Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-09-28
2002-10-15
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S334000, C428S335000, C428S336000, C427S387000, C427S532000, C427S535000, C427S536000, C525S100000, C525S105000, C525S106000, C156S329000
Reexamination Certificate
active
06465107
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to resins for films or coatings having release or peelability characteristics and modified surface tension properties, which makes them suitable for use in release films such as those used to protect adhesive films. It especially relates to so-called release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra-high molecular weight silicone polymer.
The invention relates particularly to a multi-layer film comprising the release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra-high molecular weight silicone polymer as a layer and a polyolefin forming another layer. The release film of this invention can also be adhered to or coated onto a subweb of paper, aluminum, plastics such as nylon and polyester, or other subwebs suitable for coating. The multi-layer film can be used in liquid-absorbing products, such as feminine hygiene pads, baby diapers and incontinence products.
BACKGROUND OF THE INVENTION
Films containing a polyolefin, a polysiloxane, an organo-peroxide agent and a vinyl silane are known from U.S. Pat. Nos. 4,978,436 and 5,169,900, both incorporated herein by reference. Such films are useful for their slip, release, peelability or related characteristics, making them suitable for use as peelable coatings on adhesive materials, as removable protective layers for substrates, and as slip layers used in high-speed coating and packaging apparatuses. The patents suggest a nominal film thickness of 25 microns and a gauge uniformity for such films of 25 to 30 microns.
While these films perform their functions well, they have the disadvantage of being expensive, particularly in comparison with films made entirely of polyolefin. It has now been found that a thin film, one with thickness of about 1 to about 10 microns, can be made to perform the function of the much thicker films.
In the field of feminine hygiene pads, baby diapers, incontinence products and the like, perforated polyolefin films have long been used as a topsheet. These topsheets typically have tapered capillaries of critical diameters and tapers with a base in the plane of the topsheet and an apex remote from the plane and in contact with an absorbent element. U.S. Pat. No. 3,929,135, incorporated herein by reference, describes such topsheets. The patent discusses the product's ability to allow passage of fluid through the topsheet (away from the user) to the absorbent material, while preventing backflow from the absorbent material to the user.
The most commonly used polyolefin employed in such topsheets is low density polyethylene, which is ideal from a liquid wicking standpoint. With its relatively high surface tension (about 32 dynes/centimeter), liquid drainage through the topsheet is good. On the other hand, as a result of the high surface tension, certain discharge products such as menstrual fluids and feces adhere somewhat to the surface of the film, soiling the surface in contact with the user and occluding perforations with a resultant reduction in fluid transfer.
It has now been found that polyolefin film having a thin surface layer or coating of polysiloxane, with a surface tension of about 23 dynes/centimeter, can provide superior performance in these applications. While the lower surface tension would be expected to cause reduced liquid flow (that is, fluid drainage normally decreases with decreases in surface tension), it has been found that the polysiloxane-coated polyolefin has improved soiling resistance and generally allows for more rapid transfer of liquid through the topsheet to the absorbent material.
SUMMARY OF THE INVENTION
The present invention provides a silicone-containing polyolefin resin that in film-form has superior uniformity and efficacy at surprisingly low thickness. This film or resin precursor comprises (i) a polyolefin, (ii) a dimethyl polysiloxane having functional end-groups, (iii) at least one vinyl silane compound, and (iv) ultra-high molecular weight silicone polymer. In another aspect, the resin formulation consists essentially of (a) a functionalized polyolefin copolymer in combination with (b) a dimethyl polysiloxane having functional end-groups which covalently reacts with said copolymer and (c) an ultra-high molecular weight silicone polymer. The present invention also comprises film made therefrom. Additionally, the film made from components (i)-(iv) is preferably formed using an organic peroxide and an organo-metallic moisture curing agent, the organic peroxide preferably being at a level that not all the vinyl silane grafts to the polyolefin. The film made from components (a)-(c) additionally may have a moisture curing agent. The invention provides a multi-layer structure comprising (a) a subweb layer, preferably a polyolefin, and (b) a surface layer of the silicone-containing polyolefin film of this invention placed, preferably by coextrusion, on the subweb, the surface layer being a film having a thickness of about 1 to about 10 microns. The silicone-containing polyolefin film preferably is surface treated, for example by corona discharge, to improve its release properties.
The present invention further encompasses the use of the films herein described as release layers, and, when the subweb is a polyolefin, in the aforementioned absorbent products.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the following terms have the meanings given below.
“Polyolefin”, whether used in layer (A) or layer (3) of the film of the present invention, means homopolymers and copolymers of unsaturated hydrocarbons having 2-20 carbon atoms (“unfunctionalized”) or as defined alternatively below (“functionalized”). They can be made by processes well known in the art, including metallocene processes. In particular, the polymers are homopolymers of ethylene or propylene or copolymers of ethylene with one or more alpha-olefin hydrocarbons having 3-10 carbon atoms, especially propylene, butene-1, hexene-1 and octene-1 and styrene. Suitable alpha-olefins also include dienes, that is, monomers with more than 1 site of unsaturation, especially 1,3 butadiene, 1,5 hexadiene and norbornadiene. In particularly preferred embodiments, the Polyolefins are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4-8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimeter (g/cm
3
) and especially in the range of 0.920 to 0.930 g/cm
3
. Preferably, the polymers have a melt index (MI) in the range of 0.05 to 120 dg/min, especially 0.1 to 75 dg/min and in particular 1 to 10 dg/min. (as measured per ASTM D-1238, condition E).
Mixtures and blends of the Polyolefins may be used. In general, the polymers are of the type that may be extruded in the form of film.
The Polyolefin may contain additives, for example antioxidants and other stabilizers, anti-block and slip agents and the like. The Polyolefin may also contain fillers, e.g., talc, mica, calcium carbonate, and the like and/or pigments such as titanium dioxide. In addition, the Polyolefin may contain modifying polymers, e.g., rubber-like modifying polymers such as ethylene/propylene/diene, styrene butadiene styrene, and other elastomers. It is to be understood that any additive must not cause undue adverse effects on the release and/or surface tension properties of the film.
In alternative embodiments, direct copolymers or blends of copolymers of ethylene and a polar monomer, e.g., &agr;,&bgr;-ethylenically-unsaturated C
3
-C
8
carboxylic acid (“ethylene-acid copolymers”), or ester thereof, or an ethylenically unsaturated ester of a carboxylic acid may be employed as the Polyolefins or may be blended with the Polyolefins. By “direct copolymer”, it is meant that the copolymer is made by polymerization of monomers together at the same time, as distinct from a “graft copolymer” where a monomer is attached or polymerized onto an existing polymer chain. Preparation of the direct ethylene-acid copolymers is described in U.S. Pat. No. 4,351,931.
The ethylene-acid copolymers can be E/X/Y
Clarizio Dino P.
Dawson Robert
Dimock Stratton Clarizio LLP
DuPont Canada Inc.
Robertson Jeffrey B.
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