Shipping Flexible Polyurethane Foam Product

The invention relates to flexible polyurethane foams and, more particularly, to an improvement in shipping such foam product.

A major bottleneck in the production of flexible polyurethane foam slabstock is the amount of time and space required to store the foamed slabstock prior to fabrication or shipping. Requisite conditioning for a certain period of time dependent upon the storage temperature and type of foam formulation is needed to permit the foamed product to become fully cured, i.e. develop the inherent property of restitution so that the product when compressed to a lesser size to facilitate shipping can return to its original dimensions once it arrives at the destination and the compressing force has been removed.

In addition, yields of foam are reduced due to the need for oversize cutting to meet end use specifications when the foam product is shipped in compression trailers.

Foam producers have attempted to improve the overall process for making and storing flexible polyurethane foam products by the use of infrared heat lamps on the production line, heating the storage buildings where the foam is allowed to cure, storing the foams for an extended period of time before fabricating or shipping and oversize cutting to compensate for lack of recovery. These solutions to the problem add to the costs and inefficiencies in the overall process from making the foamed product to its arrival at its ultimate destination.

The prior art is replete with examples of tertiary amines that can be used as catalysts alone and in combination for the reaction of polyols with polyisocyanates in the production of polyurethane foams. Catalysts which are generally used in the flexible foam art include, for example, triethylenediamine, bis(dimethylaminoethyl)ether and diemthylethanolamine, optionally in combination with a tin compound.

U.S. Pat. No. 3,786,005 discloses the use of 4-(2-dimethylaminoethyl)morpholine as the principal amine catalyst for the reaction of polyols and polyisocyanates to make polyurethane foams. Example 2 shows its use in a flexible polyurethane foam composition containing a polyether polyol.

The present invention provides an improvement with regard to a method for conditioning, cutting and shipping flexible polyurethane foam product. The overall procedure begins with reacting a flexible polyurethane foam composition comprising a polyisocyanate, a polyether polyol, a surfactant, a catalyst system, water, and, optionally, a halogenated hydrocarbon blowing agent to provide a foamed product. The next step comprises conditioning the foam product which involves storing the product for a sufficient time and temperature to ensure that the product attains a fully cured state necessary to optimize recovery after compression. After conditioning, a compressing force is applied to the product to reduce its size to permit greater quantity of product to be shipped in a particular volume of shipping container. The compressed foam product is shipped to the ultimate destination where the compressing force is removed so that the foam product may return to its original size. With regard to flexible molded polyurethane foam, the compression force would result from the stacking of the product in the shipping container.

The present invention provides for reducing the conditioning time prior to compressing the foam product while concomitantly ensuring the restitution of the foam product substantially to its original size upon removal of the compression force. These advantages are obtained by the use of a tertiary amine compound having a morpholine moiety in its structure, specifically an N-hydrocarbylmorpholine or an N-(dialkylaminoalkyl) morpholine, as the major portion of the catalyst system in the flexible polyurethane foam composition.

The invention provides a flexible polyurethane foam processor with numerous economic benefits which are a direct result of a shorter storage, or conditioning, time to achieve full care, namely, quicker turnaround time for the foam product, reduced inventory of finished foam product, reduced storage temperatures, reduction in scrap foam resulting from compressed shipment, and reduction in the need for oversize cutting.

In a typical flexible polyurethane foam process liquid reactants are poured onto a moving conveyor. The reactants start foaming up and produce a polyurethane bun approximately 6 ft. wide and 4 ft. high, for example. These buns are cut at designated lengths and then sent to a storage room for conditioning. After conditioning for up to 10 days, depending on the particular polyurethane formulation and temperature of the storage room, the buns may be cut and shipped or fabricated. If shipped, the buns may be transported in compression trailers which compress the foam down, for example, to approximately 30% of its original height. Typically the buns are cut larger than the desired end use specification size due to the lack of full restitution, or recovery, after removal from the compression trailers.

The operative limits on processing flexible polyurethane foam product is dependent on the type of equipment in mixing and foaming the polyurethane composition and the desired physical properties for the polyurethane foam. If the polyurethane foam buns are not stored for the proper time, they will not return sufficiently to their original height after transporting in compression set trailers. Such buns may end up as scrap foam. Often when foams are not cut greater than the desired dimensions, they will be undersized after enduring a period of compression in the shipping trailers and, thus, will also be scrap foam. Since yields are a function of the amount of scrap foam produced, improper storage and oversize cutting reduces these yields and imposes an economic penalty on the flexible polyurethane processors.

Flexible polyurethane foam formulations generally will include a polyisocyanate, a polyester or polyether polyol, a surfactant, a catalyst system, water, and in some cases, a blowing agent such as methylene chloride or trichlorofluoromethane. Additional additives such as flame retardants and fillers may also be employed.

Polyisocyanates which may be used according to the invention are those well known in the art for preparing flexible polyurethane foams. Examples of these would include the 2,4- and 2,6-toluenediisocyanates in mixtures (80:20 or 65:35) of the two isomers and methylenediphenylisocyanate.

Also suitable starting materials for the production of the flexible polyurethanes in the process according to the invention are the so-called prepolymers which are the reaction products of a polyol with excess polyisocyanate.

It has been discovered that the advantages achieved by the invention only accrue to those flexible polyurethane compositions which contain a polyether polyol and not a polyester polyol. The polyether polyols include the homopolymers of alkylene oxides such as ethylene oxide, propylene oxide and the like and alkylene oxide adducts of polyhydroxyalkanes such as, ethylene glycol, propylene glycol, trimethylol propane, pentaerythritol, sorbitol, and the like, trialkanolamines, such as triethanolamine and triisopropanolamine, mono- and polyamines, such as ethylamine, ethylenediamine, diethylenetriamine, phenylenediamines, toluenediamine, and the like, non-reducing sugars and sugar derivatives, such as sucrose and methylglucoside.

For flexible polyurethane compositions the polyol or polyol mixture employed can have hydroxyl numbers which vary from about 20 to about 70 or more. The hydroxyl number is defined as the number of milligrams of potassium hydroxide required for the complete neutralization of the hydrolysis product of the fully acetylated derivative prepared from 1 gram of polyol. The hydroxyl number can also be defined by the equation ##EQU1##

Surfactants which are normally used are the silicone surfactants such as siloxane polyalkylene oxide copolymers.

The key to speeding up the conditioning of the flexible polyurethane foamed product, that is to say shortening the time and/or lowering the temperature for the storage of the product until substantially fully cured, is the particular tertiary amine catalyst employed, namely an N-alkyl or N-(dialkylaminoalkyl)morpholine compound. Such morpholine-containing compounds may be represented by the following general formula ##STR1## Examples of suitable morpholine-containing catalysts include N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, N-butylmorpholine, N-cocomorpholine, 4-(2-dimethylaminoethyl)morpholine, 4-(2-diethylaminopropyl)morpholine, 4-(2-dimethylaminobutyl)morpholine and the like. The morpholine-containing compound may comprise the sole amine catalyst or it may be used as the major portion of the amine catalyst, i.e. greater than about 50 wt %, in combination with another tertiary amine such as triethylenediamine, bis(dimethylaminoethyl)ether and dimethylethanolamine. A tin compound such as stannous octoate or dibutyl tin dilaurate may also be included in the catalyst system. The catalyst is used in such catalytic amounts as are normally used in the art, for example about 0.1 to about 1.0 parts per 100 parts of polyol.

The following examples are intended to illustrate the invention and not restrict the scope thereof.

The following flexible polyurethane formulations were used to evaluate the relationship between the compression set properties of the foam products and the amine catalyst used:

Foam hand mixes were prepared using flexible polyurethane foam formulations A and B containing the following amine catalysts: triethylenediamine (TEDA) 0.27 g; 4-(2-dimethylaminoethyl)morpholine (DMAEM) 0.34 g; and a mixture comprising triethylenediamine, dimethylethanolamine (DMEA) and bis(dimethylaminoethyl)ether (DMEE) 0.31 g. The amount of catalyst used was chosen so that the rise time of each would be substantially the same. Six foams were prepared using each catalyst, three were placed immediately into a freezer at 23.degree. F. (-5.degree. C.) and three were placed in a controlled temperature and humidity room at 68.degree. F. (20.degree. C.) and 50% relative humidity. The foams were tested for compression set according to the procedure of ASTM D 3574-74 TEST D with the exception of the temperature and time of storage. The percent compression set values are calculated as follows: ##EQU2##

From the data in Table 1 it can be seen that 4-(2-dimethylaminoethyl)morpholine provided the flexible foamed product with superior restitution properties when subjected to a 90% compression set for the times indicated, i.e. the significantly lower values obtained with the DMAEM catalyst, particularly at the colder temperature of -5.degree. C., compared to the prior art catalysts indicate a smaller deviation from the original dimensions. With regard to the 75% compression set data the DMAEM catalyzed foam in general showed better recovery from compression in both formulations A and B at both 20.degree. C. and -5.degree. C. storage temperatures with the exception of TEDA in formulation B at -5.degree. C. for 24 hours.

Blends of DMAEM with TEDA were prepared and evaluated against TEDA and DMAEM individually. The following catalyst compositions were tested in formulation B at the use levels indicated in Table 2.

The data shows that when DMAEM is present in greater than about 50% of the catalyst combination for flexible polyurethane foam stored at -5.degree. C. for 48 hours the recovery of the compressed foam product is significantly greater than for the other catalysts. This indicates that when foam products are prepared using a catalyst composition containing as a major portion DMAEM, the resultant product need be stored for a lesser period of time at the cooler temperatures such as less than about 5.degree. C. to attain substantially complete cure.

Foam products were prepared using formulations B and either TEDA, DMAEM or N-ethylmorpholine (NEM) as the catalyst and were held under cure conditions of 20.degree. C., 50% relative humidity. Table 3 shows the data obtained for 90% compression set.

The data shows the improvement in restitution of foam products prepared using morpholine containing catalyst compounds according to the invention.

In this example numerous polyurethane catalysts were tested in polyurethane foam formulation B and the foams were subsequently cured at -5.degree. C.

The data in Table 4 shows the surprising improvement in restitution of flexible polyurethane foam products stored at -5.degree. C. using the morpholine moiety containing compounds DMAEM, NEM and NMM. Very surprisingly DMDEE which contains two morpholino moieties per molecule showed the worst compression set data.

In this example a flexible polyurethane foam composition containing a polyester polyol was prepared using DMAEM and NEM as the catalysts. The following formulation was used:

The NEM was used at a level of 1.5 g and the DMAEM was used at a level of 0.6 g. The foam products were stored at a conditioning temperature of 20.degree. C. and 50% relative humidity. Table 5 shows the data obtained for 90% compression set testing.

It is readily apparent from the data in Table 5 that the advantages in reducing the conditioning time and/or temperatures obtained using certain morpholine containing catalysts in making flexible polyurethane foamed products is only observed when such flexible polyurethane foam compositions contain a polyether polyol and not a polyester polyol.

The invention provides for improved processing of flexible polyurethane foam products by permitting processors to reduce conditioning time and/or temperature for storing the product in order to develop substantially full cure so that upon compression shipment of the products they will substantially return to their full size.