Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-01-31
2002-05-21
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...
C521S157000, C521S172000, C521S174000
Reexamination Certificate
active
06391935
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to viscoelastic polyurethane foams and a process for making them. These soft foams, which incorporate a polyoxyalkylene monol, are useful in a wide variety of applications such as bedding, shoe soles, ear plugs, and protective sports equipment.
BACKGROUND OF THE INVENTION
Flexible, viscoelastic polyurethane foam (also known as “dead” foam, “slow recovery” foam, or “high damping” foam) is characterized by slow, gradual recovery from compression. While most of the physical properties of viscoelastic foams resemble those of conventional foams, the resilience of viscoelastic foams is much lower, generally less than about 15%. Suitable applications for viscoelastic foam take advantage of its shape conforming, energy attenuating, and sound damping characteristics. For example, the foam can be used in mattresses to reduce pressure points, in athletic padding or helmets as a shock absorber, and in automotive interiors for soundproofing.
Various synthetic approaches have been used to make viscoelastic foam. Formulators have modified the amount and type of polyol(s), polyisocyanate, surfactants, foaming catalysts, fillers (see, e.g., U.S. Pat. No. 4,367,259), or other components, to arrive at foams having low resilience, good softness, and the right processing characteristics. Too often, however, the window for processing these formulations is undesirably narrow.
Most flexible, viscoelastic polyurethane foam is produced at low isocyanate index (100 times the mole ratio of —NCO groups to NCO—reactive groups in the formulation). Usually, the index is less than about 90. See, for example, U.S. Pat. No. 4,722,946 (index: 65-85), U.S. Pat. No. 4,980,386 (index: 65-90), and U.S. Pat. No. 4,839,397 (index: <80). Simply raising the index makes it difficult to achieve the required softness, as evidenced by higher-than-desirable IFD or CLD numbers (see Comparative Example 36 below).
Unfortunately, low-index foam formulations are extremely sensitive to small changes in catalyst and surfactant amounts, so the processing window is undesirably narrow and special (translation: expensive) silicones are often needed to avoid shrinkage or foam collapse. Foams made at low index are prone toward high compression sets and also tend to discolor upon exposure to heat or ultraviolet light. Moreover, when toluene diisocyanate (TDI) is used to make viscoelastic foams at low index, the foams can contain undesirably high levels of toluenediamines, particularly after the normal curing process. (Toluenediamines are now under severe public and regulatory scrutiny in Europe because they are highly toxic and possible carcinogens.) In addition, it is often difficult to make low-resilience foams having a good balance of physical properties at indices below 90.
Other approaches to making viscoelastic foam hinge on finding the right mixture of polyether polyols and other components. For example, U.S. Pat. No. 4,987,156 arrives at a soft, low-resilience foam with a mixture of high and low molecular weight polyols, each of which has a hydroxyl functionality of at least 2, and a plasticizer having a solidification point less than −20° C. U.S. Pat. No. 5,420,170 teaches to use a mixture that includes one polyol having a hydroxyl functionality of 2.3-2.8, and another polyol having functionality 2-3. Recently issued U.S. Pat. No. 5,919,395 takes a similar approach with a polyol mixture that contains a 2500 to 6500 molecular weight polyol having a functionality of 2.5 to 6 and a rigid polyol having molecular weight 300 to 1000 and a functionality of 2.5 to 6. None of these patents teaches to include a monofunctional polyether (a “monol”) in the formulation.
Monofunctional alcohols have been included in flexible polyurethane foams for various reasons, but they have rarely appeared in a viscoelastic foam. Most references that include a monol teach foams with high resilience (see, e.g., U.S. Pat. Nos. 4.981,880, 3,875,086, and 3,405,077). Other references teach the use of low molecular weight monofunctional materials. For example, U.S. Pat. No. 5,631,319 teaches to use a C
1
-C
25
monoalcohol combined with a hydroxyketone in non-viscoelastic foam. U.S. Pat. No. 4,209,593 teaches to use a naphthol or other “bulky” monohydroxy compound to make an energy-absorbing foam. Unfortunately, including low-molecular-weight (<1000), high hydroxyl number (>60 mg KOH/g) monols in viscoelastic foams can adversely impact important foam properties, particularly compression sets (see Comparative Examples 14 and 15 below). In addition, any monol can remain largely unreacted, especially in a low-index formulation, resulting in a foam that is oily to the touch (i.e., has poor “hand feel”).
U.S. Pat. No. 4,950,695 teaches to use a monofunctional alcohol or polyether to soften flexible polyurethane foams. The formulations also include a 2000 to 6500 molecular weight triol. Because the inventors did not bother to report resilience values, a skilled person would infer that the foams lack viscoelastic character.
European Pat. Appl. No. 0 913 414 teaches to make viscoelastic polyurethane foams that may contain a polyether monol. The monol, which has a molecular weight less than 1500, is used with a polyol that has a molecular weight greater than 1800. All of the examples show low-index (less than 90) foams.
In sum, most viscoelastic foams are made at isocyanate indices below 90, but the industry would benefit from a better way to formulate these low-resilience foams at higher index values. In particular, formulations that provide a wider processing window are needed. Desirable formulations would give foams with a favorable balance of properties, including low resilience, good softness, low compression sets, and good “hand feel.” A valuable TDI-based formulation would produce foams having reduced levels of toluenediamines.
SUMMARY OF THE INVENTION
The invention is a viscoelastic polyurethane foam and a process for making it. The foam is produced using a unique isocyanate-reactive mixture that includes a polyester or polyoxyalkylene polyol and from about 15 to about 70 wt. % of a polyester or polyoxyalkylene monol. The monol has a number average equivalent weight greater than about 1000, and the polyol has a number average equivalent weight less than about 600. When this isocyanate-reactive mixture is combined with a polyisocyanate, water, a surfactant, and one or more catalysts at an isocyanate index of at least 90, the result is a viscoelastic polyurethane foam having a resilience of less than 15% and an excellent overall balance of physical properties.
We surprisingly found that using the monol-containing isocyanate-reactive mixture described above is the key to formulating viscoelastic foams over a broad range of processing conditions and isocyanate indices. In spite of the relatively high molecular weight of the monols, the resulting foams retain their low resilience and good damping properties. Moreover, the foams have good softness and low compression sets. We also unexpectedly discovered that by using a “reactive” mono (i.e., a monol having a high content of primary hydroxyl groups) in TDI-based formulations at indices higher than 95, we could make foams with improved “hand feel” and reduced levels of residual toluenediamines.
DETAILED DESCRIPTION OF THE INVENTION
Viscoelastic polyurethane foams of the invention include, in addition to conventional components, a unique isocyanate-reactive mixture. The mixture includes a polyester or polyoxyalkylene monol and a polyester or polyoxyalkylene triol. Optionally, a chain extender or crosslinker is included.
The polyester or polyoxyalkylene mono has one hydroxyl group per molecule, and an average equivalent weight greater than about 1000. Thus, it also has a number average molecular weight (Mn) greater than about 1000. Preferably, the monol has an average equivalent weight greater than about 1500, and most preferably greater than about 2000. Preferred monols have a hydroxyl number less than about 56 mg KOH/g.
The monol can be a polyester. Polyesters
Hager Stanley L.
Jividen Veril C.
Joulak Faouzi
Triouleyre Sebastien P.
Bayer Antwerp N.V.
Brown N. Denise
Cooney Jr. John M.
Gil Joseph C.
Whalen Lyndanne M.
LandOfFree
Viscoelastic polyurethane foams does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Viscoelastic polyurethane foams, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Viscoelastic polyurethane foams will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856933