Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1988-01-22
1990-10-23
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 464, 264 50, B29C 6722
Patent
active
049650297
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the production of polyurethane foams which have one or more zones of hard foam encapsulated within a soft foam.
Polyurethane foams having zones or layers of differing hardness are becoming increasingly important for use in the modern seating industry. In particular, seats made from such foams are being used in the automotive industry where it is becoming important to reduce the mass of seats, for fuel efficiency reasons, without a loss in comfort or support for the driver.
Although it is known to improve the characteristics of polyurethane foam seats by use of support wires or by fabricating the seats out of individually foamed parts of differing hardness, two alternative technologies have recently been developed with a view to simplifying the manufacturing process.
The first of these alternatives has been described in U.S. Pat. No. 4,190,697. This patent discloses an integral polyurethane foam comprising layers of foam having different hardness. Thus there is disclosed a seat cushion comprising a supportive lower layer of firm foam beneath a more comfortable upper layer of soft foam. The patent also describes a process of making such polyurethane foams by adding a firm foam formulation to a mould, allowing the firm foam formulation to rise and adding a soft foam formulation to the rising firm foam formulation under conditions such that the soft foam formulation passes through the firm foam formulation to yield the layered structure. Preferably the soft foam formulation is added after the firm foam formulation has risen between about 10 and 80% of its potential rise.
The other alternative technology has been described in our European Patent No. 68820. This patent discloses a process for making an integral polyurethane foams which comprises encapsulated zones of a firm foam in a soft foam which is particularly suitable for producing side rolls and lumbar supports for automobile seats. The process for manufacturing such foams comprises adding first a soft foam formulation to a mould, allowing the soft foam formulation to rise and subsequently adding a firm foam formulation under conditions where the firm foam formulation does not pass through the soft foam formulation but is instead encapsulated by it. The firm foam is preferably added either (1) at a time where the soft foam formulation has expanded by an amount in the range 250% to 1400% of its original volume or (2) at between t+3 and t+15 (seconds t is the cream time of the soft foam formulation) after the soft foam formulation has been introduced.
With regard to the process of the later patent it is known that the optimum encapsulation of the firm formulation by the soft occurs when the density difference between the two formulations at the moment the firm foam formulation is added is as small as possible. In minimising the density difference, however, a problem is encountered. This arises because the soft foam is rising and decreasing in density when the firm foam is added whilst the firm foam is in an unrisen, relatively dense state when it is introduced into the mould. In order to overcome this problem, it has therefore been necessary to introduce the firm foam formulation relatively soon after the soft foam formulation is poured and to use soft foam formulations of relatively low reactivity so that a rapid rise of the soft foam is avoided.
A modified process has now been discovered which allows the process of EP No. 68820 to be operated with a much wider range of soft foam formulations including those of higher reactivity relative to those previously employed. In addition, for a given set of processing conditions the degree of encapsulation, as defined by the minimum thickness of the encapsulating over the encapsulated foam, is improved thereby improving product quality. The process comprises introducing, a frothing agent which causes the firm foam formulation to froth as soon as it leaves the mixing head, thereby rapidly decreasing its density. The frothing agent is added in addition to the standard blowing agents e
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Lidy Werner A.
Tenhagen Rudolf J.
Kuhns Allan R.
Polyol International BV
Silbaugh Jan H.
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