Multimodal polymeric foam containing an absorbent clay

Details Multimodal polymeric foam containing an absorbent clay Multimodal polymeric foam containing an absorbent clay

2002-09-20

2004-06-15

Foelak, Morton (Department: 1711)

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

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S083000, C521S091000

Reexamination Certificate

active

06750264

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multimodal polymeric foam containing an absorbent clay and a process for making the same.
2. Description of Related Art
A foam having a multimodal cell size distribution (multimodal foam) offers performance advantages, such as greater toughness and enhanced insulating capability, over a foam of the same polymer composition that has a generally uniform cell size distribution. A foam having a bimodal cell size distribution (bimodal foam) is one type of multimodal foam.
Many methods for preparing multimodal, particularly bimodal, polymeric foam require the presence of water. For example, European patent (EP) 353701 B1 and U.S. Pat. Nos. 4,990,542 and 5,064,874 disclose processes that utilize water in combination with a granular material that adsorbs the water onto its surface. WO 01/51551 A1 discloses a process for preparing bimodal foam that requires water in combination with 0.2 to 10 parts by weight of bentonite in 100 parts by weight of a thermoplastic resin. U.S. Pat. No. 4,559,367 discloses a method of preparing multimodal foam in the presence of organic water-containing vegetable matter. U.S. Pat. Nos. 5,210,105, 5,332,761, and 5,369,137 each disclose a method of preparing bimodal polymeric foams using water, but disclose that pinholes form in cell walls when using greater than three weight-percent (wt %) water based on blowing agent composition or 0.3 weight parts water by per hundred weight parts polymer.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to offer a novel process for preparing multimodal polymeric foam, as well as a novel multimodal foam, that offers an alternative, an improvement, or both over existing processes and foams.
In a first aspect, the present invention is a polymeric foam comprising a polymer having multiple cells defined therein and at least one absorbent clay dispersed within said polymer; wherein said foam has a multimodal cell size distribution and contains less than 0.2 parts by weight of bentonite based on 100 parts by weight of polymer. The foam can be substantially, or completely, free of nucleating agents apart from the clay.
In a second aspect, the present invention is a process for preparing the foam of the first aspect comprising (a) preparing a foamable polymer composition by combining a plasticized polymer composition that contains a polymer and at least one absorbent clay with a blowing agent composition comprising 0.5-99.5 weight-percent carbon dioxide and 0.5-80 weight-percent water, based on blowing agent composition weight, at an initial pressure that precludes foaming; and (b) expanding the foamable polymer composition into a polymeric foam containing multiple cells by reducing the pressure from the initial pressure to a lower pressure; wherein said foamable composition contains less than 0.2 parts by weight of bentonite based on 100 parts by weight of polymer and wherein said foam has a multimodal cell size distribution. Water can be present at a concentration of at least 3 weight-percent based on blowing agent weight and at least 0.3 parts per hundred based on polymer weight while less than one percent of the cells contain pinholes.
In a third aspect, the present invention is an article comprising the foam of claim 1.
DETAILED DESCRIPTION OF THE INVENTION
Herein, unless otherwise specified, a material is “essentially free” of a substance if sufficiently little of the substance is present so as not to affect physical properties of the material. Desirably, a material that is essentially free of a substance is free of that substance.
A “multimodal foam” is a foam having a multimodal cell size distribution. A foam has a multimodal cell size distribution if a plot of representative cross-sectional area versus cell size has two or more peaks.
Use a scanning electron microscope (SEM) image of a cross section of a foam to collect cell diameter and representative cross-sectional area data for the foam. The SEM image should be of a sufficient magnification so as to present a representative distribution of the cell sizes in the foam. Measure a cell diameter for each cell in the SEM image. Do not consider faults such as “blow-holes” as cells. Blow holes are spaces defined within a foam that penetrate through multiple cell walls and cell struts and have a plurality of cell wall and cell strut fragments remaining therein. A cell wall is a polymeric film between two cells. A cell strut is a polymeric domain where three or more cells meet.
Calculate cross-sectional area for each cell by assuming a circular cross-section. Estimate an appropriate diameter for non-circular cell cross-sections that will produce an appropriate cross-sectional area (e.g., for oval shaped cells use a diameter mid-way between the largest and smallest diameter). Using the cell diameters, calculate a cross-sectional area for each cell by assuming each cell has a circular cross-section. A convenient program for measuring cell diameters and calculating cross-sectional areas of a digitally scanned image is United States' National Institutes of Health (NIH) public domain NIH IMAGE software (available on the Internet at http://rsb.info.nih.gov
ih-image/). Calculate representative cross-sectional area by multiplying the cross-sectional surface area for a cell of a given size by the number of cells of that size in a SEM image. Measure cell sizes in microns and round to two significant figures. Cell size refers to cell diameter and the two terms are interchangeable herein.
Prepare a plot with cell size along the x-axis and representative surface area on the y-axis. Cells comprising a peak corresponding to the smallest cell size(s) (“small peak”) are “small cells” or “secondary cells”. Cells comprising a peak corresponding the largest cell size(s) (“large peak”) are “large cells” or “primary cells”. “Intermediate cells” comprise “intermediate peaks” in between a small peak and a large peak. Similarly, when a small peak and a large peak partially overlap, cells comprising the overlapping region are intermediate cells. Intermediate cells may have properties similar to large cells, small cells, or properties some combination of large and small cells. A “peak” is a point on a plot that has at least one point having a lower y-axis value both prior to and after it, progressing along the plot's x-axis, before there is a point having a higher y-axis value. A peak can comprise more than one point of equal y-axis values (a plateau), provided the point on either side of the plateau (progressing along the plot's x-axis) has a lower y-axis value than the points comprising the plateau.
A multimodal foam can have a “bimodal” cell size distribution. A plot of representative surface area versus cell size for a bimodal foam reveals two peaks, one corresponding to larger primary cells and one corresponding to smaller secondary cells. Generally, primary cells have a cell size of from 0.2 to 2 millimeters (mm), preferably 0.2 to 0.8 mm, more preferably from 0.2 to 0.4 mm. Generally, secondary cells have a cell size of less than 0.2 mm, preferably less than 0.15 mm and more preferably less than 0.1 mm according to ASTM method D-3576.
Generally, less than one percent of the total number of cells in a foam of the present invention contains pinholes. Pinholes are microscopic holes defined within cell walls between contiguous primary cells, contiguous secondary cells, or contiguous primary and secondary cells.
Polymer resins useful for preparing polymeric foams of the present invention are desirably thermoplastic polymer resins. Suitable thermoplastic polymer resins include any extrudable polymer (including copolymers) including semi-crystalline, amorphous, and ionomeric polymers and blends thereof. Suitable semi-crystalline thermoplastic polymers include polyethylene (PE), such as high-density polyethylene (HDPE), and low-density polyethylene (LDPE); polyesters such as polyethylene terephthalate (PET); polypropylene (PP) including linear, branched and syndiotactic PP; polyla

Affiliated with

Also associated with

Rating

Multimodal polymeric foam containing an absorbent clay does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multimodal polymeric foam containing an absorbent clay, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multimodal polymeric foam containing an absorbent clay will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3312893