WO2006027123A1

WO2006027123A1 - Use of thermoplastic polyamide composite materials having improved flow properties, for producing moulded parts according to thin wall technology

Info

Publication number: WO2006027123A1
Application number: PCT/EP2005/009263
Authority: WO
Inventors: Marcus SCHÄFER; Detlev Joachimi; Michael Schmidt; Arno Nennemann; Klaus Salewski; Kurt Jeschke
Original assignee: Lanxess Deutschland Gmbh
Priority date: 2004-09-10
Filing date: 2005-08-27
Publication date: 2006-03-16
Also published as: DE102004043825A1

Abstract

The invention relates to the use of thermoplastic moulded masses consisting of polyamide and nanofillers, for producing moulded parts having wall thicknesses of between 0.1 mm and 1.0 mm, or moulded parts comprising elements having different wall thicknesses of between 0.1 mm and 1.0 mm.

Description

Use of thermoplastic polyamide composite materials with improved flow properties for the production of molded parts in thin-wall technology.

The present invention relates to the use of thermoplastic molding compositions of polyamide and nanoscale fillers in the injection molding process for the production of thin-walled moldings or moldings with large wall thickness jumps.

Polyamides are characterized by a variety of advantageous properties, e.g. high toughness, high temperature resistance u.a. which secure their place in the market in the field of engineering thermoplastics. These basic properties of the polyamides are generally modified by the addition of additives or additives. Polyamide and additives together give the so-called composite materials or molding compounds. By processing these molding compounds in the injection molding process, the so-called moldings are obtained.

The properties of the polyamides can be significantly increased by the addition of additives, for example the reinforcement by glass fibers, glass beads, mineral fillers and mixtures thereof. An elastomer modification improves the impact resistance of polyamides. Polyamide composite materials are high-quality thermoplastics, which are characterized by high heat resistance, very good mechanical properties, high toughness, good resistance to chemicals and easy processability. Due to the large number of possible combinations, new customized products are being developed for special applications.

The range of applications of polyamides and polyamide composites includes fibers, films, hot melt adhesives and molded parts for the electrical, construction, furniture and automotive industries. Reinforced polyamides are among the high-quality engineering products that have replaced metal applications in a number of areas.

As partially crystalline polymers with a very high proportion of hydrogen bonds, the polyamides have low melt viscosities. Polyamides with relative viscosities of 3 (measured in 1% strength

Metakresollösung at 25 ⁰ C) have proven very successful for the production of moldings in injection molding. For the production of foils, profiles, tubes in the extrusion process and

Semi-finished thermoforming molds use polyamides of increased viscosities. For particularly thin-walled components, for example, polyamides with low viscosities can be used.

By adding additives such as carbon fibers, glass fibers, glass beads, glass flakes, amorphous silica, calcium silicate, calcium metasilicate, magnesium carbonate, kaolin, chalk, powdered quartz, mica, barium sulfate, feldspar, pigments, carbon black and graphite but the melt viscosity is influenced so that the melt is less flowable. This is noticeable, for example, in that a higher filling pressure is produced during injection molding. The higher the filler content in the melt, the higher is the filling pressure as a rule.

Under thin-wall technology according to the invention is understood the technology used to produce moldings with wall thicknesses between 0.1 mm and 1.0 mm or for the production of moldings with Wanddickensprüngen of basic bodies with wall thicknesses of 1.0 mm to 5.0 mm and intermediate elements with wall thicknesses from 0.1 mm to 1.0 mm is used. Exemplary of such applications are film hinges or mobile phone cases or carrier plates for electric boxes called.

The reduction of the wall thickness is the goal of an economical and functional construction. The reasons for reducing the wall thickness are the saving of material and, manufacturing costs and a reduction of the components.

In the case of molded parts with a very small wall thickness or with large wall thickness jumps, the molding composition is subjected to high mechanical and thermal stress during the injection molding process. The qualitative course of speed, shear rate and temperature as a function of the molding cross-section is known to the person skilled in the art and described, for example, in "Anwendungsstechnische Information 1118 d, e; Bayer AG, 2000. "In molded part cross-sections, the speed for thermoplastic molding compounds has a characteristic profile and the shear rate has a maximum in the layers close to the edge comes to damage the material.

The improvement of the flowability of polyamide melts can be achieved in different ways. Described are, for example, the addition of prepolymers or the post-condensation of low molecular weight polyamides or the addition of reactive components during the polymerization.

EP-A 0272 695 discloses the use of low molecular weight polyamides to improve processability. However, two extrusion steps are necessary, with the low molecular weight polyamide reacting with the high molecular weight polyamide. However, the mechanical properties are influenced by the addition of lower viscosity components.

EP-A 0 966 497 describes the copolymerization of polyamide 66 or polyamide 46 with cycloaliphatic dicarboxylic acids or diamines, wherein a flow-improving effect also occurs. However, a disadvantage of the process is that a copolymerization takes place. A Compounding is not possible because there would be no controlled reaction in the appropriate time span without decomposing the matrix.

EP-A 0 553 617 discloses the preparation of low molecular weight melts which are provided with fillers. A disadvantage, however, is that in a second step, a solid phase after-condensation takes place on the granules. The actual processing of the granules shows no processing advantages through flow improvement.

US-A-6 525 166 discloses high flow polyamides by copolymerization of lactams with tetrafunctional acids. A disadvantage of the method is that it is an autoclave process. In further process steps, the polyamide must then be extracted and dried. Furthermore, short-chain polyamides are formed, which means a loss in mechanical properties.

The stiffness of a molded part is an important aspect to be considered with decreasing wall thickness of molded parts. The stiffness of the molded part protects it against deformation under mechanical load. The rigidity of a molded part depends inter alia also on the modulus of elasticity of the material used. In addition to improved flowability, the materials for thin-wall technology should therefore also have a high rigidity.

The prior art shows improvement in the flowability of molding compositions based on polyamides by chemical modification of the base resin or addition of low-molecular compounds. An improvement in the flowability and molding compositions based on polyamides with simultaneous improvement of the modulus of elasticity, which would allow these molding compounds in micro injection molding for the production of moldings with wall thicknesses between 0.1 mm and 1.0 mm, is not yet known.

For many applications in injection molding but just low filling pressures are advantageous. This applies, for example, to the filling of cavities with small wall thicknesses or large wall thickness jumps. Furthermore, machines with lower drive power or lower injection pressure can be used at low filling pressures. Also, the injection mold is exposed to reduced filling pressure less stress, requires a lower clamping force and can be made cheaper.

The object of the invention was therefore the preparation of polyamide molding compositions, which improved with good properties such as modulus of elasticity, heat resistance, surface quality and density

Flow properties, resulting in a reduced filling pressure in the injection molding process for thin-walled moldings with wall thicknesses of 0.1 mm to 1.0 mm or molded parts with Wanddickensprünge containing elements with wall thicknesses of 0.1 mm to 1.0 mm makes noticeable.

Surprisingly, it has been found that in the production of polyamide nanofiller composites, the effects described above are achieved. It was particularly surprising that the filling pressure of the molding composition was lowered by the addition of nanoscale particles, while inorganic fillers known to the person skilled in the art increase the filling pressure of polyamide molding compositions. Furthermore, it was particularly surprising that the effect of Fülldruck¬ reduction is maintained, in particular for small wall thicknesses, even amplified. As the experiments in the context of the present invention showed, this effect is due to the wall sliding of the molding compositions according to the invention, whereby the characteristic profile described above is changed.

Object of the present invention and solution of the problem is therefore the use of thermoplastic molding compositions of polyamide and nanoscale fillers for the production of moldings with wall thicknesses between 0.1 mm and 1.0 mm or molded parts with wall thickness jump containing elements with wall thicknesses of 0.1 mm to 1 , 0 mm in the injection molding process.

The present invention further relates to injection molding processes for the production of moldings having wall thicknesses between 0.1 mm and 1.0 mm or of elements with wall thickness jump containing elements with wall thicknesses of 0.1 mm to 1.0 mm, characterized in that thermoplastic molding compositions of polyamide and nanoscale fillers.

Finally, the present invention relates to moldings produced from nanoscale particles containing polyamide molding compositions, characterized in that they have an increased modulus of elasticity and are obtained by means of reduced filling pressure in the injection molding process.

Surprisingly, the molding compositions based on polyamide and nanoscale fillers show extraordinarily improved flow properties with a simultaneously increased modulus of elasticity, which make it possible to significantly reduce the filling pressure during compression to form parts, which makes it possible to obtain molded parts with wall thicknesses of less than 1 mm, preferably 0.1 mm to 1.0 mm, more preferably from 0.15 mm to 0.95 mm.

Nanoscale fillers are particles whose length dimension is less than 1 micron in at least one dimension (a selectable direction). Nanoscale fillers may be unmodified or modified. Nanoscale fillers include, for example, phyllosilicates, which are available synthetically or naturally. These include, for example, the clay minerals allevardite, amesite, beidellite, bentonite, fluorhectorite, fluoromelicite, mica, Halloysite, hectorite, with, montmorillonite, muscovite, nontronite, palygorskite, saponite, sepiolite, smectite, stevensite, talc, vermicullite, and synthetic talc types; also the alkali metal silicates maghemite, magadiite, kenyaite, makatite, silinaite, grumantite, revdite as well as their hydrated forms and the associated crystalline silicas. In addition, other inorganic layer compounds such as hydrotalcites, double hydroxides and heteropolyacids can be used.

Modifications to the nanoscale fillers may e.g. be used to increase the layer spacings in sheet silicates, for better processability or to increase the phase compatibility between nanoscale filler and polymer matrix.

Methods of making polyamide nanofiller composites may be continuous, semi-continuous or batch-wise. The processes can be carried out in one or more stages. During processing processing aids can be used.

In the present invention, the nanoscale fillers have a reinforcing Emfluss and thus lead to an advantageous mechanical profile. For example, the stiffness and the modulus of elasticity are increased even with small proportions of nanoscale fillers. The density of the composite materials is often lower than with the addition of non-nanoscale fillers. The nanoscale fillers can be added to the polyamide molding compositions but also to improve the flame retardancy.

Examples

The following products were used in the examples:

• Polyamide 6: Durethan® B29, Lanxess Deutschland GmbH, relative viscosity η _reI . = 2.0; 0.5% by weight solution in wi-cresol; LPDU 601-204, Lanxess Deutschland GmbH, polyamide 6 containing 2% phyllosilicate, relative viscosity η _re] . =

2.0; 0.5% by weight solution in m-cresol;

• Glass fiber: CS7928, Lanxess Germany GmbH

• Nanofiller: phyllosilicate Nanomer® I.24TL, Nanocor

• Mica: Mica AK40S, Kemira Company • Talc: Mistron Vapor Regular® RP 6, Luzenac

• Carbon black: Ketjenblack® EC-600 JD, Akzo Nobel

• Graphite: graphite semolina EG32, SGL Carbon Group

The composite materials were produced on a ZSK 32/2 twin-screw extruder. The throughput was 10 kg / h, the setting temperature was 260 ⁰ C. The melt was discharged in strands in a water bath and then granulated. After drying, the granules were sprayed on an injection molding machine of the type Arburg 320-210-500 at melt temperatures of about 28O ⁰ C and a mold temperature of 80 ⁰ C to standard test specimens.

The measurement of the filling pressure takes place during spraying of the standard test specimen for the tensile test via a pressure sensor near the sprue on the injection mold. The pressure at the discontinuity in the mold internal pressure curve is determined between the shallower pressure rise during the mold filling phase and the steeper rise during the compression phase of the melt. Table 1

*: By additive is meant a powdered polyamide, which is mixed with the respective fillers (mica, Nanofiller, etc.) to ensure a high dosing accuracy.

From Table 1 it can be seen that by adding 2% phyllosilicate the filling pressure is lowered while the tensile modulus increases (Examples 1-5). This is not observed when adding other inorganic fillers.

Claims

claims

1. Use of thermoplastic molding compositions of polyamide and nanoscale fillers, characterized in that these in the injection molding process for the production of moldings with wall thicknesses between 0.1 mm and 1 mm or of moldings with wall thickness jump containing elements with wall thicknesses of 0, 1 mm to 1.0 mm are used.

2. Production of moldings with wall thicknesses between 0.1 mm and 1 mm or of moldings with wall thickness jump containing elements with wall thicknesses of 0.1 mm to 1.0 mm, characterized in that thermoplastic molding compositions of polyamide and nanoscale fillers are used.

3. Moldings with wall thicknesses between 0.1 mm and 1 mm or moldings with wall thickness jump containing elements with wall thicknesses of 0.1 mm to 1.0 mm available from nanoscale particles containing polyamide molding compositions characterized in that they have an increased modulus of elasticity and means reduced filling pressure can be obtained in the injection molding process.