Process for the production of a polymer alloy

A process for the production of moldings from a polymer alloy of multiphase morphology, in which the polymer alloy is prepared with the injection molding in one process step. For this, thermoplastically processable polymers which are incompatible or not very compatible with one another are introduced as granules, preferably having a particle size of greater than or equal to 3 mm, into the hopper of an injection molding machine and are subsequently plasticized, mixed thoroughly, and shaped in the injection molding machine; where at least one of the polymers employed is capable chemically, under the injection molding conditions, of association and/or copolymerization with at least one other of the participating polymers. The resulting polymer alloys are not inferior in their properties to corresponding conventionally produced alloys. The moldings are useful in orthopedics.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a process for the preparation of a polymer alloy
 having multiphase morphology, that includes intimately mixing
 thermoplastically processable polymers, which are incompatible or not very
 compatible, in the melt. The invention furthermore relates to a molding
 produced by this process and the use of such moldings.
 2. Description of Related Art
 The modification of polymeric materials in an injection molding machine by
 addition of additives such as dyestuffs or stabilizers, either directly or
 in masterbatch systems, is known.
 U.S. Pat. No. 5,130,076 describes a process for distributing small amounts
 of an incompatible thermoplastic in finely dispersed form in a
 thermoplastic matrix that is the main constituent of a polymer blend, by
 introduction of shear energy such that the incompatibility of the plastics
 does not lead to a reduction in the mechanical properties. This process is
 particularly suitable for modification of elastomers, for example,
 recycled plastic. However, relatively high concentrations of the second
 blend partner cannot be achieved, since the incompatibility of the
 components would lead to a decrease in the mechanical properties.
 Furthermore, at a high concentration of the incompatible blend polymer,
 agglomeration and thus phase separation are to be expected during the
 mold-filling phase, regardless of the mechanical shear energy introduced.
 This leads to a laminar phase structure. Furthermore, the phase separation
 causes non-uniform material properties in the molding. This process
 therefore allows only the preparation of polymer alloys comprising a
 matrix component and not more than 25% of an incompatible modifying
 component. Many alloys of industrial interest are therefore not accessible
 by this process.
 DE 44 43 153 describes a process for the preparation of polymer blends in
 which the components are initially introduced into the apparatus as a
 powder mixture, and part of the mixing function of the actual processing
 by injection molding is thus carried out beforehand. The advantage of this
 process lies in the lower exposure to shear and therefore lesser damage to
 the components. This effect is particularly advantageous in the production
 of light-colored moldings. However, this process proves to be expensive if
 the components are present not as a powder but as granules after the
 polymerization. Such plastics must first be ground, during which
 thermo-mechanical damage may occur. To reduce this damage, for example,
 the plastics can be cooled with liquid nitrogen, but this increases the
 costs for preparation of the powder.
 The difficult flow properties of mixtures of plastics powders in the hopper
 of the injection molding machine also proves to be a disadvantage. For
 example, if the two components have different particle sizes, demixing may
 occur, the consequence of which is non-uniform properties in the moldings.
 A stirrer in the hopper of the injection molding machine prevents demixing
 effects and also bridging. However, due to the friction of the particles
 of the plastics against one another caused by the stirrer, electrical
 charging may occur, which differs in degree in the various components of
 the plastics, depending on the electrical conductivity, and can thus lead
 to different feed properties. Furthermore, such a stirrer increases the
 overall costs of the process.
 Moreover, cleaning work during storage and transportation of powders of
 plastics, for example when changing materials, are expensive.
 SUMMARY OF THE INVENTION
 One aim of the present invention is to obtain a polymer alloy by injection
 moldings having a morphology as finely dispersed as possible with a
 process of the above-mentioned type. As a result, rough and corrugated
 surfaces of the moldings and streaking or graining, which may impair the
 mechanical, dynamic and processing-specific properties, such as, for
 example, the melt elasticity, are reduced or prevented. The influence of
 the morphology and therefore of the preparation conditions on the
 properties of the alloys are described in W. Becker; D. Braun: "Kunststoff
 Handbuch 3/2 Technische Polymerblends" [Plastics Handbook 3/2 Industrial
 Polymerblends] (Carl Hanser Verlag Munich Vienna 1993, pages 219, 220).
 The invention is therefore based on the object of eliminating the
 disadvantages described above which still exist in the prior art in
 processes for the preparation of polymer alloys in combination with
 processing by injection molding.
 Therefore, it is an object of the present invention to provide a process
 for providing moldings of polymer alloys without the disadvantages of
 prior processes.
 It is also an object of the invention to provide moldings produced by such
 methods and methods of using such moldings.
 In accordance with these objectives, according to the present invention,
 there is provided a process for the production of a polymer alloy which
 includes introducing granules of at least two types of thermo-plastically
 processable polymers, which are incompatible or not very compatible, into
 the hopper of an injection molding machine, plasticizing, mixing, and
 shaping the polymers in the injection molding machine, to form a polymer
 alloy of multiphase morphology, wherein at least one of the polymers has
 one or more functional groups or chain ends which are capable of
 association, rearrangement, or other chemical reaction with at least one
 other polymer of the alloy, so that during the injection molding,
 association or block copolymer formation occurs between at least a portion
 of the polymers employed. All polymers rendering a blend, when physically
 mixed in the molten phase, the mechanical properties like tensile
 strength, elongation at break, modulus of elasticity etc. of which are not
 as good as the properties of the respective polymers, are regarded as "not
 compatible" or "not very compatible".
 In accordance with these objectives, there is also provided moldings
 produced by the process and method of using the moldings.
 Further objects, features, and advantages of the present invention will
 become apparent from the detailed description that follows.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 The process according to the invention includes introducing the
 thermoplastically processable polymers as granules in any desired ratio
 (for example see Alloy Mixtures I to III) into the hopper of an injection
 molding machine, and subsequently plasticizing, thoroughly mixing, and
 shaping them in the injection molding machine. At least one of the
 polymers of the alloy to be formed has functional groups or chain ends
 which are capable of association, rearrangement, or other chemical
 reaction with at least one other polymer of the alloy, so that under the
 injection molding conditions, association and/or additional block
 copolymer formation between the polymers employed as alloy constituents
 takes place at least to a certain extent.
 As a result of the present invention, it is possible to prepare polymer
 alloys with specifically tailored properties, such as, for example,
 particular resistance to chemicals or stress cracking, dynamic tear
 strength, yield stress, elongation at break, impact strength, dimensional
 stability, flow properties of the polymer melt, or processing temperature
 range or shrinkage, for the particular desired molding, directly from
 polymer granules in practically any desired mixing ratios. Materials
 adapted to the optimum are also made available in this manner for
 industrially high-performance products, with a low material requirement.
 It has been found, surprisingly, that the polymers can be employed in any
 ratio with respect to one another and as granules, i.e., even having a
 particle size, i.e. an average particle diameter of '3-25 mm (preferable
 3-12 mm), if the polymers have functional groups which allow association,
 rearrangement, or other chemical reaction among the constituents of the
 alloy.
 Under the injection molding conditions, association and/or additional block
 copolymer formation then takes place--at least to a certain
 extent--between the polymers employed as alloy constituents, as a result
 of which the adhesion of the composite phases in the polymer alloy is
 optimized and the formation of mixed phases is assisted.
 Association in the context of this invention can be, for example, ionic
 association, which causes cross-linking between the various polymer
 components. An example of such crosslinking would be the association
 between a polyamide and a carboxyl ionomer:
 ##STR1##
 In particular, the function al groups can be, for example, ester, amide,
 urethane, or anhydride functions. The polymers employed as granules can
 themselves already be copolymers, preferably block copolymers, or one
 component can be a copolymer.
 To provide ester functions, for example, the following ester-containing
 polymers can be employed individually or in combination: polyethylene
 terephthalate (PET), polyethylene naphthalate (PEN), polybutylene
 terephthalate (PBT), polybutylene naphthalate (PBN), poly-bisphenol A
 carbonate (PC), liquid crystal polyesters (LCP), polyaryl esters (),
 polymethyl methacrylate (PMMA), polyvinyl acetate (PVAC), ethylene/vinyl
 acetate copolymer (EVA), and/or ethylene/ethyl acrylate copolymer (EEA).
 To provide amide functions, for example, the following amide-containing
 polymers can be employed, individually or in combination: polyamide 46 (PA
 46), polyamide 6 (PA 6), polyamide 66 (PA 66), polyamide 610 (PA 610),
 polyamide 11 (PA 11), polyamide 12 (PA 12), polyamide 6-3-T (PA 6-3-T),
 polyarylamide (PA MXD 6), polyphthalamide (PPA) and/or poly-ether-block
 amide. Furthermore, at least one of the polymers employed can contain
 carbonyl functions.
 To provide anhydride functions, for example, the following
 anhydride-containing polymers can be employed, individually or in
 combination: styrene/maleic anhydride copolymer (S/MAH) or maleic
 anhydride-containing poly-propylene (PP-MAH).
 To form the polymer alloy, at least two different polymers are employed, it
 being possible for the polymers to have different functional groups. When
 choosing the polymers to be employed, it should be remembered that under
 the injection molding conditions, which of course are to be varied as
 such, as is known (melt temperature, rate of throughput, shear rate, and
 the like), association with or among these functional groups,
 rearrangement, or other chemical reactions, for example additional block
 copolymer formation, occurs between the participating partners, as a
 result of which an improved adhesion of the composite phases is obtained.
 If appropriate, a phase mediator and/or a compatibilizing agent can be
 added to the melt, and this is preferably done as a mixture with the
 polymer granules, or in the form of a masterbatch. However, pulverulent
 compatibilizing agents could also be applied in a drum to the granules of
 at least one of the polymers employed. Any desired phase mediator or
 catalyst can be used in effective amounts.
 Depending on the choice of the polymer components, it may be necessary or
 advantageous to accelerate the reaction between these by means of a
 catalyst. As a result, the conversion during the injection molding
 operation can be increased, if appropriate, to the desired extent. If the
 copolymerization in the alloy is to take place by transesterification or
 transamination, for example, a transesterification or transamination
 catalyst, for example a tetra-alkyl titanate or antimony oxide, can be
 added, which is preferably done with the addition of the granules.
 However, any desired catalyst can be used in effective amounts.
 The conversion--for example the transesterification or transamination
 reaction--during the copolymer formation depends on the residence time
 distribution in the injection molding machine, the melt temperature, and
 the mechanical shear energy introduced.
 Since these process parameters are monitored for optimization of the
 mold-filling process, the conversion of the copolymer formation can be
 controlled merely by the nature and the concentration of the catalyst or
 deactivator. The catalyst or deactivator concentration necessary therefore
 depends not only on the nature of the polymers employed, on the screw
 speed, and on the melt temperature, but also on the injection molding
 machine employed (residence time) and on the molding (shot weight).
 The multiphase morphology within the polymer alloy is obtained usually only
 if the copolymerization or the associative compatibilization does not
 progress too far. In particular, with long residence times or at high
 temperatures, it may therefore be advantageous to add a deactivator to the
 polymer mixture. Deactivators or inhibitors furthermore cause the phase
 stability necessary for multiple processing or recycling. If they are
 present in liquid form, for example, they can be injected into the
 processing unit upstream of a static mixer or upstream of any desired
 mixing nozzle, into the polymer melt.
 Possible deactivators include, for example, diisodecyl phenyl phosphite, a
 2-hydroxy-benzophenone derivative or a diacylhydrazine. However, any
 desired deactivators can be used in effective amounts.
 In an embodiment of the invention, further substances may be added, with
 the granules, as additives, for example release agents, calcium carbonate,
 talc or mica, or, for example, reinforcing agents, such as, for example,
 glass fibers, carbon fibers or aramid fibers. The mediators,
 compatibilizing agents, catalysts and/or other additves can be initially
 introduced, if present, in a masterbatch. In that case the polymer matrix
 of the masterbatch has to be compatible with the plastic provided. They
 can be introduced at any time during the process so that the desired
 results are achieved.
 It is also possible to initially introduce externally formed block
 copolymers with the alloy constituents in the hopper of the injection
 molding machine and thus separate in terms of process technology the
 copolymer formation on the one hand from the alloying and injection
 molding on the other hand. Simpler process control is an advantage here,
 although the additional process step must be considered a disadvantage.
 Comparison between moldings produced from polymer alloys by conventional
 methods and by the process according to the invention showed no difference
 in respect of yield stress, elongation at break, modulus of elasticity,
 fatigue limit, solubility, and resistance to stress cracking.
 Mixing of the polymers employed according to the invention as granules, for
 example in the hopper of the injection molding machine, has accordingly
 proved to be sufficient to realize morphologies which ensure an optimum
 level of chemical and mechanical properties. Mixing of granules is also
 sufficient for homogeneous material properties. Premixing of the polymers,
 for example as a powder mixture, can therefore be omitted. In particular,
 it is not necessary for polymers commercially obtainable as granules to be
 ground before alloying, which saves additional effort and costs. In spite
 of the increased melt temperature, the polymer alloys are also processed
 by the process according to the invention under conditions which are very
 gentle on the material, since a damaging processing operation is
 eliminated for the overall process by omitting the prior separate alloying
 step. As a result of the omission of the separate alloying process, the
 process is very inexpensive.
 On the basis of the optimized adhesion of the compsite phases, the alloying
 constituents can furthermore be employed in any desired ratio with respect
 to one another. Moreover, because of the high composite adhesion between
 the phases of the polymer alloys prepared by the process according to the
 invention, the introduction of energy required is reduced such that
 conventional injection molding screws can be employed. This effect saves
 changing the screw when changing over a product and thus further reduces
 the costs of the process.
 Any desired injection molding machine can be used. For example, the
 conventinal injection molding screw can be a universal screw, which
 preferably has a length of between 16 and 20 D (16 and 20 times the
 diameter), where approximately 50% of the length is assigned to the feed
 section, 30% of the length to the compression zone and 20% to the
 discharge zone. No additional shear or mixing elements are necessary. The
 compression should be in the range between 1,5 and 3. Conventional
 injection molding conditions can be as follows:
 injection rate: 10-16 cm.sup.3/ s
 injection pressure: 1000-2000 bar
 max. holding pressure: 500-1000 bar
 holding pressure time: 2-20s
 back pressure: 60-120 bar
 Costs can furthermore be saved if the components are not initially
 introduced as a mixture of granules, but a divided hopper is used.
 By the process according to the invention, the product-specific adjustment
 of the nature and concentration of the alloy constituents is possible for
 each individual injection molding, which allows the production of
 individual components having a specific design of properties. Precisely as
 a result of this, the use of the moldings produced by the process
 according to the invention is particularly suitable for prostheses in
 orthopedics.
 Examples of polymer mixtures from which moldings can be produced by the
 process according to the invention are given below. These examples are
 only for illustrative purposes, and do not limit the scope of the
 invention.

ALLOY MIXTURE I Recipe
 Polymer 1 PA 70%
 by weight
 Polymer 2 PP-MAH
 28.5% by weight
 Catalyst
 Deactivator
 Masterbatch PA, 50% metal iodide pigments 1.5%
 by weight
 Melt temperature
 240-260.degree. C.
 Mean residence time 4-8
 minutes
 Injection molding shaft attachment
 Shot weight 220
 g
 Polymer 1: PA
 Polymer 2: PP-MAH
 ##STR2##
 ##STR3##
 ALLOY MIXTURE III Recipe
 Polymer 1 PBT
 49.5% by weight
 Polymer 2 PC
 49.5% by weight
 Catalyst tetra-alkyl titanate 0.4%
 by weight
 Deactivator trilauryl phosphite 0.6%
 by weight
 Melt temperature
 250-270.degree. C.
 Mean residence time
 2.5-5 minutes
 Injection molding tension bar
 Shot weight: 11 g
 Polymer 1: PBT
 Polymer 2: PC
 ##STR4##
 ##STR5##
 ##STR6##
 ALLOY MIXTURE III Recipe
 Polymer 1 PET 75%
 by weight
 Polymer 2 EVA 23%
 by weight
 Catalyst antimony oxide 0.8%
 by weight
 Deactivator oxalic acid dihydrazide 1.2%
 by weight
 Melt temperature
 280-290.degree. C.
 Mean residence time 3-7
 minutes
 Injection molding knee fitting
 Shot weight 165
 g
 Polymer 1: PET
 Polymer 2: EVA
 ##STR7##
 ##STR8##
 ##STR9##
 FIG. 1 shows a diagram of a longitudinal section through the plasticizing
 cylinder of an injection molding machine. The position of the injection
 nozzle 1 for a liquid inhibitor between the restricted flow space 2 and
 mixing nozzle 3 is shown.
 FIG. 2 shows the comparison of the resistance to stress cracking, adhesion
 to acrylate resin systems (bondability, coatability) and of the dynamic
 tear resistance (ISO A 100) between the starting polymers PC and PBT and
 the alloy mixture II, and the alloys PBT/PC produced by the process
 according to the invention and by the conventional process.
 Although only a few exemplary embodiments of this invention have been
 described in detail above, those skilled in the art will readily
 appreciate that many modifications are possible in the exemplary
 embodiments without materially departing from the novel teachings and
 advantages of this invention. Accordingly, all such modifications are
 intended to be included within the scope of this invention.