Note: Descriptions are shown in the official language in which they were submitted.
This. invention relates to thermoplastic shapeable compositions
and to an improved process for preparing shaped articles from
thermoplastic resin compositions.
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Shapeable thermoplastic resin comp,ositions made from
: , condensation polymers generally have excellent physical
, properties and in particular have outstanding thermal stability
I due to their ~enerally high melting points and dimensional
stability due to their low moisture absorption. These
properties permit the use of thermoplastic resin compositions,
, such as those made from crystalline polyethylene teraphthalate,
; for high temperature meohanical applications requiring close
`~ tolerances; for example, for electrical applioations and for
, load bear1ng gears.
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While such compositions do have certain desirable properties
such compositions, in particular those made from, for instance,
polyethylene terephthalate, crystallize slowly from the melt,
which has limited the use of such polymers for articles formed
; by injection molding equipment; further, shaped articles such
as molded articles made from polyethylene terephthalate have
internal stresses in part caused by non-uniform spherulite
growth and longer crystallization times. This confers low
~ ductility and low impact resistance to low or high molecular
weight resin compositions.
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The addition of nucleating agents to thermoplastic resin
compositions generally reduces crystallization time by
providing a large number of sites which initiate crystal
formation. A suitable nucleating agent must promote rapid
crystallization under conditions of rapid cooling from the
melt, such as occurs in injection molding. Since
crystallization is dependent upon polymer chain mobility, the
molecular weight of the polymer is also a factor in
crystallization, and higher molecular weight, long chain
polymers will have a longer induction time than lower molecular
weight polymers. Thus, a nucleating agent which is in the
liquid phase and is hence readily dispersible in molten
; themoplastic resin compositions and which is highly effective
at low concentrations to promote crystal formation in such
; resin coFpositions is highly desirable. Such nucleating agent
` should function to increase molding rates and to reduce
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internal stresses in the formed articles, thereby improving
their physical characteristics such as, for instance, impact
strength.
~ It is known that certain materials in combination with finely
S divided solid metals, metal oxides, or metal salts promote the
crystallization of themoplastic resin compositions such as
polyethylene terephthalate. For example, one commercial
thermoplastic polyethylene terephthalate molding composition
contains benzophenone and talc as nucleating agents However,
nucleating agents which contain non-melting solids present
problems of incorporation into the molten polymer and are
difficult to disperse uniformly in the polymer.
It, therefore, would be highly desirable to provide
thermoplastic resin compositions substantially free of olefinic
~ unsaturation made from condensation polymers such as
polyethylene terephthalate which are suitable for making into a
shaped article. It would also be highly desirable to provide
nucleating agents for thermoplastic resin compositions which
are readily dispersible and which have improved crystallization
properties.
Accordingly, it has been found that a shapeable resin I
composition which consists essentially of a thermoplastic
condensation polymer substantially free of olefinic
unsaturation, such as polyethylene terephthalate, other
polyesters and polyamides may be provided which contain a minor
effective amount suffioient to improve orystallization
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properties, e.g., from about .01 to about 2 percent by weight,
of a cyclic acetal as a nucleating agent, said cyclic acetal
being at least one member selected from the polyhydric alcohol
acetals of benezaldehyde or its nucleically substituted
derivatives, said polyhydric alcohols having 5 to 7 hydroxyl
groups. Such compositions exhibit generally improved
crystallization properties and provide products having improved
physical characteristics.
In the molecular structures of the cyclic acetal compounds
defined above, the alcohol portion which is acetalized by
unsubstituted or substituted benzaldehyde preferably is a
sugar alcohol of the formula, HOCH2(CHOH)nCH2OH, wherein n
is 3 to 5, preferably 3 to 4, such as xylitol, sorbitol or
; mannitol. Preferable as the ring substituents for benzalde-
hyde are halogen~ alkyl groups~with one to eight carbon
atoms and preferably with one to four carbon atoms, alkoxyl
groups with one to eight carbon atoms and preferably with one
to four carbon atoms~
As is clear from the foregoing, preferable cyclic acetals
usable as a nucleating agent according to the present inven-
tion are sugar alcohol acetals of benzaldehyde which may be
ring substituted, said sugar alcohol having the formula,
HOCH2(CHOH)nCH2OH, wherein n is 3 to 5, preferably 3 to 4.
A number of examples are given below.
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Dibenzylidene-xylitol (= xylitol acetal of benzaldehyde),
dibenzylidene-sorbitol (= sorbitol acetal of benzaldehyde) and
dibenzylidene-mannitol (= mannitol acetal of benzaldehyde), as
well as their derivatives wherein the benzene nucleus in eitner
one or both of two benzylidene moieties has been substituted
with chlorine, bromine, an alkyl group (e.g. methyl, ethyl,
propyl, isopropyl, n-butyl, isobutyl, sec-butyl, octyl, etc.)
and/or an alkoxy group (e.g. methoxy, ethoxy, n-propoxy;
isopropoxy, butoxy, octoxy, etc.)
One of these typical cyclic acetals has the following chemical
structures:
-HC HC - O
- CH CH-
HC - O
HCOH
H2COH
1,3;2,4-dibenzylidene-sorbitol (1,3;2,4 sorbitol acetal of
benzaldehyde).
In the above-mentioned cyclic acetal compound, the alcohol
portion thereof is sorbitol, and the aldehyde portion thereof
is benzaldehyde.
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The cyclic acetals of the present invention can be prepared in
any method which per se is known for the preparation of
acetals. Such method is described, for example, in
Kirk-Othmer, "Encyclopedia of Chemical Technology," Vol. 1,
pages 579 and 580.
Dibenzylidene sorbitol (DBS), the preferred nucleating agent
for thermoplastic resin compositions according to the present
invention, is known as a gelling agent for organic liquids (U.
S. Patent 3,880,794 and as a flocculating agent (U. S. Patent
3,872,000) and as a modifier for polyolefin resins (U. S.
Patent 4,016,118). The compound may be prepared in a crude
form, e.g., containing about 75 percent DBS and about 25
percent tribenzylidene sorbitol (TBS) by reacting d-sorbitol
with a molar excess of benzaldehyde in water or certain organic
liquids as a reaction medium in the presence of an acid
catalyst at an elevated temperature to perform
dehydrocondensation (U. S. Patent 3,721,6a2). The crude DBS
formed by this reaction may be further puri~ied by mixing with
a lower aliphatic alcohol to dissolve the impurities,
separating and recovering the undissolved DBS (U. S. Patent
4,131,612). According to the present invention, however,
either crude or purified DBS may be used as a nucleating agent
for thermoplastic resin compositions. For instance, it has
been found that compositions containing about 75 percent DBS
and about 25 percent TBS are very useful and frequently more
convenient to use.
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According to the present invention cyclic acetal nucleating
agent may be added to the thermoplastic resin composition in
amounts which are effective to nucleate the resin composition.
Generally, the amount of cyclic acetal nucleating agent which
may be added may be from about 0.01 to about 2 percent,
preferably from about 0.1 to about 1 percent by weight of the
thermoplastic resin. At least about 0.01 percent of nucleat-
ing agent will be required to significantly reduce crystal-
lization induction times in the resin, whereas when more than
about 2 percent is added little additional nucleating effect
is noted. Large amounts, in excess of about 10 percent by
weight, may have an adverse effect on the properties of
the resin product.
The cyclic acetal nucleating agent of the present in~ention
lS should be dispersed uniformly throughout the thermoplastic
resin in order to obtain the benefits of the present inven-
tion. Molten thermoplastic resin and the nucleating agent
may be simply mixed together until a good dispersion is
obtained. Generally at temperatures at which the resin is
molten the nucleating agent will melt and be incorporated
uniformly into the resin as a liquid which is desirable.
While the compositions of the present invention are
particularly suitable for shaping in injection molding
equipment, they can also be extruded through a suitable die
2, to form sheets, tubes, rods, fibers, films and the like and
they can be cast to form film and sheet.
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As mentioned, it has been found that cyclic acetals may be used
to nucleate thermoplastic resin compositions made from
condensation polymers as the predominate polymeric component.
As used herein, the term "thermoplastic resin composition" is
meant to include those thermoplastic resin compositions which
are shapeable and which are made from condensation polymers.
I The condensation polymers furthermore are substantially free of
olefinic unsaturation and are not to be confused with
unsaturated polyester resins of the type disclosed by Murai et
~- al. in U. S. 3,767,729. As disclosed by Murai, his unsaturated
polyester resin compositions are prepared by dissolving an
I unsaturated polyester in a vinyl monomer. The unsaturated
; polyester is produced by a condensation reaction of polyhydric
alcohols with ~,~-unsaturated polybasic acids or with a mixture
, of such acids and other polybasic acids. Thus, the Murai
polyesters are unsaturated and may be thermoset by means of
cross-linking. By contrast the thermoplastic resin
compositions of the present invention contain substantially no
olefinic unsaturation and thus they are thermoplastic resins.
,I Such polymers of the present invention may include homopolymers
ii of polyethylene terephthalate, copolymers of polyethylene
terephthalate such as copolymers containing up to about 20
percent of a polyester prepared from an aromatic dicarboxylic
, acid other than terephthalic acid such as isophthalic acid, or
I' from an alkylene glycol other than ethylene glycol such as
propylene glycol. Such polymers further include blends of
homopolymers and/or copolymers, such as blends of polyethylene
; ,, terephthalate and polybutylene terephthalate. Other
,
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condensation polymers include, for instance, other polyesters,
polyamides, polycarbonates and polyacetals, etc. Generally,
thermoplastic resin compositions useful for making shaped
articles have an intrinsic viscosity of from about 0.1 to 5,
r! preferably 0.4 to 2, e.g., about 0.6 to about 1.6.
In addition to the dibenzylidene sorbitol nucleating agent, the
thermoplastic resin composition of the present invention may
also contain conventional fillers, pigments, mold release
agents, reinforcing agents such as, for instance, fiber glass
and the like. Even more importantly, the composition may
further include a minor effective amount, e.g., from about 0.1
to about 10 percent by weight of a pl~sticizer, such as esters
of dicarboxylic acids, e.g., phthalic, adipic, sebacic acids;
esters, based on glycols such as ethylene glycol, butylene
glycol and an appropriate carboxylic acid; tricresyl phosphate;
and the like.
The shaped articles formed from the compositions of the present
invention may be further treated, as by heating below the
polymer melting point at from about 80-150C, which may further
improve the physical properties of the shaped article such as
impact resistance and ductility.
The invention may be further illustrated by reference to the
following examples, although the invention is not to be limited
to the details described therein. In the examples, a]l parts
and percentages are by weight unless otherwise indicated. `~
_g_
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In the examples, unless otherwise indicated, viscosity was
determined from solutions of the resin composition in a mixture
of equal parts by volume of sym~tetrachloroethane and phenol.
Intrinsic viscosity data were obtained by extrapolation of the
r inear plot of the ratio of specific viscosity to concentration
against concentration of the polymer in solution. Viscosities
of the solvent and solutions were measured at 25 C in a water
bath using the Canon-Ubbelhode Dilution Viscometer.
E AMPLE I
Commercially available polyethylene terephthalate resin pellets
(A) having an intrinsic viscosity of .94 were ground into a
fine powder, heated to about 100C in a glass jar. Then 0.5%
by weight dibenzylidene sorbitol was added, and the powder was
mixed thoroughly in a paint shaker. After mixing, the powder
was dried thoroughly at 120C under vacuum conditions for about
24 hours. The mixture was then made into a thin film of from
about 3 to 5 Mils t10 3 in.) in thickness by compression
molding under a nitrogen atmosphere at a temperature of between
280-290C.
EXAMPLE 1l
Example I was repeated except that the commercially available
terephthalate resin, pellets B, used had an intrinsic viscosity '
of 0.60, as disclosed by the manufacturer.
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EXAM_LE III
Example I was again repeated except that the resin employed was
polybutylene terephthalate resin pellets (Eastman PBT 6 PR0).
EXAMPLE IV
Polyethylene terephthalate resin pellets C havinB an intrinsic
viscosity Or .71 were ground into a fine powder, heated to a
- temperature of about 100C in a glass jar and .5 percent by
weight dibenzylidene sorbitol was added. The mixture was mixed
thoroughly in a paint shaker and dried in a vacuum oven at
120 C for about 24 hours.
EXAMPLE V
*
A sample of Rynite resin, a polyethylene terephthalate molding
resin available from DuPont Corporation, was mixed with
dibenzylidene sorbitol according to the procedure set forth in
Example IV.
EXAMPLE VI
Commercially available Nylon 6 resin pellets were ground into
a fine powder, heated to about 100C in a glass jar. Then, 0.5
percent by weight dibenzylidene sorbitol was added, and the
powder was mixed thoroughly in a paint shaker. After mixing,
the powder was dried thoroughly at 120C under vacuum
conditions for about 24 hours. The mixture was then made into
* Trademark -11-
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a thin film of from about 3 to 5 Mils (10 3 in.) in thickness
by compression molding under a nitrogen atmosphere at a
temperature of between 250-270 C.
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ThlJs, as khe Table illustrates addition of dibenzylidene
sorbitol to thermoplastic resin compositions promotes faster
crystallization than was observed for the same therrnoplastic
resin compositions containing no dibenzylidene sorbitol.
Furthermore, photomicrographs taken of the film products reveal
that the spherulite crystals in the thermoplastic resin
composlt.ions used in the Examples wherein dibenzylidene
sorbitol has been added to the composition generally are much
more uniform and are about half the size of the crystals
observed in the control samples of the resin without any
dibenzylidene sorbitol nucleating agent having been added.
