Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
2001-05-03
2004-01-27
Wu, David W. (Department: 1713)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C524S300000, C524S322000, C524S425000, C427S220000
Reexamination Certificate
active
06682775
ABSTRACT:
DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a particulate alkaline earth metal carbonate, e.g., calcium carbonate, for use with a polymer composition for producing a polymer based end product, i.e., a thermoplastic film product, which may have a high mineral film loading. In particular, the present invention relates to a coated carbonate, with an unusually low level of interfering particles, and the processing and use of this carbonate.
2. Background of the Invention
Alkaline earth metal carbonates, particularly calcium carbonates are used as a particulate filler in end products comprising compositions incorporating thermoplastic polymers, such as film products. Such films, porous or non-porous, are manufactured for a number of consumer products such as garbage bags, backing materials, masking films, labeling, plastic paper, house wrap, roofing membranes, grocery sacks, diapers, bandages, training pants, sanitary napkins, surgical drapes, and surgical gowns. The compositions from which these films are made may include two basic components, the first being a thermoplastic polymer, usually a predominantly linear polyolefin polymer such as a linear low density polyethylene and the second being an inorganic particulate filler such as calcium carbonate. A third component, namely a bonding or tackifying agent may often be present. These components are mixed and compounded together to form a compound or concentrate which is formed (usually in a subsequent process) into a film layer using any one of a variety of film-producing processes known to those of ordinary skill in the film making art including casting or blowing. Alternatively, the film may be laid down on a substrate such as paper or board in a process known as extrusion coating.
After the film is fabricated into its desired form, and if the film is to be a porous breathable film, the film can then be stretched, uniaxially or biaxially, by any of the well-known techniques in the art including by hydraulics, by pinch rolls moving at different rates, by interdigiting rolls or by tentering.
Particulate filler loading levels determine to a great extent how far the precursor film must be stretched to attain a given degree of overall porosity. Below a lower end of the loading range, the pores are less numerous and less interconnected, and therefore, the film is less permeable at a given draw ratio than when a higher particulate filler loading is employed. Above a higher end of the loading range, either the materials will not blend uniformly or the sheet made from the composition will not stretch. The preferred loading in some applications, such as that in manufacturing the microporous film of U.S. Pat. Nos. 5,008,296 and 5,011,698, is very high, e.g., 60% to 75% by weight of the composition, with the filler preferably being a calcium carbonate.
U.S. Pat. No. 4,698,372 discloses a microporous polymeric film having good water vapor transmission rates and hydrostatic resistance to water penetration thereof. The film has a filler loading of 25-35 volume % of inorganic fillers such as calcium carbonate, among others, and uses a coating such as stearic acid, in order to reduce the effective surface tension of the filler to the approximate level of that of the matrix polymer.
U.S. Pat. No. 3,903,234 discloses gas permeable biaxially oriented film prepared from compositions of polyolefins containing 26% to 50% by weight of inorganic filler particles.
U.S. Pat. No. 4,176,148 discloses microporous oriented films composed of polybutene containing 3% to 80% by weight of inorganic fillers.
U.S. Pat. Nos. 5,376,445, 5,695,868, and 5,733,628 disclose breathable film or film laminates or composites which may or may not consist of fillers.
A smooth surface which is free from voids is necessary to enable the film to be stretched uniformly, a process which is generally employed in the production of breathable and other films. The present invention provides among other characteristics, reduced surface roughness.
The aforesaid U.S. Pat. Nos. 5,008,296 and 5,011,698 teach a method of maintaining the moisture level of a melt blended composition below 700 parts per million (ppm) and preferably below 300 ppm by cooling the extruded strands and/or pellets composed of polymer plus filler, which are used in the film composition using flowing air or employing vacuum-drying. However, this additional processing step is time consuming and costly.
Conventionally in the film making art, usage levels of a mineral filler, such as a ground calcium carbonate, in a host material have been less than about 20% by weight loading. Conventional fillers suffer from agglomeration problems associated with insufficient coating and/or the presence of moisture within the filler resulting in greater failure rates during the production of breathable films.
The present invention provides a product having reduced amounts of interfering particles and thereby results in a film product that is smoother and subjected to less failure. The product of the present invention having low levels of interfering particles also improves the rate at which film products can be produced.
SUMMARY OF THE INVENTION
Further advantages of the invention will be set forth in part in the description which follows. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention as embodied and broadly described herein, there is disclosed:
A method of consistently producing a coated particulate material having a reduced level of interfering particles and having particles of an alkaline earth metal carbonate with an median particle size between about 0.8 &mgr;m and 1.95 &mgr;m comprising:
(a) producing a coated particulate by treating particles of an inorganic particulate material of an alkaline earth metal carbonate compound with a median particle size between about 0.8 &mgr;m and about 1.95 &mgr;m by reaction with a hydrophobizing surface treatment agent comprising one or more aliphatic carboxylic acids having at least 10 chain carbon atoms to produce a hydrophobic coating on the particles;
(b) treating the coated particulate to result in a carbonate product having a level of interfering particles at or below 0.285% by weight.
There is further disclosed:
A method of producing a breathable film including:
(a) producing a coated particulate by treating particles of an inorganic particulate material comprising an alkaline earth metal carbonate compound by reaction with a hydrophobizing surface treatment agent of one or more aliphatic carboxylic acids having at least 10 chain carbon atoms to produce a hydrophobic coating on the particles;
(b) treating the coated particulate to result in a carbonate product having a level of interfering particles at or below 0.285% by weight;
(c) producing a filled thermoplastic composition by mixing the inorganic particulate having a reduced level of interfering particles produced in steps (a)-(c) with a heated thermoplastic polymer; and
(d) shaping the composition produced in step (d) by heat processing to form a film product.
Finally, there is disclosed:
A film product produced according to the method above.
DESCRIPTION OF THE INVENTION
The purpose of the present invention is to provide a mineral particulate comprising an alkaline earth metal carbonate, especially calcium carbonate, which has properties allowing a film end product comprising a thermoplastic polymeric material together with the particulate to be easily and successfully produced with loadings of at least 10% by weight, preferably at least 20% by weight, and, surprisingly, in some cases at least 40% by weight and in some cases even up to 75% by weight. Particulate or filler, especially calcium carbonates, produced in a conventional manner would in many cases be unsuccessful in producing such film products without the application of special time consuming and costly additional processing ste
Calhoun Allison Anne
McConnell Anthony D.
Miller Charity W.
Mobley Gary R.
Shurling Dickey S.
Finnegan Henderson Farabow Garrett & Dunner
Hu Henry S.
Imerys Pigments, Inc.
Wu David W.
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