Aqueous dispersions of olefin copolymers

ES 2 155 609 T3

DESCRIPTION

Aqueous dispersions of olefin copolymers.

This invention relates to an aqueous dispersion of an olefin copolymer. These dispersions can be film-forming at room temperature and can have excellent phosphorous and mechanical properties.

Aqueous polyolefin dispersions are known in the art, although none have been reported to have been made from polyolefins having molecular weights above 40,000. For example, in US Patent 3,734,686, Douglas et al. Co-workers describe a mechanically stable aqueous emulsion of polyethylene particles having an average molecular weight in the range from 7000 to 40,000. These dispersions are indicated to be useful for treating carpets.

In US Patent 3,418,265. McClain shows that aqueous loatex of sub-micrometer size film-forming ethylene polymers can be prepared by dispersion in water of an ethylene polymer and a water-soluble block copolymer of ethylene oxide and propylene oxide. Examples of stable dispersions of ethylene polymers having a molecular weight above 27,000 are not reported.

Many of the previously described polyolefin loatexes are not really purely polyolephonic, but rather contain polar groups, such as acids or halides. Since the film-forming properties of these so-called polyolefin latexes are often adversely influenced by the presence of these polar substituents, it would be desirable to prepare latexes obtained from higher molecular weight polyethylenes that did not contain polar groups. It would be of additional value if these loatex were film formers at ambient temperatures.

The present invention is a film-forming artificial latex comprising an aqueous dispersion of an ethylene copolymer and a C3-C20 alpha-olefin, the olefin polymer being characterized as having:

a) an absence of polar groups;

b) a polydispersity onyx from about 1.5 to about 2.5;

c) an I10 / I2 of at least 6;

d) a chromic intensity of shear at the beginning of surface melt fracture of at least 50 percent greater than the chromic intensity of shear at the beginning of surface fracture in melt of a linear olefin polymer having the same I2 e polydispersity onyx;

e) a weight average molecular weight of at least 45,000; Y

f) a density of about 0.85 to about 0.9 g / cm³.

In another aspect, the present invention is a film-forming aqueous dispersion comprising a copolymer of ethylene and an alpha-olefin.

C3-C20 having a narrow molecular weight distribution, a random distribution of comonoomer units along the base structure of the polymer, and a homogeneity onyx of at least 75.

It has surprisingly been discovered that film-forming laotexes can be prepared from these olefin polyomers in the absence of polar substituents.

The olefin polymer used to prepare the aqueous dispersion of the present invention is from a family of olefin polymers, which are described in US Patents 3,645,992; 5,272,236; and 5,278,272. The class of olefin polymers described in US Pat. 3,645,992, hereinafter referred to as Elston's olefin polymer, is characterized by being a copolymer of ethylene and at least one other alpha-olefin having four or more carbon atoms, such as 1-butene, 1-hexene, 1-octene , and 1-octadecene. Interpolymers, such as those of ethylene-octene-butene or ethylene-octene-propylene are also suitable for the preparation of the aqueous dispersions of the present invention. Elston's olefin polymer is further characterized by a narrow molecular weight distribution and a homogeneity index of at least 75 as described in Patent 3,645,992.

The olefin polyomers described in Patents 5,272,236 and 5,278,272 (collectively referred to as substantially linear olefin polyomers) are ethylene-C3-C20 alpha-olefin copolymers characterized by having 1) high melt elasticity; 2) high working capacity; 3) a polydispersity onyx of less than 3.5; 4) 0.01 to long chain branches per 1000 carbon atoms along the base structure of the polymer; and 5) a melt flow onyx that is essentially independent of the polydispersity onyx. The olefin polymer of the Patent 5,272,236 is further characterized by having a chromic intensity of shear stress at the beginning of the global melt fracture greater than 4 x 10⁶ dynes / cm²; and the olefin polymer of Patent 5,278272 is further characterized by having a crotic intensity of shear at the beginning of the superficial melt fracture of at least 50 percent higher than the chromic intensity of shear at the beginning of the superficial melt fracture. of a linear olefin polymer having the same I2 and the same Mw / Mn.

The substantially linear olefin polyomers from which the aqueous dispersions are prepared can be homopolymers of C2-C20 olefins, such as ethylene, propylene, 4-methyl-1-pentene, or they can be interpolymers of ethylene and at least one alpha-olefin. C3-C20, and / or a C2-C20 acetyloenically unsaturated monoomer and / or a C4-C18 diolefin. Preferred monomers include C2-C10 alpha-olefins, especially ethylene, propylene, isobutylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Other preferred monoomers include styrene and 1,4-hexadiene.

The substantially linear olefin polyomers have 0.01, preferably 0.3 to 3, and more

ES 2 155 609 T3 preferably 1 long chain branch per 1000 carbon atoms along the basic structure of the polymer. Long chain branching is defined herein as a chain length of at least 6 carbon atoms, above which the length cannot be distinguished by carbon NMR spectroscopy. The long chain branching can be as long as the basic structure of the polymer.

The polydispersity index of the substantially linear olefin polymers (that is, the molecular weight distribution, or the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn)), is preferably from 1.5 to 2, 5. The melt flow index (ie I10 / I2) of substantially linear olefin polymers is at least 5.63, preferably at least 6, more preferably at least 7, and is essentially independent of the polydispersity number. , in contrast to conventional polyolefins which show a dependence of melt flow index on polydispersity index. This property is illustrated in Figure 2 in the patent of 5,272,236.

The preparation of the substantially linear olefin polymers is described in detail in the patent 5,272,236.

The density of the olefin polymer described in the patent 5,278,272 is preferably from 0.85 g / cm³, more preferably from 0.86 g / cm³, at 0.90 g / cm³, and more preferably 0.88 g / cm³.

The weight average molecular weight of the substantially linear olefin polymers used to prepare the aqueous dispersion is preferably at least 45,000 amu (atomic mass unit), more preferably at least 60,000 amu. Molecular weights are measured as described in US Patent 5,278,272, column 5, line 56 to column 6, line 20. The olefin preferably does not contain polar groups, such as acetate, ester, ether, amine, alcohol, acrylic, methacrylic, halogen, nitrile, nitro, sulfate, phosphate, or mercaptan groups; and there is preferably no subsequent modification step to add polar groups.

The laatexes of the substantially linear olefin polymers are prepared in the presence of a stabilizing and emulsifying amount of a suitable surfactant. A preferred surfactant is an ethoxylated phenol sulfate represented by the formula:

X-0-O- (CH₂-CH₂-OR)_n-SW₃^-Z + wherein X is a linear or branched C6-C18 alkyl group, preferably octyl, nonyl, or lauryl, most preferably octyl or nonyl, and most preferably nonyl; 0 is phenylene, preferably p-phenylene; n is from 4 to 32, preferably from 4 to 12; and Z is sodium, potassium, or ammonium, preferably ammonium. Some of the preferred ethoxylated alkyl phenol sulfates are commercially available, for example, the ammonium salt of poly (oxy-1,2-ethanediyl) alpha-sulfoω (nonylphenoxy).

Aqueous dispersions of the substantially linear olefin polymers can be prepared by any suitable technique, including those described in US Patents 3,360,599; 3,503,917; 4,123,403; and 5,037,864. It has surprisingly been discovered that a film having a substantially uniform thickness across a substrate or shape can be prepared from the aqueous dispersion described hereinbefore. The film is further characterized by an absence of cracks or holes. Finally, the film has useful phasic properties, such as high tensile strength, and can be formed at room temperature, and in the absence of polar substituents.

The film can be prepared by any suitable means such as casting, coagulation, or spraying. If films are prepared by coagulation, it is generally preferred to use fatty acid based surfactants, such as the sodium salt of oleic acid.

The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example 1

A cast film of an ethylene-1-octene latex

An artificial laatex of ethylene-octene elastomer ENGAGE will be prepared.^TM CL 8002 (trademark of The Dow Chemical Company), which has a melt index of 1, a density of 0.87 g / cm³, an I10 / I2 of 7.8, a weight average molecular weight of 129,800, and a Mw / Mn of 2.2. To a 2 liter reactor vessel was added 612 g of the ethylene-octene copolymer solution containing 61 g of the copolymer in 551 g of cyclohexane; 3.06 g of RHODAPEX surfactant^TMCO 436 (trademark of Rhone Poulenc); and 288 g of water. These ingredients were emulsified using a Gifford-Woods homogenizer by mixing at nominally 10,000 rpm for 10 minutes. 0.2 g of DF37 defoamer (obtained from Air Products) is added to reduce foam. The cyclohexane solvent will be removed from the emulsion by rotary evaporation at 80 ° C. The artificial latex that is obtained will be concentrated to 30 percent in solids by applying a partial vacuum to the latex with continued heating.

The particle size of the latex, which is analyzed using a Coulter Counter Multisizer, was found to be 0.9 microns, with 74 percent of the particles being less than 1.25 microns.

20ml of salt will be poured onto a clean glass substrate, and spread evenly using a movable stick. The latex was allowed to air dry at room temperature. As the latex dries, a coherent film formed. The film, still on the substrate, was annealed at 60^°C for 5 minutes to loosen any remaining water, then allow to cool to room temperature. The resulting film had a tensile strength of 11,000 kPa, a 100 percent modulus of 1860 kPa, and a percentage elongation of 1270 percent.

ES 2 155 609 T3

Example 2

A cast film of an ethylene-1-octene latex

An artificial latex was prepared as described in Example 1 from an ethylene-octene copolymer having a melt index of 11, a density of 0.887 g / cm³, an I10 / I2 of 7.8, a weight average molecular weight of 60,000, and an ethylene / octene ratio of 2.1: 1, and was prepared according to the indications of the patent 5,278,272. The film obtained had a tensile strength of 15,000 kPa, a 100 percent modulus of 323 kPa, and a percentage elongation of 1,300 percent.