Process for the production of a polymer alloy

Details Process for the production of a polymer alloy Process for the production of a polymer alloy

1997-11-06

2001-10-16

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Shaping against forming surface

C264S328170, C264S331110, C264S331130, C264S331180, C264S331190, C264S331210

Reexamination Certificate

active

06303069

ABSTRACT:

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.


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