CA1128851A - Formable metal-plastic-metal structural laminates - Google Patents
Formable metal-plastic-metal structural laminatesInfo
- Publication number
- CA1128851A CA1128851A CA357,173A CA357173A CA1128851A CA 1128851 A CA1128851 A CA 1128851A CA 357173 A CA357173 A CA 357173A CA 1128851 A CA1128851 A CA 1128851A
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- Prior art keywords
- laminate
- metal
- core
- thickness
- mils
- Prior art date
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Abstract
A metal-plastic-metal structural laminate which can be formed into various useful articles having compound curves using conventional metal forming techniques. The laminate comprises two metal skin layers and a centrally disposed polymer layer comprising a core layer, and optionally first and second adhesive layers. Each metal skin layer is 2 to 20 mils, the ratio of the core thickness to skin thickness is less than 9:1 and the total laminate thickness is 5 to 65 mils. The laminate can be bent to 90.degree. to a critical radius, the distance between the pivot point and the inner skin surface of the laminate, without metal rupture. 27,470-F
Description
8~S~
FORMA~3LE METAL - PLAST I C -METAL
STRUCTURAL LAMINATES
; - This invention relates to laminates of metal and plastic and to their preparation. More particularly, this in~ention relates to novel metal plastic-metal structuxal laminates which can be formed into various useful articles having compound curves using conventional metal forming techniques.
, Metal plastic laminates are well known items of commerce. They include relatively thin laminates useful in flexible packaging end use applications as well as relatively thick laminates used as construction materials. Methods of preparing such laminates are also known. One method includes bringing at least one layer of plastic and at least one layer of metal into intimate contact and subjecting them to suitable heat and pressure, using, for example, a molding press. A
; more efficient and continuous method involves the well known extrusion processes - extrusion coating or extrusion lamination. Often an intermediate layer of adhesive or primer, in the form of a film or coating, 27, 470-F -1 , .
- - ` .
FORMA~3LE METAL - PLAST I C -METAL
STRUCTURAL LAMINATES
; - This invention relates to laminates of metal and plastic and to their preparation. More particularly, this in~ention relates to novel metal plastic-metal structuxal laminates which can be formed into various useful articles having compound curves using conventional metal forming techniques.
, Metal plastic laminates are well known items of commerce. They include relatively thin laminates useful in flexible packaging end use applications as well as relatively thick laminates used as construction materials. Methods of preparing such laminates are also known. One method includes bringing at least one layer of plastic and at least one layer of metal into intimate contact and subjecting them to suitable heat and pressure, using, for example, a molding press. A
; more efficient and continuous method involves the well known extrusion processes - extrusion coating or extrusion lamination. Often an intermediate layer of adhesive or primer, in the form of a film or coating, 27, 470-F -1 , .
- - ` .
-2- 11~8~S~
is used in conjunction with these methods to ensure adequate adhesion between the metal substrate and plastic.
Metal plastic laminates have also been the subject of numerous patents. An exemplary selection of such patents includes U.S. Patent Nos. 3,298,559;
is used in conjunction with these methods to ensure adequate adhesion between the metal substrate and plastic.
Metal plastic laminates have also been the subject of numerous patents. An exemplary selection of such patents includes U.S. Patent Nos. 3,298,559;
3,340,714; 3,348,995; 3,382,136; 3,542,605; 3,594,249;
3,616,019; 3,711,365; 3,721,597 and 3,826,628. Most metal plastic laminates known in the art are satis-factory for many commercial uses as stated above.However, such laminates lack, among other things, satisfactory formability.
Accordingly, it is an object of this inven-tion to provide a metal-polymer-metal structural lami-nate capable of being formed into an article using, forexample, conventional metal-forming equipment.
- The laminate of the present invention comprises two metal skin layers and a centrally disposed polymer comprising a core layer and optionally first and second adhesive layers. More specifically, the laminate comprises a core of polymeric resinous material having tightly adhered to each side thereof a metal skin layer wherein each metal skin layer is from about ~ to about 20 mils thick, the xatio of the core thickness to skin thickness is less than 9:1 and the total laminate thickness is from about 5 to about 65 mils. The materials of construction of the polymer core and the metal skins and the geometry of the laminate are such that the laminate has (1) a flexural stiffness at 27,470-F -2-..
, ~ , , - :
3 ~
least about 40 percent that of the solid metal of the skin layer of the lower modlllus having the same thickness as the laminate as measured by ASTM D~790 on a one inch wide sample having four inch span under three point loadi.ng conditions, (2) a density from about 25 percent to 90 percent that of the average of two solid metal skin layers, (3) as a measure of stretch formability, a "limiting dome height" of at least about 60 percent of the limiting dome height of the solid metal of the skin layer of the lower ultimate elongation having the same thickness AS the laminate, (4) the capability of being subjected to a no load oven test, subsequent to forming of the laminate, at a temperature of at least 190F for a period of 30 minutes without delamination, and (5) the capability of being bent at room temperature to 90 to a critical radius without metal rupture. The critical radius, defined as the distance rom the pivot point to the inner skin surface of the laminate, is about equal to the total laminate thickness.
The present invention resides in a metal--polymer-metal laminate comprising a core of polymeric resinous material having tightly adhered to each side thereof a metal skin layer wherein each metal skin layer is from about 2 to about 20 mils thick, said laminate further having a ratio of core thickness to skin thick-ness of less than 9:1, and a total thickness of from abou~ 5 to about 65 mils; the materials of construc-tion of said polymeric core and metal skins and the geometry of the laminate being such that the laminate has a flexural stiffness at least 40% that of the solid metal of the skin layer of the lower modulus having the same thickness as said laminate as measu~ed by ASTM D790 on a one inch wide sample having four inch ~7,470-F -3-
3,616,019; 3,711,365; 3,721,597 and 3,826,628. Most metal plastic laminates known in the art are satis-factory for many commercial uses as stated above.However, such laminates lack, among other things, satisfactory formability.
Accordingly, it is an object of this inven-tion to provide a metal-polymer-metal structural lami-nate capable of being formed into an article using, forexample, conventional metal-forming equipment.
- The laminate of the present invention comprises two metal skin layers and a centrally disposed polymer comprising a core layer and optionally first and second adhesive layers. More specifically, the laminate comprises a core of polymeric resinous material having tightly adhered to each side thereof a metal skin layer wherein each metal skin layer is from about ~ to about 20 mils thick, the xatio of the core thickness to skin thickness is less than 9:1 and the total laminate thickness is from about 5 to about 65 mils. The materials of construction of the polymer core and the metal skins and the geometry of the laminate are such that the laminate has (1) a flexural stiffness at 27,470-F -2-..
, ~ , , - :
3 ~
least about 40 percent that of the solid metal of the skin layer of the lower modlllus having the same thickness as the laminate as measured by ASTM D~790 on a one inch wide sample having four inch span under three point loadi.ng conditions, (2) a density from about 25 percent to 90 percent that of the average of two solid metal skin layers, (3) as a measure of stretch formability, a "limiting dome height" of at least about 60 percent of the limiting dome height of the solid metal of the skin layer of the lower ultimate elongation having the same thickness AS the laminate, (4) the capability of being subjected to a no load oven test, subsequent to forming of the laminate, at a temperature of at least 190F for a period of 30 minutes without delamination, and (5) the capability of being bent at room temperature to 90 to a critical radius without metal rupture. The critical radius, defined as the distance rom the pivot point to the inner skin surface of the laminate, is about equal to the total laminate thickness.
The present invention resides in a metal--polymer-metal laminate comprising a core of polymeric resinous material having tightly adhered to each side thereof a metal skin layer wherein each metal skin layer is from about 2 to about 20 mils thick, said laminate further having a ratio of core thickness to skin thick-ness of less than 9:1, and a total thickness of from abou~ 5 to about 65 mils; the materials of construc-tion of said polymeric core and metal skins and the geometry of the laminate being such that the laminate has a flexural stiffness at least 40% that of the solid metal of the skin layer of the lower modulus having the same thickness as said laminate as measu~ed by ASTM D790 on a one inch wide sample having four inch ~7,470-F -3-
-4- ~
span under three point loading conditions, a density from about 25% to 90% that of the average of two solid metal skin layers, a limiting dome heiyht of at least about 60 percent of the limiting dome height of the solid metal of the skin layer of the lower ultimate elongation having the same thickness, the capability of being subjected to a no load oven test, subsequent to forming of said laminate, at a temperature of at least 190F (87.8C) for a period of 30 minutes without delaminating, and the capability of being bent at room temperature to 90 to a critical radius without metal rupture, the critical radius defined as the . distance from the pivot po.int to the inner skin surface.
of the laminate, being about equal to the total laminate 15 thickness.
As used herein, the term "limiting dome height" is that height measured when testing sheet - metal blank or laminate blanks in accordance with General Motors Corporation test procedures described in "Metal Progess", May 1975, pp. 52 54 and "Metals Engineering Quarterly", August 1975, pp. 53-57, using a blank width to clamp diameter ratio of abouc 1Ø
As used herein, the term "tightly adhered"
means a lap shear value of at least about 500 psi at : 25 room temperature as measured by ASTM D 3165-73 using a lap length of about 0.25 inch.
Metal skin layers which are used in accor-dance with this invention each have a thickness from about 2 to about 20 mils and, preferably, from 5 to 15 mils. A metal skin layer can be formed, for example, from aluminum, aluminum alloys, alloy-clad aluminum, 27,470-F -*-&~5~
surface modified copper, bronze, magnesium or magnesium alloys, steel, tin-free steel, tin-plate steel, aluminized s~eel, stainless steel, surface modified copper-clad stainless steel, terneplate steel, gal-vanized steel, chrome or chrome treated steel and thelike~ These metals may also be surface treated or have thereon surface conversion coatings. ~ preferred group of metals are aluminum and aluminum alloys.
Another preferred group of metals are steel and steel alloys, particularly the chrome/-chrome oxide coated steel substrate or so-called tin-free steel (TFS) described in Canadian Patent 808,630 and U.S. Patents 3,526,486 and 3,826,6280 The thickness of discrete layers of chromium metal and chromium oxide may be controlled by varying plating bath parameters as is well known in the art.
The metal skin layers on each side of the core can be formed of the same metal or of different metals and can have same or different thicknesses.
The polymer core of thi~ i~vention can be formed from any polymeric resinous material which when laminated to the metal skin layer, ei~her directly thexeto or by use of an intermediate adhesive layer, can pass a no load oven test withou~ any delamination, after being subjected to a temperature of at least 190F (87.8C) for a period of 30 minutes. The polymer core can have a thickness from about 1 to about 61 mils, preferably from about 10 to 45 mils, inclusive of any adhesive layer~s) which may be employed. In general, rubber-type polymers are ineffective because of poor 27,470-F -5-,~ .
high temperature properties. Glassy-type pol~hers are ineffective because of room temperature brittleness.
Exemplary polymers within the present invention include homopolymers and copolymers of olefins such as ethylene, propylene and 4-methyl pentene-1; polymers of vinyl halides such as vinyl chloride; and copolymers of vinylidene chloride. Also suitable are cellulosic polymers such as ethyl cellulose, cellulose butyrate and cellulose acetate; polyamides such as nylon; poly-esters such as poly(ethylene terephthalate~; polycar-bonates; thermoplastic epoxy resins; and po]yurethanes.
Especially preferred resinous materials aEe the ethylene polymers and copolymers and the propylene pol~mers and copolymers having a brittle temperature of less than about 30F (-1.1C) (as measured by ASTM D-746) and a Vicat softening point of greater than about 170F
(76.7C) (as measured by ASTM D-1875). Such materials include polypropylene, low density or high density poly-ethylene, ethylene/vinyl acetate copolymer, ethylene/-acrylic acid copolymer, and ethylene/butene-l and other alkene-1 copolymers.
The polymeric resinous materials of the core can be bonded directly to the metal skin layers or by the use of an intermediate adhesive layer therebetween. The intermediate adhesive layer can have a thickness from about 0.1 to 5 mils, preferably from about 0.3 to 2.5 mils. Such layer may be formed from any thermoplastic polymeric resinous material which will tightly adhere the core layer to the metal skin layers. A particularly preferred ad-hesive layer is a normally solid thermoplastic ethylene-bas~d polymer modified by monomers having re-active carboxylic ~cid groups, particularly a co-polymer of a ma~or proportion of ethylene and a 27,470-~ -6-_7~ 5.~
minor proportion, typically from 1 to 30, prefer-ably from 2 to 20, percent by weight, of an ethy-lenically unsaturated carboxylic acid. Speciflc examples of such suitable ethylenically unsaturated carboxylic acids (which term includes mono- and polybasic acids, acid anhydrides, and partial esters of polybasic acids) are acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, maleic anhydride monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, tripropylene glycol monornethyl ether acid maleate, or ethylene ~lycol monophenyl ether acid maleate. Th~ carboxylic acid monomer is preferably selected from ~ ethylenically unsatu-15 rated mono- and polycarboxylic acids and acid anhydrides having from 3 to 8 carbon atoms pe~
molecule and partial esters of such polycarboxylic acid wherein the acid moiety has at least one car-boxylic acid group and the alcohol moiety has from 1 to 20 carbon atoms. The copolymer can also - contain other copolymerizable monomers including an ester of acrylic acid. The comonomers ca~ be combined in the copolymer in any way, e.g., as random copolymers, as block or sequential copoly-mers, or as graft copolymers. Materials of these kinds and methods of making them are readily known in the art. Specific examples of such copolymers are ethylene acrylic acid copolymer, ethylene meth-acrylic acid copolymer, ethylene maleic acid co-polymer and the like.
The adhesive layer can first be applied tothe metal skin layers, first be applied to the core, o~ can be applied to the metal s~in layer and the 27,470-F -7-8~5~
core simultan~ously. The adhesive layer can be applied using well known application techniques, such as, for example, solvent casting, roll coating, or, preferably, extrusion processes and the like.
When the adhesive layer is to be combined with the core prior to the lamination thereof to the metal skins, such layers can advantageously be introduced into the laminates by the well known coextrusion process or combining the conventional extrusion process with a film lamination technique.
In one embodiment of this inYention, the core of po~lymeric resinous material may be irradiated with a high energy ionizing radiation source to achieve at least a partial crosslinking thereof for improved creep properties and thermal stability.
In another embodiment of this invention, the core is made electrsconductive by incorporating conductive particulates, e.g., carbon black and metal particles, thereinto. The conductive core enhances the weldability of the resulting metal--polymer-metal laminates.
In yet another embodiment of this invention, the core o~ polymeric resinous material contains at least one reinforcing element embedded therein to en-hance the mechanical properties of the resultinglaminates. Such elements can be made from ~lass fibers, a perforated metallic sheet, an expanded metallic sheet, or a metallic wire screen and the like.
Numerous solid fillers, pi~ments, lubricants, antioxidants and the like well known in the art can also be incorporated into the core or adhesive 27,47~-F -8-layers, provided the resultant laminate retains the hereinbefore prescribed characteristics.
In one embodiment of this inve~tion, a metal-polymer~metal laminate is produced by dis-posing a layer of polymer resinous material, whichlayer is continuously extruded from a conventional, screw-type extruder, between two metallic skin layers which are fed continuously to a nip formed by a pair of opposing and counter-rotating laminating rolls. Heat and pressure sufficient to affect a bond between the metal skin layers and the polymeric resinous material are applied to the skin layers.
This is accomplished by heating one or both of the laminating rolls, by preheating metal skin layers, or through the heat of extrusion of the polymeric resinous material or combination of such heating steps. The distance between the laminating rolls at the nip can be controlled to exert effective pressure to metal-polymer-metal laminate to ensure ~0 adequate bond between the metal skins and the polymer core. ~he laminating rolls can be covexed with a layer of polytetrafluoroethylene to prevent sticking of polymeric resinous material to the rolls.
In another embodiment of this invention, the metal skin layers are first coated with an adhesive layer on one side thereof and axe fed con-tinuously to the combining nip with the coated sides facing toward each other. A layer of polymeric resinous material is disposed between the two ad-hesive coated skin layers by continuous extrusionas described hereinabove.
- 27,470-F -9-- ~
8~
In yet another embodiment of this inven-tion, a multi-layered extrudate comprising an ad-hesive layer - a core layer - an adhesive layer is disposed continuously and simultaneously between the two metal skin layers or precoated metal skin layers by the well known coextrusion process.
The present invention is not limited by the process used to prepare the metal-polyn~er--metal structural laminates. Extrusion processes, i.e., extrusion coating or extrusion lamination;
film lamination techniques; solution coating technigues or combination of such techniques well known in the art can readily be used to produce the laminates of this invention. It is essential, however, that the thermoplastic polymeric resinous material of the adhesive layer and core layer be subjected to a t~mperature at least equal to the softening point thereof, for a period of time sufficient to cause the polymer to tightly adhere but not undergoing significant degradation thereof, and effective pressure to achieve intimate contact between the polymer layers and the métal skin layers.
A preferred laminate with the present invention comprises steel or steel alloy skin layers, most preferably tin-free steel, each skin layer being within the range of from about 5 to 10 mils thick, with a core of ethylene or propylene homopolymers or copolymers having a brittle tem~era-ture of less than about 30F (-1.1C) ~as measured by ASTM D-746) and a Vicat softening point of greater than about 170F (76.7C) (as measured by ASTM D-1575) the total laminate thickness being within the range o~
from about 25 to 48 mil.
27,470-F -10-8~
When a chrome/chrome oxide coated steel is used as the metal skin layer in laminates ol this invention, the layers of chromium and of chromium oxide are too thin to be measured by conventional techniques.
Therefore, their thickness is determined by the value in milligrams of chromium that can be leached from one square foot of surface of the substrate: the chromium oxide by leaching with a base, the chromium metal by leaching with an acid. Preferably, the layers are of approximately e~ual thickness, the chromium values for the composite coating varying between above about 0.1 mg./ft.2 to about 15 mg./ft.2. It is widely known that below 0.1 mg./ft.2 corrosion resistance of metal substrate is unsatisfactory while above 15 mg./ft.~ a cohesive failure within the coating is possible. The preferred ranye of values for each layer is from about 1 mg./ft.2 to about 4 mg./ft.2.
Chromium-in-oxide is the accepted method in : the industry for reporting the thickness of the oxide layer of the coating. The chromium oxide consists essentially of Cr 3 plus minor amounts of Cr 6. The weight or thickness of oxide would be meaningless because of the degree of hydration is indefinite and variable~ Therefore, the chromium-in-oxide value is the total non-metallic chromium leached from the sub-strate. In this description chromium metal value will refer to the total metallic chromium leached from the substrate.
Another preferred laminate within the present invention comprises aluminum or aluminum allo~s skin layers, each skin being within the range of ~rom about 6 to 12 mils thick, with the same preferred core material 27,470-F -11-specified with the steel or steel alloy skin layers, the total laminate thickness being w thin the range of from about 30 to 60 mils.
With each of the preferred laminates noted above, an adhesive can be employed between the metal skin and the polymer core. The preferred adhesive layer is made from a copolymer of ethylene and an ethylenically unsaturated carboxylic acid previously described. Most preferably ethylene acrylic acid copolymer.
In a "no load oven test", used to determine the effect of heat on metal-plastic-metal laminates of the present invention, a metal-plastic-metal laminate is placed in a circulating-air oven maintained at a temperature of 190F (87.8C) for a period of 30 minutes. Following the test, the laminiate is examined for a change in appearance, dimension or other properties or a sign of delamination between individual layers.
The specific working examples that follow are intended to illustrate the invention but are not to be taken as limiting its scope.
Examples The following general procedures were used to make laminates within the scope of the present invention, which laminates are described in Table-I.
In one such procedure, two coils of metal skin material were extrusion coated on one side thereof with about 2 mils of an adhesive copolymer. Two webs of the adhesive coated metal were fed into a combining nip with the adhesive coated side facing toward each other. The combining nip was formed between a pair of opposed 27,470-F -12-counter-rotating laminating rolls preheated to a tem-perature of about 350F (176.7C). The laminating rolls were adjusted to allow the desired amount of pressure to be applied as the webs (about 27 inches wide) passed between the rolls. A molten polymeric resin core material was forced through a slot in a sheeting die of a conventional screw type extruder at a temperature of about 400F (204.4C) into the combining nip and disposed between the two adhesive coated metal webs. The slot of the die had a gen-erally rectangular configuration about 30 inches wide with a gap of approximately 0.016 inch. The lami-nating rolls had a diameter o 8 inches and were rotated at a speed of about 1.15 rpm.
A similar procedure described hereinabove, was used to make laminates of the present invention having no adhesive layers between the polymeric resin core and the metal skins. However, the initial extrusion coating step, whereby t~e adhesive copolymer was applied to the metal skin layers, was ]~ot employed.
In another procedure, shee~s of polymeric resin core were prepared from resin granules using well known compression molding techni~ues. A sheet of core material was positioned between two sheets of adhesive copolymer. The three-layer assembly comprising adhesive/-core/adhesive was then positioned between two metal skin layers, and the resulting assembly was placed in a molding press and was treated at a temperature of 302F
(150C) for a period of 10 minutes under a pressure of about 20 psi. The pressure in the mold was then increased to about lO0 psi. At the same time, the mold was allowed to cool to ambient temperature under the same pressure - 27,470-F -13-while cooling water was circulated through the platens of the molding press.
When the adhesive layer was applied in the form of powder or solvent based suspension, such layer was first applied to one side of each metal skin. Two adhesive coated metal skins were placed on each side of the polymeric core with the coated sides facing toward the core. The three-layer assembly was then placed in the mo`ld press and laminated under the conditions described hereinabove.
Certain properties of laminates of the present invention are reported in Table II.
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span under three point loading conditions, a density from about 25% to 90% that of the average of two solid metal skin layers, a limiting dome heiyht of at least about 60 percent of the limiting dome height of the solid metal of the skin layer of the lower ultimate elongation having the same thickness, the capability of being subjected to a no load oven test, subsequent to forming of said laminate, at a temperature of at least 190F (87.8C) for a period of 30 minutes without delaminating, and the capability of being bent at room temperature to 90 to a critical radius without metal rupture, the critical radius defined as the . distance from the pivot po.int to the inner skin surface.
of the laminate, being about equal to the total laminate 15 thickness.
As used herein, the term "limiting dome height" is that height measured when testing sheet - metal blank or laminate blanks in accordance with General Motors Corporation test procedures described in "Metal Progess", May 1975, pp. 52 54 and "Metals Engineering Quarterly", August 1975, pp. 53-57, using a blank width to clamp diameter ratio of abouc 1Ø
As used herein, the term "tightly adhered"
means a lap shear value of at least about 500 psi at : 25 room temperature as measured by ASTM D 3165-73 using a lap length of about 0.25 inch.
Metal skin layers which are used in accor-dance with this invention each have a thickness from about 2 to about 20 mils and, preferably, from 5 to 15 mils. A metal skin layer can be formed, for example, from aluminum, aluminum alloys, alloy-clad aluminum, 27,470-F -*-&~5~
surface modified copper, bronze, magnesium or magnesium alloys, steel, tin-free steel, tin-plate steel, aluminized s~eel, stainless steel, surface modified copper-clad stainless steel, terneplate steel, gal-vanized steel, chrome or chrome treated steel and thelike~ These metals may also be surface treated or have thereon surface conversion coatings. ~ preferred group of metals are aluminum and aluminum alloys.
Another preferred group of metals are steel and steel alloys, particularly the chrome/-chrome oxide coated steel substrate or so-called tin-free steel (TFS) described in Canadian Patent 808,630 and U.S. Patents 3,526,486 and 3,826,6280 The thickness of discrete layers of chromium metal and chromium oxide may be controlled by varying plating bath parameters as is well known in the art.
The metal skin layers on each side of the core can be formed of the same metal or of different metals and can have same or different thicknesses.
The polymer core of thi~ i~vention can be formed from any polymeric resinous material which when laminated to the metal skin layer, ei~her directly thexeto or by use of an intermediate adhesive layer, can pass a no load oven test withou~ any delamination, after being subjected to a temperature of at least 190F (87.8C) for a period of 30 minutes. The polymer core can have a thickness from about 1 to about 61 mils, preferably from about 10 to 45 mils, inclusive of any adhesive layer~s) which may be employed. In general, rubber-type polymers are ineffective because of poor 27,470-F -5-,~ .
high temperature properties. Glassy-type pol~hers are ineffective because of room temperature brittleness.
Exemplary polymers within the present invention include homopolymers and copolymers of olefins such as ethylene, propylene and 4-methyl pentene-1; polymers of vinyl halides such as vinyl chloride; and copolymers of vinylidene chloride. Also suitable are cellulosic polymers such as ethyl cellulose, cellulose butyrate and cellulose acetate; polyamides such as nylon; poly-esters such as poly(ethylene terephthalate~; polycar-bonates; thermoplastic epoxy resins; and po]yurethanes.
Especially preferred resinous materials aEe the ethylene polymers and copolymers and the propylene pol~mers and copolymers having a brittle temperature of less than about 30F (-1.1C) (as measured by ASTM D-746) and a Vicat softening point of greater than about 170F
(76.7C) (as measured by ASTM D-1875). Such materials include polypropylene, low density or high density poly-ethylene, ethylene/vinyl acetate copolymer, ethylene/-acrylic acid copolymer, and ethylene/butene-l and other alkene-1 copolymers.
The polymeric resinous materials of the core can be bonded directly to the metal skin layers or by the use of an intermediate adhesive layer therebetween. The intermediate adhesive layer can have a thickness from about 0.1 to 5 mils, preferably from about 0.3 to 2.5 mils. Such layer may be formed from any thermoplastic polymeric resinous material which will tightly adhere the core layer to the metal skin layers. A particularly preferred ad-hesive layer is a normally solid thermoplastic ethylene-bas~d polymer modified by monomers having re-active carboxylic ~cid groups, particularly a co-polymer of a ma~or proportion of ethylene and a 27,470-~ -6-_7~ 5.~
minor proportion, typically from 1 to 30, prefer-ably from 2 to 20, percent by weight, of an ethy-lenically unsaturated carboxylic acid. Speciflc examples of such suitable ethylenically unsaturated carboxylic acids (which term includes mono- and polybasic acids, acid anhydrides, and partial esters of polybasic acids) are acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, maleic anhydride monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, tripropylene glycol monornethyl ether acid maleate, or ethylene ~lycol monophenyl ether acid maleate. Th~ carboxylic acid monomer is preferably selected from ~ ethylenically unsatu-15 rated mono- and polycarboxylic acids and acid anhydrides having from 3 to 8 carbon atoms pe~
molecule and partial esters of such polycarboxylic acid wherein the acid moiety has at least one car-boxylic acid group and the alcohol moiety has from 1 to 20 carbon atoms. The copolymer can also - contain other copolymerizable monomers including an ester of acrylic acid. The comonomers ca~ be combined in the copolymer in any way, e.g., as random copolymers, as block or sequential copoly-mers, or as graft copolymers. Materials of these kinds and methods of making them are readily known in the art. Specific examples of such copolymers are ethylene acrylic acid copolymer, ethylene meth-acrylic acid copolymer, ethylene maleic acid co-polymer and the like.
The adhesive layer can first be applied tothe metal skin layers, first be applied to the core, o~ can be applied to the metal s~in layer and the 27,470-F -7-8~5~
core simultan~ously. The adhesive layer can be applied using well known application techniques, such as, for example, solvent casting, roll coating, or, preferably, extrusion processes and the like.
When the adhesive layer is to be combined with the core prior to the lamination thereof to the metal skins, such layers can advantageously be introduced into the laminates by the well known coextrusion process or combining the conventional extrusion process with a film lamination technique.
In one embodiment of this inYention, the core of po~lymeric resinous material may be irradiated with a high energy ionizing radiation source to achieve at least a partial crosslinking thereof for improved creep properties and thermal stability.
In another embodiment of this invention, the core is made electrsconductive by incorporating conductive particulates, e.g., carbon black and metal particles, thereinto. The conductive core enhances the weldability of the resulting metal--polymer-metal laminates.
In yet another embodiment of this invention, the core o~ polymeric resinous material contains at least one reinforcing element embedded therein to en-hance the mechanical properties of the resultinglaminates. Such elements can be made from ~lass fibers, a perforated metallic sheet, an expanded metallic sheet, or a metallic wire screen and the like.
Numerous solid fillers, pi~ments, lubricants, antioxidants and the like well known in the art can also be incorporated into the core or adhesive 27,47~-F -8-layers, provided the resultant laminate retains the hereinbefore prescribed characteristics.
In one embodiment of this inve~tion, a metal-polymer~metal laminate is produced by dis-posing a layer of polymer resinous material, whichlayer is continuously extruded from a conventional, screw-type extruder, between two metallic skin layers which are fed continuously to a nip formed by a pair of opposing and counter-rotating laminating rolls. Heat and pressure sufficient to affect a bond between the metal skin layers and the polymeric resinous material are applied to the skin layers.
This is accomplished by heating one or both of the laminating rolls, by preheating metal skin layers, or through the heat of extrusion of the polymeric resinous material or combination of such heating steps. The distance between the laminating rolls at the nip can be controlled to exert effective pressure to metal-polymer-metal laminate to ensure ~0 adequate bond between the metal skins and the polymer core. ~he laminating rolls can be covexed with a layer of polytetrafluoroethylene to prevent sticking of polymeric resinous material to the rolls.
In another embodiment of this invention, the metal skin layers are first coated with an adhesive layer on one side thereof and axe fed con-tinuously to the combining nip with the coated sides facing toward each other. A layer of polymeric resinous material is disposed between the two ad-hesive coated skin layers by continuous extrusionas described hereinabove.
- 27,470-F -9-- ~
8~
In yet another embodiment of this inven-tion, a multi-layered extrudate comprising an ad-hesive layer - a core layer - an adhesive layer is disposed continuously and simultaneously between the two metal skin layers or precoated metal skin layers by the well known coextrusion process.
The present invention is not limited by the process used to prepare the metal-polyn~er--metal structural laminates. Extrusion processes, i.e., extrusion coating or extrusion lamination;
film lamination techniques; solution coating technigues or combination of such techniques well known in the art can readily be used to produce the laminates of this invention. It is essential, however, that the thermoplastic polymeric resinous material of the adhesive layer and core layer be subjected to a t~mperature at least equal to the softening point thereof, for a period of time sufficient to cause the polymer to tightly adhere but not undergoing significant degradation thereof, and effective pressure to achieve intimate contact between the polymer layers and the métal skin layers.
A preferred laminate with the present invention comprises steel or steel alloy skin layers, most preferably tin-free steel, each skin layer being within the range of from about 5 to 10 mils thick, with a core of ethylene or propylene homopolymers or copolymers having a brittle tem~era-ture of less than about 30F (-1.1C) ~as measured by ASTM D-746) and a Vicat softening point of greater than about 170F (76.7C) (as measured by ASTM D-1575) the total laminate thickness being within the range o~
from about 25 to 48 mil.
27,470-F -10-8~
When a chrome/chrome oxide coated steel is used as the metal skin layer in laminates ol this invention, the layers of chromium and of chromium oxide are too thin to be measured by conventional techniques.
Therefore, their thickness is determined by the value in milligrams of chromium that can be leached from one square foot of surface of the substrate: the chromium oxide by leaching with a base, the chromium metal by leaching with an acid. Preferably, the layers are of approximately e~ual thickness, the chromium values for the composite coating varying between above about 0.1 mg./ft.2 to about 15 mg./ft.2. It is widely known that below 0.1 mg./ft.2 corrosion resistance of metal substrate is unsatisfactory while above 15 mg./ft.~ a cohesive failure within the coating is possible. The preferred ranye of values for each layer is from about 1 mg./ft.2 to about 4 mg./ft.2.
Chromium-in-oxide is the accepted method in : the industry for reporting the thickness of the oxide layer of the coating. The chromium oxide consists essentially of Cr 3 plus minor amounts of Cr 6. The weight or thickness of oxide would be meaningless because of the degree of hydration is indefinite and variable~ Therefore, the chromium-in-oxide value is the total non-metallic chromium leached from the sub-strate. In this description chromium metal value will refer to the total metallic chromium leached from the substrate.
Another preferred laminate within the present invention comprises aluminum or aluminum allo~s skin layers, each skin being within the range of ~rom about 6 to 12 mils thick, with the same preferred core material 27,470-F -11-specified with the steel or steel alloy skin layers, the total laminate thickness being w thin the range of from about 30 to 60 mils.
With each of the preferred laminates noted above, an adhesive can be employed between the metal skin and the polymer core. The preferred adhesive layer is made from a copolymer of ethylene and an ethylenically unsaturated carboxylic acid previously described. Most preferably ethylene acrylic acid copolymer.
In a "no load oven test", used to determine the effect of heat on metal-plastic-metal laminates of the present invention, a metal-plastic-metal laminate is placed in a circulating-air oven maintained at a temperature of 190F (87.8C) for a period of 30 minutes. Following the test, the laminiate is examined for a change in appearance, dimension or other properties or a sign of delamination between individual layers.
The specific working examples that follow are intended to illustrate the invention but are not to be taken as limiting its scope.
Examples The following general procedures were used to make laminates within the scope of the present invention, which laminates are described in Table-I.
In one such procedure, two coils of metal skin material were extrusion coated on one side thereof with about 2 mils of an adhesive copolymer. Two webs of the adhesive coated metal were fed into a combining nip with the adhesive coated side facing toward each other. The combining nip was formed between a pair of opposed 27,470-F -12-counter-rotating laminating rolls preheated to a tem-perature of about 350F (176.7C). The laminating rolls were adjusted to allow the desired amount of pressure to be applied as the webs (about 27 inches wide) passed between the rolls. A molten polymeric resin core material was forced through a slot in a sheeting die of a conventional screw type extruder at a temperature of about 400F (204.4C) into the combining nip and disposed between the two adhesive coated metal webs. The slot of the die had a gen-erally rectangular configuration about 30 inches wide with a gap of approximately 0.016 inch. The lami-nating rolls had a diameter o 8 inches and were rotated at a speed of about 1.15 rpm.
A similar procedure described hereinabove, was used to make laminates of the present invention having no adhesive layers between the polymeric resin core and the metal skins. However, the initial extrusion coating step, whereby t~e adhesive copolymer was applied to the metal skin layers, was ]~ot employed.
In another procedure, shee~s of polymeric resin core were prepared from resin granules using well known compression molding techni~ues. A sheet of core material was positioned between two sheets of adhesive copolymer. The three-layer assembly comprising adhesive/-core/adhesive was then positioned between two metal skin layers, and the resulting assembly was placed in a molding press and was treated at a temperature of 302F
(150C) for a period of 10 minutes under a pressure of about 20 psi. The pressure in the mold was then increased to about lO0 psi. At the same time, the mold was allowed to cool to ambient temperature under the same pressure - 27,470-F -13-while cooling water was circulated through the platens of the molding press.
When the adhesive layer was applied in the form of powder or solvent based suspension, such layer was first applied to one side of each metal skin. Two adhesive coated metal skins were placed on each side of the polymeric core with the coated sides facing toward the core. The three-layer assembly was then placed in the mo`ld press and laminated under the conditions described hereinabove.
Certain properties of laminates of the present invention are reported in Table II.
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- 27, 470-F -16-.
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5~
As shown in Table II, metal-plastic-metal laminates of the present invention are of light weight and can readily be formed as evidenced by relatively high values for the limiting dome height ratio. At the same time, the laminates have surprisingly high stiffness and lap shear values.
In addition, Examples 1-4 and 11-13 were tested and passed the 90 bend test. Other examples were not tested. Further, Example 13 was subjected to and passed the no load oven test.
.
27,470-F -19-.~ , . .
" .
As shown in Table II, metal-plastic-metal laminates of the present invention are of light weight and can readily be formed as evidenced by relatively high values for the limiting dome height ratio. At the same time, the laminates have surprisingly high stiffness and lap shear values.
In addition, Examples 1-4 and 11-13 were tested and passed the 90 bend test. Other examples were not tested. Further, Example 13 was subjected to and passed the no load oven test.
.
27,470-F -19-.~ , . .
" .
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A metal-polymer-metal structural laminate comprising a core of polymeric resinous material having tightly adhered to each side thereof a metal skin layer wherein each metal skin layer is from about 2 to about 20 mils thick, said laminate further having a ratio of core thickness to skin thickness of less than 9:1, and a total thickness of from about 5 to about 65 mils; the materials of construction of said polymeric core and metal skins and the geometry of the laminate being such that the laminate has a flexural stiffness at least 40% that of the solid metal of the skin layer of the lower modulus having the same thickness as said laminate as measured by ASTM D790 on a one inch wide sample having four inch span under three point loading con-ditions, a density from about 25% to 90% that of the average of two solid metal skin layers, a limiting dome height of at least about 60 percent of the limiting dome height of the solid metal of the skin layer of the lower ultimate elongation having the same thickness, the capability of being subjected to a no load oven test, subsequent to forming of said laminate, at a temperature of at least 190°F (87.8°C) for a period of 30 minutes without delaminating, and the capability of being bent at room temperature to 90° to a critical 27,470-F -20-radius without metal rupture, the critical radius defined as the distance from the pivot point to the inner skin surface of the laminate, being about equal to the total laminate thickness.
2. The structural laminate of Claim 1 wherein the metal skin layers on each side of the core are different thicknesses.
3. The structural laminate of Claim 1 wherein the metal skin layers on each side of the core are of different metals.
4. The structural laminate of Claim 1 wherein the core of polymeric resinous material is selected from a group consisting of homopolymers and copolymers of ethylene or propylene and having a brittle tempera-ture of less than about 30°F (-1.1°C) and a Vicat softening point of greater than about 170°F (76.7°C).
5. The structural laminate of Claim 1 wherein the core of polymeric resinous material has been irradi-ated for improved creep properties and thermal stability.
6. The structural laminate of Claim 1 wherein the core of polymeric resinous material is electroconductive.
7. The structural laminate of Claim 1 wherein the core of polymeric resinous material contains at least one reinforcing element embedded therein.
8. The structural laminate of Claim 7 wherein the reinforcing element is an expanded metallic sheet.
27,470-F -21-
27,470-F -21-
9. The structural laminate of Claim 1 having a thickness from about 20 to 45 mils.
10. The structural laminate of Claim 1 wherein the metal skin layer has a thickness of from about 5 to 15 mils.
11. The structural laminate of Claim 1 wherein the polymeric resinous material of the core is selected from homopolymers and copolymers of propylene or ethylene having a brittle temperature of less than about 30°F (-1.1°C) and a Vicat soft-ening point of greater than about 170°F (76.7°C) and the metal skin layers are steel or steel alloys, the thickness of each skin being within the range of from about 5 to 10 mils and the total laminate thick-ness being within the range of from about 23 to 48 mils.
12. The structure laminate of Claim 2 wherein the polymeric resinous material is high density polyethylene.
13. The structural laminate of Claim 1 wherein the polymeric resinous material of the core is selected from homopolymers and copolymers of propylene or ethylene having a brittle temperature of less than about 30°F (-1.1°C) and a Vicat softening point of greater than about 170°F (76.7°C) and the metal skin layers are aluminum or aluminum alloys, the thickness of each skin being within the range of from 6 to 12 mils and the total laminate thickness being within the range of from about 30 to 60 mils.
27,470-F -22-
27,470-F -22-
14. The structural laminate of Claim 5 wherein the polymeric resinous material is high density polyethylene.
15. The structural laminate of Claims 1, 10 or 12 wherein the core is tightly adhered to the metal skin layers by the use of an intermediate adhesive layer therebetween.
16. The structural laminate of Claim 14 wherein the intermediate adhesive comprises a co-polymer of ethylene and ethylenically unsaturated carboxylic acid.
17. The structural laminate of Claim 15 wherein the carboxylic acid is acrylic acid.
27,470-F -23-
27,470-F -23-
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA357,173A CA1128851A (en) | 1980-07-28 | 1980-07-28 | Formable metal-plastic-metal structural laminates |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA357,173A CA1128851A (en) | 1980-07-28 | 1980-07-28 | Formable metal-plastic-metal structural laminates |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128851A true CA1128851A (en) | 1982-08-03 |
Family
ID=4117523
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA357,173A Expired CA1128851A (en) | 1980-07-28 | 1980-07-28 | Formable metal-plastic-metal structural laminates |
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| Country | Link |
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| CA (1) | CA1128851A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108839395A (en) * | 2018-07-03 | 2018-11-20 | 南京工业大学 | A kind of enhanced composite board of tooth plate and its production technology |
-
1980
- 1980-07-28 CA CA357,173A patent/CA1128851A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108839395A (en) * | 2018-07-03 | 2018-11-20 | 南京工业大学 | A kind of enhanced composite board of tooth plate and its production technology |
| CN108839395B (en) * | 2018-07-03 | 2024-01-23 | 南京工业大学 | Toothed plate reinforced composite plate and production process thereof |
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