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 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, benzophenones and/or combinations thereof, wherein component (C) is present in an amount of 0.0001 to 0.35 wt. % of the polyolefin composition, and/or at least one UV stabilizer selected from triazines, wherein component (D) is present in an amount of 0.0001 to 2.0 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, benzophenones and/or combinations thereof, wherein component (C) is present in an amount of 0.0001 to 0.35 wt. % of the polyolefin composition; and/or (D) at least one UV stabilizer selected from triazines, wherein component (D) is present in an amount of 0.0001 to 2.0 wt. % of the polyolefin composition.

2. The polyolefin composition according to claim 1, wherein component (C) is selected from benzophenones; and/or component (D) is selected from a UV stabilizer according to formula (III) ##STR00005## 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.

3. The polyolefin composition according to claim 1, wherein component (C) is selected from a UV stabilizer according to formula (I) ##STR00006## 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 (II) ##STR00007## 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.

4. The polyolefin composition according to claim 1, further comprising component (E) according to formula (IV) ##STR00008## 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 is a hydrogen atom, a hydrocarbon or an alkoxy residue; wherein component (E) is present in an amount of 0.0001 to 0.1 wt. % of the polyolefin composition.

5. The polyolefin composition according to claim 1, wherein component (C) is present in an amount of 0.001 to 0.35 wt. %, preferably 0.01 to 0.30 wt. % and more preferably of 0.1 to 0.30 wt. % of the polyolefin composition; and/or wherein component (D) is present in an amount of 0.001 to 2.0 wt. %, preferably 0.01 to 1.5 wt. % and more preferably of 0.1 to 1.0 wt. % of the polyolefin composition.

6. The polyolefin composition according to claim 1, wherein component (E) is present in an amount of 0.0005 to 0.08 wt. %, preferably 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 C-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 composition with monomer units with polar groups; or wherein the polyolefin composition further comprises a polyolefin composition with monomer units with polar groups wherein in the polyolefin composition 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 comprises 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  (VII) 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 (VII) 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 the article from the polyolefin composition of 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 pipe, wire, cable, or film.

Description

EXAMPLES

[0146] 1. Measurement Methods

[0147] a) Melt Flow Rate

[0148] 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.

[0149] The MFR.sub.2 of polyethylene (co-)polymers is measured at a temperature of 190° C. and at a load of 2.16 kg.

[0150] b) Density

[0151] 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.

[0152] c) Elongation at Break/Tensile Elongation at Break after Exposure in SEPAP Oven

[0153] 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. 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.

[0154] d) Hot Set Elongation Test

[0155] Tape samples as prepared below in 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 mm+/−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.

[0156] 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 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.

[0157] e) Crosslinking

[0158] 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.

[0159] 2. Compositions

[0160] a) Materials

[0161] Tinuvin® 120, Tinuvin® 622, Chimassorb® 944 and Flamestab® NOR 116 are distributed by BASF SE.

[0162] Cyasorb® 531 and Cyasorb® UV-1164 are distributed by Cytec (Solvay Group).

[0163] b) Master Batches

[0164] A master batch for Comparative example 1 (CE1) was produced comprising: [0165] a matrix resin: an ethylene butylacrylate copolymer with 17 wt. % butylacrylate, a density of 926 kg/m.sup.3 and a MFR.sub.2 of 4.5 g/10 min, [0166] an acidic silanol condensation catalyst: dodecylbenzenesulfonic acid (DBSA) [0167] a silane containing compound: hexadecyltrimethoxysilane (HDTMS) [0168] an antioxidant: Lonol® LC distributed by Degussa (CAS 68610-51-5) [0169] an antiblocking agent: Hoechstwax E (CAS 73138-45-1)

[0170] 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.

[0171] 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 Matrix 86.5 DBSA 1.5 HDTMS 3.0 Antioxidant 8.0 Antiblocking agent 1.0

[0172] c) Compositions

[0173] 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 MFR.sub.2 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 E20T tape extruder with a 4.2:1, 20 D Compression screw, D=20 mm at a temperature profile of 135/145/155° C. and with a screw speed of 30 rpm.

[0174] For ageing the samples a SEPAP oven was used, as described in NF C.sub.32-062-2 (The Effect of UV Light and Weather on Plastics and Elastomers, Laurence W. McKeen, 4.sup.th edition, 2019, Elsevier, p. 38).

[0175] The SEPAP oven used a mercury arc generating a radiation between 200-400 nm, with peaks at 254 nm, 310 nm 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.

[0176] 3. Results

[0177] Elongation at break was measured before ageing and after ageing for 350 h according to above mentioned test methods.

[0178] Hot set was measured according to the above mentioned test method.

[0179] The results of the hot set and the elongation at break measurements are given in Table 2.

[0180] As can be derived from IE1 to IE3 in Table 2 the addition of UV stabilizers according to components (C) and (D) improves the UV stability of the polyolefin composition when compared with CE 1. Besides, cross-linking of the polyolefin composition is not negatively influenced when using UV stabilizers according to IE1 to IE3 when an acidic silanol condensation catalyst is used. Using a UV stabilizer of the HALS type such as Tinuvin 622 (CE2) shows clearly that sufficient cross-linking does not take place.

TABLE-US-00002 TABLE 2 Elongation at Elongation Remaining Hot set break at break elongation.sup.1 C1164 T120 C531 C944 T622 F116 90°, 24 h before aging after 350 h after 350 h ppm ppm ppm ppm ppm ppm [%] [%] [%] [%] IE1 3000 — — — — — 64.9 382.9 142.0 37 IE2 — 3000 — — — — 52.3 399.0 24.6 6 IE3 — — 3000 — — — 49.0 408.6 91.1 22 CE1 — — — — — — 52.4 484.1 9.09 2 CE2 — — — 3000 — — SP 378.5 405.07 107 CE3 — — — — 3000 — SP 346.0 78.7 23 CE4 — — — — — 3000 SP 484.1 378.2 107 .sup.1Remaining elongation after ageing; Abbreviations: T120 (Tinuvin 120), T622 (Tinuvin 622), C1164 (Cyasorb UV-1164), C531 (Cyasorb 531), C944 (Chimasorb 944), F116 (Flamestab NOR-116), SP = Snap Break