Non-Flammable Hydrofluorocarbon Blowing Agent Composition

Field of the Invention

The present invention relates to thermosetting foam foamable compositions, such as polyurethane, which include non-flammable blowing agents. More particularly, the present invention relates to thermosetting foam foamable compositions which incorporate a non-flammable blowing agent combination including HFC- 134a and HFC-32.

Description of the Invention

The foamable compositions of the present invention generally are formed from one or more components capable of forming foam having a generally cellular structure and a blowing agent combination. In certain embodiments, the one or more components comprise a thermosetting composition capable of forming foam and/or foamable compositions. Examples of thermosetting compositions include polyurethane and polyisocyanurate foam compositions, and also phenolic foam compositions. In such thermosetting foam embodiments, the blowing agent compositions of the present invention are included as a blowing agent in the foamable composition, or as a part of one or more of a two or more part foamable mixture. The one or more parts include one or more components capable of reacting and/or foaming under the proper conditions to form a foam or cellular structure.

The Montreal Protocol for the protection of the ozone layer, signed in October 1987, mandated the phase out of the use of chlorofluorocarbons (CFCs) which had been used as blowing agents for thermosetting foams. Materials more "friendly" to the ozone layer, such as hydrofluorocarbons (HFCs) eg HFC- 134a replaced chlorofluorocarbons. HFC 134a (1,1,1,2-tetrafluoroethane) is non-flammable and contributes to long-term thermal insulation for thermosetting foams, such as polyurethane foams. However, HFC 134a exhibits a lower solubility in foaming mixture components, relative to previous materials. This lower solubility makes HFC134a less desirable than previous materilas for the urethane industry. The present inventors found that use of HFC 134a in combination with HFC32 (difluoromethane) provided a foaming agent blend that exhibits

a higher, acceptable solubility in polyol mixtures. Use of HFC32 has been limted due to it's flammability. The present inventors discovered that HFC 134a suppressses the undesirable flammability of HFC32. The present inventors have found that blends of HFC 134a and HFC32 that consist of less than about 30 wt% of HFC32 are not flammable. Working with such non-flammable blends, the inventors found improved solubility in polyol mixtures over HFC 134a alone. As a result of improved solubility, foams made with this blowing agent blend exhibited improved processing and performance.

The blowing agent combinations of the present invention can be used as a foaming agent for polyolefm foams by being mixed in a polyol mixture (typically referred to as the B side) which form foam when mixed with a polyisocyante mixture (typically referred to as the A side). The resulted foam products exhibit superior properties including decreased density and improved k-factor. The foaming agent combination readily dissolves in the components of thermosetting foams, and provides a degree of plasticization sufficient to produce acceptable foams.

Prior art teaches that HFC32 can be used as a foam blow agent for thermoplastic plastic polymer such as polystyrene. US 4,927,863 teaches that HCFC123, HCFC123a, and HCFC 14 IbI owing agents can be combined with shrinkage reducing hydrocarbons including CFC-11, CFC-12, HCFC-22, HFC-32, CFC-113, CFC-114, HCFC-124, HCFC- 133a, HFC- 134a, HCFC- 142b and HFC-152a to produce polyurethane which exhibits reduced foam shrinkage.

HFC32 is flammable which has limited its acceptance in certain applications. However, the present inventors found that HFC 134a can be combined with HFC32 to suppress its flammability. This is desirable for polyurethane foams especially for applications which are less tolerable to flammability.

The present inventors have examined blends including HFC 134a and HFC32 for flammability, solubility in polyol mixtures and performance in pour-in-place rigid polyurethane foam. It was found that when the blend consists of less than about 30 wt% of HFC32, the blend is not flammable. In addition, the blend was found to exhibit

improved solubility in polyol mixtures over HFC 134a alone. As a result of the improved solubility, foams made with this blend exhibited improved processing and performance.

The HFCl 34a and HFC32 blend of the present invention can be used with other additives such as: co-blowing agent including but not limited to HFC245fa, HFC365mfc, HFC227, HFC125, and trans- 1,2-dichloroethylene; hydrogen bond forming blocking agents (e.g. organic ether, ester, or ketone) which reduce vapor pressure and reduce the escape of blowing agent from the foam to improve the thermal insulation value of the produced foam. Blocking agents are typically used in amounts less than about 1 wt% of the foam.

EXAMPLES

Example 1 Solubility of Blowing Agents in Polyol Mixtures

A typical polyol mixture as set forth in Table 1 was used to measure the solubility of blowing agents. The formulations tested (all had an Iso Index of 114) each contained: Rubinate M, a polymeric methyl diphenyl diisocyanate (MDI) available from Huntsman; Jeffol R-425-X, a polyol available from Huntsman; Voranol 490, a polyol available from Dow Chemical; Terate 2541, a polyol available from Invista; TCPP, a flame retardant available from Rhodia; TegostabB 8465 a surfactant available from Evonik-Degussa; Polycat 8 (DMCHA) and 5 (PMDETA) available from Air Products. The total blowing level was 24.5 mls/g. Table 1 summarizes the test formula when HFC 134a was used alone.

Table 1 Foam Formula

A B-side made up of a mixture of the polyol, surfactant, catalysts, and other components without the blowing agent was pre-blended externally before pouring into the B-tank of Edge-Sweets high-pressure foam machine. The B-tank was then sealed and agitated, and circulation started. The B-tank was cooled to 7O ⁰ F with a cooling jacket. The blowing agent was added to the B-tank mixture by static mixing in a circulation loop. After two hours of agitation and circulation, the B-tank pressure reached equilibrium. Table 2 summarizes the tank pressure of different blowing agent mixtures at equilibrium.

Table 2 Solubility of Blowing Agents in Polyol Blend

^correction after excluding contribution from air in the tank

The data in Table 2 shows that the measured tank pressures were significantly lower than theoretical tank pressures when HFC32 was mixed with HFCl 34a. The theoretical tank pressures were calculated based upon the assumption that HFC32 has

same solubility in the polyol mixture as HFC 134a. The lower tank pressures for the mixtures that include HFC32 indicate that HFC32 has significantly better solubility than HFC 134a.

Example 2 k-Factor of Foams

The A-side, polymeric MDI and B-side mixture were mixed in the impingement mixer of the Edge-Sweets high-pressure foam machine and dispensed into a container. The resulting foam had free rise density of 1.8 to 1.9 lb/ft ³ . Molded foam was also made by dispensing the material in to a closed mold that was pre-heated at 115 ⁰ F and allowing the mixture to expand. The mold was kept closed for approximately 30 minutes before releasing the foam.

The k-factor measurements (in accordance with ASTM C518) on the resulting foams were conducted between 10°F and 130 ⁰ F. Initial k- factors are taken within 24 hours after removing the foam skin with a band saw. Lower k-factors indicate better insulation values. The results are summarized in Table 3.

Table 3 k-Factor of Foam

The results in Table 3 show that as the level of HFC32 increased, k- factor decreased up to a point, thereafter, further increase in the HFC32 level resulted in increased k-factor.

Example 3 Dimensional Stability of Foams

The dimensional stability of resulted foam was measured according the ASTM

D2126.

Table 4 Dimensional Stability of Foam

The results were as shown in Table 4 show that the higher the percentage of HFC32, the better the dimensional stability.

Example 4 Closed Cell Content of Foam

The closed cell content was measured according to ASTM 2856.

Table 5 Closed Cell Content of Foam

The data in Table 5 shows that the closed cell content increases as the percentage of HFC32 is increase up to a point, thereafter, further increase in the HFC32 level resulted in reducing the number of closed cells.

The present invention provides a method for producing a thermosetting foam. The blowing agent combination comprises a combination of HFC 134a and HFC32 comprising of less than about 30 wt% of HFC32.

While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.