Cutting – Processes
Utility Patent
1998-10-06
2001-01-02
Rachuba, M. (Department: 3724)
Cutting
Processes
C083S039000, C083S861000, C083S879000
Utility Patent
active
06167790
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to polymer foams. In particular, the invention relates to polymer foams having low densities with enhanced physical properties.
Foam structures are useful in the areas of packaging, athletics, water sports, and construction. In general, the foams are low density polymeric materials with good physical properties that are capable of supporting loads without adverse deformation. In general, the physical properties required by these applications suggest the use of high density foams. It is generally required that the foams have good proportional limit, compressive properties, shear properties, fatigue properties, and buckling limits, as defined, for example, in “Machinery's Handbook,” E. Oberg, et al., Green, Ed., Industrial Press Inc., New York, 1992, pages 166, 168 and 253.
Physically-blown foams, particularly foams with enhanced physical properties are useful, for example, in packaging, automotive, construction, contact sports, water sports, exercise, and appliance applications. It is important to maintain good foam properties (e.g., cushioning and resistance to creasing) at low foam densities.
Packaging design has focused on the use of systems such as end caps which fit on opposite ends of the packaged product (e.g., televisions, computers, and electronic equipment, or high value artifacts such as glass vases or fragile art work) and suspend the product in the center of a container during shipping and storage. Previous suspension-type packaging systems have been composed of corrugated or paperboard materials, molded low density foams such as polystyrene, protective films or sheeting, wood, plastic, organic or inorganic fill, or combinations of the above materials that are glued together. Molded packaging materials, such as styrofoam end caps, are bulky to transport and store. It is most desirable for the structure to provide the required packaging protection with the lowest amount of added weight.
SUMMARY OF THE INVENTION
The invention features foam structures that are laminated and have enhanced physical properties, making them useful in the areas of packaging, athletics, water sports, and construction. In general, these structures include a core of a low density foam and one or more skins of relatively high density foam covering the core. The skins provide improved physical properties to the foam structures by, for example, improving the flexural strength, resistance to bending (or crimping), and resulting damage from bending in the laminated foam structure. The foam structures have improved stiffness, resist creasing, and more effectively dissipate loading forces of the foam. The outer surface of the foam structures is smooth and flat relative to the surface of the low density case. The low density core provides a relatively low-weight product that uses relatively small amounts of polymer material. The laminated foam structure can be die cut so that the skin of higher density foam on the outside of the structure can act as a hinge allowing the die cut piece to be folded to make a collapsible packaging system. Examples of physically-blown foams are described in U.S. Ser. No. 08/638,122, filed Apr. 26, 1996 and entitled “Cross-Linked Low-Density Polymer Foam”, which is incorporated herein by reference.
In one aspect, the invention features a laminated foam structure that includes a first foam article laminated to a first surface of a second foam article and a third foam article laminated to a second surface of the second foam article. The first foam article and the third foam article each have an average foam density that is at least 1.5 times greater than the average foam density of the second foam article and a volume that is at least 1.5 times smaller than the second foam article. The flexural stiffness of the laminated foam structure is 2-20 times higher than the flexural stiffness of the second foam article. Flexural stiffness can be determined directly from beam bending tests.
In preferred embodiments, the second foam article is a laminated foam article including at least two foams. Each of the two foams have an average foam density of less than 4 pounds per cubic foot. Preferably, each of the two foams has a thickness between about ¼ and 1 inches. It is preferred that the first foam article and the third foam article each have an average foam density of between about 4 and 15 pounds per cubic foot. Preferably, each of the first foam article and the third foam article has a thickness between about {fraction (1/16)} and {fraction (5/16)} inches.
Preferably, the second foam article has an average foam density of between 1 and 3 pounds per cubic foot, the first foam article has an average foam density of between about 4 and 12 pounds per cubic foot, and the third foam article has an average foam density of between about 4 and 12 pounds per cubic foot. The first foam article and the third foam article each can be laminated foam articles including two foams each having an average foam density of greater than 4 pounds per cubic foot.
In preferred embodiments, the second foam article can further include a foam layer having an average foam density greater than about 4 pounds per cubic foot. Preferably, the foam layer has an average foam density between 4 and 15 pounds per cubic foot and a thickness between about {fraction (1/16)} and ½ inches.
In preferred embodiments, the structure has a total thickness between about ¾ and 12 inches.
In another aspect, the invention features a laminated foam structure including a first skin laminated to a first surface of a core, and a second skin laminated to a second surface of the core. The core includes a first foam having an average foam density of between about 1 and 4 pounds per cubic foot, the first skin includes a second foam and the second skin includes a third foam each having an average foam density of between about 4 and 15 pounds per cubic foot and a thickness less than ½ inches, and the laminated foam structure has a total thickness of less than about 12 inches. The flexural stiffness of the laminated foam structure is 2-20 times higher than the flexural stiffness of the core.
In yet another aspect, the invention features a body board that includes a laminated foam structure. The laminated foam structure includes a first skin laminated to a first surface of a core, and a second skin laminated to a second surface of the core. The core includes a first foam having an average foam density of between about 1 and 4 pounds per cubic foot, the first skin includes a second foam and the second skin includes a third foam each having an average foam density of between about 4 and 15 pounds per cubic foot and a thickness less than ½ inches, and the laminated foam structure has a total thickness of less than about 3 inches. The higher densities of the first and second skins can make the structure more resistant to mechanical damage from impact, shear, and abrasive loads due to the higher polymer and lower air content of the higher density foam.
In preferred embodiments, the first foam includes at least two laminated foam articles. The second foam can include at least two laminated foam articles or the third foam can include at least two laminated foam articles. Preferably, each of the foam articles has an average foam density of between 1 and 4 pounds per cubic foot and a thickness of between ¼ and 1 inches. It is preferred that the first foam further include a foam layer having an average foam density greater than about 4 pounds per cubic foot and a thickness less than ½ inch.
In another aspect, the invention features a method of increasing the flexural strength of a core foam structure including the steps of laminating a first skin to a first surface of the structure, and laminating a second skin to a second surface of the core foam structure. The first skin includes a first foam having an average density that is at least 1.5 times greater than the average density of the core foam structure and a thickness that is at least 1.5 times sma
Bambara John D.
Bambara Richard
Smith Scott C.
Smith Thomas W.
Fish & Richardson P.C.
Rachuba M.
Sentinel Products Corp.
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