Film used as an interleaf between substrates

Abstract

To provide an interleaf that replaces current interleaf sheets for glass sheets, which is stiff enough to deform during handling, facilitates placement of a paper-like sheet interleaf, minimizes or eliminates particulates, and provides a buffering effect between adjacent glass sheets. [Solution] A film used as an interleaf between substrates, comprising: a foamed core layer including a polyolefin matrix having a plurality of microvoids defining a first surface and a second surface opposite the first surface; a first skin layer on the first surface; and a second skin layer on the second surface, the film having a basis weight of about 60 gsm to about 80 gsm, a thickness of about 90 microns to about 200 microns, and a stiffness of about 250 grams to about 550 grams as measured by the Circular Bend Stiffness Test.

Description

[Technical Field]

[0001] The present invention is directed to a film used as an interleaf between substrates such as glass sheets or slabs. [Background technology]

[0002] Slip sheets are commonly used by glass sheet manufacturers as a protective sheet during handling or transport, where multiple glass sheets are typically stacked side-by-side or one above the other on an inclined surface. Slip sheets provide protection by acting as a physical barrier that reduces impact and abrasion between stacked glass sheets. However, slip sheets often leave particulates on the surface of the glass sheets, which can stain, stain, and / or scratch the surface of the glass sheets.

[0003] It would be desirable to provide an alternative interleaf to current interleaves for glass sheets that is stiff enough to deform during handling, facilitates placement of a paper-like sheet interleaf, minimizes or eliminates particulates, and provides a buffering effect between adjacent glass sheets. Summary of the Invention [Means for solving the problem]

[0004] According to one aspect of the present invention, a film is provided for use as an interleaf between glass panes.

[0005] According to one embodiment, a film used as an interleaf between substrates comprises a polyolefin and has a basis weight of about 30 gsm to about 70 gsm, an embossing thickness of about 150 microns to about 800 microns, and a stiffness of about 150 grams to about 750 grams according to the Circular Bend Stiffness Test.

[0006] In another embodiment, the polyolefin includes polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, highly crystalline polypropylene, homopolymer polypropylene, nucleated polypropylene, copolymer polypropylene, and / or blends thereof.

[0007] The polyolefin may be polypropylene.

[0008] The film may include at least one additive including, but not limited to, a slip agent, a nucleating agent, and an antioxidant stabilizer.

[0009] In one embodiment, the film may include a plurality of raised portions on one side thereof and a plurality of protrusions on the opposing side thereof.

[0010] Furthermore, the plurality of raised portions may be a plurality of substantially parallel ribs aligned in a single direction.

[0011] The plurality of raised portions may be a first plurality of substantially parallel ribs aligned in a first direction and a second plurality of substantially parallel ribs aligned in a second direction at an angle to the first direction.

[0012] The angle may be in the range of 0° to 90°.

[0013] The first direction may be at about 45° to the machine direction of the film.

[0014] The second direction may be approximately 90 degrees from the first direction.

[0015] The substrate may be made of glass, polycarbonate, poly(methyl methacrylate), or stainless steel.

[0016] The present invention also encompasses a film for use as an interleaf between substrates, the film comprising a foamed core layer formed of a polyolefin matrix having a plurality of microvoids. The foamed core layer is intended to define a first surface and a second surface opposite the first surface. A first skin layer is disposed on the first surface. A second skin layer is disposed on the second surface. The film has a basis weight of about 60 gsm to about 80 gsm, a thickness of about 90 microns to about 200 microns, and a stiffness of about 250 grams to about 550 grams as measured by the Circular Bend Stiffness Test.

[0017] For films with a foam core layer, the stiffness may be from about 300 grams to about 350 grams according to the Circular Bend Stiffness Test.

[0018] Films with foam core layers may also have a compressibility of about 5% to about 20%.

[0019] It is contemplated that films with foam core layers are constructed to have a resilience of from about 80% to about 99%.

[0020] In the case of films with a foamed core layer, the first skin layer and / or the second skin layer may also be foamed.

[0021] Furthermore, in the case of films with a foamed core layer, the first skin layer may have an embossed outer surface having integrally formed therewith a regular or irregular pattern of foamed macrostructure.

[0022] Here, the second skin layer may be and / or include an adhesive surface.

[0023] A film with a foam core layer may be constructed so that one outer surface of the film has an average surface roughness Ra of from about 0.1 μm to about 10 μm.

[0024] In addition, one outer surface of the film may have a surface roughness Rz of about 1 μm to about 35 μm.

[0025] Furthermore, one outer surface of the film may have an average spacing Sm between surface peaks of about 100 μm to about 350 μm.

[0026] For films with a foamed core layer, the polyolefin matrix is ​​contemplated to include polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, highly crystalline polypropylene, homopolymer polypropylene, nucleated polypropylene, copolymer polypropylene, or blends thereof.

[0027] The polyolefin matrix may also include at least one additive, including, but not limited to, a slip agent, a nucleating agent, and an antioxidant stabilizer.

[0028] For this embodiment, the first skin layer and / or the second skin layer may comprise polyethylene, polypropylene, or a blend thereof.

[0029] Furthermore, in the case of films with a foamed core layer, the first skin layer and / or the second skin layer may incorporate at least one additive such as a slip agent, a nucleating agent, and an antioxidant stabilizer.

[0030] Substrates include glass, polycarbonate, poly(methyl methacrylate), and stainless steel, among other materials.

[0031] These and other aspects, features, and characteristics of the present invention, as well as the methods and functions of manufacture and economies of manufacture of associated structural elements and combinations of parts, will become more apparent from a consideration of the following description and the appended claims, taken in conjunction with the accompanying drawings, all of which form a part of this specification. It is to be expressly understood, however, that the drawings are for the purposes of illustration and description only and are not intended to define the limits of the invention. As used in this specification and claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0032] The components in the following drawings are illustrated to emphasize the general principles of the present disclosure and are not necessarily to scale. For consistency and clarity, reference numerals designating corresponding components are repeated where necessary throughout the drawings. [Brief explanation of the drawings]

[0033] [Figure 1a] 1 is a schematic top view illustrating a film according to one embodiment of the present invention. [Figure 1b] FIG. 1b is a schematic side view of the film of FIG. 1a. [Figure 2a] 1 is a schematic top view illustrating a film according to one embodiment of the present invention. [Figure 2b] FIG. 2b is a schematic side view of the film of FIG. 2a. [Figure 2c] 2b is a microphotograph showing the top surface of one embodiment of the film of FIG. 2a. [Figure 2d] 2b is a microphotograph showing the underside of the film of FIG. 2a. [Figure 2e] 2c is a microphotograph showing a perspective view of the top surface of the film of FIG. 2c. [Figure 2f] FIG. 2c is a microphotograph showing a perspective view of the underside of the film of FIG. 2d. [Figure 3] FIG. 1 is a schematic diagram illustrating one embodiment of an apparatus for producing the embossed film shown in FIGS. 1a-2f. [Figure 4]1 is a schematic perspective view showing a film according to one embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram illustrating one embodiment of an apparatus for producing the film shown in FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a nip roller that may be used in the apparatus shown in FIG. [Figure 7a] 1 is a microphotograph showing the top surface of a film according to one embodiment of the present invention. [Figure 7b] 7b is a microphotograph showing the underside of the film of FIG. 7a. DETAILED DESCRIPTION OF THE INVENTION

[0034] 1a and 1b illustrate a film 100 according to one embodiment of the present invention. The film 100 has an x-dimension, a y-dimension, and a z-dimension. The x-dimension corresponds to the machine direction of the film 100 when produced on the apparatus shown in FIG. 3 and described in more detail below. The y-dimension corresponds to the cross direction of the film 100, which is perpendicular to the x-dimension and machine direction, when produced on the apparatus shown in FIG. 3, and the z-dimension is perpendicular to both the x-dimension and the y-dimension. The film 100 has an embossment height or thickness 120 extending in the z-dimension from a first side 110 of the film 100 to a second side 130 of the film. The embossment height 120 may range from about 30 microns (μm) to about 800 microns (μm). In one embodiment, the embossment height 120 may range from about 150 microns (μm) to about 800 microns (μm). In one embodiment, the embossment height 120 may range from about 100 microns (μm) to about 300 microns (μm).

[0035] 1a and 1b, the film 100 includes a plurality of "ribs" or raised portions 140 offset from the base portion 160 of the film 100. The raised portions 140 are substantially parallel to one another and are separated by segments of the base portion 160 that are also substantially parallel to one another. Each segment of the base portion 160 includes a plurality of recesses 180 extending in the z-dimension in a direction opposite the raised portions 140. The recesses 180 appear as a plurality of protrusions 190 on the opposing surface of the base portion 160 that coincides with the second side 130 of the film, as shown. When the second side 130 of the film 100 is placed on a flat surface, such as a glass sheet, only the tips of the protrusions 190 contact the flat surface. Conversely, when the first side 110 of the film 100 is placed on a flat surface, only the tops of the raised portions 140 contact the flat surface.

[0036] When another glass sheet is then placed on or adjacent to the exposed surface of film 100, either the tops of raised portions 140 or the tips of protrusions 190 will contact the second glass sheet, depending on the orientation of film 100. Raised portions 140 provide cushioning and increase the bending stiffness of the glass sheet compared to a film of the same basis weight but without the embossed structure and with substantially parallel, continuous first and second surfaces (i.e., a "flat" film). For use as an interleaf between glass sheets, it is desirable for film 100 to have paper-like stiffness.

[0037] 2a-2f illustrate a film 200 according to one embodiment of the present invention. The film 200 has an x-dimension, a y-dimension, and a z-dimension. The x-dimension corresponds to the machine direction (MD) of the film 200 when manufactured on the apparatus shown in FIG. 3 and described in more detail below. The y-dimension corresponds to the transverse direction (TD) of the film 200, which is perpendicular to the x-dimension and machine direction, when manufactured on the apparatus shown in FIG. 3, and the z-dimension is perpendicular to both the x-dimension and the y-dimension. The film 200 has an embossment height or thickness 220 extending in the z-direction from a first side 210 of the film 200 to a second side 230 of the film 200. The embossment height 220 may range from about 30 microns (μm) to about 800 microns (μm). In one embodiment, the embossment height 220 may range from about 150 microns (μm) to about 800 microns (μm). In one embodiment, the embossment height 220 may range from about 100 microns (μm) to about 300 microns (μm).

[0038] The film 200 includes a plurality of "ribs" or raised portions 240 offset from a base portion 260 of the film 200. The raised portions 240 are arranged in two parallel pairs intersecting at 90° angles to form a grid, with each section of the base portion 260 having an overall square shape and surrounded by raised portions 240. In the illustrated embodiment, the raised portions 240 are aligned at an angle of approximately 45° relative to the x-dimension. In other embodiments, the raised portions 240 may generally be aligned at an angle between 0° and 90° relative to the x-dimension. In one embodiment, the length of each raised portion 240 surrounding each section of the base portion 260 may range from approximately 2000 microns (μm) to approximately 2500 microns (μm), and the width of each raised portion 240 may range from approximately 150 microns (μm) to approximately 200 microns (μm).

[0039] Each section of base portion 260 includes a plurality of recesses 280 extending in the z-dimension opposite to raised portions 240. The plurality of recesses 280 appear as a plurality of protrusions 290 on the opposing surface of base portion 260 that coincides with second surface 230 of the film, as shown. When second surface 230 of film 200 is placed on a flat surface, such as a glass sheet, only the tips of protrusions 290 contact the flat surface. Conversely, when first surface 210 of film 200 is placed on a flat surface, only the tops of raised portions 240 contact the flat surface.

[0040] When another glass sheet is then placed on or adjacent to another exposed surface, either the tops of the raised portions 240 or the tips of the protrusions 290 will contact the second glass sheet, depending on the orientation of the film 200. The raised portions 240 provide cushioning and increase the bending stiffness of the glass sheet compared to a film having the same basis weight but without the embossed structure and having substantially parallel and continuous first and second surfaces (i.e., a "flat" film). As will be described in more detail below, for use as an interleaf between glass sheets, it is desirable for the film 200 to have paper-like stiffness.

[0041] FIG. 3 illustrates an apparatus 300 that may be used to manufacture films according to embodiments of the present invention, including the films 100 and 200 described above. As illustrated, the apparatus 300 includes an extrusion die 302 disposed at the end of at least one extruder (not shown) and configured to form a polymer web 304, also known as an extrudate or melt curtain. The polymer web 304 may be a single-layer or multi-layer polymer web. The material used to form the polymer web 304 may be a blend of polyethylene (PE), HDPE, PP, low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), with high-density polyethylene (HDPE) and / or polypropylene (PP) as the primary components. The polypropylene may be any one and / or combination of highly crystalline PP, homopolymer PP, nucleated PP, and copolymer PP. Furthermore, additives may be included in the polyolefin. Additives include, but are not limited to, slip agents, nucleating agents, and antioxidant stabilizers.

[0042] In the embodiment shown in FIG. 3 , the polymer web 304 exits the extrusion die 302 and is deposited onto a forming structure 306 that rotates around a fixed vacuum slot 308 through which a vacuum is drawn. The forming structure 306 and the fixed vacuum slot 308 are part of a forming station 307. The forming structure 306 includes a plurality of openings 306 a and a plurality of raised portions (not shown) arranged in one or more patterns. As the polymer web 304 on the forming structure 306 passes over the vacuum slot 308, the portions of the polymer web 304 directly above the openings 306 a on the forming structure 306 are drawn into the openings 306 a, forming protrusions on the surface of the polymer web 304 facing the forming structure 306, while the portions of the polymer web 304 directly above the raised portions on the forming structure 306 conform to the shape of the raised portions to form an embossed film 310. If the drawn vacuum is sufficiently large (more negative), apertures may be formed at the ends of the protrusions, forming a perforated web.

[0043] Forming structure 306 also cools polymer web 304 as it is converted into embossed film 310, which may be separated from forming structure 306 by roller 312 and transported via further rollers 316, 318 to winder 314, which may wind it into roll 320. The illustrated embodiment is not intended to be limiting in any way. For example, in another embodiment, instead of extruding polymer web 304 directly onto forming structure 306, a polymer web that has already been extruded onto chilled rolls and quenched into a solid polymer web may be reheated and transported to forming station 307.

[0044] In one embodiment, the basis weight of the embossed film 310 may be from about 20 grams per square meter (gsm) to about 200 gsm. In one embodiment, the basis weight of the embossed film 310 may be from about 35 grams per square meter (gsm) to about 70 gsm. In one embodiment, the basis weight of the embossed film 310 may be from about 40 grams per square meter (gsm) to about 65 gsm. In one embodiment, the embossed film 310 may have an embossing thickness of from about 30 microns (μm) to about 800 microns (μm). In one embodiment, the embossed film 310 may have an embossing thickness of from about 120 microns (μm) to about 300 microns (μm). In one embodiment, the embossed film 310 may have an embossing thickness of from about 200 microns (μm) to about 250 microns (μm).

[0045] FIG. 4 illustrates a film 400 according to one embodiment of the present invention. As illustrated, the film 400 includes a foam core layer 410 sandwiched between two skin layers 412, 414 on opposite sides of the film 400. The foam core layer 410 includes a polymer matrix 416 and a plurality of microvoids 418, which may be formed using the apparatus illustrated in FIG. 5, as described in more detail below. The size and distribution of the microvoids 418 may be adjusted to achieve a desired bending stiffness for the film 400, such that the film 400 may be used as an interleaf between glass panes. In the illustrated embodiment, one skin layer 412 has an embossed outer surface 420, which may function as a release surface that will not adhere to the adjacent surface of a substrate (such as glass) protected by the film 400.

[0046] The polymer matrix 416 of the foam core layer 410 may be a blend of primarily HDPE or PP with minor components selected from various LDPEs, LLDPEs, and slip or antiblocking agents. The opposing skin layers 412, 414 of the foam core layer 410 may be blends of PE, HDPE, PP, LDPE, and LLDPE with HDPE and / or PP as the primary component. The PP may be any one or combination of highly crystalline PP, homopolymer PP, nucleated PP, and copolymer PP. Furthermore, additives may be included in the polyolefin, including, but not limited to, slip agents, nucleating agents, and antioxidant stabilizers.

[0047] FIG. 5 schematically illustrates an apparatus 500 that may be used to produce the film 400. As illustrated, the apparatus 500 includes a main extruder 502 and two satellite extruders 504, 506 that feed a feed block 508. The main extruder 502 is adapted to include an injection system 510 that injects a blowing agent according to the so-called Mucel method, as described, for example, in U.S. Patent Nos. 6,051,174 and 6,284,810 and U.S. Patent Application Publication No. 2013 / 0303645. In one embodiment, one or both of the satellite extruders 504, 506 may also be adapted to include an injection system that injects a blowing agent according to the Mucel method. The blowing agent may be carbon dioxide, nitrogen, or a mixture thereof. As described in the above-referenced patents, the blowing agent may be introduced into the extruder 502 as a supercritical fluid. A main extruder 502 with an injection system 510 is configured to create the foam core layer 410, and satellite extruders 504, 506 are configured to create the aforementioned skin layers 412, 414. A feed block 508 supplies an extrusion die 512, which outputs a molten curtain or extrudate 514 onto a smooth or textured (surface roughness Ra of 0.01 microns (μm) to about 20 microns (μm)) chrome-plated metal casting roller 516. As the extrudate 514 quenches on the casting roller 516, it may be embossed using a smooth, polished, and / or textured rubber embossing roller 518 with a surface roughness (Ra) of 20 microns (μm) or less to create a film 520, such as the film 400 shown in FIG. 4. The film 520 may be transported by rollers 524, 526 to a winder 522 and wound onto a roll 528.

[0048] The outer surface 530 of the embossing roller 518 may be textured, polished, and / or engraved with a fixed or random array of moon-shaped concave depressions or dimples (similar to the outer surface of a golf ball), as shown in more detail in FIG. 6. The purpose of embossing the fixed or random depressions is to intentionally create an isotropic "repeating defect" array (i.e., dimples, depressions, or indentations) in the film, such that a portion of the film thickness is elongated or protrudes above the embossed surface 420, as shown in FIG. 4. The regular, periodic protrusions created on the embossed surface 420 of the film 400 create a release surface that will not adhere to adjacent surfaces of the substrate protected by the film 400. As will be appreciated by those skilled in the art, the "repeating defects" (i.e., dimples, depressions, or indentations) on the embossed surface 420 may have any pattern, density, shape, height, etc., as desired.

[0049] In one embodiment, apparatus 500 may be configured to produce blown film instead of cast film as shown in Figure 5. In such an embodiment, extrusion die 512 may be configured as a circular die used in conventional blown film production lines, and air may be used to expand the extrudate into bubbles, as will be understood by those skilled in the art.

[0050] The total basis weight of film 400 may range from about 20 gsm to about 200 gsm. In one embodiment, the basis weight of film 400 may range from about 50 gsm to about 100 gsm. In one embodiment, the basis weight of film 400 may range from about 50 gsm to about 80 gsm. In one embodiment, the basis weight of film 400 may be about 60 gsm. The total thickness 422 of film 400 may range from about 30 microns (μm) to about 800 microns (μm), depending on the final desired bending stiffness. In one embodiment, the total thickness may be from about 50 microns (μm) to about 200 microns (μm). In one embodiment, the total thickness 422 of film 400 may range from about 90 microns (μm) to about 200 microns (μm). In one embodiment, the total thickness 422 of film 400 may range from about 80 microns (μm) to about 120 microns (μm).

[0051] It is contemplated that other techniques may be used to create the foam core layer 410. For example, chemical blowing agents and / or fillers may be used to create microvoids 418 within the polymer matrix 416 of the foam core layer 410.

[0052] Figures 7a and 7b are photomicrographs of a film 700 made using the Mueller process in a blown film manufacturing apparatus (not shown). The film 700 has a polymer matrix 710 containing HDPE and a plurality of microvoids 720. Various microvoid measurements are shown in Figure 7b and range from about 100 microns (μm) to about 1000 microns (μm). It is contemplated that smaller microvoids, with diameters as small as 5 microns (μm), may be achieved.

[0053] In applications where it is desirable to improve the adhesion of the film to the substrate it protects, an additional adhesive layer may be added, particularly to the non-embossed side of the film.

[0054] Film samples made according to the above method were produced and tested for two types of stiffness, compressibility, and resilience. Example 1 was made with the structure shown in Figures 2a-2f and a basis weight of approximately 49 grams per square meter (gsm). Example 2 was made with the structure shown in Figures 2a-2f and a basis weight of approximately 70 gsm. Example 3 was made with the structure shown in Figures 7a-7b and a basis weight of approximately 60 gsm. Comparative Example A had a basis weight of approximately 49 gsm and was a paper used as an interleaf for thick glass. Comparative Example B had a basis weight of approximately 76 gsm and was a standard printing paper used in copiers and desktop printers. As described below, all samples from Examples 1-3 and Comparative Examples A and B were tested for Gurley stiffness, Examples 1-3 and Comparative Example B were tested for circular bend stiffness, and Examples 1-3 were tested for compressibility and resilience.

[0055] The Gurley stiffness test method utilized a Teledyne Gurley, Model #4171, Digital Model, Genuine Gurley Stiffness Tester, testing equipment that measures the force required to bend a wide variety of flat materials and products with dimensions under controlled, repeatable conditions. The measured force can be equated to the stiffness, flexibility, or pliability of the tested material. For each sample, three specimens (n=3) were cut and tested in the machine direction (MD), and three specimens (n=3) were cut and tested in the transverse direction (TD), perpendicular to the machine direction. The stiffness values ​​for the MD and TD specimens were averaged and listed in Table 1 below.

[0056] The circular bend stiffness test method utilizes a plunger with a 25.4 mm (1 inch) diameter flat face to force a sample of material into an orifice in a platform. A force measurement gauge was used to measure the maximum force required to force the sample into a 38.1 mm (1.5 inch) orifice during a 57 mm (2.25 inch) downward stroke, beginning 3 mm (1 / 8 inch) above the top of the platform. The maximum force measured indicates material stiffness by measuring resistance to simultaneous bending in more than one plane.

[0057] The compressibility and resilience test method was used to evaluate the film's ability to withstand compression and recovery after compression by measuring the change in thickness after a 30.4 oz (862.60 g) weight was applied to the sample and removed from the sample. A pressure of 0.98 psi (6.76 kPa) was applied to the sample at 12.90 cm. 2 (2 square inches). The change in thickness before and after the application of the weight measures the compressive resistance of the film, and the reduction in thickness under pressure gives the compressibility of the film. The combined thickness before the application of the weight and after the weight is removed indicates the resilience (ability to recover) of the film. As used below, compressibility is a measure of the ability of a film to withstand compressive pressure and is defined as the compressed thickness divided by the original thickness (multiplied by 100). As used below, resilience measures the ability of a film to recover after compression and is defined as the rebound thickness of the film (after removal of pressure) divided by the original thickness (multiplied by 100).

[0058] [Table 1]

[0059] The compressibility and resilience data provide a measure of the cushioning effect provided by Examples 1-3. Higher compressibility values ​​indicate better cushioning effects, associated with higher resilience values ​​approaching 100%. By optimizing the film basis weight and structure according to the above-described embodiments of the invention, it is expected that the resulting film will provide the desired stiffness and cushioning effect for use as an interleaf between rigid substrates such as glass sheets or plates.

[0060] Additional comparative paper examples were tested for basis weight, circular bend stiffness, compressibility, and resilience (as described above), as well as low and high load calipers (as described above). Test results for the additional comparative examples are listed below in Table 2.

[0061] As mentioned above, the low load thickness test method for measuring the embossed thickness of a film uses a 50.8 mm (2 inch) diameter anvil and a 612.9 g / cm 2 A motorized micrometer with a dead load of 95 g / in² and a dwell time of 2 to 5 seconds was utilized. Five measurements were taken from a single film sample, and four different film samples were measured. All measurements were averaged for each example and reported as the "low load thickness" in microns (µm).

[0062] The high-load thickness test method, commonly used to measure the thickness of flat (i.e., non-embossed) films, utilized a micrometer with an anvil size of 0.48 cm (3 / 16 inch) and a dead load of 113 g. Five measurements were taken from a single film sample, and four different film samples were measured. All measurements were averaged for each example and reported as the "high-load thickness" in microns (μm).

[0063] Comparative Example C was a strip obtained from Steno Pads sold by Staples. Comparative Example D was a strip obtained from Steno Pads (item no. 1379800) sold by OfficeMax / Office Depot.

[0064] [Table 2]

[0065] Additional samples were made in accordance with embodiments of the present invention and tested for various physical properties as described herein. Examples 4-6 were made using apparatus 300 shown generally in FIG.

[0066] In Example 4, a blend of 85% polypropylene and 15% low density polyethylene was fed into the extruder and a monolayer melt curtain was extruded onto the forming structure 307 to form an embossed film having the structure generally shown in Figures 1a-1b and a basis weight of 44.6 gsm.

[0067] For Example 5, a three-layer melt curtain was extruded onto a forming structure 307 to form an embossed film having the structure generally shown in Figures 2a and 2b, except that the ribs 240 were oriented parallel to the x- and y-axes, which coincided with the machine direction (MD) and transverse direction (TD) of the film. The resulting film had a basis weight of 46.8 gsm. All three layers had the same blend of 99% high-density polyethylene and 1% low-density polyethylene masterbatch containing a slip agent.

[0068] For Example 6, the same blend of materials used in the three-layer film of Example 5 was extruded onto a forming structure 307 designed to provide the film with a pattern of raised ribs all disposed at a 45° angle to the machine direction (MD) of the film, as shown, for example, in Figure 2a. The resulting film had a basis weight of 64.1 gsm.

[0069] The samples were tested for low load thickness, high load thickness, circular bend stiffness, compressibility, and resilience according to the test methods described above. The results of such tests for Examples 4-6 are listed in Table 3 below.

[0070] [Table 3]

[0071] It is expected that samples with a circular bend stiffness of at least 200 grams will have the desired stiffness to replace paper as an interleaf material.

[0072] The residue measurement test method was used to determine how much residue was deposited on clean glass surfaces by film samples after aging under load at high temperature and humidity, and how much of the deposited residue washed off when the glass was subsequently washed. Specifically, each film sample was laminated to a clean glass surface and aged for 72 hours at 55°C and 85% relative humidity under a 1.2 kg weight. Prior to lamination, the clean glass surface was analyzed by interferometry at 25 locations, each measuring 1.40 mm x 1.05 mm, within a 50 mm x 50 mm area to determine the amount of underlying residue already present on the glass. After aging, the film was removed, and the amount of surface residue on the glass surface was measured at the same 25 locations to determine how much residue was deposited on the glass by the film. The glass was then washed in an automatic dishwasher, and the glass surface was measured again at the same 25 locations to determine how much residue remained on the glass. The results for Examples 4, 5, and 6 are listed in Table 4 below.

[0073] The particle count test method was completed according to the Helmuk Drum method (Institute of Environmental Science and Technology (IEST) RP-CC003.3). A film sample measuring 125 mm x 125 mm square was introduced into the Helmuk Drum chamber and rotated at 10 rpm for 10 minutes. An airborne particle counter connected to the chamber provided particle counts with sizes greater than 0.3 microns (μm) and greater than 0.5 microns (μm). The results for Examples 4-6 are also listed in Table 4 below.

[0074] [Table 4]

[0075] Apparatus 500 shown in FIG. 5 was used to prepare Examples 7-11, which are described below.

[0076] For Example 7, a three-layer melt curtain was extruded onto a casting roller with a surface roughness Ra of 0.01 μm, and an embossing roller with a surface roughness Ra of 1.14 μm was contacted with the film on the side opposite the film that had cooled on the casting roller. The core layer of the three-layer structure was a blend of 98% polypropylene and 2% polypropylene masterbatch containing a nucleating agent. The core layer of this sample was not foamed. The skin layers of the three-layer film were a blend of 98% polypropylene and 2% polypropylene masterbatch containing a nucleating agent. The resulting film had a basis weight of 68.8 gsm.

[0077] In Example 8, a three-layer melt curtain was extruded onto a casting roller with a surface pattern having a surface roughness of 4.19 μm (Ra), and an embossed roller with a surface roughness of 2.03 μm (Ra) was placed in contact with the film on the side opposite the film that had cooled on the casting roller. The core layer of the three-layer structure was a blend of 92% high-density polyethylene and 8% polyethylene masterbatch containing talc. The core layer was foamed using the Muesel process to create a foamed core layer with a polymer matrix and multiple microvoids, typically with outer diameters ranging from about 0.5 μm to about 12 μm. The skin layers of the three-layer film were a blend of 59% high-density polyethylene, 40% polypropylene, and 1% polypropylene masterbatch containing a nucleating agent. The resulting film had a basis weight of 71.8 gsm.

[0078] In Example 9, a three-layer melt curtain was extruded onto a casting roller with a surface roughness Ra of 3.81 μm, and an embossing roller with a surface roughness Ra of 7.62 μm was placed in contact with the film on the side opposite the film that had cooled on the casting roller. The core layer of the three-layer structure was a blend of 92% high-density polyethylene and 8% polyethylene masterbatch containing talc. The core layer was foamed using the Muesel process to create a foamed core layer with a polymer matrix and a plurality of microvoids, typically with major axis diameters ranging from about 0.3 μm to about 45 μm. The skin layers of the three-layer film were a blend of 59% high-density polyethylene, 40% polypropylene, and 1% polypropylene masterbatch containing a nucleating agent. The resulting film had a basis weight of 67.1 gsm.

[0079] In Example 10, a three-layer melt curtain was extruded onto a casting roller with a surface roughness Ra of 0.02 μm, and an embossing roller with a surface roughness Ra of 2.54 μm was placed in contact with the film on the side opposite the film that had cooled on the casting roller. The core layer of the three-layer structure was a blend of 88% polypropylene, 8% polyethylene masterbatch with talc, 2% low-density polyethylene masterbatch with antioxidant, and 2% polyethylene masterbatch with nucleating agent. The core layer was foamed using the Mucel process to create a foamed core layer with a polymer matrix and multiple microvoids, typically with major axis diameters ranging from about 0.3 μm to about 50 μm. The skin layers of the three-layer film were a blend of 96% polypropylene, 2% low-density polyethylene masterbatch with antioxidant, and 2% polyethylene masterbatch with nucleating agent. The resulting film had a basis weight of 69.9 gsm.

[0080] In Example 11, a three-layer melt curtain was extruded onto a casting roller with a surface roughness Ra of 8.89 μm, and an embossing roller with a surface roughness Ra of 7.62 μm was placed in contact with the film on the side opposite the film that had cooled on the casting roller. The core layer of the three-layer structure was a blend of 91% high-density polyethylene, 8% polyethylene masterbatch containing talc, and low-density polyethylene masterbatch containing antioxidants. The core layer was foamed using the Muesel process to create a foamed core layer with a polymer matrix and multiple microvoids, typically with major axis diameters ranging from about 0.3 μm to about 50 μm. The skin layers of the three-layer film were a blend of 65% polypropylene, 34% high-density polyethylene, and 1% polypropylene masterbatch containing a nucleating agent. The film was annealed at 85°C for 72 hours. The resulting film had a basis weight of 70.2 gsm.

[0081] The samples made for Examples 7-11 were each tested for low load thickness, high load thickness, circular bend stiffness, compressibility, and resilience, and the results of such tests are listed in Table 5 below.

[0082] [Table 5]

[0083] The surfaces of each side (i.e., the side that contacted the casting roller and the side that contacted the embossing roll) of the samples prepared for Examples 7-11 and Comparative Example D were tested for surface roughness, including Ra (surface roughness average), Rz (average height of the five highest peaks and five lowest valleys), and Sm (average spacing between peaks), using a surface roughness measuring instrument manufactured by Kosaka Laboratory Ltd. The results of the surface roughness tests are listed in Table 6 below.

[0084] [Table 6]

[0085] The samples prepared for Examples 7-10 were further tested according to the Residue Measurement Test Method and Particle Count Test Method as described above, and the results are listed in Table 7.

[0086] [Table 7]

[0087] It should be noted that any of the film and / or foam embodiments described herein may be modified by adding high crystalline polypropylene to the polypropylene in the blend, which is understood to increase the overall stiffness of the material in which it is incorporated.

[0088] The polymer film provided by the present invention is designed to replace paper currently used in the glass industry as an interleaf material to protect multiple stacks of glass sheets during storage and transport to user destinations. Generally, "repeated defects," i.e., dimples, depressions, indentations, and / or raised portions in the embossed film, are considered detrimental to soft, delicate optical substrates that transfer to functional substrates, thereby rendering the substrate unusable for high-resolution displays. In contrast, when glass or similar hard surfaces, such as polycarbonate (PC), poly(methyl methacrylate) (PMMA), or polished stainless steel, are the substrates to be protected, the hardness of such substrates resists any deformation caused by the repeated defects and embossed surface of the polymer film. The regularly or irregularly repeated defects or raised protrusions can help create a release surface, allowing one glass sheet to be cleanly separated from an adjacent glass sheet during unloading from a multi-sheet pack during storage or transport, even after a significant period of shelf time.

[0089] Embodiments of the present invention are directed to addressing a chronic problem faced by optical glass manufacturers, who are significantly affected by glass yield loss during storage and shipping due to stains and scratches caused by ingredients used in the manufacture of slipsheets. Potential advantages of films according to embodiments of the present invention include reusability, tunable coefficient of friction, fewer mobile species and particles than paper, low static charge, and / or cushioning.

[0090] It is contemplated that embodiments of the present invention may also be used to protect other substrates in addition to glass. For example, any hard, incompressible surface may be protected with a polymer film according to embodiments of the present invention, such as the surface of a metal such as steel, a plate or plank made of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and / or other thermoplastic or thermoset polymer.

[0091] The embodiments described herein represent many possible implementations and examples and are not intended to necessarily limit the disclosure to any particular embodiment. Instead, these embodiments can be modified in many ways, as will be understood by those skilled in the art. All such modifications are intended to be within the spirit and scope of the disclosure and protected by the following claims.

Claims

1. a foamed core layer having a uniform thickness and including a polyolefin matrix having a plurality of microvoids, the foamed core layer defining a first surface and a second surface opposite the first surface; a first skin layer on the first surface; a second skin layer on the second surface; Basis weight of 60gsm to 80gsm, a thickness of 90 microns to 200 microns; Circular bend stiffness test: 250 grams to 550 grams. Compression ratio of 5% to 20%; and an elasticity of 80% to 99%; the polyolefin matrix comprises as a major component (a) high density polyethylene, or (b) a polypropylene selected from high crystalline polypropylene, homopolymer polypropylene, and nucleated polypropylene, or (c) a blend thereof; the first skin layer and / or the second skin layer comprises polyethylene, polypropylene, or a blend thereof; The plurality of microvoids have a major axis diameter of 0.3 μm to 1000 μm. A film used as an interleaf between substrates.

2. 10. The film of claim 1, wherein the stiffness is from 300 grams to 350 grams by the Circular Bend Stiffness Test.

3. 10. The film of claim 1, wherein the first skin layer comprises an embossed outer surface having a regular or irregular pattern integrally formed thereon.

4. 4. The film of claim 3, wherein the second skin layer comprises an adhesive surface that adheres to glass, polycarbonate, poly(methyl methacrylate), and stainless steel.

5. 10. The film of claim 1, wherein at least one outer surface of the film has an average surface roughness Ra of 0.1 μm to 10 μm.

6. 10. The film of claim 1, wherein at least one outer surface of the film has a surface roughness Rz of 1 μm to 35 μm.

7. 10. The film of claim 1, wherein at least one outer surface of the film has an average spacing Sm between surface peaks of 100 μm to 350 μm.

8. 10. The film of claim 1, wherein the polyolefin matrix further comprises at least one additive selected from the group consisting of slip agents, nucleating agents, and antioxidant stabilizers.

9. 10. The film of claim 1, wherein the first skin layer and / or the second skin layer further comprises at least one additive selected from the group consisting of slip agents, nucleating agents, and antioxidant stabilizers.

10. The film of claim 1 , wherein the substrate is composed of glass, polycarbonate, poly(methyl methacrylate), or stainless steel.

11. 2. The film of claim 1, wherein the plurality of microvoids have a major axis diameter of 100 μm to 1000 μm.

12. 10. The film of claim 1, wherein the plurality of microvoids have a major axis diameter of 0.3 μm to 50 μm.

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