Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-08-01
2004-04-27
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S160000, C521S170000, C521S174000
Reexamination Certificate
active
06727292
ABSTRACT:
BACKGROUND OF THE INVENTION
TDI based polyurethane foams have been manufactured by the slabstock process for over 50 years. TDI has been the isocyanate of choice for this segment because it produces very low density foams and also a very wide range of foams with the proper selection of formulation components. There is one composition of TDI 8020 (80% 2,4′/20% 2,6′) used for polyether flexible slabstock manufacture and TDI 6535 (65% 2,4′/35% 2,6′) is sometimes blended with TDI 8020 for the manufacture of polyester slabstock. The two attributes that make TDI the material of choice for slabstock are its low density potential and very linear and predictable response in terms of density versus water level.
MDI based polyurethane foams have mainly served the rigid foam, elastomer, and molded flexible foam markets and has not significantly entered into the slabstock flexible market. While MDI flexible foams cannot make the good quality low density and soft foams that TDI is capable, MDI makes excellent medium to higher density both soft and hard foams. There are numerous commercial compositions of MDI for flexible foams, due to the necessity of changing its composition depending on both the formulation components and more importantly the water level. MDI compositions based on high levels of 4,4′ MDI normally lead to foam collapse. It is well known in the art that foam process stability is achieved by increasing the level of 2,4′ MDI and polyfunctional MDI species in the composition. It is also understood that the optimum 2,4′ MDI level and overall MDI functionality is a direct function of the water content of the formulation. A given composition of MDI can only cover a moderate range of water levels, while still giving the desired performance processability (stable yet-open celled foam) and physical properties. Numerous MDI patents illustrate and explain the problems of making stable low density foams from all MDI and also attest to the need for using many compositions. See for example U.S. Pat. Nos. 4,365,025; 5,621,016; 5,089,534; and 5,491,252.
MDI isocyanates have not gained wide acceptance in the TDI slabstock market for two reasons: 1) It would require at least 2 and more likely 3 MDI product compositions to allow for on-the-fly adjustments to the isocyanate composition for varying flexible foam grades. The all-MDI approach would require multiple tank and metering installations for practical slabstock manufacture, making this approach very uneconomical and unwieldy compared to TDI; and 2) The complex non-linear behavior of MDI based flexible foam in regards to its density yield versus water content, makes it very difficult to make predictable adjustments.
MDI/TDI preblends have been widely used with good success in molded application areas and limited success to date in the slabstock area. There is much prior art covering the preparation, processing, and properties of MDI/TDI blends, but none address the issue of a single specific MDI composition blended with TDI to cover all grades and types of flexible polyether polyol based foams. See for example U.S. Pat. Nos. 3,492,251; 5,674,920; 5,132,334; 5,436,277; 5,459,221; 5,491,252; 5,607,982; 5,500,452; 5,232,956; and 4,803,220.
An improved process for the continuous or semi-continuous production of flexible foams, where MDI is the major component and TDI the minor component has now been found. This process substantially obviates the disadvantages described above and allows the use of certain preferred mixtures of diphenyl methane diisocyanates and oligomer polyphenyl-polymethylene polyisocyanates in combination with TDI 8020 or TDI 6535. Good quality, stable yet open celled foam, which does not collapse or shrink, can be achieved over a wide range of densities using a single MDI composition.
SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of flexible polyurethane foam using at least three reactive chemical component streams, wherein the components are fed separately to a mixing device; where at least one component consists essentially of a TDI series isocyanate composition and one component comprises predominantly (i.e., at least 50 weight percent) an MDI series isocyanate component (on a weight basis) and the third component may comprise polyol or another MDI or TDI. It is most preferred that the third component comprises a polyol component.
In an aspect of the invention, the overall isocyanate composition (sum of all isocyanate streams) comprises:
(I) 1 to 40% by weight of toluene dissocyanate and
(II) about 60 to 99% of a mixture of diphenylmethane diisocyanates and polyphenylmethylene polyisocyanates comprising:
(1) 51 to 87% by weight of 4,4′-diphenylmethane dissocyanate
(2) 0.5 to 16% by weight of 2,4′-diphenylmethane dissocyanate
(3) 12.5 to 33% by weight of polyphenyl polymethylene polyisocyanates having 3 or more NCO groups per molecule, wherein the sum of (1),(2) and (3) total 100%.
A more preferred polyisocyanate mixture is one in which component (II) comprises:
(1) 59 to 81% by weight of 4,4′-diphenylmethane dissocyanate
(2) 1 to 13% by weight of 2,4′-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates
A most preferred polyisocyanate mixture is one in which component (II) comprises:
(1) 65 to 81% by weight of 4,4′-diphenylmethane dissocyanate
(2) 1 to 7% by weight of 2,4′-diphenylmethane dissocyanate
(3) 18 to 28% by weight of polyphenyl polymethylene polyisocyanates
In accordance with the invention the 2,4′-MDI content in isocyanate component (II) is low, so that, additional TDI from isocyanate stream (I) is necessary to achieve stable, yet open celled flexible foam. Addition of TDI improves the processing and physical properties of these predominantly MDI based foams compared to the alternative approach of using higher levels of 2,4′ MDI.
An aspect of the invention is the complete control of the MDI/TDI blend ratio by separate metering to a mix device. Preblending or master blending of some of the TDI with the MDI is not the preferred method, but can be done when the MDI composition is extremely low in 2,4′ MDI content, to improve the room temperature liquidity of the MDI composition.
In support of this invention, a new method for the determination of the level of TDI to be used with the particular MDI composition was devised. A guideline empirical calculation allows an overall stability factor to be calculated for any ratio of MDI/TDI. This stability factor for a given formulation is a function of the water level and needs to be increased with increasing water level. This method fulfills the need for making predominantly MDI based flexible polyurethane foams more predictable, like all-TDI based foams. Surprisingly, this empirical model is based on the premise that 2,4′ MDI can be replaced with TDI (both 2,4′ and 2,6′ isomers) on an equivalent molar basis to achieve stable flexible foam.
This invention is directed mainly to flexible foam compositions that contain mainly MDI in the overall isocyanate composition. In this respect, it is a purpose of this invention to modify and improve the performance of predominantly MDI based flexible foams, then to make these hybrid MDI/TDI foams totally equivalent in performance to TDI based foams.
DETAILED DESCRIPTION OF THE INVENTION
The reactive chemical component streams used for the production of the flexible polyurethane foams according to the invention are described in detail. The overall isocyanate composition comprises at least 2 isocyanate streams (I) & (II) fed separately to a mixing device.
The isocyanate stream (I) can be any commercially available form of toluene diisocyanate (TDI). The most common to the ok slabstock industry is TDI 8020 (80% 2,4′ and 20% 2,6 isomers), but TDI 6535 (65% 2,4′ and 35% 2,6′ isomers) is often blended with the TDI 8020 for polyester slabstock.
The isocyanate stream (II) is a specific mixture of diphenylmethane diisocyanate
Cooney Jr. John M.
Graham Nicole
Huntsman International LLC
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