Modifiers based on ethylenes or amorphous olefin elastomers...

Details Modifiers based on ethylenes or amorphous olefin elastomers... Modifiers based on ethylenes or amorphous olefin elastomers...

1999-04-21

2001-02-13

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S240000

Reexamination Certificate

active

06187869

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of modifiers based on ethylenes or amorphous olefin elastomers for reducing the surface tack of amorphous polypropylenes.
2. Prior Art
Soft, predominantly or completely thermoplastic polyolefins are of great interest, both technically and commercially. Specifically highly amorphous polypropylenes, as known from, for example, EP-A-632062 (PCD Polymere GmbH) or EP-A-475307 (REXENE Corp.), have behavior which diverges markedly from that of conventional isotactic polypropylene. Their particular features are softness, elasticity and impact strength coupled with substantial retention of the relatively high melting point which is an inherent advantage of polypropylene (PP). This combined with the chemical makeup of the material (it is chemically inert and a pure polyolefin, containing neither halogens nor plasticizers, and therefore has extremely good environmental compatibility) opens up application sectors which are new and not hitherto accessible to PP, for example replacement of plasticized PVC or of thermoplastic elastomers.
However, these materials often have a degree of surface tack, which is felt to be a problem or hindrance in a large number of applications. The surface deposit is formed when, for example, components which increase gloss or opacity and, in addition, are tacky bleed out onto the surface of, for example, moldings or films made from materials of this type, either when they are being processed or subsequently when the parts are stored. Efforts have therefore been made to find ways of preventing this process by subsequent modification without altering the production process, and while maintaining the property profile as substantially as possible. For example, in WO 96/22327 PP a very complicated grafting process is used to reduce tack, and JP-Kokai 90/48882 and JP-Kokai 80/67779 on the one hand and DE-A 2127709 on the other mixing with styrene elastomers and organic additives, respectively. These known processes, however, are in some respects very complicated and result in only unsatisfactory or inadequate reduction in surface tack.
BRIEF SUMMARY OF THE INVENTION
Surprisingly, it has now been found that the addition of specific polyethylenes or olefin elastomers to amorphous PPs can be a particularly efficient way of reducing their surface tack.
DETAILED DESCRIPTION OF THE INVENTION
The invention accordingly provides for the use of a modifier selected from the following classes of materials:
a) high-pressure uncatalyzed ethylene homopolymers or ethylene-higher-&agr;-olefin copolymers with a proportion of more than 90 mol % of ethylene and with a density of not more than 0.92 g/cm
3
(LDPE),
b) low-pressure catalyzed ethylene-higher-&agr;-olefin copolymers with a proportion of more than 75 mol % of ethylene and with a density of not more than 0.93 g/cm
3
(LLDPE), and
c) highly amorphous olefin elastomers with an enthalpy of fusion of not more than 15 J/g, composed of copolymers of ethylene and propylene (EPR) or of terpolymers of ethylene, propylene and dienes (EPDM) having a density of not more than 0.88 g/cm
3
, or else mixtures of these olefin elastomers with polyethylenes or with isotactic polypropylenes, where the proportion of the olefin elastomer by weight is in each case more than 50%,
as a component for adding to a highly amorphous polypropylene (base polymer) with an enthalpy of fusion of not more than 40 J/g and a melt flow index of from 0.1 to 50 g/10 min, where the highly amorphous polypropylene is a homopolymer of propylene or a copolymer of propylene with one or more a-olefins and has a proportion of at least 80 mol % of propylene, for reducing surface tack.
The invention further provides a process for reducing the surface tack of highly amorphous polypropylene (base polymer) with an enthalpy of fusion of not more than 40 J/g and a melt flow index of from 0.1 to 50 g/10 min, where the highly amorphous polypropylene is a propylene homopolymer or a copolymer of propylene with one or more &agr;-olefins and has a proportion of not less than 80 mol % of propylene, which comprises admixing modifiers selected from the following classes of materials:
a) high-pressure uncatalyzed ethylene homopolymers or ethylene-higher-&agr;-olefin copolymers with a proportion of more than 90 mol % of ethylene and with a density of not more than 0.92 g/cm
3
(LDPE),
b) low-pressure catalyzed ethylene-higher-&agr;-olefin copolymers with a proportion of more than 75 mol % of ethylene and with a density of not more than 0.93 g/cm
3
(LLDPE), and
c) highly amorphous olefin elastomers with an enthalpy of fusion of not more than 15 J/g, composed of copolymers of ethylene and propylene (EPR) or of terpolymers of ethylene, propylene and dienes (EPDM) having a density of not more than 0.88 g/cm
3
1
or else mixtures of these olefin elastomers with polyethylenes or with isotactic polypropylenes, where the proportion of the olefin elastomer by weight is in each case more than 50% into the highly amorphous polypropylenes.
The amount of the modifiers added is preferably from 5 to 60% by weight, particularly preferably from 10 to 40% by weight, based on the total amount of polymer. The highly amorphous PP used as base polymer here preferably has an enthalpy of fusion of not more than 30 J/g and a melt flow index of from 0.5 to 25 g/10 min, and is preferably a homopolymer of propylene or a copolymer of propylene with one or more &agr;-olefins and has a proportion of at least 85 mol % of propylene.
If amorphous copolymers of propylene are used, these are preferably random copolymers or heterophasic copolymers with one or more comonomers selected from the class consisting of the C
2
olefins and C
4
-C
10
olefins, particular preference being given to ethylene as comonomer. The highly amorphous PPs used as base polymers may be prepared by known processes, as described in EP 768338 A, for example. They are also commercially available, for example as Rexflex® from Huntsman.
The high-pressure polyethylene modifiers defined in (a) may likewise be prepared by known processes, for example as described in Acta Polym. 37 (1986), pages 241-247. They are also available commercially, for example as Daplen® LDPE from PCD Polymere or Novolen® LDPE from BASF. The low-pressure polyethylene copolymers used defined in (b) may similarly be prepared by known processes, for example as described in Proc. of Metallocenes '96, Düsseldorf, pages 59-86 and 99-109. They are also available commercially, for example as Engage® from Dow or Exact® from Exxon. The highly amorphous olef in elastomers defined in (c), and the isotactic PPs and the polyethylenes used for the mixtures, may likewise be prepared by known processes, as described, for example, in Adv. Polym. Blends Alloys Technol. 2 (1989), pages 12-24. They are also available commercially, for example as Dutral® from Enichem, or Exxelor from Exxon. Isotactic PP and polyethylene are obtainable, for example, as Daplen grades, such as Daplen KD10 or Daplen 2425K from PCD Polymere. The melt index (MFI, melt flow index, or MFR, melt flow rate) was determined in accordance with ISO 1133/DIN 53735 at 230° C. and 2.16 kg. Crystallinity was determined by DSC in accordance with ISO 3146, evaluating the second heating procedure in a cycle between 10 and 190° C. with heating/cooling rates of 10 K/min. The enthalpy of fusion (H
m
) was calculated here for the peak typical of crystalline PP and having a maximum between 140 and 170° C. Test specimens produced by injection molding (in accordance with DIN 16774 (1988) at a melt temperature of 250° C. and a mold temperature of 30° C.) were used to determine mechanical properties of the mixtures and reference materials in the tensile test at +23° C. on the F3/3 injection-molded dumbbell specimen in accordance with DIN 53457 (1981). Surface tack was measured by the following method (bleed-out test):
Injection-molded plaques (40×40×2 mm) were suspended at 100° C. in a heated cabinet, whereupon constituents causing tack mig

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