U.S. patent application number 13/282540 was filed with the patent office on 2012-05-03 for composite structures having improved heat aging and interlayer bond strength.
This patent application is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to Andri E. Elia, Olaf Norbert Kirchner, Martyn Douglas Wakeman, Shengmei Yuan.
Application Number | 20120108125 13/282540 |
Document ID | / |
Family ID | 44936546 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120108125 |
Kind Code |
A1 |
Elia; Andri E. ; et
al. |
May 3, 2012 |
COMPOSITE STRUCTURES HAVING IMPROVED HEAT AGING AND INTERLAYER BOND
STRENGTH
Abstract
Disclosed herein are composite structures having improved heat
aging, processes for making them, and end use articles. The
composite structures comprise a polyamide matrix resin composition
comprising a matrix heat stabilizer ; a fibrous material and a
polyamide surface resin composition comprising copper based heat
stabilizer; wherein: the matrix heat stabilizer is different than
the copper based heat stabilizer; and wherein the fibrous material
is impregnated with the polyamide matrix resin composition.
Inventors: |
Elia; Andri E.; (Chadds
Ford, PA) ; Kirchner; Olaf Norbert; (Genolier,
CH) ; Wakeman; Martyn Douglas; (Gland, CH) ;
Yuan; Shengmei; (Newark, DE) |
Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
44936546 |
Appl. No.: |
13/282540 |
Filed: |
October 27, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61408166 |
Oct 29, 2010 |
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61410093 |
Nov 4, 2010 |
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61410100 |
Nov 4, 2010 |
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61410104 |
Nov 4, 2010 |
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61410108 |
Nov 4, 2010 |
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Current U.S.
Class: |
442/59 ; 428/221;
428/297.4 |
Current CPC
Class: |
B32B 5/26 20130101; B32B
2260/023 20130101; B32B 2307/546 20130101; B32B 2307/308 20130101;
B32B 2260/046 20130101; Y10T 428/31725 20150401; Y10T 442/2762
20150401; B32B 27/12 20130101; Y10T 442/2721 20150401; B29K 2709/08
20130101; C08L 2205/02 20130101; Y10T 442/2984 20150401; B29C
45/14786 20130101; B29K 2077/00 20130101; B32B 2260/021 20130101;
Y10T 442/20 20150401; Y10T 428/31623 20150401; Y10T 442/674
20150401; Y10T 442/2861 20150401; Y10T 442/2992 20150401; Y10T
428/31728 20150401; B32B 2262/101 20130101; B32B 2307/306 20130101;
C08K 7/20 20130101; Y10T 428/249921 20150401; B32B 2605/00
20130101; C08L 77/06 20130101; Y10T 428/249924 20150401; B29C
45/0001 20130101; B32B 2264/12 20130101; Y10T 442/2041 20150401;
Y10T 442/2631 20150401; C08J 2377/06 20130101; B32B 27/34 20130101;
C08L 77/06 20130101; C08K 7/20 20130101; C08L 77/06 20130101; C08L
77/06 20130101; C08J 5/043 20130101; B32B 5/024 20130101; B29K
2677/00 20130101; Y10T 428/24994 20150401; B32B 2264/10 20130101;
C08L 77/06 20130101 |
Class at
Publication: |
442/59 ; 428/221;
428/297.4 |
International
Class: |
B32B 5/02 20060101
B32B005/02; B32B 27/04 20060101 B32B027/04; B32B 27/34 20060101
B32B027/34 |
Claims
1. A composite structure comprising: a polyamide matrix resin
composition comprising from 0.1 to at or about 3 weight percent of
a matrix heat stabilizer based on the weight of the polyamide
matrix resin composition; a fibrous material selected from woven or
non-woven structures, felts, knits, braids, textiles, fibrous
battings or mats, and combinations of these; and a polyamide
surface resin composition comprising 0.1 to 3 weight percent of a
copper based heat stabilizer based on the weight of the polyamide
surface resin composition wherein: the matrix heat stabilizer is
different than the copper based heat stabilizer; and wherein the
fibrous material is impregnated with the polyamide matrix resin
composition.
2. The composite structure of claim 1 wherein the polyamide in the
matrix resin composition and the polyamide in the surface resin
composition, are independently selected from the group consisting
of PA6; PA11; PA12; PA4,6; PA6,6; PA,10; PA6,12; PA10,10; PA6T;
PA6I, PA6I/6T; PA6,T/6,6; PAMXD6; PA6T/DT and copolymers and blends
of the same.
3. The composite structure of claim 1 wherein the matrix heat
stabilizer is selected from the group consisting of
dipentaerythritol, tripentaerythritol, pentaerythritol and mixtures
thereof.
4. The composite structure of claim 1 wherein the copper based heat
stabilizer is a mixture of 10 to 50 weight percent copper halide,
50 to 90 weight percent potassium iodide, and from zero to 15
weight percent metal stearate.
5. The composite structure of claim 1 wherein the fibrous material
is from 30 weight percent to 60 volume percent of the composite
structure.
6. The composite structure of claim 1 wherein the surface resin
composition and/or the matrix resin composition further comprise
one or more impact modifiers, one or more oxidative stabilizers,
one or more reinforcing agents, one or more ultraviolet light
stabilizers, one or more flame retardant agents or mixtures
thereof.
7. An article made from the composite structure of claim 1.
8. The article of claim 7 in the form of components for
automobiles, trucks, commercial airplanes, aerospace, rail,
household appliances, computer hardware, hand held devices,
recreation and sports, structural component for machines,
structural components for buildings, structural components for
photovoltaic equipments or structural components for mechanical
devices.
9. The article of claim 7 in the form of automotive powertrain
covers and housings, engine cover brackets, steering columns frame,
oil pans, and exhaust system components.
10. A process for making the composite structure of claim 1, the
process comprising the step of: impregnating the fibrous material
under heat and pressure with the matrix resin wherein at least a
portion of the surface of the composite structure comprises the
surface resin composition;
11. The process of claim 10 wherein the matrix heat stabilizer is
selected from dipentaerythritol, tripentaerythritol,
pentaerythritol and mixtures of these.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Application No. 61/408,166, filed Oct. 29, 2010, which
is now pending, the entire disclosure of which is incorporated
herein by reference; and U.S. Provisional Application Nos.
61/410,093, filed Nov. 4, 2010; 61/410,100, filed Nov. 4, 2010;
61/410,104, filed Nov. 4, 2010; and 61/410,108, filed Nov. 4, 2010;
all of which are now pending, the entire disclosures of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of composite
structures having improved heat aging, processes for making them,
and end use articles.
BACKGROUND OF THE INVENTION
[0003] With the aim of replacing metal parts for weight saving and
cost reduction while having comparable or superior mechanical
performance, structures based on composite materials comprising a
polymer matrix containing a fibrous material have been developed.
With this growing interest, fiber reinforced plastic composite
structures have been designed because of their excellent physical
properties resulting from the combination of the fibrous material
and the polymer matrix and are used in various end-use
applications. Manufacturing techniques have been developed for
improving the impregnation of the fibrous material with a polymer
matrix to optimize the properties of the composite structure.
[0004] In highly demanding applications, such as for example
structural parts in automotive and aerospace applications,
composite materials are desired due to a unique combination of
light weight, high strength and temperature resistance.
[0005] High performance composite structures can be obtained using
thermosetting resins or thermoplastic resins as the polymer matrix.
Thermoplastic-based composite structures present several advantages
over thermoset-based composite structures including the ability to
be post-formed or reprocessed by the application of heat and
pressure. Additionally, less time is needed to make the composite
structures because no curing step is required and they have
increased potential for recycling.
[0006] Among thermoplastic resins, polyamides are particularly well
suited for manufacturing composite structures. Thermoplastic
polyamide compositions are desirable for use in a wide range of
applications including parts used in automobiles,
electrical/electronic parts, household appliances and furniture
because of their good mechanical properties, heat resistance,
impact and chemical resistance and because they may be conveniently
and flexibly molded into a variety of articles of varying degrees
of complexity and intricacy.
[0007] With the aim of improving the manufacturing process for
making composite structures and integrated composite structures and
allowing an easier, shorter and uniform mixing or impregnation of
fibrous materials, several ways have been developed to decrease the
melt viscosity of the polymer matrix. By having a low melt
viscosity, polymer compositions flow faster and are thus easier to
process. By reducing the melt viscosity of the polymer matrix, the
time needed to reach the desired degree of mixing may be shortened,
thereby increasing the overall manufacturing speed and thus leading
to increased productivity.
[0008] However, the use of a low melt viscosity polyamide
composition for improving or accelerating the mixing or
impregnation of fibrous materials may lead to composite structures
that are not ideal for highly demanding applications such as the
automotive field due to inferior mechanical and heat aging
properties.
[0009] The addition of heat stabilizers to polymer matrix
compositions can allow for a higher impregnation temperature which
lowers the viscosity of the polymer matrix composition but these
heat stabilizers can also interfere with adhesion of the
overmolding resin.
[0010] U.S. Pat. No. 7,763,674 discloses a fiber reinforced
polyamide composition heat stabilized with a copper
iodide/potassium iodide mixture.
[0011] US 2010/0120959 discloses polyamide compositions comprising
a transition metal ion-modified clay as a heat-stabilizer. The
metal ion for use in modifying the clay is a transition metal
selected from the transition metals in Group IB, VIIB, VIIB and
VIII of the Periodic Table and combinations thereof.
[0012] US 2009/0269532 teaches a multilayer structure comprising at
least one stabilized layer. The stabilized layer is stabilized with
0.5% stabilizer based on copper iodide and potassium iodide. This
stabilizer is constituted of 10% copper iodide, 80% potassium
iodide and 10% zinc stearate.
[0013] US 2008/0146718 discloses a non-fibrous-reinforced
thermoplastic molding composition comprising a metal powder as a
heat stabilizer wherein the metal powder has a weight average
particle size of at most 1 mm and the metal in the metal powder is
selected from the group consisting of elementary metals from Group
VB, VIIB, VIIB and VIIIB of the Periodic Table, and mixtures
thereof.
[0014] U.S. Pat. No. 7,811,671 discloses films which comprise
polyamide compositions which use potassium iodide and cuprous
iodide with a magnesium stearate binder as a heat stabilizer.
[0015] FR 2,158,422 discloses a composite structure made of a low
molecular weight polyamide matrix and reinforcing fibers. Due to
the low molecular weight of the polyamide, the polyamide has low
viscosity. The low viscosity of the polyamide matrix allows an
efficient impregnation of the reinforcing fibers.
[0016] U.S. Pat. No. 7,323,241 discloses a composite structure made
of reinforcing fibers and a branched polyamide resin having a star
structure. The disclosed polyamide having a star structure is said
to exhibit a high fluidity in the molten state thus making possible
a good impregnation of the reinforcing fibers so as to form a
composite structure having good mechanical properties.
[0017] WO 2007/149300 discloses a semi-aromatic polyamide composite
article comprising a component comprising a fiber-reinforced
material comprising a polyamide matrix composition, an overmolded
component comprising a polyamide composition, and an optional tie
layer there between, wherein at least one of the polyamide
compositions is a semi-aromatic polyamide composition
[0018] However, there is still a need for a composite structure
comprising a matrix resin composition that can rapidly and
efficiently impregnate a fibrous material and wherein the composite
structure exhibits good long-term heat stability.
SUMMARY OF THE INVENTION
[0019] There is disclosed and claimed herein a composite structure
comprising: [0020] a polyamide matrix resin composition comprising
[0021] from 0.1 to at or about 3 weight percent of a matrix heat
stabilizer based on the weight of the polyamide matrix resin
composition; [0022] a fibrous material selected from woven or
non-woven structures, felts, knits, braids, textiles, fibrous
battings or mats, and combinations of these; and [0023] a polyamide
surface resin composition comprising [0024] 0.1 to 3 weight percent
of a copper based heat stabilizer based on the weight of the
polyamide surface resin composition [0025] wherein: [0026] the
matrix heat stabilizer is different than the copper based heat
stabilizer; and [0027] the fibrous material is impregnated with the
polyamide matrix resin composition.
[0028] Preferably, in the composite structures of the invention,
the matrix heat stabilizer is selected from dipentaerythritol,
tripentaerythritol, pentaerythritol and mixtures of these. More
preferably, the matrix heat stabilizer is selected from
dipentaerythritol.
[0029] In a second aspect, the invention provides articles prepared
from the composite structures of the invention.
[0030] In yet another aspect, the invention discloses and claims a
process to manufacture the composite structure of the
invention.
DETAILED DESCRIPTION
[0031] The composite structures according to the present invention
offer good thermal stability during their manufacture, good heat
aging properties, retention of mechanical properties after
long-term high temperature exposure. Furthermore, good retention of
bond strength between the composite structure and the overmolding
component is achieved in the overmolded composite structure.
[0032] For making overmolded composite structures and to increase
the performance of polymers, it is often desired to "overmold" one
or more polymer compositions onto the top portion, or all of the
surfaces of a component so as to surround or encapsulate the
component structure. Overmolding involves molding a second polymer
(second component) directly onto one or more surfaces of the
component structure (first component) to form an overmolded
composite structure, wherein the first component and second
component are adhered one to the other at least at one interface to
make an overmolded composite structure. The first component can be
a composite structure and the first component can comprise various
polymeric and fibrous materials. The polymer compositions of this
invention used to impregnate fibrous materials of the first
component or composite structure (i.e. the matrix polymer
composition) are different compositions from the resin(s) which
comprise the surface of the first component or composite structure
(i.e. surface resin composition) but they may comprise the same
polyamide polymer. The first component or composite structure and
the second component of the overmolded composite structure are
desired to have good adhesion to each other. The composite
structure and/or overmolded composite structure are desired to have
good dimensional stability and retain their mechanical properties
under adverse conditions, including thermal cycling.
[0033] Polyamides are excellent examples of polymers that can be
used to make composite structures or overmolded composite
structures due to their excellent mechanical properties.
Unfortunately, polyamide compositions may suffer from an
unacceptable deterioration of their mechanical properties during
their manufacture and upon long-term high temperature exposure
during use and therefore, they may be non-ideal for making
overmolded composite structures used in highly demanding
applications such as the automotive field. Indeed, there is a
current and general desire in the automotive field to have high
temperature resistant, lightweight structures. Such high
temperature resistant structures are required to maintain their
mechanical properties when they are exposed to temperatures higher
than 120.degree. C. or even higher than 200.degree. C., such as
those often reached in underhood areas of automobiles or to
maintain their mechanical properties at an intermediate
temperature, such as for example 90.degree. C., for long periods of
time. When plastic parts are exposed to such combinations of time
and temperature, it is a common phenomenon that the mechanical
properties tend to decrease due to the thermo-oxidation of the
polymer. This phenomenon is called heat aging.
[0034] Unfortunately, the existing technologies fail to combine
easy and efficient processability in terms of the impregnation rate
of the fibrous material by a polymer with good thermal resistance,
good retention of mechanical properties against long-term high
temperature exposure, and excellent adhesion to overmolding
compositions.
[0035] The present invention relates to composite structures and
processes to make them. The composite structure according to the
present invention comprises at least one polyamide matrix resin
impregnated into at least one fibrous material and wherein the
polyamide matrix resin comprises a matrix heat stabilizer.
Preferably, the matrix heat stabilizer is selected from
dipentaerythritol, tripentaerythritol, pentaerythritol and mixtures
of these and even more preferably, the matrix heat stabilizer is
dipentaerythritol. The composite structure additionally comprises a
polyamide surface resin composition comprising a copper based heat
stabilizer. The polyamide used in the polyamide matrix resin
composition and the polyamide surface resin composition can be the
same polyamide or different polyamides or blends of two or more
polyamides.
[0036] The second component used to overmold the first component or
composite structure is a polyamide resin composition optionally
comprising a copper based heat stabilizer and optionally comprising
a reinforcing agent.
Definitions
[0037] As used throughout the specification, the phrases "about"
and "at or about" are intended to mean that the amount or value in
question may be the value designated or some other value about the
same. The phrase is intended to convey that similar values promote
equivalent results or effects according to the invention.
[0038] As used herein, the term "overmolded composite structure"
means a structure comprising a first component or a composite
structure and a second component. The second component is
overmolded onto the first component or composite structure to make
the overmolded composite structure.
[0039] As used herein, the term "first component" or "composite
structure" means a composition comprising at least one polyamide
matrix resin composition, at least one fibrous material, and a
polyamide surface resin composition. The polyamide surface resin
composition is the outermost surface of the entire surface of the
first component, or composite structure, or only a portion of the
surface of the first component or composite structure depending on
what percentage of the first component surface or composite
structure surface is to be overmolded. The polyamide surface resin
composition can be the outermost top, the outermost bottom, or both
the outermost top and outermost bottom surfaces of the first
component or composite structure.
[0040] As used herein, the term "polyamide matrix resin" means the
polyamide resin composition that is used to impregnate the fibrous
material.
[0041] As used herein, the term "matrix heat stabilizer" means a
stabilizer used in the polyamide matrix resin composition. The
matrix heat stabilizer is not a copper based heat stabilizer and
does not contain copper or copper ions.
[0042] As used herein, the term "fibrous material" means a material
that is any suitable mat, fabric, or web form known to those
skilled in the art. The fibers or strands used to form the fibrous
material are interconnected (i.e. at least one fiber or strand is
touching at least one other fiber or strand to form a continuous
material) or touching each other so that a continuous mat, web or
similar structure is formed.
[0043] As used herein, the term "polyamide surface resin" means a
polyamide composition which comprises the outer surface of the
first component or composite structure. The polyamide surface resin
composition can comprise the entire outer surface of the first
component or composite structure or a portion of the outer surface
of the first component or composite structure depending on the end
use.
[0044] As used herein, the term "copper based heat stabilizer"
means a heat stabilizer that comprises a copper halide compound and
a alkali metal halide compound or combinations of different copper
halides or alkali metal halides.
[0045] As used herein, the term "second component" or "overmolding
component" means a composition comprising a polyamide resin
composition and optionally a reinforcing agent. The second
component is used to overmold the first component or composite
structure.
[0046] As used herein, the term "overmolded" means molding and
casting processes used to overmold a substrate, structure, or
article with a polymeric composition. It is the process of molding
over a substrate, structure, article, wherein the overmolding
polymeric composition is bonded to and becomes an integral part of
the substrate, structure, or article (i.e. the exterior part) upon
cooling.
[0047] As used herein, the term "impregnated" means the polyamide
matrix resin composition flows into the cavities and void spaces of
the fibrous material As used herein, the term "bond strength" means
the strength of the bond between the first component or composite
structure and second component or overmolding component of the
overmolded composite structure.
[0048] As used herein, the term "heat aging" means exposing the
component structure, the composite structure and/or the overmolded
composite structure to elevated temperatures for a given period of
time.
[0049] As used herein, the term "high temperature long-term
exposure" refers to a combination of exposure factors, i.e. time
and temperature. Polymers which demonstrate heat aging performance
under lab conditions or under conditions of the lifetime of the
polymers such as those reached in underhood areas of automobiles
(e.g. at a temperature at or in excess of 120.degree. C.,
preferably at or in excess of 160.degree. C., more preferably at or
in excess of 180.degree. C. and still more preferably at or in
excess of 200.degree. C. and the aging or exposure being at or in
excess of 500 hours and preferably at or in excess of 1000 hours)
can be shown to exhibit similar performance at lower temperatures
for a much longer period of aging or exposure. The temperature
dependence of the rate constants of polymer degradation is known
from the literature such as for example in Journal of Materials
Science, 1999, 34, 843-849, and is described by Arrhenius law; as
an example aging at 180.degree. C. for 500 hours is more-or-less
equivalent to aging at 80.degree. C. for 12 years.
First Component or Composite Structure
[0050] The first component or composite structure comprises one or
more fibrous materials impregnated with one or more polyamide
matrix resin compositions and comprises one or more surface resin
compositions. The first component or composite structure can have a
total thickness of from about 50 to 20000 microns, preferably from
about 50 to 5000 microns, more preferably from about 500 to 3000
microns, and most preferably from about 800 to 2000 microns. The
first component or composite structure can have multiple fibrous
materials.
[0051] The polyamide surface resin composition may be both the top
and bottom surface of the first component or composite structure
(essentially completely encapsulating the first component or
composite structure). Such a composition may be useful when it is
desired to encapsulate or overmold the entire surface of the first
component or composite structure with the second component. The
polyamide surface resin composition may also be only the top or
bottom surface, or a portion of the top or bottom surface of the
first component or composite structure depending on what percentage
of the first component surface or composite structure surface is to
be overmolded.
[0052] If the first component or composite structure is to be
overmolded only on one surface or part of surface, then the
polyamide surface resin composition may be present only on the
surface or portion of the surface that is to be overmolded by the
second component.
Fibrous Material
[0053] The fibrous material impregnated with the polyamide matrix
resin composition may be in any suitable mat, fabric, or web form
known to those skilled in the art. Suitable examples of such
fibrous materials include woven or nonwoven fabrics or mats,
unidirectional strands of fiber, and the like and different layers
of fibrous material in the first component or composite structure
may be formed from different kinds of fibers, mats, or fabrics. The
first component or composite structure may contain multiple layers
of fibrous materials which are impregnated with one or more
polyamide matrix resin compositions. Additionally, any given
fibrous layer may be formed from two or more kinds of fibers (e.g.,
carbon and glass fibers). The fibers may be unidirectional, bi
directional, or multidirectional. Preimpregnated unidirectional
fibers and fiber bundles may be formed into woven or nonwoven mats
or other structures suitable for forming the fibrous material. The
fibrous material may be in the form of a unidirectional
preimpregnated material or a multiaxial laminate of a
preimpregnated material.
[0054] The fibrous material is preferably selected from woven or
non-woven structures (e.g., mats, felts, fabrics and webs)
textiles, fibrous battings, a mixture of two or more materials, and
combinations thereof. Non-woven structures can be selected from
random fiber orientation or aligned fibrous structures. Examples of
random fiber orientation include without limitation material which
can be in the form of a mat, a needled mat or a felt. Examples of
aligned fibrous structures include without limitation
unidirectional fiber strands, bidirectional strands,
multidirectional strands, multi-axial textiles. Textiles can be
selected from woven forms, knits, braids and combinations
thereof.
[0055] As used herein, the term "a fibrous material being
impregnated with a polyamide matrix resin composition" means that
the polyamide matrix resin composition encapsulates and embeds the
fibrous material so as to form an interpenetrating network of
fibrous material substantially surrounded by the matrix resin
composition. For purposes herein, the term "fiber" is defined as a
macroscopically homogeneous body having a high ratio of length to
width across its cross-sectional area perpendicular to its length.
The fiber cross section can be any shape, but is typically round or
oval shaped. Depending on the end-use application of the composite
structure and/or overmolded composite structure and the required
mechanical properties, more than one fibrous material can be used,
either by using several of the same fibrous materials or a
combination of different fibrous materials. An example of a
combination of different fibrous materials is a combination
comprising a non-woven structure such as for example a planar
random mat which is placed as a central layer and one or more woven
continuous fibrous materials that are placed as outside layers or
layers above or below or both above and below the central layer.
Such a combination allows an improvement of the processing and
thereof of the homogeneity of the first component or composite
structure thus leading to improved mechanical properties of the
composite structure and/or overmolded composite structure. The
fibrous material may be made of any suitable material or a mixture
of materials provided that the material or the mixture of materials
withstand the processing conditions used during the impregnation by
the polyamide matrix resin composition and the polyamide surface
resin composition and during overmolding of the first component or
composite structure by the second component.
[0056] Preferably, the fibrous material comprises glass fibers,
carbon fibers, aramid fibers, graphite fibers, metal fibers,
ceramic fibers, natural fibers or mixtures thereof; more
preferably, the fibrous material comprises glass fibers, carbon
fibers, aramid fibers, natural fibers or mixtures thereof; and
still more preferably, the fibrous material comprises glass fibers,
carbon fibers and aramid fibers or mixture mixtures thereof. By
natural fiber, it is meant any material of plant origin or of
animal origin. When used, the natural fibers are preferably derived
from vegetable sources such as for example from seed hair (e.g.
cotton), stem plants (e.g. hemp, flax, bamboo; both bast and core
fibers), leaf plants (e.g. sisal and abaca), agricultural fibers
(e.g., cereal straw, corn cobs, rice hulls and coconut hair) or
lignocellulosic fiber (e.g. wood, wood fibers, wood flour, paper
and wood-related materials). As mentioned above, more than one
fibrous materials can be used. A combination of fibrous materials
made of different fibers can be used such as for example a first
component or composite structure comprising one or more central
layers made of glass fibers or natural fibers and one or more outer
layers (relative to central layer) made of carbon fibers or glass
fibers. Preferably, the fibrous material is selected from woven
structures, non-woven structures or combinations thereof, wherein
said structures are made of glass fibers and wherein the glass
fibers are E-glass filaments with a diameter between 8 and 30 .mu.m
and preferably with a diameter between 10 to 24 .mu.m. The fibrous
material used in the first component or composite structure of the
invention cannot be chopped fibers or particles. To be clear, the
fibrous material in the first component or composite structure
cannot be fibers or particles which are not interconnected to form
a continuous mat, web or similar layered structure. In other words,
they cannot be independent or single fibers or particles surrounded
by the polyamide matrix resin composition.
[0057] The fibrous material may further comprise a thermoplastic
material, for example the fibrous material may be in the form of
commingled or co-woven yarns or a fibrous material impregnated with
a powder made of a thermoplastic material that is suited to
subsequent processing into woven or non-woven forms, or a mixture
for use as a uni-directional material.
[0058] Preferably, the ratio between the fibrous material and the
polymer materials in the first component or composite structure
(i.e. the fibrous material in combination with the matrix resin
composition and the surface resin composition), is at least 30
percent fibrous material and more preferably between 40 and 60
percent fibrous material, the percentage being a volume-percentage
based on the total volume of the first component structure or
composite structure.
Copper Based Heat Stabilizer
[0059] The heat stabilizer used in the polyamide surface resin
composition (first component or composite structure) and optionally
in the second component is a copper halide based inorganic heat
stabilizer. The heat stabilizer comprises at least one copper
halide or copper acetate and at least one alkali metal halide.
Nonlimiting examples of copper halide include copper iodide and
copper bromide. The alkali metal halide is selected from the group
consisting of the iodides and bromides of lithium, sodium, and
potassium with potassium iodide or bromide being preferred.
Preferably, the copper based heat stabilizer is a mixture of 10 to
50 weight percent copper halide, 50 to 90 weight percent potassium
iodide, and from zero to 15 weight percent metal stearate. Even
more preferably, the copper based heat stabilizer is a mixture of
10 to 30 weight percent copper halide, 70 to 90 weight percent
potassium iodide, and from zero to 15 weight percent metal stearate
and most preferably the copper based heat stabilizer is a mixture
of 10 to 20 weight percent copper halide, 75 to 90 weight percent
potassium iodide, and from zero to 12 weight percent metal
stearate. An example of a copper based heat stabilizer of the
invention is Polyadd P201 from Ciba Specialty Chemicals comprising
a blend of 7:1:1 weight ratio (approximately 78:11:11 percent ratio
by weight) of potassium iodide, cuprous iodide, and aluminum
stearate respectively. A preferred heat stabilizer is a mixture of
copper iodide and potassium iodide (Cul/KI). The heat stabilizer is
present in an amount from at or about 0.1 to at or about 3 weight
percent, preferably from at or about 0.1 to at or about 1.5 weight
percent, or more preferably from at or about 0.1 to at or about 1.0
weight percent, the weight percentage being based on the total
weight of the polyamide surface resin composition in the first
component or composite structure or based on the total weight of
the polyamide resin composition of the second component, as the
case may be. The amount of copper halide based heat stabilizer in
the polyamide surface resin composition or the polyamide resin
composition of the second component will depend on the anticipated
use. If extremely high temperature environments are envisioned,
then a higher concentration of copper halide heat stabilizer is
needed.
Matrix Heat Stabilizer
[0060] The matrix heat stabilizer of the polyamide matrix resin
composition is different than the copper based heat stabilizer of
the polyamide surface resin composition. The one or more matrix
heat stabilizers in the polyamide matrix resin composition are
present in an amount from 0 to at or about 3 weight percent,
preferably from at or about 0.1 to at or about 3 weight percent,
more preferably from at or about 0.1 to at or about 1 weight
percent, or more preferably from at or about 0.1 to at or about 0.7
weight percent, the weight percentage being based on the total
weight of the polyamide matrix resin composition in the first
component or composite structure.
[0061] The matrix heat stabilizer used in the polyamide matrix
resin composition can be any heat stabilizer as long as it is not a
copper halide based heat stabilizer. Heat stabilizers useful in the
polyamide matrix resin composition include polyhydric alcohols
having more than two hydroxyl groups. The one or more polyhydric
alcohols may be independently selected from aliphatic hydroxylic
compounds containing more than two hydroxyl groups,
aliphatic-cycloaliphatic compounds containing more than two
hydroxyl groups, cycloaliphatic compounds containing more than two
hydroxyl groups and saccharides containing more than two hydroxyl
groups.
[0062] An aliphatic chain in the polyhydric alcohol can include not
only carbon atoms but also one or more hetero atoms which may be
selected, for example, from nitrogen, oxygen and sulphur atoms. A
cycloaliphatic ring present in the polyhydric alcohol can be
monocyclic or part of a bicyclic or polycyclic ring system and may
be carbocyclic or heterocyclic. A heterocyclic ring present in the
polyhydric alcohol can be monocyclic or part of a bicyclic or
polycyclic ring system and may include one or more hetero atoms
which may be selected, for example, from nitrogen, oxygen and
sulphur atoms. The one or more polyhydric alcohols may contain one
or more substituents, such as ether, carboxylic acid, carboxylic
acid amide or carboxylic acid ester groups.
[0063] Examples of polyhydric alcohols containing more than two
hydroxyl groups include, without limitation, triols, such as
glycerol, trimethylolpropane,
2,3-di-(2'-hydroxyethyl)cyclohexan-1-ol, hexane-1,2,6-triol,
1,1,1-tris-(hydroxymethyl)ethane,
3-(2'-hydroxyethoxy)-propane-1,2-diol,
3-(2'-hydroxypropoxy)-propane-1,2-diol,
2-(2'-hydroxyethoxy)-hexane-1,2-diol,
6-(2'-hydroxypropoxy)-hexane-1,2-diol,
1,1,1-tris-[(2'-hydroxyethoxy)-methyl]-ethane,
1,1,1-tris-[(2'-hydroxypropoxy)-methyl]-propane,
1,1,1-tris-(4'-hydroxyphenyl)-ethane,
1,1,1-tris-(hydroxyphenyl)-propane,
1,1,3-tris-(dihydroxy-3-methylphenyl)-propane,
1,1,4-tris-(dihydroxyphenyl)-butane,
1,1,5-tris-(hydroxyphenyl)-3-methylpentane, di-trimethylopropane,
trimethylolpropane ethoxylates, or trimethylolpropane propoxylates;
polyols such as pentaerythritol, dipentaerythritol, and
tripentaerythritol; and saccharides containing more than two
hydroxyl groups, such as cyclodextrin, D-mannose, glucose,
galactose, sucrose, fructose, xylose, arabinose, D-mannitol,
D-sorbitol, D-or L-arabitol, xylitol, iditol, talitol, allitol,
altritol, guilitol, erythritol, threitol, and D-gulonic-y-lactone
and the like.
[0064] Preferred polyhydric alcohols include those having a pair of
hydroxyl groups which are attached to respective carbon atoms which
are separated one from another by at least one atom. Especially
preferred polyhydric alcohols are those in which a pair of hydroxyl
groups is attached to respective carbon atoms which are separated
one from another by a single carbon atom. Preferably, the one or
more polyhydric alcohols comprised in the polyamide matrix resin
composition described herein are independently selected from
pentaerythritol, dipentaerythritol, tripentaerythritol,
di-trimethylopropane, D-mannitol, D-sorbitol, xylitol and mixtures
thereof. More preferably, the one or more polyhydric alcohols
comprised in the polyamide composition described herein are
independently selected from dipentaerythritol, tripentaerythritol,
pentaerythritol and mixtures thereof. Still more preferably, the
one or more polyhydric alcohols comprised in the polyamide
composition described herein are dipentaerythritol and/or
pentaerythritol.
[0065] The one or more polyhydric alcohols are present in the
polyamide matrix resin composition described herein from 0.25
weight percent to 15 weight percent, more preferably from 0.5
weight percent to 10 weight percent and still more preferably from
0.5 weight percent to 5 weight percent, the weight percentages
being based on the total weight of the polyamide matrix resin
composition in the first component or composite structure.
[0066] Preferably, the one or more polyhydric alcohols comprised in
the polyamide composition described herein are dipentaerythritol
and/or pentaerythritol and are present in the polyamide matrix
resin composition described herein from at or about 0.1 to at or
about 3 weight percent, more preferably from at or about 0.1 to at
or about 1 weight percent, or more preferably from at or about 0.1
to at or about 0.7 weight percent, the weight percentage being
based on the total weight of the polyamide matrix resin composition
in the first component or composite structure.
Polyamide Resins
[0067] Polyamide resins used in the manufacture of the composite
structure of the invention and/or in the manufacture of the
overmolded composite structure are condensation products of one or
more dicarboxylic acids and one or more diamines, and/or one or
more aminocarboxylic acids, and/or ring-opening polymerization
products of one or more cyclic lactams. The polyamide resins are
selected from fully aliphatic polyamide resins, semi-aromatic
polyamide resins and mixtures thereof. The term "semi-aromatic"
describes polyamide resins that comprise at least some aromatic
carboxylic acid monomer(s) and aliphatic diamine monomer(s), in
comparison with "fully aliphatic" which describes polyamide resins
comprising aliphatic carboxylic acid monomer(s) and aliphatic
diamine monomer(s).
[0068] Fully aliphatic polyamide resins are formed from aliphatic
and alicyclic monomers such as diamines, dicarboxylic acids,
lactams, aminocarboxylic acids, and their reactive equivalents. A
suitable aminocarboxylic acid includes 11-aminododecanoic acid. In
the context of this invention, the term "fully aliphatic polyamide
resin" refers to copolymers derived from two or more such monomers
and blends of two or more fully aliphatic polyamide resins. Linear,
branched, and cyclic monomers may be used.
[0069] Carboxylic acid monomers useful in the preparation of fully
aliphatic polyamide resins include, but are not limited to,
aliphatic carboxylic acids, such as for example adipic acid (C6),
pimelic acid (C7), suberic acid (C8), azelaic acid (C9), sebacic
acid (C10), dodecanedioic acid (C12) and tetradecanedioic acid
(C14). Useful diamines include those having four or more carbon
atoms, including, but not limited to tetramethylene diamine,
hexamethylene diamine, octamethylene diamine, decamethylene
diamine, 2-methylpentamethylene diamine, 2-ethyltetramethylene
diamine, 2-methyloctamethylene diamine; trimethylhexamethylene
diamine and/or mixtures thereof. Suitable examples of fully
aliphatic polyamide resins include PA6; PA6,6; PA4,6; PA6,10;
PA6,12; PA6,14; P 6,13; PA 6,15; PA6,16; PA11; PA 12; PA10; PA
9,12; PA9,13; PA9,14; PA9,15; PA6,16; PA9,36; PA10,10; PA10,12;
PA10,13; PA10,14; PA12,10; PA12,12; PA12,13; PA12,14 and copolymers
and blends of the same. Preferred examples of fully aliphatic
polyamide resins comprised in the polyamide compositions described
herein include PA6; PA11; PA12; PA4,6; PA6,6; PA,10; PA6,12;
PA10,10 and copolymers and blends of the same.
[0070] Semi-aromatic polyamide resins are homopolymers, copolymers,
terpolymers, or higher polymers wherein at least a portion of the
acid monomers are selected from one or more aromatic carboxylic
acids. The one or more aromatic carboxylic acids can be
terephthalic acid or mixtures of terephthalic acid and one or more
other carboxylic acids, like isophthalic acid, substituted phthalic
acid such as for example 2-methylterephthalic acid and
unsubstituted or substituted isomers of naphthalenedicarboxylic
acid, wherein the carboxylic acid component preferably contains at
least 55 mole percent of terephthalic acid (the mole percent being
based on the carboxylic acid mixture). Preferably, the one or more
aromatic carboxylic acids are selected from terephthalic acid,
isophthalic acid and mixtures thereof and more preferably, the one
or more carboxylic acids are mixtures of terephthalic acid and
isophthalic acid, wherein the mixture preferably contains at least
55 mole percent of terephthalic acid. Furthermore, the one or more
carboxylic acids can be mixed with one or more aliphatic carboxylic
acids, like adipic acid; pimelic acid; suberic acid; azelaic acid;
sebacic acid and dodecanedioic acid, adipic acid being preferred.
More preferably the mixture of terephthalic acid and adipic acid
comprised in the one or more carboxylic acids mixtures of the
semi-aromatic polyamide resin contains at least 25 mole percent of
terephthalic acid. Semi-aromatic polyamide resins comprise one or
more diamines that can be chosen among diamines having four or more
carbon atoms, including, but not limited to tetramethylene diamine,
hexamethylene diamine, octamethylene diamine, nonamethylene
diamine, decamethylene diamine, 2-methylpentamethylene diamine,
2-ethyltetramethylene diamine, 2-methyloctamethylene diamine;
trimethylhexamethylene diamine, bis(p-aminocyclohexyl)methane;
m-xylylene diamine; p-xylylene diamine and/or mixtures thereof.
Suitable examples of semi-aromatic polyamide resins include
poly(hexamethylene terephthalamide) (polyamide 6,T),
poly(nonamethylene terephthalamide) (polyamide 9,T),
poly(decamethylene terephthalamide) (polyamide 10,T),
poly(dodecamethylene terephthalamide) (polyamide 12,T),
hexamethylene adipamide/hexamethylene terephthalamide copolyamide
(polyamide 6,T/6,6), hexamethylene terephthalamide/hexamethylene
isophthalamide (6,T/6,I), poly(m-xylylene adipamide) (polyamide
MXD,6), hexamethylene adipamide/hexamethylene terephthalamide
copolyamide (polyamide 6,T/6,6), hexamethylene
terephthalamide/2-methylpentamethylene terephthalamide copolyamide
(polyamide 6,T/D,T), hexamethylene adipamide/hexamethylene
terephthalamide/hexamethylene isophthalamide copolyamide (polyamide
6,6/6,T/6,I); poly(caprolactam-hexamethylene terephthalamide)
(polyamide 6/6,T) and copolymers and blends of the same. Preferred
examples of semi-aromatic polyamide resins comprised in the
polyamide composition described herein include PA6,T; PA6,T/6,6,
PA6,T/6,I; PAMXD,6; PA6,T/D,T and copolymers and blends of the
same.
[0071] Any combination of aliphatic or semi-aromatic polyamides can
be used as the polyamide for the polyamide matrix resin
composition, polyamide surface resin composition, and the polyamide
resin of the second component. It is within the normal skill of one
in the art to select appropriate combinations of polyamides
depending on the end use.
Second Component or Overmolding Component
[0072] The second component of the overmolded composite structure
used to overmold the first component or composite structure is a
polyamide resin composition optionally comprising a copper based
heat stabilizer as described above and optionally a reinforcing
agent. The one or more polyamides may be the same or different from
the one or more polyamides of the first component or composite
structure matrix resin and surface resin composition.
Reinforcing Agent
[0073] The polyamide resin composition of the second component may
further comprise one or more reinforcing agents such as glass
fibers, glass flakes, carbon fibers, mica, wollastonite, calcium
carbonate, talc, calcined clay, kaolin, magnesium sulfate,
magnesium silicate, barium sulfate, titanium dioxide, sodium
aluminum carbonate, barium ferrite, and potassium titanate. The
reinforcing agent in the second component cannot be a mat or woven
fabric such as those used in the first component or composite
structure. Preferably, the reinforcing agent comprises independent
fibers or particles uniformly blended into the polyamide. Any
reinforcing agent used in the second component must allow the
polyamide resin composition to be injection or flow molded. When
present, the one or more reinforcing agents are present in an
amount from at or about 1 to at or about 60 weight percent,
preferably from at or about 1 to at or about 40 weight percent, or
more preferably from at or about 1 to at or about 35 weight
percent, the weight percentages being based on the total weight of
the polyamide resin composition of the second component.
Overmolded Composite Structure
[0074] Addition of matrix and copper based heat stabilizers to the
components of the invention improves thermal stability of the first
component or composite structure and optionally of the second
component during processing as well as upon use and time of the
composite structure or overmolded composite structure. In addition
to the improved heat stability, the presence of heat stabilizers
may allow an increase of the temperature that is used during the
impregnation of the fibrous material, thus reducing the melt
viscosity of the matrix resin described herein. As a consequence of
a reduced melt viscosity of the matrix resin, impregnation rates of
the fibrous material may be increased.
[0075] The use of different heat stabilizers in the polyamide
matrix resin composition and the polyamide surface resin
composition of the first component or composite structure is an
important aspect of the invention. The use of a copper based heat
stabilizer in the polyamide surface resin composition and
optionally in the second component improves bond strength of the
second component to the first component or composite structure
while simultaneously providing adequate heat aging properties of
the overmolded composite structure.
[0076] In a preferred embodiment, the matrix heat stabilizer is
selected from dipentaerythritol, tripentaerythritol,
pentaerythritol and mixtures of these and the surface heat
stabilizer in the surface resin composition is a copper based heat
stabilizer.
[0077] The overmolded composite structure comprises a second
component overmolded onto the first component or composite
structure. The second component is adhered to the first component
or composite structure described above over at least a portion of
the top or bottom surface of the first component or composite
structure, the entire top or bottom surface of the first component
or composite structure, or both, or completely encapsulates the
first component or composite structure. Regardless of what portion
of the surface of the first component or composite structure is
overmolded, the surface of the first component or composite
structure that is overmolded must comprise the polyamide surface
resin composition to assure good bond strength of the first and
second components. The second component comprises one or more
polyamide resin compositions selected from aliphatic polyamide
resins, semi-aromatic polyamide resins, or combinations thereof
such as those described above.
Additives
[0078] The polyamide resin of any component of the composite
structure or overmolded composite structure may further comprise
one or more common additives, including, without limitation,
ultraviolet light stabilizers, flame retardant agents, flow
enhancing additives, lubricants, antistatic agents, coloring agents
(including dyes, pigments, carbon black, and the like), nucleating
agents, crystallization promoting agents and other processing aids
or mixtures thereof known in the polymer compounding art.
[0079] Fillers, modifiers and other ingredients described above may
be present in amounts and in forms well known in the art, including
in the form of so-called nano-materials where at least one of the
dimensions of the particles is in the range of 1 to 1000 nm.
[0080] Preferably, any additives, including heat stabilizers but
excluding fibrous materials used in the first component or
composite structure of the invention, added to the polyamide resins
used in any component of the composite structure and/or overmolded
composite structure are well-dispersed within the polyamide resin.
Any melt-mixing method may be used to combine the polyamide resins
and additives of the present invention. For example, the polyamide
resins and additives may be added to a melt mixer, such as, for
example, a single or twin-screw extruder; a blender; a single or
twin-screw kneader; or a Banbury mixer, either all at once through
a single step addition, or in a stepwise fashion, and then
melt-mixed. When adding the polyamide resins and additional
additives in a stepwise fashion, part of the polyamide resin and/or
additives are first added and melt-mixed with the remaining
polyamide resin(s) and additives being subsequently added and
further melt-mixed until a well-mixed or homogeneous composition is
obtained.
[0081] The overmolded composite structure according to the present
invention may be manufactured by a process comprising a step of
overmolding the first component or composite structure with the
second component. By "overmolding", it is meant that the second
component is molded or extruded onto at least one portion of the
surface of the first component or composite structure.
[0082] In one example of an overmolding process, the second
component is injected into a mold already containing the first
component or composite structure, the latter having been
manufactured beforehand as described hereafter, so that the first
and second components are adhered to each other over at least a
portion of the surface of the first component or composite
structure. The first component or composite structure is positioned
in a mold having a cavity defining the outer surface of the final
overmolded composite structure. The second component may be
overmolded on one side or on both sides of the first component or
composite structure and it may fully or partially encapsulate the
first component or composite structure. After having positioned the
first component or composite structure in the mold, the second
component is then introduced in molten form. The two components are
preferably adhered together by injection or compression molding as
an overmolding step, and more preferably by injection molding.
[0083] The first component or composite structure can be made by a
process that comprises a step of impregnating the fibrous material
with the polyamide matrix resin composition, wherein at least a
portion of the surface of the first component or composite
structure comprises the polyamide surface resin composition.
Preferably, the fibrous material is impregnated with the polyamide
matrix resin composition by thermopressing. During thermopressing,
the fibrous material(s), the polyamide matrix resin composition and
the polyamide surface resin composition undergo heat and pressure
in order to allow the polymers to melt and penetrate through the
fibrous material and, therefore, to impregnate said fibrous
material.
[0084] Typically, thermopressing is made at a pressure between 2
and 100 bars and more preferably between 10 and 40 bars and a
temperature which is above the melting point of the polyamide
matrix resin composition and the polyamide surface resin
composition, preferably at least about 20.degree. C. above the
melting point to enable a proper impregnation. Heating may be done
by a variety of means, including contact heating, radiant gas
heating, infra red heating, convection or forced convection,
induction heating, microwave heating or combinations thereof. Even
though the polyamide compositions are in the melt state during
thermopressing, the polyamide surface resin composition does not
migrate from the surface to any significant degree. After
thermopressing, the first component or composite structure is no
longer considered a laminate structure having separate layers but a
unified component structure.
[0085] Due to the improved heat stability obtained by adding a
matrix heat stabilizer to the polyamide matrix resin composition,
the temperature that is used during the impregnation of the fibrous
material can be increased relative to a polyamide resin composition
without a matrix heat stabilizer. The reduced melt viscosity of the
polyamide matrix resin composition obtained by this increase of
temperature allows a more rapid impregnation rate of the fibrous
material which translates into a faster overall manufacturing cycle
for the composite structure and/or overmolded composite structure.
Addition of the copper halide based heat stabilizer to the
polyamide surface resin composition provides heat stability to the
polyamide surface resin composition during the impregnation and
additionally provides improved bond strength of the second
component to the first component or composite structure of the
overmolded composite structure.
[0086] Pressure used during the impregnation process can be applied
by a static process or by a continuous process (also known as a
dynamic process), a continuous process being preferred for reasons
of speed. Examples of impregnation processes include without
limitation vacuum molding, in-mold coating, cross-die extrusion,
pultrusion, wire coating type processes, lamination, stamping,
diaphragm forming or press-molding, lamination being preferred.
[0087] One example of a process used to impregnate the fibrous
material is a lamination process. The first step of the lamination
process involves heat and pressure being applied to the fibrous
material, the polyamide matrix resin composition and the polyamide
surface resin composition through opposing pressured rollers or
belts in a heating zone, preferably followed by the continued
application of pressure in a cooling zone to finalize consolidation
and cool the impregnated fibrous material by pressurized means.
Examples of lamination techniques include without limitation
calendering, flatbed lamination and double-belt press lamination.
When lamination is used as the impregnating process, preferably a
double-belt press is used for lamination. The lamination process
may comprise various layer combinations of the polyamide matrix
resin composition and the fibrous material. The polyamide surface
resin composition is always used as the top layer or both the top
and bottom layer during the lamination process. For example, the
multi-layer laminate may comprise two polyamide matrix resin
composition layers, one layer of woven continuous glass fiber
textile as the fibrous layer, two polyamide matrix resin
composition layers, one layer of woven continuous glass fiber
textile, two polyamide matrix resin composition layers, one layer
of woven continuous glass fiber textile and two polyamide surface
layers to make an 11 layer laminate. After impregnation of the
fibrous materials using the lamination process, the end product is
the first component or composite structure of the invention which
can then be overmolded. A first component or composite structure
prepared by this process is no longer a multi-layer laminate but a
unified structure (a polymer continuum) with no discernable
individual layers.
[0088] The polyamide matrix resin composition and the polyamide
surface resin composition can also be applied to the fibrous
material by conventional means such as for example powder coating,
film lamination, extrusion coating or a combination of two or more
thereof, provided that the polyamide surface resin composition is
applied on at least a portion of the surface of the first component
or composite structure so as to be accessible when the polyamide
overmolding resin composition is applied onto at least a portion of
the surface of the first component or composite structure.
[0089] During a powder coating process, a polymer powder which has
been obtained by conventional grinding methods is applied to the
fibrous material. The powder may be applied onto the fibrous
material by scattering, sprinkling, spraying, thermal or flame
spraying, or fluidized bed coating methods. Multiple powder coating
layers can be applied to the fibrous material. Optionally, the
powder coating process may further comprise a step which consists
in a post sintering step of the powder on the fibrous material. The
polyamide matrix resin composition and the polyamide surface resin
composition are applied to the fibrous material such that at least
a portion of the surface of the first component or composite
structure comprises the polyamide surface resin composition.
Subsequently, thermopressing is performed on the powder coated
fibrous material, with an optional preheating of the powder coated
fibrous material outside of the pressurized zone.
[0090] During film lamination, one or more films comprising the
polyamide matrix resin composition and one or more films made of
the polyamide surface resin composition which have been obtained by
conventional extrusion methods known in the art such as for example
blow film extrusion, cast film extrusion and cast sheet extrusion
are applied to one or more layers of the fibrous material, e.g. by
layering. The polyamide surface resin composition is again the top
or bottom or both top and bottom layers of the film laminate before
thermopressing. Subsequently, thermopressing is performed on the
film laminate comprising the one or more films made of the
polyamide matrix resin composition, the polyamide surface resin
composition, and the one or more fibrous materials. During
thermopressing, the films melt and penetrate around the fibrous
material as a polymer continuum surrounding the fibrous material
with the polyamide matrix resin. The polyamide surface resin
composition remains on the surface of the first component or
composite structure.
[0091] During extrusion coating, pellets and/or granulates made of
the matrix resin composition and pellets and/or granulates made of
the surface resin composition are melted and extruded through one
or more flat dies so as to form one or more melt curtains which are
then applied onto the fibrous material by laying down the one or
more melt curtains in a manner similar to the film lamination
procedure. Subsequently, thermopressing is performed on the layered
structure to provide the first component or composite structure of
the invention.
[0092] With the aim of improving bond strength between the first
component or composite structure and the second component, the
first component or composite structure is typically heated at a
temperature close to but below the melt temperature of the
polyamide matrix resin composition prior to the overmolding step
and then the heated first component or composite structure is
rapidly transferred into the heated mold that will be used for the
overmolding step. Such a preheating step may be done by a variety
of means, including contact heating, radiant gas heating, infra red
heating, convection or forced convection air heating, induction
heating, microwave heating or combinations thereof.
[0093] Depending on the end-use application, the first component or
composite structure may be shaped into a desired geometry or
configuration, or used in sheet form prior to the overmolding step.
The first component or composite structure may be flexible, in
which case it can be rolled and then unrolled for overmolding.
[0094] One process for shaping the first component or composite
structure comprises a step of shaping the first component or
composite structure after the impregnating step. Shaping the first
component or composite structure may be done by compression
molding, stamping or any technique using heat and/or pressure,
compression molding and stamping being preferred. Preferably,
pressure is applied by using a hydraulic molding press. During
compression molding or stamping, the composite structure is
preheated to a temperature above the melt temperature of the
polyamide surface resin composition and preferably above the melt
temperature of the polyamide matrix resin composition by heated
means and is transferred to a forming or shaping means such as a
molding press containing a mold having a cavity of the shape of the
final desired geometry whereby it is shaped into a desired
configuration and is thereafter removed from the press or the mold
after cooling to a temperature below the melt temperature of the
polyamide surface resin composition and preferably below the melt
temperature of the polyamide matrix resin composition.
[0095] One problem during the manufacture of composite structures
and/or overmolded composite structures is related to the
thermo-oxidation and degradation of the first component or
composite structure and especially the thermal degradation of the
surface of the first component or composite structure during the
preheating step(s) described above and during the shaping step. The
present invention not only provides a first component or composite
structure having good heat stability but also provides a first
component or composite structure having excellent bond strength to
the second component. This leads to composite structures and/or
overmolded composite structures that resist degradation of
mechanical performance during exposure to high temperature
operational manufacturing environments and provides excellent long
term flexural strength (bond strength).
[0096] With the aim of improving adhesion between the first
component or composite structure and second component of the
overmolded composite structure, the surface of the first component
or composite structure may be a textured surface so as to increase
the relative surface available for overmolding. Such textured
surfaces may be obtained during the shaping step by using a press
or a mold having for example porosities or indentations on its
surface.
[0097] Alternatively, a one step process comprising the steps of
shaping and overmolding the first component or composite structure
in a single molding station may be used. This one step process
avoids the step of compression molding or stamping the first
component or composite structure in a mold or press and avoids the
optional preheating step and the transfer of the preheated first
component or composite structure to the molding station or cavity.
During this one step process, the first component or composite
structure is heated outside, adjacent to or within the molding
station at a temperature at which the first component or composite
structure is conformable or shapable during the overmolding step,
preferably the first component or composite structure is heated to
a temperature above its melt temperature. The shape of the first
component or composite structure is conferred by the mold followed
by overmolding.
[0098] The composite structures and/or overmolded composite
structures according to the present invention may be used in a wide
variety of applications such as for example components for
automobiles, trucks, commercial airplanes, aerospace, rail,
household appliances, computer hardware, portable hand held
electronic devices, recreation and sports equipment, structural
component for machines, buildings, photovoltaic equipment or
mechanical devices.
[0099] Examples of automotive applications include, without
limitation, seating components and seating frames, engine cover
brackets, engine cradles, suspension arms and cradles, spare tire
wells, chassis reinforcement, floor pans, front-end modules,
steering column frames, instrument panels, door systems, body
panels (such as horizontal body panels and door panels), tailgates,
hardtop frame structures, convertible top frame structures, roofing
structures, engine covers, housings for transmission and power
delivery components, oil pans, airbag housing canisters, automotive
interior impact structures, engine support brackets, cross car
beams, bumper beams, pedestrian safety beams, firewalls, rear
parcel shelves, cross vehicle bulkheads, pressure vessels such as
refrigerant bottles, fire extinguishers, and truck compressed air
brake system vessels, hybrid internal combustion/electric or
electric vehicle battery trays, automotive suspension wishbone and
control arms, suspension stabilizer links, leaf springs, vehicle
wheels, recreational vehicle and motorcycle swing arms, fenders,
roofing frames and tank flaps.
[0100] Examples of household appliances include without limitation
washers, dryers, refrigerators, air conditioning and heating.
Examples of recreation and sports include without limitation
inline-skate components, baseball bats, hockey sticks, ski and
snowboard bindings, rucksack backs and frames, and bicycle frames.
Examples of structural components for machines include
electrical/electronic parts such as for example housings for hand
held electronic devices, and computers.
[0101] Preferably, the composite structures and/or overmolded
composite structures of the invention are used as under the hood
automotive components where high temperature environments
exist.
EXAMPLES
[0102] The following materials were used for preparing examples
(abbreviated as "E" in the table) of composites structures
according to the present invention and comparative examples
(abbreviated as "C" in the table) of composite structures. [0103]
Polyamide 1 (PA1): polyamide comprising adipic acid and
1,6-hexamethylenediamine with a weight average molecular weight of
around 32000 Daltons and is commercially available from E. I. du
Pont de Nemours and Company as PA66. PA1 has a melting point of
about 260.degree. C. to about 265.degree. C. and a glass transition
of about 40.degree. C. to about 70.degree. C., measured by DSC
Instrument first heating scan at 10.degree. C./min. [0104]
Polyhydric alcohol based heat stabilizer (DPE): dipentaerythritol
commercially available from Perstorp Speciality Chemicals AB,
Perstorp, Sweden as Di-Penta 93. [0105] Copper based heat
stabilizer (Cul/KI): a blend of 7-1-1 (by weight) blend of
potassium iodide, cuprous iodide, and aluminum stearate, available
from Ciba Specialty Chemicals.
Preparation of Films
[0106] Matrix resin compositions and surface resin compositions of
example E1 and comparative examples C1, C2, C3 and C4 shown in
Table 1 were melted or melt-blended in a twin-screw extruder at
about 280.degree. C. The melted or melt-blended polyamide
compositions (Table 1) were made into films by exiting the extruder
through an adaptor and a film die at about 280.degree. C. and cast
onto a casting drum oil-heated at 100.degree. C., then drawn in air
and wound around a core at room temperature. The matrix resin and
surface resin compositions were made into about a 250 micron thick
film. The thickness of the films was controlled by the rate of
drawing.
Preparation of the Composite Structures
[0107] Preparation of the composite structures of example E1 and
comparative examples C1 to C4 was accomplished by first making a
seven layer laminate having a thickness of about 1.5 mm. The
laminate comprises multiple layers of film of compositions shown in
table 1 and woven continuous glass fiber textile (prepared from
E-glass fibers having a diameter of 17 microns, sized with 0.4% of
a silane-based sizing agent and a nominal roving tex of 1200 g/km
that have been woven into a 2/2 twill (balanced weave) with an
areal weight of 600 g/m.sup.2) in the following sequence: two
layers of film of surface resin composition, one layer of woven
continuous glass fiber textile, two layers of film of matrix resin
composition, one layer of woven continuous glass fiber textile, two
layers of film of matrix resin composition, one layer of woven
continuous glass fiber textile and two layers of film of surface
resin composition. The laminates were compression molded by a Dake
Press (Grand Haven, Mich.) Model 44-225 (pressure range 0-25K) with
an 8 inch platten. A 6.times.6'' specimen of film and glass textile
layers as described above was placed in the mold and heated to a
temperature of about 320.degree. C., held at the temperature for 2
minutes without pressure, then pressed at the 320.degree. C.
temperature with the following pressures: about 6 bar for about 2
minutes, then with about 22 bar for about 2 additional minutes, and
then with about 45 bar for about 2 additional minutes; it was
subsequently cooled to ambient temperature. The thusly formed
composite structure had a thickness of about 1.6 mm. The composite
structures had melting ranges between about 245.degree. C. (onset
of melting) to about 268.degree. C. (completion of melting) with
melting peaks at about 260.degree. C. to about 265.degree. C.,
measured by DSC Instrument first heating scan at 10.degree.
C./min.
Heat Ageing
[0108] The composite structures obtained as described above were
cut into 1/2'' (about 12.7 mm) by 3'' (about 76 mm) long tests
specimens (bars) using a MK-377 Tile Saw with a diamond edged blade
and water as a lubricant. Half of the specimens were then heat aged
in a re-circulating air oven at 210.degree. C. for 250 hours or for
500 hours.
Flex Strength of Composite Structures of Table 1
[0109] Flexural Strength was tested on the heat aged test specimens
via a 3-point bend test. The apparatus and geometry were according
to ISO method 178, bending the specimen with a 2.0'' support width
with the loading edge at the center of the span. The tests were
conducted with 1 KN load at 2 mm/min until fracture. The results
are shown in Table 1, along with test results from the specimens
that were not heat aged. The % retention of flex strength after
heat aging is also recorded in Table 1. It is seen in Table 1 that
example E1 containing the copper based heat stabilizer in the
surface resin composition and DPE in the matrix resin composition
retains flexural strength after being heat aged in air at
210.degree. C. for 250 hours (121% flexural strenght retention) and
retains 46% flexural strength after being heat aged in air at
210.degree. C. for 500 hours. In contrast, comparative examples C1,
C2 , C3 and C4 containing respectively, no heat stabilizers (C1),
copper based heat stabilizer in both the matrix and surface resin
composition (C2), DPE in both the matrix and surface resin
composition (C3), and both copper based heat stabilizer and DPE in
both the matrix and the surface resin composition (C4) lose bond
strength after heat aging in air at 210.degree. C. for 250 hours
and for 500 hours.
TABLE-US-00001 TABLE 1 E1 C1 C2 C3 C4 Matrix Resin Composition PA1
98.5 100.0 99.0 98.5 98.75 DPE 1.5 1.5 0.75 CuI/KI 1.0 0.5 Surface
Resin Composition PA1 99.0 100.0 99.0 98.5 98.75 DPE 1.5 0.75
CuI/KI 1.0 1.0 0.5 Flex Strength of laminate ISO-178 (Mpa) As
laminated 517 360 531 504 402 After 250 hrs in air 625 230 538 485
363 oven at 210.degree. C. % Retention 121 64 101 96 90 After 500
hrs in air 238 63 217 161 119 oven at 210.degree. C. % Retention 46
18 41 32 30
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