SILANE CROSSLINKABLE FOAMABLE POLYOLEFIN COMPOSITION AND FOAM

Abstract

The present invention is directed to a foamable polyolefin composition which is crosslinkable by silane groups, to a crosslinked foam obtained from such a foamable polyolefin composition, and to a process for producing a crosslinked foam based on the foamable polyolefin composition. The foamable polyolefin composition comprises a polyethylene bearing hydrolysable silane groups and comonomer units comprising a polar group selected from the group consisting of acrylic acid, methacrylic acid, acrylates, methacrylates, vinyl esters, and mixtures thereof, a silanol condensation catalyst, a physical blowing agent, and a cell nucleating agent.

Claims

1. A polyolefin composition comprising: (A) a polyethylene bearing hydrolysable silane groups, (B) a silanol condensation catalyst, (C) a blowing agent, and (D) a cell nucleating agent, wherein the polyethylene bearing hydrolysable silane groups (A) is a copolymer of ethylene and a comonomer comprising a hydrolysable silane group and further comprises comonomer units comprising a polar group, wherein the comonomer units comprising a polar group are obtained from a comonomer selected from the group consisting of acrylic acid, methacrylic acid, acrylates, methacrylates, vinyl esters, and mixtures thereof, and wherein the blowing agent (C) comprises a physical blowing agent or a mixture of physical blowing agents.

2. The polyolefin composition according to claim 1, wherein the comonomer comprising a hydrolysable silane group is represented by the following formula:
R.sup.1SiR.sup.2.sub.qY.sub.3-q wherein R.sup.1 is an ethylenically unsaturated hydrocarbyl, hydrocarbyloxy or (meth)acryloxy hydrocarbyl group, each R.sup.2 is independently an aliphatic saturated hydrocarbyl group, Y, which may be the same or different, is a hydrolysable organic group, and q is 0, 1 or 2.

3. The polyolefin composition according to claim 1, wherein the comonomer comprising a hydrolysable silane group is represented by the following formula:
CH.sub.2═CHSi(OA).sub.3 wherein A is a hydrocarbyl group having 1 to 8 carbon atoms.

4. The polyolefin composition according to claim 1, wherein the silanol condensation catalyst (B) comprises an organic sulphonic acid or a precursor thereof including an acid anhydride thereof, or an organic sulphonic acid that has been provided with at least one hydrolysable protective group.

5. The polyolefin composition according to claim 1, wherein the content of the comonomer units comprising a polar group is 2.0 to 35.0 wt % based on the weight of the polyethylene bearing hydrolysable silane groups (A).

6. The polyolefin composition according to claim 1, wherein the content of the hydrolysable silane groups is 0.2 to 4.0 wt % based on the weight of the polyethylene bearing hydrolysable silane groups (A).

7. The polyolefin composition according to claim 1, wherein the amount of the polyethylene bearing hydrolysable silane groups (A) is 20.0 to 98.0 wt % based on the weight of the polyolefin composition.

8. The polyolefin composition according to claim 1, wherein the amount of the silanol condensation catalyst (B) is 1.0 to 9.0 wt % based on the weight of the polyethylene bearing hydrolysable silane groups (A).

9. The polyolefin composition according to claim 1, wherein the amount of the blowing agent (C) is 0.1 to 10 wt % based on the weight of the polyolefin composition.

10. The polyolefin composition according to claim 1, wherein the amount of the cell nucleating agent (D) is 0.1 to 5.0 wt % based on the weight of the polyolefin composition.

11. The polyolefin composition according to claim 1, wherein the cell nucleating agent (D) is a physical nucleating agent.

12. A crosslinked foam obtained from a polyolefin composition according to claim 1.

13. A process for producing a crosslinked foam comprising the following steps: a) providing a polyolefin composition, wherein the polyolefin composition is as defined in claim 1, b) extruding the polyolefin composition through a die of an extruder, c) allowing the extruded polyolefin composition to expand at ambient conditions, and d) allowing the extruded polyolefin composition to crosslink at ambient conditions.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0110] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

1.1 Ethylene Content

[0111] Quantitative .sup.13C {.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probe head at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent {8}. To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme {3, 4}. A total of 6144 (6 k) transients were acquired per spectra.

[0112] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed {7}.

[0113] The comonomer fraction was quantified using the method of Wang et. al. {6} through integration of multiple signals across the whole spectral region in the .sup.13C {.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regiodefects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents. For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et al. was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:

E=0.5(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

[0114] Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

using the same notation used in the article of Wang et al. {6}. Equations used for absolute propylene content were not modified.

[0115] The mole percent comonomer incorporation was calculated from the mole fraction:

E [mol %]=100*fE

[0116] The weight percent comonomer incorporation was calculated from the mole fraction:

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

BIBLIOGRAPHIC REFERENCES

[0117] 1) Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443. [0118] 2) Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251. [0119] 3) Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225. [0120] 4) Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128. [0121] 5) Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253. [0122] 6) Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157. [0123] 7) Cheng, H. N., Macromolecules 17 (1984), 1950. [0124] 8) Singh, G., Kothari, A., Gupta, V., Polymer Testing 285 (2009), 475. [0125] 9) Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150. [0126] 10) Randall, J. Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201. [0127] 11) Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253.

1.2 Melt Flow Rate

[0128] Melt flow rate MFR.sub.2 of polyethylene is determined according to ISO 1133 at 190° C. under a load of 2.16 kg.

1.3 Hardness

[0129] Hardness is determined by a Shore durometer according to DIN EN ISO 868.

1.4 Density

[0130] Density is measured according to ISO 1183-1—method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007. Foam densities are measured according to ISO 854

1.5 Density Reduction

[0131] The density of the base resin is compared with the density of the foam. The reduction of density in percent is calculated.

1.6 Cell Density

[0132] For the determination of the mean cell size, the cross-sectional area of about 60 cells (if available) was measured. Therefor the cells were marked manually in the picture analysing software of the Alicona system. The mean diameters of the cells were calculated under the assumption that the bubbles have a circular cross section. This method helps to compare the foam morphologies of the different samples, because the geometry of most of the cells differs from the ideal round shape and so a reasonable comparison of direct measured diameters is not possible.

[0133] By using equation 1 and subsequently averaging the calculated values of each bubble diameter the mean diameter was determined.

[00001]$\begin{array}{cc}{D}_{z,\mathrm{kreis}}=\sqrt{\frac{4A_z}{\pi }}& \left(1\right)\end{array}$

Using:

[0134] D.sub.z,kreis=diameter of one foam cell under the assumption of a circular cross section in μm
A.sub.z=cross section of one foam bubble in μm.sup.2

1.7 Average Cell Size

[0135] To calculate the cell density, the cell diameter, and the density the following equation is needed.

[00002]$\begin{array}{cc}{N}_b=\frac{1-\frac{{\rho }_F}{{\rho }_m}}{\frac{\pi }{6}{D}^3}& \left(3\right)\end{array}$

With:

[0136] ρF=density of the foamed specimen in g/cm.sup.3
ρm=density of the polymer matrix

1.8 Crosslinking Degree (XHU)

[0137] Degree of crosslinking was measured by decaline extraction (Measured according to ASTM D 2765-01, Method A) on the crosslinked material.

1.9 Si Content and Content of the Hydrolysable Silane Groups

[0138] The amount of hydrolysable silane groups (SiR.sup.2.sub.qY.sub.3-q) was determined using X-ray fluorescence analysis. The pellet sample was pressed to a 3 mm thick plaque (150° C. for 2 minutes, under pressure of 5 bar and cooled to room temperature). Si-atom content was analysed by wavelength dispersive XRF (AXS S4 Pioneer Sequential X-ray Spectrometer supplied by Bruker). Generally, in XRF-method. the sample is irradiated by electromagnetic waves with wavelengths 0.01-10 nm. The elements present in the sample will then emit fluorescent X-ray radiation with discrete energies that are characteristic for each element. By measuring the intensities of the emitted energies, quantitative analysis can be performed. The quantitative methods are calibrated with compounds with known concentrations of the element of interest e.g. prepared in a Brabender compounder. The XRF results show the total content (wt %) of Si and are then calculated and expressed as content (wt %) of hydrolysable silane groups based on the weight of the polyethylene bearing hydrolysable silane groups.

2. Examples

[0139] The following materials and compounds are used in the Examples. [0140] LDPE Low density polyethylene having an MFR.sub.2 (190° C., 2.16 kg) of 0.75 g/10 min, a density of 923 kg/m.sup.3, and a hardness Shore D of 52, commercially available as FT5230 from Borealis AG Austria [0141] LDPE-Si-1 Low density polyethylene which is copolymerized with vinyl silane having an MFR.sub.2 (190° C., 2.16 kg) of 1.0 g/10 min, a density of 923 kg/m.sup.3, and a hardness Shore D of 52, commercially available as Visico™ LE4423 from Borealis AG Austria [0142] LDPE-Si-2 Low density polyethylene which is copolymerized with vinyl silane having an MFR.sub.2 (190° C., 2.16 kg) of 2.0 g/10 min, a density of 948 kg/m.sup.3, and a hardness Shore A of 63, commercially available as LE8824E from Borealis AG Austria [0143] Plastomer Copolymer of ethylene and 1-octene, commercially available as Queo 6201 from Borealis AG Austria [0144] Cat Silanol condensation catalyst masterbatch comprising organic sulphonic acid, commercially available as Ambicat™ LE4476 from Borealis AG Austria [0145] CO.sub.2 Supercritical carbon dioxide [0146] Talc-MB Masterbatch containing 50 wt % talc and 50 wt % LDPE

[0147] The recipes of the compositions of inventive and comparative examples are indicated in Table 1 below. The respective polyethylene (bearing hydrolysable silane groups or not) is the so-called base resin.

TABLE-US-00001 TABLE 1 Compositions of Examples Si-content of base resin/ Talc-MB/ Cat/ CO.sub.2/ Base resin wt % wt % wt % wt % CE1 LDPE 0 — — 0.5 CE2 LDPE 0 2.0 — 0.5 CE3 LDPE-Si-1 1.1 2.0 — 0.5 CE4 LDPE-Si-2 1.8 2.0 — 0.35 IE1 LDPE-Si-1 1.1 2.0 5.0 0.5 IE2 LDPE-Si-1 1.1 2.0 5.0 0.7 IE3 LDPE-Si-1 1.1 2.0 5.0 0.3 IE4 LDPE-Si-2 1.8 2.0 5.0 0.35 IE5 LDPE-Si-2 1.8 2.0 5.0 0.5

[0148] The compositions of these comparative and inventive examples were prepared as follows.

[0149] The grooved single screw extrusion line Rosendahl RE45 (Rosendahl Maschinen GmbH, Austria) equipped with a screw of 45 mm diameter was used. The extruder has a total length of 32 D, including an 8 D long, oil tempered cylinder elongation used for a better control of the polymer melt temperature. To realize a higher dwell time and a better homogenization a static mixer, type SMB-R (Sulzer, Switzerland) with a length of 4 D is mounted between the cylinder elongation and the extrusion die. Round die inserts was used having a diameter of 2.5 mm.

[0150] Table 2 shows process parameters, while Table 3 illustrates the temperature profile.

TABLE-US-00002 TABLE 2 Process parameters and injected gas amount of the different material formulations Screw speed/ Mass flow/ Gas amount/ Gas pressure/ rpm kg/h ml/min bar CE1 10 4.4 0.46 119 CE2 10 4.4 0.46 119 CE3 10 4.3 0.47 113 CE4 25 6.3 0.52 80 IE1 10 4.3 0.48 106 IE2 10 4.3 0.67 104 IE3 10 4.3 0.28 105 IE4 20 5.2 0.39 76 IE5 20 5.2 0.57 79

[0151] Due to the different material behaviour and the resulting pressure profiles, it was necessary to variate the extrusion speed for the different formulations. In consideration of changing process parameters (pressure and mass flow) during the extrusion of different material formulations, the amount of CO.sub.2 (in ml per minute) has to be adapted to ensure a constant and correct dosage of the blowing agent for all samples.

[0152] To guarantee constant parameters and reproducible samples the process has to run for a certain time until stationary conditions set in. Then the mass flow was determined, the required volume of CO.sub.2 is calculated and set at the syringe pump. After stationary conditions have set in, again three samples for a later characterization of the foam morphology were taken.

TABLE-US-00003 TABLE 3 Temperature profile in extruder (values in degree centigrade) Base resin T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 Die LDPE 40 140 160 170 180 190 200 200 200 200 200 200 200 LDPE-Si-1 40 140 160 170 180 190 200 200 200 200 200 200 200 LDPE-Si-2 20 120 145 155 170 180 190 190 190 190 190 190 190

[0153] The resulting properties of the foams obtained from the polyolefin compositions are indicated in Table 4 below.

TABLE-US-00004 TABLE 4 Properties of Foams Average Foam density/ cell Cell density/ Density XHU/ kg/m.sup.3 size/μm Nb/cm.sup.3 reduction/% wt % CE1 298 1705 261 67.7 0 CE2 266 515 9980 71.2 0 CE3 252 295 53800 72.7 <0.1 CE4 370 238 86500 61.0 0.28 IE1 217 313 47500 76.5 97 IE2 251 328 39200 72.8 n.d. IE3 398 293 43100 56.8 n.d. IE4 384 244 78400 59.5 97 IE5 405 246 73800 57.3 n.d. n.d.: not determined

[0154] As can be derived from Table 4 above, the polyolefin compositions according to the present invention enable producing crosslinked foams with high degree of crosslinking XHU.

[0155] The recipes of the compositions of further inventive and comparative examples are indicated in Table 5 below. The respective polyethylene (bearing hydrolysable silane groups or not) is the so-called base resin. Table 5 does also indicate the extruder settings and the temperature profiles. The resulting properties of the foams obtained from the polyolefin compositions are indicated in Table 6 below.

TABLE-US-00005 TABLE 5 Compositions of Examples, Extruder Settings, and Temperature Profiles CE5 CE6 IE6 IE7 CE7 LDPE-Si-1 /wt % 98.0 93.0 LDPE-Si-2 /wt % 98.0 93.0 Plastomer /wt % 93.0 Cat /wt % 5.0 5.0 5.0 Talc-MB /wt % 2.0 2.0 2.0 2.0 2.0 CO.sub.2 /wt % 0.5 0.35 0.5 0.35 0.5 Srew speed /rpm 10 25 10 20 7 Mass flow /kg/h 4.3 6.3 4.3 5.2 1.7 Gas amount /ml/min 0.47 0.52 0.48 0.39 0.13 Gas pressure /bar 113 80 106 76 244 Die insert /mm 2.5 2.5 2.5 2.5 4.0 T1 /° C. 40 30 40 30 20 T2 /° C. 140 120 140 120 50 T3 /° C. 160 145 160 145 100 T4 /° C. 170 155 170 155 125 T5 /° C. 180 170 180 170 140 T6 /° C. 190 180 190 180 150 T7 /° C. 200 190 200 190 160 T8 /° C. 200 190 200 190 160 T9 /° C. 200 190 200 190 170 T10 /° C. 200 190 200 190 170 T11 /° C. 200 190 200 190 180 T12 /° C. 200 190 200 190 180 Die /° C. 200 190 200 190 190

[0156] The compositions of these comparative and inventive examples were prepared as follows.

[0157] A dry mixture of a polyethylene bearing hydrolysable silane groups, talc masterbatch, and silanol condensation catalyst was fed into Rosendahl RE45 (Rosendahl Maschinen GmbH, Austria) extruder equipped with 45 mm diameter screw. The extruder had a total length of 32 D, including 8 D long oil tempered cylinder elongation for polymer melt temperature control. A static mixer, type SMB-10 R (Sulzer, Switzerland) with a length of 4 D was mounted between the cylinder elongation and the extrusion die. Two different round die inserts were used having diameters of 2.5 and 4.0 mm. Carbon dioxide was added into the extruder once the mixture was completely molten.

[0158] Due to the different material behaviour and the resulting pressure profiles, it was necessary to variate the extrusion speed for the different formulations. In consideration of changing process parameters (pressure and mass flow) during the extrusion of different material formulations, the amount of CO.sub.2 (in ml per minute) has to be adapted to ensure a constant and correct dosage of the blowing agent for all samples.

[0159] To guarantee constant parameters and reproducible samples the process has to run for a certain time until stationary conditions set in. Then the mass flow was determined, the required volume of CO.sub.2 is calculated and set at the syringe pump. After stationary conditions have set in, again three samples for a later characterization of the foam morphology were taken.

[0160] Because of the very high pressures of the formulations based on the Queo polymer, the foaming was performed at very low mass flow rates using a larger round die.

TABLE-US-00006 TABLE 6 Properties of Foams CE5 CE6 IE6 IE7 CE7 Mean cell size /μm 295 238 313 244 460 Foam density /kg/m.sup.3 252 370 217 384 768 Density reduction /% 72.7 61.0 76.5 59.5 10.7 Cell density /Nb/cm.sup.3 53800 86500 47500 78400 2090 XHU /wt % 0.07 0.28 97.12 97.48 98.66

[0161] As can be derived from Tables 5 and 6 above, the process according to the present invention enables producing crosslinked foams with high degree of crosslinking XHU in one step and without application of radiation or heat in an oven. Heat is merely applied in the extruder which is in any case required to melt and extrude the polyolefin composition. Less energy is consumed compared to prior art processes requiring an additional heat treatment. Further, the process according to the present invention does not require special production lines or equipment but relies on an extruder. The present invention provides a one-step process for preparing a crosslinked foam starting with a crosslinkable polyolefin composition.