Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CREEP-RESISTANT COMPOSITE STRUCTURES AND PROCESSES
FOR THEIR PREPARATION
FIELD OF THE INVENTION
The recited invention relates to the field of composite structures and
s processes for their preparation.
BACKGROUND OF THE INVENTION
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
io 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
15 developed for improving the impregnation of the fibrous material with a
polymer matrix to optimize the properties of the composite structure.
In highly demanding applications, such as structural parts in automotive
and aerospace applications, composite materials are desired due to a
unique combination of lightweight, high strength and temperature
20 resistance.
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 such as, for example, the fact
25 that they can be post-formed or reprocessed by the application of heat and
pressure, that a reduced time is needed to make the.composite structures
because no curing step is required, and their increased potential for
recycling. indeed, the time consuming chemical reaction of cross-iinking
for thermosetting resins (curing) is not required during the processing of
30 thermoplastics. Among thermoplastic resins, polyamides and polyesters
are particularly well suited for manufacturing composite structures.
Thermoplastic polyamide compositions and thermoplastic polyester
compositions are desirable for use in a wide range of applications
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including motorized vehicles 'applications; recreation and sport, parts;
household applicances, electrical/electronic parts; power equipment; and
buildings or mechanical devices because of their good mechanical
properties, heat resistance, impact resistance and chemical resistance
s and because they may be conveniently and flexibly molded into a variety
of articles of varying degrees of complexity and intricacy.
Examples of composite structures based on thermoplastic
polyesters or thermoplastic polyamides are disclosed in U.S. Pat: App.
io Pub. No. 2008/0176090. The disclosed composite structures.are said to
have good mechanical properties and smooth surface appearance.
Examples of composite structures based on thermoplastic
polyesters are disclosed in U.S. Pat. No 4,549,920 and U.S. Pat. No
6,369,157.
is U.S. Pat. No 4,549,920 discloses a fiber-reinforced composite
structure made of a thermoplastic polyester, e.g. a polyethylene
ter,ephthalate (PET) resin, and reinforcing filaments encased within said
resin.
U.S. Pat. No 6,369,157 discloses a thermoplastic polyester
20 composite structure. The disclosed composite structure is made by
impregnating a fibrous material with oligomers of polyesters that rapidly
polymerize in situ to form said composite structure.
U.S, Pat. App. Pub. No. 2007/0182047 discloses a method for
producing a thermoplastic polyester composite structure. The disclosed
25 method comprises the. steps .of impregnating a fibrous material with
oligomers of polyester, particularly cyclic oligomers of PBT, and coating on
one.or both sides with an outer layer container a polymerized polyester.
The oligomers of polyester rapidiy polymerize during the.manufaciure of
the composite structure.
30 U.S. Pat. No 5,011,523 discloses.a thermoplastic composite made
of a commingled fibrous material that is formed from commingled
thermoplastic polyester fibers and glass fibers. The fibrous material, i.e.
the glass' fibers, is impregnated by heat and pressure with the
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'thermoplastic polyester present in the commingled fibrous material.
U.S. Pat. No. 4,255,219 discloses a thermoplastic sheet material
useful in forming composites. The disclosed thermoplastic sheet material
is made of polyamide 6 and a dibasic carboxylic acid or anhydride or
s esters thereof and at least one reinforcing mat of long glass fibers
encased within said layer. However, composites made from polyamide 6
may show a loss of their mechanical properties over a typical end-use
application temperature range, such as for example from a low
temperature (e.g. -40 .C) to a high temperature (e.g. +120 C).
io For making integrated composite structures and to increase the
performance of polymers, it is often desired to "overmold" one or more
parts made of a polymer onto a portion or all of the surfaces of a
composite structure so as to surround or encapsulate said surfaces.
Overmolding involves shaping, e.g. by injection molding, a second
is polymer part directly onto at least a portion of one or more surfaces of
the
composite structure, to,form a two-part composite structure, wherein the
two parts are adhered one to the other at least at one interface. The
polymer compositions used to impregnate the fibrous material (i.e. the
matrix polymer composition) and the polymer compositions used to
20 overmold the impregnated fibrous material (i.e. the overmolding polymer
composition) are desired to have good adhesion one to the other,
extremely good, dimensional stability and retain their mechanical,
properties under adverse conditions, including thermal cycling, so that the
composite structure is protected under operating conditions and thus has
25 an increased lifetime. Examples of polyamides that can be used to
'impregnate'a fibrous layer and to overmold the impregnated layer are
semi-aromatic polyamides. WO 2007/149300 discloses a semi-aromatic
polyamide composite article comprising a component comprising a fiber-
reinforced material comprising a polyamide matrix composition, an
30 overmolded component comprising a polyamide composition, and an
optional tie layer therebetween, wherein at least one of the poiyamide
compositions is a semi-aromatic polyamide composition.
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Unfortunately, conventional polyamidecompositions or polyester
compositions that are used to impregnate one or more fibrous
.reinforcement layers in composite .structures.and overmolded composite
structures may not have sufficient creep-resistance (i.e. tendency to resist
s to permanent deformation under the influence of stress) may not have
sufficient dimensional stability and may have reduced mechanical
properties for the most highly demanding applications, all of which may
impair the durability and safety of the article upon use and time. An
example of a reduced mechanical property that deteriorate upon use and
io time is the flexural modulus, i.e. the ratio of stress to strain in
flexural
deformation or the tendency for a material to bend. Flexural modulus is
commonly used as an indication of a material's, stiffness when flexed.
When overmolding a resin composition onto at least a portion of a
composite structure, high mechanical performance of the structure may be
is impaired because of poor bonding strength between the composite
structure and the overmolding resin, e. g. in the case of flexural modulus,
the interface breaks first because of poor bonding strength, therefore the
flex strength of the structure is less than either of its components.
There is a need for a composite structure that combines good
20 creep-resistance and good mechanical properties, especially flexural
modulus.
.SUMMARY OF THE INVENTION
It has been surprisingly found that the above mentioned problems
can be overcome by composite structures having a surface, which surface
25 has at least a portion made of a surface resin, and comprising a fibrous
material selected from non-woven structures, textiles, fibrous battings and
combinations thereof, said fibrous material being impregnated with a
matrix resin composition, wherein the surface resin composition and the
matrix resin composition are identical or different and are'chosen from
3o thermoplastic compositions comprising a) one or more thermoplastic
resins selected from polyesters, polyamides and mixtures thereof; and b)
from at or about 0.5 to at or about 6.0 wt-% of nanoclays, the weight
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percentages being based on the total weight of the thermoplastic
composition.
Also described herein are processes for making the composite
structures, The processes for making the composite structure described
s above comprise, a step of i) impregnating with the matrix resin composition
the fibrous material, wherein at least a portion of the surface of the
composite structure is made of the surface resin composition.
Also described herein are processes for making the composite
structures described herein. The process for making the composite
io structure described herein comprises a step of applying a surface resin
composition to a surface-of the fibrous material which is impregnated with
a .matrix resin composition described herein.
Also described herein are uses of from at or about 0.5 to 6.0 wt-%,
of nanoclays in thermoplastic compositions comprising a) one or more
15 thermoplastic resins selected from polyesters, polyamides and mixtures
thereof described above for improving the flexural strength of a composite
structure having a surface, which surface has at least a portion made of a
surface resin composition, and comprising a fibrous material selected from
non-woven structures, textiles, fibrous battings and combinations thereof,
20 said fibrous material being impregnated with a matrix resin composition,
wherein the surface resin composition and the matrix resin composition
are identical or different and are chosen from the thermoplastic
compositions comprising a) one or more thermoplastic resins selected
from polyesters, polyamides and mixtures thereof, the,weight percentages
2s being based on the total weight of the thermoplastic composition.
Also described herein are overmolded composite structures
comprising:
i) a first component having a surface, which surface has at least a
portion.made of the surface resin composition, and comprising the
30 fibrous material, said fibrous material being impregnated with the
matrix resin composition,
ii) a second component comprising an overmolding resin composition
comprising one or more thermoplastic resins,
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wherein the matrix, resin: and the 'surface resin composition are identical or
different and are chosen from thermoplastic compositions comprising a)
one or more thermoplastic resins selected from polyesters, polyamides
and mixtures, thereof; and b) from at or about 0.5 to at or about 6.0, wt-% of
s the nanoclays described herein, the weight percentages being based on
the total weight of the thermoplastic composition,
and wherein said second component is adhered to said first component
over at least.a portion of the surface of said first component.
Also described herein are uses of from at or about 0.5 to 6.0 wt-%,
to of nanoclays.in thermoplastic compositions comprising a) one or more
thermoplastic resins selected from polyesters, polyamides and mixtures
thereof described above for improving the flexural strength of an
overmolded composite structure comprising a first component having a
surface and a second component of an overmolded composite structure,
i s the weight percentage being based on the total weight of the nanoclay and
the one or more thermoplastic resins selected from polyesters, polyamides
and mixtures thereof,
wherein the second component is adhered to said first component over at
least a portion of the surface of said first component,
20 wherein the surface of the first component has at least a portion made of a
surface resin composition, and comprises a fibrous material selected from
non-woven structures, textiles, fibrous battings and combinations thereof
such as those described above, said fibrous material being impregnated
with a matrix resin composition,
25 wherein the second component comprises an overmolding resin
composition comprising one or more thermoplastic resins, and
wherein the matrix resin composition and the surface resin. composition
are identical or different and are chosen from thermoplastic compositions
comprising a) one or more thermoplastic resins selected from polyesters,
30 polyamides and mixtures thereof described above.
Also described herein are processes for making the overmolded
composite structures described herein. The process comprises a step of
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overmolding the composite structure described herein with the
overmolding resin composition.
The composite structure and overmolded composite structures
according to the present invention exhibit a combination of improved long-
s term creep performance, improved flexural modulus, i.e. stiffness when
flexed, and an increased bonding strength so that the interface between
the composite structure and the overmolding resin does not fail early,
thereby allowing the structure to realize the bonding strength of its
components.
io DETAILED DESCRIPTION
Definitions
The following definitions are to-be used to interpret the meaning of the
terms discussed in the description and recited in the claims.
As used herein, the article "a" indicates-one as well as more than
15 one and does not necessarily limit its referent noun to the singular.
As used herein, the terms "about" and at or about" 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,
20 COMPOSITE STRUCTURES
The composite structures described herein comprise a fibrous
material that is impregnated with a matrix resin composition. At least a
portion of the surface of the composite structure is made of a surface resin
composition.
25 Fibrous Material
For purposes herein, "a fibrous material being impregnated with a
matrix resin composition" means that the matrix resin composition
encapsulates and embeds the fibrous, material so as to form an
interpenetrating network of fibrous material substantially surrounded by
30 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.
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The fibrous material may be in any suitable form known to those
skilled in the art and is preferably selected from non-woven structures,
textiles, fibrous battings and combinations thereof. Non-woven. structures
can be selected from random fiber orientation or aligned fibrous structures.
s Examples.of random fiber orientation include without limitation chopped
and continuous 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,
io braids and combination thereof.
The fibrous material can be continuous or discontinuous in form.
Depending on the end-use application of the composite structure and the
required mechanical properties, more than one fibrous materials can be
used, either by using several same fibrous materials or a combination of
is different fibrous materials,,i.e. the composite structure described herein
may comprise one or more 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
20 materials that are placed as outside layers. Such a combination allows an
improvement of the processing and thereof of the homogeneity of the
composite structure thus leading to improved mechanical properties. The
fibrous material may be made of any suitable material ora mixture of
materials provided that the material or the mixture of materials withstand
25 the processing conditions used during impregnation by the matrix resin
composition and the polyamide surface. resin composition.
Preferably, the fibrous material is made. of glass-fibers, carbon
fibers, aramid fibers, graphite fibers, metal fibers, ceramic fibers, natural
fibers or mixtures thereof; more preferably, the fibrous material is made of
30 glass fibers, carbon fibers, aramid fibers, natural fibers or mixtures
thereof;
and still more preferably, the fibrous material is made of glass fibers,
carbon fibers and aramid fibers or mixture mixtures thereof. As mentioned
above, more than one fibrous materials can be used. A combination of
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fibrous. materials made of different fibers can be used such as for example
a,composite structure comprising one or more central layers made of
glass fibers or natural fibers and one or more surface layers made of
carbon fibers or glass fibers. Preferably, the fibrous material is selected
s 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 pm and
preferably with a diameter between 10 to 24 pm.
The fibrous material may be a mixture of a thermoplastic material
io and the materials described above, 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 the thermoplastic material that is
suited to subsequent processing into woven or non-woven forms, or a
mixture for use as a uni-directional material.
15 Preferably, the ratio between the fibrous material and the polymer
materials, i.e. the combination of the matrix resin composition and surface
resin composition is at least 30% and more preferably between 40 and
60%, the percentage being a volume-percentage based on the total
volume of the composite structure'.
20 Matrix Resin Compositions and Surface Resin Compositions
The matrix resin composition and the surface resin composition are
identical or different and are chosen from thermoplastic compositions
comprising a) one or more thermoplastic resins independently selected
from polyesters, polyamides and mixtures thereof; and b) from at or about
25 0.5 to at or about 6.0 wt-% of nanoclays, the .weight percentages being
based on the total weight of the thermoplastic composition. Depending on
the end-use applications and the desired creep performance and
mechanical properties, the-one or more thermoplastic resins comprised in
the thermoplastic compositions described herein are selected from
30 polyesters, aliphatic polyamides, semi-aromatic polyamides and mixtures
thereof.
Thermoplastic polyesters are typically derived from one or more
dicarboxylic acids (where herein the term "dicarboxylic acid" also refers to
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dicarboxylic acid derivatives such as esters) and diols. In preferred
polyesters the. dicarboxylic acids comprise one or more of terephthalic
acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid, and the diol
component comprises one or more of HO(CH2)õ OH (1); 1,4-
cyclohexanedimethanol; HO(CH2CH2O)mCH2CH2OH (II); and
HO(CH2CH2CH2CH2O)ZCH2CH2CH2CH2OH (III), wherein n is an integer of
.2 to 10, m on average is 1 to 4, and z is on average about 1 to about 40.
Note that (II): and (III) may be a mixture :of compounds in which m and z,
respectively, may vary and that since m and z are averages, they do not
io have to be integers. Other dicarboxylic acids that may be used to form.the
thermoplastic polyester include sebacic and adipic acids.
Hydroxycarboxylic acids such as hydroxybenzoic acid may be used as
comonomers. Examples of thermoplastic polyesters that can be
comprised in the compositions described herein include without limitation
is selected from polyethylene terephthalate) (PET), poly(trimethylene
terephthalate) (PTT), poly(1,4-butylene terephthalate) (PBT),
polyethylene 2,6-naphthoate) (PEN), poly (1,4-cyclohexyldimeth ylehe
terephthalate) (PCT) and copolymers and blends of the same.
Polyamides are condensation products of one or more dicarboxylic
20 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 one or more polyamides are preferably selected from fully
aliphatic polyamides, semi-aromatic polyamides and blends. of the same,
semi-aromatic polyamides being preferred.
25 The, term "semi-aromatic" describes polyamides that comprise at
least some monomers containing aromatic groups, in comparison with
"fully aliphatic" polyamide which describes polyamides comprising aliphatic
carboxyiic acid monomer(s) and aiiphatic diamine monomer(s).
Semi-aromatic polyamides may be derived from one or more
3o aliphatic carboxylic acid components and aromatic diamine components
such as for example m-xylylenediamine and p-xylylenediamine, may
derived be from one or more aromatic carboxylic acid components and
one or more diamine components or may be derived from carboxylic acid
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components and diamine components.
Preferably, semi-aromatic polyamides are formed from one or more
aromatic carboxylic acid components and one or more diamine
components. 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 contains-at least .55 mole-% of terephthalic acid (the mole-%
io 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 contains at least 55 mole-% of terephthalic acid. More preferably,
is the one or more carboxylic acids is 100% 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
20 one or more carboxylic acids mixtures of the semi-aromatic polyamide
contains at least 55 mole-% of terephthalic acid. one. or more semi-
aromatic polyamides described herein comprises one or more diamines
that can be chosen among diamines having four or more carbon atoms,
including, but not limited to tetramethylene diamine, hexamethylene
2s diamine, octamethylene diamine, decamethylene diamine, 2-
methylpentamethylene diamine, 2-ethyltetramethylene diamine, 2-
methyloctamethylene diamine; trimethylhexamethylene diamine, bis(p-
aminocyciohexyi)methane; and/or mixtures thereof. Preferably, the one or
more diamines of the semi-aromatic polyamides described herein are
30 selected from hexamethylene diamine, 2-methyl pentamethylene diamine
and mixtures _thereof, and more preferably the one or more diamines of the
semi-aromatic polyamides described herein are selected from
hexamethylene diamine and mixtures of hexamethylene diamine and 2-
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methyl pentamethylene diamine wherein the mixture contains at least 50
mole-% of hexamethylene diamine (the mole-% being based on the
diamines mixture): Examples of semi aromatic polyamides useful in the
compositions describedr herein are commercially available under the
s trademark Zytel HTN from E. I. du Pont de Nemours and Company,
Wilmington, Delaware.
Fully aliphatic polyamides are homopolymers, copolymers, or
terpolymers formed from aliphatic and alicyclic monomers such as
diamines; dicarboxylic acids, lactams, aminocarboxylic acids, and their
io reactive equivalents. Fully aliphatic polyamides preferably consist of
aliphatic repeat units derived from monomers selected from one or more
of the group consisting of:
i) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and aliphatic
diarnines having 4 to 20 carbon atoms; and
15 ii) lactams and/or aminocarboxylic acids having 4 to 20 carbon atoms.
As used herein; the term "fully aliphatic polyamide" also refers to
copolymers derived from two or more of such monomers and blends of
two or more fully aliphatic polyamides.
Suitable aliphatic dicarboxylic acids having 6`to 20 carbon atoms
20 include adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic
acid
(C9), decanedioic acid (C10), undecanedioic acid (C11), dodecanedioic
acid (C12), tridecanedioic acid (C13), tetradecanedioic acid (C14), and
pentadecanedioic acid (C15), hexadecanoic acid (C16), octadecanoic acid
(C18) and eicosanoic acid (C20).
25 Suitable aliphatic diamines having 4 to 20 carbon atoms include
tetramethylene diamine, hexamethylene diamine, octamethylene diamine,
nonamethylenediamine, dexamethylene diamine, dodecamethylene
diamine, 2-methyipentamethyienediamine, 2-ethyitetramethyiene
diamine,2-methyioctamethylenediamine, trimethylhexamethylenediamine,
3o and bis(p-aminocyclohexyl)methane.
Suitable lactams are caprolactam and laurolactain.
Preferred fully aliphatic polyamides include PA46, PA6; PA66;
PA610; PA612; PA613; PA614; PA 615; PA616; PA10; PA11; PA 12;
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PA1010; PA1012; PA1013; PA1014; PA1210; PA1212; PA1213; 1214 and
copolymers and blends of the same. More preferred examples of fully
aliphatic polyamides in the matrix resin composition and/or surface resin
composition and/or overmolding resin composition described herein are
s PA66 (poly(hexamethylene adipamide), PA612,(poly(hexamethylene
dodecanoamide) and blends-of the same and are commercially available
under the trademark Zytel from E. I. du Pont de Nemours and Company,
Wilmington, Delaware.
In repeat units comprising a diamine and a dicarboxylic acid, the
io diamine is designated first. Repeat units.derived from other amino acids
or lactams are designated as single numbers designating the number of
carbon atoms. The following list exemplifies the abbreviations used to
identify monomers and repeat units in the polyamides (PA).
HMD hexamethylene diamine (or 6 when used in combination with a
is diacid)
AA Adipic acid
DMD Decamethylenediamine
DDMD Dodecamiet,hylenedia mine
TMD Tetra methylenediarnine
20 46 polymer repeat unit formed from TMD and AA
6 polymer repeat unit formed from E-caprolactam
66 polymer repeat unit formed from HMD and AA
610 polymer-repeat unit formed from HMD and decanedioic acid
612 polymer repeat unit formed from HMD and dodecanedioic acid
2s 613 polymer repeat unit formed from HMD and tridecanedioic acid
614 polymer repeat unit formed from HMD and tetradecanedioic acid
615 polymer repeat unit formed from HMD and pentadecanedioic acid
616 polymer repeat unit formed from HMD and hexadecanoic acid
polymer repeat unit formed from 10-aminodecanoic acid
30 1010 polymer repeat unit formed from DMD and decanedioic acid
1012 polymer repeat unit formed from DMD and dodecanedioic acid
1013 polymer repeat unit formed from DMD and tridecanedioic acid
1014 polymer repeat unit formed from DMD and tetradecanedioic acid
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11. polymer repeat unit formed from 11-aminoundecanoic acid
12 polymer repeat unit formed from 12-aminododecanoic acid
1210 polymer repeat unit formed from DDMD and decanedioic acid
1212 polymer repeat unit formed from DDMD and dodecanedioic acid
1213 polymer repeat unit formed from DDMD and tridecanedioic acid
1214 polymer repeat unit formed from DDMD and tetradecanedioic acid
Nanoclays
The thermoplastic compositions described herein comprise from at
or about 0.5 to at or about 6.0 wt-%, preferably-form at or about 1.0 to at.
io or about 5.0 wt-% of nanoclays, the weight percentages being based on
the total weight of the thermoplastic composition. The nanoclays are
available in different forms, e.g. as the compound itself or as a concentrate
or masterbatch containing, relatively high concentrations of nanoclays in a
polymer matrix.
is Nanoclays may be layered silicates, and preferably aluminum
and/or magnesium silicates. The nanoclays may be inthe form of fibrils,
platelets, or other shapes and have a diameter in the range of at or about
to at or about 5000 nm. The layer thickness is less than about 2 nm.
The nanoclays may be naturally occurring or synthetically prepared.
Preferred- nanoclays are fibrils having number average diameters
less than or equal to about 70 nanometers and number average lengths of
up to about 1000 nanometers. Preferably, the nanoclays comprised in the
thermoplastic compositions described herein are independently selected
from sepiolite-type clays, smectite clays such as montmorillonite,hectorite,
saponite, beidelllite, nontronite, bentonite or saponite and mixtures
thereof. More preferably,the nanoclays comprised. in the thermoplastic
compositions described herein are sepiolite-type clays
Sepiolite-type clays are layered fibrous materials in which each
layer is made up of two sheets of tetrahedral silica units bonded to a
3o central sheet of octahedral units containing magnesium ions (see, e:g.,
Polymer International, 53, 1060-1065 (2004) and figures 1 and 2 in L.
Bokobza et al., Polymer International, 53, 1060-1065 (2004)). . As used
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herein, the term "sepiolite-type clays" includes attapulgite as well as
sepiolite itself.
Sepiolite (Mg4Si6O15(OH)2.6(H20) is a hydrated magnesium silicate
'filler that exhibits a high aspect ratio due to its fibrous structure. Unique
s among the~silicates, sepiolite 'is composed of long lath-like crystallites
in
which the silica chains run parallel to the axis of, the fiber. The material
has
been shown to consist of two forms, an a and a R form. The a form is
known to be long bundles of fibers and the 0 form is present as
amorphous aggregates.
Aftapulgite (also known as palygorskite) is almost structurally and
chemically identical to sepiolite except that attapulgite has a slightly
smaller unit cell.
Sepiolite-type clays are available in a high purity, unmodified form
(also referred as uncoated form); examples of such sepiolite-type clays
is include PangelO S-9 sepiolite clays from the Tolsa Group, Spain.
Preferably the nanoctay is in the form of a fine particulate, so it may be
readily dispersed in the thermoplastic melt.
The sepiolite-type: clays used in the thermoplastic compositions
described herein may unmodified modified sepiolite-type clays. The term
"unmodified" means that the surface of the sepiolite-type clays has not
been treated with an organic compound such as an onium compound (for
example, to make its surface less polar).
Sepiolite-type clay fibers comprised in the thermoplastic
compositions described herein have a width (x) and thickness (y) of less
than 50 nm each, and in addition have a length (z). In an embodiment, the
sepiolite-type clay is a Theological grade, such as described in European
Pat. No. EP0454222 and EP0170299 and marketed under the trademark
Pangel by Tolsa, S. A., Spain. The term "rheological.grade" refers to
sepiolite-type clasy with a specific surface area greater than 120 m2/g (N2,
BET), and typical fiber dimensions: 200 to.2000 nm long, 10-30 nm wide,
and 5-10 nm thick. Rheological grade sepiolite-type clays may be
obtained from natural sepiolite-type clays by means of special
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micronization processes that substantially prevent'breakage of the
sepiolite fibers, such that the sepiolite-type clays. disperses easily in
water
and other polar liquids, and has an external surface with.a high degree of
irregularity, a high specific. surface, preferably greater than 300 m2/g, and
a high.density of active centers for adsorption. The active centers allow
significant hydrogen bonding that provide the rheological grade.sepiolite-
type clays,a high water retaining capacity. The microfibrous nature.of the
rheological grade sepiolite-type clays makes sepiolite-type clays a material
with high porosity and low apparent density. Additionally, rheological
io grade sepiolite has a very low cationic exchange capacity (10-20 meq/100
g) and the interaction with electrolytes is very weak, which in turn causes
rheological grade sepiolite not to be practically affected by the presence of
salts in the medium in which it is found, and therefore, it remains stable in
a' broad pH range,
is The above-mentioned qualities of rheological grade sepiolite can
also be attributed to rheological grade attapulgite with particle sizes
smaller than 40 microns, such as for example the range of ATTAGEL
goods (for example ATTAGEL 40 and ATTAGEL 50 attapulgite)
manufactured and marketed by BASF, Florhan Park, N.J. 07932, and the
20 MIN-U-GEL range of Floridin Company.
Additives
The surface resin composition described herein. and/or the matrix
resin composition may fur ther comprise one or more impact modifiers, one
or more heat stabilizers, one or more reinforcing agents, one or more
25 ultraviolet light stabilizers; one or more flame retardant agents or
mixtures
thereof.
The matrix resin composition and/or the surface resin composition
may further comprise one or more heat stabilizers.
The one or more heat stabilizers may be selected from hindered
36 phenol. antioxidants, hindered amine antioxidants, phosphorus
antioxidants (e.g. phosphite or phosphonite stabilizers), aromatic amine
stabilizers, thioesters, phenolic based anti-oxidants, and mixtures of these.
When present, the one or more heat stabilizers are present in an amount
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from at or about 0.1 to at or about 5 weight percent, or preferably from at
or about 0.1 to at or about 3 weight percent, or more preferably from at or
about 0.1 to at or about 1 weight percent, the weight percent being based
on the total weight of the surface resin composition or the matrix resin
s composition, as the case may be. When the matrix resin composition
and/or the surface resin composition comprises one or more polyamides,
the one or more heat stabilizers may also be selected from copper salts
and/or, derivatives thereof such as for example copper halides or copper
acetates; divalent.manganese salts and/or derivatives thereof and
io mixtures thereof. Preferably, copper salts are used in combination with
halide compounds and/or phosphorus compounds and more preferably
copper salts are used in combination with iodide or bromide compounds,
and still more preferably, with potassium iodide or potassium bromide.
When present, the one or more heat stabilizers selected from copper salts
15 and/or derivatives are present in an amount from at or about 0.1 to at or
about 3 wt-%, or preferably from at or about 0.1 to at or about 1 wt-%, or
more preferably from at or about 0.1 to at or about 0.7 wt-%, the weight
percentage being based on the total weight of the surface resin
composition or the matrix resin composition, as the case may be. The
20 addition of the one or more heat stabilizers improves the thermal stability
of the composite structure during its manufacture (i.e. a. decreased
molecular weight reduction) as well as its thermal stability upon use and
time. In addition to the improved heat.stability, the presence of the one or
more heat stabilizers may allow an increase of the temperature that is
25 used during the impregnation of the composite structure thus reducing the
melt viscosity of the matrix resin and/or the surface resin composition
described herein. As a consequence of a reduced melt viscosity of the
matrix resin and/or the surface resin composition, impregnation raie:may
be increased.
30 The surface resin composition described herein and/or the matrix
resin composition may further comprise one or more reinforcing agents
such as glass fibers, glass flakes, carbon fibers, carbon nanotubes, mica,
wollastonite, calcium carbonate, talc, calcined clay, kaolin, magnesium
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sulfate, magnesium silicate, boron nitride, barium sulfate, titanium dioxide,
sodium aluminum carbonate, barium ferrite, and potassium titanate.
When present, the one or more reinforcing agents are present in an
amount from at or about 1 to ,at or about 60 wt-%, preferably from at or
s about 1 to at or about 40 wt-%, or more preferably from at or about 1 to at
or about 35 wt-%, the-weight percentage being based on the total weight
of the surface: resin composition or the matrix resin composition, as the
case may be.
The surface resin composition described herein and/or the matrix
io resin composition may further comprise one or more ultraviolet tight
stabilizers such as hindered amine light stabilizers (HALS), carbon black,
substituted resorcinols, salicylates, benzotriazoles, and benzophenones.
The surface resin composition described herein and/or the matrix
resin composition may further comprise one or more flame retardant
15 agents such as.metal oxides (wherein the. metal may be aluminum, iron,
titanium, manganese; ,magnesium, zirconium, zinc, molybdenum, cobalt,
bismuth, chromium, tin,, antimony, nickel, copper and tungsten), metal
powders (wherein the metal may be aluminum, iron, titanium, manganese,
zinc, molybdenum, cobalt, bismuth, chromium, tin, antimony, nickel,
20 copper and tungsten), metal salts such as zinc borate, zinc metaborate,
barium metaborate,. zinc carbonate, magnesium carbonate, calcium
carbonate and barium carbonate, metal phosphinates (wherein the metal
may be aluminum, zinc or calcium), halogenated organic compounds like
decabromodiphenyl ether, halogenated polymer such as
25 poly(bromostyrene) and brominated polystyrene, melamine
pyrophosphate, melamine cyanurate, melamine polyphosphate, red
phosphorus, and the like.
With the aim of increasing the impregnation rate of the fibrous
material, the melt viscosity of the surface resin composition and/or may be
30 reduced and especially the melt viscosity of the matrix resin composition.
In general, it is an advantage to have a flow "rate of material as high as
possible to make the most efficient use of, the processing machine and
thereby reduce costs by increasing the impregnation rate of the fibrous
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material. For this reason, highly flowable polymer compositions in molten
state are of interest. By having a low melt viscosity, highly flowable
polymer compositions flow faster and are thus easier to be processed. By
reducing the meltyiscosity of the polymer composition, the rate of the
impregnation step maybe.shortened thereby increasing the overall
manufacturing. speed and thus leading to an, increased productivity of the
manufacture of the composite structures and a decrease of energy
consumption associated with a shorter,cycle time that is beneficial also for
environmental concerns. In addition to the improved throughput, the
io increased impregnation rates also minimize the thermal-degradation of the
polymer composition. With the aim of reducing the melt viscosity of the
surface resin composition and/or the matrix resin composition, the surface
resin composition described herein and/or the matrix resin composition
may further comprise one or more rheology modifiers selected from
hyperbranched dendrimers and more preferably one or more
hyperbranched polyester dendrimers. Preferred examples of
hyperbranched dendrimers are those described in US 5,418,301 US
2007/0173617. The use of such dendrimers in thermoplastic resins is
disclosed in US 6,225,404, US 6,497,959, US 6,663,966, WO
2003/004546, EP 1424360 and WO 2004/111126. This literature teaches
that the addition of hyperbranched dendritic polyester macromolecules to
thermoplastic compositions leads to improved rheological and, mechanical
properties due to the reduction of the melt viscosity of the composition
and, therefore, lead to an improved processability of the thermoplastic
composition. When present, the one or more hyperbranched dendrimers
comprise from at or about 0.05 to at or about 10 wt-%, or more preferably
from at or about 0.1 to at or about 5 wt-%, the weight percentage being
based on the total weight of the surface resin composition or the matrix
resin composition, as the case may be. When the matrix resin
composition and/or the surface resin composition comprise one or more
polyamides and with the aim of reducing their melt viscosity of so as to
improve the impregnation rate of the composite structure, the surface resin
composition and/or :the matrix resin composition may further comprise one
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or more molecular chain breaking agents. Examples of molecular chain
breaking agents include without limitation aliphatic dicarboxylic acids and
aromatic dicarboxylic acids. Specific examples thereof are oxalic acid,
malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid,
s dodecanedioic acid, isomers of phthalic acid. When present, the one ore
more molecular chain breaking agents comprise from at or about 0.05 to
at or about 5 wt-%o, or more preferably from at or about 0.1 to at or about 3
wt-%, the weight percentage being based on the total weight of the
.surface resin composition or the matrix resin composition, as the case
io maybe.
The surface resin composition described herein and/or the matrix
resin composition may further comprise modifiers and other ingredients,
including; without limitation, flow enhancing additives, lubricants,
antistatic
agents, coloring agents (including dyes, pigments, carbon black, and the
15 like), flame retardants, nucleating agents, crystallization promoting
agents
and:other processing aids known in the polymer compounding art.
Fillers, modifiers and'other ingredients described above may be
present in the composition 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
20 dimensions of the particles is in the range of 1 to 1000 rim.
Making The Compositions
Preferably, the surface resin compositions and the matrix resin
compositions described herein are melt-mixed blends, wherein all of the
polymeric components are well-dispersed within each other and all of
25 the non-polymeric ingredients are well-dispersed in and bound by the
polymer matrix, such that the blend forms ,a unified whole. Any melt-
mixing method may be used to combine the polymeric components and
non-polymeric ingredients of the present invention. For example, the
polymeric components and non-polymeric ingredients may be added to
3o 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 polymeric components and non-polymeric
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ingredients in a stepwise fashion,. part of the polymeric components
and/or non-polymeric ingredients are first added and melt-mixed with the
remaining polymeric components-and non-polymeric ingredients being
subsequently added and further melt=mixed until a well-mixed
composition is obtained.
Depending on the end-use application, the composite structure
described herein may. have any shape. Preferably, the composite
structure described herein is in the form of.a sheet structure.
Making the Composite Structures
Also descried herein are processes for making the composite
structures described above and the composite structures obtained thereof.
The processes comprise a step of i) impregnating with the matrix resin
composition the fibrous material, wherein at least a portion.of the surface
of the composite structure is made of the surface resin composition.
Preferably, the fibrous material is impregnated with the matrix resin by
thermopressing. During thermopressing, the fibrous material, the matrix
resin composition and the surface resin composition undergo heat. and
pressure in order to allow the plastics to melt and penetrate through the
fibrous material and, therefore, to impregnate said fibrous material.
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 matrix resin composition, and the polyamide
composition, preferably at least about 20 C above the melting point to
enable a proper impregnation. The heating step may be done by a variety
of thermal means; including. contact heating, radiant gas heating, infra red
heating, convection or forced convection air heating or microwave heating.
The driving impregnation pressure can be applied by a static process or by
a continuous process (also known as dynamic process); a continuous
process being preferred. 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. During lamination,
heat and pressure are applied to the fbrous,matehal,,.the matrix resin
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composition and the surface resin composition through opposing
pressured rollers in a heating zone. Examples of lamination techniques
include without limitation calendering, flatbed lamination and double-belt
press lamination, When lamination is used as, the impregnating process,
s preferably a double-belt press is used' for lamination.
The matrix resin composition and the surface resin composition
are 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 surface resin
io composition is applied on at least a portion of the surface of the
composite structure so as to be accessible if an overmolding resin is
applied onto the.composite structure.
During a powder coating process, a polymer powder which has
been obtained by conventional grinding methods is applied to the fibrous
15 material. The powder may be applied onto the fibrous material by
.scattering, sprinkling, spraying, thermal or flame spraying, or fluidized
bed coating methods. 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 matrix. resin composition and the
20 surface resin' composition are applied to the fibrous material such that at
least of portion of surface.of the composite structure is made of the
polyamide surface resin composition. Subsequently, thermopressing is
achieved on the powder coated fibrous material, with an optional
preheating of the powdered fibrous material outside of the pressurized
25 zone, During film lamination, one or more films made of the matrix resin
composition and one or more films made of the surface resin
composition which have been obtained by conventional extrusion
methods known in the art such as for example biow film extrusion, cast
film extrusion and cast sheet extrusion are applied to the fibrous
3o material. Subsequently, thermopressing is achieved on the assembly
comprising the one or more films made of the matrix resin composition
and the one or more films made of the surface resin composition and the
one or more fibrous materials. In the resulting composite structure, the
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film resins have penetrated into the fibrous material as a polymer
continuum surrounding the fibrous material. 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
s 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.
Also described herein are processes for making the composite
structures described herein, wherein the processes comprise a step of
io applying a surface resin composition to at least a portion of the surface
of
the fibrous material which is impregnated with a matrix resin composition
described herein.
Depending on the end-use application, the composite structure
obtained under the impregnating step i) may be shaped into a desired
15 geometry or configuration,. or used in sheet form. The process for making
a composite structure described herein may further comprise a step ii) of
shaping the composite structure, said step arising after the impregnating
step i). The step of. shaping the composite structure obtained under step i)
may be done by compression molding, stamping or any technique using
20 heat and pressure. 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
surface resin composition and is transferred to a forming means such as a
molding press containing a mold having a cavity of the shape of the final
25 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 surface resin composition.
OVERMOLDED.COMPOSITE STRUCTURES
In another aspect, the present invention relates to overmolded
30 composite structures and processes to make them. The overmolded
composite structure according to the present invention comprises at least
two components, i.e. a first component and a second component. The
first component consists of the composite structure described above and
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the second component comprises an overmolding resin composition. The
overmolded composite structure may comprise more than one first
components, i.e. it may comprise more than one composite structures.
The overmolding resin composition comprises one or more thermoplastic
s resins. The overmolding resin composition comprises one or more
thermoplastic resins that are compatible with the surface resin
composition. Preferably, the overmolding resin composition comprises
one or more thermoplastic resins selected from polyesters, polyamides
and mixtures thereof such as those described herein for the matrix resin
io compositions and the surface resin compositons.
The overmolding resin 'composition described herein may further
comprise one or more impact modifiers; one or more heat stabilizers, one
or more oxidative stabilizers, one or more reinforcing agents, one or more
ultraviolet light stabilizers, one or more flame retardant agents or mixtures
15 thereof such as those' described herein for the surface resin composition
and/or the matrix resin composition, When comprised in the overmolding
resin compositions, these additives are present' in amounts described
above for the surface resin composition and/or the matrix resin
composition.
20 The second component is adhered to the-first component over at
least a, portion of the surface of said first component, said portion of the
surface being made of the surface. resin composition described above.
Preferably, the second component is adhered to the first component over
at least a portion of the surface of said first component without any
25 additional adhesive, tie layer or adhesive layer. The first component, i.e.
the composite structure, may be fully or. partially encapsulated by the
second component. Preferably, the first component, i.e. the composite
structure described above, is in the form of a sheet structure.
The-overmolding resin compositions described herein are
30 preferably melt-mixed blends, wherein all of the polymeric components
are well-dispersed within each other and all of the non-polymeric
ingredients are well-dispersed in and bound by the polymer matrix, such
that the blend forms a unified whole. Melt-mixing methods that can be
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used are described above for the.preparation of the polyamide surface
resin compositions and the matrix resin compositions.
Making the Overmo/ded Composite Structures
In another aspect, the present invention relates to a process for
s making the overmolded composite structures described above and the
overmolded composite structures obtained thereof. The process for
making the overmolded composite structure. compri sing a step of
overmolding the first component, i.e. the composite structure described
above, with the overmolding resin composition. By "overmolding", it is
1o meant that a second component is molded onto at least one portion of the
surface of a first component.
The first component, i:e. the composite structure described above,
is positioned in a molding station comprising a mold having a cavity
defining the greater portion of the outer surface configuration of the final
15 overmolded composite structure. The overmolding resin composition may
be overmolded on one side or on both sides of the composite structure
and it may fully or partially encapsulate the first component. After having
positioned the first component in the molding station, the overmolding
resin composition is:then introduced in a molten form, The first
20 component and the second component are adhered together by
overmolding.
The overmolding process includes that the second component is
molded in a mold already containing the first component, the latter having
been manufactured beforehand as described above, so that first and
25 second components are adhered to, each other over at least a portion of
the surface of said first component. The at,least two parts are preferably
adhered together by injection or compression molding as an overmolding
step, and more preferably by injection molding. When the overmolding
resin composition is introduced in a molten form in the molding station so
30 as to be in contact with the first component, at least a thin layer of an
element of the first component is melted and becomes intermixed with the
overmolding resin composition.
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Depending on the end-use application, the first component, i.e. the
composite structure may be shaped into a desired geometry or
configuration prior to.the step of overmolding theovermolding resin
composition. As mentioned above, the step of shaping the composite
s structure may done by compression molding, stamping or any technique
using heat and pressure, compression molding and stamping being
preferred. During stamping, the composite structure is preheated to a
temperature above the melt temperature of the polyamide surface resin
composition and is transferred to a stamping press or a mold having a
io cavity of the shape of the final desired geometry and, it is then stamped
into a desired configuration and is thereafter removed from the press or
the mold. With the aim of improving the adhesion between the
overmolding resin and-the polyamide surface resin composition, the.,
surface of the composite structure may be a textured surface so as to
15 increase the relative surface available for overmolding. Such textured
surface may be obtained during, the step of shaping by using a press or a
mold having for example porosities or indentations on its surface.
Alternatively, a one step process comprising the steps of shaping
and overmolding the first component in a single molding station may be
20 used. This one step process avoids the step of compression molding or
stamping the first component in a mold or a press, avoids the optional
preheating step and the transfer of the preheated first component to the
molding station. During this one. step process, the first component,.i.e. the
composite structure, is heated outside, adjacent to or within the molding
25 station, to a temperature at which the first component is conformable or
.shapable during the overmolding step, and preferably it is heated to a
temperature below the melt temperature of the composite structure. In
such a one step process, the molding station comprises a mold having a
cavity of the shape of the final desired geometry. The shape of the first
30 component is thereby obtained during overmolding.
Also described herein are uses of from at or about 0.5 to 6.0 wt-%,
of the nanoclays described above in thermoplastic compositions
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comprising a) one or more thermoplastic resins selected from polyesters,
polyamides and mixtures thereof described above for improving the
flexural strength of a composite structure having a surface, which surface
has at least a portion made of a surface resin composition, and comprising
a fibrous material selected from non-woven'structures, textiles, fibrous
battings and combinations thereof, said fibrous material being
impregnated with a matrix resin composition, wherein the surface resin
composition and the matrix resin composition are identical or different and
are chosen from the. thermoplastic compositions comprising a) one or
io more thermoplastic resins selected from polyesters, polyamides and
mixtures thereof, the weight percentages being based on the total weight
of the thermoplastic composition.
Also described herein are uses. of from at or about 0.5 to 6.0 wt-%,
is of the nanoclays described above in thermoplastic compositions
comprising a) one or more thermoplastic resins selected from polyesters,
polyamides and mixtures thereof described above for improving the
flexural strength of an overmolded composite structure comprising a first
component having a surface and a second component of an overmolded
20 composite structure, the weight percentage being based on the total
weight of the nanoclay and .the one or more thermoplastic resins selected
from polyesters, polyamides and mixtures thereof,
wherein the second componenCis adhered to said first component over at
least a portion of the surface of said first component,
25 wherein the surface of the first component has at least a portion made of a
surface resin composition, and comprises a fibrous material selected from
non-woven structures, textiles, fibrous battings and combinations thereof
such as those described above, said fibrous material being impregnated
with a matrix resin composition,.
30 wherein the second component comprises an overmolding resin
composition comprising one or more thermoplastic resins, and
wherein the matrix resin composition and the surface resin composition
are identical or different and are chosen from thermoplastic compositions
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comprising a) one or more thermoplastic resins, selected from polyesters,
polyamides and mixtures thereof described above.
Articles
The composite structures and the overmolded composite structures
s described herein may be used in a wide variety of applications such as
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
io equipments or structural components for mechanical devices.
Examples of automotive applications include without limitation
seating components and.seating frames, engine cover brackets, engine
cradles; suspension cradles, spare tire wells, chassis reinforcement, floor
pans, front-end modules, steering column frames, instrument panels, door
1s 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,
20 bumper beams, pedestrian safety beams, firewalls, rear parcel shelves,
cross vehicle bulkheads, pressure vessels such as refrigerant bottles and
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
25 springs, vehicle wheels, recreational vehicle and motorcycle, swing arms,
fenders, roofing frames and tank flaps.
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,
3o 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 housings for hand
held electronic devices, computers.
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EXAMPLES
The following materials were used for preparing the composites structures'
and overmolded composite structures according to the present invention
and comparative examples.
s Materials
The materials below make up the compositions used in the Examples and
Comparative Examples
Semi-aromatic polyamide 1 (PA1): polyanide (PA) made of terephthalic
acid and 1,6-hexamethylenediamine (HMD) and 2-
io methylpentamethylenediamine (MPMD)(HMD:MPMD = 50:50) and having
a melting point of about 305-315 C. This semi-aromatic polyamide is
commercially available from E. 1. du Pont de Nemours.
Overmolding resin composition: a composition comprising 50 wt-% of long
glass fibers and comprising the semi-aromatic PA1. This composition is
15 commercially available from E., I. du Pont de Nemours.
Nanoclav: a nanodispersed sepiolite supplied by Tolsa, Spain under the
trademark Pangel S9.
Preparation of films
Compositions comprising a blend of 97 wt-% of the semi-aromatic
20 polyamide PA1 and 3 wt-% of nanoclays were prepared by melt blending a
mixture of the_two ingredients in a ZSK 30 mm twin-screw extruder
equipped with a vacuum port for devolatilization.
Films having a thickness of about 10 mil (254 microns) and made of the
compositions listed in Table 1 were prepared by melting the semi-aromatic
2s polyamide PA1 or the`serr-i-aromatic polyamide PA1 comprising the
nanoclays in a ZSK 28 mm twin-screw extruder equipped with a film die
and a casting drum. The films were processed with a melt temperature of
about 337 C and cast at a temperature of about 150 C.
Preparation of the composite structures
3o The composite structures C1 and El and the composite structures Cl and
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El used for preparing the overmolding. composite structures C3 and E2
were prepared by compression molding a stack of nine layers made of the
films obtained as described above alternating with eight layers of woven
continuous glass fiber sheets into a 2 mm thick sheet.
s Preparation of the overmolded composite structures
The composite structures Cl and El were cut into 1.0 in x 8 in (2.5 cm x
20.3 cm) rectangular bars and preheated to 150 C for at least 15 minutes,
and then placed in a mold cavity of an injection molding machine (125 ton
Engel). The mold was electrically heated at 150 C and fitted with a 1.0 in
io x 8 in x 3/16 in bar cavity with a bar gate. The injection machine was set
at 325 C.
The composite structures C1 and El were overmolded with the
overmolding resin composition (a composition comprising 50 wt-%o of long
glass fibers and comprising the polyamide (PA) made of terephthalic acid
is and 1,6-hexamethylehediamine (HMD) and 2-
methylpentamethylenediaMine (MPMD) (HMD:MPMD = 50:50) described
above) such that the resulting overmolded composite structures had a
thickness of about 0.18 (3/16) in (4.5 mm).
Flexural modulus
20 The composite structures (Cl and El) were cut into about 0.5 in x about 5
in (1.3 cm x 12.7 cm) rectangular bars (specimen test size as per method
iso 178) and flexural modulus was measured without pre-heating.
For comparison, a test specimen (C2:C2) of overmolding resin
composition (C2) overmolded on itself was prepared. The overmolding
25 resin composition (C2) was injection molded onto parts (specimen test
size as per method ISO 178) having the same thickness as those
prepared from the composite structures.
The overmolded composite structures (C3 and E2), the overmoiding resin
parts (C2:C2) and two composite structures (Cl and E1) listed in Table 1
30 were cut with a water jet into the. required geometry (specimen test size
as
per method ISO 178, e.g. about 0.5 in x about 5 in (1.3 cm x 12.7 cm)
rectangular bars) for the determination of flexural modulus, and the
corresponding test results are shown in Table 3.
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Flexural testing was performed according to ISO 178 with a strain rate of
50mm/min. For the overmolded composite structures C3 and E2, the test
specimens were positioned with the composite structure face or with the
overmolded composite face up, and these two results from each are
reported in Table 3.
Table 3 gives average values obtained from five specimens.
Creep-resistance
The composite structures (Cl and E1) were prepared as described-above
and had the same thickness as above. Specimens were cut using a water
to jet into 13 x 60 mm bars that were used for accelerated creep testing in a
TA Instruments 983 DMA instrument in creep. mode under nitrogen purge
of 20 mL/min. The bars were first annealed at 200 C for two hours, then
the mid-section of the bar was clamped between jaws of the DMA
instrument allowing 10:1 in length to thickness. Length correction was
carried at ambient condition using three lengths. A 2000-minute
experiment was set up consisting of a series of isothermal steps of 30
minutes temperature equilibration, 15 minutes loading, and 60 minutes
recovering without load. The temperature was then increased by 5 C for a
next cycle of the above three isothermal steps of equilibration, loading,
and unloading, beginning with a temperature of 25 C to 220 C. The short-
term compliances vs time curves using 25 C as the reference temperature
were then shifted horizontally along the logarithmic time scale till they
overlapped. A master compliance curve was thus created, and then used
to calculate the percent (%) of strain.
Table 2 gives average values obtained from five specimens.
In the Tables, composites and overmolded composites of the Examples
are identified as "E" and composites and overmolded composites of the
Comparative Examples as "C-.
31
CA 02799250 2012-11-13
WO 2011/155947 PCT/US2010/038377
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CA 02799250 2012-11-13
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CA 02799250 2012-11-13
WO 2011/155947 PCT/US2010/038377
As shown in Table 2, a comparative composite structure comprising a
matrix resin and a surface resin compositions made of a semi-aromatic
polyamide (Cl) exhibit a lower creep-resistance compared to the
composite structure according to the present invention. The comparative
s composite structure (Cl) showed, so much deformation after 100000 hours
that is was not possible to measure. the.% strain. In contrast, the
.incorporation of nanoclays in the matrix, resin and in-the. surface resin
compositions of a composite structure strongly improved the creep-
resistance of the composite structure of the present invention (El) in
io comparison with a composite structure comprising compositions lacking
nanoclays.
As shown in Table 3, a comparative composite structure comprising a
matrix resin and a surface resin compositions made of a semi-aromatic
polyamide (Cl) suffered from low flexural modulus. In contrast, the
Is incorporation of nanoclays in the matrix resin and in the surface resin
compositions of a composite structure improved the flexural modulus of
the composite structure of the present invention (El) in comparison with a
composite structure comprising compositions lacking nanoclays. Indeed,
a flexural modulus value of 17.3 GPa was obtained for the composite
20 structure according to the present invention (El) in comparison with a
value.of 14.4 GPa for the comparative composite structure (Cl). As
shown in Table 3, the comparative overmolded composite structure (C3)
comprising a matrix resin and a surface resin compositions made of a
semi-aromatic polyamide suffered from low flexural modulus. In contrast,
25 the incorporation of nanoclays in the matrix resin and in the surface resin
compositions of an overmolded composite structure strongly improved the
flexural modulus of the overmolded composite structure of the present
invention (E2). indeed, a flexural modulus value on the overmolded
composite face of 13.1 GPa was obtained for the overmolded composite
30 structure according.to the present invention (E2) in comparison with a
value of 5.5 GPa for the comparative overmolded composite structure
(C3): The low value of the flexural modulus maybe attributed to the
interface breaking at a low value because of low adhesion between the
CA 02799250 2012-11-13
WO 2011/155947 PCT/US2010/038377
composite structure and the overmolding resin, while a high flexural
modulus may be attributed to`the interface-being strong and not failing
before the failure point is reached for one of the composite structure or the
overmolding resin.
s The composite structures and overmolded composite structures of
the present invention (E1-E2) exhibited not only an improved creep-
resistance but also strongly improved mechanical properties, especially
flexural modulus. Both of which contribute to the durability and safety of
the article upon use and time.
16
