Articles which include a hinged starch-bound cellular matrix

• US 5,843,544 A
• Filed: 06/10/1996
• Issued: 12/01/1998
• Est. Priority Date: 02/07/1994
• Status: Expired due to Term

• Current Assignee: Earthshell Spe, LLC
• Original Assignee: E. Khashoggi Industries, LLC
• Inventors: Andersen, Per Just, Hodson, Simon K.
• Primary Examiner(s): McCamish, Marion E.
• Assistant Examiner(s): Copenheaver, Blaine R.
• Application Number:
  US08/661,223
• Time in Patent Office: 904 Days
• Field of Search: 16/221, 16/277, 16/385, 206/524.7, 206/562, 428/158, 428/108, 428/182, 428/213, 428/317.9, 428/339, 428/532, 428/36.4, 428/36.5, 428/35.7, 428/35.8, 428/318.8
• US Class Current: 428/36.5
• CPC Class Codes: B01F 23/511 characterised by the composition of the liquids or solids
• CPC Class Codes: B01F 23/56 by introducing solids in liquids, e.g. dispersing or dissolving
• CPC Class Codes: B05B 1/34 designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl designed to control volume of flow B05B1/30
• CPC Class Codes: B05B 11/0037 Containers for several components B05B11/0078
• CPC Class Codes: B05C 1/0826 the work being a web or sheets B05C1/0804, B05C1/0808, B05C1/0813, B05C1/0817, B05C1/0821, B05C1/10, B05C1/12 take precedence
• CPC Class Codes: B05C 1/0834 the coating roller co-operating with other rollers, e.g. dosing, transfer rollers
• CPC Class Codes: B05C 3/18 only one side of the work coming into contact with the liquid or other fluent material B05C3/02 takes precedence
• CPC Class Codes: B05C 5/0245 for applying liquid or other fluent material to a moving work of indefinite length, e.g. to a moving web B05C5/0241, B05C5/0254, B05C5/027, B05C5/0283 take precedence
• CPC Class Codes: B27N 3/002 characterised by the type of binder compositions of macromolecular compounds C08L
• CPC Class Codes: B27N 3/007 and at least partly composed of recycled material
• CPC Class Codes: B28B 1/00 Producing shaped prefabricated articles from the material using presses B28B3/00; shaping on moving conveyors B28B5/00; producing tubular articles B28B21/00 ; producing articles with embedded elements B28B23/00
• CPC Class Codes: B28B 1/52 specially adapted for producing articles from mixtures containing fibres, e.g. asbestos cementby wrapping on to mandrels B28B1/42
• CPC Class Codes: B28B 11/00 Apparatus or processes for treating or working the shaped or preshaped articles specially adapted for tubular articles B28B21/92; decoration or surface treatment in general B05, B44; compacting concrete in situ in connection with building E04G21/06; drying F26
• CPC Class Codes: B28B 11/003 the shaping of preshaped articles, e.g. by bending B28B11/08 takes precedence
• CPC Class Codes: B28B 11/008 Blow moulding, e.g. with or without the use of a membrane
• CPC Class Codes: B28B 11/0863 for profiling, e.g. making grooves
• CPC Class Codes: B28B 13/021 by fluid pressure acting directly on the material, e.g. using vacuum, air pressure
• CPC Class Codes: B28B 13/06 Removing the shaped articles from moulds by means incorporated in, or carried by, the moulds B28B7/10
• CPC Class Codes: B28B 23/00 Arrangements specially adapted for the production of shaped articles with elements wholly or partly embedded in the moulding material; Production of reinforced objectsB28B21/00 takes precedence; in units for prefabricated buildings B28B7/22
• CPC Class Codes: B28B 23/0081 Embedding aggregates to obtain particular properties
• CPC Class Codes: B28B 23/0087 : Lightweight aggregates for making lightweight articles
• CPC Class Codes: B28B 3/00 : Producing shaped articles from the material by using presses shaping on moving conveyors B28B5/00; Presses specially adapted therefor presses in general B30B
• CPC Class Codes: B28B 3/02 : wherein a ram exerts pressure on the material in a moulding space; Ram heads of special form
• CPC Class Codes: B28B 3/126 : on material passing directly between the co-operating rollers
• CPC Class Codes: B28B 3/20 : wherein the material is extruded extrusion moulding of plastics B29C48/00
• CPC Class Codes: B28B 3/2645 : using means for inserting reinforcing members
• CPC Class Codes: B28B 7/42 : for heating or cooling, e.g. steam jackets , by means of treating agents acting directly on the moulding material
• CPC Class Codes: B28C 7/02 : Controlling the operation of the mixing
• CPC Class Codes: B29C 2043/3433 : using dispensing heads, e.g. extruders, placed over or apart from the moulds
• CPC Class Codes: B29C 2043/463 : corrugated, patterned or embossed surface
• CPC Class Codes: B29C 2043/464 : having projections or knives, e.g. for cutting-out or for forming local depressions
• CPC Class Codes: B29C 2043/5841 : for accommodating variation in mould spacing or cavity volume during moulding
• CPC Class Codes: B29C 2049/4608 : Nitrogen
• CPC Class Codes: B29C 33/04 : using liquids, gas or steam tyre moulds with incorporated heating or cooling means using liquids, gas or steam B29D30/0601
• CPC Class Codes: B29C 33/10 : with incorporated venting means
• CPC Class Codes: B29C 33/20 : Opening, closing or clamping
• CPC Class Codes: B29C 33/36 : continuously movable in one direction, e.g. in a closed circuit B29C49/0021 takes precedence
• CPC Class Codes: B29C 39/003 : characterised by the choice of material
• CPC Class Codes: B29C 39/42 : Casting under special conditions, e.g. vacuum
• CPC Class Codes: B29C 43/00 : Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor by liberation of internal stresses B29C61/006
• CPC Class Codes: B29C 43/003 : characterised by the choice of material
• CPC Class Codes: B29C 43/06 : continuously movable in one direction, e.g. mounted on chains, belts
• CPC Class Codes: B29C 43/08 : with circular movement , e.g. mounted on rolls, turntables
• CPC Class Codes: B29C 43/222 : characterised by the shape of the surface
• CPC Class Codes: B29C 43/34 : Feeding the material to the mould or the compression means B29C43/085 takes precedence
• CPC Class Codes: B29C 43/36 : Moulds for making articles of definite length, i.e. discrete articles
• CPC Class Codes: B29C 43/46 : Rollers
• CPC Class Codes: B29C 44/0407 : by regulating the temperature of the mould or parts thereof, e.g. cold mould walls inhibiting foaming of an outer layer
• CPC Class Codes: B29C 44/3402 : Details of processes or apparatus for reducing environmental damage or for working-up compositions comprising inert blowing agents or biodegradable components
• CPC Class Codes: B29C 45/0013 : using fillers dispersed in the moulding material, e.g. metal particles
• CPC Class Codes: B29C 48/0011 : combined with compression moulding
• CPC Class Codes: B29C 48/0012 : combined with shaping by internal pressure generated in the material, e.g. foaming
• CPC Class Codes: B29C 48/03 : characterised by the shape of the extruded material at extrusion
• CPC Class Codes: B29C 48/07 : Flat, e.g. panels
• CPC Class Codes: B29C 48/08 : flexible, e.g. films
• CPC Class Codes: B29C 49/0005 : characterised by the material
• CPC Class Codes: B29C 49/04 : Extrusion blow-moulding
• CPC Class Codes: B29C 49/0691 : using sheet like material, e.g. sheet blow-moulding from joined sheets
• CPC Class Codes: B29C 49/6605 : Heating the article, e.g. for hot fill
• CPC Class Codes: B29C 51/002 : characterised by the choice of material
• CPC Class Codes: B29C 51/04 : Combined thermoforming and prestretching, e.g. biaxial stretching
• CPC Class Codes: B29C 51/10 : Forming by pressure difference, e.g. vacuum
• CPC Class Codes: B29C 53/063 : combined with folding
• CPC Class Codes: B29C 55/18 : by squeezing between surfaces, e.g. rollers
• CPC Class Codes: B29C 67/202 : comprising elimination of a solid or a liquid ingredient
• CPC Class Codes: B29C 67/24 : characterised by the choice of material
• CPC Class Codes: B29C 67/242 : Moulding mineral aggregates bonded with resin, e.g. resin concrete shaping ceramic compositions without binder or water-setting cementitious material B28B; compositions per se C04B
• CPC Class Codes: B29C 67/243 : for making articles of definite length
• CPC Class Codes: B29C 70/025 : with particular filler
• CPC Class Codes: B29C 70/12 : using fibres of short length, e.g. in the form of a mat non-woven fabrics per se D04H1/00
• CPC Class Codes: B29C 70/50 : for producing articles of indefinite length, e.g. prepregs, sheet moulding compounds [SMC] or cross moulding compounds [XMC]
• CPC Class Codes: B29C 71/0009 : using liquids, e.g. solvents, swelling agents spectacle cases, e.g. for cleaning contact lenses A45C11/04; disinfecting or sterilising contact lenses A61L12/00, using liquid substances A61L2/20; cleaning involving the use of liquid in general B08B3/00; for hydrating contact lenses B29D11/00067
• CPC Class Codes: B29K 2003/00 : Use of starch or derivatives as moulding material
• CPC Class Codes: B29K 2105/0064 : Latex, emulsion or dispersion
• CPC Class Codes: B29K 2105/04 : cellular or porous
• CPC Class Codes: B29K 2105/06 : containing reinforcements, fillers or inserts
• CPC Class Codes: B29K 2105/16 : Fillers
• CPC Class Codes: B29K 2995/0059 : Degradable
• CPC Class Codes: B29L 2031/712 : Containers; Packaging elements or accessories, Packages closures therefor B29L2031/56; ink or toner cartridges B29L2031/7678; squeeze tubes B29L2023/20; suitcases B29L2031/7418
• CPC Class Codes: B31B 2105/00 : Rigid or semi-rigid containers made by assembling separate sheets, blanks or webs
• CPC Class Codes: B31B 2110/10 : having a cross section of varying size or shape, e.g. conical or pyramidal
• CPC Class Codes: B31B 2110/35 : rectangular, e.g. square
• CPC Class Codes: B31B 50/32 : in circular paths
• CPC Class Codes: B31D 1/005 : making bottoms or caps
• CPC Class Codes: B32B 13/02 : with fibres or particles being present as additives in the layer
• CPC Class Codes: B32B 27/04 : as impregnant, bonding, or embedding substance not used
• CPC Class Codes: B32B 27/20 : using fillers, pigments, thixotroping agents
• CPC Class Codes: B32B 37/144 : using layers with different mechanical or chemical conditions or properties, e.g. layers with different thermal shrinkage, layers under tension during bonding constructional features for tensioning B32B38/1825
• CPC Class Codes: B32B 5/02 : characterised by structural features of a fibrous or filamentary layer layer formed of metallic wires B32B15/02; layer formed of natural mineral fibres B32B19/02; layer formed of wood fibres B32B21/02
• CPC Class Codes: B32B 5/14 : characterised by a layer differing constitutionally or physically in different parts, e.g. denser near its faces
• CPC Class Codes: B32B 5/18 : characterised by features of a layer of foamed material
• CPC Class Codes: B32B 9/00 : Layered products comprising a layer of a particular substance not covered by groups B32B11/00 - B32B29/00
• CPC Class Codes: B65D 11/02 : of curved cross-section thermally insulated B65D81/3813
• CPC Class Codes: B65D 2301/20 : made of plastic material
• CPC Class Codes: B65D 2565/385 : especially suited for or with means facilitating recycling
• CPC Class Codes: B65D 43/162 : the container, the lid and the hinge being made of one piece B65D43/161 takes precedence
• CPC Class Codes: B65D 5/00 : Rigid or semi-rigid containers of polygonal cross-section, e.g. boxes, cartons or trays, formed by folding or erecting one or more blanks made of paper rigid pallets with side walls B65D19/02
• CPC Class Codes: B65D 65/38 : Packaging materials of special type or form
• CPC Class Codes: B65D 65/466 : Bio- or photodegradable packaging materials
• CPC Class Codes: C04B 14/064 : Silica aerogel
• CPC Class Codes: C04B 16/02 : Cellulosic materials cellulosic waste materials, e.g. sawdust, rice husks, C04B18/24
• CPC Class Codes: C04B 20/002 : Hollow or porous granular materials
• CPC Class Codes: C04B 20/0048 : Fibrous materials
• CPC Class Codes: C04B 22/04 : Metals, e.g. aluminium used as blowing agent
• CPC Class Codes: C04B 24/00 : Use of organic materials as active ingredients for mortars, concrete or artificial stone, e.g. plasticisers
• CPC Class Codes: C04B 24/02 : Alcohols; Phenols; Ethers
• CPC Class Codes: C04B 24/14 : Peptides; Proteins; Derivatives thereof
• CPC Class Codes: C04B 24/32 : Polyethers, e.g. alkylphenol polyglycolether
• CPC Class Codes: C04B 24/38 : Polysaccharides or derivatives thereof C04B24/243 takes precedence
• CPC Class Codes: C04B 26/00 : Compositions of mortars, concrete or artificial stone, containing only organic binders , e.g. polymer or resin concrete mechanical aspects of moulding polymer or resin concrete B29C67/242
• CPC Class Codes: C04B 26/02 : Macromolecular compounds
• CPC Class Codes: C04B 26/026 : Proteins or derivatives thereof
• CPC Class Codes: C04B 26/28 : Polysaccharides or derivatives thereof
• CPC Class Codes: C04B 28/00 : Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
• CPC Class Codes: C04B 28/02 : containing hydraulic cements other than calcium sulfates
• CPC Class Codes: C04B 38/0006 : Honeycomb structures from one or more corrugated sheets by winding or stacking C04B38/0083
• CPC Class Codes: C04B 38/02 : by adding chemical blowing agents
• CPC Class Codes: C04B 40/00 : Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability active ingredients C04B22/00 - C04B24/00; hardening of a well-defined composition C04B26/00 - C04B28/00; making porous, cellular or lightening C04B38/00; mechanical aspects B28, e.g. conditioning the materials prior to shaping B28B17/02
• CPC Class Codes: C04B 40/0028 : Aspects relating to the mixing step of the mortar preparation
• CPC Class Codes: C04B 40/006 : involving the elimination of excess water from the mixture
• CPC Class Codes: C04B 41/45 : Coating or impregnating paints C09D, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements ion-implantation C04B41/0027
• CPC Class Codes: C04B 41/48 : Macromolecular compounds
• CPC Class Codes: C04B 41/61 : Coating or impregnation
• CPC Class Codes: C08J 2201/0504 : the liquid phase being aqueous
• CPC Class Codes: C08J 2303/00 : Characterised by the use of starch, amylose or amylopectin or of their derivatives or degradation products
• CPC Class Codes: C08J 2323/02 : not modified by chemical after treatment
• CPC Class Codes: C08J 5/18 : Manufacture of films or sheets
• CPC Class Codes: C08J 9/0085 : Use of fibrous compounding ingredients C08J9/0076 takes precedence
• CPC Class Codes: C08J 9/12 : by a physical blowing agent
• CPC Class Codes: C08J 9/28 : by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
• CPC Class Codes: C08J 9/365 : Coating
• CPC Class Codes: C08L 1/28 : Alkyl ethers
• CPC Class Codes: C08L 1/286 : substituted with acid radicals, e.g. carboxymethyl cellulose [CMC] C08L1/282 takes precedence
• CPC Class Codes: C08L 2666/02 : Organic macromolecular compounds, natural resins, waxes or and bituminous materials
• CPC Class Codes: C08L 2666/04 : Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: C08L 3/00 : Compositions of starch, amylose or amylopectin or of their derivatives or degradation products
• CPC Class Codes: C08L 3/02 : Starch; Degradation products thereof, e.g. dextrin
• CPC Class Codes: C08L 5/02 : Dextran; Derivatives thereof
• CPC Class Codes: C08L 5/12 : Agar or agar-agar , i.e. mixture of agarose and agaropectin; Derivatives thereof
• CPC Class Codes: C08L 5/14 : Hemicellulose; Derivatives thereof
• CPC Class Codes: C08L 89/06 : derived from leather or skin , e.g. gelatin
• CPC Class Codes: C08L 97/02 : Lignocellulosic material, e.g. wood, straw or bagasse manufacture of articles made from lignocellulosic material by dry processes B27N
• CPC Class Codes: E05D 1/02 : made of one piece
• CPC Class Codes: E05Y 2900/602 : for containers
• CPC Class Codes: Y02W 90/10 : Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics
• CPC Class Codes: Y10T 428/1372 : Randomly noninterengaged or randomly contacting fibers, filaments, particles, or flakes
• CPC Class Codes: Y10T 428/1376 : Foam or porous material containing
• CPC Class Codes: Y10T 428/24496 : Foamed or cellular component
• CPC Class Codes: Y10T 428/2495 : Thickness [relative or absolute]
• CPC Class Codes: Y10T 428/249986 : Void-containing component contains also a solid fiber or solid particle
• CPC Class Codes: Y10T 428/249989 : Integrally formed skin

Abstract

Methods and systems for forming hinged starch-bound matrices. Starch-based compositions are molded between heated molds in order to form a cellular matrix and also to remove the water from the starch-based compositions in order to form a binding matrix of solidified starch. The molding apparatus is configured to form one or more creases within the hinge area in order to define one or more lines upon which the hinge will bend. The molding apparatus is also configured such that the region of the mold corresponding to the inner surface of the hinge area will transfer heat more slowly to the inner hinge surface, resulting in reduced thickness of the skin of the inner hinge. This increases the collapsibility, or ability of the inner surface of the hinge to fold or buckle, during the bending action. This in turn reduces the bending radius of hinge such that the hinging action exerts less strain on the outer surface of the hinge. The inner surface of the hinge may optionally be treated with glycerin or other polyols soften the inner surface. The outer surface of the hinge may optionally be coated with an elastomeric material, such as polyvinyl alcohol, in order to strengthen the outer surface and reduce its tendency to fracture during the hinging action.

Claims

1. An article of manufacture including a hinge structure, the hinge structure having a starch-bound cellular matrix and comprising an interior skin portion separated from an exterior skin portion by an intermediate cellular core, the interior skin portion including a crease such that the hinge structure has a reduced cross-section at the crease, the exterior skin portion having a thickness and the interior skin portion having a thickness that is less than the thickness of the exterior skin portion.

2. An article of manufacture as defined in claim 1, wherein the interior skin portion has been treated with a softening agent for imparting to the interior skin portion increased bendability or collapsibility during bending of the hinge structure.

3. An article of manufacture as defined in claim 2, wherein the softening agent comprises a polyol.

4. An article of manufacture as defined in claim 3, wherein the polyol comprises glycerin.

5. An article of manufacture as defined in claim 3, wherein the polyol is selected from the group consisting of polyethylene glycol, propylene glycol, polypropylene glycol, sorbitol, and mixtures of the foregoing.

6. An article of manufacture as defined in claim 1, wherein the exterior skin portion has been treated with an elastomeric coating for imparting increased resistance against fracture due to elongation of the exterior skin portion during bending of the hinge structure.

7. An article of manufacture as defined in claim 6, wherein the elastomeric coating comprises polyvinyl alcohol.

8. An article of manufacture as defined in claim 6, wherein the elastomeric coating is selected from the group consisting of polylactic acid, natural latex, derivatives of the foregoing, and mixtures of the foregoing.

9. An article of manufacture as defined in claim 1, wherein the reduced cross section at the crease reduces the bending angle of the hinge such that strain on the exterior skin portion is reduced during bending of the hinge structure.

10. An article of manufacture as defined in claim 1, wherein the hinge structure further includes one or more additional creases substantially parallel to the crease to form a multiple hinge structure.

11. An article of manufacture as defined in claim 10, wherein the hinge structure further includes a swell between the crease and the one or more additional creases.

12. An article of manufacture as defined in claim 1, wherein the interior skin and the exterior skin have respective densities that are substantially similar.

13. An article of manufacture as defined in claim 1, wherein the article includes two main structural elements integrally connected to either side of the hinge structure.

14. An article of manufacture as defined in claim 1, wherein the article comprises a clam shell container.

15. An article of manufacture comprising a hinge structure having a starch-bound cellular matrix, the hinge structure including an intermediate cellular core disposed between an interior skin portion and an exterior skin portion, the hinge structure including a bending region at or near a depression in the interior skin portion, the exterior skin having a thickness at the bending region, the interior skin portion having a thickness at the bending region that is less than the thickness of the exterior skin portion at the bending region.

16. An article of manufacture as defined in claim 15, wherein the article comprises a clam shell container.

17. An article of manufacture as defined in claim 16, wherein the clam shell container further includes a coating material.

18. An article of manufacture as defined in claim 17, wherein the coating material comprises polyvinyl alcohol.

19. An article of manufacture as defined in claim 17, wherein the coating material increases the strength of the exterior skin portion of the hinge.

20. An article of manufacture as defined in claim 15, wherein the interior skin portion of the hinge has been treated with a polyol.

21. An article of manufacture as defined in claim 20, wherein the polyol comprises glycerin.

22. An article of manufacture comprising a multiple hinge structure having a starch-bound cellular matrix, the multiple hinge structure comprising an interior skin portion separated from an exterior skin portion by an interior cellular core, the multiple hinge structure also including at least two depressions that are substantially parallel to each other in the interior skin portion of the hinge structure, the intermediate skin portion having a thickness that is less than the thickness of the exterior skin portion.

23. An article of manufacture as defined in claim 22, wherein the article comprises a clam shell container.

24. An article of manufacture as defined in claim 23, wherein the clam shell container further includes a coating material.

25. An article of manufacture as defined in claim 24, wherein the coating material comprises polyvinyl alcohol.

26. An article of manufacture as defined in claim 24, wherein the coating material increases the strength of the exterior skin portion of the hinge.

27. An article of manufacture as defined in claim 22, wherein the interior skin portion of the hinge has been treated with a polyol.

28. An article of manufacture as defined in claim 27, wherein the polyol comprises glycerin.

29. An article of manufacture having a starch-bound cellular matrix and comprising first and second halves and a hinge structure disposed between the first and second halves, the first half being connected to the hinge structure by a first arm and the second half being connected to the hinge by a second arm, the hinge structure including an interior skin portion, an exterior skin portion, an intermediate cellular core disposed between the interior skin portion and the exterior skin portion, and at least one depression within the interior skin portion between the first and second arms defining a bending region of reduced cross section, the exterior skin portion having a thickness at the bending region, the interior skin portion having a thickness at the bending region that is less than the thickness of the exterior skin portion at the bending region.

30. An article of manufacture as defined in claim 29, wherein the article comprises a clam shell container.

31. An article of manufacture as defined in claim 30, wherein the clam shell Container includes an interior side that has been treated with a wax coating to render the interior side more resistant to moisture.

32. An article of manufacture as defined in claim 29, wherein the interior skin portion has been treated with a polyol.

33. An article of manufacture as defined in claim 29, wherein the exterior skin portion has been treated with an elastomeric coating.

34. An article of manufacture as defined in claim 29, wherein the elastomeric coating comprises polyvinyl alcohol.

35. An article of manufacture comprising an integrally molded article having a starch-bound cellular matrix, the article including a first half connected to a second half by means of a hinge structure that is integrally molded with the first and second halves and which also comprises the starch-bound cellular matrix, the hinge structure providing means for pivoting the first and second halves relative to each other at the hinge structure, said hinge structure comprises an interior skin portion separated from an exterior skin portion by an intermediate cellular core, the interior skin portion having a depression such that the hinge structure has a reduced cross-section at the depression.

36. An article of manufacture as defined in claim 35, wherein the integrally molded article comprises a clam shell container.

37. An article of manufacture as defined in claim 35, wherein the exterior skin portion having a thickness and the interior skin portion having a thickness that is less than the thickness of the exterior skin portion.

38. An article of manufacture as defined in claim 37, wherein the hinge structure includes at least one bending initiation groove in the exterior skin portion.

39. An article of manufacture as defined in claim 35, wherein the interior skin portion having a plurality of depressions such that the hinge structure is a multiple hinge structure and has reduced cross-section at each of the plurality of depressions, the exterior skin portion having a thickness and the interior skin portion having a thickness that is less than the thickness of the exterior skin portion.