U.S. patent application number 11/007957 was filed with the patent office on 2005-09-29 for blends of high temperature resins suitable for fabrication using powdered metal or compression molding techniques.
Invention is credited to Krizan, Timothy D., Schmeckpeper, Mark R..
Application Number | 20050215715 11/007957 |
Document ID | / |
Family ID | 34713118 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050215715 |
Kind Code |
A1 |
Schmeckpeper, Mark R. ; et
al. |
September 29, 2005 |
Blends of high temperature resins suitable for fabrication using
powdered metal or compression molding techniques
Abstract
The invention relates to a resin blend comprising at least two
dry blended, non-melt processible resin particulates, wherein the
at least two dry blended, non-melt processible resin particulates
are molded by compression molding. The invention also relates to a
process for producing a resin blend comprising mixing at least two
non-melt processible resin particulates by dry blending and molding
the mixture by compression molding. Another aspect of the invention
is a resin blend comprising at least two blended, non-melt
processible polyimide resin particulates, wherein the at least two
blended, non-melt processible resin particulates are molded by
compression molding.
Inventors: |
Schmeckpeper, Mark R.;
(Kennett Square, PA) ; Krizan, Timothy D.;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
34713118 |
Appl. No.: |
11/007957 |
Filed: |
December 9, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60531123 |
Dec 19, 2003 |
|
|
|
Current U.S.
Class: |
525/191 |
Current CPC
Class: |
B29C 43/006 20130101;
C08L 79/08 20130101; B29C 43/003 20130101; C08L 79/08 20130101;
C08L 79/08 20130101; B29K 2079/08 20130101 |
Class at
Publication: |
525/191 |
International
Class: |
C08F 008/00 |
Claims
We claim:
1. A resin blend comprising at least two dry blended, non-melt
processible resin particulates, wherein the at least two dry
blended, non-melt processible resin particulates are molded by
compression molding.
2. The resin blend of claim 1 having a moisture pickup level less
than an expected moisture pickup level of the at least two dry
blended, non-melt processible resin particulates.
3. The resin blend of claim 1 or 2, wherein at least one dry
blended, non-melt processible resin particulate is a polyimide
resin particulate.
4. The resin blend of claim 3, wherein the polyimide resin
particulate is present in an amount of from about 5 weight percent
to about 95 weight percent of the total resin blend.
5. The resin blend of claim 1 or 2, wherein the at least two dry
blended, non-melt processible resin particulates are polyimide
resin particulates.
6. The resin blend of claim 1 or 2, wherein the at least two dry
blended, non-melt processible resin particulates have an average
particle size of from about 5 .mu.m to about 500 .mu.m.
7. The resin blend of claim 1 or 2, further comprising at least one
encapsulated filler.
8. The resin blend of claim 7, wherein the at least one
encapsulated filler is present in an amount of from about 1 weight
percent to about 70 weight percent of the total resin blend.
9. The resin blend of claim 1 or 2, further comprising at least one
unencapsulated filler.
10. The resin blend of claim 9, wherein the at least one
unencapsulated filler is present in an amount of from about 1
weight percent to about 15 weight percent of the total resin
blend.
11. A compression molded article comprising the resin blend of any
of claims 1-10.
12. A method of producing a compression molded article comprising:
(a) mixing at least two non-melt processible resin particulates by
dry blending; and (b) molding the mixture of step (a) by
compression molding.
13. The method of claim 12, wherein at least one non-melt
processible resin particulate is a polyimide resin particulate.
14. The method of claim 12, wherein the at least two non-melt
processible resin particulates are polyimide resin
particulates.
15. The method of claim 12 further comprising the step of adding at
least one filler.
16. A compression molded article produced by the method of claim
12.
17. A resin blend comprising at least two blended, non-melt
processible polyimide resin particulates, wherein the at least two
blended, non-melt processible polyimide resin particulates are
molded by compression molding.
18. A compression molded article comprising the resin blend of
claim 17.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/531,123, filed Dec. 19, 2003.
FIELD OF THE INVENTION
[0002] This invention relates to a dry blended, particulate, high
temperature polymer, which is moldable using powdered metal or
compression molding technology.
BACKGROUND OF THE INVENTION
[0003] High temperature resins are increasingly replacing metals in
the fabrication of machinery parts and mechanical components. As a
result, significant reductions in production and replacement costs
for the machinery parts and mechanical components have been
realized. To replace metals in machinery parts and mechanical
components, the high temperature resins should have high resistance
to mechanical wear, surface stress, and extreme temperature
conditions. Additionally, the performance characteristics of the
high temperature resins should equal or exceed that of the metals
being replaced.
[0004] Polyimides are particularly preferable high temperature
resins because of their mechanical strength, dimensional stability,
thermal stability, chemical stability, flame retardance, and
dielectric properties. Polyimides, such as those described in U.S.
Pat. No. 3,179,614 issued to Edwards on Apr. 20, 1965, can be used
in a wide variety of commercial applications. The outstanding
performance characteristics of these polymers under stress and at
high temperatures have made them useful in the form of bushings,
seals, electrical insulators, compressor vanes and impellers,
pistons and piston rings, gears, thread guides, cams, brake
linings, and clutch faces.
[0005] Blending of resin polymers to improve the physical
characteristics of the blend over the individual resin polymers is
well known in the art. Known techniques used in processing resin
polymers include dry blending, direct compression, wet granulation,
melt blending, coprecipitation from solution, and spray freezing of
frozen particles. Dry blending of resins is advantageous because of
the absence of solvents and other liquids that may contribute to
residual moisture. Dry blending is also advantageous because of its
simplicity compared to other mixing methods.
[0006] It is important that a molded article have low moisture
pickup because absorbed moisture can negatively affect: the
dimensional stability of the molded article through, for example,
hygroscopic expansion; mechanical properties such as tensile
strength; electrical properties; and hydrolytic stability. Thus, it
is desirable to lower the moisture pickup of a molded article
without changing any of the properties of the article.
[0007] U.S. Pat. No. 4,820,781 issued to Policastro et al. on Apr.
11, 1989, discloses polyetherimide-silicone copolymer blends with a
glass transition temperature of at least 190.degree. C.
[0008] U.S. Pat. No. 4,987,197 issued to Ohta et al. on Jan. 22,
1991, discloses melt processible polyimide-aromatic polyamideimide
blends that can be used in various molding applications such as
injection molding, compression molding, transfer molding, and
extrusion molding.
[0009] U.S. Pat. No. 5,179,153 issued to George on Jan. 12, 1993,
discloses polyimide compositions containing graphite filler and
polytetrafluoroethylene filler.
[0010] Accordingly, one aspect of this invention is to provide dry
blended resin particulates wherein the moisture pickup of a molded
article comprising the dry blended resin particulates is lower than
the level expected based on the moisture pickups of the individual
components of the blend. Another aspect of the invention is that
these dry blended resin particulates are suitable for compression
molding.
SUMMARY OF THE INVENTION
[0011] One aspect of this invention is to provide a resin blend
comprising at least two dry blended, non-melt processible resin
particulates, wherein the at least two dry blended resin
particulates are molded by compression molding. Another aspect of
the invention is a compression molded article comprising the resin
blend. Another aspect of this invention is to provide a process for
producing a compression molded article comprising mixing at least
two non-melt processible resin particulates by dry blending and
molding the mixture by compression molding. Another aspect of the
invention is a resin blend comprising at least two blended,
non-melt processible polyimide resin particulates, wherein the at
least two blended, non-melt processible polyimide resin
particulates are molded by compression molding.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Applicants specifically incorporate the entire content of
all cited references in this disclosure. Where a range of numerical
values is recited herein, unless otherwise stated, the range is
intended to include the endpoints thereof, and all integers and
fractions within the range. It is not intended that the scope of
the invention be limited to the specific values recited when
defining a range.
[0013] In the context of this disclosure, a number of terms shall
be utilized.
[0014] The term "compression molding" as used herein means a method
for preparing parts from a polymer or polymeric mixture by the
application of both heat and pressure whereby the polymer is not
melted. The application of heat and pressure can be simultaneous or
sequential. Methods of compression molding include direct forming
and sintering, isostatic molding, and other methods known to one of
ordinary skill in the art.
[0015] The term "dry blending" as used herein means the process by
which two or more particulate resins are thoroughly mixed while
maintaining the integrity of the individual particles and without
benefit of an additional material such as a solvent to aid in the
processing. A "dry blend" is thus a resultant mixture of a dry
blending process.
[0016] The term "resin particulate" as used herein means polymers,
optionally comprising encapsulated filler, with an average particle
size of from about 5 .mu.m to about 500 .mu.m. Preferably, the
resin particulate has an average particle size of from about 20
.mu.m to about 400 .mu.m. More preferably, the resin particulate
has an average particle size of from about 30 .mu.m to about 300
.mu.m. Average particle size can be determined by methods such as
an aqueous slurry using a Coulter Multisizer.
[0017] The term "moisture pickup" means the weight percent of water
absorbed by a tensile bar after immersion in water for two weeks at
room temperature. Thus, the "expected moisture pickup" for a resin
blend is the amount of weight gain predicted from calculating the
weighted average of the moisture pickups of two or more tensile
bars prepared from each of the individual base resins used to
prepare the blend.
[0018] The present invention relates to a resin blend comprising at
least two dry blended, non-melt processible resin particulates,
wherein the at least two dry blended resin particulates are molded
by compression molding. Another aspect of the invention is a
compression molded article comprising the resin blend.
[0019] It was unexpectedly discovered that dry blending followed by
compression molding of non-melt processible resin particulates
resulted in reduced moisture pickup of the resin blend compared to
that expected from the weighted average of the moisture pickup of
the individual resin particulates. Improvements in moisture pickup
of up to 55% below expected values in compression molded articles
comprising the resin blends have been observed.
[0020] A desirable group of polymers suitable for use in the
present invention are those that retain excellent mechanical
properties at high temperatures. Polymers in this group, however,
often melt at very high temperatures or decompose without melting.
In addition, their viscosities in the melt phase are extremely
high. Therefore, these polymers are considered to be intractable,
that is, non-melt processible. Thus, forming these polymers into
shaped articles is expensive at best and impossible in many
cases.
[0021] For example, nylons of hexamethylene diamine and
terephthalic acid exhibit excellent temperature resistance but
cannot be melt-spun or molded because they decompose before their
crystalline melting temperatures are reached. Likewise, many other
wholly aromatic polymers such as polyimides of pyromellitic
anyhydride and aromatic diamines cannot be melt processed. Powder
processing and sintering techniques have been used to process such
intractable polymers into useable articles.
[0022] Thus, in the context of the present invention, "non-melt
processible" refers to resin particulates that either have a
melting transition temperature ("T.sub.m") of at least 400.degree.
C. in the case of resin particulates that have a discernable
melting point or have no discernable melting point but are stable
in temperatures up to at least 400.degree. C.
[0023] The resin particulate is derived from a base polymer that is
non-melt processible. The base polymer is preferably an organic
polymer and is more preferably a synthetic polymer that is prepared
in a polymerization reaction. The base polymer can be, for example,
a polyimide, a polybenzoxazole, a polybenzimidazole, a polyaramide,
a polyarylene, a polyether sulfone, a polyarylene sulfide, a
polyimidothioether, a polyoxamide, a polyimine, a polysulfonamide,
a polysulfonimide, a polyimidine, a polypyrazole, a polyisoxazole,
a polythiazole, a polybenzothiazole, a polyoxadiazole, a
polytriazole, a polytriazoline, a polytetrazole, a polyquinoline, a
polyanthrazoline, a polypyrazine, a polyquinoxaline, a
polyquinoxalone, a polyquinazolone, a polytriazine, a
polytetrazine, a polythiazone, a polypyrrone, a polyphenanthroline,
a polycarbosilane, a polysiloxane, a polyamideimide, or copolymers
or blends thereof.
[0024] Preferably, at least one of the dry blended resin
particulates is a polyimide resin particulate. More preferably, at
least two of the dry blended resin particulates are polyimide resin
particulates. Even more preferably, all of the dry blended resin
particulates are polyimide particulate resins.
[0025] In embodiments wherein at least two of the resin
particulates are polyimide resin particulates, the invention
provides for a resin blend comprising at least two blended,
non-melt processible polyimide particulates, wherein the at least
two blended, non-melt processible polyimide particulates are molded
by compression molding. Resin blends of these polyimide embodiments
can optionally contain water and/or additional solvents as known to
one of ordinary skill in the art and are thus not necessarily a dry
blend. In these polyimide embodiments, water and/or additional
solvents can be added in amounts as is necessary to produce
functional blends.
[0026] The polyimide contains the characteristic --CO--NR--CO--
group as a linear or heterocyclic unit along the main chain of the
polymer backbone. The polyimide can be obtained, for example, from
the reaction of monomers such as an organic tetracarboxylic acid,
or the corresponding anhydride or ester derivative thereof, with an
aliphatic or aromatic diamine.
[0027] A polyimide precursor as used to prepare a polyimide is an
organic polymer that becomes the corresponding polyimide when the
polyimide precursor is heated or chemically treated. In certain
embodiments of the thus-obtained polyimide, about 60 to 100 mole
percent, preferably about 70 mole percent or more, more preferably
about 80 mole percent or more, of the repeating units of the
polymer chain thereof has a polyimide structure as represented, for
example, by the following formula: 1
[0028] wherein R.sub.1 is a tetravalent aromatic radical having 1
to 5 benzenoid-unsaturated rings of 6 carbon atoms, the four
carbonyl groups being directly bonded to different carbon atoms in
a benzene ring of the R.sub.1 radical and each pair of carbonyl
groups being bonded to adjacent carbon atoms in the benzene ring of
the R.sub.1 radical; and R.sub.2 is a divalent aromatic radical
having 1 to 5 benzenoid-unsaturated rings of carbon atoms, the two
amino groups being directly bonded to different carbon atoms in the
benzene ring of the R.sub.2 radical.
[0029] Preferred polyimide precursors are aromatic, and provide,
when imidized, polyimides in which a benzene ring of an aromatic
compound is directly bonded to the imide group. An especially
preferred polyimide precursor includes a polyamic acid having a
repeating unit represented, for example, by the following general
formula, wherein the polyamic acid can be either a homopolymer or
copolymer of two or more of the repeating units: 2
[0030] wherein R.sub.3 is a tetravalent aromatic radical having 1
to 5 benzenoid-unsaturated rings of 6 carbon atoms, the four
carbonyl groups being directly bonded to different carbon atoms in
a benzene ring of the R.sub.3 radical and each pair of carbonyl
groups being bonded to adjacent carbon atoms in the benzene ring of
the R.sub.3 radical; and R.sub.4 is a divalent aromatic radical
having 1 to 5 benzenoid-unsaturated rings of carbon atoms, the two
amino groups being directly bonded to different carbon atoms in the
benzene ring of the R.sub.4 radical.
[0031] Typical examples of a polyamic acid having a repeating unit
represented by the general formula above are those obtained from
pyromellitic dianhydride ("PMDA") and diaminodiphenyl ether ("ODA")
and 3,3',4,4'-biphenyltetracarboxylic dianhydride ("BPDA") and ODA.
When subjected to ring closure, the former becomes
poly(4,4'-oxydiphenylenepyr- omellitimide) and the latter becomes
poly(4,4'-oxydiphenylene-3,3',4,4'-bi- phenyltetracarboxy
imide).
[0032] A typical example of a polyimide prepared by a solution
imidization process is a rigid, aromatic polyimide composition
having the recurring unit: 3
[0033] wherein R.sub.5 is greater than 60 to about 85 mole percent
paraphenylene diamine ("PPD") units and about 15 to less than 40
mole percent metaphenylene diamine ("MPD") units.
[0034] The tetracarboxylic acids preferably employed in the
practice of the 5 invention, or those from which derivatives useful
in the practice of this invention can be prepared, are those having
the general formula: 4
[0035] wherein A is a tetravalent organic group and R.sub.6 to
R.sub.9, inclusive, comprise hydrogen or a lower alkyl, and
preferably methyl, ethyl, or propyl. The tetravalent organic group
A preferably has one of the following structures: 5
[0036] wherein X comprises at least one of 6
[0037] --O--, --S--, --SO.sub.2--, --CH.sub.2--,
--CH.sub.2CH.sub.2--, 7
[0038] As the aromatic tetracarboxylic acid component, there can be
mentioned aromatic tetracarboxylic acids, acid anhydrides thereof,
salts thereof and esters thereof. Examples of the aromatic
tetracarboxylic acids include 3,3',4,4'-biphenyltetracarboxylic
acid, 2,3,3',4'-biphenyltetracarboxylic acid, pyromellitic acid,
3,3',4,4'-benzophenonetetracarboxylic acid,
2,2-bis(3,4-dicarboxyphenyl)p- ropane,
bis(3,4-dicarboxyphenyl)methane, bis(3,4-dicarboxyphenyl)ether,
bis(3,4-dicarboxyphenyl)thioether,
bis(3,4-dicarboxyphenyl)phosphine,
2,2-bis(3',4'-dicarboxyphenyl)hexafluoropropane, and
bis(3,4-dicarboxyphenyl)sulfone.
[0039] These aromatic tetracarboxylic acids can be employed singly
or in combination. Preferred is an aromatic tetracarboxylic
dianhydride, and particularly preferred are
3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic
dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and
mixtures thereof.
[0040] As an organic aromatic diamine, use is preferably made of
one or more aromatic and/or heterocyclic diamines, which are
themselves known to the art. Such aromatic diamines can be
represented by the structure: H.sub.2N--R.sub.10--NH.sub.2, wherein
R.sub.10 is an aromatic group containing up to 16 carbon atoms and,
optionally, containing up to one hetero atom in the ring, the
hetero atom comprising --N--, --O--, or --S--. Also included herein
are those R.sub.10 groups wherein R.sub.10 is a diphenylene group
or a diphenylmethane group. Representative of such diamines are
2,6-diaminopyridine, 3,5-diaminopyridine, meta-phenylene diamine,
para-phenylene diamine, p,p'-methylene dianiline, 2,6-diamino
toluene, and 2,4-diamino toluene.
[0041] Other examples of the aromatic diamine components, which are
merely illustrative, include benzene diamines such as
1,4-diaminobenzene, 1,3-diaminobenzene, and 1,2-diaminobenzene;
diphenyl(thio)ether diamines such as 4,4'-diaminodiphenylether,
3,4'-diaminodiphenylether, 3,3'-diaminodiphenylether, and
4,4'-diaminodiphenylthioether; benzophenone diamines such as
3,3'-diaminobenzophenone and 4,4'-diaminobenzophenone;
diphenylphosphine diamines such as 3,3'-diaminodiphenylphosphine
and 4,4'-diaminodiphenylphosphine; diphenylalkylene diamines such
as 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane,
3,3'-diaminodiphenylpropane, and 4,4'-diaminodiphenylpropane;
diphenylsulfide diamines such as 3,3'-diaminodiphenylsulfide and
4,4'-diaminodiphenylsulfide; diphenylsulfone diamines such as
3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone; and
benzidines such as benzidine and 3,3'-dimethylbenzidine.
[0042] Other useful diamines have at least one non-heteroatom
containing aromatic rings or at least two aromatic rings bridged by
a functional group.
[0043] These aromatic diamines can be employed singly or in
combination. Preferably employed as the aromatic diamine component
are 1,4-diaminobenzene, 1,3-diaminobenzene,
4,4'-diaminodiphenylether, and mixtures thereof.
[0044] A polyamic acid can be obtained by polymerizing an aromatic
diamine component and an aromatic tetracarboxylic acid component
preferably in substantially equimolar amounts in an organic polar
solvent. The amount of all monomers in the solvent can be in the
range of about 5 to about 40 weight percent, more preferably in the
range of about 6 to about 35 weight percent, and most preferably in
the range of about 8 to about 30 weight percent. The temperature
for the reaction generally is not higher than about 100.degree. C.,
preferably in the range of about 10.degree. C. to 80.degree. C. The
time for the polymerization reaction generally is in the range of
about 0.2 to 60 hours.
[0045] The process by which a polyimide is prepared can also vary
according to the identity of the monomers from which the polymer is
made up. For example, when an aliphatic diamine and a
tetracarboxylic acid are polymerized, the monomers form a complex
salt at ambient temperature. Heating of such a reaction mixture at
a moderate temperature of about 100 to about 150.degree. C. yields
low molecular weight oligomers (for example, a polyamic acid), and
these oligomers can, in turn, be transformed into higher molecular
weight polymer by further heating at an elevated temperature of
about 240 to about 350.degree. C. When a dianhydride is used as a
monomer instead of a tetracarboxylic acid, a solvent such as
dimethylacetamide or N-methylpyrrolidinone is typically added to
the system. An aliphatic diamine and dianhydride also form
oligomers at ambient temperature, and subsequent heating at about
150 to about 200.degree. C. drives off the solvent and yields the
corresponding polyimide.
[0046] As an alternative to the use of an aliphatic diamine and/or
an aliphatic diacid or dianhydride, as described above, an aromatic
diamine is typically polymerized with a dianhydride in preference
to a tetracarboxylic acid, and in such a reaction a catalyst is
frequently used in addition to a solvent. A nitrogen-containing
base, phenol, or amphoteric material can be used as such a
catalyst. Longer periods of heating can be needed to polymerize an
aromatic diamine.
[0047] The ring closure can also be effected by conventionally used
methods such as a heat treatment or a process in which a
cyclization agent such as pyridine and acetic anhydride, picoline
and acetic anhydride, 2,6-lutidine and acetic anhydride, or the
like is used.
[0048] In the formation of a polyetherimide from a bisphenol and a
dinitrobisimide, the bisphenoxide salt of the bisphenol is first
obtained by treatment with caustic soda, followed by an azeotropic
distillation to obtain the anhydrous bisphenoxide salt. Heating the
bisphenoxide salt and the dinitrobisimide at a temperature of about
80 to about 130.degree. C. in a solvent yields the
polyetherimide.
[0049] As the organic polar solvent employable in the
above-described polymerization reaction, there can be mentioned
solvents capable of homogeneously dissolving each monomer of the
aromatic diamine component or the aromatic tetracarboxylic acid
component, an oligomer produced by the monomers or a low-molecular
polyamic acid. Examples of such organic polar solvents include
amide solvents such as N,N-dimethylformamide,
N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam,
pyrrolidone; and dimethylsulfoxide, hexamethylsulfonamide,
dimethylsulfone, tetramethylenesulfone,
dimethyltetramethylenesulfone, pyridine, tetrahydrofuran, and
butyrolactone. These organic polar solvents can be used in
combination with other solvents such as benzene, toluene,
benzonitrile, xylene, solvent naphtha, and dioxane.
[0050] In addition to other methods known in the art, a polyimide
can also be prepared from the reaction of a polyisocyanate and a
dianhydride.
[0051] When only one of the resin particulates is a polyimide resin
particulate, the polyimide resin particulate can be used in the
range of about 5 weight percent to about 95 weight percent and
preferably the polyimide resin particulate can be used in the range
of about 20 weight percent to about 80 weight percent, the
percentages being based on the total weight of all of the resin
particulates in the resin blend.
[0052] When at least two polyimide resin particulates are present,
the polyimide resin particulates in addition to any other resin
particulates present in the blend can be used in any amount as one
of ordinary skill in the art would recognize as being advantageous
for the intended use of the resin blend.
[0053] In an alternative embodiment, a particulate filler and/or a
fibrous filler uniformly dispersed in an organic solvent can be
added to the production system at an appropriate stage from before
the time of the synthesis of the polymeric precursor and, in the
embodiments containing polyimides, through to the time of the
imidization of the polyimide precursor. When fillers encapsulated
in polyimides are desired, the organic solvent that can be used for
uniformly dispersing a particulate filler and/or a fibrous filler
is usually the same as used for the polymerization of the acid
dianhydride and the diamino compound. Although the particulate or
fibrous filler can be added as such, it is preferred that the
filler is sufficiently dispersed in a prescribed amount of such
organic solvent. Addition of the filler in a dispersed state in an
organic solvent can be preferred because the filler previously
wetted with the organic solvent can be uniformly dispersed in the
reaction system and be more easily incorporated into the particle
of the base polymer.
[0054] The filler is typically not added directly to the reaction
system but typically is uniformly dispersed in an organic solvent
in advance and then added to the system. Thus, the filler can
uniformly be dispersed in the reaction system, and, in one
embodiment, a polymeric particle is precipitated around the
dispersed filler.
[0055] In embodiments containing polyimides, the addition of the
organic solvent having uniformly dispersed therein the filler can
be effected at any stage before commencement of imidization of the
polyimide precursor, that is, before precipitation of a polymeric
particle. For example, the uniform filler dispersion can be added
before addition of the acid dianhydride, for example, aromatic
tetracarboxylic acid dianhydride, or the diamino compound, for
example, aromatic diamino compounds, or it can be added to the
polyimide precursor solution prior to imidization.
[0056] Uniform dispersion of the filler in the organic solvent can
be carried out by using a dispersing device, for example a ball
mill, a sand mill, attritor, a three-roll mill, a bead mill, a jet
mill, a vibration mill, a disper, an impeller mill, a flow jet
mixer, a homogenizer, a colloid mill, etc., or a general stirrer,
for example, agitator.
[0057] Suitable fillers include various kinds, such as those
imparting high strength properties to polymeric molded products,
for example, glass fibers, carbon fibers, ceramic fibers, boron
fibers, glass beads, whiskers, or diamond powders; those imparting
heat dissipation properties to polymeric molded products, for
example, alumina or silica; those imparting corona resistance, for
example, natural mica, synthetic mica, or alumina; those imparting
electric conductivity, for example, carbon black, a silver powder,
a copper powder, an aluminum powder, or a nickel powder; or those
imparting heat resistance to polymeric molded products, for
example, aramide fibers, metal fibers, ceramic fibers, whiskers,
silicon carbide, silicon oxide, alumina, a magnesium powder, or a
titanium powder. In addition, a fluorine-containing fine powder,
for example, polytetrafluoroethylene, can be used in order to
reduce a coefficient of friction. These fillers can be used
individually or in combination of two or more thereof.
[0058] When encapsulated fillers are included, the polymeric
component can be present in a range of about 30 weight percent to
about 99 weight percent, the percentages being based on the total
weight of all of the resin particulates in the resin blend.
[0059] The amount of the encapsulated filler to be used can
appropriately be determined depending on characteristics required
for the polymeric products, and usually ranges from about 1 weight
percent to about 70 weight percent, the percentages being based on
the total weight of all of the resin particulates in the resin
blend.
[0060] In an alternative embodiment where fillers are added to the
resin particulates, but are not encapsulated in the resin
particulates, the fillers can be used in a range from about 1 to
about 15 weight percent, the percentages being based on the total
weight of all of the resin particulates in the resin blend. In this
embodiment, polymeric particulates can be used in a range of from
about 85 to about 99 weight percent, the percentages being based on
the total weight of all of the resin particulates in the resin
blend.
[0061] Resin blends resulting from mixtures of resin particulates
comprising both encapsulated and unencapsulated fillers are also
within the scope of the present invention.
[0062] Another aspect of the invention provides for a method of
producing a resin blend comprising mixing at least two non-melt
processible resin particulates. A further aspect of the invention
provides for a method of producing a compression molded article
comprising mixing at least two non-melt processible resin
particulates by dry blending and molding the mixture by compression
molding.
[0063] Suitable blending hardware includes, but is not limited to,
drum rollers, ribbon blenders, v-cone blenders, double cone
blenders, tote bin tumblers, a fluid bed, a Littleford-type mixer,
a Nauta-type blender, a Forberg, a rotating drum with internal
baffles, and gravity fall through static mixer. Other blending
hardware known to one of ordinary skill in the art can also be
used.
[0064] The resin blend can further include other additives that do
not depreciate the overall characteristics of the blend, as would
be evident to one of ordinary skill in the art. For example, a wide
variety of polymer particles, such as those made from any of the
aforementioned base particles, can be blended with the non-melt
processible resin particulates of the invention. Additives, like
the resin particulates of the invention, should be non-melt
processible. Other additives such as antioxidants, heat
stabilizers, ultraviolet absorbers, flame retardants, auxiliary
flame retardants, antistatic agents, lubricants, and coloring
agents can also be added as long as the essential properties of the
blend are not affected.
[0065] Molded articles that demonstrate lower moisture gain offer
benefits. For example, moisture pick-up of a part, that is, a
constituent member of a machine or other apparatus, can alter the
dimensions of the part, impacting the ability to install easily the
component part into an assembly and/or impacting the performance of
the part.
[0066] For example, aircraft bushings can be produced to certain
toleranced dimensions, but after production the bushings can
pick-up moisture in humid environments, causing the dimensions to
change from the die. The inspection of the bushings can be based on
either the saturated state or the dry state. Or, if such states are
not controlled, the resulting capability to maintain a specific
tolerance will be reduced, potentially requiring the design
tolerances of the mating components to be more tightly controlled
for effective functioning of the assembly, impacting costs.
[0067] If inspected while in the saturated state, the bushings can
dry in operation when exposed to high thermal conditions, causing
dimensional change, impacting the clearance between the bushing and
the mating components. Non-optimal clearance can impact bushing
wear life and/or increase actuation torque thereby requiring
heavier actuation systems that can provide more torque to actuate
the system.
[0068] If the bushing is inspected in the dry state, the part can
become saturated during the time between inspection and assembly,
causing dimensional change, potentially causing installation
difficulty if the product is not pre-dried before assembly or
stored in a manner to prevent moisture uptake. The pre-drying step
adds cost as does delays in assembly.
[0069] Another example a use in which low-moisture uptake
properties are advantages is in articles for semiconductor chip
manufacturing. At various testing or processing steps, articles
with very small holes are machined into the article comprising a
resin blend of the invention. The accurate size and position of
these holes within the article is important to the function and
life of the component. Moisture gain during machining or use can
cause either dimensional inaccuracy during machining, leading to
the loss of the machining value, or can cause a dimensional shift
during use of the part leading to ineffective performance of the
article.
[0070] Another example of a material's low-moisture uptake
properties benefiting an article is the material's use in
environments that require low-outgassing.
[0071] These aforementioned examples are meant for illustration
purposes only and are not meant to encompass the only possible
beneficial uses of a low-moisture uptake material.
EXAMPLES
[0072] The present invention is further defined in the following
Examples. It should be understood that these Examples, while
indicating preferred embodiments of the invention, are given by way
of illustration only. From the above discussion and these Examples,
one skilled in the art can ascertain the preferred features of this
invention, and without departing from the spirit and scope thereof,
can make various changes and modifications of the invention to
adapt it to various uses and conditions.
[0073] The meaning of abbreviations is as follows: "min." means
minute(s), "ml" means milliliter(s), "g" means gram(s), "PMDA"
means pyromellitic dianhydride, "ODA" means diaminodiphenyl ether,
"BPDA" means 3,3',4,4'-biphenyltetracarboxylic dianhydride, "BTDA"
means 3,3',4,4'-benzophenone tetracarboxylic dianhydride, "PPD"
means paraphenylene diamine, "MPD" means metaphenylene diamine,
"kpsi" means thousand pounds per square inch, and "wt %" means
weight percent(age).
General Method for Preparation and Testing of Blends
[0074] Resin blends were prepared by placing a total of 30 g of two
of the base resins described in Table 1 in a 250 ml jar. The
mixture was gently tumbled for 5 min. and dried overnight in a
vacuum oven at 150.degree. C. Tensile bars were prepared by the
method set forth in U.S. Pat. No. 4,360,626. Moisture pickup
studies were conducted by immersing dried tensile bars in water at
room temperature and measuring the change in weight after two
weeks. Tensile bars comprising resin blends and tensile bars
comprising the individual base resins used to prepare the resin
blends were tested simultaneously.
1TABLE 1 mole %/ Additive % Moisture Description Dianhydride
Diamine wt % Pickup Base Resin 1 BPDA 70% PPD none 0.57 30% MPD
Base Resin 2 BPDA 70% PPD none 0.47 30% MPD Base Resin 3 BPDA 70%
PPD graphite 9% 0.60 30% MPD kaolinite 1% Base Resin 4 BPDA 70% PPD
graphite 50% 0.29 30% MPD Base Resin 5 BTDA ODA none 2.97 Base
Resin 6 PMDA ODA none 2.19 Base Resin 7 PMDA ODA none 2.59 Base
Resin 8 PMDA ODA none 2.51 Base Resin 9 PMDA ODA graphite 15% 1.91
Base Resin 10 PMDA ODA graphite 15% 1.74 Base Resin 11 PMDA ODA
graphite 15% 2.00 Base Resin 12 PMDA ODA graphite 65% 0.64 Base
Resin 13 PMDA ODA graphite 10% 3.54 Base Resin 14 BPDA PPD graphite
2.5% 0.39 Base Resin 15 BPDA PPD graphite 2.5% 0.34 Base Resin 16
BPDA PPD graphite 2.5% 1.47
Examples 1-15
[0075] As shown in Table 2, all resin blends exhibited reduced
moisture pickup.
2TABLE 2 % Moisture % Moisture Pickup Example Component A wt %
Component B wt % Pickup (actual) (expected) 1 Base Resin 1 75 Base
Resin 6 25 0.75 0.98 2 Base Resin 1 50 Base Resin 6 50 1.18 1.38 3
Base Resin 1 25 Base Resin 6 75 1.53 1.78 4 Base Resin 9 75 Base
Resin 3 25 1.48 1.55 5 Base Resin 9 50 Base Resin 3 50 1.17 1.26 6
Base Resin 9 25 Base Resin 3 75 0.85 0.93 7 Base Resin 2 75 Base
Resin 8 25 0.69 1.10 8 Base Resin 2 50 Base Resin 8 50 1.19 1.53 9
Base Resin 2 25 Base Resin 8 75 1.83 2.09 10 Base Resin 14 50 Base
Resin 13 50 0.88 1.97 11 Base Resin 15 50 Base Resin 10 50 0.77
1.04 12 Base Resin 7 50 Base Resin 5 50 2.52 2.74 13 Base Resin 11
50 Base Resin 16 50 1.61 1.74 14 Base Resin 4 60 Base Resin 12 40
0.41 0.43 15 Base Resin 4 40 Base Resin 12 60 0.47 0.50
* * * * *