Dow polyol additives for auto seat foam

The automotive industry and its suppliers have been at the leading edge of process efficiency for many years. Suppliers to the auto industry have very little margin for error, they need processes which are tolerant of variation. The processes must be efficient with acceptable cycle times to allow just-in-time delivery of components to suppliers further along the chain or directly to the OEM.

OEMs face a number of challenges themselves. One of the largest challenges the global automotive industry faces is fuel efficiency. In the US, this is articulated through CAFE regulations. Within the European Union this is shown in increasingly stringent regulations designed to reduce the amount of carbon dioxide emitted/km travelled.

Consumer environmental awareness within the passenger cabin is also growing, and car makers are demanding ever-lower emission and odour levels from the materials used to make interior components.

These environmental challenges must be met with increased performance. Globalisation of component design, more stringent safety regulations and higher levels of sustainability complete one set of challenges.

Environment and efficiency

Overlaid, cross-cutting and amplifying these are the drive to light weighting, and life cycle analysis of all of the components within the car; electrification, global specifications and the need to reduce the mass of the powertrain.

These challenges call for materials which have lower emissions than established predecessors. Materials which are of low density and provide good performance. Materials which enable thinner, comfortable components to be produced and also have a proportion of renewable content.

In practice, this translates into two different sets of requirements. OEMs demand materials, especially for automotive interiors, which have lower emissions than their predecessor platforms with possible density savings. At the same time, materials must have enhanced physical properties to enable them to meet the physical specifications of the OEM.

Tier one and two suppliers need easy to process materials and systems that enable them to produce the parts needed by OEMs in the most efficient way possible. In practice this means they need products which do not require special handling or storage, process easily, are easy to demould, have fairly fast cure properties and, for automotive seating, are available in variable hardnesses.

Automotive seats are the largest interior components by volume. Their size, and the relatively large volume of PU foam they contain makes them good candidates for emission reduction. A reduction in seating emissions will have a significant impact on the overall emissions within the cabin.

To address the interior emission topic, Dow Automotive Systems has developed a new range of Additive Polyols called Specflex Activ which are enablers of the first viable amine emission – free solution for interior Polyurethane (PU) applications. Traditionally, PU foams have required amine catalysts to promote reaction between polyols and water with the isocyanate component, to generate gelling and blowing reactions respectively. Until now, these added catalysts can be one of the main contributors to PU foam amine- emission issues and / or have a potential negative impact on physical mechanical properties, particularly after aging, and decreased process latitude.

The Specflex Activ additive polyol family, with high and specifically balanced catalytic activity, allows the foam makers to reduce or even eliminate the addition of catalysts resulting in outstanding foam processing advantages, physical and mechanical properties, including ageing. The new additive polyol has been developed in response to the complex matrix of specifications in automotive design.

Drop in replacement

The new additive polyol has excellent compatibility with the isocyanate and the other polyol components. This facilitates the mixing process both for the formulated polyol and with the isocyanate. Once mixed the foaming system has the catalytic activity evenly dispersed through the system.

The Specflex Activ additive polyols are designed to be easy to implement as a drop in replacement in formulations by Tier’s. Specifications are typical of polyols used in automotive seating formulations (hydroxyl number between 31 and 40 mg/g; colour is 75 max, viscosity at 25° C is in the range 1050-1350 cSt). Additionally, packaging carries standard safety labelling as other polyols in the market.

Process Latitude

Table 1 shows the wide range of process latitude which the new additives offer to seat foam manufacturers.

Table 1: Specflex Process Lattitude
Components	Reference	Low Emission Best Alternate	Voranol Voractive	Vroanol Voractive + Catalyst	Specflex Activ1	Specflex Activ2	Specflex Activ3
Dow copolymer polyol	40	40	40	40	40	40	40	PBW
Dwo Base polyol	60	60	40	40	48	48	48
Specfelx Activ 2306 polyol					12	12	12
Voranol Voractiv VM779 polyol			20	20
Conventional Catalyst Package	0.4	0.4	ZERO	ZERO	ZERO	ZERO	ZERO
Low Emission Catalyst Package	ZERO	1.2	ZERO	ZERO	ZERO	ZERO	ZERO
Water	3.4	3.4	3.4	3.4	3.4	3.4	3.4
Index (T80)	100	100	100	100	100	110	80
Moulded Foam	Tight	Tight	NM	Tight	Open1	Open1	Open1
Hardness CFC 40% kPa	5.7	5.8	NM	5.5	6.3	8.4	4.6
Source: Dow Chemical	NM= Not moulded, part collapsed				1 Easily crushed

All the reactions were carried out on the same machine. The first column shows a traditional “pre-low emission era” standard formulation. This suffers from a narrow process window and produces foams which are very tight and need to be heavily crushed before they can be further processed. The formulation produces foams with an acceptable density range and good physical properties. The next best alternative (NBA) formulation, “low emission era”, has good hardness and again produces a tight foam, which needs to be heavily crushed as well before use. About 11 years ago Dow started to address the need for lower emission automotive foam formulation with the launch of Voranol Voractiv polyols. This range was designed to help reduce the amount of catalyst needed to produce successful automotive foams. It has had success in formulations but requires the use of additionally relatively small amount of low emission reactive catalysts. Table 1 also shows three different formulations produced with Specflex Activ additive polyol (highlighted). These are identical except in their isocyanate index, chosen for the comparability studies with foaming at Tiers. An index of 80, typically used to make softer seating foam, intermediate as 100 and 110 which can be used to increase hardness in bolsters for cushions and backrests. Hardness The hardness of the foam varies from 8.4kPa in Specflex Activ example Formulation 2 with 110 index to 4.6 kPa for Specflex Activ Example Formulation 3. There was no need to adjust the other components to accommodate the index change. Table 1 shows it is possible to produce a wide range of hardnesses in the finished foam by very simply manipulating the isocyanate index of the formulation. This demonstrates the superior process latitudes without issues related to foam tightness. In practice this would mean that various hardness foams could be made on a single production carousel without the need to adjust the water level. Thus, making the production process more straightforward. In reality, different moulds each with different foam requirements could more easily be accommodated on a single seat production unit. Density Table 2 shows the much greater range of density possible with the Specflex Activ polyols when the water component of the formulation is altered. Again, these foams have been produced without further modifications to the formulation and still it was possible to make excellent quality open cellular materials across the density range. This affords a much greater level of fine tuning in use than is possible with historical standard or lower emission formulations.

Table2: Specflex Activ Properties
Components	Reference	Low Emission Best Alternate	Voranol Voractive + Catalyst	Specflex Activ 1	Specflex Activ 2	Specflex Activ 3
Dow copolymer polyol	40	40	40	40	40	40	PBW
Dow Base polyol	60	60	40	48	48	48
Specfelx Activ 2306 polyol				12	12	12
Voranol Voractiv VM779 polyol			20
Conventional Catalyst Package	0.4	0.4	ZERO	ZERO	ZERO	ZERO
Low Emission Catalyst Package	ZERO	1.2	ZERO	ZERO	ZERO	ZERO
Water	3.4	3.4	3.4	3.4	3.4	3.4
Index (T80)	100	100	100	100	110	80
Density (kg/m3)	50-55	50-55	50-58	46-65	50-70	35-55
Possible density ranges (kg/m3)	5.7	5.8	5.5	6.3	8.4	4.6
Source: Dow Chemical	Standard		up 50%	up 200%

Even new seat foam system solutions are often limited in their ability to be overpacked without causing tightness or cell stability issues. The historical standard and NBA formulations give a 5kg/m³ density range. Specflex Activ polyols allow a 20kg/m³ range within each of the three different example formulations. This is considerably broader than the traditional formulation. The mid-point densities of the Specflex Activ formulations range from 35 for the 4.2 parts by weight (pbw) water formulation to 70 for the 3 pbw water formulation. This is the start of our work in this area and it is possible that a much wider range of foam densities may be possible with viable foam formulations. The bottom line is that up until now extreme hardness requirements in same TDI seating foams have needed specialized knowledge, practices, and processing equipment to be employed in the manufacturing plants at the tiers. With the use of Specflex Activ additive polyols it is possible to process very different hardness foams to a variety of specifications, that are consistently open and are less sensitive to process variations. Un-aged and aged properties Table 3 compares the un-aged and aged physical mechanical properties of foams made with the Specflex Activ polyols with traditional formulations. In this case, the new Dow polyols exhibit similar tear resistance test results and have properties which are very close to the reference formulation. This is shown in Table 3.

Table3: Specflex Activ Foam Properties
Components	Target Specs		Reference	Low Emission Best Alternate	Voranol Voractive + Catalyst	Specflex Activ 1	Specflex Activ 2	Specflex Activ 3
Dow copolymer polyol			40	40	40	40	40	40	PBW
Dow Base polyol			60	60	40	48	48	48
Specfelx Activ 2306 polyol						12	12	12
Voranol Voractiv VM779 polyol					20
Conventional Catalyst Package			0.4	0.4	ZERO	ZERO	ZERO	ZERO
Low Emission Catalyst Package			ZERO	1.2	ZERO	ZERO	ZERO	ZERO
Water			3.4	3.4	3.4	3.4	3.4	3.4
Index (T80)			100	100	100	100	110	80
Properties	Standard	Target
Tear (N/cm)	D3574	>2	3.2-2.8	2.9	3.1	2.9	3.1
Compression set	ISO 1856		6.3-6.2	6.8	6.3	8.1	6.1
Resilance		60	61-63	61	64	59	65
Humid Age CS	DIN EN ISO 2440		10.5	17	12	32	11.1	14
Wet CS, 70%	D 1046		17-26	23	18	19	16
Source: Dow Chemical

Tear resistance is an important property in moulded seat foam. Demoulding foam can be a rough process. OEM’s demand small-radius corners and deep undercuts in the mould as well as metal or Velcro-type inserts (See picture X). This offers many opportunities for stress concentrations and cuts to occur when foam is demoulded. Cushions may also be treated fairly roughly in the seat assembly process. Additionally, the high flow which characterise Specflex Activ based formulations mean that inserts are properly wetted by the foam and form good interfaces. There is less chance of air bubbles being entrained within the foam or trapped around inserts because of the low viscosity of the Specflex Activ foams. In terms of resilience, the Specflex Activ example formulations meet the performance the ASTM standard demands. Meeting ageing properties requirements and humid-aged compression set in particular, is a demanding test for current available low emission foam alternatives compared to the historical reference foam. Typically, the reference foam has a 10.5% set; the standard demands less than 21%. The NBA foam also passes the test with 17% compression. All of the Specflex Activ formulations pass the test and the 80 index Formulation 3 exceeds the performance of the historical reference foam. The same is true of the wet compression set, where all the Specflex Activ foams pass the standard and perform at or better than the reference foam. The new Specflex Activ additive polyols allows for broad processing latitude, multiple hardness TDI foams with the ability to meet aged and un aged physical property demands. Odour and volatiles Car makers are currently demanding much lower levels of emissions from interior car components. They often set over-all limits for total emissions of VOC plus specific emissions for certain chemical compounds. In this study we have used the example of acetaldehyde detection according to the PV3942 test as such a specific substance. As can be seen from Table 4, the 100 and 80 index Specflex Activ formulations also have much lower emissions of acetaldehyde than the specification PV 3942 requires. Further more, the three foams are amine emissions free with total values for VOC, FOG and odour according to requirements.

Table4: Specflex Activ Foam Properties
Components	Target Specs		Reference	Low Emission Best Alternate	Voranol Voractive + Catalyst	Specflex Activ 1	Specflex Activ 2	Specflex Activ 3
Dow copolymer polyol			40	40	40	40	40	40	PBW
Dow Base polyol			60	60	40	48	48	48
Specfelx Activ 2306 polyol						12	12	12
Voranol Voractiv VM779 polyol					20
Conventional Catalyst Package			0.4	0.4	ZERO	ZERO	ZERO	ZERO
Low Emission Catalyst Package			ZERO	1.2	ZERO	ZERO	ZERO	ZERO
Water			3.4	3.4	3.4	3.4	3.4	3.4
Index (T80)			100	100	100	100	110	80
Properties	Standard	Target
Total VOC (ug/g)	VDA 278 (2011)		6000	115	190	90	77	117
Total FOG (ug/g)	VDA 278 (2011)		900	2302	470	220	217	236
Total Amines/cats (ug/g)	DBL 8585		474	15	24	ZERO	ZERO	ZERO
Acetaldehyde (ug/g)	PV93942		200	130	45	16	ZERO	9
Odour	PV 3900	=	4	3	3	2.5	tbd	2
Source: Dow Chemical	tbd= to be determined

Specflex Activ example Formulation 1, at 100 index, generates emission of 16 µg/g which is 8% of the total maximum allowed. Example Formulation 3, the 80 index, generates even lower emission at 9 µg/g which is 4.5% of the maximum allowed by the P3942 This again shows that even over a broad index range, allowing broad hardness, broad process and mechanical property window, these new Specflex Activ based formulations are also allowing a strong degree of VOC emission robustness. They can be successfully formulated to fully meet stringent emission requirements, even at the lower index which is well known to be more sensitive to emissions for historical and NBA formulations. Conclusion Foam formulations based on the Specflex Activ additive polyols enable low emission amine free foams with physical and ageing properties equal to or better than foams made with the traditional reference formulation. Additionally, a wide range of hardnesses and densities of foam can be produced using the new additive polyols by simply altering the proportion of water, the isocyanate index of the system and/or over packing in the mold. This break-through wide processing window for hardness and densities could make it simpler for tiers using same carrousel or in same mould. This paper was presented at Europur/Euro-Moulders conference in Vienna in June 2014. It was written by Adrian Birch, Jean-Paul Masy and Esther Quintanilla.