DE10229298A1 - Making fibre-reinforced polypropylene with improved impact strength involves melt-compounding and tempering in an extruder with filaments of highly-crystalline polymer, e.g. polyethylene naphthalate - Google Patents

Abstract

A method for making fibre-reinforced polypropylene (PP) with high impact strength involves adding filaments of highly-crystalline poly(ethylene-2,6-naphthalate), poly(dimethylcyclohexyl terephthalate) and/or LCP-modified polyethylene to PP granules in an extruder or plasticizers and inducing post-crystallisation by tempering, with a nucleating action on the PP matrix.

Description

The invention relates to a method to improve the mechanical properties of polypropylenes (PP), the reinforcing acting polymer filaments already in the feed zone of the extruder to be added to the PP granules, which causes the polymer filaments in surprising advantageously have time for recrystallization and thus can also have a nucleating effect on the crystallization of the PP matrix. Essential is that the polymer filaments are based on highly crystalline Poly (ethylene-2,6-naphthalate) (PEN), poly (cyclohexyldimethyl terephthalate) (PCT) or LC modified Polyethylene (PET) exist.

[State of the art]

In recent years there has been an unbroken one Development of consumption in the polypropylene (PP) market with regard to new products. But also with further developments processing technologies and modification options of materials to the optimization of products in established Areas of application are trying to gain additional market share within to secure the rapidly growing sales figures.

A widespread and often above all on an industrial scale opportunity used to improve special material properties of PP compounds in special areas of application are filling and reinforcement of PP with various types of inorganic or organic synthetic Filling or Fibers as effective material additives. The different ones possibilities a targeted modification of PP such as short or long fiber reinforcement, mineral filling, cross-linking, nucleation and ultimately the profiling of metallocene PP leads to specific property improvements. While the addition is cheaper, mineral fillers to plastics earlier The cost reduction served today by filling and reinforcing thermoplastic Plastics targeted targeted improvements in properties, which also through Synergy effects in the construction of material properties in Rigidity, strength, toughness and dimensional stability can be accompanied.

Incorporation of mineral fillers and glass fibers in the PP matrix is state of the art. Especially through the cheap Price-performance ratio for the reinforcement PP uses such PP compounds in large quantities in automotive, electrical and and the mechanical engineering industry. Increasing attention PP compounding currently applies to glass and natural fiber reinforcement Use of high modulus synthetic fibers like PA, PET or PEI their use requirements also in higher-priced engineering plastics Fulfills can be (e.g. R. Mühlhaupt, F. Stricker in Kunststoffe 87 (1997), p. 182). Looking for New synthetic short fibers to improve properties often become fibers made of aramid, PET, carbon or PTFE, but one comes across often on financial limits of technical applicability.

Another way to improve the material properties of polypropylene is the influencing the crystallization processes by nucleation. The concept, mechanical and optical properties of PP through the use of nucleating agents and transparency enhancers improving has been known for more than three decades and is winning especially in recent years (e.g. M. Gahleitner, Handbook “Crystallization of polyolefins ", 1999).

The mechanical properties of PP materials are largely determined by their degree of crystallization and shaped the morphology of the crystalline phase. Crystallization and training The crystalline phase begins during the processing of the Polymers and are dependent on temperature profile of the cooling phase, Processing pressure, chain orientation and by the presence of Crystallization nuclei influenced. Slow crystallite growth, different size of the structures and their superstructures and spherulite shear in the processing process (reprint) are responsible for material inhomogeneities, which lead to strong receding and warping of the finished parts. Known is that through the use of nucleating agents Morphologieinhomogenitäten crystalline and amorphous structures caused property anisotropy the materials can be effectively countered. nucleating form a key role in the optimization of mechanical and optical material properties and determine as heterogeneous foreign particles in the polymer matrix the course of crystallization in the processing process. Through her Effect as a nucleating agent, the crystallization is accelerated and there will be products with higher crystallinity receive. This can result in rigidity and strength of the compounds increase. The crystallization temperatures of nucleated PP materials are increased reduced the spherulite sizes and their distribution more homogeneous. In addition to improving certain Product nucleation is also economical Interesting aspect, because molded parts at higher tool temperatures demolded and thus the cycle times in injection molding processing shortened can be.

The effects on the mechanical properties of PP compounds through a coupling of nucleation and reinforcement through the use of fibrous reinforcing materials, which simultaneously have been described satisfactorily. Some working groups have carried out studies on PP reinforcement with synthetic fibers on model materials and at the same time observed the crystallization processes with regard to a nucleating effect of the reinforcing components in the compounds. In some cases, in which PP was reinforced with Kevlar, PET or certain C fibers, an effect which influenced the crystallization was observed in some cases, but the price of the materials or the coloring were disadvantageous for further product development or technical conversion the PP matrix (Avella et al. in Polymer Eng. and Science 234, 1992, 5, pp. 376-382; Varga et al. in J. Material Sci. Lett. 13, 1994, pp. 1069-1071).

In others, especially recently conducted Work was particularly interested in studies on nucleating Effect of reinforcing materials in PP with semi-quantitative statements about crystallization processes and observations on transcrystallization effects. In addition to the already mentioned materials also show chemically treated natural fibers, modified glass fibers or PTFE filaments for PP nucleating effect (C.Wang, C.-R. Liu in Polymer 40, 1999 pp. 289-298; or I.Mildner and others, in “Die Angew. Macromolecular Chemistry "272, 1999, pp. 27-33). Clear information about the influencing of the material properties by such additives are however not described.

(Object of the invention]

The aim of the invention is a method to develop in which the polymer filaments introduced into the PP matrix improved mechanical properties, especially an improved one impact strength and at the same time an improved property anisotropy of the materials effect and are financially and technically feasible.

Surprisingly could this object be achieved according to the invention that a joint addition of the polymer filaments and the PP granules already takes place in the feed zone of the extruder, whereby the polymer filaments Have time to recrystallize and thus nucleate at the same time the crystallization of the PP matrix can act, being essential to the invention is that the polymer filaments based on highly crystalline poly (ethylene-2,6-naphthalate) (PEN), poly (cyclohexyldimethyl terephthalate) (PCT) or LCP modified Polyethylene (PET) exist. The production of the finest filaments as reinforcement components was done by melt spinning. The reinforcement of isotactic PP is made with synthetic short fibers, which also a possible have a nucleating effect. The reinforcement filaments should be under Processing conditions of PP do not melt and therefore must preferably have high melting points. The selection from commercially available products was preferably based on the criteria of high intrinsic crystallinity, if possible high stereo regularity in their structural structure and according to softening points of over 230 ° C. As essential to the invention for the Polymer filaments used in the process is that it succeeded the basis of the temperature differences between the onset of transcrystallization and matrix crystallization to improve nucleation efficiency. On various filament-reinforced Material compositions could be the effect of one of the reinforcing materials starting effective nucleation on the crystallization processes in the PP matrix due to the occurrence of primary transcrystallization the filament surface be detected.

The generation of very fine and from it assembled short fibers are made by melt spinning on a High temperature spinning stand and subsequent cutting of the continuous filaments. The respective spinning conditions for producing the finest titers are the different materials according to their physical and adapt chemical product properties. Is oriented on achieving good textile-physical characteristics in the end product with if possible high fiber strength and moduli.

The chemical modification of the reinforcing materials and the coupling of nucleation-active substrates to the surfaces of reinforcing fibers are possible and advantageous. The use of PET modified with LCP precondensates containing special anhydro groups to introduce additional polar molecular segments was proven to be advantageous for the polymer filaments to be used. PET was modified with LCP precondensates containing anhydrous groups to introduce additional polar molecular segments. To modify PET, the synthesis of low molecular weight liquid crystalline polyester imide anhydrides (LCP) with side and terminal anhydride groups was successful. Under extrusion conditions, they react with terminal hydroxyl groups of the polyesters to form graft block copolymers by cocondensation. With a micro-phase distribution of the modification components, advantages are often achieved in the processing of the resulting materials. Such rigid or semi-rigid LCP modifiers were synthesized by reacting mixtures of the monomers trimellitic anhydride, hydroquinone diacetate, p-acetoxybenzoic acid, 6- (4-carboxyphthalimido) -n-hexanoic acid and 3,6-diacetoxyphthalic acid-1,2-anhydride according to the following scheme:

Synthesis of polyester imide anhydrides (LCP)

LCP-Vorkondensat Some of the monomers used were commercially available or easily accessible by preparative preparation on a laboratory scale. The LCP was synthesized in the melt of the monomer mixtures under elevated temperature up to 270 ° C. and under vacuum. The number of pendant anhydride groups could be adjusted by varying the molar proportions of the different monomer components. Also advantageous for the preparative preparation of the LCP was a cocondensation of the monomers with pre-prepared precondensates containing anhydride groups, which, for. B. were synthesized from 6- (4-carboxyphthalimido-n-hexanoic acid and diacetoxyphthalic anhydride:

LCP precondensate

As part of the project, various LCP products with four or eight pendant anhydride groups synthesized. For this, these were during filament spinning in the extrusion process as modifier components worked into the polyester. It turned out that with the installation the LCP and the associated sequentially into the polymer chains introduced polarity differences they influence the crystallization properties of the matrix polymer PP.

The experimental investigations the crystallization properties of fine fiber reinforced isotactic Polypropylene (it-PP) in compounds using polarizing microscopy and following it Processing tests for the production of compounds and their characterization of properties can be found in the application example and tables.

The reinforcement materials can by Melting spinning can be obtained. On the one hand, fine titre synthetic Filaments by melt spinning commercially available higher melting polymers and in addition from polymer-chemical with by additive with LCP modified PET base granules and subsequently Short fibers cut.

The investigations of the crystallization properties was carried out on the compounds by polarization microscopy with PC coupled data and image documentation.

The distinctive temperatures for the occurrence of the relevant crystallization events were recorded and evaluated under defined, dynamic heating and cooling processes of compound melts:
Existence and beginning of a transcrystallization of the it-PP on the reinforcing material and triggered by the filament surfaces
- Start of spontaneous PP crystallization of the matrix.

[Example]

Detailed technological spinning parameters were required for the production of the filaments for each of the Processing of existing polymers is either newly developed in separate individual experiments or transferred on the basis of existing spinning experience. The results from the large number of spinning tests can be summarized as follows:

Poly (1,4-dimethyl-cyclohexyl terephthalate) (PCT)

The ThermX product from Eastman settled easily analogous to a polyester spinning technology for filaments Process after the spinner head temperature is raised to 300 ° C has been. The multifilaments were first drawn off at 350 m / min, the spinning speed was easy effortlessly also increase to 1000 or 2000 m / min. As beneficial in the sense The goal he ultimately showed was a driving style at 1000 m / min with subsequent Stretching the filament cable with a stretch ratio of 1: 2.

polyethylene (PEN)

This special polyester could careful Drying at 120 ° C in a vacuum and with spinning head temperatures above 300 ° C to filaments are processed. It started with products from the trading company Goodfellow, for the production of test materials for processing tests came homopolymer products from DuPont (USA) are used. Optimal working temperatures were at 315-325 ° C Nozzle reached, in the higher molecular Type X-92 had to the temperature on the spinning head can be increased by 10 ° C. The materials were withdrawn at 1000 m / min and over according to the FDY technology Stretched godets heated to 160 ° C with final take-off speeds of 2800 m / min 2.8-3 times stretched.

LCP reinforced PET (PET LCP)

Two different ones were used Test materials in which standard PET with 1.5 or 3 mass% of a liquid crystalline Polyesterimide precondensates with 4 anhydride groups (see 5.1.3.) were modified. The modification and spinning of the products succeeded by reactive extrusion and implementation of the additiv LCP component during the melting phase with the submitted PET at elevated processing temperatures. Beneficial for The use of spinnerets was a smooth spinning process a bore diameter of 400 μm. That with 1.5 mass% LCP addition modified PET could at 312 ° C be spun stably. Starting with a print speed of 420 m / min was based on FDY technology and worked with a drawing of 1: 3.3 godets tempered at 190 ° C, subsequently the filaments wound up at 1400 m / min. The spinning process for that with 3 LCP spiked material was regarding spinning and stretching godet temperature varied little. They were 301 and 180 ° C, respectively. The material left a higher draw with a factor of 5.45.

Tab. 1: Overview of the polymers for filament production by melt spinning

The main results of Spin tests for filament production are in the table below compiled.

Tab. 2: Filament production after largely optimized spinning conditions by melt spinning

For a comprehensive characterization of those in the crystallization experiments The filaments used were the textile-physical parameters of materials.

In addition, the test methods fineness DIN EN ISO 2060, Tensile strength, elongation DIN EN ISO 2062 and initial modulus based on DIN EN ISO 2062 applied.

The results are in the table 3 included.

Table 3:

The experimental results of the Polarization microscopic crystallization experiments are in the table 4 compiled. The results of the crystallization were evaluated regarding the respective matrix in the material composite

• - melting range the PP matrix,
• - appearance a transcrystallization and crystallization temperature
• - Start of crystallization the matrix.

One sets as an evaluation criterion for the ability of polymer filaments, in addition to reinforcement, also nucleating to act on the crystallization of the PP matrix, the temperature difference between the beginning of transcrystallization of the PP on the surfaces of the Filaments on the one hand and the start of crystallization of isolated areas on the other hand, the basis of the PP matrix is as follows derive from the data (Table 4).

Table 4:

On the basis of the results of the crystallization studies, compound systems were selected for processing into test specimens for determining the mechanical parameters. The reinforcing materials, which showed an effective nucleation ability by the occurrence of transcrystallization effects at high melt temperatures, were given special consideration. These were in detail:
PEN (DuPont), type X-92
PEN (DuPont), type X-61
PCT (Eastman), type PCTA 13319
PET-LCP (TITK), 1.5% LCP with 4 anhydride side groups.

The results are in Table 5 and 6.1 and 6.2 respectively.

The test materials were on processed a ZSK 40 twin-screw extruder. The Fiber dosing via a sidestream extruder with additive balance.

The 1% mixtures were hand-dosed.

The material of variant 2 was like all compounds under the same conditions, but without additives further processing, granulated into test specimens. Original 1 came with variant 1 PP granulate without prior granulation for injection molding processing for use.

They were manufactured in succession Shoulder stick, standard bending stick and plates 60 × 60 × 1.5 mm.

The following material tests were carried out on the test specimens:
Tensile test according to DIN EN ISO 527-1
Bending test according to DIN EN ISO 178 (standard bending stress)
Charpy impact strength according to DIN EN ISO 179 / leAU

Selected test parameters are in the tables 6.1 and 6.2 included, the material properties of the PP compounds based on HD 120 MO of the individual variants for the tensile module, bending module and the Charpy impact strength according to the invention of particular Meaning.

Tab. 6.1: Materialkennwerte der PP-Compounds auf Basis von HD 120 MO

Tabelle 6.2: Materialkennwerte der PP-Compounds auf Basis von HD 120 MO (Fortsetzung)

Table 5: Overview of PP compounds based on HD 120 MO Borstar with different reinforcement materials and parts

Tab.6.1: Material properties of the PP compounds based on HD 120 MO

Table 6.2: Material properties of the PP compounds based on HD 120 MO (continued)

Microscopic crystallization studies under polarized light were carried out repeatedly with the short fibers produced for the processing experiments. You confirm the results already found. The two PEN materials from DuPont, Therm X short fibers (Eastman) and the modified PET-LCP led to transcrystallization in PP starting at a melt temperature of approx. 130 ° C ( 4 and 5 ).

Claims (7)

Process for the production of synthetic fiber reinforced polypropylene with improved impact strength, thereby characterized in that polymer filaments based on highly crystalline Poly (ethylene-2,6-naphthalate) (PEN) and / or poly (cyclohexyldimethyl terephthalate) (PCT) and / or LCP modified polyethylene (PET) in the feed zone of the extruder or plasticizer added to the polypropylene granules are excited and post-crystallized in this way under tempering that these are nucleating on the crystallization of the polypropylene matrix acts. A method according to claim 1, characterized in that the Softening points of the polymer filaments are above 230 degrees C. A method according to claim 1 to 2, characterized in that the polymer fiber proportions at 1 to 40% by weight, preferably at 20-30% by weight lie. A method according to claim 1 to 3, characterized in that the polymer fiber portions of fine titre synthetic filaments of 2 are up to 15 tex. A method according to claim 1 to 4, characterized in that the polymer fiber portions to short fibers with a length of 4 to 10 mm, preferably 5 to 6 mm, are cut. Method according to one of the preceding claims, characterized in that the modification with LCP products with four or eight pendant anhydride groups is made. A method according to claim 1 to 6, characterized in that the temperature difference between the beginning of transcrystallization of polypropylene on the surfaces the filaments on the one hand and the start of crystallization more isolated Areas of the polypropylene matrix, on the other hand, between 4 and 7 degrees C, preferably 6 to 7 degrees.