CA1100726A - Method of co-extrusion with foam core - Google Patents
Method of co-extrusion with foam coreInfo
- Publication number
- CA1100726A CA1100726A CA305,094A CA305094A CA1100726A CA 1100726 A CA1100726 A CA 1100726A CA 305094 A CA305094 A CA 305094A CA 1100726 A CA1100726 A CA 1100726A
- Authority
- CA
- Canada
- Prior art keywords
- plastic
- manufacturing
- core
- solid
- cellular
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Extrusion Moulding Of Plastics Or The Like (AREA)
Abstract
METHOD OF EXTRUDSION WITH FOAM CORE
ABSTRACT OF THE DISCLOSURE
Disclosed is a method of manufacturing a co-extruded article comprising the steps of mixing ingredients for a cellular plastic including a chemical blowing agent and a thermoplastic resin in a plastic state for forming a core and at a temperature range of 300°F. to 400°F. Other ingredients for at least one solid thermoplastic resin are mixed in a plastic state at a temperature differing from the temperature by at least 25°F for forming a skin for the core, and then simultaneously co-extruding the cellular plastic and solid plastic through a die.
ABSTRACT OF THE DISCLOSURE
Disclosed is a method of manufacturing a co-extruded article comprising the steps of mixing ingredients for a cellular plastic including a chemical blowing agent and a thermoplastic resin in a plastic state for forming a core and at a temperature range of 300°F. to 400°F. Other ingredients for at least one solid thermoplastic resin are mixed in a plastic state at a temperature differing from the temperature by at least 25°F for forming a skin for the core, and then simultaneously co-extruding the cellular plastic and solid plastic through a die.
Description
110~7Z6 METHOD OF CO-EXTRUSION WITH FOAM CORE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a method of manufacturing integrally formed plastic sandwiches. More particularly, the invention relates to a process for the extrusion of integral plastic members having solid skins and a cellular inner portion.
DESCRIPTION OF THE PRIOR ART
Attempts have been made in the past to provide for the production of plastic sandwich structural elements by bonding solid plastic skin members to the top and bottom surfaces of a cellular plastic core. However, this method of fabrication is costly since it requires the individual fabrication of the indi-vidual skin and core members, the application of a relatively costly adhesive material and the clamping of the bonded struc-tural element until the adhesive is set. In addition, the difficulty in obtaining a high strength bond over an extended surface using an adhesive results in a product having a less than desirable level of reliability.
Other methods for the fabrication of plastic sandwich members have in the past included a molding process in which inert gas is dispersed in a polymer melt, the polymer melt is introduced into a mold and as the mold fills, the gas expands within the material forming a cellular core while a solid plastic skin forms along the walls of the mold. This method has the disadvantages of not permitting close control over the skin thickness, not permitting variations in material between the skin and the core and requiring a large and consequently expen-sive mold for the production of large plastic members.
'~
" ~ ~OU7Z6 Attempts have been made to co-extrude a multi-layer plastic sandwich such as disclosed in the U.S. patent to Chisholm et al, No. 3,557,265. This patent nowhere discloses the concept of providing a foamed core. In Thomas, U.S.
No. 3,331,900 there is disclosed a skin coated foamed plastic article. Shippers, U.S.No. 3,782,870 discloses an apparatus for partially foaming a portion of extruded ma-terial by separating melt streams and then rejoining the separate melt streams and partially foaming one of the melt streams.
SUMMARY OF THE INVENTION
The present invention contemplates control of the cellular core characteristics co-extruding method utilizing the concept of temperature differences in the materials being co-extruded.
In one broad aspect, the invention comprehends a method of manufacturing a co-extruded article, which comprises the steps of mixing ingredients for a cellular plastic including a chemical blowing agent and a thermoplastic resin in a plastic state for forming a core, and at a temperature range of 300F.
to 400F. Other ingredients for at least one solid thermo-plastic resin are mixed in a plastic state at a temperaturediffering from the temperature by at least 25F. for forming the skin for the core, and then simultaneously co-extruding the cellular plastic and solid plastic through a die.
More particularly, a first extruder is charged with essential ingredients for production of cellular plastic at a predetermined temperature. At least one second extruder is charged with essential ingredients for production of solid plastic at a temperature differing from said predetermined temperature by at least 2~ degrees Farenheit. Control means are provided for the simultaneous operation of the first and second extruders thus resulting in the extrusion of a sandwich ~0~7Z6 member having a core of cellular plastic and one or more integrally forrned skin members of solid plastlc. The characteristics of the resulting plastic sandwich element can be controlled to feature, as desired, high flexural strength, hardness, relatively hiyh flexural rigidity, relatively low weight and relatively low cost. By increasing and decreasing the speed of operation of the second extruders, the thickness of skin members may be increased or decreased.
It is therefore an object of the present invention to provide a method for the manufacture of an integrally formed co-extruded plastic member having a core of cellular plastic and skin members of solid plastic.
Some of the advantages of the present invention are that the plastic sandwich material so produced is desirable for use as a cap liner. The product prevents product penetration in to the liner when used as a liner for caps, and any product penetration stagnating behind the liner and attracting germs. The final product assures a smooth surface in contact with the contents of the product. The concept of temperature differential co-extrusion of the foam core provides for different degrees of resilience while also greatly providing for price advantage in that less mat-erial can be used.- Further, the layers enable a better stamped liner allowing a sharp definition while providing for a stronger product. The layers encasing the foam core at a various temperature when co extruded provide for a desired cell structure while in the event some cells blow too much and are open, the layers will seal these open cells thus forming a very resilient liner.
These, together with various ancillary aspects of the present invention, are obtained by this method of manufacture of plastic sandwich elements, preferred embodiments being shown in the accompanying drawing by way of example only, wherein:
110()7Z6 BRIEF DESCRIPTION OF THE DRAWING
_ Fig. l is a longitudinal sectional view through a portion of an embodiment of an apparatus which can be used according to the present invention;
Fig. 2 is a cross sectional view illustrating sche-matically the construction of a co-extruded plastic sandwich with a retaining thick skin at a temperature of at least 25 degrees Farenheit hotter than the core shown immediately after co-extrusion;
Fig. 2A is a view similar to Fig. 2 after the core has additionally foamedî
~ igs. 3 and 3A are views similar to Fig5. 2 and 2A but illustrating the co-extruded plastic sandwich having a relatively thin skin co-extruded at a temperature of at least 25 degrees Farenheit hotter than the core;
Figs. 4 and 4A are views similar to Figs. 2 and 2A
but illustrating the co-extruded plastic sandwich having a relative-ly thick skin co-extruded at a temperature of at least 25 degrees Farenheit cooler than the core;
Figs. 5 and 5A are views similar to Figs. 2 and 2A
but illustrate the co-extruded plastic sandwich having the same re-latively thin skin as Figs. 3 and 3A co-extruded at a temperature of at least 25 degrees Farenheit cooler than the core.
DETAILED DESCRIPTION OF THE INVENTION
With continuing reference to the accompanying drawing, whexein like reference numerals designate similar parts throughout the various views, reference numeral 10 is used to generally designate a typical apparatus which can be used for the co-extruding of the plastic sandwich.
As shown three extruders are employed arranged with the extruder 12 for the core being arranged horizontally with its auger 14 feeding longitudinally. The extruders 16 and 20 and their augers 18 and 22 are shown arranged vertically. It is to be understood that while this is a space saving and convenient typical ~l()a726 installation, in accordance Wit31 the concePts of the present invention the extruders can be dlsposed in any suita~le arrangement such as side by side, angularly clisposed, or even remote from each other, the material to be co-extruded being fed to a size-able die 24.
In the illustrated embodiment, the first extruder 12 includes a perforated plate 26 and a tapered nozzle 29 through which core ma-terial C to be extruded is fed to the die 24. Like-wise, skin material A fed by auger 18 passes through a perforated plate 30 and throuqh tapered nozzle 32 onto the foamed core mat-erial C and thence through die 24. The skin material B fed by auger 22 passes through perforated plate 34 and tapered nozzle 36 onto the core material C and thence through die 24. This facilitat-es the formation of top skin A of solid plastic and a bottom skin B of solid plastic on the center core C of cellular plastic of the integral plastic sandwich member 100. The extruder 12 is charged with essential ingredients for the production of cellular plastic and the second extruder 16 and the third extruder 20 are each charged with essential ingredients for the production of solid plastics.
Control means are provided to control the relative speeds of rotation of the augers 14, 18 and 22 to provide for del-ivery of selected and sufficient quantities of tlle esse3ltial in~red-ients to provide core material C and skin material A and B.
The present invention is adapted to use practically all thermoplastic materials. The thickness of the material may range from between .010 inches to an inch or two while the thickness of the skin material A and for B is in the order of .001 to .010 in-ches, the balance being in the thickness of core material C. A
material for the integrally formed plastic sandwich element 100 maybe polyethylene which forms A and B of solid polyethylene and a core C of closed cell foam polyethylene. The use of polyethylene is indicated by way of example only, and other thermoplastics materials having properties adapted for fabrication by an extrusion process 110~J7Z6 and which can be formed into a foam or cellular state may be util~
ized using the process and apparatus according to the present in-vention. Of course, two, three, or more layers may be used to obtain the desired thickness and properties where this material is used as a cap liner.
EXAMPLE I
As shown in Fig. 2, a plastic sandwich 100 is formed with the core material C being formed from a mixture of melted polyethylene, and zinc powder such as zinc stearate in amounts as conventionally employed as a stabilizer and activator. A product sold by Uni-Royal under the trade mark of "CELOGEN" is employed as a foaming agent. Other conventional foaming agents may alternativ-ely be employed. The extrusion temperature of the core material C
may range from 300 to 400 degrees Fahrenheit at optimum operation and in this example the core material tempe~ature selected is 300 degrees Farenheit. The skin material A and B employed is delivered at a rate so that the thickness is .010 inches and is relatively thick. The temperature of this polyethylene may range from 200 to 450 degrees Farenheit.
The use of thick skin permits for reasonable tensile strength while the added heat of the skin will promote further ex-pansion in a controlled manner of the cellular material C because of free release of pressure after passing through the die. The thick layer promotes eveness of the final sandwich even if the added heat will expand the resiliency of the material, allow for sufficient tensile stress and hardness while permitting expansion of the thickness of material in the order of 240% as compared to the thickness of an equal amount of material without foaming.
In Figs. 3 and 3A there is shown an embodiment of the invention wherein a thin skin of a thickness of .001 inch is used at the same temperature as set for-th in Example 1. This embodiment 11007~
causes an expansion factor in the order o~ 600% with great resiliency, a shore hardness of 65 on a durometer and sufficient tensile stress to function well as a cap liner. The added heat of the thin skin unexpectedly enhances tensile strength rather than inhibits the tensile strength by providing intimate coexistance of the skin and core.
In Figs. 4 and 4~ the followin~ are the charac~eristics of the materials used:
Core material C is at temperature of 300F; skin materials A and B are each of .010 inch thickness and at a temperature of 250F. This gives great tensile strength and a shore hardness of 90 on the durometer. Further, the thick cool skin inhibits further expansion after extrusion permitting rapid and accurate extrusion.
In Figs. 5 and ~A, the characteristics are the same as Example 3, except that the skin materials A and B are relatively thin being .001 inch thick. While this thin skin at a cooler temperature will permit the core to expand, this expansion is un~
expected even and the cooler skin prevents blowing of cells even though a gooa expanslon factor is obtained.
It is to be understood that the skin thickness may be increased or decreased as desired by increasing or decreasing the output (speed) of the extruder for the skin material without making any changes in the temperature of extruding.
A latitude of modification, substitution and change is intended in the foregoing disclosure, and in some instances, some features of the present invention may be employed without a corresponding use of other features.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a method of manufacturing integrally formed plastic sandwiches. More particularly, the invention relates to a process for the extrusion of integral plastic members having solid skins and a cellular inner portion.
DESCRIPTION OF THE PRIOR ART
Attempts have been made in the past to provide for the production of plastic sandwich structural elements by bonding solid plastic skin members to the top and bottom surfaces of a cellular plastic core. However, this method of fabrication is costly since it requires the individual fabrication of the indi-vidual skin and core members, the application of a relatively costly adhesive material and the clamping of the bonded struc-tural element until the adhesive is set. In addition, the difficulty in obtaining a high strength bond over an extended surface using an adhesive results in a product having a less than desirable level of reliability.
Other methods for the fabrication of plastic sandwich members have in the past included a molding process in which inert gas is dispersed in a polymer melt, the polymer melt is introduced into a mold and as the mold fills, the gas expands within the material forming a cellular core while a solid plastic skin forms along the walls of the mold. This method has the disadvantages of not permitting close control over the skin thickness, not permitting variations in material between the skin and the core and requiring a large and consequently expen-sive mold for the production of large plastic members.
'~
" ~ ~OU7Z6 Attempts have been made to co-extrude a multi-layer plastic sandwich such as disclosed in the U.S. patent to Chisholm et al, No. 3,557,265. This patent nowhere discloses the concept of providing a foamed core. In Thomas, U.S.
No. 3,331,900 there is disclosed a skin coated foamed plastic article. Shippers, U.S.No. 3,782,870 discloses an apparatus for partially foaming a portion of extruded ma-terial by separating melt streams and then rejoining the separate melt streams and partially foaming one of the melt streams.
SUMMARY OF THE INVENTION
The present invention contemplates control of the cellular core characteristics co-extruding method utilizing the concept of temperature differences in the materials being co-extruded.
In one broad aspect, the invention comprehends a method of manufacturing a co-extruded article, which comprises the steps of mixing ingredients for a cellular plastic including a chemical blowing agent and a thermoplastic resin in a plastic state for forming a core, and at a temperature range of 300F.
to 400F. Other ingredients for at least one solid thermo-plastic resin are mixed in a plastic state at a temperaturediffering from the temperature by at least 25F. for forming the skin for the core, and then simultaneously co-extruding the cellular plastic and solid plastic through a die.
More particularly, a first extruder is charged with essential ingredients for production of cellular plastic at a predetermined temperature. At least one second extruder is charged with essential ingredients for production of solid plastic at a temperature differing from said predetermined temperature by at least 2~ degrees Farenheit. Control means are provided for the simultaneous operation of the first and second extruders thus resulting in the extrusion of a sandwich ~0~7Z6 member having a core of cellular plastic and one or more integrally forrned skin members of solid plastlc. The characteristics of the resulting plastic sandwich element can be controlled to feature, as desired, high flexural strength, hardness, relatively hiyh flexural rigidity, relatively low weight and relatively low cost. By increasing and decreasing the speed of operation of the second extruders, the thickness of skin members may be increased or decreased.
It is therefore an object of the present invention to provide a method for the manufacture of an integrally formed co-extruded plastic member having a core of cellular plastic and skin members of solid plastic.
Some of the advantages of the present invention are that the plastic sandwich material so produced is desirable for use as a cap liner. The product prevents product penetration in to the liner when used as a liner for caps, and any product penetration stagnating behind the liner and attracting germs. The final product assures a smooth surface in contact with the contents of the product. The concept of temperature differential co-extrusion of the foam core provides for different degrees of resilience while also greatly providing for price advantage in that less mat-erial can be used.- Further, the layers enable a better stamped liner allowing a sharp definition while providing for a stronger product. The layers encasing the foam core at a various temperature when co extruded provide for a desired cell structure while in the event some cells blow too much and are open, the layers will seal these open cells thus forming a very resilient liner.
These, together with various ancillary aspects of the present invention, are obtained by this method of manufacture of plastic sandwich elements, preferred embodiments being shown in the accompanying drawing by way of example only, wherein:
110()7Z6 BRIEF DESCRIPTION OF THE DRAWING
_ Fig. l is a longitudinal sectional view through a portion of an embodiment of an apparatus which can be used according to the present invention;
Fig. 2 is a cross sectional view illustrating sche-matically the construction of a co-extruded plastic sandwich with a retaining thick skin at a temperature of at least 25 degrees Farenheit hotter than the core shown immediately after co-extrusion;
Fig. 2A is a view similar to Fig. 2 after the core has additionally foamedî
~ igs. 3 and 3A are views similar to Fig5. 2 and 2A but illustrating the co-extruded plastic sandwich having a relatively thin skin co-extruded at a temperature of at least 25 degrees Farenheit hotter than the core;
Figs. 4 and 4A are views similar to Figs. 2 and 2A
but illustrating the co-extruded plastic sandwich having a relative-ly thick skin co-extruded at a temperature of at least 25 degrees Farenheit cooler than the core;
Figs. 5 and 5A are views similar to Figs. 2 and 2A
but illustrate the co-extruded plastic sandwich having the same re-latively thin skin as Figs. 3 and 3A co-extruded at a temperature of at least 25 degrees Farenheit cooler than the core.
DETAILED DESCRIPTION OF THE INVENTION
With continuing reference to the accompanying drawing, whexein like reference numerals designate similar parts throughout the various views, reference numeral 10 is used to generally designate a typical apparatus which can be used for the co-extruding of the plastic sandwich.
As shown three extruders are employed arranged with the extruder 12 for the core being arranged horizontally with its auger 14 feeding longitudinally. The extruders 16 and 20 and their augers 18 and 22 are shown arranged vertically. It is to be understood that while this is a space saving and convenient typical ~l()a726 installation, in accordance Wit31 the concePts of the present invention the extruders can be dlsposed in any suita~le arrangement such as side by side, angularly clisposed, or even remote from each other, the material to be co-extruded being fed to a size-able die 24.
In the illustrated embodiment, the first extruder 12 includes a perforated plate 26 and a tapered nozzle 29 through which core ma-terial C to be extruded is fed to the die 24. Like-wise, skin material A fed by auger 18 passes through a perforated plate 30 and throuqh tapered nozzle 32 onto the foamed core mat-erial C and thence through die 24. The skin material B fed by auger 22 passes through perforated plate 34 and tapered nozzle 36 onto the core material C and thence through die 24. This facilitat-es the formation of top skin A of solid plastic and a bottom skin B of solid plastic on the center core C of cellular plastic of the integral plastic sandwich member 100. The extruder 12 is charged with essential ingredients for the production of cellular plastic and the second extruder 16 and the third extruder 20 are each charged with essential ingredients for the production of solid plastics.
Control means are provided to control the relative speeds of rotation of the augers 14, 18 and 22 to provide for del-ivery of selected and sufficient quantities of tlle esse3ltial in~red-ients to provide core material C and skin material A and B.
The present invention is adapted to use practically all thermoplastic materials. The thickness of the material may range from between .010 inches to an inch or two while the thickness of the skin material A and for B is in the order of .001 to .010 in-ches, the balance being in the thickness of core material C. A
material for the integrally formed plastic sandwich element 100 maybe polyethylene which forms A and B of solid polyethylene and a core C of closed cell foam polyethylene. The use of polyethylene is indicated by way of example only, and other thermoplastics materials having properties adapted for fabrication by an extrusion process 110~J7Z6 and which can be formed into a foam or cellular state may be util~
ized using the process and apparatus according to the present in-vention. Of course, two, three, or more layers may be used to obtain the desired thickness and properties where this material is used as a cap liner.
EXAMPLE I
As shown in Fig. 2, a plastic sandwich 100 is formed with the core material C being formed from a mixture of melted polyethylene, and zinc powder such as zinc stearate in amounts as conventionally employed as a stabilizer and activator. A product sold by Uni-Royal under the trade mark of "CELOGEN" is employed as a foaming agent. Other conventional foaming agents may alternativ-ely be employed. The extrusion temperature of the core material C
may range from 300 to 400 degrees Fahrenheit at optimum operation and in this example the core material tempe~ature selected is 300 degrees Farenheit. The skin material A and B employed is delivered at a rate so that the thickness is .010 inches and is relatively thick. The temperature of this polyethylene may range from 200 to 450 degrees Farenheit.
The use of thick skin permits for reasonable tensile strength while the added heat of the skin will promote further ex-pansion in a controlled manner of the cellular material C because of free release of pressure after passing through the die. The thick layer promotes eveness of the final sandwich even if the added heat will expand the resiliency of the material, allow for sufficient tensile stress and hardness while permitting expansion of the thickness of material in the order of 240% as compared to the thickness of an equal amount of material without foaming.
In Figs. 3 and 3A there is shown an embodiment of the invention wherein a thin skin of a thickness of .001 inch is used at the same temperature as set for-th in Example 1. This embodiment 11007~
causes an expansion factor in the order o~ 600% with great resiliency, a shore hardness of 65 on a durometer and sufficient tensile stress to function well as a cap liner. The added heat of the thin skin unexpectedly enhances tensile strength rather than inhibits the tensile strength by providing intimate coexistance of the skin and core.
In Figs. 4 and 4~ the followin~ are the charac~eristics of the materials used:
Core material C is at temperature of 300F; skin materials A and B are each of .010 inch thickness and at a temperature of 250F. This gives great tensile strength and a shore hardness of 90 on the durometer. Further, the thick cool skin inhibits further expansion after extrusion permitting rapid and accurate extrusion.
In Figs. 5 and ~A, the characteristics are the same as Example 3, except that the skin materials A and B are relatively thin being .001 inch thick. While this thin skin at a cooler temperature will permit the core to expand, this expansion is un~
expected even and the cooler skin prevents blowing of cells even though a gooa expanslon factor is obtained.
It is to be understood that the skin thickness may be increased or decreased as desired by increasing or decreasing the output (speed) of the extruder for the skin material without making any changes in the temperature of extruding.
A latitude of modification, substitution and change is intended in the foregoing disclosure, and in some instances, some features of the present invention may be employed without a corresponding use of other features.
Claims (11)
1. A method of manufacturing a coextruded article comprising the steps of mixing ingredients for a cellular plastic including a chemical blowing agent and a thermo-plastic resin in a plastic state for forming a core and at a temperature range of 300°F. to 400°F., mixing other ingredients for at least one solid thermoplastic resin in a plastic state at a temperature differing from said temperature by at least 25°F., for forming a skin for said core, and then simultaneously coextruding said cellular plastic and solid plastic through a die.
2. A method of manufacturing a coextruded article according to Claim 1, wherein said solid plastic is hotter than said cellular plastic to promote foaming of said cellular plastic and increase the size of cells of cellular plastic adjacent said solid plastic.
3. A method of manufacturing a coextruded article according to Claim 1, wherein said solid plastic is cooler than said cellular plastic to inhibit foaming of said cellular plastic and to reduce size of cells of cellular plastic adjacent said solid plastic.
4. A method of manufacturing a coextruded article according to Claim 1, wherein said solid plastic is relatively thin so as to permit enlargement of said extruded article by foaming after extrusion through said die.
5. A method of manufacturing a coextruded article according to claim 1, wherein said solid plastic is relatively thick so as to inhibit enlarge-ment of said extruded article.
6. A method of manufacturing a coextruded article according to claim 2, wherein said solid plastic is relatively thick in the order of .010 inch so that the enlargement of said core is maintained even.
7. A method of manufacturing a coextruded article according to claim 2, wherein said solid plastic is relatively thin on the order of .001 inch to permit for full expansion of said core while maintaining tensile strength.
8. A method of manufacturing an coextruded article according to claim 3, wherein said solid plastic is relatively thick on the order of .010 inch so as to inhibit expansion of said core.
9. A method of manufacturing an extruded article according to claim 3 wherein said solid plastic is relatively thin on the order of .001 inch so as to inhibit open cells and to maintain an even expansion.
10. A method of manufacturing according to claim 1, including the step of increasing the speed and amount of the solid plastic being extruded to increase the thickness of said skin.
11. A method of manufacturing according to claim 1, including the step of decreasing the speed and amount of the solid plastic being extruded to decrease the thickness of said skin.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA305,094A CA1100726A (en) | 1978-06-09 | 1978-06-09 | Method of co-extrusion with foam core |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA305,094A CA1100726A (en) | 1978-06-09 | 1978-06-09 | Method of co-extrusion with foam core |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100726A true CA1100726A (en) | 1981-05-12 |
Family
ID=4111658
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA305,094A Expired CA1100726A (en) | 1978-06-09 | 1978-06-09 | Method of co-extrusion with foam core |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1100726A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6440241B1 (en) | 1997-12-08 | 2002-08-27 | Dow Global Technologies Inc. | Multilayer foams |
-
1978
- 1978-06-09 CA CA305,094A patent/CA1100726A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6440241B1 (en) | 1997-12-08 | 2002-08-27 | Dow Global Technologies Inc. | Multilayer foams |
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| MKEX | Expiry |