DE102007015318A1 - Process for the preparation of reinforced thermoplastic composites and associated apparatus for carrying out, and composites produced in this way - Google Patents

Abstract

The process according to the invention for producing fibril-reinforced plastic composites is characterized in that: the composites consist of 50 to 95% of a thermoplastic matrix and 5 to 50% of one or more thermoplastic reinforcing components which are incompatible with one another and in which the Matrix has a lower melt temperature than the reinforcing component, - the materials are mixed in the molten state, - the plasticized mixture is discharged through a nozzle and then hot drawn in a ratio of 2 to 20 and - the stretched mixture is cooled under tension.

Description

The The invention relates to a process for the production of reinforced thermoplastic composites with improved compatibility between the components and excellent physical and mechanical Properties, the associated device and the like produced composites.

The Composites consist of a thermoplastic matrix and one or more thermoplastic additives which a reinforcement due to their fibrillar structure cause the plastic mixture.

State of the art

fiber-reinforced Plastic composites with increased strength, stiffness and heat resistance found for a long time Time very wide application.

The most important reinforcing fibers are glass and carbon fibers.

The Reinforcing materials include conventional ones thermoplastic polymers with mostly amorphous or partially crystalline Structure.

For the production of fiber-reinforced polymer composites are high energy inputs for mixing and Blending the matrix polymer with the reinforcing fibers required. Since the fibers are usually in solid form and a length of 0.1 to 5 mm and an aspect ratio from 50 to 100 (macrofibres), can be used for the compounding no ordinary mixing equipment be applied, so special methods and equipment necessary are. High shear in the production and processing of compounds often lead to unwanted shortening of the reinforcing fibrous component and thus undesirable Property changes, such as a certain embrittlement.

Also the use of synthetic polymer fibers for reinforcement thermoplastic molding compositions has already been described several times.

For example, in the DE 199 34 377 describes a process for producing polyester-reinforced polypropylene compounds in which polyester fibers are mixed into a polypropylene melt by means of a twin-screw extruder.

The Compound is characterized by increased impact resistance for the same or increased strength and rigidity. The high financial expenditure for the production or procurement suitable polyester fibers and necessary facilities for uniform Fiber feeding into the extrusion process, however, prevent one economical production of the compound.

It It is also known in the art that microfibers (length 0.1 μm to 1000 μm with an aspect ratio from 10 to 1000) in situ in a polymer matrix can.

In the US 724 698 For example, in-situ formation of fibers in a polymer matrix is disclosed by adding a liquid crystal polymer to a base polymer followed by mixing and extrusion.

As in the EP 0 642 556 As shown, the resulting fibers are aligned in the flow direction of the thermoplastic matrix melt and cause an improvement in the mechanical properties.

The However, the polymer mixtures mentioned above have the disadvantage that their properties in the transverse direction, such as the Notched impact strength are worse than those of the corresponding ones unmixed plastics.

This Phenomenon is a consequence of the anisotropic structure and the poor adhesion between the liquid crystalline polymer phase and the thermoplastic phase.

The in the pamphlets EP 0 369 734 . EP 0 380 112 . WO 92/18568 recommended additions of compatibilizers to reduce the surface tension between the phases and to improve adhesion and dispersion cause only a slight improvement in notched impact strength.

In the DE 241 88 03 For example, a thermoplastic material is described in which a polymer in the form of elongated fibrils is dispersed, thus imparting high strength to the multicomponent material.

The polymeric fibrils are in situ due to strong shear Kneading the melt mixture produced and by cooling fixed under tension in the matrix. As for the fibrillating Component polyolefins are claimed, the spectrum is possible to be reinforced polymers on standard plastics with relative low melt temperature and low mechanical properties limited.

adversely The prior art in this field is the absence a simple process, with the cost in continuous Meadow fibrillar reinforced thermoplastic composites can be made, with a wide range of materials can be used.

Object of the invention

task The present invention is a simple process for continuous Producing fibrillar reinforced thermoplastic Specify composites that cost effectively improve physical Properties can be achieved which are based on a wide range of materials is applicable and the basis for a variety of processing methods, also for injection molding applications.

The The invention is primarily based on the improvement of the mechanical Properties of thermoplastic standard plastics such as polyethylene and polypropylene by reinforcement with engineering plastics, such as polyamide, polyester and polycarbonate aligned.

The The object is achieved according to the invention that in a first step, at least two incompatible Polymers with different melting points in an extrusion process be blinded.

The Higher melting point polymer is said to be the reinforcing Achieve effect and has a share of 5 to 50% of the total polymer content of the composite.

The Extrusion conditions are chosen so that both polymers be mixed in the molten state and the higher melting Component as evenly as possible small spherical particles dispersed in the matrix is.

The sheared longitudinal stretching of the Particles go under the conditions of conventional extrusion extrusion with exit of the melt from the nozzle channel as far as possible lost.

in the second step is the blend by round, wide or profile nozzles discharged to it afterwards in the still hot Condition to stretch.

It was found to be discharged at certain temperatures Composites are given conditions in which by stretching long Fibrils of both components arise that have a diameter of 1 to 4 microns and a length of 0.1 to 5 mm.

The Fibrils are made by stretching the composite.

to Achieving pronounced fibril structures is suitable a roller drafting system, in which the blend with a first pair of rollers, which approximately the speed of the melt in the nozzle channel has, is fixed, and a second pair of rollers, which with 2- up to 20 times higher speed causes a stretching.

The Stretching the blend, roll temperatures, gap widths, etc. should be adjusted so that the temperature of the extruded blend at the moment of stretching below the melting temperature of the reinforcing Polymers is available and still sufficient stretchability allowed.

The in the third step necessary cooling below the melt temperature of the matrix material fixes the fibrils in the matrix. It is done undervoltage.

The Cooling can be done either by long air distances or in take place in a water bath.

Around To obtain the fibrillated state of the disperse phase and the avoid elastic contraction of the elongated fibrils it is important to carry out the cooling under tension.

A advantageous embodiment is given by a Cooling in a water bath already between drafting systems is carried out.

The further design of the method is essentially due to the nature of the product to be produced, the drawing preferably cutting into free-flowing granules follows.

The Blend according to the present invention may according to usual Processing methods, such as injection molding, extrusion, Pressing at temperatures below the melting point of the reinforcing Component to be reshaped.

the Blend can also be added to known plastic additives become. Such additives include, for example, stabilizers, Colorants, dyeing aids, lubricants, antistatic agents and flame retardants.

These Substances can be dosed individually or with a polymer be premixed.

• • 50 bis 95% eines thermoplastischen Polymers mit 5 bis 50% eines oder mehrerer höherschmelzenden, mit der Matrix nicht verträglichen thermoplastischen Polymers vermischt und durch gemeinsame Extrusion in der Schmelze geblendet werden,
• • das plastifizierte Material durch Rund-, Breit- oder Profildüsen ausgetragen und anschließend im noch heißen Zustand unter gezielten Bedingungen verstreckt wird,
• • danach eine Abkühlung erfolgt, und
• • eine Weiterverarbeitung unter Bedingungen erfolgt, bei denen die Schmelzetemperatur der höherschmelzenden Komponenten nicht überschritten und nur geringe Scherwirkung auf das Material ausgeübt wird.

The invention comprises the preparation of the composites described above by a process in which

• 50 to 95% of a thermoplastic polymer is mixed with 5 to 50% of one or more higher-melting, matrix-incompatible thermoplastic polymers and blended by co-extrusion in the melt,
• The plasticized material is discharged through round, wide or profile nozzles and then stretched under targeted conditions while still hot,
• • then cool down, and
• • further processing takes place under conditions in which the melt temperature of the higher-melting components is not exceeded and only minor shearing action is exerted on the material.

According to the invention the production of composites with the processing methods injection molding, pressing, Linked to extrusion and winding.

The Solution to the problem of providing plastic composites takes place according to claim 15.

embodiments

The following Examples show an advantageous embodiment of the reinforcement of polypropylene (PP) with polyethylene terephthalate (PET).

The dried granules of both materials are metered in the desired ratio and blended with the aid of a co-rotating twin-screw extruder at a melt temperature of about 270 ° C. The extruder with a screw diameter of 25 mm and a speed of 100 rpm is driven at a total throughput of 12 kg / h. The melt is discharged via a spray head with 4 round nozzle openings of 4 mm diameter. While the strands of the comparative product (A) are passed directly through a water bath and then granulated, the strands for the new material (B) pass through a drafting system with two roller pairs of different speeds. After the first pair of rolls, which pulls the strands from the spray head at a speed (v ₁ ) of 5 m / min, a stretching to about 8 times the speed (v ₂ ) takes place. The strands dilute very strong and are passed through a water bath before the second pair of rollers. The granulation of the stretched blend takes place directly after the second pair of rolls.

The Material testing is carried out on test specimens, which are produced by injection molding.

Table 1 shows the achieved mechanical properties of the compound (B) according to the invention when using 20% PET in comparison to the unstretched polymer composition (A) and the starting polymers PP and PET. exam unit standard PP PET A B Component 1 % 100 pp - 80 pp 80 pp Component 2 % - 100 PET 20 PET 20 PET stretching v ₂ / v ₁ - - - 7.7 density g / cm ³ DIN 55990 0.9 1.4 0.97 0.97 tensile strenght MPa DIN EN ISO 527-1 32.3 56.2 29.3 35.6 Train modulus MPa DIN EN ISO 527-1 1378 2198 1838 2226 Impact strength Charpy 23 ° C kJ / m ² DIN EN ISO 179/1 110 No break 30.7 50.6 Notched impact strength Charpy 23 ° C kJ / m ² DIN EN ISO 179/1 2.4 3.6 1.9 2.5 Table 1

The Results show that according to the invention produced product a higher strength and clear better stiffness compared to the unreinforced PP and the undrawn PP / PET (A), but in the case of Toughness to be expected with certain losses is.

Further results on the system PP / PET (consisting of 80% PP and 20% PET) show the following tests: attempt 80 PP 20 PET 80 PP 20 PET 80 PP 20 PET Stretch ratio in the area of the nozzle - 1st drafting system v ₂ / v ₁ 6.6 1.3 13.5 Stretching ratio in the area 1. drafting system - 2. drafting system v ₃ / v ₂ 2.5 6.9 - Total draw ratio v ₃ / v ₁ 16.5 9.0 13.5 strength MPa 27.8 36.4 31.4 Modulus MPa 1786 2282 1950 impact strength kJ / m ² 22.3 58.9 78.7 Impact strength kJ / m ² 1.95 2.5 2.1 MVI (230 ° C, 2.16 kg) cm ^3/10 min 1.0 11.2 Table 2

Interesting is that over the undrawn blend of the same composition both strength, rigidity and impact strength can be increased according to Table 2. Compared to pure PP, however, a reduced impact resistance determine. With the help of grid electronic recordings, the structural changes caused by stretching the blends are caused to be visualized.

The undrawn materials show the typical in both matrices Behavior of a blend of incompatible plastics. The PET component lies as spherical embedded in the matrix of relatively uniform diameter in front.

The Formation of fibrillar structures by the stretching process is clearly noticeable. Both longitudinal and transverse to the pulling direction are the PET fibrils with diameters from 1 to 2 μm in a scanning microscope image.

The stretching procedure was as follows:
First, a stretching of the blast discharged from the nozzle takes place between the nozzle and the first drafting device, the associated value being indicated as the drawing ratio v ₂ / v ₁ . The draw ratio, which occurs between the first drafting arrangement and the second drafting arrangement, is designated as v ₃ / v ₂ . The total stretching ratio (given as v ₃ / v ₁ ) is obtained by multiplying the two aforementioned stretching ratios.

It were also experiments with a blend of HDPE (high polyethylene Density) and PET performed.

The following results were achieved: attempt HDPE PET 80 HDPE 20 PET 80 HDPE 20 PET 80 HDPE 20 PET 80 HDPE 20 PET Without extrusion Zero sample unreinforced Stretched between roller pair 1 and roller pair 2 stretching v ₂ / v ₁ 15.8 10.0 5.7 strength MPa 22.3 56.2 24.1 25.0 23.4 23.7 Modulus MPa 902 2198 1081 1115 1139 1141 bending stress MPa 17.2 71.9 22.1 23.2 Flexural modulus MPa 878 2260 1143 1156 Impact strength (N = no fracture) kJ / m ² 5 * N 5 * N 5 * N 124 6 * N 5 * N Impact strength kJ / m ² 13.0 3.6 2.3 2.6 2.7 3.6 Table 3

In the overview according to Table 3 are the mechanical properties of the individual components the conventional prepared blends and the fibrillar reinforced Compounds of the same composition faced.

While the mechanical properties have only insignificant differences microscopic examinations allowed the formation of microfibrils beeing confirmed.

The PET component was able to dissolve and wash out the HDPE matrix be made visible from the stretched strands.

Further results on the system HDPE / PET are shown in Table 4: attempt 80 HDPE 20 PET 80 HDPE 20 PET 80 HDPE 20 PET 80 HDPE 20 PET Stretch ratio in the area of the nozzle - 1st drafting system v ₂ / v ₁ 5 6.6 9.7 9.5 Stretching ratio in the area 1. drafting system - 2. drafting system v ₃ / v ₂ 3,35 1.0 1.0 2.4 Total draw ratio v ₃ / v ₁ 16.7 6.6 9.7 22.8 strength MPa 25.1 26.4 26.3 25.2 Modulus MPa 1152 1232 1170 1171 impact strength kJ / m ² 28.8 94.6 84.4 21.6 Impact strength kJ / m ² 3.1 2.9 2.4 2.0 Table 4

Tries, the use of polyamide as a reinforcing component in a matrix of polypropylene are also according to the inventive technique successfully under formation have been performed by reinforcing fibrils.

contraption

The Solution to the problem, a device for carrying out of the process according to the invention for the preparation indicate fibril-reinforced plastic composites, takes place according to claim 12.

1 shows an apparatus for carrying out the method according to the invention for the production of fibril-reinforced plastic composites.

The device 1 consists of a co-rotating twin-screw extruder 2 who with means 4a and 4b is provided to dose at least two polymer materials. Through a spray head 3 the melt is discharged as a strand.

The strand passes through a drafting system with two pairs of rollers 5 and 7 different speed. After the first pair of rollers 5 , which pulls the strand from the spray head, the stretching takes place. This is caused by the second pair of rollers 7 operated at a higher speed than the first pair of rollers 5 , The strand dilutes very strong and is still before the second pair of rollers 7 through a water bath 6 guided.

The granulation of the strand-shaped blend takes place directly after the second pair of rolls 7 in a granulator 8th ,

alternative The string-shaped stretched blend may also be initially wound up or placed in a container and cut or granulated at a later date become.

It but also sees the possibility of the string-shaped To introduce stretched blend in the feeder of an extruder. It is advantageous if several such strands the Extruder be supplied.

It become apparent to those skilled in an innovative way without further ado various other design options, which are encompassed by the inventive concept.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19934377 [0008]
• US 724698 [0011]
• - EP 0642556 [0012]
• - EP 0369734 [0015]
• - EP 0380112 [0015]
• WO 92/18568 [0015]
• - DE 2418803 [0016]

Claims (15)

Process for producing fibril-reinforced plastic composites, characterized in that: - the composites are formed from a thermoplastic matrix and from at least one thermoplastic reinforcing component which are incompatible with each other and in which the matrix has a lower melt temperature than the reinforcing component; Mix the matrix and the reinforcing component in the molten state, - The plasticized mixture is discharged through a nozzle, - The discharged plasticized mixture is then stretched while hot, and - The stretched mixture is cooled under tension. Method according to claim 1, characterized in that that as a thermoplastic matrix polyolefins or low-melting Polyamides or fusible derived from renewable raw materials Polymers are selected. Method according to claim 1 or 2, characterized as reinforcing materials, polyamides or polyesters or polycarbonates. Method according to one of the preceding claims, characterized in that a plurality of reinforcing components be used. Method according to one of the preceding claims, characterized in that the proportion of the matrix to 50 to 95 Wt .-% and the proportion of the reinforcing component to 5 bis 50 wt .-% is selected. Method according to one of the preceding claims, characterized in that the composite is stretched. Method according to one of the preceding claims, characterized in that stretched in the ratio 2 to 20 becomes. Method according to one of the preceding claims, characterized in that the composite by two pairs of rollers is stretched at different speeds. Method according to one of the preceding claims, characterized in that the stretched composite under tension is cooled. Method according to claim 8 or 9, characterized that the stretched composite in a water bath between the two Roller pairs is cooled. Method according to one of the preceding claims, characterized in that in the composite fibrils with a middle Length of 0.1 to 5 mm are formed. Apparatus for carrying out the method according to one of claims 1 to 11, consisting of a co-rotating twin-screw extruder 2 who with means 4a and 4b is provided to dose at least two polymer materials and a spray head 3 to discharge the melt as a strand and two pairs of rolls 5 and 7 that have different speeds and stretch the strand. Apparatus according to claim 12 with a water bath after the first pair of rollers 5 , Device according to one of claims 12 or 13 with a granulating device 8th after the second pair of rollers 7 , Fibril-reinforced plastic composites, prepared according to the method according to one of Claims 1 to 11.