POLYOLEFIN GASKETS FOR CLOSURES

Abstract

The present disclosure provides a gasket for closures made from or containing a polyolefin composition (I) made from or containing A) from about 25 to about 62% by weight of a copolymer of butene-1 with ethylene having a copolymerized ethylene content of up to about 18% by mole and without a melting peak detectable at the DSC at the second heating scan; B) from about 38 to about 75% by weight of (i) a propylene homopolymer, or (ii) a propylene copolymer, or (iii) a mixture of two or more of (i) and (ii), having a melting temperature T.sub.m, measured by DSC at the second heating scan, of from about 130 C. to about 165 C.;

wherein the amounts of A) and B) are referred to the total weight of A)+B) and the DSC second heating scan is carried out with a heating rate of about 10 C. per minute.

Claims

1. A gasket for closures comprising: (I) a polyolefin composition (I) comprising A) from about 25 to about 62% by weight, based upon the total weight of the polyolefin composition, of a copolymer of butene-1 with ethylene having a copolymerized ethylene content of up to about 18% by mole, based upon the molar composition of the copolymer, and without a melting peak detectable at the DSC at the second heating scan and B) from about 38 to about 75% by weight, based upon the total weight of the polyolefin composition, of (i) a propylene homopolymer, or (ii) a propylene copolymer, or (iii) a mixture of two or more of (i) and (ii), having a melting temperature T.sub.m, measured by DSC at the second heating scan, of from about 130 C. to about 165 C. wherein the amounts of A) and B) are referred to the total weight of A)+B) and the DSC second heating scan is carried out with a heating rate of 10 C. per minute.

2. The gasket of claim 1, wherein the polyolefin composition (I) has a MIE value of from about 0.5 to about 8 g/10 min., where MIE is the melt flow index at 190 C. with a load of 2.16 kg, determined according to ISO 1133.

3. The gasket of claim 1, wherein the polyolefin composition (I) has a H.sub.fus value of-from about 30 to about 55 J/g.

4. The gasket of claim 1, wherein the butene-1 copolymer component A) has Shore A equal to or lower than about 80.

5. The gasket of claim 1, wherein the butene-1 copolymer component A) has a Mw/Mn value of equal to or lower than about 3.

6. The gasket of claim 1, wherein the butene-1 copolymer component A) has at least one of the following additional features: MIE of from about 0.5 to about 3 g/10 min.; a lower limit of the copolymerized ethylene content of about 12% by mole, based upon the molar composition of the copolymer; a Shore A value equal to or lower than about 80; a Shore D value equal to or lower than about 20; a Mw/Mn value, where Mw is the weight average molar mass and Mn is the number average molar mass, both measured by GPC, equal to or lower than about 3; a tension set of less than about 30% at 100% of deformation at 23 C. (ISO 2285); a percentage of butene-1 units in form of isotactic pentads (mmmm%) greater than about 80% tensile stress at break, measured according to ISO 527, of from about 3 MPa to about 20 MPa; tensile elongation at break, measured according to ISO 527, of from about 550% to about 1000%; intrinsic viscosity (I.V.) equal to or higher than about 1 dl/g; crystallinity of less than about 30% measured via X-ray; density of about 0.895 g/cm.sup.3 or less; and content of xylene insoluble fraction at 0 C. of less than about 15% by weight, based upon the total weight of the butene-1 copolymer.

7. The gasket of claim 1, wherein the propylene homopolymer or copolymer component B) has MFRL values of from about 0.5 to about 9 g/10 min, where MFRL is the melt flow rate at 230 C. with a load of 2.6 kg, determined according to ISO 1133.

8. A twist closure comprising: (a) a gasket for closures comprising (I) a polyolefin composition (I) comprising A) from about 25 to about 62% by weight, based upon the total weight of the polyolefin composition, of a copolymer of butene-1 with ethylene having a copolymerized ethylene content of up to about 18% by mole, based upon the molar composition of the copolymer, and without a melting peak detectable at the DSC at the second heating scan and B) from about 38 to about 75% by weight, based upon the total weight of the polyolefin composition, of (i) a propylene homopolymer, or (ii) a propylene copolymer, or (iii) a mixture of two or more of (i) and (ii), having a melting temperature T.sub.m, measured by DSC at the second heating scan, of from about 130 C. to about 165 C.; wherein the amounts of A) and B) are referred to the total weight of A)+B) and the DSC second heating scan is carried out with a heating rate of 10 C. per minute.

9. The twist closure of claim 8, wherein the twist closure is for food containers.

10. The twist closure of claim 9, wherein the twist closure is in the form of a cap.

11. A process for preparing a gasket comprising the following steps: a) laying down a polyolefin composition (I) in a molten state on the inner surface of a closure having an inner surface and an outer surface; b) forming the laid polyolefin composition (I), wherein the gasket comprises (I) the polyolefin composition (I) comprising A) from about 25 to about 62% by weight, based upon the total weight of the polyolefin composition, of a copolymer of butene-1 with ethylene having a copolymerized ethylene content of up to about 18% by mole, based upon the molar composition of the copolymer, and without a melting peak detectable at the DSC at the second heating scan and B) from about 38 to about 75% by weight, based upon the total weight of the polyolefin composition, of (i) a propylene homopolymer, or (ii) a propylene copolymer, or (iii) a mixture of two or more of (i) and (ii), having a melting temperature T.sub.m, measured by DSC at the second heating scan, of from about 130 C. to about 165 C.; wherein the amounts of A) and B) are referred to the total weight of A)+B) and the DSC second heating scan is carried out with a heating rate of 10 C. per minute.

Description

EXAMPLES

[0107] These Examples are illustrative, and are not intended to limit the scope of this disclosure in any manner whatsoever.

[0108] The following analytical methods are used to characterize the polymer compositions.

[0109] Thermal Properties (Melting Temperatures and Enthalpies)

[0110] Determined by Differential Scanning calorimetry (DSC) on a Perkin Elmer DSC-7 instrument. [0111] The melting temperatures of the butene-1 copolymer A) were determined according to the following method: [0112] TmII (measured in second heating scan): a weighted sample (5-10 mg) obtained from the polymerization was sealed into aluminum pans and heated at 200 C. with a scanning speed corresponding to 10 C./minute. The sample was kept at 200 C. for 5 minutes to allow a complete melting of the crystallites, thereby cancelling the thermal history of the sample. Successively, after cooling to 20 C. with a scanning speed corresponding to 10 C./minute, the peak temperature was taken as crystallization temperature (T.sub.c). After standing 5 minutes at 20 C., the sample was heated for the second time at 200 C. with a scanning speed corresponding to 10 C./min. In this second heating run, the peak temperature, when present is taken as the melting temperature of the polybutene-1 (PB) crystalline form II (TmII) and the area as global melting enthalpy (HfII). The butene-1 copolymer component A) of the polyolefin composition (I) did not have a TmII peak. [0113] In order to determine the TmI, the sample was melted, kept at 200 C. for 5 minutes and then cooled down to 20 C. with a cooling rate of 10 C./min. [0114] The sample was then stored for 10 days at room temperature. After 10 days, the sample was subjected to DSC, cooled to 20 C., and then heated at 200 C. with a scanning speed corresponding to 10 C./min. In this heating run, the first peak temperature coming from the lower temperature side in the thermogram was taken as the melting temperature (TmI). The melting temperatures of (i) the propylene homopolymer or copolymer component B) and (ii) the overall composition made from or containing the polymer components A) and B) were measured at the second heating scan under the same conditions as above reported for the determination of TmII of the butene-1 copolymer component A). [0115] Both component B) and the overall composition of the examples show a single melting peak between 130 and 165 C., corresponding to the melting temperature T.sub.m. [0116] The area of such melting peak of the overall composition was taken as the melting enthalpy H.sub.fus of the polyolefin composition.

[0117] Flexural Elastic Modulus

[0118] According to norm ISO 178, measured 10 days after molding.

[0119] Shore A and D

[0120] According to norm ISO 868, measured 10 days after molding.

[0121] Tensile Stress and Elongation at Break

[0122] According to norm ISO 527 on compression molded plaques, measured 10 days after molding.

[0123] Tension Set

[0124] According to norm ISO 2285, measured 10 days after molding.

[0125] Compression Set

[0126] According to norm ISO 815, measured 10 days after molding; MIE

[0127] Determined according to norm ISO 1133 with a load of 2.16 kg at 190 C.

[0128] MFRL

[0129] Determined according to norm ISO 1133 with a load of 2.16 kg at 230 C.

[0130] Intrinsic Viscosity

[0131] Determined according to norm ASTM D 2857 in tetrahydronaphthalene at 135 C.

[0132] Density

[0133] Determined according to norm ISO 1183 at 23 C.

[0134] Comonomer Contents

[0135] Determined by IR spectroscopy or by NMR.

[0136] For the butene-1 copolymers, the amount of comonomer was calculated from .sup.13C-NMR spectra of the copolymers. Measurements were performed on a polymer solution (8-12 wt %) in dideuterated 1,1,2,2-tetrachloro-ethane at 120 C. The .sup.13C NMR spectra were acquired on a Bruker AV-600 spectrometer operating at 150.91 MHz in the Fourier transform mode at 120 C. using a 90 pulse, 15 seconds of delay between pulses and CPD (WALTZ16) to remove .sup.1H-.sup.13C coupling. About 1500 transients were stored in 32K data points using a spectral window of 60 ppm (0-60 ppm).

[0137] Copolymer Composition

[0138] Diad distribution was calculated from .sup.13C NMR spectra using the following relations:

PP=100 I.sub.1/

PB=100 I.sub.2/

BB=100 (I.sub.3I.sub.19)/

PE=100 (I.sub.5+I.sub.6)/

BE=100 (I.sub.9+I.sub.10)/

EE=100 (0.5(I.sub.15+I.sub.6+I.sub.10)+0.25(I.sub.14))/

Where =I.sub.1+I.sub.2+I.sub.3I.sub.19+I.sub.5+I.sub.6+I.sub.9+I.sub.10+0.5(I.sub.15+I.sub.6+I.sub.10)+0.25(I.sub.14)

The molar content was obtained from diads using the following relations:

P(m %)=PP+0.5(PE+PB)

B(m %)=BB+0.5(BE+PB)

E(m %)=EE+0.5(PE+BE)

[0139] I.sub.1, I.sub.2, I.sub.3, I.sub.5, I.sub.6, I.sub.9, I.sub.6, I.sub.10, I.sub.14, I.sub.15, I.sub.19 are integrals of the peaks in the .sup.13C NMR spectrum (peak of EEE sequence at 29.9 ppm as reference). The assignments of these peaks were made according to J. C. Randal, Macromol. Chem Phys., C29, 201 (1989), M. Kakugo, Y. Naito, K. Mizunuma and T.sub.m Miyatake, Macromolecules, 15, 1150, (1982), and H. N. Cheng, Journal of Polymer Science, Polymer Physics Edition, 21, 57 (1983), incorporated herein by reference. The data were collected in Table A (nomenclature according to C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 10, 536 (1977), incorporated herein by reference).

TABLE-US-00001 TABLE A I Chemical Shift (ppm) Carbon Sequence 1 47.34-45.60 S.sub. PP 2 44.07-42.15 S.sub. PB 3 40.10-39.12 S.sub. BB 4 39.59 T.sub. EBE 5 38.66-37.66 S.sub. PEP 6 37.66-37.32 S.sub. PEE 7 37.24 T.sub. BBE 8 35.22-34.85 T.sub. XBX 9 34.85-34.49 S.sub. BBE 10 34.49-34.00 S.sub. BEE 11 33.17 T.sub. EPE 12 30.91-30.82 T.sub. XPE 13 30.78-30.62 S.sub. XEEX 14 30.52-30.14 S.sub. XEEE 15 29.87 S.sub. EEE 16 28.76 T.sub. XPX 17 28.28-27.54 2B.sub.2 XBX 18 27.54-26.81 S.sub. + 2B.sub.2 BE, PE, BBE 19 26.67 2B.sub.2 EBE 20 24.64-24.14 S.sub. XEX 21 21.80-19.50 CH.sub.3 P 22 11.01-10.79 CH.sub.3 B

[0140] For the propylene copolymers the comonomer content was determined by infrared spectroscopy by collecting the IR spectrum of the sample vs. an air background with a Fourier Transform Infrared spectrometer (FTIR). The instrument data acquisition parameters were: [0141] purge time: 30 seconds minimum; [0142] collect time: 3 minutes minimum; [0143] apodization: Happ-Genzel; [0144] resolution: 2 cm.sup.1.

[0145] Sample Preparation

[0146] Using a hydraulic press, a thick sheet was obtained by pressing about 1 g of sample between two aluminum foils. If homogeneity was uncertain, a minimum of two pressing operations occurred. A small portion was cut from this sheet to mold a film. The film thickness was between 0.02-:0.05 cm (8-20 mils).

[0147] Pressing temperature was 18010 C. (356 F.) and about 10 kg/cm.sup.2 (142.2 PSI) pressure for about one minute. Then the pressure was released and the sample was removed from the press and cooled the to room temperature.

[0148] The spectrum of a pressed film of the polymer was recorded in absorbance vs. wavenumbers (cm.sup.1). The following measurements were used to calculate ethylene and butene-1 content: [0149] Area (At) of the combination absorption bands between 4482 and 3950 cm .sup.1 which was used for spectrometric normalization of film thickness. [0150] If ethylene was present, Area (AC2) of the absorption band between 750-700 cm.sup.1 after two proper consecutive spectroscopic subtractions of an isotactic non additivated polypropylene spectrum was measured and then, if butene-1 was present, a reference spectrum of a butene-1-propylene random copolymer in the range 800-690 cm.sup.1 was used. [0151] If butene-1 was present, Height (DC4) of the absorption band at 769 cm.sup.1 (maximum value), after two proper consecutive spectroscopic subtractions of an isotactic non additivated polypropylene spectrum was measured and then, if ethylene is present, a reference spectrum of an ethylene-propylene random copolymer in the range 800-690 cm.sup.1 was used.
To calculate the ethylene and butene-1 content, calibration straight lines for ethylene and butene-1 were obtained by using reference samples of ethylene and butene-1.

[0152] Mw/Mn determination by GPC

[0153] The determination of the means Mn and Mw, and Mw/Mn derived therefrom was carried out using a Waters GPCV 2000 apparatus, which was equipped with a column set of four PLgel Olexis mixed-gel (Polymer Laboratories) and an IR4 infrared detector (PolymerChar). The dimensions of the columns were 3007.5 mm and their particle size was 13 m. The mobile phase used was 1-2-4-trichlorobenzene (TCB) and its flow rate was kept at 1.0 ml/min. The measurements were carried out at 150 C. Solution concentrations were 0.1 g/dl in TCB and 0.1 g/1 of 2,6-diterbuthyl-p-chresole were added to prevent degradation. For GPC calculation, a universal calibration curve was obtained using 10 polystyrene (PS) standard samples supplied by Polymer Laboratories (peak molecular weights ranging from 580 to 8500000). A third order polynomial fit was used to interpolate the experimental data and obtain the relevant calibration curve. Data acquisition and processing were done using Empower (Waters). The Mark-Houwink relationship was used to determine the molecular weight distribution and the relevant average molecular weights: the K values were K.sub.PS=1.2110.sup.4 dL/g and K.sub.PB=1.7810.sup.4 dL/g for PS and PB respectively, while the Mark-Houwink exponents =0.706 for PS and =0.725 for PB were used.

[0154] For butene-1/ethylene copolymers, it was assumed that the composition was constant in the whole range of molecular weight and the K value of the Mark-Houwink relationship was calculated using a linear combination as reported below:

K.sub.EB=x.sub.EK.sub.PE+x.sub.PK.sub.PB

[0155] where K.sub.EB was the constant of the copolymer, K.sub.PE (4.0610.sup.4, dL/g) and K.sub.PB (1.7810.sup.4 dl/g) were the constants of polyethylene and polybutene, x.sub.Eand x.sub.B were the ethylene and the butene-1 weight % content. The Mark-Houwink exponents =0.725 was used for all the butene-1/ethylene copolymers.

[0156] Fractions Soluble and Insoluble in Xylene at 0 C. (XS-0 C.)

[0157] 2.5 g of the polymer sample were dissolved in 250 ml of xylene at 135 C. under agitation. After 30 minutes, the solution was allowed to cool to 100 C., still under agitation, and then placed in a water and ice bath to cool down to 0 C. Then, the solution was allowed to settle for 1 hour in the water and ice bath. The precipitate was filtered with filter paper. During the filtering, the flask was left in the water and ice bath to keep the flask inner temperature as near to 0 C. as possible. Once the filtering was finished, the filtrate temperature was balanced at 25 C., dipping the volumetric flask in a water-flowing bath for about 30 minutes and then, divided in two 50 ml aliquots. The solution aliquots were evaporated in nitrogen flow, and the residue dried under vacuum at 80 C. until constant weight was reached. If the weight difference between the two residues was not less than 3%, the test was repeated. The percent by weight of polymer soluble (Xylene Solubles at 0 C.=XS 0 C.) was calculated from the average weight of the residues. The insoluble fraction in o-xylene at 0 C. (xylene Insolubles at 0 C.=XI % 0 C.) was:

XI % 0 C.=100XS % 0 C.

[0158] Fractions Soluble and Insoluble in Xylene at 25 C. (XS-25 C.)

[0159] 2.5 g of polymer were dissolved in 250 ml of xylene at 135 C. under agitation. After 20 minutes, the solution was allowed to cool to 25 C., still under agitation, and then allowed to settle for 30 minutes. The precipitate was filtered with filter paper, the solution was evaporated in nitrogen flow, and the residue was dried under vacuum at 80 C. until constant weight was reached. The percent by weight of polymer soluble (Xylene SolublesXS) and insoluble at room temperature (25 C.) were calculated.

[0160] As used herein, the percent by weight of polymer insoluble in xylene at room temperature (25 C.) was considered the isotactic index of the polymer. It is believed that this measurement corresponds to the isotactic index determined by extraction with boiling n-heptane, which constitutes the isotactic index of polypropylene polymers as the term is used herein.

[0161] Determination of Isotactic Pentads Content

[0162] 50 mg of each sample were dissolved in 0.5 ml of C.sub.2D.sub.2Cl.sub.4.

[0163] The .sup.13C NMR spectra were acquired on a Bruker DPX-400 (100.61 Mhz, 90 pulse, 12 s delay between pulses). About 3000 transients were stored for each spectrum; the mmmm pentad peak (27.73 ppm) was used as reference.

[0164] The microstructure analysis was carried out as described in literature (Macromolecules 1991, 24, 2334-2340, by Asakura T.sub.m et Al. . and Polymer, 1994, 35, 339, by Chujo R. et Al., incorporated herein by reference).

[0165] The percentage value of pentad tacticity (mmmm%) for butene-1 copolymers was the percentage of stereoregular pentads (isotactic pentad) as calculated from the relevant pentad signals (peak areas) in the NMR region of branched methylene carbons (around 27.73 ppm assigned to the BBBBB isotactic sequence), with due consideration of the superposition between stereoirregular pentads and of those signals, falling in the same region, due to the comonomer.

[0166] Determination of X-Ray Crystallinity

[0167] The X-ray crystallinity was measured with an X-ray Diffraction Powder Diffractometer using the Cu-Kal radiation with fixed slits and collecting spectra between diffraction angle 2=5 and 2=35 with step of 0.1 every 6 seconds.

[0168] Measurements were performed on compression molded specimens in the form of disks of about 1.5-2.5 mm of thickness and 2.5-4.0 cm of diameter. These specimens were obtained in a compression molding press at a temperature of 200 C.5 C. without applying pressure for 10 minutes, then applying a pressure of about 10 Kg/cm.sup.2 for a few seconds and repeating the last operation for 3 times.

[0169] The diffraction pattern was used to derive the components for the degree of crystallinity by defining a linear baseline for the whole spectrum and calculating the total area (Ta), expressed in counts/sec.Math.2, between the spectrum profile and the baseline. Then an amorphous profile was defined, along the whole spectrum, that separate, according to the two phase model, the amorphous regions from the crystalline ones. The amorphous area (Aa), expressed in counts/sec.Math.2, was calculated as the area between the amorphous profile and the baseline; and the crystalline area (Ca), expressed in counts/sec.Math.2, was calculated as Ca=TaAa. The degree of crystallinity of the sample was then calculated according to the formula:

% Cr=100Ca/Ta

Examples 1-3 and Comparative Examples 1 and 2

[0170] Materials Used in the Examples [0171] PB-1: butene-1/ethylene copolymer containing 16% by moles of copolymerized ethylene, was prepared according to the process disclosed in Patent Cooperation Treaty Publication No. WO2009000637, incorporated herein by reference, and in-line blended with a propylene copolymer composition (I) added in amount of 7% by weight with respect to the total weight of the butene-1/ethylene copolymer and the propylene copolymer composition (i). [0172] Such propylene copolymer composition (i) had MFRL of 5.5 g/10 min., total copolymerized ethylene content of 3% by weight, total copolymerized butene-1 content of 6% by weight; XS-25 C. of 19% by weight and T.sub.m of 133 C., and was made of the following two components: [0173] i) 35% by weight of a copolymer of propylene with ethylene (3.2% by weight in the copolymer), and [0174] i) 65% by weight of a copolymer of propylene with ethylene (3.2% by weight in the copolymer) and butene-1 (6% by weight in the copolymer); wherein the amounts of i) and i) were referred to the total weight of i)+i); [0175] PP: copolymer of propylene with ethylene, containing 6% by weight of ethylene, based upon the total weight of the copolymer, having T.sub.m of 133 C., MFRL of about 7 g/10 min., XS-25 C. of 20% by weight; [0176] Stabilizers: blend of 0.05% by weight of pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1010, sold by BASF) and 0.05% by weight of tris (2.4-di-tert-butylphenyl) phosphite (Irgafos 168, sold by BASF), the percent amounts being referred to the total weight of the polyolefin composition; [0177] Lubricants: blend of 1% by weight of erucamide (Crodamide ER, sold by Croda), 1% by weight of Oleamide (Crodamide OR, sold by Croda) and 1% by weight of Glyceryl Stearate (Atmer 129, sold by Croda), the percent amounts being referred to the total weight of the polyolefin composition; [0178] Pigment: Titanium dioxide Ti-Pure R-104, sold by DuPont.

[0179] No melting peak was detected in the DSC analysis (second scan) of the above described PB-1.

[0180] The materials were melt-blended in a co-rotating twin screw extruder Coperion ZSK40SC, with screw diameter of 40 mm and screw length/diameter ratio of 43:1, under the following conditions: [0181] extrusion temperature of 180-200 C.; [0182] screw rotation speed of 220 rpm; [0183] production rate of 60 kg/hour.

[0184] The properties of the final compositions are reported in Table 1.

[0185] In Table 1 are also reported the properties of the above described PP and PB-1 components (Comparison Examples 1 and 2).

TABLE-US-00002 TABLE I Example 1 2 3 Comp. 1 Comp. 2 PB-1 Weight % 57.95 48.3 37 100 PP Weight % 38.65 48.3 59.6 100 Stabilizers Weight % 0.1 0.1 0.1 Lubricants Weight % 3.0 3.0 3.0 Pigment Weight % 0.3 0.3 0.3 Amount of A)* Weight % 55.8 46.5 35.6 0 93 Amount of B)* Weight % 44.2 53.5 64.4 100 7 Composition Properties H.sub.fus J/g 34.45 40.47 48.23 71 0 T.sub.m C. 132.6 132.8 131.8 133 Shore A 91 91 91 60 Shore D 25.5 29.6 37.7 58 <20 MIE gr/10 3.94 3.84 4.14 1.4 Stress at Break MPa 17 19.9 21.1 11 Elongation at Break % 1090 1150 1040 790 Compression Set 22 hours % 52 51 51 32 23 C. after 10 min. in Autoclave Compression Set 22 hours % 71 69 70 100 70 C. after 10 min. in Autoclave Compression Set 22 hours % 90 88 100 100 C. after 10 min. in Autoclave Note: *weight % with respect to the total weight of A) + B).