RU2803570C1 - Foamed polypropylene beads, a method for producing foamed polypropylene beads, molded articles obtained from foamed polypropylene beads, and a method for producing such molded articles - Google Patents

Abstract

FIELD: chemistry technology.

SUBSTANCE: group of inventions relates to foamed polypropylene beads, a method for manufacturing foamed polypropylene beads, moulded products obtained from foamed polypropylene beads, and a method for manufacturing such moulded products. Foamed polypropylene beads for the manufacture of moulded articles are described containing a polypropylene composition (K) having: a) a melt flow index MFR₂ determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg, 1.5 to 15.0 g/10 min, b) melting point Tm, determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158°C, and c) loss tangent tanδ at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00, while the polypropylene composition (K) comprises more than 90.0 wt.%, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt.% comonomer or comonomers selected from ethylene and C₄ -C₁₀ alpha-olefins, and an active foam nucleator. A polypropylene composition (K) is used to obtain foamed polypropylene beads having a density of 25 to 150 g/dm³ and a content of closed cells greater than or equal to 80%, and the use of foamed polypropylene beads containing composition (K) to obtain moulded products. having a density of 25 to 150 g/dm³ and the content of closed cells greater than or equal to 80%.

EFFECT: provision of foamed polypropylene beads having an advantageous low content of open cells and good density, suitable for obtaining moulded products by means of a moulding process in a steam chamber at a pressure equal to or less than 0.4 MPa (4 bar), with a short steam treatment time.

17 cl, 4 tbl, 8 ex

Description

The present invention relates to foamed polypropylene beads, a method for making foamed polypropylene beads, molded products made from foamed polypropylene beads, and a method for making such molded products.

State of the art

Foamed and porous polyolefins have long been used in applications requiring lightweight materials with properties such as thermal and sound insulation. One of the most common polyolefin foams is expanded polystyrene (XPS), commonly used for packaging materials. An alternative to XPS is polypropylene foam (EPF). Foamed polypropylene is a versatile foam material that exhibits superior energy absorption, impact resistance, water and chemical resistance, an exceptionally high strength-to-weight ratio and 100% recyclability.

The most efficient method for making foamed polypropylene products involves first forming foamed polypropylene beads, which are then molded together to form the product. A typical method for producing these foam beads involves an autoclave process which produces excellent results, however such processes are notoriously expensive and complex. A more economical method involves producing foamed polypropylene beads directly during the extrusion process. Effective methods have been developed, but beads produced by such processes typically require much more stringent conditions to fuse the beads together when molding foam products. Balls formed in the autoclave process typically require 0.3 to 0.4 MPa (3 to 4 bar) steam pressure during the steam chamber molding process, while extruded balls typically require 0.4 to 0 steam pressure .8 MPa (4 to 8 bar). This higher pressure requirement means that only specialized equipment can be used in the molding process, while lower pressure steam chamber molding equipment is much more common as it can also be used to fuse XPS beads and autoclaved runway beads.

Therefore, there is a need for new polypropylene foam beads suitable for molding in steam chambers at lower pressures to enable highly economical production of polypropylene foam products.

It is generally accepted in the art, for example in KR 101014002 B1, that the formation of polypropylene foam beads having multiple melting points is useful for producing molded articles therefrom.

In US 6315931 B1 a similar effect is achieved by forming foam particles enclosed in a film, while in EP 0778310 B1 multiple foaming stages are used.

EP 3489287 A1 describes pre-foamed polypropylene beads with low open cell content and favorable molding properties, manufactured by selecting highly specialized polypropylene resins according to the equation: tan δ≤0.32×V+0.1. Although this is a promising development in theory, very strict restrictions on the selection of polypropylene-based resins mean that the process is limited in practice.

Further development is needed to identify suitable polypropylene foam beads for widespread use.

Brief description of the invention

The present invention is based on the discovery that by selecting a polypropylene composition having suitable properties, polypropylene foam beads can be produced having an advantageous low open cell content and good density and, most importantly, are suitable for producing molded articles through the spin molding process. steam chamber at a pressure equal to or less than 0.4 MPa (4 bar), and only a short steaming time is required.

The present invention is directed to propylene foam beads containing a polypropylene composition (K) having:

a) melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00,

wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins.

In another aspect, the present invention relates to a method for producing foamed propylene beads by extruding a polypropylene composition (K) using a physical blowing agent in which the pressure drop rate defined in equation (ii) is greater than or equal to 5000 bar/s:

where the pressure drop is expressed in bars,

line productivity is expressed in kg/h,

the melt density for all samples is approximately 1000 kg/ ^m3 ,

the radius (r) of the holes in the matrix plate is expressed in m and the length of the area of the holes in the matrix plate is expressed in m,

and to foamed propylene beads obtained by the specified method.

The present invention further relates to a method for producing molded articles from foamed polypropylene beads of the present invention using a steam chamber molding process, preferably a pressure-fill steam chamber molding process, using a steam pressure equal to or less than 0.4 MPa (4 bar ).

In another aspect, the present invention relates to molded articles obtained from foamed polypropylene beads of the present invention, obtained by the process of the present invention, having a density of from 25 to 150 g/dm ³ and a closed cell content of more than 80 wt. %.

The present invention is further directed to the use of a polypropylene composition (K) having:

a) melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00,

wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins,

in an extrusion process using a physical blowing agent in which the pressure drop rate defined in equation (ii) is greater than or equal to 5000 bar/s:

where the pressure drop is expressed in bars,

line productivity is expressed in kg/h,

the melt density for all samples is approximately equal to 1000 kg/m ³ for all samples,

the radius (r) of the holes in the matrix plate is expressed in m and the length of the platform of the holes in the matrix is expressed in m,

to produce foamed polypropylene balls having a density of 25 to 150 g/dm ³ and a closed cell content of more than 80 wt. %.

In addition, the invention relates to the use of foamed polypropylene beads containing a polypropylene composition (K) having:

a) melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 1.90 to 4.00,

wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins,

using a steam chamber molding process, preferably a pressurized steam chamber molding process, using a steam pressure equal to or less than 0.4 MPa (4 bar),

to produce molded products having a density from 25 to 150 g/dm ³ and a closed cell content of more than 80 wt. %.

Definitions

An active foam nucleator is a foam nucleator that further contains a chemical foaming agent, thus having the dual effect of bubble formation and crystal nucleation. These may be organic (eg azodicarbonamide) or inorganic (eg hydrocerol type) nucleating agents, although they may sometimes additionally include particulate auxiliary nucleating agents.

Foamed polypropylene beads are polypropylene particles produced by the so-called "pressure release expansion method (from a high pressure state to a low pressure state to expand the particles)", in which a volatile blowing agent is dissolved in polypropylene under high pressure, followed by a decrease in pressure, resulting in whereby the volatile foaming agent either chemically produces gas or simply boils, forming gas bubbles (or cells) within the polypropylene matrix.

A complete part is defined as a homogeneous molded product of foam beads with a smooth surface. The runway part has clearly defined corners and edges and consists of runway balls connected to each other. The surface of the part can be scratched manually with a pen without releasing individual balls. Less than 5% of individual beads fall out of the mold when it is opened after steaming and cooling.

Inorganic particulate cell nucleators

Inorganic cell nucleating agents are insoluble in polyolefin compositions and are thus present in particulate form, unlike organic cell nucleating agents which are partially soluble in polyolefin compositions under certain conditions. A typical inorganic cell nucleator may be talc or mica.

Organic nucleating agents are partially soluble in polyolefin compositions and promote crystal growth. They are generally not considered to be particulate nucleators, unlike talc or mica.

Detailed Description of the Invention

Polypropylene composition (K)

An essential feature of the present invention is the selection of a suitable polypropylene composition for the formation of foamed polypropylene beads. As such, the polypropylene foam beads of the present invention contain a polypropylene composition (K) having specific properties.

The polypropylene composition (K) of the present invention has a melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min, more preferably from 1.8 to 10.0 g/10 min, most preferably 2.0 to 8.0 g/10 min.

The polypropylene composition (K) of the present invention has a melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158°C, preferably from 135 to 155°C, more preferably from 138 to 152°C , most preferably from 140 to 150°C.

Contrary to conventional wisdom in the art, it is not necessary to maintain two separate melting temperatures, but rather it is preferable that the polypropylene foam beads have only one melting point.

The polypropylene composition (K) of the present invention has a loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200° C. from 2.00 to 4.00, more preferably from 2.10 to 3.50, most preferably 2.20 to 3.00.

The polypropylene composition (K) of the present invention preferably has a maximum breaking force (Fmax), determined in the Rheotens test in accordance with ISO 16790, from 20 to 100 cN, more preferably from 22 to 70 cN, most preferably from 24 to 40 cN.

The polypropylene composition (K) of the present invention preferably has a maximum burst velocity (Vmax) determined in the Rheotens test according to ISO 16790 of 180 to 500 mm/s, more preferably 200 to 500 mm/s, most preferably 220 to 300 mm /With.

The polypropylene composition (K) of the present invention preferably has a foamability parameter (PV) defined in equation (i) from 300 to 1700,

in this case, the melt flow index (MFR ₂ ) is determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg and is expressed in g/10 min,

The melting point (Tm) is determined using differential scanning calorimetry in accordance with ISO 11357 and is expressed in °C,

and the maximum breaking force (Fmax) is determined in the Rheotens test in accordance with ISO 16790 and is expressed in cN.

More preferably, the foaming parameter is from 400 to 1700, even more preferably from 450 to 1650, and most preferably from 490 to 1600.

As such, the polypropylene composition of the present invention has:

a) melt flow index ( _MFI2 ), determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min, more preferably from 1.8 to 10.0 g/10 min, most preferably from 2.0 to 8.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 155°C, more preferably from 138 to 152°C, most preferably from 140 to 150°C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00, more preferably from 2.10 to 3.50, most preferably from 2.20 to 3.00.

In addition, the polypropylene composition of the present invention has one or more, preferably all, of the following properties:

a) maximum breaking force (Fmax), determined in the Rheotens test in accordance with ISO 16790, from 20 to 100 cN, more preferably from 22 to 70 cN, most preferably from 24 to 40 cN;

b) maximum burst velocity (Vmax), determined in the Rheotens test in accordance with ISO 16790, from 180 to 500 mm/s, more preferably from 200 to 500 mm/s, most preferably from 220 to 300 mm/s, and

c) the foaming parameter (FC) defined in equation (i) is from 450 to 1700, more preferably from 470 to 1650, most preferably from 490 to 1600.

The polypropylene composition (K) of the present invention contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (c-PP).

The long-chain branched copolymer (c-PP) of the present invention contains up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins.

Preferably, the long-chain branched copolymer (c-PP) of the present invention contains from 0.5 to 8.0 wt. %, more preferably from 1.0 to 7.0 wt. %, even more preferably from 2.0 to 6.0 wt. %, most preferably from 3.0 to 5.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins.

The long chain branched copolymer (c-PP) comonomer(s) are selected from ethylene and C ₄ -C ₁₀ alpha-olefins, more preferably ethylene. In a particularly preferred embodiment, ethylene is the only comonomer present in the long-chain branched copolymer (c-PP).

The long chain branched copolymer (c-PP) of the present invention preferably has a branching index g' less than 0.95, more preferably less than 0.90, most preferably less than 0.85. The branching index g' is usually not lower than 0.50.

When attempting to produce foamed polypropylene beads, a nucleating agent is typically used to promote the formation of cells of regular size. Typical cell nucleation agents are talc, calcium carbonate and cellulose powder.

Inorganic particulate cell nucleators have been found to be detrimental to closed cell formation in the context of the present invention.

Thus, preferably the polypropylene composition (K) contains less than 0.20 wt. % talc based on the total weight of the polypropylene composition (K), more preferably less than 0.10 wt. % talc, most preferably the polypropylene composition (K) does not contain talc.

In addition, preferably the polypropylene composition (K) contains less than 0.20 wt. %, based on the total weight of the polypropylene composition (K), inorganic cell nucleating agents in the form of particles, more preferably less than 0.10 wt. % inorganic particulate cell nucleating agents, most preferably the polypropylene composition (C) does not contain particulate inorganic cell nucleating agents.

To stimulate cell nucleation, it is useful to use an active cell nucleator.

Thus, preferably the polypropylene composition (K) contains from 0.01 to 0.30 wt. %, based on the total weight of the polypropylene composition (K), the active cell nucleator, more preferably from 0.05 to 0.25 wt. %, most preferably from 0.10 to 0.20 wt. %.

Particularly preferably, the active cell nucleator is an organic active foam nucleator.

Therefore, preferably the polypropylene composition (K) contains from 0.01 to 0.30 wt. %, based on the total weight of the polypropylene composition (K), organic active foam nucleator, more preferably from 0.05 to 0.25 wt. %, most preferably from 0.10 to 0.20 wt. %.

In addition, preferably the polypropylene composition (K) contains from 0.01 to 0.30 wt. %, based on the total weight of the polypropylene composition (K), hydrocerol, more preferably from 0.05 to 0.25 wt. %, most preferably from 0.10 to 0.20 wt. %.

Foamed polypropylene balls

The foamed polypropylene beads of the present invention contain a polypropylene composition (K).

Preferably, the polypropylene foam beads have a density of 25 to 150 g/dm ³ , more preferably 25 to 100 g/dm ³ , most preferably 25 to 80 g/dm ³ .

The polypropylene foam beads of the present invention preferably have a closed cell content greater than or equal to 80%, more preferably greater than or equal to 85%, most preferably greater than or equal to 90%.

Moreover, preferably, the foamed polypropylene beads according to the present invention have a melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230° C. and a load of 2.16 kg on crushed samples of molded articles obtained from said beads, from 3.0 up to 20.0 g/10 min, more preferably from 3.0 to 15.0 g/10 min, most preferably from 3.5 to 10.0 g/10 min.

Method for producing foamed polypropylene balls

The present invention also relates to a method for producing foamed polypropylene beads.

It has been found that producing foamed polypropylene beads by extruding a polypropylene composition using a physical blowing agent having characteristics suitable for producing molded articles by steam molding can be dependent on a number of process parameters.

In particular, the key determining factor was found to be the pressure drop rate (PDR) of the polypropylene composition as it exits the die plate.

Thus, the process of producing foamed polypropylene beads by extruding a polypropylene composition using a physical blowing agent has a pressure drop rate, as defined in equation (ii), greater than or equal to 5000 bar/s:

where the pressure drop is expressed in bar, the line capacity is expressed in kg/h,

the melt density for all samples is approximately equal to 1000 kg/m ³ for all samples,

the radius (r) of the holes in the die plate is expressed in m and the length of the pad of the holes in the die is expressed in m.

The maximum pressure drop rate is typically 20,000 bar/s.

Preferably, the pressure drop rate defined in equation (ii) is from 5000 to 20000 bar/s.

In the method for producing foamed polypropylene beads by extruding a polypropylene composition, a physical foaming agent is used. This physical blowing agent is preferably selected from isobutane and carbon dioxide, more preferably it is isobutane.

The requirement for a physical blowing agent does not mean that chemical blowing agents, such as those present in the active foam nucleator, cannot also be present.

The method of producing foamed polypropylene beads by extruding a polypropylene composition using a physical foaming agent is preferably carried out using:

a) a single-screw or twin-screw melt extruder where the energy consumption of the extruder is less than 0.1 kWh/kg;

b) static or dynamic cooling equipment;

c) multi-hole die plates and

d) underwater granulation systems.

Extruder energy consumption is defined as the energy of the main drive motor excluding heating and/or cooling energy.

Preferably, the polypropylene composition used, extruded using a foaming agent in accordance with the method of the invention, is a polypropylene composition (K) as defined above.

The present invention further relates to the polypropylene foam beads described in the preceding sections, which are obtained by the method described in this section.

Molded Products and Applications

Another aspect of the present invention is the use of foamed polypropylene beads for the manufacture of molded articles.

The method for producing molded articles in accordance with the present invention involves using a steam chamber molding process using a steam pressure equal to or less than 0.4 MPa (4 bar), more preferably equal to or less than 0.38 MPa (3.8 bar), most preferably equal to or less than 0.35 MPa (3.5 bar) to bind the balls into a complete part.

Preferably, the steam treatment time during the forming process in steam chambers is less than 30 seconds, more preferably less than 25 seconds, even more preferably less than 20 seconds, even more preferably less than 15 seconds, even more preferably less than 10 seconds, most preferably less than 6 seconds.

Further preferably, the steam chamber molding process is a pressure filled steam chamber molding process using steam pressure and possibly steaming time as stated above.

In addition, the present invention relates to molded articles obtained from foamed polypropylene beads, as described in the preceding sections.

The present invention is further directed to foamed polypropylene beads, as described in the preceding sections, which, after being subjected to a steam chamber molding process as defined in this section, form a complete part.

The molded articles of the present invention have a density of 25 to 150 g/dm ³ , more preferably 25 to 140 g/dm ³ , most preferably 25 to 130 g/dm ³ .

The molded articles of the present invention have a closed cell content greater than or equal to 80 wt. %, more preferably greater than or equal to 85%, most preferably greater than or equal to 90%.

The molded articles of the present invention preferably have a melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg on ground samples of the molded article, from 3.0 to 20.0 g/10 min, more preferably 3.0 to 15.0 g/10 min, most preferably 3.5 to 10.0 g/10 min.

Preferably, the molded articles of the present invention are produced using a steam chamber molding process, preferably a steam chamber molding process at a pressure equal to or less than 0.4 MPa (4 bar) as described above.

The present invention is also directed to the use of a polypropylene composition (K) having:

a) melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00;

wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins,

in an extrusion process using a physical blowing agent, where the pressure drop rate, as defined in equation (ii), is greater than or equal to 5000 bar/s,

to produce foamed polypropylene beads having a density of 25 to 150 g/dm ³ and a closed cell content greater than or equal to 80%.

The present invention is also directed to the use of foamed polypropylene beads containing a polypropylene composition (K) having:

a) melt flow index (MFI ₂ ), determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min;

b) melting point (Tm), determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and

c) loss tangent (tan δ) at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00;

wherein the polypropylene composition (C) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (C), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer(s) selected from ethylene and C ₄ -C ₁₀ alpha-olefins,

in a steam chamber molding process, preferably in a pressure steam chamber molding process, using a steam pressure equal to or less than 0.4 MPa (4 bar),

to produce molded products having a density of 25 to 150 g/dm ³ and a closed cell content greater than or equal to 80%.

All preferred ranges disclosed for the polypropylene composition (K) and expanded polypropylene beads, as well as the method of producing polypropylene beads using a physical blowing agent and the method of producing molded articles containing expanded polypropylene beads, are also suitable for the applications described above.

Examples

1. Definitions/Measurement Methods

Melt flow rate

The melt flow index (MFI) is determined in accordance with ISO 1133 and is indicated in g/10 min. MFR is an indicator of the fluidity and, therefore, the manufacturability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. MFR2 of polypropylene is determined at a temperature of 230°C and a load of 2.16 kg.

Differential scanning calorimetry (DSC)

In differential scanning calorimetry (DSC) analysis, the melting point (Tm) and melting enthalpy (Hmel), crystallization temperature (Tcr) and heat of crystallization (Hk, Hcr) are measured using a differential scanning calorimetry (DSC) TA Instrument Q200 device on samples weighing from 5 to 7 mg. DSC is carried out in accordance with ISO 11357/part 3/method C2 in a heating/cooling/heating cycle with a scan rate of 10°C/min over a temperature range of -30 to +225°C. The crystallization temperature (Tk) and the heat of crystallization (Hk) are determined at the cooling stage, and the melting temperature (Tm) and the enthalpy of fusion (Hmel) are determined at the second heating stage.

Density

Density was measured according to Archimedes' principle by determining the mass (t) and volume (V) of the sample and calculating its density (d), respectively (d=m/V).

In a graduated cylinder containing water at 23°C, approximately 500 ml (weight W1) of polypropylene beads are immersed using a wire mesh and maintained at 23°C and 50% relative humidity for 48 hours. The apparent volume V1 (l) is determined by the rise in water level. The apparent density is obtained by dividing the weight W1 (g) of the polypropylene beads (b) by the apparent volume V1 ( ^cm3 )

Density=W1/V1

Rheotens test (Fmax and Vmax)

The test described here is in accordance with ISO 16790:2005.

The nature of strain hardening is determined by the method described in the article “Rheotens-Mastercurves and Drawability of Polymer Melts”, M.H. Wagner, Polymer Engineering and Science, Vol. 36, pp. 925-935. The contents of the document are incorporated by reference. The strain hardening of polymers is analyzed using a Rheotens device (from Gottfert, Siemensstr. 2, 74711 Buchen, Germany), in which the melt filament is elongated by drawing at a certain acceleration.

The Rheotens experiment simulates industrial spinning and extrusion processes. Basically the melt is pressed or extruded through a round head and the resulting filament is drawn. The load on the extrudate is recorded depending on the properties of the melt and the measured parameters (in particular, the relationship between the exit speed and the peel speed, which is practically a measure of the rate of extension). To obtain the results presented below, the materials were extruded using a HAAKE Polylab system laboratory extruder and a cylindrical head gear pump (L/D=6.0/2.0 mm). The gear pump was preset at a flow rate of 2.1 g/min, the pressure upstream of the gear pump was 3 MPa (30 bar), and the melt temperature was set at 200°C. The length of the spinning line between the die and the Rheotens wheels was 100 mm. At the beginning of the experiment, the winding speed of the Rheotens wheels was adjusted according to the speed of the extruded polymer filament (tensile force equal to zero). The experiment was then started by slowly increasing the winding speed of the Rheotens wheels until the polymer thread broke. The acceleration of the wheels was small enough that the tensile force was measured under quasi-stationary conditions. The acceleration of the melt thread (2) pulled down is 120 mm/s ² . Rheotens was operated in conjunction with the computer program EXTENS. It is a real-time data acquisition program that displays and stores measured data of tensile force and drawing speed. The end points of the Rheotens curve (force versus pulley speed) are taken to be Fmax and Vmax.

Comonomer content

Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers. Quantitative ^13C { ^1H } NMR spectra were recorded in the dissolved state on a Bruker Advance III 400 NMR spectrometer operating at frequencies of 400.15 and 100.62 MHz for 1H and 13C, respectively. All spectra were recorded using a ^13C optimized 10mm extended temperature sensor head at 125°C using nitrogen gas for all pneumatics.

Approximately 200 mg of the material was dissolved in 3 ml of 1,2-tetrachloroethane-d2 (TCE-d2) with chromium (III) acetylacetonate (Cr(acac)3), resulting in a solution of relaxant with a concentration of 65 mM in the solvent (Singh, G ., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure the homogeneity of the solution, after the initial preparation of the sample in the thermoblock, the NMR tube was additionally heated in a rotating oven for at least 1 hour. After insertion into the magnet, the tube rotated at a frequency of 10 Hz. This setup was chosen primarily due to the high resolution and quantitative requirements for accurate ethylene quantification. Standard single-pulse excitation was used without NOE, using an optimized tip angle, a 1-second recycle delay, and a WALTZ16 two-level decoupling circuit (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong).,R. , Taha, A., Baugh, D. Winniford, V., J. Mag Reson., 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R. Severn, J., Talarico, G., Macromol. Rapid Commun., 2007, 28, 1 128). A total of 6144 (6k) transition states were obtained per spectrum.

Quantitative ^13C { ^1H } NMR spectra were processed, integrated, and corresponding quantitative properties were determined from integrals using proprietary computer programs. All chemical shifts were indirectly attributed to the central methylene group of the ethylene block (EEE) at 30.00 ppm. using solvent chemical shift. This approach allowed for comparable references even in the absence of this structural unit. Characteristic signals consistent with the incorporation of ethylene were observed (Cheng, HN, Macromolecules 17 (1984), 1950).

The comonomer fraction was quantified using the method of Wang et. others (Wang, W.J., Zhu, S., Macromolecules 33 (2000), 1 157) by integrating multiple signals across the entire spectral range in 13C spectra. This method was chosen due to its robust nature and ability to accommodate the presence of regio-defects when necessary. The integral regions have been slightly adjusted to improve applicability across the range of comonomer contents encountered. For systems in which only isolated ethylene in PPEPP sequences was observed, the method of Wang et. etc. has been modified to reduce the influence of non-zero center integrals that are known to be missing. This approach reduced the overestimation of ethylene content for such systems and was achieved by reducing the number of centers used to determine the absolute ethylene content to:

E=0.5(Spββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

When using this set of centers, the corresponding integral equation takes the form:

E=0.5(IH+IG+0.5(IC+ID))

using the same notation as in the paper by Wang et. others (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1 157). The equations used for absolute propylene content were not modified. The molar percentage of comonomer incorporation was calculated from the mole fraction:

E [moln. %] = 100*fE

The mass percentage of comonomer inclusion was calculated from the mole fraction:

E [wt %] = 100*(fE*28.06) / ((IE*28.06)+((1-IE)*42.08))

Branching index g'

The branching index g' is defined as g'=[IV]br/[IV]lin, where g' is the branching index, [IV]br is the intrinsic viscosity of branched polypropylene measured in decalin at 135°C, and [IV]lin represents is the intrinsic viscosity of linear polypropylene having the same mass average molecular weight (in the range of ±10%) as branched polypropylene, calculated on the basis of size exclusion chromatography (SEC) in trichlorobenzene at 140°C. Thus, a low g' value is indicative of a highly branched polymer. In other words, if the value of g' decreases, the branching of polypropylene increases. In this context, reference is made to V.N. Zimm and W.H. Stockmeyer, J. Chem. Phys. 17, 1301 (1949).

Loss tangent tan δ

The polypropylene resin was heat-pressed for 5 minutes at 190°C using a 1.5 mm thick spacer to obtain a 1.5 mm thick press plate, and a test specimen was punched out of the press plate using a φ25 mm punch. The measuring device used was an ARES device for measuring viscoelastic properties produced by TA Instruments. A φ25 mm parallel plate type device was attached to the device for measuring viscoelastic properties. The constant temperature bath was positioned to surround the jig, and the constant temperature bath was maintained at 200° C. so that the jig was preheated. The constant temperature bath was then opened and a 25 mm diameter test piece was inserted between the parallel plates. The constant temperature bath was then closed and the test sample was preheated for 5 minutes. After this, the gap between the parallel plates was narrowed to 1 mm, so that the sample was compressed. After compression, the constant temperature bath was opened again and the resin protruding from the parallel plates was removed using a brass spatula. The constant temperature bath was closed and the constant temperature bath was heated for 5 minutes. After this, the measurement of dynamic viscoelastic characteristics began. The measurement was carried out at an angular frequency from 0.1 rad/s to 100 rad/s. The storage modulus and loss modulus at each angular frequency were obtained, and the loss tangent tan δ at each angular frequency was obtained as the calculated value. From these results, the value of the loss tangent tan δ was used at an angular frequency of 0.1 rad/s. In this case, the measurement was carried out with a deformation value of 5% in a nitrogen atmosphere.

Calculation of pressure drop rate

The rate of pressure drop in bar/s is calculated based on the test pressure during operation in front of the die plate (bar), the extruder capacity in kg/h, the assumed density of 1000 kg/m ³ , the number of holes in the die plate, the radius of the holes and the length of the die pad in meters.

Testing runway balls with open cells

The open cell content of the extruded AFFF beads was determined according to ISO 4590 Method 1 using an automatic gas pycnometer (Quantachrom Ultapyc 1200e). The test was carried out on 4 g beads in a 50 cm ³ test cell at 20°C using helium as a gas under a pressure of 2 MPa (20 mbar). The AFFF beads were treated for 12 hours at 60°C under a vacuum of 50 kPa (500 mbar) to remove foaming agent and conditioned for 24 hours at 20°C and 50% air humidity before the pycnometer test procedure.

Evaluation of the moldability of foam beads

Runway ball molding tests

The runway balls were formed into a test piece using Teubert TransTec72/52 using two different metal molds: a) 280*195*22 mm for tensile tests and b) 280*195*50 mm for compression tests.

Two mold filling technologies were tested: a) crack filling and b) pressure filling.

Using crack filling, AFFF beads were transported under low pressure in a hopper while the equipment was left slightly open (crack position). Compression of the rolls was achieved through mechanical closure of the crack. The ratio of the change in roll height upon closing the mold to the initial height is expressed as compression in %.

In runway pressure filling mode, the beads were transported using a higher pressure than the pressure (0.25 MPa (2.5 bar)) in the chamber (back pressure).

When evaluating the moldability of the foam beads in Table 3, the molding steam pressure and time were optimized until a uniform bead molding product with a smooth surface was obtained. The preferred filling technology was pressure filling, which was tested for the runway balls of Example IE1 and all comparative examples. Crack filling was only tested for those runway balls where pressure filling did not result in a uniform molded product.

The molded product was then kept in an oven at 80°C for 12 hours to obtain a molded PP bead sample.

Compression test of a molded runway sample

The compressive stress at 50% strain of the bead molded product is a value obtained using a Zwick 1485 universal testing machine. From each expansion molded product sample, a sample of 50 mm long, 50 mm wide and 30 mm high was cut, and This specimen was used to test at a specimen temperature of 23°C and a loading rate of 3 mm/min in accordance with ISO 844, and a graph of stress versus strain during loading on the specimen was obtained from the test data. From this graph, the compression at the moment of deformation of 50% was found, which was considered as the compressive stress of the sample of the product molded with expansion.

Three repetitions of the test were performed and the average values are shown in Table 4.

Elongation at break

The elongation at break of molded foam bead products was measured according to the method specified in DIN ISO 1789. More specifically, a test piece with dimensions of 155x25x10 mm, test piece type A (all surfaces are cut surfaces), cut from the molded products made from foam beads using a water jet were measured with an autograph (manufactured by Zwick model Z 1485) with a span of 55 mm between the support points and a test speed of 500 mm/min.

Flow index of a polymer melt in a runway ball

The AFFF balls were treated for 12 hours at 60°C under a vacuum of 50 kPa (500 mbar) to remove foaming agent and conditioned for 24 hours at 20°C and 50% air humidity before this test procedure.

10 g of AFFF beads were molded by pressing at 220°C into a hard plate 1 mm thick using a hot heated press. This solid polymer plate was crushed into 1-2 mm pieces before being tested at a melt flow rate of 230° C./2.16 kg.

1. Experimental part

Typical procedure for preparing polypropylene beads according to the invention

The AFFF foam line used includes a combination of metering devices, a unidirectional rotating twin screw extruder, a melt conditioning section including a melt cooler and a granulator for underwater granulation.

The foam line used in this work is a twin-screw foam extrusion line from Sulzer Ltd. It includes a 45 mm twin screw extruder with L/D=42 and 6 gravimetric feeders and a gas dosing station capable of supplying 3 different foaming agents, a melt cooler type 425 Torpedo, a static mixer SMB Plus DN40 and a die plate. Foaming agent(s) can be added to the extruder. The extruder contains heating elements and a water cooling system controlled by a patented algorithm to maintain a constant and uniform temperature distribution throughout the bodies and melt. The impregnation melt is fed into the conditioning section, which mainly consists of a heat exchanger, which allows the temperature to be uniformly controlled throughout the melt. The polymer melt is then volumetrically dosed by a gear pump and optionally passed through a screen before entering the diverter valve. A gear pump is used to provide constant melt flow and pressure for granulation, which is carried out in underwater granulation. The temperature of the melt cooler, gear pump, filter, diverter valve and pilot plant matrix is controlled by three independent heat transfer devices (HTUs) with coolant oil.

PP3 (Daploy™ WB260HMS) and 0.15 wt. % hydrocerol CF20 is dosed separately using gravimetric dosers into a twin-screw extruder with foaming at a speed of 20 kg/h. Isobutane is injected directly into the extruder through an injection valve. The melt temperature is brought to 133°C using a melt cooler, and the temperature on the matrix plate is brought to 142°C. To achieve an SOP of more than 5000 bar/s, a high SOP die plate was used, having 12 channels, each with a diameter of 1.1 mm and a pad length of 5.0 mm.

Preparation of comparative polypropylene balls

Comparative beads were prepared similarly to the beads of the invention using the conditions specified in Table 2, using polypropylenes as described in Table 1. Example IE2 demonstrates that carbon dioxide can also be used in the process of the present invention as an alternative to isobutane.

Preparation of products from foamed polypropylene balls according to the invention The resulting balls according to Table 2 were used in the production of molded products either by filling under pressure (as described in the "Methods" section) or by filling cracks when filling under pressure could not ensure the integrity of the part at maximum steam pressure of 0.48 MPa (4.8 bar) and a maximum steaming time of 15 seconds on each side.

The conditions for the formation of these products are given in Table 3, and the properties of the products thus obtained are given in Table 4.

As can be seen from Table 3, the balls obtained in CE1, CE2 and CE3 did not form an integral part when using the pressure filling method with a maximum back pressure of 0.25 MPa (2.5 bar) at a steam pressure of up to 0.48 MPa (4, 8 bar) and steaming time up to 15 seconds. To form a complete CE2 part, a crack filling method and a steam pressure of >0.4 MPa (4 bar) are required. Similarly, CE4 balls require a crack filling method due to their high open cell content, whereas IE1 balls according to the invention are suitable for a pressure filling method and can be processed using steam at a pressure of <0.4 MPa (4 bar).

The data in Table 4 demonstrates that foam products made from comparative AFFF beads have not only an undesirably higher open cell content, but also a much lower elongation at break. Product CE4 has lower compressive strength at both 25% and 50% strain. While CE2b exhibits good compressive strength, the large number of open cells will affect the insulating properties, and the requirement for a crack filling method in the steam chamber with long steaming times limits the production of molded parts.

Claims (59)

1. Foamed polypropylene balls for the manufacture of molded products containing a polypropylene composition (K) having: a) melt flow index PTR ₂ , determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min; b) melting point Tm, determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and c) loss tangent tan δ at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00, wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer or comonomers selected from ethylene and C ₄ -C ₁₀ alpha-olefins, and an active foam nucleator. 2. Foamed polypropylene balls according to claim 1, where the polypropylene composition (K) has: a) maximum breaking force Fmax, determined in the Rheotens test in accordance with ISO 16790, from 20 to 100 cN; b) maximum burst speed Vmax, determined in the Rheotens test according to ISO 16790, from 180 to 500 mm/s; and/or c) foaming parameter (FC) defined in equation (i), from 300 to 1700, , in this case, the melt flow index PTR2 is determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg and is expressed in g/10 min, The melting point Tmelt is determined using differential scanning calorimetry in accordance with ISO 11357 and is expressed in °C, and the maximum breaking force Fmax is determined in the Rheotens test in accordance with ISO 16790 and is expressed in cN, wherein the melting temperature Tmel has a value in the range from 138 to 152°C. 3. Foamed polypropylene balls according to any one of paragraphs. 1 or 2, wherein the long chain branched copolymer (c-PP) has a branching index g', determined from equation (iii), of less than 0.95: g'=[IV]br/[IV]lin (iii), where [IV]br is the intrinsic viscosity of branched polypropylene measured in decalin at 135° C. and [IV]lin is the intrinsic viscosity of linear polypropylene having the same weight average molecular weight, within the ±10% range, as branched polypropylene. 4. Foamed polypropylene beads according to any of the previous paragraphs, where the polypropylene composition (K) contains less than 0.3 wt. % inorganic cell nucleators in particle form. 5. Foamed polypropylene beads according to any of the previous paragraphs, where the polypropylene composition (K) contains from 0.01 to 0.3 wt. % active foam nucleating agent, preferably hydrocerol. 6. Foamed polypropylene beads according to any of the preceding claims, having a density of from 25 to 150 g/dm ³ and a closed cell content, determined in accordance with ISO 4590 method 1, greater than or equal to 80%. 7. A method for producing foamed polypropylene beads by extruding a polypropylene composition (K) having the properties defined in any of paragraphs. 1-5, using a physical blowing agent in which the pressure drop rate defined in equation (ii) is from 5000 to 20000 bar/s: , where the pressure drop at the outlet of the matrix plate is expressed in bars, line productivity is expressed in kg/h, The melt density for all samples is 1000 kg/ ^m3 , the radius (r) of the holes in the die plate is expressed in m and the length of the hole area in the matrix plate is expressed in m. 8. The method according to claim 7, in which the physical blowing agent is selected from isobutane and carbon dioxide. 9. The method according to any one of claims 7 or 8, in which the extrusion is carried out using a device including: a) single screw or twin screw melt extruder, where the energy consumption of the extruder is less than 0.1 kWh/kg; b) static or dynamic cooling equipment; c) a die plate with multiple holes and d) underwater granulation system. 10. Foamed polypropylene balls according to any one of paragraphs. 1-6, obtained by the method according to any one of paragraphs. 7-9. 11. A method for producing molded products from foamed polypropylene balls according to any one of paragraphs. 1-6 or 10 or obtained by the method according to any one of paragraphs. 7-9, using a steam chamber molding method using steam pressure equal to or less than 0.4 MPa (4 bar) to form the balls into a complete part. 12. The method according to claim 11, in which the steam treatment time is less than 30 s. 13. Foamed polypropylene balls according to any one of paragraphs. 1-6 or 10 or obtained by the method according to any one of paragraphs. 7-9, suitable for forming an integral part when processed by the method according to any one of paragraphs. 11 or 12. 14. A molded product made from foamed polypropylene beads according to any one of paragraphs. 1-6, 10 or 13 or beads obtained by the method according to any one of paragraphs. 7-9, having a density from 25 to 150 g/dm ³ and a closed cell content, determined according to ISO 4590 method 1, greater than or equal to 80%. 15. The molded product according to claim 14, which is obtained by the method according to any one of claims. 11 or 12. 16. Application of a polypropylene composition (K) having: a) melt flow index PTR ₂ , determined in accordance with ISO 1133 at 230 ° C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min; b) melting point Tm, determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158 °C, and c) loss tangent tan δ at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00, wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer or comonomers selected from ethylene and C ₄ -C ₁₀ alpha-olefins, in an extrusion process using a physical blowing agent in which the pressure drop rate determined by equation (ii) is between 5,000 and 20,000 bar/s: , where the pressure drop at the outlet of the matrix plate is expressed in bars, line productivity is expressed in kg/h, The melt density for all samples is 1000 kg/ ^m3 , the radius (r) of the holes in the die plate is expressed in m and the length of the hole area in the matrix plate is expressed in m, to produce foamed polypropylene beads having a density of 25 to 150 g/dm ³ and a closed cell content greater than or equal to 80%. 17. The use of foamed polypropylene balls, including a polypropylene composition (K) having: melt flow index PTR ₂ , determined in accordance with ISO 1133 at 230°C and a load of 2.16 kg, from 1.5 to 15.0 g/10 min; melting point Tm, determined by differential scanning calorimetry in accordance with ISO 11357, from 135 to 158°C, and loss tangent tan δ at an angular frequency of 0.1 rad/s when measuring dynamic viscoelastic characteristics at 200°C from 2.00 to 4.00, wherein the polypropylene composition (K) contains more than 90.0 wt. %, based on the total weight of the polypropylene composition (K), long-chain branched propylene copolymer (s-PP), including up to 8.0 wt. % comonomer or comonomers selected from ethylene and C ₄ -C ₁₀ alpha-olefins, during the molding process in a steam chamber using a steam pressure equal to or less than 0.4 MPa (4 bar), to produce molded products having a density of 25 to 150 g/dm ³ and a closed cell content greater than or equal to 80%.