CA2564406C - Low density structural laminate - Google Patents

Low density structural laminate Download PDF

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Publication number
CA2564406C
CA2564406C CA2564406A CA2564406A CA2564406C CA 2564406 C CA2564406 C CA 2564406C CA 2564406 A CA2564406 A CA 2564406A CA 2564406 A CA2564406 A CA 2564406A CA 2564406 C CA2564406 C CA 2564406C
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Prior art keywords
low density
layer
composite layer
metal skin
structural laminate
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CA2564406A
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French (fr)
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CA2564406A1 (en
Inventor
Michael Slywchuk
Diane Stogiannes
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Individual
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2305/00—Condition, form or state of the layers or laminate
    • B32B2305/22—Fibres of short length
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/558—Impact strength, toughness
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2310/00—Treatment by energy or chemical effects
    • B32B2310/14—Corona, ionisation, electrical discharge, plasma treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2311/00—Metals, their alloys or their compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2607/00—Walls, panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/12—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by using adhesives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/0008—Electrical discharge treatment, e.g. corona, plasma treatment; wave energy or particle radiation

Abstract

The present invention provides a structural laminate comprising a low density core layer formed from a mix of thermoplastic resin and natural fiber.

Description

LOW DENSITY STRUCTURAL LAMINATE
FIELD OF THE INVENTION
[0001] The present invention relates to a structural laminate and more particularly to a low density structural laminate. The present invention further relates to a method for producing a low density structural laminate.
BACKGROUND OF THE INVENTION
[0002] Sheet steel is used extensively to form panels. The required structural characteristics, such as stiffness, vary depending upon the specific application. When higher stiffness values are required, the steel thickness is typically increased.
Increasing sheet steel thickness, however, produces a panel that is not only heavier, but also more expensive.
[0003] A number of approaches have been taken in the past to provide improved structural characteristics of panels, without substantially increasing weight or material cost. For example, composites of steel sheets having a solid polymer core have been used in applications where sound deadening and vibration dampers are required. The specific stiffness of polymer core products, however, is less than desirable.
[0004] United States Patent 5,985,457 [Clifford (Clifford #1)] teaches a structural panel which comprises a metal and paper composite. The paper core is a web which is adhesively bonded to the metal skins and which may have openings to create paths for adhesive bridges between the metal skins to minimize failure caused by buckling.
[0005] United States Patent 6,171,705 [Clifford (Clifford #2)] teaches a structural laminate having first and second skins of sheet metal. A fibrous core layer is provided between the sheet metal skins and is bonded to the skins. In one aspect, the fibrous core layer is impregnated with an adhesive resin which bonds the core layer directly to the skins. In another aspect, layers of adhesive are placed between the core material and the metal skins that bond the core to the skins.
[0006] While the paper core and fibrous core laminates of Clifford #1 and Clifford #2 represent a significant improvement in the art, there remains room for improvement.
[0007] There is a continual need to produce a panel having the required structural properties discussed above and also having a lower density and a lower cost compared with traditional panels.
SUMMARY OF THE INVENTION
[0008] In one aspect, the present invention provides a structural laminate comprising a core layer disposed between and bonded to each of a first metal skin layer and a second metal skin layer, the core layer comprising a low density composite layer.
[0009] In an alternative embodiment the present invention provides a structural laminate comprising a composite layer disposed between and bonded to each of a first metal skin layer and a second metal skin layer, the composite layer comprising a mixture of thermoplastic resin and natural fiber.
[0010] In a further embodiment the present invention provides a structural laminate comprising a composite layer disposed between and bonded to each of a first metal skin layer and a second metal skin layer, the composite layer comprising a mixture of thermoplastic resin, natural fiber and at least one foaming agent.
[0011] In another aspect, the present invention provides a process for producing a low density structural laminate comprising the steps of: forming a composite layer comprising thermoplastic resin and natural fiber; placing an adhesive layer on each surface of the composite layer; disposing the composite layer between a first metal skin layer and a second metal skin layer to define an interim laminate; and pressing and optionally heating the interim laminate at a first pressure to produce the structural laminate.
[0012] In an alternate embodiment, the present invention provides a process as described above with the additional step of surface treating the composite layer prior to application of the adhesive layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will be described in further detail with reference to the accompanying drawings in which:
[0014] Figure 1 illustrates a sectional side view of one embodiment of the low density panel of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention provides a low density structural laminate, indicated generally at numeral 10 in Figure 1.
[0016] The low density panel 10 includes a first metal skin layer 12 and a second metal skin layer 14. Interposed between the first and second metal skin layer 12, 14 is a low density composite layer 16.
[0017] Disposed between the first metal skin layer 12 and the low density composite layer 16 is a first adhesive layer 18. A second adhesive layer 20 is disposed between the second metal skin layer 14 and the low density composite layer 16.
[0018] The first adhesive layer 18 serves to bond the low density composite layer 16 to the first metal skin 12. Likewise, the second adhesive layer 20 serves to bond the second metal skin 14 to the low density composite layer 16.
[0019] The first and second adhesive layers 18, 20 may be the same or different, although preferably the same. Suitable adhesives that may be used include adhesives that are compatible with the composite layer and the metal skins to which the adhesive will be applied. Suitable quantities of adhesive will depend on the properties of the adhesive used, and the choice of adhesive quantity will be within the purview of persons skilled in the art.
Examples of adhesives that may be used include, but are not limited to, thermoplastic adhesives, thermoset adhesives or combination adhesives such as reactive hot melt polyurethane (PUR). The adhesive may be applied to the metal skin layer or the composite layer. Examples of suitable adhesives that may be used include, but are not limited to Rohm and Haas 1223 PE resin or 5003 PUR resin. When this resin is used, first adhesive layer 18 and second adhesive layer 20 can suitably each be applied in a layer between about 0.0005 inches and about 0.010 inches in thickness and more preferably between about 0.001 inches and 0.005 inches in thickness.
[0020] The particular choice of metal for metal skin layers 12 and 14 used in structural laminate 10 is not particularly restricted. First metal skin layer 12 and second metal skin layer 14 may be the same or different. Non-limiting examples of suitable metal skin layers for use in the present invention include aluminum, cold rolled steel, galvanized steel, tin-coated steel, zinc coated steel, low carbon micro-alloyed high-strength steel and stainless steel. In a preferred embodiment of the present structural laminate, one or both of first metal skin layer 12 and second metal skin layer 14 comprise steel. In a particularly preferred embodiment of the present structural laminate, one or both of first metal skin layer 12 and second metal skin layer 14 comprise pre-painted zinc-coated steel.
[0021] Preferably, first metal skin layer 12 and second metal skin layer 14 have the same or different thicknesses and the thickness of each is at least 0.005 inches.
More preferably, first metal skin layer 12 and second metal skin layer 14 have the same or different thicknesses and the thickness of each is in the range of from about 0.005 inches to about 0.030 inches. Most preferably, first metal skin layer 12 and second metal skin layer 14 have the same or different thicknesses and the thickness of each is about 0.019 inches.
[0022] The low density composite layer 16 is a low density natural-fiber plastic composite. The low density composite layer 16 is made from a material including a mixture of thermoplastic resin and natural fiber. Preferably the low density layer is formed from uniformly distributed thermoplastic resin and natural fiber that are extruded together to form a thin flat board of uniform thickness. Preferably a foaming agent is incorporated into the composite layer which will enable a composite layer to be produced that has a reduced weight.
An example of a suitable foaming agent that may be used includes the commercially available product Expancele, manufactured by Akzo Nobel. Other foaming agents known to a person skilled in the art may also be used. The foaming agent may be incorporated in the range of between about 1% and about 5% and preferably in the range of about 2% and about 3%.
[0023] The thermoplastic resin that is used in the low density core may be selected from any thermoplastic resin material. The thermoplastic resin may also be a mix of more than one type of thermoplastic resin. Preferably the thermoplastic resin is polypropylene or polyethylene.
[0024] The natural fiber that is used in the low density composite layer may be any natural fiber. Examples of the type of natural fiber that may be used include wood fiber, for example oak flour, and rice husks. Preferably the natural fiber is rice husks.
[0025] The low density composite layer includes a mixture of the thermoplastic resin and the natural fiber. Preferably the low density composite layer includes between about 50% and about 70% of thermoplastic resin and between about 30% and about 50% of natural fiber. More preferably, in order to reduce cost and to improve the mechanical properties of the composite layer, the low density composite layer includes a 50:50 mix of thermoplastic resin and natural fiber. Preferably, the low density composite layer has a thickness of between about 0.075 inches and about 0.5 inches
[0026] In one embodiment the low density layer is formed by combining thermoplastic pellets with the natural fiber and at least one foaming agent and extruding the composite layer.

An example of the type of extruder that may be used to mix and extrude the composite layer is a melt screw extruder. The extruded product will be a flattened composite layer.
[0027] The low density composite layer provides a solid board that may be used as a core layer in a structural laminate allowing for easy manufacturing while providing the structural properties required in a panel. The foamed solid board provides a light weight core that reduces the overall weight of the panel.
[0028] The low density composite layer also provides an improved impact resistance compared with some of the conventional panels. The use of a pre-formed solid board as the core reduces issues with defective cores since the core is pre-fabricated.
[0029] To form a low density composite laminate or panel initially the composite layer is manufactured, as described above. A panel is then formed by securing the composite layer between first and second metal skins. A person skilled in the art will know several ways of producing the panel that are known in the art. The following methods provide examples of different ways of forming the panel but are not meant to be limiting.
[0030] The composite panel may be formed using a batch press which places the composite layer between two metal skins including an adhesive layer between the composite layer and each metal skin. The batch press will apply both pressure and temperature to the panel to form the panel and adhere the composite layer to the skins. The amount of pressure that may be applied using this method is in the range of between about 50 psi and about 150 psi. The batch press may be used at a temperature in the range of about 250 F to about 400 F
. More preferably the batch press method is conducted at a temperature about 300 F. It will be understood that if a thermoplastic adhesive is used, the panel must be cooled to below about 200 F
to solidify the adhesive layer before removing pressure from the panel.
[0031] The composite panel may be formed using a continuous laminator which places the composite layer between two metal skins, including an adhesive layer between the composite layer and each metal skin, between two moving belt presses. The continuous laminator will apply both pressure and temperature to the panel to form the panel and adhere the composite layer to the skins. The amount of pressure, temperature and cooling that may be applied are similar to the ranges discussed above in relation to the batch press method.
[0032] The composite panel may also be formed using a roll coater which places a liquid adhesive between the composite layer and each of the metal skins and allows the liquid adhesive to cure and secure the composite layer in place. This process uses a batch press, continuous laminator, nip roller or multiple nip rollers to apply a low pressure to provide good contact between the composite layer and each of the metal skins in order to form the panel. For example, the applied pressure may be in the range of about 25 to about 50 psi.
[0033] In an alternative embodiment, the structural laminate is formed by extruding the composite layer between a first and second metal skin without the requirement of an adhesive layer.
[0034] In an alternative embodiment, the composite layer may be surface treated prior to being placed in the structural laminate. The surface treatment may include the use of flame, plasma or corona treating. The use of the surface treatment provides a more reactive surface on the composite layer allowing the adhesive to bond more readily to the composite layer.
[0035] Examples of the type of applications for the low density structural laminate of the present invention include, but are not limited to the following: side and/or wall panels in truck trailers, interior liner panels in truck trailers, architectural and/or decorative panels and automotive applications.
[0036] The following panel was made according to the present invention.
The structural panel included two 0.018 inch HSLA skins and a composite layer placed therebetween in accordance with the description provided above. The total thickness of the panel was 0.240 inches and the panel had a flexural stiffness of 1250 lbs/inch (based on a 1 inch x 6 inch sample) with a nominal weight of 2.351bs/ft2.
[0037] While this invention has been described with reference to illustrative embodiments and examples, the description is not intended to be construed in a limiting sense.
Thus, various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description.

22428397.1

Claims (16)

What is claimed is:
1. A structural laminate comprising: a core layer disposed between and bonded to each of a first metal skin layer and a second metal skin layer, the first and second metal skin layers each.
having a thickness selected from between about .005 and about .030 inches, the core layer comprising a low density composite layer, being selected from the group consisting of: at least one of a low density natural-fiber plastic composite and a mixture of thermoplastic resin and natural fiber, wherein the low density composite layer is a flattened low density composite having a uniform thickness selected from between about .075 and about .5 inches;
wherein the core layer further comprises: a first adhesive layer, a thickness selected from between about .0005 and about .010 inches, interposed between the first metal skin layer and the low density composite layer, and a second adhesive layer, having a thickness selected from between about .0005 and about .010 inches, interposed between the second metal skin layer and the low density composite layer;
wherein the first and second adhesive layers comprise a reactive hot melt polyurethane adhesive; and wherein said structural laminate is in the form of a panel comprising a door or wall panel of an automotive or truck trailer.
2. The structural laminate as defined in claim 1, wherein the composite layer further comprises at least one foaming agent.
3. The structural laminate as defined in claim 1, wherein the low density composite layer is a foamed low density natural-fiber plastic composite.
4. The structural laminate as defined in claim 1, wherein the low density composite layer comprises between about 50 % and about 70 % thermoplastic resin.
5. The structural laminate as defined in claim 1, wherein the low density composite layer comprises between about 30% and about 50% natural fiber.
6. The structural laminate as defined in claim 1, wherein the low density composite layer comprises a 50/50 mixture of thermoplastic resin and natural fiber.
7. The structural laminate as defined in claim 1, wherein the first and second metal skin layers are the same or different and are formed of a material selected from the group consisting of: aluminum, cold rolled steel, tin-coated steel, zinc-coated steel, low carbon micro-alloyed high-strength steel and stainless steel.
8. The structural laminate as defined in claim 7, wherein the first and second metal skin layers are pre-painted on at least one side.
9. A process for producing a low density structural laminate comprising the steps of:
forming a low density composite layer being selected from the group consisting of: at least one of a low density natural-fiber plastic composite and a mixture of thermoplastic resin and natural fiber, wherein the low density composite layer is a flattened low density composite having a uniform thickness selected from between .075 and about .5 inches;
placing a first adhesive layer, with a thickness selected from between about .0005 and about .010 inches on a first side of the composite layer;
placing a second adhesive layer, having a thickness selected from between .0005 and about .010 inches on the second side of the composite layer;
wherein the first and second adhesive layers comprise a reactive hot melt polyurethane adhesive;
disposing the composite and adhesive layers between a first metal skin layer and a second metal skin layer to define an interim laminate, the first and second metal skin layers each having a thickness selected from between about .005 and about .030 inches;
pressing the interim laminate at a pressure to produce the structural laminate; and wherein said structural laminate is in the form of a panel comprising a door or wall panel of an automotive or truck trailer.
10. The process as defined in claim 9, wherein the step of forming the composite layer includes co-extruding a mixture of thermoplastic resin and natural fiber.
11. The process as defined in claim 9, the step of forming the composite layer includes co-extruding a mixture of thermoplastic resin, natural fiber and at least one foaming agent.
12. The process as defined in claim 9, wherein the interim laminate is heated to a temperature in the range of from about 250° F to about 400° F
and is then cooled to below about 200° F during pressing.
13. The process as defined in claim 12, wherein the interim laminate is heated to a temperature of about 300° F and is then cooled to below about 200° F during pressing.
14. The process as defined in claim 9, wherein the pressure is in the range of between about 50 to about 150 psi.
15. The process as defined in claim 10, wherein the pressure is in the range of between about 25 to about 50 psi.
16. The process as defined in claim 10, comprising an additional step of surface treating the composite layer prior to the step of placing the first and second adhesive layers.
CA2564406A 2006-10-17 2006-10-17 Low density structural laminate Active CA2564406C (en)

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Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
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CA2564406C true CA2564406C (en) 2016-01-19

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