BACKGROUND

Sound-absorbing panels are sometimes used to reduce noise in, for example, automobiles and other modes of transportation. There exists a need for thin panels that can absorb acoustical frequencies below 1400 Hz. Fibrous absorption is very effective above 2000 Hz, but very thick (over 50 mm) layers are required for absorption below 1400 Hz. Helmholtz resonator designs can effectively absorb low frequency sound, but the need for a cavity of sufficient volume often leads to a thickness in excess of 40 mm. Panels of less than 20 mm thickness, particularly less than 10 mm thickness, that can absorb frequencies below 1400 Hz, are particularly desirable for use in industrial, office and home settings. Lightweight panels that may be shaped into finished articles with curved surfaces would be especially useful in transportation. Panels made of recyclable thermoplastic materials would offer a further sustainability advantage.

SUMMARY

Thus, in one aspect, the present disclosure provides a method, the method comprising, obtaining a first panel, wherein the first panel comprises a layer having first and second opposed major surfaces and a core comprising a plurality of walls extending from the second major surface of the layer providing a series of connected open-faced cells, wherein some of the cell walls have openings providing fluid communication between a series of at least three cells, wherein each cell wall has a plurality of sides, and wherein the first panel has at least a first opening extending between the first and second major surfaces of the layer into at least one cell in the series; obtaining a second panel, wherein the second panel comprises first and second layers each having first and second opposed major surfaces and a core disposed there between, wherein the core has a plurality of walls extending from the second major surface of the first layer providing a series of connected cells, wherein some of the cell walls have openings providing fluid communication between a series of at least three cells, wherein each cell wall has a plurality of sides, and wherein the second panel has at least a second opening extending between the first and second major surfaces of the first layer into at least one cell in the series; contacting the first and second panels such that the open-faced cells of the first panel face the first major surface of the first layer of the second panel; registering the first and second panels by aligning the open-faced cells of the first panel with the cells of the second panel; and welding the first panel and the second panel in contact to form a bond between the core of the first panel and the core of the second panel as the first and second panels cool to form an article. In another aspect, the present disclosure provides an article, the article comprising, a first panel, wherein the first panel comprises a layer having first and second opposed major surfaces and a core comprising a plurality of walls extending from the second major surface of the layer providing a series of connected open-faced cells, wherein some of the cell walls have openings providing fluid communication between a series of at least three cells, wherein each cell wall has a plurality of sides, and wherein the first panel has at least a first opening extending between the first and second major surfaces of the layer into at least one cell in the series; a second panel, wherein the second panel comprises first and second layers each having first and second opposed major surfaces and a core disposed therebetween, wherein the core has a plurality of walls extending from the second major surface of the first layer providing a series of connected cells, wherein some of the cell walls have openings providing fluid communication between a series of at least three cells, wherein each cell wall has a plurality of sides, and wherein the second panel has at least a second opening extending between the first and second major surfaces of the first layer into at least one cell in the series; wherein the first panel and the second panel are bonded between the core of the first panel and the core of the second panel; and wherein the open-faced cells of the first panel face the first major surface of the first layer of the second panel.

Various aspects and advantages of exemplary embodiments of the present disclosure have been summarized. The above Summary is not intended to describe each illustrated embodiment or every implementation of the present disclosure. Further features and advantages are disclosed in the embodiments that follow. The Drawings and the Detailed Description that follow more particularly exemplify certain embodiments using the principles disclosed herein.

DEFINITIONS

For the following defined terms, these definitions shall be applied for the entire Specification, including the claims, unless a different definition is provided in the claims or elsewhere in the Specification based upon a specific reference to a modification of a term used in the following definitions:

The terms “about” or “approximately” with reference to a numerical value or a shape means +/- five percent of the numerical value or property or characteristic, but also expressly includes any narrow range within the +/- five percent of the numerical value or property or characteristic as well as the exact numerical value. For example, a temperature of “about” 100°C refers to a temperature from 95°C to 105°C, but also expressly includes any narrower range of temperature or even a single temperature within that range, including, for example, a temperature of exactly 100°C. For example, a viscosity of “about” 1 Pa-sec refers to a viscosity from 0.95 to 1.05 Pa-sec, but also expressly includes a viscosity of exactly 1 Pa-sec. Similarly, a perimeter that is “substantially square” is intended to describe a geometric shape having four lateral edges in which each lateral edge has a length which is from 95% to 105% of the length of any other lateral edge, but which also includes a geometric shape in which each lateral edge has exactly the same length.

The term “substantially” with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited. For example, a substrate that is “substantially” transparent refers to a substrate that transmits more radiation (e.g. visible light) than it fails to transmit (e.g. absorbs and reflects). Thus, a substrate that transmits more than 50% of the visible light incident upon its surface is substantially transparent, but a substrate that transmits 50% or less of the visible light incident upon its surface is not substantially transparent.

The terms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a material containing “a compound” includes a mixture of two or more compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

Fig 1 is a perspective view of one embodiment of an article of the present disclosure;

Fig. 1A is a cross-section view of the article in Fig. 1;

Fig. IB is a planar view of the first panel in the article of Fig. 1;

Fig. 1C is a planar view of the second panel in the article of Fig. 1;

Fig. ID is a perspective view of an open-face cell in the first panel of Fig. 1; and

Fig. IE is a planar view of an alternative second panel in the article of Fig. 1.

While the above-identified drawings, which may not be drawn to scale, set forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed invention by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure. DETAILED DESCRIPTION

Before any embodiments of the present disclosure are explained in detail, it is understood that the invention is not limited in its application to the details of use, construction, and the arrangement of components set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways that will become apparent to a person of ordinary skill in the art upon reading the present disclosure. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure.

As used in this Specification, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5, and the like).

Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the Specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

There may be a need for thicker panels, for example, either for increased mechanical rigidity or lower frequency absorption. It is possible to combine two panels into a thicker one in several configurations and by several methods.

Referring to FIGS. 1, 1A, IB, 1C and ID, article 10 can have a first panel 100 that has a layer 110 having first and second opposed major surfaces, 111, 112, and core 120. Core 120 has plurality of walls 141 extending from second major surface 112 of first layer 110 providing a first series 160, 160’ of connected open-faced cells 140, 140’. Also shown are second and third series of cells 1160, 1160’, and 1170, 1170’. Some of cell walls 141a, 141b, 141c have openings 150 providing fluid communication between first series 160 of five cells 140. Each cell wall 141 has a plurality of sides 171, 172. Each side 171, 172 of cell wall 141 has area A. Opening 150 in cell wall 141a has area A’ that is at least 50 percent of area A. First layer 110 has at least first opening 190a, 190b extending between the first and second major surfaces 111, 112 of first layer 110 into at least one cell in series 160, 160’, respectively. Note that first openings 190a, 190b, 190c, etc., are displayed as circles, but can be any of a variety of shapes including squares, triangles, rectangles, hexagons, or other polygons. Multiple openings could also be used, including openings having at least two holes, or openings which include a woven or non- woven permeable material.

In some embodiments, at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, or even at least 100) percent of openings 150 in a cell wall 141 emanate from the first layer 110. Opening 150 can have contours having curved and straight portions, and any straight portions can be either perpendicular to or tilted at another angle to layer 110. Optionally the center cell 188 could have an opening in the first layer 110.

Article 10 can further have a second panel 200 that has first and second layers 210, 230 each having first and second opposed major surfaces 211, 212, 231, 232, and core 220 disposed there between. Second layer 230 is free of any openings between first and second major surfaces 231, 232 of second layer 230. Core 220 has a plurality of walls 241 extending from second major surface 212 of first layer 210 to first major surface 231 of second layer 230 providing first series 260, 260’ of connected cells 240, 240’. Also shown are second and third series of cells 2160,

2160’ and 2170, 2170’. Some of cell walls 241a, 241b, 241c have openings 250 providing fluid communication between first series 260 of five cells 240. First layer 210 can have second opening 290a, 290b extending between the first and second major surfaces 211, 212 of first layer 210 into at least one cell in series 260, 260’, respectively. Note that second openings 290a, 290b, 290c, etc., displayed as circles, but can be any of a variety of shapes including squares, triangles, rectangles, hexagons, or other polygons. Multiple openings could also be used, including openings having at least two holes, or openings which include a woven or non- woven permeable material.

At least 50 percent of openings 250 in cell walls 241 emanate from either first or second layer 210, 230. In some embodiments of panels 200, each cell wall has a plurality of sides, wherein each side of a cell wall has an area (A), and wherein the opening in a cell wall has an area (A’) that is at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, or even at least 80; in some embodiments, in a range from 50 to 80) percent of the area of a side of that cell wall. Optionally, the center cell 288 can have an opening in the first layer 210.

The first panel 100 and the second panel 200 are bonded between the cell walls 141 of the open-faced cells of the first panel 100 and the first major surface 211 of the first layer 210 of the second panel 200. The open-faced cells of the first panel face the first major surface 211 of the first layer 210 of the second panel 200. The first panel 100 and the second panel 200 are aligned in the thickness direction and the opening, for example, 190a from the layer of the first panel 100, is aligned with the opening, for example, 290a from the first layer 210 of the second panel 200 so that a hole extends through the first layer 210 of the second panel 200 to interconnect channels. For example, the first series 160 of connected open-faced cells of the first panel 100 interconnect with the first series 260 of connected cells of the second panel 200 through the openings 150 and 250 of cell walls 141 and 142 and opening 290a. In an alternative embodiment, at least one open- faced cell of the first panel 100 aligns with the opening of an alternative second panel, as illustrated in Fig. IE, such that a series of connected open-faced cells of die first panel connect to series of connected cells of the alternative second panel. In these embodiments, the volume of connected cells are increased (doubled in the embodiment in Fig. 1) without significantly increasing the thickness of the articles.

In some embodiments, the series of cells of die first panel has a first cell in the series and a last cell in the series, and wherein the first opening of the first panel extends into either the first or last cell in the series. In some embodiments, the series of cells of the second panel has a first cell in the series and a last cell in the series, and wherein the second opening of the second panel extends into either the first or last cell in the series. In some embodiments, the series of cells includes a middle cell in the series.

In some embodiments, the series of cells has a first cell in a series, a last cell in the series, and at least one cell between the first and second cells, and wherein first opening extends into one of the cells between the first and second cells. In some embodiments, one of the cells between the first and last cells is a middle cell.

In some embodiments of panels described herein, each cell has at least 3 (in some embodiments, at least 4, 5, 6, 7, 8, 9, or even at least 10) walls.

In some embodiments of panels described herein, each cell has a largest distance between two opposed walls of at least 3 mm (in some embodiments, at least 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, or even at least 30 mm; in some embodiments, in a range from 3 mm to 30 mm, 7 mm to 30 mm, 15 mm to 30 mm, or even 20 mm to 30 mm). In some embodiments of panels described herein, each cell has a largest distance between two opposed vertices of at least 5 mm (in some embodiments, at least 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, or even at least 40 mm; in some embodiments, in a range from 15 mm to 40 mm, 20 mm to 40 mm, or even 30 mm to 40 mm).

In some embodiments of panels described herein, each cell has a distance from the second surface of the first layer to the first surface of the second layer of at least 2 mm (in some embodiments, at least 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or even at least 15 mm; in some embodiments, in a range from 4 mm to 15 mm, 7 mm to 15 mm, or even 10 mm to 15 mm).

In some embodiments of panels described herein, each cell has a volume of at least 0.04 cm ³ (in some embodiments, at least 0.1 cm ³ , 0.5 cm ³ , 1 cm ³ , 2 cm ³ , 3 cm ³ , 4 cm ³ , 5 cm ³ , 10 cm ³ , 15 cm ³ , 20 cm ³ , 25 cm ³ , or even at least 30 cm ³ ; in some embodiments, in a range from 0.04 cm ³ to 30 cm ³ , 0.1 cm ³ to 30 cm ³ , 0.5 cm ³ to 30 cm ³ , 2 cm ³ to 30 cm ³ , or even 15 cm ³ to 30 cm ³ ).

In some embodiments of panels described herein, a series of cells has a cumulative volume of at least 0.5 cm ³ (in some embodiments, at least 1 cm ³ , 1.5 cm ³ , 2 cm ³ , 3 cm ³ , 4 cm ³ , 5 cm ³ , 10 cm ³ , 25 cm ³ , 50 cm ³ , 75 cm ³ , 100 cm ³ , 150 cm ³ , or even at least 200 cm ³ ; in some embodiments, in a range from 1.5 cm ³ to 200 cm ³ , 10 cm ³ to 120 cm ³ , or even 50 cm ³ to 200 cm ³ ).

In some embodiments of panels described herein, a series of cells has a cumulative length of at least 20 mm (in some embodiments, at least 30 mm, 40 mm, 50 mm, 75 mm, 100 mm, 150 mm, or even at least 200 mm; in some embodiments, in a range from 30 mm to 200 mm, 50 mm to 200 mm, or even 100 mm to 200 mm).

In some embodiments, a series of cells of panels described herein has a cumulative length of at least 20 mm (in some embodiments, at least 25 mm, 30 mm, 40 mm, or even at least 50 mm).

In some embodiments of panels described herein, the first layer comprises at least one of polymeric, metallic, ceramic, or composite materials (e.g., fiber reinforced, woven or non-woven in a resin matrix). In some embodiments of panels described herein, the second layer comprises at least one of polymeric, metallic, ceramic, or composite materials (e.g., fiber reinforced, woven or non-woven in a resin matrix). In some embodiments of panels described herein, the core comprises at least one of polymeric, metallic, ceramic, or composite materials (e.g., fiber reinforced, woven or non-woven in a resin matrix).

Exemplary polymeric materials include polyethylenes, polypropylenes, polyolefins, polyvinylchlorides, polyurethanes, polyesters, polyamides, polystyrene, copolymers thereof, and combinations thereof (including blends). The polymeric materials may be thermosetting by, for example, heat or ultraviolet (UV) radiation, or thermoplastic.

Exemplary metallic materials include aluminum, steel, nickel, copper, brass, bronze, and alloys thereof.

Exemplary ceramic (including glass, glass-ceramic, and crystalline ceramic) materials include oxides, nitrides, and carbides.

Exemplary fiber containing materials include fibers such as cellulose, carbon, thermoplastic fibers (polyamide, polyester, and aramid, polyolefin), steel, and glass, as may be applicable to the particular type of material.

In some embodiments, materials for panels described herein may be in the form of multilayers.

Optionally materials for panels described herein may also include fillers, colorants, plasticizers, dyes, etc., as may be applicable to the particular type of material. In some embodiments, panels described herein have a single composition. Such embodiments are desirable to enhance recyclability.

In some embodiments of panels described herein, the series of cells is in a regular pattern. For example, a group of regular repeating hexagonal arrays of connected cells and openings.

In some embodiments of panels described herein, the first layer has a thickness of at least 0.01 mm (in some embodiments, at least 0.05 mm, 0.1 mm, 0.25 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, or even at least 3 mm; in some embodiments, in a range from 0.025 mm to 0.5 mm, 0.1 mm to 2 mm, 0.25 mm to 3 mm or even 0.5 mm to 3 mm). In some embodiments of panels described herein, the second layer has a thickness of at least 0.01 mm (in some embodiments, at least 0.05 mm, 0.1 mm, 0.25 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, or even at least 3 mm; in some embodiments, in a range from 0.025 mm to 0.5 mm, 0.1 mm to 2 mm, 0.25 mm to 3 mm or even 0.5 mm to 3 mm). In some embodiments, panels described herein have a thickness of at least 4 mm (in some embodiments, at least 7 mm, 10 mm, or even at least 15 mm; in some embodiments, in a range from 4 mm to 8 mm, 6 mm to 10 mm, or even 8 mm to 15 mm).

In some embodiments of panels described herein, the cell walls have a thickness of at least 0.01 mm (in some embodiments, at least 0.05 mm, 0.1 mm, 0.2 mm, or even at least 0.5 mm; in some embodiments, in a range from 0.01 mm to 0.2 mm, 0.05 mm to 0.5 mm, or even 0.1 mm to 0.5 mm).

In some embodiments of panels described herein, the first series of cells comprises at least 4 (in some embodiments, at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or more) cells. In some embodiments, panels described herein further comprising a second series of at least 3 (in some embodiments, at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or more) cells. In some embodiments, panels described herein further comprise a third series of at least 3 (in some embodiments, at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or more) cells.

In some embodiments, panels described herein further comprise a tie layer on at least a portion of the second of the major surface of the first layer. In some embodiments, panels described herein further comprising a tie layer on at least a portion of the first of the major surface of the second layer. Although not wanting to be bound by theory, the tie layer is believed to facilitate adhesion between first or second layer 110, 210 and core layer 120. In some cases, the same polymer used for the skin and core may also be used as the tie layer. This approach forms a desirable recyclable panel as all components have substantially the same composition (i.e., at least 85 percent by weight is the same composition). In some embodiments, similar polymers for both the core and skins can be used. In some embodiments, additives to slow the crystallization rate and/or reduce the viscosity of the tie layer may be used. These minor additives desirably do not affect the recycling of polymers. In some embodiments, additives that promote a chemical bond between the tie layer and the skin and/or the core can be employed. In some embodiments, block copolymers can be useful where the copolymer has blocks containing polymers with affinity for the skin and blocks with affinity for the core. In some embodiments, techniques for compatibilizing incompatible polymer blends may be useful. In some embodiments, hot melt adhesives, pressure sensitive adhesives and/or curable adhesives may be used.

In some embodiments, panels described herein exhibit indicia (including alphanumerics). In some embodiments, the indicia is in the form of a trademark or copyrighted material, including a registered trademark or registered copyright as defined under any of the countries, territories, etc., of the world (including the United States). In some embodiments, the indicia is on at least one of the first major surface of the first layer, on the second major surface of the second layer. In some embodiments, the panel is in the form of the indicia.

In some embodiments, panels described herein exhibit at least one absorption band less than 1400 Hz (in some embodiments, less than 1300 Hz, or even less than 1200 Hz). In some embodiments, panels described herein exhibit at least one absorption band in a range from at least 800 Hz to 1200 Hz (in some embodiments, in a range from at least 500 Hz to 1300 Hz, at least 200 Hz to 1400 Hz, or even at least 20 Hz to 1400 Hz). The absorption bands of panels described herein are measured as described in the Examples using the “Normal Incidence Acoustical Absorption Test” and the “Reverberation Chamber Test.”

Advantageously, in some embodiments, panels (or articles comprising one or more panels) described herein have a thickness in a range from 4 mm to 8 mm, 6 mm to 10 mm, or even 8 mm to 15 mm, and exhibiting at least one absorption band less than 1400 Hz (in some embodiments, less than 1300 Hz or even less than 1200 Hz). In some embodiments, panels (or articles comprising one or more panels) described herein have a thickness in a range from 4 mm to 8 mm, 6 mm to 10 mm, or even 8 mm to 15 mm, and exhibiting at least one absorption band in a range from at least 800 Hz to 1200 Hz (in some embodiments, in a range from at least 500 Hz to 1300 Hz, at least 200 Hz to 1400 Hz, or even at least 20 Hz to 1400 Hz). For instance, each of Examples 5 and 6, described below, include panels comprising a thickness of less than 15 mm (more particularly 6.2 mm) and exhibit at least one absorption band less than 1400 Hz. In some embodiments, laminated articles described herein comprising at least two panels laminated together (or three, four, five, or more stacked panels laminated together) have a thickness in a range from 8 mm to 50 mm, 10 mm to 30 mm, or even 12 mm to 40 mm, and exhibiting at least one absorption band in a range from at least 600 Hz to 1000 Hz (in some embodiments, in a range from at least 500 Hz to 1300 Hz, at least 200 Hz to 1400 Hz, or even at least 20 Hz to 1400 Hz). In some embodiments, panels described herein exhibit an acoustical absorption of at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, or even 80) percent. The acoustical absorption of panels described herein are measured as described in the Examples using the “Normal Incidence Acoustical Absorption Test” and the “Reverberation Chamber Test.”

In some embodiments, panels described herein exhibit a flexural rigidity of at least 1 N-m ² (in some embodiments, at least 5 N-m ² , 10 N-m ² , 15 N-m ² , 20 N-m ² , 25 N-m ² , 30 N-m ² , 35 N-m ² , 40 N-m ² , 45 N-m ² , 50 N-m ² , 55 N-m ² , or even 60 N-m ² ) per meter of width. The flexural rigidity of panels described herein are measured as described in the Examples using the “3 Point Flexure Test.”

In some embodiments, panels described herein exhibit a compression strength of at least 0.35 MPa (in some embodiments, at least 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 3 MPa, or even 4 MPa). The compression strength of panels described herein are measured as described in the Examples using the “Compression Test.”

Advantageously, in some embodiments, panels (or articles comprising one or more panels) described herein exhibit both a flexural rigidity of at least 1 N-m ² (in some embodiments, at least 5 N-m ² , 10 N-m ² , 15 N-m ² , 20 N-m ² , 25 N-m ² , 30 N-m ² , 35 N-m ² , 40 N-m ² , 45 N-m ² , 50 N-m ² , 55 N- m ² , or even 60 N-m ² ) per meter of width and at least one absorption band less than 1400 Hz (in some embodiments, less than 1300 Hz or even less than 1200 Hz). In some embodiments, panels (or articles comprising one or more panels) described herein exhibits both a flexural rigidity of at least 1 N-m ² (in some embodiments, at least 5 N-m ² , 10 N-m ² , 15 N-m ² , 20 N-m ² , 25 N-m ² , 30 N-m ² , 35 N-m ² , 40 N-m ² , 45 N-m ² , 50 N-m ² , 55 N-m ² , or even 60 N-m ² ) per meter of width and at least one absorption band in a range from at least 800 Hz to 1200 Hz (in some embodiments, in a range from at least 500 Hz to 1300 Hz, at least 200 Hz to 1400 Hz, or even at least 20 Hz to 1400 Hz). For instance, Examples 5 and 6, described below, includes panels exhibiting both a flexural rigidity of at least 1 N-m ² per meter of width and at least one absorption band less than 1400 Hz.

Both modeling and physical experimental measurements have shown that the acoustic absorption behavior of a panel according to the present disclosure is a function of each of the panel thickness, cell sizes, passageway percentage, skin hole sizes, and number of connected cells. This is demonstrated in Jonza, T, Herdtle, T., Kalish, T, Gerdes, R. et ah, “Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels,” SAE Int. J. Veh. Dyn., Stab., and NVH 1(2):2017, doi: 10.4271/2017-01-1813, incorporated herein by reference. For instance, 1) as the number of connected cells is increased, the frequency of the peak absorption decreases; 2) as the skin hole size (whether provided by one hole or multiple holes) increases, the frequency of the peak absorption increases; 3) as the width of the cell decreases, more cells need to be connected to exhibit absorption at the same frequency; 4) as the cell height decreases, the frequency of the peak absorption increases; 5) as the passageway size decreases, the frequency of the peak absorption decreases (plus with less total absorption and narrower absorption peaks); and 6) as the skinthickness increases, the frequency of peak absorption decreases. Hence, multiple variables can be adjusted to optimize (e.g., tune) the acoustic absorption of a panel or article for a particular end use application.

In another aspect, the present disclosure describes a method for making articles from panels described herein comprising obtaining the first panel and the second panel; contacting the first and second panels such that the open-faced cells of the first panel face the first major surface of the first layer of the second panel; registering the first and second panels by aligning the open-faced cells of the first panel with the cells of the second panel; and welding the first panel and the second panel in contact to form a bond between the core of the first panel and the core of the second panel as the first and second panels cool to form an article. As used herein, “weld” refers to the attachment of two polymeric materials using heat. The heat may be provided through various mechanisms, including for instance and without limitation, conduction, vibration, oscillation, radiant energy (e.g., laser or infrared energy), or convection of a fluid. Typically, two polymeric materials are welded together by applying heat to a surface of each of the materials, bringing the two heated surfaces together, and allowing the heated surfaces to cool and form a bond, such as through entanglement of polymers from each surface. Pressure is usually applied to hold the two polymeric materials together and promote the formation of a weld between the two polymeric materials as they cool. These welding techniques have the advantage that no new materials are introduced into the construction, so that recyclability of the finished parts is more facile. The welding is typically provided by conduction, vibration, oscillation, radiant energy, or convection of a fluid. In certain embodiments, the method is a continuous method of forming the article whereas in other embodiments the method is a batch method of forming the article.

The method can further comprise holding the first and second panels in place through mechanical means. Mechanical means can include alignment features or locating pins.

The following working examples are intended to be illustrative of the present disclosure and not limiting.

EXAMPLES

Dual-Sided (Closed-Faced) Honeycomb Preparation

Honeycomb/Bottom-Skin Preparation. A three-roll stack casting station was used. The first roll was a chrome roll of 10 inch (254 mm) diameter, controlled to 160 °F (71 °C). The center roll was a 20 inch (508 mm) diameter roll and was a tooling roll that had multiple 11.5 mm (width dimension) connected hexagons cut 0.32 inch (8.1 mm) deep into its surface. The grooves forming the hexagonal pattern had a draft angle of 1.6° and were 0.028 inch (0.7 mm) wide at the bottom and 0.51 inch (1.3 mm) wide at the roll surface. The hexagonal grooves are interconnected as depicted in in Jonza, James, et al. "Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels," INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Vol. 254, No. 2, Institute of Noise Control Engineering, 2017). One wall of each hexagon had an archway as depicted in Figure 2A of the same reference. Polypropylene resin (obtained under the trade designation “PRO FAX 8523” from LyondellBasell, Rotterdam, Netherlands) was fed to a 63 mm extruder (obtained under the trade designation “NRM” from Davis-Standard, LLC, Pawcatuck, CT), operated at 110 rpm, with barrel zone temperatures ramped from 380 °F (193 °C) to 500 °F (232 °C), and extruded into the gap between the chrome roll and the tooling roll. For this purpose, a 40 inch (1016 mm) film die set to 500 °F (260 °C) was used, and was configured to drop the extrudate into the nip such that it was between the chrome roll and the tooling roll. The gap between the chrome roll and the tooling roll was 0.018 inch (0.46 mm). There was an excess of resin extruded, such that a 0.018 inch (0.46 mm) bottom skin was formed in addition to the honeycomb structure. The line speed was 3.2 feet/minute (1 m/min.) and the honeycomb tooling roll was set to 170 °F (77 °C). The extrudate crystallized while in contact with the tooling roll, and after travelling about 180° around the tooling roll, the skin side came into contact with the third roll, a silicone roll. A belt puller located beyond the silicone roll was used to control the pulling force at 35 lbs. (156 N); a force sufficient to remove the solidified extrudate from the tooling roll onto the silicone roll, but insufficient to elongate (distort) the hexagonal geometry. The honeycomb was measured to have 0.270 inch (6.86 mm) wall height.

Top Skin Lamination to the Honeycomb/Bottom-Skin Assembly. A 0.010 inch (0.25 mm) thick black polypropylene copolymer film (obtained under the trade designation “MC900F” from CharterNex, Bloomer, WI) was unwound over the top of the belt puller and continuously contacted the top belt. A molten tie layer of the polypropylene (“PROFAX 8523”) was extruded, using a 1.5 inch (37.5 mm) extruder (obtained from Davis-Standard, EEC) operating at 45 rpm, onto the open side of the honeycomb just prior to contacting the top skin in the entrance to the belt puller. The barrel temperatures of the tie layer extruder were ramped from 350 °F (177 °C) to 500 °F (260 °C) and the die was set to 500 °F (260 °C). The resulting panel was 0.36 inch (9.1 mm) thick with a 0.021 inch (0.53 mm) thick top skin. The panel was passed through a double belt laminating machine (obtained under the trade designation “MEYER” from Maschinenfabrik Herbert Meyer GmbH, Roetz, Germany), with 0.010 inch (0.25 mm) PTFE/glass fabric belts. Zones 1 and 2 had the top belt temperature set at 139 °C and the bottom belt set at 147 °C. The belt separation in zones 1 and 2 was set to 9.5 mm, the nip rolls at 9.4 mm and the cooling zone at 9.5 mm separation with the water at 19 °C. Single-Sided (Open-Faced) Honeycomb Preparation

The Open-Faced Honeycomb was made in the same fashion as the Honeycomb/Bottom- Skin above, but instead of the lamination of a Top Skin, it was simply cut into 1 m x 1.3 m sheets.

Example 1

Both dual sided and single sided (closed-faced and open-faced, respectively) 8 mm thick polypropylene sandwich composite panels were produced as described above. A repeating pattern of 6 perforations was drilled, using a computer numeric control (CNC) machine, through the first skin of the dual sided sandwich composite panel; each perforation was positioned within either terminal cell of an independent channel. For this Example, the 800-1200 Hz frequency absorption pattern (as described in Jonza, James, et al. "Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels," INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Vol. 254, No. 2, Institute of Noise Control Engineering, 2017) was selected for the repeat pattern. Next, a repeating pattern of perforations was drilled by hand through the opposite terminal cell of each independent channel of the single sided, open-faced panel. For this Example, identical perforation diameters were used in each panel with respect to the specific channels. Next, both panels were laser cut to 99 mm diameter discs using a 100W C02 laser cutting system (obtained under the trade designation “VLS6.60” from Universal Laser Systems, Inc., Scottsdale, AZ) positioned on the center of the 37 hexagon repeat pattern. Figure IB shows the 37 hexagon repeat pattern. The various length (i.e. various cell count) acoustic chambers were identified on each specimen and the discs were laid out in the identical orientation. The single sided, open faced disc was placed by hand onto the dual sided sandwich panel with the open-face side in contact with the drilled skin. The stacked panels were positioned between the platens of a vibration welding machine (obtained under the trade designation “BRANSON MINI II” from Emerson Electric Co., St. Louis, MO) which had been previously covered with medium grit anti-slip safety tread material (obtained under the trade designation “3M SAFETY-WALK 7733” from 3M Co., St. Paul, MN). The vibration welding machine was programmed to perform a welding process with an amplitude of 0.05 inches (1.27 mm), frequency of 230 Hz and welding time of 5 seconds with clamping pressure of 80 psi (550 kPa). Once welded, the open face honeycomb walls were uniformly bonded to the skin of the dual sided sandwich panel providing acoustically sealed chambers. The 16 mm thick sandwich panel disc assembly was then evaluated for acoustic properties using an impedance tube (obtained under the trade designation “B&K 4206” from Bruel & Kjaer, Naerum, Denmark) with type 2716C amplifier and type 2670 microphone. Results indicate that effectively doubling the acoustic chamber length and volume dramatically reduced the absorption frequency of the panels. Example 2 (Visible Camera)

Both dual sided and single sided (closed-faced and open-faced, respectively) 8mm thick polypropylene sandwich composite panels were produced as described above. A repeating pattern of 6 perforations was drilled, using a computer numeric control (CNC) machine, through the first skin of the dual sided sandwich composite panel; each perforation was positioned within either terminal cell of an independent channel. For this Example, the 800-1200Hz frequency absorption pattern (as described in Jonza, James, et al. "Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels," INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Vol. 254, No. 2, Institute of Noise Control Engineering, 2017) was selected for the repeat pattern. Next, a repeating pattern of perforations was drilled by hand through the opposite terminal cell of each independent channel of the single sided, open-faced panel. For this Example, identical perforation diameters were used in each panel with respect to the specific channels. Next, both panels were laser cut to 99 mm diameter discs using a 100W C02 laser cutting system (obtained under the trade designation “VLS6.60” from Universal Laser Systems, Inc., Scottsdale, AZ) positioned on the center of the 37 hexagon repeat pattern. Figure IB shows the 37 hexagon repeat pattern. The polypropylene closed faced panel was affixed to an imaging platform using a generic adhesive tape, with the perforated skin facing the camera, and imaged using an area scan camera (obtained under the trade designation “BASLER ACE ACA1920-155UM” from Basler AG, Ahrensburg, Germany) and a 25 mm FI.8 lens (obtained under the trade designation “KOWA” from i4 Solutions, LLC, Mendota Heights, MN) under ambient lighting conditions. An image was captured of a first panel and stored as a reference image using standard PC software. The open-faced panel was positioned on top of the closed faced panel with the perforated skin facing towards the camera. The various length (i.e., various cell count) acoustic chambers were identified on each specimen and the discs were laid out in the identical orientation. A second image was collected of the stacked honeycomb structure and processed by subtracting the reference image to form a combined image which was displayed to the operator. To achieve panel alignment, the open-faced panel was repositioned via translation and rotation by hand until the perforations in the combined image were overlapped. Once sufficient alignment was achieved (i.e., the honeycomb walls are mostly overlapping, and each of the perforations is in the correct cell), the panels were affixed using a generic adhesive tape and transitioned to a vibration welding machine (obtained under the trade designation “BRANSON MINI II ” from Emerson Electric Co., St. Louis, MO) for further processing. Example 3 (IR Camera)

Both dual sided and single sided (closed-faced and open-faced, respectively) 8 mm thick polypropylene sandwich composite panels were produced as described above. A repeating pattern of 6 perforations was drilled, using a computer numeric control (CNC) machine, through the first skin of the dual sided sandwich composite panel; each perforation was positioned within either terminal cell of an independent channel. For this Example, the 800-1200 Hz frequency absorption pattern (as described in Jonza, James, et al. "Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels," INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Vol. 254, No. 2, Institute of Noise Control Engineering, 2017) was selected for the repeat pattern. Next, a repeating pattern of perforations was drilled by hand through the opposite terminal cell of each independent channel of the single sided, open-faced panel. For this Example, identical perforation diameters were used in each panel with respect to the specific channels. Next, both panels were laser cut to 99 mm diameter discs using a 100W C02 laser cutting system (obtained under the trade designation “VLS6.60” from Universal Laser Systems, Inc., Scottsdale, AZ) positioned on the center of the 37 hexagon repeat pattern. Figure IB shows the 37 hexagon repeat pattern. The polypropylene open-faced panel was affixed to an imaging platform using generic adhesive tape with the perforated skin facing away from the camera. A heat gun (obtained under the trade designation “MASTER- MITE 10008” from Master Appliance Corp., Racine, WI) was used to elevate the temperature of the honeycomb core walls with respect to the perforated skin of the open face panel. An image was recorded as Image 1 using a high-resolution science grade LWIR thermal imaging camera (obtained under the trade designation “FLIR A655SC” from FLIR Systems, Inc., Wilsonville, OR) using a 24.6 mm lens. Image 1 was processed using a thresholding method implemented with Java-based image processing software (“ImageJ”, public domain software developed at the National Institutes of Health and the Laboratory for Optical and Computational Instrumentation (LOCI, University of Wisconsin)) resulting in a binary image with the core wall sections denoted with black color. The closed-faced panel was presented beneath the thermal imaging camera with the perforated skin facing opposite. The various length (i.e., various cell count) acoustic chambers were identified on each specimen and the discs were laid out in the identical orientation. The temperature of the non- perfbrated skin was elevated with respect to the core walls using the heat gun (“MASTER-MITE 10008”) and an image was acquired using the thermal imaging camera and stored as Image 2. Image 2 was further processed using a thresholding method implemented with the image processing software (“ImageJ”) resulting in a binary image with the core wall sections denoted in black color. Image 2 was overlaid on Image 1 to create a combined stacked image with the closed-faced panel core walls denoted in red color. To achieve panel alignment, the closed-faced panel was repositioned via translation and rotation by hand until the red core wall segments in the combined image were overlapped with the black colored open-faced core wall segments. Once sufficient alignment was achieved (i.e., the honeycomb walls are mostly overlapping, and each of the perforations is in the correct cell), the panels were affixed using a generic adhesive tape and transitioned to the vibration welding machine (“Branson Mini II”) for further processing.

All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure. Illustrative embodiments of this invention are discussed and reference has been made to possible variations within the scope of this invention. For example, features depicted in connection with one illustrative embodiment may be used in connection with other embodiments of the invention. These and other variations and modifications in the invention will be apparent to those skilled in the art without departing from the scope of the invention, and it should be understood that this invention is not limited to the illustrative embodiments set forth herein. Accordingly, the invention is to be limited only by the claims provided below and equivalents thereof.