Extruded foam product with 134a and alcohol blowing agent

Details Extruded foam product with 134a and alcohol blowing agent Extruded foam product with 134a and alcohol blowing agent

2001-04-30

2002-02-26

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...

C521S079000, C521S098000, C521S146000, C521S910000

Reexamination Certificate

active

06350789

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to methods for preparing extruded foam products and more particularly to a methods for producing such products with a blowing agent containing 134a and an alcohol.
BACKGROUND OF THE INVENTION
Extruded synthetic resinous foams are useful materials for many applications including thermal insulation, decorative purposes, packaging and the like. Extruded foams are generally made by melting a polymer with any other additives to create a polymer melt, mixing a blowing agent with the polymer melt at an appropriate temperature and pressure to produce a mixture whereby the blowing agent becomes soluble, i.e. dissolves, in the polymer melt. This mixture may then be extruded into a zone of reduced pressure so that the blowing agent becomes insoluble in the polymer melt and converts into a gas. As the blowing agent converts to a gas, bubbles are produced within the polymer melt. At this point, the polymer melt is cooled thereby producing a foam structure comprising closed cells resulting from the expansion of the blowing agent.
Traditional blowing agents used for extruded foam manufacture include chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). One of the advantages of CFC and HCFC blowing agents is their high solubility in a polymer melt. Higher blowing agent solubility promotes viscosity reduction when mixed with the polymer melt. In turn, lower viscosity leads to lower energy requirements for mixing. A major disadvantage to traditional blowing agents is that an increasing number of governments worldwide have mandated the elimination of CFCs and HCFCs blowing agents due to growing environmental concerns.
Accordingly, there has been a movement to replace traditional blowing agents in favor of more environmentally friendly blowing agents such as hydrofluorocarbons. Unfortunately, hydrofluorocarbons (HFCs), and in particular tetrafluoroethane (134a), have a lower solubility in polymer melts compared to traditional blowing agents. The present invention is directed, in part, to increasing the solubility of 134a in a polymer melt by addition of an alcohol.
U.S. Pat. No. 5,182,308 issued to Volker et al. (“Volker”) discloses a laundry list of blowing agent compositions some of which include HFCs and alcohols. However, the blowing agent compositions of Volker produce extruded foams which have poor thermal insulating properties. Specifically, none of Volker's examples show extruded foams having a coefficient of thermal conductivity higher than 0.0376 W/mK as measured by DIN 52 612.
Applicants have surprisingly discovered that by use of a blowing agent containing only 134a and alcohol, extruded foams may be produced with superior thermal insulating properties. The extruded foams made by the present invention have a coefficient of thermal conductivity lower than 0.035 W/mK and preferably lower than 0.030 W/mK as measured by DIN 52 612.
SUMMARY OF THE INVENTION
The present invention is directed to extruded foam products and their manufacture. The extruded foam products of the present invention have a plurality of closed cells containing a gas comprising 99% by volume of 134a and have a coefficient of thermal conductivity lower than 0.035 W/mK and preferably lower than 0.030 W/mK as measured by DIN 52 612. The extruded foam products of the present invention are made with a blowing agent composition consisting of 134a and alcohol. The blowing agent composition preferably consists of 4-8 weight percent 134a and 2-5 weight percent alcohol with the weight percentage based on the total weight of the dry feed. The term “dry feed” used herein means all the materials except the blowing agent which are used to make the polymer melt which is extruded. For example, the dry feed may comprise polymer pellets, nucleating agents, plasticizers, and any other ingredients to produce the polymer melt.
DESCRIPTION OF PREFERRED EMBODIMENTS
Extruded Foam Manufacture Process
Although the blowing agent composition of the present invention may be incorporated in any process for making extruded foam products, the preferred extruded foam manufacture process comprises heating, to a first temperature, a resin mixture comprising a polymer to produce a plastified resin mixture; and thoroughly mixing a fluid blowing agent consisting of 134a and an alcohol with the plastified resin mixture under a first pressure and under conditions preventing foaming of the mixture. Once the blowing agent composition is incorporated and thoroughly mixed with the plastified resin mixture the resulting combination is referred to as a foamable gel. The foamable gel is then cooled to a second temperature (generally referred to as die melt temperature), and is extruded into a zone of reduced pressure (second pressure) resulting in foaming of the gel and formation of the desired extruded foam product.
The first temperature must be sufficient to plastify or melt the mixture. Preferably the first temperature is from 135-240° C., more preferably is from 145-210° C., and most preferably from 150-165° C. Preferably the second temperature or die melt temperature is cooler than the first temperature. The die melt temperature is preferably from 140-105° C., more preferably from 130-110° C., most preferably from about 125-115° C.
The first pressure must be sufficient to prevent prefoaming of the foamable gel which contains the blowing agent. Prefoaming involves the undesirable premature foaming of the foamable gel before extrusion into a region of reduced pressure. Accordingly, the first pressure varies depending upon the identity and amount of blowing agent in the foamable gel. In one embodiment, the first pressure is from 700-4500 psia (4.826-31.02 MPa). In another embodiment, the first pressure is from 840-4000 psia (5.791-27.57 MPa). In a preferred embodiment, the first pressure is from 1150-3500 psia (7.928-27.57 MPa). In the most preferred embodiment, the first pressure is from 2200-3495 psia (15.16-24.1 MPa).
The second pressure is sufficient to induce conversion of the foamable gel into a foam body and may be above, at, or below atmospheric pressure. In one embodiment, the second pressure is from 0-28 psia (0-193 kPa). In another embodiment, the second pressure is from 1.4-21 psia (9.652-144.7 kPa). In a preferred embodiment, the second pressure is from about 2.8-15 psia (19.30-103.4 kPa).
Polymer
Any polymer capable of being foamed may be used as the polymer in the resin mixture. The polymer may be thermoplastic or thermoset. Suitable plastics include polyolefins, polyvinylchloride, alkenyl aromatic polymers, polycarbonates, polyetherimides, polyamides, polyesters, polyvinylidene chloride, polymethylmethacrylate, polyurethanes, polyisocyanurates, phenolics, copolymers and terpolymers of the foregoing, thermoplastic polymer blends, rubber modified polymers, and the like. Suitable polyolefins include polyethylene and polypropylene, and ethylene copolymers.
A preferred thermoplastic polymer comprises an alkenyl aromatic polymer material. Suitable alkenyl aromatic polymer materials include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. The alkenyl aromatic polymer material may further include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be comprised solely of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends of any of the foregoing with a non-alkenyl aromatic polymer. Regardless of composition, the alkenyl aromatic polymer material comprises greater than 50 and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units.
Suitable alkenyl aromatic polymers include those derived from alkenyl aromatic compounds such as styrene, alphamethylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlor

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