UV stabilization of a cross-linkable polyolefin composition comprising an acidic silanol condensation catalyst

Abstract

The present invention relates to a polyolefin composition comprising a cross-linkable polyolefin with hydrolysable silane groups; an acidic silanol condensation catalyst, wherein the acidic silanol condensation catalyst (B) is present in an amount of 0.0001 to 3 wt. % of the polyolefin composition; at least one UV stabilizer selected from the group consisting of phenols, triazines, benzophenones, triazoles and/or combinations thereof; and at least one UV stabilizer of the hindered amine type (HALS) which is present in an amount of 0.0001 to 0.1 wt. % of the polyolefin composition. The present invention also relates to an article comprising such a composition, and to the use of such a composition for the production of an article.

Claims

1. A polyolefin composition comprising (A) a cross-linkable polyolefin with hydrolysable silane groups; (B) an acidic silanol condensation catalyst, wherein the acidic silanol condensation catalyst (B) is present in an amount of 0.0001 to 3 wt. % of the polyolefin composition; (C) at least one UV stabilizer selected from the group consisting of phenols, triazines, benzophenones, triazoles and/or combinations thereof; and (D) at least one UV stabilizer of the hindered amine type which is present in an amount of 0.0001 to 0.1 wt. % of the polyolefin composition.

2. The polyolefin composition according to claim 1, wherein the triazines are a compound (C) according to formula (II) ##STR00012## with R.sup.4 and R.sup.5 being independently the same or different non-substituted or substituted aliphatic or aromatic hydrocarbon residues which independently may comprise hetero atoms with the proviso that the hetero atoms of at least one of R.sup.4 and R.sup.5 are selected from the group consisting of O, P, S, F, Cl, Br and/or I, and with R.sup.6 being any substituent; and/or wherein component (D) is present in an amount of 0.0005 to 0.08 wt. %.

3. The polyolefin composition according to claim 2, wherein component (C) is selected from a UV stabilizer according to formula (I) ##STR00013## with R.sup.1 and R.sup.2 being independently the same or different non-substituted or substituted aliphatic or aromatic hydrocarbon residues which independently may comprise hetero atoms, with R.sup.3 being any substituent, and with X.sup.1, X.sup.2, and X.sup.3 independently being H or OH, with the proviso that at least one of X.sup.1, X.sup.2 and X.sup.3 is OH; and/or according to formula (III) ##STR00014## with R.sup.7 to R.sup.16 being any substituent, preferably R.sup.7 to R.sup.16 being independently the same or different hetero atoms, substituted or non-substituted hydrocarbon residues, which may comprise hetero atoms, or hydrogen atoms with the proviso that at least one of R.sup.7 to R.sup.16 is OH; more preferably R.sup.7 to R.sup.16 being independently the same or different hetero atoms, substituted or non-substituted hydrocarbon residues, which may comprise hetero atoms, or hydrogen atoms with the proviso that at least one of R.sup.7 to R.sup.11 is OH; and/or according to formula (IV) ##STR00015## with R.sup.17 being a substituted or non-substituted hydrocarbon residue with at least 6 carbon atoms; and R.sup.18 to R.sup.21 being independently the same or different substituted or non-substituted hydrocarbon residues, hydrogen atoms or hetero atoms.

4. The polyolefin composition according to claim 1, wherein component (D) comprises a UV stabilizer according to formula (V) ##STR00016## with R.sup.22 and R.sup.25 being any substituent, and R.sup.23, R.sup.24, R.sup.26 and R.sup.27 being independently the same or different hydrocarbon residues, preferably R.sup.22 being a hydrogen atom or R.sup.22 being —O—R.sup.28 with R.sup.28 being any substituent.

5. The polyolefin composition according to claim 1, wherein component (C) is present in an amount of less than or equal to 2.0 wt. %, preferably less than or equal to 1.0 wt. %, more preferably of less than or equal to 0.5 wt. % of the polyolefin composition.

6. The polyolefin composition according to claim 1, wherein component (D) is present in an amount of 0.001 to 0.06 wt. % and more preferably of 0.005 to 0.04 wt. % of the polyolefin composition.

7. The polyolefin composition according to claim 1, wherein the acidic silanol condensation catalyst (B) comprises an organic sulfonic acid comprising 10 to 200 carbon atoms, the sulfonic acid further comprising at least one aromatic group.

8. The polyolefin composition according to claim 1, wherein the cross-linkable polyolefin with hydrolysable silane groups (A) comprises a polyethylene with hydrolysable silane groups.

9. The polyolefin composition according to claim 1, wherein in the cross-linkable polyolefin with hydrolysable silane groups (A) the silane groups are present in an amount of 0.001 to 15 wt. %, preferably 0.01 to 5 wt. %, more preferably 0.1 to 3 wt. % and even more preferably 0.4 to 2.4 wt. % of component (A).

10. The polyolefin composition according to claim 1, wherein the polyolefin composition further comprises a polyolefin with monomer units with polar groups; or wherein the polyolefin composition further comprises a polyolefin with monomer units with polar groups wherein in the polyolefin the monomer units with polar groups are present in an amount of 0.1 to 40 wt. %, preferably 1.0 to 35 wt. %, more preferably 2.0 to 25 wt. % and even more preferably 3.0 to 20 wt. %.

11. The polyolefin composition according to claim 10 wherein the cross-linkable polyolefin with hydrolysable silane groups (A) is a terpolymer also containing monomer units with polar groups; and/or wherein the monomer units with polar groups comprise monomer units with acrylate and/or acetate units.

12. The polyolefin composition according to claim 1, wherein the acidic silanol condensation catalyst (B) comprises an organic sulfonic acid with the structural element:
Ar(SO.sub.3H).sub.x  (VIII) with Ar being an aryl group which may be substituted or non-substituted and x being at least 1; and/or wherein the acidic silanol condensation catalyst (B) is present in an amount of 0.001 to 2 wt. % and preferably 0.005 to 1 wt. % of the polyolefin composition.

13. The polyolefin composition according to claim 12 wherein in formula (VIII) Ar is substituted with at least one C.sub.1 to C.sub.30-hydrocarbyl group, preferably a C.sub.4 to C.sub.30-alkyl group.

14. An article comprising a polyolefin composition according to claim 1.

15. A method for producing an article, comprising forming a film or a layer from the polyolefin composition according to claim 1.

16. The article of claim 14, wherein the article is a pipe, wire, cable, or film.

17. The method of claim 15, wherein the article is a film or a layer of a wire or cable.

18. The polyolefin composition according to claim 1, wherein component (C) is selected from a UV stabilizer according to formula (I) ##STR00017## with R.sup.1 and R.sup.2 being independently the same or different non-substituted or substituted aliphatic or aromatic hydrocarbon residues which independently may comprise hetero atoms, with R.sup.3 being any substituent, and with X.sup.1, X.sup.2, and X.sup.3 independently being H or OH, with the proviso that at least one of X.sup.1, X.sup.2 and X.sup.3 is OH; and/or according to formula (III) ##STR00018## with R.sup.7 to R.sup.16 being any substituent, preferably R.sup.7 to R.sup.16 being independently the same or different hetero atoms, substituted or non-substituted hydrocarbon residues, which may comprise hetero atoms, or hydrogen atoms with the proviso that at least one of R.sup.7 to R.sup.16 is OH; more preferably R.sup.7 to R.sup.16 being independently the same or different hetero atoms, substituted or non-substituted hydrocarbon residues, which may comprise hetero atoms, or hydrogen atoms with the proviso that at least one of R.sup.7 to R.sup.11 is OH; and/or according to formula (IV) ##STR00019## with R.sup.17 being a substituted or non-substituted hydrocarbon residue with at least 6 carbon atoms; and R.sup.18 to R.sup.21 being independently the same or different substituted or non-substituted hydrocarbon residues, hydrogen atoms or hetero atoms.

Description

EXAMPLES

1. Measurement Methods

[0167] a) Melt Flow Rate

[0168] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer.

[0169] The MFR.sub.2 of polyethylene (co-)polymers is measured at a temperature of 190° C. and at a load of 2.16 kg.

[0170] b) Density

[0171] Density of the polymer was measured according to ISO 1183-1:2004 Method A on compression moulded specimen prepared according to EN ISO 1872-2 and is given in kg/m.sup.3.

[0172] c) Elongation at Break/Tensile Elongation at Break After Exposure in SEPAP Oven

[0173] The tensile elongation at break was measured in accordance with ISO 527-1: 2012 at 23° C. and 50% relative humidity on an Alwetron TCT 10 tensile tester at a speed of 250 mm/min. The extensometer used was MFE-900.

[0174] The test specimens were extruded tapes with a thickness of 1.8 mm. The specimens were conditioned for minimum 16 hours at 23° C. +/−2° C. and 50% relative humidity prior testing. The average value out of 6 to 10 samples is reported herein.

[0175] d) Hot Set Elongation Test

[0176] Tape samples as prepared below in the experimental part were used to determine the hot set properties. Three dumb-bells sample, taken out along extrusion direction were prepared according to ISO 527 5A from the 1.8+/−0.1 mm thick crosslinked tape. The hot set tests were made according to EN 60811-2-1 (hot set test) by measuring the thermal deformation.

[0177] Reference lines, were marked 20 mm apart on the dumb-bells. Each test sample was fixed vertically from upper end thereof in the oven and the load of 0.2 MPa are attached to the lower end of each test sample. After 15 min, 200° C. in the oven the distance between the pre-marked lines were measured and the percentage hot set elongation calculated, elongation %. For permanent set %, the tensile force (weight) was removed from the test samples and after recovered in 200° C. for 5 minutes and then let to cool in room temperature to room temperature. The permanent set % was calculated from the distance between the marked lines. The average of the three tests was reported.

[0178] e) Crosslinking

[0179] Prior to hot set test and exposure in the Sepap oven, the 1.8 m thick tapes were put into a water bath at 90° C. for 24 hours.

2. Compositions

[0180] a) Materials

[0181] Tinuvin® 326, Chimassorb® 944 and Flamestab® NOR 116 are distributed by BASF SE.

[0182] Cyasorb® UV-1164 is distributed by Cytec (Solvay Group).

[0183] b) Master Batches

[0184] A master batch for Comparative example 1 (CE1) was produced comprising: [0185] a matrix resin: an ethylene butylacrylate copolymer with 17 wt. % butylacrylate, a density of 926 kg/m.sup.3 and a MFR2 of 4.5 g/10 min; [0186] an acidic silanol condensation catalyst: dodecylbenzenesulfonic acid (DBSA) [0187] a silane containing compound: hexadecyltrimethoxysilane (HDTMS) [0188] an antioxidant: lonol® LC distributed by Degussa (CAS 68610-51-5) [0189] an antiblocking agent: Hoechstwax E (CAS 73138-45-1)

[0190] The components were used in the master batches of all examples in the amounts as indicated in Table 1 (data given in wt. %). Compounding of the master batches at 180° C. were performed using a Brabender kneader (small chamber, 47 cm.sup.3). The master batches were grinded in a cryo mill to a suitable size for the mixing with the silane-ethylene copolymer prior to tape extrusion. Dog bones were made from tape, 1.8 mm thick.

[0191] For the other examples master batches were produced using the same principle and using the same ingredients as for CE1, with the exception that the matrix polymer was reduced to balance the further addition of UV additives.

TABLE-US-00001 TABLE 1 Master batch (wt. %) Matrix 86.5 DBSA 1.5 HDTMS 3.0 Antioxidant 8.0 Antiblocking agent 1.0

[0192] c) Compositions

[0193] The different master batches were dry blended in an amount of 5 wt. % with 94.6 wt. % of a silane group containing polyethylene having a density of 923 kg/m.sup.3, a MFR2 of 1 g/10 min and a silane copolymer content of 1.1 wt. % The dry blends were then extruded to 1.8 mm thick tapes in a Collin TeachLine E2OT tape extruder with a 4.2:1, 20D Compression screw, D=20 mm at a temperature profile of 135/145/155° C. and with a screw speed of 30 rpm.

[0194] For ageing the samples a SEPAP oven was used, as described in NF C32-062-2 (The Effect of UV Light and Weather on Plastics and Elastomers, Laurence W. McKeen, 4.sup.th edition, 2019, Elsevier, p. 38).

[0195] The SEPAP oven used a mercury arc generating a radiation between 200 -400 nm, with peaks at 254 nm, 310nm and 366 nm. The oven operated under a temperature of 60° C.+/−2° C. making it a harsh UV test. The samples were aged for 350 h.

3. Results

[0196] Elongation at break was measured before ageing and after ageing for 350 h according to above mentioned test methods.

[0197] Hot set was measured according to the above mentioned test method.

[0198] The results of the hot set and the elongation at break measurements are given in Table 2.

TABLE-US-00002 TABLE 2 Elongation Elongation Remaining Hot set at break at break elongation.sup.1 T326 C1164 C944 F116 90°, 24 h before aging after 350 h after 350 h ppm ppm ppm ppm [%] [%] [%] [%] IE1 3000 — 100 — 125.2 490.2 81.4 17 IE2 3000 — — 100 72.3 412.2 344.0 83 IE3 — 3000 100 — 101.6 420.1 251.1 60 IE4 — 3000 — 100 116.4 428.1 150.7 35 CE1 — — — — 52.4 484.1 9.09 2 .sup.1Remaining elongation after ageing Abbreviations: T326 (Tinuvin 326), C1164 (Cyasorb UV-1164), C944 (Chimasorb 944), F116 (Flamestab NOR-116)

[0199] From Inventive Example 1 to Inventive Example 4 (IE1 to 1E4) of Table 2 can be derived that a combination of UV absorbers of the benzotriazole and triazine type and a small portion of HALS UV absorbers improve UV stability. This is demonstrated by the improved elongation at break after 350 h. As can also be derived by the comparison with CE1, which does not contain UV absorber, the combination of different kinds of UV absorbers has only a minor influence on the cross-linking.

[0200] Particularly 1E2 shows a strong improvement in the elongation at break after 350 h and concomitantly the influence of the combination of UV absorbers as used in IE 2 on the hot set value is low.

[0201] In conclusion, using a combination of UV stabilizers as demonstrated in IE1 to 1E4 leads to UV stabilization of the polyolefin composition whereby concomitantly cross-linking is good.