KR19990007827A - Long chain side chain introduction into straight polyethylene - Google Patents

Abstract

The process of the present invention improves the transformation efficiency of the peroxide through the appropriate choice of antioxidant additives and extrusion environment.

Description

Long chain side chain introduction into straight polyethylene

The present invention relates to altering straight chain polyethylene to provide long chain side chains to the straight polyethylene. The present invention relates to an article produced by a method comprising contacting a straight chain polyethylene with a peroxide and a solid antioxidant in the presence of nitrogen to introduce the long chain side chain into the straight chain backbone of the straight chain polyethylene.

The method of the present invention provides a method of crosslinking the resin in the presence of both primary and secondary antioxidants in a single step. The use of nitrogen blankets greatly improves the efficiency of high temperature peroxides. The result is a high increase in viscosity or kinematic viscosity when measured by I ₂ at very low concentrations of peroxide. This process can be carried out with a wide range of combination apparatuses with various polyethylene resins produced by Ziegler catalysts, chromium or metallocene catalysts.

According to the invention, the raw uncrosslinked polyethylene is contacted with peroxides and antioxidants under a blanket of nitrogen in a feed woofer at a temperature of 180-300 ° C. The amount of antioxidant will range from 100 to 3000 ppm based on the mixture of HDPE, antioxidant and peroxide.

LLDPE is combined with primary and secondary antioxidants. The role of antioxidant stabilizer in polyethylene is to preserve the strength by protecting the polymer from oxidative degradation after combination. The mechanism of degradation of polyethylene by oxidation is a self-catalyzed, free radical chain reaction. During this process hydroperoxides are formed, which are broken down into radicals to accelerate the decomposition of polyethylene. Antioxidants (1) remove radicals to stop oxidative chain reactions by hydroperoxide decomposition and (2) consume hydroperoxides to prevent polyethylene degradation.

Primary antioxidants contain one or more reactive hydrogen atoms which interfere with free radicals, in particular peroxide radicals, to form relatively stable antioxidant species with the polymerization hydroperoxide groups. Phenolic antioxidants are currently the most widely used primary antioxidants in plastics, including phenols, bisphenols, thiobisphenols and polyphenols. Interfered phenols such as Ciba Gauge's Irganox 1076, 1010, and Ethyl 330 meet this first requirement and are considered primary antioxidants. Other examples are as follows:

2,6-bis (1-methylheptadecyl) -p-cresol

Butylated hydroxyanisole [BHA], [(CH ₃ ) ₃ CC ₆ H ₃ OH (OCH ₃ )]

Butylated hydroxytoluene [BHT], [DBPC], [di-t-butyl-p-cresol]

Butylated Octylated Phenolic

4,4'-butylidenebis (6-t-butyl-m-cresol) [Santowhite powder]

2,6-di-t-butyl methylamino-p-cresol

Hexamethylenebis (3,5-di-t-butyl hydroxy-cinnamate) [Iganox 259]

2,2'-methylenebis (4-methyl-6-t-butyl phenol) [CAO 5], [bis (2-hydroxy-3-t-butyl-5-methyl phenyl) methane], [cyanox ( Cyanox) 2246]

Octadecyl 3,5-di-t-butyl-4-hixicyhydrosinamate [Iganox 1076]

Tetrakis (methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane [Iganox 1010]

4,4'-thiobis (6-t-butyl-m-cresol) [Santonox]

Thiodiethylenebis (3,5-di-t-butyl-4-hydroxy) hydrocinamate [Iganox 1035]

1,3,5-tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) 1,3,5-triazine-2,4,6- (1H, 3H, 5H) -tree On [Cyanox 1790]

Tris (2-Methyl-4-hydroxy-5-t-butylphenyl) -butane [Topanol CA]

Monopoly Phenolic Product

Antioxidant MBP-5P, 5T

Antioxidant SP

Antioxidant TBE-9

Antioxidant TBM-6P, 6T [thiophenol]

CAO-42

Escoflex A-122, A-123

Hostanox 03

Isonox 129 [bisphenolic]

MO-14

Naugard 431 [Interfered Phenolic Compounds]

Now Guard XL-1

Prodox 120

PRODOX 147

PRODOX 247

Prodox 340, 341, 343

PRODOX B113

PRODOX B121

Stabilite 49-467, 49-470

Uvi-Nox 1492

Vanox GT

Banox SKT

Banox 1290, 1320

Wingstay C

Wingstay L [polymerized interference phenol]

Wingstay S [Styrene Phenol]

Wingstay T

Wingstay V

Now Guard P, PHR

Weston 399

Weston 626

Weston 430, 474, 491, 494, DHOP, PTP, PNPC, THOP

Tetrakis (2,4-di-t-butyl) phenyl- (1,1-bi-phenyl) -4,4'-diylbisphosphite [Sandostab P-EPQ]

Triisodecyl Phosphite [Weston TDP]

Triisooctyl phosphite [Weston TIOP]

Triloryl Phosphite [Weston TLP]

Trisnonylphenyl phosphite

Didecyl phosphite

Di lauryl phosphite [(C ₁₂ H ₂₉ O) ₂ PHO]

Trisnonylphenyl phosphite / formaldehyde polymer [Wytox 438]

Witox 320 (alkylaryl phosphite)

The main group of secondary antioxidants includes phosphoric acid based antioxidants, generally phosphites. Phosphites work by converting hydroperoxides into non-chain proliferating alcohols and oxidizing themselves to phosphates. These are selected when the stability of the method is concerned. Trisnonylphenyl phosphite is the most widely used phosphite. Common secondary antioxidants are GE's Weston TNPP, Ciba Gage's Ultranox 626 and Irgafos 168. A list of primary and secondary antioxidants is disclosed in Chemical Additives for the Plastics Industry, Radian Corporation, Noyes Data Corporation, NJ, 1987. Another example is as follows:

Tetrakis (2,4-di-t-butyl) phenyl- (1,1-bi-phenyl) -4,4'-diylbisphosphite [acid step P-EPQ];

Triisodecyl phosphite [Weston TDP];

Triisooctyl phosphite [Weston TIOP];

Triloryl phosphite [Weston TLP];

Trisnonylphenyl phosphite;

Didecyl phosphite;

Di lauryl phosphite [(C ₁₂ H ₂₉ O) ₂ PHO]

Trisnonylphenyl phosphite / formaldehyde polymer [Witox 438]

Witox 320 (alkylaryl phosphite).

According to the present invention, the mixture of primary and secondary antioxidants in LLDPE may constitute up to 3000 ppm of the total mixture.

Preferably, the antioxidant is solid at ambient conditions.

The amount of peroxide will range from 10 to 1000 ppm based on the mixture of HDPE, antioxidant and peroxide.

Preferably, however, the amount of peroxide will range from 10 to 500 based on the PE weight. Most preferably, the peroxide of the mixture is 10-300 ppm.

The type of peroxide used is a high temperature peroxide that can be almost completely decomposed at normal combination temperatures (200-260 ° C.). At 0.1 hours, the half-life should be at least 130 ° C. At a given time, the half-life is the temperature at which half of the peroxide decomposes. Suitable examples of such peroxides include: dicumyl peroxide, 2,5-dimethyl-2,5-di- (tert butyl peroxy) hexane, ter-butyl cumyl peroxide, di- (2-ter- Butylperoxy-isopropyl) hexin-3, cumene hydroperoxide. These contain 2 to 20 carbon atoms. Peroxides may be premixed with PE or supplied separately as liquid by a variety of known methods.

Treatment of polyethylene should be done under nitrogen. Nitrogen will be introduced into the polyethylene treatment zone in accordance with the present invention at the feed port of the combined extruder to minimize exposure to oxygen. Combination under these conditions greatly increases the crosslinking efficiency of the peroxide.

The polyethylene used as a reactant to be treated in accordance with the present invention may be a high density polyethylene, sometimes denoted by the acronym HDPE, or may be a straight chain low density polyethylene, sometimes denoted by the acronym LLDPE. HDPE will have a specific gravity of 0.94 to 0.97 g / cc and LLDPE will have a specific gravity of 0.89 to 0.94 g / cc. Thus, polyethylene that can be used in the present invention will have a density in the range of 0.89 to 0.97 [ASTM D-1505]. These straight chain polyethylenes actually have a straight chain backbone and no side chains. Thus, the reactant polyethylene may be a homopolymer of ethylene or a copolymer of ethylene and may be an alpha olefin of 3 to 10 carbon atoms, preferably an alpha olefin of 4 to 10 carbon atoms. Preferred monomers are olefins, preferably 1-olefins containing 3 to 10 carbon atoms, for example 1-propene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1 -Heptene and 1-octene. Preferred olefin comonomers are 1-butene, 1-hexene and 1-octene; When the polyethylene resin contains comonomers the resin will contain at least 80, preferably at least 90 mole% ethylene units. The process of the present invention can be carried out with a wide range of polyethylene resins produced by Ziegler catalysts, chromium or metallocene catalysts, as shown in the examples below.

The polyethylene used as reactant to be treated has less shear reduction (dependence of viscosity on shear rate) than the peroxide treated product of the present invention. MFR [ASTM D-1238 to the ₂ terms E I and a I ₂₁ / I ₂ ratio measured in accordance with the condition F to the I _21] is a reflection of shear reduction; Shear decrease appears to increase with increasing levels of MFR.

The polyethylene used as reactant to be treated has a lower kinematic viscosity than the product realized by the process of the invention. Kinematic viscosity is measured at 190 ° C. using a dynamic melt flow meter outlined in ASTM D4440-84. The increase in viscosity is based on the viscosity of the untreated LLDPE.

The polyethylene used as reactant in the process of the invention has a higher I ₂ than the product of the process. In other words, the effect of the process of the invention is to reduce the I ₂ of the polyethylene. Since I ₂ is inversely related to the low shear rate viscosity [ASTM D-1238 Condition E] of the resin, the decrease in I ₂ reflects an increase in viscosity as a result of peroxide utilization. A greater decrease in I ₂ in the nitrogen blanket (Sample B, Example 1) shows an increase in the crosslinking efficiency of the peroxide in the presence of the nitrogen blanket.

The presence of long chain side chains in the product of the invention produced by the process of the invention is indicated by a sharp increase in low shear rate viscosity, a decrease in I ₂ and an increase in MFR as compared to the parent resin. According to the invention, the amount of long chain side chains that can be introduced can be measured in terms of the change in these properties.

Characteristics Wide range Desirable range Most desirable range % Increase in kinematic viscosity for the parameter at 0.1 frequency 25-1000% 25-500% 50-300% % Decrease in I _{2 on} the parameters 15-500% 20-200% 25-100% % Increase in MFR for parameter 15-500% 20-200% 25-100%

The process of the present invention can be carried out in various combination plants with various polyethylene resins which are homopolymers and copolymers in densities ranging from 0.89 to 0.97, produced by Ziegler catalysts, chromium or metallocene catalysts, as shown in the examples below. have. In addition, instead of nitrogen being used to provide an inert environment at the feed port of the extruder, any other inert (non-oxidizing) gas may be used.

Example 1

The granular LLDPE (.9 MI, nominal .918 density 1-hexene copolymer) resin produced with the Ziegler catalyst is mixed with 500 ppm of Iganox 1010 and 500 ppm of Igafos 168.

The effects of nitrogen blanket and peroxide addition on feed woofers during the combination were studied. For these experiments, a 5% solution of Trigonox 101 E5 (provided by Akzo) in mineral oil was used. Peroxide was added to the granular LLDPE resin in a 1% masterbatch. The mixture was combined in an experimental 3/4 Brabender Pair Screw Extruder at 220 ° C. and 25 RPM. The table below shows the effect of peroxides and nitrogen blankets:

sample Peroxide Concentration ppm Nitrogen blanket I2 I21 / I2 % Decrease in I2 % Increase in I21 / I2 A 0 has exist 0.89 24.7 - - B 100 has exist 0.26 53.6 70.8 117 C 100 none 0.55 35.3 38.2 42.9

Large decreases in I2 in the presence of a nitrogen blanket (Sample B) show increased crosslinking efficiency of the peroxide in the presence of the nitrogen blanket. Since I2 is inversely related to the low shear rate viscosity of the resin, the decrease in I2 reflects the increase in viscosity as a result of peroxide utilization.

Example 2

Combination conditions were similar to those used in Example 1. The only difference was that the chromium oxide catalyst and polymerized HDPE (.58MI, nominally .953 density 1-hexene copolymer) were used as a source instead of LLDPE and there was no secondary antioxidant. Only 500 ppm of Iganox 1010 was used. The results are as follows:

sample Peroxide Concentration ppm Nitrogen blanket I2 I21 / I2 % Decrease in I2 % Increase in I21 / I2 D 0 has exist 0.058 72.4 - - E 100 has exist 0.09 213 84.5 194.2 F 100 none 0.24 128 58.6 76.8

Similar to Example 1, sample E with a nitrogen blanket caused a much larger decrease in I2 (ie, increase in viscosity). The use of a nitrogen blanket increases the crosslinking efficiency of the peroxide.

Example 3

This example shows the importance of selecting a suitable secondary antioxidant to increase the crosslinking efficiency of the peroxide. Combination conditions were similar to those used in Example 1 except that other LLDPE sources (.8 MI, .918 density 1-hexene copolymer) were used and all samples had a nitrogen blanket at the woofer feed port. Do. The primary antioxidant Iganox 1010 was present at 500 ppm and the selected secondary antioxidant (phosphite) was also 500 ppm.

sample Peroxide Concentration ppm Secondary antioxidant I2 I21 / I2 % Decrease in I2 % Increase in I21 / I2 G 0 Igafos 168 0.8 27 - - H 100 Weston 399 0.6 31.6 25 17 I 100 Igafos 168 0.29 48.9 63.8 54.7

Comparison of samples H and I suggests that the choice of secondary antioxidants is important for the efficiency of peroxide crosslinking (measured in I2 reduction rates). Weston 399, a liquid at room temperature, disperses fairly efficiently and reduces the crosslinking efficiency of radicals produced by peroxides. The solid Igafos 168 (melting point 180-185 ° C.) does not disperse quickly and thus allows peroxide radicals to participate in the crosslinking of polyethylene molecules. Solid antioxidants are therefore preferred in the present invention.

Example 4

This example demonstrates the use of the method of the present invention in introducing low concentrations of long chain side chains in metallocene catalyzed LLDPE resins. I2 (MI) of .8, I21 / I2 of 17 and metallocene catalyzed (1-hexene copolymer) LLDPE granular resin of nominal density of .917 were used as the parent LLDPE. Granular LLDPE was premixed with 100 ppm peroxide (used as a granulation masterbatch), 500 ppm Iganox 1010, 500 ppm Igafos 168. The mixture was combined on a 2-inch Brampton single screw extruder with a blanket of nitrogen at the feed at 465 ° F. at 75 lbs / hr. The resulting pelletized LLDPE (Sample J) had the following characteristics:

I2 = .44

I21 / I2 = 23

Reduction ratio of I2 = 45%

I21 / I2 growth rate = 35%

The increase rate of kinematic viscosity at .1 sec-1 @ 190 ℃ was 122.5%. The rate of increase in viscosity was measured relative to the raw granular LLDPE resin. Kinematic viscosity is measured by the procedure described in ASTM D4440-84.

The presence of long chain side chains is indicated by a sharp increase in low shear rate viscosity, a decrease in I2 and an increase in MFR as compared to the metallocene catalyst LLDPE resin.

Example 5

In this example, a large scale method of carrying out the method of the present invention is shown. For this purpose a 4 inch Farrel combiner was used. Dry LLDPE (nominal .65MI, .922 density 1-hexene copolymer, I21 / I2 of 27, 123,200 poises at .1 sec-1 measured at 190 ° C) with 500 ppm Iganox 1010 and 500 ppm Iganox 168 -Mixed. Instead of using the peroxide granule masterbatch described in the above examples, a 5% Trigonox solution in mineral oil was injected directly into the Farrell mixing vessel. The flow rate of the peroxide solution was adjusted to achieve the desired concentration in the final polymer. Nitrogen flowed from the hopper. The combination speed was 550 lbs / hr at a specific energy input of 0.11 (hp.hr) / lb. The melt temperature in the mixer was approximately 460 ° F. The results are as follows.

sample Peroxide Concentration ppm I2 I21 / I2 I2 decrease% Viscosity @ .1 1 / sec poises (1) Viscosity increase (1) % Increase in I21 / I2 K 100 0.26 46 60 369,500 200 70 L 150 0.14 70 78.5 630,400 412 160

Kinematic viscosity is measured at 190 ° C. using a dynamic melt flow meter as described in ASTM D4440-84.

The increase in viscosity is based on the viscosity of the untreated LLDPE.

The present method provides a very effective means of modifying the parent polyethylene at low concentrations of 100 ppm peroxide and in the presence of both primary and secondary antioxidants.

It is therefore evident that the present invention provides methods and products that meet the above objects and advantages. While the present invention has been disclosed in conjunction with certain embodiments, it will be apparent that many variations will be possible to those skilled in the art. Accordingly, all such modifications will fall within the scope of the claims.

The product polyethylene, whether homopolymer or copolymer, will contain long chain side chains. The presence of long chain side chains will greatly increase the low shear viscosity of the polyethylene. This increase in viscosity results in higher melt tension during PE melting. Increased melt tension allows PE to be used in applications that were not previously easy, such as sheet extrusion, high stalk film blowing, foaming and blow molding.

Claims (7)

Mixing in a inert atmosphere of the extruder feed with a melt temperature of 180-300 ° C., a parent resin containing an uncrosslinked polymer or ethylene copolymer of ethylene, an antioxidant and a high temperature peroxide having a half life temperature of at least 130 ° C. at 0.1 hour. Wherein the amount of hot peroxide is 10-1000 ppm and the total amount of antioxidant is 100-3000 ppm; 15-500% increase in I ₂₁ / I ₂ values (measured at 190 ° C according to ASTM 1238) for the parent resin, 15-500% decrease in I ₂ values for the parent resin and kinematic viscosity for the parent resin [ASTM D4440- Allowing a 25-1000% increase in measurement according to 84; Recovering the product containing the long chain side chain, A process for introducing a long chain side chain and crosslinking an uncrosslinked polymer or ethylene copolymer of ethylene with an alpha olefin of 3 to 10 carbon atoms. The method of claim 1 wherein the uncrosslinked homopolymer or copolymer has a specific gravity of 0.89 to 0.97. The method of claim 1 wherein said antioxidant is a solid at room temperature. The method of claim 1 wherein said uncrosslinked PE is produced by the use of a Ziegler catalyst, a chromium based or metallocene catalyst and mixtures thereof. The product produced by the method of claim 1. The product produced by the method of claim 2. The product produced by the method of claim 3.