacing (Rsm). Others are core roughness parameters known as the Abbott-Firestone curve or bearing area curve or material ratio curve, from which many such parameters can be derived that describe the two- or three-dimensional shape of a textured planar surface (see, for example, DIN EN ISO13565-1 and DIN EN ISO13565-2:1998, which describe such shapes and parameters in detail).

[0011]

[0017] The primary device used for R-parameter (Rz, Rsm, Mr1, Mr2) surface measurements is the Mahr Perthometer S3P v2.5 ("S3P"). It is a needle-contact instrument that allows for the evaluation of standard parameters. The measurement device comprises a drive (PGK), a probe (RFHTB), and an LED output screen. The evaluation of S3P device parameters is generally performed according to the DIN 4776 standard. A two-dimensional image of the profile is generated via the movement of the needle tip across the surface structure. This movement is converted into digital values ​​and initially stored in a D-profile containing approximately 8,000 values ​​uniformly distributed over the trajectory length. For these measurements, a trajectory length of 17.5 mm was used (according to DIN 4776), including a 2.5 mm cutoff length.

[0012]

[0018] The three-dimensional parameters, S-parameters, were determined by a Keyence violet laser light microscope with a 1 / 4'' x 1 / 4'' spot size according to ISO 25178. These parameters are not measured by the S3P surface profilometer.

[0013]

[0019] In a first aspect, the present invention provides a poly(vinyl acetal) sheet having at least one textured surface, said surface comprising: a. Mr2 / Mr1 ratio determined by ISO13565-2: approximately 3 to approximately 10; b. Surface roughness Rz approx. 20 μm to approx. 60 μm; c. Sdr value of approximately 0.1 or more and less than approximately 0.414 as determined by ISO 25178; d. Rsm value of approximately 230 μm to approximately 600 μm; and e. Surface retention rate at 100°C (Rz2 / Rz1) less than 85% The present invention provides a poly(vinyl acetal) sheet characterized by:

[0014]

[0020] In one embodiment, the surface roughness Rz is measured by a Mahr Perthometer S3P v2.5 instrument. Rz is determined by averaging three different measurements. In one embodiment, the surface roughness Rz is about 25 μm to about 50 μm.

[0015]

[0021] In one embodiment, the ratio Mr2 / Mr1 is from about 4 to about 10, and in another embodiment from about 4 to about 9 or from about 5 to 9, as measured according to ISO 13565-2.

[0016]

[0022] In another embodiment, the textured poly(vinyl acetal) sheet may be further characterized by having an Str value, as determined by ISO 25178, that is greater than zero but less than about 0.9 (unitless), from about 0.15 to about 0.9, or from about 0.4 to about 0.7.

[0017]

[0023] In one embodiment, the poly(vinyl acetal) is poly(vinyl butyral).

[0018]

[0024] Returning to the drawing, Figure 1 is a depiction of defects known as "ice flowers" that form in an installed windshield due to incomplete degassing during the formation of the glass-interlayer laminate. A description of how to simulate ice flowers is described and provided below.

[0019]

[0025] Figure 2 is the material curve output of an Abbott-Firestone curve analysis according to ISO 13565-2 for a poly(vinyl acetal) sheet of the present invention having a textured surface. The x-axis is plotted as a percentage and the y-axis is plotted as the distance in microns (µm) from the intersection point.

[0020]

[0026] Figure 3 shows the comparative material curve output of an Abbott-Firestone curve analysis according to ISO 13565-2 for a poly(vinyl acetal) sheet with a randomly roughened surface formed by melt fracture of the polymer melt exiting the die lip during the extrusion process. The x-axis is plotted as a percentage, and the y-axis is plotted as the distance in microns (μm) from the intersection point. The sheet in Figure 3 is outside the scope of the claims.

[0021]

[0027] FIG. 4 is a best-fit line depiction of the curves of FIG. 2. The x-axis is plotted as a percentage, and the y-axis is plotted as the distance in microns (μm) from the intersection point. FIG. 4 shows Mr1, the minimum material ratio of the core roughness profile, and Mr2, the maximum material ratio of the core roughness profile. A1 is the material filled profile area peak, which is the cross-sectional area of ​​the peak that protrudes (up) from the core roughness profile per millimeter of measurement length. A2 is the material filled profile area valley, which is the cross-sectional area of ​​the peak that protrudes (down) from the core roughness profile per millimeter of measurement length. As can be seen in FIG. 4, A1 is greater (by area) than A2. For the sheet shown in FIG. 4, Mr1 is 18%, Mr2 is 93%, and the Mr2 / Mr1 ratio is 5.2. This value for the Mr2 / Mr1 ratio is within the scope of claim 1.

[0022]

[0028] Figure 5 is a best-fit line depiction of the curves of Figure 3. The x-axis is plotted as a percentage and the y-axis is plotted as the distance in microns (μm) from the intersection point. Similar to Figure 4, Figure 5 shows A1, A2, Mr1, and Mr2. As shown in Figure 5, A1 is larger than A2 (by area), Mr1 is 8%, and Mr2 is 91%, resulting in an Mr2 / Mr1 ratio of 11.7, which is outside the scope of claim 1.

[0023]

[0029] Figure 6 is a roughness profile, i.e., a two-dimensional depiction, of the sheet of Figure 2 above, showing the core line (lower line) and the peaks rising above that line, as well as the defined valleys hanging below the core line. The x-axis is in microns (250 microns per grid line); the y-axis is also in microns (25 microns per grid line).

[0024]

[0030] Figure 7 is a roughness profile, i.e., a two-dimensional depiction, of the comparative sheet of Figure 3 above, showing the core line (lower line) and the peaks rising above that line, as well as the significant valleys hanging below the core line. The x-axis is in microns (250 microns per grid line); the y-axis is also in microns (25 microns per grid line).

[0025]

[0031] This novel textured surface of such sheets provides better de-airing performance and defect elimination during the relatively short nip roll processes utilized in some parts of the safety glass industry, as described more fully below.

[0026]

[0032] The textured surface can be applied to the poly(vinyl acetal) sheet by stamping, laser beam, or spalling-type devices that penetrate the polymer surface to create the textured surface. In one embodiment, spalling-type devices are rollers that are "blasted" or surface-modified by the kinetic energy of various grades of randomly sized hard material, thus resulting in a roller with a random texture that is the negative of the desired poly(vinyl acetal) sheet with a textured surface. In one embodiment, the roller is constructed of carbon steel. In the blasting method, particulate blasting material can be sprayed against the surface of the roll at high speed. The blasting material can be, for example, alundum (artificial fused alumina), emery grit obtained by spalling steel shot, and steel grit. In one embodiment, the blasting material is silicon carbide having a grit size of about 20-24 (i.e., a mixture of 20- and 24-grit sizes).

[0027]

[0033] Once the roll has been blasted in this manner, it should be ground, e.g., by polishing or "grinding" the surface, from an original surface roughness Rz of about 85-100 μm to a final value Rz of about 70 μm, 60 μm, 50 μm, or 40 μm. By grinding the peaks, this also reduces the Mr2 / Mr1 ratio of the final poly(vinyl acetal) sheet. See Figure 6, which shows that grinding the roll effectively reduces the value because the roll is the "negative" of the texture that appears in the polymer sheet, and the grinding step is also effective in reducing the magnitude and "flattening" the negative peaks (which are the valleys in the sheet). Compare this to Figure 7, where the roughness is formed by melt fracture and there is no grinding step on the roller. As shown in Figure 7, there are many peaks and valleys in the sheet, and the Mr2 / Mr1 ratio is significantly higher.

[0028]

[0034] The textured surface ultimately obtained in the poly(vinyl acetal) sheets of the present invention can be described using the following parameters:

[0029]

[0035] First, let us explain surface roughness (Rz). For a given surface pattern, the surface roughness or specific peak height of the roughened surface from the imaginary plane of the flattened poly(vinyl acetal) interlayer sheet is the Rz value of the surface. As described herein, the two-dimensional surface roughness or Rz of the surface of the polymer interlayer sheet is expressed in microns (μm), as measured by the 10-point average roughness according to DIN EN ISO-4287 of the International Organization for Standardization (ISO) and ASME B46.1 of the American Society of Mechanical Engineers (ASME). (Note that DIN EN ISO-428 replaces DIN4776, the standard referenced by the S3P device used to measure roughness (Rz) in the examples. See ISO13565-2, DIN EN ISO-4287, which defines roughness material ratio values ​​(i.e., Mr1 and Mr2).)

[0030]

[0036] Generally, at these scales, Rz is calculated as the arithmetic mean value of one roughness depth Rzi (i.e., the vertical distance between the highest peak and deepest valley within the sampling length) of a continuous sampling length (or surface trace), as shown in the following equation:

[0031] Rz=1 / N×(Rz1+Rz2+...Rz n )

[0037] In general, Rz is not limited to measuring the textured surface of polymer interlayer sheets. Rz can be used to measure the surface topography of both textured and non-textured polymer interlayer sheets (non-textured polymer interlayer sheets are also referred to as randomly roughened sheets). While Rz is one of many values ​​or measurements conventionally used to describe the surface of polymer interlayer sheets, it should be noted that the Rz value alone does not characterize the complete profile of the surface. The Rz value is considered a two-dimensional measurement used to describe the surface of a polymer interlayer sheet. In the case of multilayer structures, the final interlayer formed from either extrusion or coextrusion has, in certain embodiments, a randomly roughened surface topography, made possible by the use of blasted and ground rolls as described above. Surface texture allows for certain micro-ridges and micro-dimples in the surface of the polymer interlayer, which have been shown to be effective in improving degassing and reducing the occurrence of air bubbles and ultimately ice flower defects in the final safety glass structure. In this regard, the sheets of the present invention have a textured interlayer that has a surface roughness retention (i.e., Rz2 / Rz1) (%) of less than 85% after heating at 100° C. for 5 minutes. In other embodiments of the present invention, the range of surface roughness retention (%) after heating at 100° C. for 5 minutes is less than 80% or less than 75%. In embodiments, the range of surface roughness retention (%) after heating at 100° C. for 5 minutes is greater than 30%.

[0032]

[0038] Second, we describe the surface texture ratio (Str). Str is a three-dimensional spatial parameter used solely to describe three-dimensional surfaces. Str is a measure of the texture aspect ratio of the surface of a polymer interlayer sheet. The texture aspect ratio of the surface of a polymer interlayer sheet is important because it is an indicator of surface isotropy. Str parameter values ​​are unitless and range from 0 to 1. Str values ​​of 0 or near 0 represent a strongly anisotropic surface and reflect a highly regular pattern, while Str values ​​of 1 or near 1 represent an isotropic surface and reflect a highly random pattern. A surface is isotropic if it exhibits the same characteristics regardless of the measurement direction. For a random surface texture or pattern, the texture or pattern is not noticeable. Conversely, an anisotropic surface has a pattern or oriented surface that can be described as a regular surface pattern. For additional information about three-dimensional parameters, see, for example, "New 3D Parameters and Filtration Techniques for Surface Metrology," Francois Blateyron, 2006, the entire disclosure of which is incorporated herein.

[0033]

[0039] In certain embodiments, the surface texture has a high degree of randomness, as described by a variable Str ("texture aspect ratio") that is greater than about 0 and less than about 0.9, or greater than 0.15 but less than about 0.9, or greater than about 0.4 and less than about 0.7. In other words, as described in ISO 25178, Str is a measure of the homogeneity of the surface texture.

[0034]

[0040] In this aspect of the invention, the surface texture has a surface peak-to-valley distribution as determined by S3P (in accordance with DIN 4776 and DIN 4762:01:89 (DIN 4762)). In this regard, Mr1 is defined as the separation between the peak and core profile (i.e., peak-core profile). Mr2 is defined as the separation between the core profile and valley (i.e., core profile-valley). The material ratio (Mr2 / Mr1) defined above is, in one embodiment, from about 3 to about 10. In one embodiment, the Mr1 value (peak-core profile) may be greater than about 10. In one embodiment, the Mr1 value may be less than about 20.

[0035]

[0041] Third, the low surface area profile is described or reflected by a variety of Sdr ("Developed Area Ratio"), which in one embodiment is less than about 0.414, but greater than about 0.01, or greater than about 0.05, and less than about 0.25, or between about 0.1 and 0.2. Per ISO 25178, the Sdr variable defines the level of deviation from a flat surface. This parameter is expressed as the percentage of additional surface area of ​​a defined area contributed by texture compared to a flat defined area. In certain embodiments, this value is intentionally lower due to the relatively short compression time of the nip roller method.

[0036]

[0042] A fourth parameter used to describe the surface is the roughness spacing (Rsm). In embodiments, the surface of the sheet has an Rsm value of greater than 230 μm up to about 600 μm, or from about 350 μm to about 450 μm (measured using S3P and according to DIN 4776).

[0037]

[0043] In one embodiment, the polymer sheet comprises a polymer selected from poly(vinyl acetals), such as poly(vinyl butyral), because such polymers, such as Butvar® PVB resins available from Eastman Chemical Company, are known for their use as interlayers in the safety glass or architectural glass industry. In one embodiment, the polymer sheet is composed of poly(vinyl butyral).

[0038]

[0044] In one embodiment, the polymer sheet is a single-layer interlayer. In one embodiment, the polymer sheet is a multi-layer interlayer. In one embodiment, the polymer sheet is a three-layer interlayer including two skin layers and a core layer, where the skin layers and the core layers have different compositions, such as those disclosed in U.S. Patent Nos. 5,340,654, 5,190,826, and 7,510,771, which are incorporated herein by reference. In one embodiment, the polymer sheet is a wedge-shaped interlayer, such as those disclosed in U.S. Patent Nos. 7,846,532, 8,574,706, 7,886,871, 8,033,360, and 8,695,756, which are incorporated herein by reference.

[0039]

[0045] As used herein, the terms "multilayer" and "multiple layers" refer to an interlayer having two or more layers, and the terms "multilayer" and "multiple layers" can be used interchangeably. Multilayer interlayers typically contain at least one flexible layer and at least one rigid layer. Interlayers with a flexible "core" layer sandwiched between two or more rigid or hard "skin" layers are designed for acoustical properties for glass panels. The reverse configuration, i.e., an interlayer with a rigid layer sandwiched between two or more flexible layers, has been found to improve the impact performance of glass panels and may also be designed for acoustical properties. Examples of multilayer interlayers include interlayers containing at least one "clear" or untinted layer and at least one tinted layer or at least one conventional layer, e.g., a non-acoustic layer, and at least one acoustical layer. Other examples of multilayer interlayers include interlayers containing at least two layers with different colors for aesthetic appeal. The tinted layer typically contains a pigment or dye, or some combination of a pigment and a dye. Each layer of the interlayer is generally produced by mixing a polymer resin, such as poly(vinyl butyral), with one or more plasticizers and melt processing the mixture into a sheet by any applicable method or methods known to those skilled in the art, including, but not limited to, extrusion, and the layers are combined by methods such as coextrusion and lamination. Other additional components may optionally be added for a variety of other purposes. After being formed, the interlayer sheet is typically collected and rolled up for transportation and storage, and later use in multiple layer glazing panels, as described below.

[0040]

[0046] Multi-layer interlayers, such as three-layer interlayers having a soft core layer and two harder skin layers, are commercially available. The hard skin layers provide the interlayer with ease of handling, processability, and mechanical strength; the soft core layer provides acoustic damping properties. In embodiments, the residual vinyl acetate groups and / or residual hydroxyl groups in the polyvinyl acetal resin of the soft core layer are at least 2 wt.% less than the residual vinyl acetate groups and / or residual hydroxyl groups in the polyvinyl acetal resin of the hard skin layers. In embodiments, the plasticizer content of the soft core layer is at least 8 phr (parts by weight per 100 parts by weight of resin) higher than the plasticizer content of the hard skin layers. In embodiments, the glass transition temperature of the soft core layer is less than about 20°C. Whether constructed in a single-layer or multi-layer structure, the polymer sheet of the present invention has at least one textured surface, as described herein.

[0041]

[0047] As noted above, the textured surface, in certain embodiments, is generally somewhat random, having the appearance of peaks and valleys, with the relative number of peaks exceeding the number of valleys, a valley in this context being understood to be an "inverted peak" that extends below the overall median surface (see comparative example FIG. 7), and the valley being significantly flatter (see FIG. 6). In this way, there are ultimately far fewer valleys in which air can become trapped and nucleate, resulting in, for example, ice flower defects, upon breakdown and finishing of the glass / interlayer / glass structure.

[0042]

[0048] Generally, the method of the present invention can be carried out using a two oven / two nip degassing method according to the following steps: a. attaching a PVB interlayer having the surface characteristics set forth herein above to a panel, such as a piece of glass, and attaching another piece of glass thereto, wherein the glass is heated in an oven to a temperature in the range of about 30°C to 70°C (or the laminated glass and interlayer structure is heated to this range); b. then passing the laminated structure through nip rollers, where initial compression is achieved with a predetermined gap, generally about 60-85% of the total structure thickness, and a nip roller pressure of about 275 kPa (40 psi) to 758 kPa (110 psi); c. placing the laminated structure in a second oven at a temperature of about 75°C to about 125°C for a short period of time (which may vary depending on product geometry and available customer equipment); d. passing the laminated structure through a second nip roll having the same gap distance and nip roller pressure as in step b; followed by e. Placing in an autoclave for final finishing, with peak autoclaving temperature and pressure between 125°C and 155°C and between 40 psi and 200 psi, respectively, and a peak hold time between 20 and 60 minutes.

[0043]

[0049] The unique surface texture noted above is found to remain largely unchanged between steps (a) and (b), but begins to disintegrate during short oven cycles at temperatures between about 90°C and 110°C, a temperature range that appears to be critical for forming poly(vinyl butyral) (PVB) sheets, degassing the PVB in glass laminates, and the formation of various defects. As the temperature is again raised during the degassing step, as in the second oven / nip step, the structural features of the PVB surface continue to degrade as desired, in one embodiment, to less than 60% of their original value. Thus, the improved method of the present invention, which relies on the unique surface texture of the polymer sheet, advantageously enables the utilization of existing nip roller manufacturing equipment to provide proper construction of laminated PVB / glass structures and faster material throughput. In this regard, the method may be a single oven / nip process followed by an autoclave in which the oven temperature is between about 40°C and about 80°C. Accordingly, in another aspect, the present invention is a method of making a glass laminate, the method comprising degassing and laminating two glass panels and a textured polymer sheet disposed between said panels, the method comprising: a. attaching a textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of about 40°C to 80°C to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, wherein initial compression is performed with the nip rollers at a predetermined gap that is about 60 to about 85% of the thickness of the laminated structure and at about 275 kPa (40 psi) to 758 kPa (110 psi), thereby resulting in a light transmittance value greater than about 80%; c. subsequently autoclaving the laminate using a peak autoclave temperature of 125°C to 155°C, a peak pressure of 344 kPa (50 psi) to 1378 kPa (200 psi), and a peak hold time of 20 minutes to 60 minutes; Including, A method of making a glass laminate is provided, wherein the textured polymer sheet is as set forth herein above.

[0044]

[0050] In practicing this method, step (c) may be repeated one or more times, as desired. In one aspect, the present invention provides a method that can utilize only two consecutive "nip" steps, with an overall lower temperature for the first nip and a higher temperature for the second nip. Accordingly, in another aspect, the present invention provides a method for degassing and laminating two glass panels and a textured polymer sheet disposed between said panels, the method comprising: a. attaching a textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of about 30°C to 70°C to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, wherein initial compression is achieved with a predetermined gap of about 60 to about 85% of the thickness of the laminated structure and a nip roller pressure of about 275 kPa (40 psi) to 758 kPa (110 psi); c. Subsequently, the laminate is heated to a temperature of about 90°C to about 110°C; d. subsequently processing the laminated structure again through nip rollers, with initial compression being performed with a predetermined gap of about 60 to about 85% of the thickness of the laminated structure and a nip roller pressure of about 275 kPa (40 psi) to 758 kPa (110 psi), thereby resulting in a laminated structure having a light transmittance value greater than about 80%; Including, A method is provided wherein the textured polymer sheet is as set forth herein above.

[0045]

[0051] The textured polymer sheet of the present invention may be a single layer or a multilayer structure, as described herein. Thus, in another embodiment, the present invention provides the above two aspects, wherein the textured polymer sheet is a multilayer interlayer.

[0046]

[0052] As noted above, the polymer sheet is a textured sheet of the present invention, which allows for improved degassing due to the surface properties, and the "peaks" tend to collapse in the desired temperature range as indicated above.

[0047]

[0053] Referring to Figure 1, this is a depiction of defects known as "ice flowers" that form in an installed windshield as a result of incomplete degassing during the formation of the glass-interlayer laminate. When degassing is incomplete, bubble initiation and expansion at high temperatures (e.g., 50°C to 100°C) experienced during windshield use, stresses from bending gaps or glass misfits, tend to cause the bubbles to expand in random radial directions within the core layer (e.g., within the three-ply interlayer) along the path of least resistance. As the defects continue their radial expansion, they form branching and dendritic features, giving rise to the undesirable optical appearance of ice flowers. The defects also typically result in separation between the layers, thereby reducing the structural integrity of the panel.

[0048]

[0054] The surface texture provided by the present invention results in reduced defects and considerable processing flexibility, as shown in the experimental data below and in Table 1. In this regard, the inventors have discovered that while nip roller systems typically use two consecutive nip rollers, the thermal and degassing performance of the sheets of the present invention is compatible with the use of just one such nip roller, thus greatly expanding the processing flexibility of laminators using such poly(vinyl acetal) sheets. This performance can be measured by the clarity of the laminate after the first nip, as measured by a photometer, and by the trapped air, as determined by bubbles after autoclaving the laminate and, optionally, subjecting the laminate to baking temperatures, e.g., 100°C or higher. As seen in the experiments below, no bubbles were observed and there was high clarity after only the first nip roller operation, which was superior to the comparative example described above. [Example]

[0049] Example 1

[0055] Three (3) rollers were surface treated using silicon carbide grit blasting to a roughness target of 85 μm + / - 5 μm Rz and approximately 300 μm Rsm. The rollers were then ground using standard methods known in the art to achieve levels of 0% (roller 1), 20% (roller 2), and 40% (roller 3) reduction in roughness (Rz) from the starting level. The final roller levels after grinding were approximately 85 μm Rz (roller 1), 70 μm Rz (roller 2), and 50 μm Rz (roller 3). PVB sheets were then separately textured with each roller to a target Rz of 40 μm + / - 5 μm. These textured sheets were then placed between two sheets of glass, processed using the two-oven / two-nip method, and evaluated using the ice flower (defect) test procedure described further below. The results are shown in Table 1 below.

[0050] [Table 1]

[0051]

[0056] The results in Table 1 suggest that the defect ratio correlates well with the Mr2 / Mr1 ratio. As the ratio increases, the level (or number) of defects increases. Grinding the roller increased the flatness of the "inversion peaks" or valleys on the textured surface of the sheet, thereby decreasing the Mr2 / Mr1 ratio.

[0052] Example 2

[0057] A fourth roller (Roller 4) was surface treated using the silicon carbide grit blasting method described above to a target Rz of 50 μm without additional grinding. Using Roller 4, a PVB sheet was embossed to a target surface roughness of Rz 40 μm + / - 5 μm and laminated between glass according to the ice flower test described below. The results are shown in Table 2 below.

[0053] [Table 2]

[0054]

[0058] The data in Table 2 suggest that the texturing of the roller(s) (or roller texture or surface roughness) and the sheet roughness (Rz) level alone only partially contribute to the superior performance of the sheets of the present invention. The flatter valleys of the sheet produced from ground (40%) Roller 3 result in a lower Mr2 / Mr1 ratio, which is primarily attributed to the superior performance of the sheet.

[0055] Example 3

[0059] Various samples were tested to determine how well they performed. Samples tested for various properties included:

[0060] Disclosed Sample 1 (D1) - a PVB three-layer sample of the present invention having a randomly textured surface formed using a roller prepared as described herein

[0061] Comparative Sample 1 (C1) - A PVB three-layer sample commercially available from Eastman Chemical Company with an embossed surface pattern and surface roughness level (Rz) similar to Sample D1. The pattern for C1 is as disclosed in U.S. Patent No. 7,883,761.

[0056]

[0062] Comparative Sample 2 (C2) - A commercially available 3-layer (from a source other than Eastman Chemical Company) PVB 3-layer sample with an embossed surface and surface roughness level (Rz) similar to Sample D1.

[0063] Comparative Sample 3 (C3) - A PVB monolithic sheet sample commercially available from Eastman Chemical Company that has a randomly roughened surface formed by melt fracture of the polymer melt present at the die lip during the extrusion process.

[0064] The degassing efficiency was measured by preparing three different interlayer samples (D1, C1, and C2 above) and passing them through a single nip roll. Table 3 shows the transparency (also referred to as prepress transmission) of the laminates after a single nip and before autoclave finishing at three different temperatures (40°C, 55°C, and 75°C). The number of bubble defects in the laminates is observed immediately after the autoclave cycle is completed. The results are shown in Table 3 below.

[0057] [Table 3]

[0058]

[0065] As shown by the data in Table 3, compared to commercially available interlayers, the interlayers of the present invention have superior transparency, as indicated by the high light transmission after one nip roll degassing at each degassing temperature. The interlayers of the present invention also exhibit no bubbles after autoclaving, suggesting that the surface pattern of the present invention allows for better degassing.

[0059]

[0066] The samples were also tested to determine the change in roughness level after heating at various temperatures. The amount of surface retention (%) was also determined by measuring the roughness (Rz) before and after heating the samples to 100°C. Surface retention is expressed as a percentage. The samples were also tested to determine various surface properties, including Sdr, Str, and Mr2 / Mr1 ratio, and to quantitatively measure light transmission (transparency), ice flowering performance, and air bubble performance. Ice flowering and air bubble performance are observed after laminating the samples using the two-oven / two-nip degassing method and completing the subsequent autoclaving cycle, and after the laminates were subjected to a simulated ice flowering test and exposed to a 100°C baking temperature for 16 hours, respectively. The data are shown in Tables 4 and 5 below.

[0060] [Table 4]

[0061] [Table 5]

[0062]

[0067] As shown by the data in Tables 4 and 5, the inventive samples have better thermal behavior at 100°C, which is considered the critical glass temperature in conventional nip roll processing operations. Above 100°C, the individual components begin to form a laminate as the interlayer flows between and adheres to the glass. The data also show that Sample D1, with an Mr2 / Mr1 ratio of 5.2, Str of 0.6, Sdr of 0.1, and a surface retention of 76% at 100°C, has excellent transparency, ice flowering, and bubble performance, which is better than comparative Samples C1, C2, and C3. Sample C2, with an Mr2 / Mr1 ratio of 8.6, has higher surface retention and acceptable transparency, ice flowering, and bubble performance. Samples C1 and C3, both of which have higher Mr2 / Mr1 ratios, have poor transparency and poor or acceptable bubble performance. Sample C1 also has acceptable / poor ice flowering performance. Sample C3 was not tested for ice flowering performance because it is a monolithic or single-layer interlayer. The relative incidence of ice flowering (ice flowering performance, ranked as "excellent," "fair," and "poor" by ice flower defect simulation, as further shown below) is ranked by the percentage of laminates that exhibited ice flower defects (or, in other words, the number of laminates that exhibited defects out of the total number of laminates tested). "Excellent" ice flowering performance means that the defect percentage is less than 20% or between 0 and 20%; "fair" ice flowering performance means that the defect percentage is greater than 20% or between 20% and 40%; and "poor" ice flowering performance means that the defect percentage is greater than 40%. Similar to bubble performance, "excellent" means no bubbles, "poor" means many bubbles, and "fair" means some bubbles. As can be seen from Tables 4 and 5, when the surface roughness (Rz) is approximately the same, the bubble performance and ice flower performance are mainly determined by the Mr2 / Mr1 ratio of the intermediate layer and the surface retention at 100°C.

[0063] Test Techniques / Test Procedures: Surface Retention Rate Procedure:

[0068] Surface retention is a measure of the amount of surface roughness retained after heating. It is calculated by measuring the surface roughness of the interlayer before (Rz1) and after (Rz2) heating. To determine surface retention, measure and record the original roughness (Rz1) in the extrusion (machine) direction or the direction most representative of obtaining the surface pattern design. Cut an approximately 6" x 6" square piece of PVB around the area to be measured (containing the first roughness measurement, Rz1 area). Using the previously made 6" x 6" metal frame (two pieces) for support, place the sample in the frame to form a "sandwich" (side view) as follows:

[0064] [Table 6]

[0065]

[0069] The assembly is secured by attaching clamps (e.g., alligator clamps) around the perimeter of the frame. The purpose is to prevent any linear contraction or expansion of the interlayer during heating. The frame assembly is placed in an oven heated to 100°C, with the frame oriented parallel to the oven airflow (the specimen faces forward). The oven is closed and a holding time of 5 + / - 0.5 minutes is allowed in the oven. After 5 minutes, the frame is removed from the oven with the warm specimen still in the frame, and the assembled specimen is allowed to cool to room temperature (approximately 15 minutes). It is important to ensure that the specimen is cooled to room temperature (after 5 minutes at 100°C) before measuring the surface again. If the specimen is removed from the frame while still warm, shrinkage will occur, which will affect the surface reading of the remeasurement. Once the specimen has cooled, the surface roughness of the specimen (which will become Rz2) is measured again in the same direction and at the same location as the first measurement (Rz1). Surface retention is calculated as Surface Retention (%) = Rz2 / Rz1.

[0066]

[0070] For example, to measure and calculate surface retention, an interlayer sample is measured and has a starting roughness Rz of 40 μm (Rz1). The sample is then heated at 100° C. for 5 minutes, followed by the test described above. After heating, the sample is measured again and the surface roughness after heating is 32 μm (Rz2). To calculate surface retention, the following formula is used: Surface Retention=Rz2 / Rz1. For the example, surface retention Rz2 / Rz1=32 / 40=80%.

[0067] Ice flower defect simulation procedure

[0071] The formation of ice flowers in three-layer acoustic PVB laminates can be tested by simulating real-world conditions in windshields and other glass, where a combination of large bending gaps and poor degassing is known in the art to be one of the root causes of ice flower development. First, a 30 cm x 30 cm three-layer interlayer containing a centrally placed polyethylene terephthalate (PET) membrane ring (inner diameter 7.5 cm; outer diameter 14 cm; and thickness 0.10 mm to 0.18 mm) is sandwiched between two 30 cm x 30 cm pieces of glass to form a structure. The structure is then pre-laminated and autoclaved for degassing, typically using a two-oven / two-nip method. The resulting laminate is allowed to condition at room temperature for 48 hours, baked in a conventional oven (80 °C) for 48 hours, and then cooled. The laminate is then visually inspected to determine the ice flower formation rate in the laminate (e.g., the percent of the laminate that exhibits ice flower defects) and the percent of the area within the PET ring that has ice flower defects. Additionally, the laminate is visually inspected to determine the percentage of ice flower formation within the entire laminate (including both inside and outside the PET film area).

[0068] Glass transmittance level measurement

[0072] Percent light transmittance values ​​(in the visible region of the spectrum) were determined using an adhesion photometer (Tokyo Denshoku #S-904356). Four (4) measurements were taken for each sample tested here. The glass laminate was inserted into the photometer and the values ​​were recorded. The sample was then removed and one (1) measurement was taken at each corner of the 12" x 12" glass laminate. The results were averaged to give the percent light transmittance. Measurements were taken at glass temperatures ranging from about 23°C to 27°C. These measurements can be made using any apparatus and any method described in either JIS K7361 or ISO 13468-1 to determine the total luminous transmittance in the visible region of the spectrum for flat, transparent, substantially colorless plastics using a single-beam photometer equipped with a specialized CIE standard light source and photodetector.

[0069]

[0073] Although the invention has been described in detail with particular reference to certain specific embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The present invention includes the following embodiments. [1] A poly(vinyl acetal) polymer sheet having at least one outer textured surface, said textured surface comprising: a. Mr2 / Mr1 ratio determined by ISO13565-2: approximately 3 to approximately 10; b. Surface roughness Rz approx. 20 μm to approx. 60 μm; c. Sdr value of approximately 0.05 or more and less than approximately 0.414 as determined by ISO 25178; d. Rsm value of approximately 230 μm to approximately 600 μm; and e. Surface retention rate at 100°C (Rz2 / Rz1) less than 85% A poly(vinyl acetal) polymer sheet comprising: [2] The sheet according to [1], wherein the surface roughness Rz is about 25 μm to about 50 μm. [3] The sheet according to [1] or [2], wherein the Mr2 / Mr1 ratio is about 4 to about 10. [4] The sheet according to any one of [1] to [3], wherein the Mr2 / Mr1 ratio is about 4 to about 9. [5] The sheet according to any one of [1] to [4], wherein the Mr2 / Mr1 ratio is about 5 to about 9. [6] The sheet according to any one of [1] to [5], wherein the sheet is further characterized by an Str value greater than 0 and less than about 0.9. [7] The sheet according to [6], wherein the Str value is greater than about 0.15 and less than about 0.9. [8] The sheet according to [6], wherein the Str value is greater than about 0.4 and less than about 0.7. [9] The sheet according to any one of [1] to [8], wherein the Sdr value as determined by ISO25178 is greater than about 0.05 but less than about 0.25.

[10] The sheet according to [9], wherein the Sdr value determined according to ISO25178 is about 0.1 to about 0.2.

[11] The sheet according to any one of [1] to

[10] , wherein the Rsm value is about 350 μm to about 450 μm.

[12] The sheet according to any one of [1] to

[11] , wherein the polymer sheet comprises poly(vinyl butyral).

[13] The sheet according to any one of [1] to

[12] , wherein the polymer sheet is a multilayer polymer sheet.

[14] A method for degassing and laminating two glass panels and a textured polymer sheet according to any one of [1] to

[13] disposed between the panels, comprising: a. attaching the textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of about 40°C to 80°C to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, wherein initial compression is achieved with nip rollers at a predetermined gap of about 60 to about 85% of the thickness of the laminated structure and at about 40 psi to 110 psi, thereby resulting in a light transmittance value of greater than about 80%; c. subsequently autoclaving the laminate using a peak autoclave temperature of 125°C to 155°C, a peak pressure of 275 kPa (40 psi) to 1378 kPa (200 psi), and a peak hold time of 20 minutes to 60 minutes. A method comprising:

[15] A method for degassing and laminating two glass panels and the textured polymer sheet according to any one of [1] to

[13] , wherein the textured polymer sheet is placed between the glass panels, the method comprising: a. attaching the textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of about 30°C to 70°C to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, wherein initial compression is achieved with a predetermined gap of about 60 to about 85% of the thickness of the laminated structure and a nip roller pressure of about 275 kPa (40 psi) to 758 kPa (110 psi); c. subsequently, heating the laminate to a temperature of about 90°C to about 110°C; d. subsequently processing the laminated structure again through nip rollers, with initial compression being performed with a predetermined gap of about 60 to about 85% of the thickness of the laminated structure and a nip roller pressure of about 275 kPa (40 psi) to 758 kPa (110 psi), thereby resulting in a laminated structure having a light transmittance value greater than about 80%. A method comprising:

[16] The method according to

[14] or

[15] , wherein the light transmittance value is greater than 85%.

Claims

1. 1. A poly(vinyl acetal) polymer sheet having at least one outer textured surface, said textured surface comprising: a. Mr2 / Mr1 ratio as determined by ISO 13565-2 of 3 to 10; b. Surface roughness Rz 20 μm to 60 μm; c. Sdr value determined by ISO 25178 is 0.05 or more and less than 0.414; d. Rsm value of 230 μm to 600 μm; and e. Surface retention rate at 100°C (Rz2 / Rz1) less than 85% It is characterized by Poly(vinyl acetal) polymer sheets are used as interlayers laminated between pieces of glass.

2. The sheet according to claim 1, wherein the surface roughness Rz is 25 μm to 50 μm.

3. 3. The sheet according to claim 1, wherein the Mr2 / Mr1 ratio is 4 to 10.

4. 4. A sheet according to claim 1, wherein the Mr2 / Mr1 ratio is between 4 and 9.

5. 5. A sheet according to any one of claims 1 to 4, wherein the Mr2 / Mr1 ratio is between 5 and 9.

6. 6. The sheet of claim 1, wherein the sheet is further characterized by a Str value greater than 0 and less than 0.

9.

7. 7. The sheet of claim 6, wherein the Str value is greater than 0.15 and less than 0.

9.

8. 7. The sheet of claim 6, wherein the Str value is greater than 0.4 and less than 0.

7.

9. 9. The sheet according to claim 1, wherein the Sdr value, as determined by ISO 25178, is greater than 0.05 but less than 0.

25.

10. The sheet according to claim 9, wherein the Sdr value determined according to ISO 25178 is 0.1 to 0.

2.

11. The sheet according to any one of claims 1 to 10, wherein the Rsm value is from 350 µm to 450 µm.

12. 12. The sheet of any one of claims 1 to 11, wherein the polymer sheet comprises poly(vinyl butyral).

13. 13. The sheet of any one of claims 1 to 12, wherein the polymer sheet is a multilayer polymer sheet.

14. 14. A method of degassing and laminating two glass panels and a textured polymer sheet according to any one of claims 1 to 13 disposed between said panels, comprising: a. attaching the textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of 40° C. to 80° C. to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, wherein initial compression is achieved with nip rollers at a predetermined gap of 60-85% of the thickness of the laminated structure and at 275 kPa (40 psi) to 758 kPa (110 psi), thereby resulting in a light transmission value greater than 80%; c. subsequently autoclaving the laminate using a peak autoclave temperature of 125°C to 155°C, a peak pressure of 275 kPa (40 psi) to 1378 kPa (200 psi), and a peak hold time of 20 minutes to 60 minutes. A method comprising:

15. 14. A method for degassing and laminating two glass panels and the textured polymer sheet of any one of claims 1 to 13, wherein the textured polymer sheet is placed between the glass panels, the method comprising: a. attaching the textured polymer sheet to a sheet of glass and attaching a second piece of glass thereon to form a glass / polymer sheet / glass structure, and heating the glass or structure to a temperature of 30° C. to 70° C. to result in a laminated structure; followed by b. processing the laminated structure through nip rollers, with initial compression being performed with a predetermined gap of 60-85% of the thickness of the laminated structure and a nip roller pressure of 275 kPa (40 psi) to 758 kPa (110 psi); c. Subsequently, the laminate is heated to a temperature of 90°C to 110°C; d. Subsequently, processing the laminated structure again through nip rollers, with initial compression being performed with a predetermined gap of 60-85% of the thickness of the laminated structure and a nip roller pressure of 275 kPa (40 psi) to 758 kPa (110 psi), thereby resulting in a laminated structure having a light transmittance value greater than 80%. A method comprising:

16. 16. The method of claim 14 or 15, wherein the light transmission value is greater than 85%.

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