Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1997-05-02
2001-10-16
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S133000, C521S910000, C521S917000, C252S067000, C252S367100, C239S337000, C264S053000
Reexamination Certificate
active
06303667
ABSTRACT:
The invention relates to blowing agents, containing liquid carbon dioxide, as well as to their use in methods for producing foamed plastics.
The invention also relates to blowing agent compositions, which are suitable for the production of 1-component or multi-component polyurethane foams from pressure vessels.
The use of chlorofluorohydrocarbons (CFHCs) as blowing agents for the production of foamed plastics is no longer desirable for ecological reasons. Gaseous substances, such as carbon dioxide, have also been proposed as substitutes. However, as a gaseous, physical blowing agent, carbon dioxide has the disadvantage that, because of its relatively low critical temperature, it can be metered out only with difficulty under the conditions existing during production. Furthermore, the use of carbon dioxide according to previously known methods usually leads to open-celled foams with an undesirably high water-absorption capacity and frequently still unsatisfactory heat insulation properties. Until now, the production of foamed plastics with predominantly closed cells also has been associated with difficulties when carbon dioxide was used as the only blowing agent or as a co-blowing agent in combination with other physical blowing agents.
One-component or multi-component polyurethane foams, which are dispensed from a pressure vessel, such as a spray can, are used mainly in building construction or automobile production for filling cavities or interstices with foam. In so-called 1-component polyurethane foams (referred to hereinafter as 1K-PUR-Foam), a polyol premix is reacted with an excess of diisocyanate and/or polyisocyanate in the presence of a catalyst and optionally further auxiliary materials and additives in a pressure vessel to form a prepolymer containing isocyanate groups. By actuating the spray valve of the pressure vessel, the prepolymer is forced out of the can by a blowing agent. At the same time, a spontaneous foaming of the prepolymer occurs. By reaction of the remaining isocyanate groups with the moisture in the air, a substantially closed-cell, rigid foam is formed.
In a 2-component polyurethane foam (referred to hereinafter as a 2K-PUR-Foam), an additional component having hydroxy groups, such as a polyol, which is first added just before the foaming operation, is required for curing the prepolymer foam. Usually, this polyol is located in the pressure vessel in a space, which is separated from the remaining components and is first added to the prepolymer component only immediately before it emerges from the pressure vessel when the spray valve is actuated.
Most of the prepolymers used for polyurethane foams to be dispensed from pressure vessels, have a very high viscosity, so that the blowing agent used must have good solvent properties, in order to be able to foam the components without difficulty from the pressure vessel. The use of chlorofluorohydrocarbons (CFHCs) as blowing agents for such applications is no longer desirable for ecological reasons. Many of the previously proposed substitute materials have disadvantages in use, such as a still unsatisfactory heat insulation or an evaporation rate which is too low.
The international patent application WO 91/12287 discloses that liquefied CO
2
can be used with co-blowing agents, for example water or higher boiling sovents. In this manner a controlled pre- and post-expansion of the foam can be achieved.
The Japanese patent application JP-A 1/254 742 discloses that polyethylene resins can be foamed with a mixture of CO
2
and a readily volatile organic blowing agent.
The international patent application WO 91/08243 relates to the production of open-pored polyurethane foams. Preferably, liquified CO
2
, which additionally may contain small amounts of water or other blowing agents, is used as the blowing agent.
It was therefore an object of the invention to make available new methods for the production of foamed plastics and also for the generation of polyurethane foams from pressure containers, which overcome the disadvantages of the prior art. It was a further object of the invention to make new blowing agent compositions available for these methods.
Surprisingly, it has now been found that compositions, which contain carbon dioxide in liquid form in addition to at least one other liquid component, are suitable as blowing agent compositions in methods for the production of foamed plastics. Blowing agent compositions, which contain liquefied carbon dioxide, are also suitable for producing polyurethane foams from pressurized containers.
The invention relates to blowing agent compositions which contain 0.5 to 50% by weight of liquid CO
2
. Preferred blowing agent compositions contain 5 to 50% by weight of liquid carbon dioxide, particularly 10 to 50% by weight.
In addition to liquid carbon dioxide, at least one other liquid component or pressure-liquefiable component is contained. The other liquid component or components preferably represents or represent the remainder up to 100% by weight of the blowing agent composition. The liquid component or components may, for example, be liquid or pressure-liquefied physical blowing agents and/or liquid flame retardants selected, for example, from the group of phosphate esters or phosphonic acid esters. In addition, known additives or auxiliaries, such as stabilizers or plasticizers, may also be contained.
The invention further relates to a method for the production of foamed plastics with the aid of blowing agents, in which a liquid blowing agent composition is used, which contains 0.5 to 50% by weight, preferably 5 to 50% by weight, particularly 10 to 50 wt.-%, and especially 10 to 20% by weight of liquefied carbon dioxide.
Liquefied carbon dioxide as used in this invention can be obtained by any of the known methods of liquefying gases, preferably by pressure liquefaction.
At room temperature and atmospheric pressure (1.01325×10
5
Pa), carbon dioxide is a colorless gas, which can be pressure liquefied through application of a pressure of 56.5 atmospheres (=5.72486×10
6
Pa) at a temperature of 20° C. to a colorless, highly volatile liquid. Methods for the pressure liquefaction of carbon dioxide are generally known.
One embodiment of the present invention relates to the production of foamed plastics, for example, by casting or extrusion methods. A different embodiment of the invention, which will be described later, relates particularly to the production of 1-component or 2-component polyurethane foams from pressurized containers (PUR=polyurethane). Initially, the first-named embodiment will be explained in greater detail in the following.
As further liquid components besides the pressure-liquefied carbon dioxide, all conventional liquid, physical blowing agents used for the production of foamed plastics, namely highly volatile organic compounds such as ethers, for example, diethyl ether, ketones such as acetone, hydrocarbons such as pentane, hexane, heptane, petroleum ether mixtures, halogen-containing hydrocarbons or halogen-containing ethers, can be used. Gases which have been liquefied under pressure, such as propane or butane, can also be used in addition to the liquefied carbon dioxide. Furthermore, water is a possible liquid blowing agent component.
Preferably, for producing foamed plastics, a blowing agent composition is used, which contains or consists of 10 to 20 parts by weight of liquefied carbon dioxide and 30 to 90 parts by weight of at least one liquid or pressure liquefied physical blowing agent selected from the group of alcohols with 1 to 5 carbon atoms, aliphatic hydrocarbons with 2 to 12 carbon atoms, cyclic hydrocarbons with 3 to 12 carbon atoms, halogen-containing hydrocarbons with 1 to 5 carbon atoms or halogen-containing ethers with a total of 2 to 6 carbon atoms. Ethanol and isopropanol, in particular, are preferred as alcohols. Examples of aliphatic hydrocarbons are pentane, hexane, heptane and petroleum ether fractions, especially light petroleum ether fractions with a boiling point in the range from 15° to 80° C. Fur
Crowell & Moring , L.L.P.
Gorr Rachel
Solvay Fluor und Derivate
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