AU4278978A - Eliminating dens ification inthe manufacture of polyurethane foam blocks - Google Patents

Description

00i AU.-A1 42789/78 2 L'to a ralue TR; -at the moment the valu-e TR is attained the endless b~lt is again put in-to motion, operation is started of the devices for supplyinig and taicinG up tJhe web o~f material,, preferably paper, which covers the s'7urface of said endles' belt, controlling at the sai-e time the teraIperature of thsurface of the upper portion of the bolt forming thle floor

of the tunnel so -that in a first re~action area situated upstream of said endless bslt it acquireo a const-ant value TRInud in a 1 second consolidation area another constan.t val1ue PC sai d tenp- eratur(e. valuCes beingn oonltant for each type of foam, and in tha- the time said tCoiAperaturo is maiitztinod for eiach type of foai-m, i~ dtr::ind bytherato 7t t 4 being the t~otal tiiii of per!Imanclnce of' the foaiv, i the reaction tunnol, t, Cen the time it takes a foam element to traverse the reacil{on area, a fixed value foxr each type of foam and t0C being the time it takes a foam element to traverse the consolidation area; and ir that after leaving the foaming tunnel the block in for- mation undergoes, in at least one area located either before the drawing conveyers, between them or after the last of said conveyers which constitute the drawing means, drying in the lower part of the block in so-called dryinC area which is held at a constant temperature 9' 8 notably higher than TRand

To, after the passing of 'which removal. is ade of the web of material,~ preferably paper, to which is adhered a thin: film of foam, thus obtaining a MJock of pYurhane foam having no densified bottom, and a uniform surface which does not require final trimminp;.

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Form COIAMONINEALTH OF AUSTRALIA 'PATENTS ACT 1952469

COMPLETE SPECIFICATION (ORIGINAL)

4 278918 Class Int. Class Application Number: Lodged:

pomplete Specification Lodged: Accepted: Published: i P'viority I'

Ipated Art:

Namt of Applicant: TECFOAV S.A.

X*ddress of Applicant: PUXEIROS, VIGO, SPAIN

l tual Inventor: Roman Yarza Luaces

0:0 00:

dress for Service: Ad* EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, .61STRALIA, 3000.

Complete Specification for the invention entitled: "PROCESS FOR ELIMINATING DENSIFICATION OF THE BOTTOM AREA DURING THE MANUFACTURE OF BLOCKS OF POLYURETHANE FOAM"

The following staternent is a full description at this invention, including the best method of performing It known to :US:

N l. J.J- I

I OBJECT OF THE INVENTION

The present invention relates to an important improvement

0 obtained in the manufacture of blocks of polyurethane foam.

4M Specifically, it relates to obtaining blocks of polyurethane 00 t- foam which do not havr the densified bottom of the blocks i I

S* 5 obtained by the usual process. S* S

0*

S* STATE 0F THE ART *5 S

o* 4 As is known, polyurethane foam is a plastic which has i o@

acquired increasing importance over recent years. It is. a *OS

10 product of many uses in such different industrial sectors

such as, for example, the automotive industry and the textile' o S S 0 industry. In Spain, the distribution of consumption of poly- o urethane foam is represented by the following approximate 0

percentages: •So•• Upholstery

S.b Mattresses 38% o• Automotive 146 es

Textile industry Others (containers for foods, toys, etc.)

TOTAL 100%

I

Polyurethane foam is basically the product of the re-

action of a polyol with a polyisocyanate, which are the

principal ingredients. Other products are also necessary,

such as water, catalyst, activator, blowing agents, dyes,

etc. As is known to experts in the art there is a great

PR variety of types of foams, which is the result of the possi-

bility of variation in the nature of the various components Cli t- of which they are made, and in their relative proportions. C% Among mne characteristics which can be varied, according to

the selection of components and proportions, are stiffness,

density, resistance to degradation, tensile strength, cell

size, etc. Among the parameters involved, of special import- 0*

ance are the nature of the polyol and of the polyisocyanate,

and the ratio between polyol/polyisocyanate/water/blowing agent.

Industrially, polyurethane foam is obtained in the form of blocks. These blocks can have a length of even more than

100 metres, their width normally being 2 metres and their

height varying between 80 cm and 130 cm. The shape of the

cross-section of the blocks of foam obtained by the convent-

ional process is represented in Figure 1 of the drawings,

Swhich shall be described below on in this specification.

Independently of the type of foam produced, a serious S

problem associated with the manufacture of the block is the densification occurring in the bottom thereof. As a result

O of this densification it is necessary to waste an important

part of the finished material, because its density is notably

greater and its mechanical characteristics are very much in-

ferior to those of the rest of the block.

As experts in the art will admit, frea ently the percent- age of the densified area comes to be 5% by weight, even reaching in relation to the total weight of the block. The disadvantage supposed by obtaining blocks of foam having a densified bottom is obvious, if the following fac- tors are considered: a) The amount of wasted raw material can be of consider- able importance, in light of the fact that the daily product- ion of an average-sized polyurethane foam installation exceeds 20,000 kg. b) There is the added cost of trimming with proper mech- anical means, preferably saws designed specifically for this purpose, the densified layer of foam which can have a length of more than 100 metres (the length of the block), a width of two metres and a thickness of 10-15 mm. •oS c) The difficulty of marketing said trimmed densified

S layer as a by-product. S 00 d) Since an important part of the components of the foam is of petrochemical origin, the need is readily seen to econo- *•oO mize those materials to the maximum considering the present high cost of petroleum and its derivatives. It is deduced from the foregoing that the object of ob- taining blocks without the lower densified area is highly desirable for the polyurethane foam industry. The preceding problems and inconveniences are solved by the process of the invention which provides a block without the densified area, thus attaining notable utilization of the raw materials and a substantial saving in manufacturing costs.

BPIEF DESCRIPTIEON{ 0F TIE', 1RAWIIGS

In order that the invention may be better understood,

drawings are accompanied in which:

Figure 1 illustrates the cross-section of a block of foam

as obtained by the conventional process.

Figure 2 is a schematic side view of the installation

a for producing polyurethane foam blocks in which the invention

0C is carried out; and finally oO t- Figure 3 is a graph showing temperature in 20 on the ver-

tical axis, and time on the horizontal axis. The horizontal

length 00' represents the time during which, with the endless

conveyor belt of the foaming tunnel in operation without any feed- ing of the components of the foam, a hinged element thereof passes *0*

from ambient temperature to a value Tp. The length O'O" represents the time during which said endless belt remains stopped. The length

15. O"B' represents the time it takes an element of said belt, upon oS S which foam is being formed, to pass through the foaming tunn'?l. Finally, the length B'G' represents the time it takes an element of the block of foam to travel the distance between the end of the foaming tunnel and the end of the drying area. BRIEF DESCRIPTIONT OP THE PROCESS OF THE PRIOR ART

With reference to Figure 2, the following is a descrip-

tion of the conventional process for manufacturing blocks of

polyurethane foam. The fundamental parts of the installation

are: A foaming tunnel constituted by an inclined conveyor belt

1, formed by hinged plates P, the upper or conveying run of

said belt constituting the floor of the foaming tunnel. The

rest of said tunnel is formed by walls 5 and the roof T, in

which as may be seen in the Figure there are three conduits i 5 for evacuating the gases which are formed and/or released during the reaction, such as CO2 and the blowing agent. In the upstream part of the foaming tunnel there is a mixeafeeder head MA, in which the various components of the foam are mixed in the proper proportions and then fed to the endless belt.

6C Situated beyond the endless converyor belt, the upper 00 or conveying run of which constitutes the floor of the foaming

C4 tunnel, are several drawing conveyors, represented as 2 and 3

in Figure 2, which draw the foam formed in the foaming tunnel

to an arrangement of idle rollers 6, from which the block of

foam E is then cut and stored.

A web, which moves over the surfaces of the conveyors

1, 2 and 3 and has the same width as said conveyors, is interposed between the mass of foam E and said surface of

the conveyors. Said web, fed from a supply reel 4, moves at

the same speed as conveyors 1, 2 and 5, and Ls removed by a

take-up reel The web can be of paper, polyethylene film

or any other material which has the necessary properties

of strength, stiffness and resistance to rupture. The need for said web, which for convenience will hereafter be called "paper web", is because as has already been said,

the moving conveyor does not have a continuous surface but

rather is formed by a plurality of hinged plates having a

space between them. Thus the indispensable need for a web

of paper or of other material is easily understood if it is borne in mind that the foam ingredients deposited at

the start of the tunnel are liquid at the moment of mixture

in the mixer-feeder head, so that without the paper web said

I- -6'

mixed liquid would pass into the hinges of the endless con-

veyor belt.

With respect to Figure 2 just briefly described, it must

be noted that:

1) it represents merely a schematic representation and

does not include all elements such as reactant tanks, pumps,

conveyor drive motors, etc.

2) in the installation in which the conventional process

is carried out there are no elements as are represented here

by S1 S 2 and S 3 which constitute an aspect of the present

invention which will be described farther on in this descriptive o* SO o* specification. This means that conveyors 1, 2 and 3, as well as

the arrangement of idle rollers 6, are contiguous and do not 0@• have the separations or spaces between said conveyors as shown

in Figure 2. 0*

In the said installation, oce operation commences at the

programmed speed, conveyors 1, 2 and 3 as well as the devices OS

for supply 4 and take-up 4' of the weA, the liquid mixture of reactants is fed at the proper flow rite from the mixer-feeder

head MA, and the liquid mixture of reactants is deposited at the 0Oe S upstream end of the foaming tunrel 'atA,upon the web 6f mater-

ial which moves along with the floor of said foaming tunnel.

At the moment of its deposit the reactant mixture is a vis-

cous liquid which progressively reacts exothermically, in-

creasing its volume and forming the block of foam. This phase

of formation of the foam is represented in Figure 2 by an

ascending curve the position of which varies from one type of

foam to another, so that point C of the tunnel surface, which

corresponds to the projection of the end of said ascending curve, can be moved to the right or to the left of its posi- tion in Figure 2, depending upon the reactivity of the formu- lation. After attaining its maximum height the formed block grows progressively in length, being drawn by the movement of conveyors 1, 2 and 3. Upon passing the. last of the drawing G conveyors, represented by 3 in the Figure, and the paper web

Shaving been removed, the block is cut into pieces of varying 00 size and after a curing period of 24 hours is stored.

The cross-section of said block is represented in Figure

1, in which can be seen the densified bottom area P whose under

surface is not smooth. Therefore said densified bottom F must

be trimmed to remove the densification and surface irregulari-

ties, with the inconveniences this supposes as explained above.

L DETAIL13D DESCRIPTION CPF TIE INVENTION The improved process of the invention comprises, as a first

step, running the endlesa conveyor belt of the foaming tunnel

without any feeding of the components of the foam, and raising

*o 0oo-- the temperature of the enclosure of said endless conveyor belt.

.1"20 The result of this heating is that the temperature of the upper portion of the belt forming the floor of the cited foaming

tunnel passes, in. a period of time ranging between 0 and

minutes, from room temperature (T to a temperature (Tp) *a p of about 802C. This temperature variation is represent-ed in "Ai the left part of Figure 3.

The movement of the endless conveyor belt is then stopped for

a proper period of time, the paper web~is placed on the belt to be

interposed between the plates of the belt and the block of foam,

and the in the upstream part of the said foaming tunnel the mixtLne

'8 :i I

of the readtants which create the foam begins to be fed through the

mixer-feeder head onto the paper web. During this period when

the belt is stopped the temperature drops from Tpto a value called

reaction temperature TR, fixed for each type of foam, at which

moment (point A of Figures 2 and 3) movement of the endless

belt is resumed, and simultaneously the devices for feeding

and taking up the paper web are activated.

Commencing from this moment, the temperature of the sur-

face of the upper portion of the endless belt of the foaming

:io tunnel which is substantially the same as that of the con-

tir As paper web and consequently substantially equal to that 6@O* 0* of the bottom part of the block of foam in formation which S S.

SO 6S 0 rests upon said paper web is regulated so that f" a first S. 6 0e area called the reaction area the aforesaid value TR is main-

15 tained, and in a second area downstream of the first, called S the consolidation area, a value superior to TR is maintained,

hereafter called T

In at least one area downstream of the foaming tunnel,

the bottom of the consolidated moving block is subjected to a

20. drying temperature called Tg as it passes through a drying 0 area. In Figure 2 three drying areas are represented as S1, 82 and S3. 0

Following the drying process, the paper web is taken up

S and wound onto the take-up device and adhered to it can be 0 seen a thin uniform layer o' foam. The block passing to the

idle rollers has a bottom with no densification and a smooth

and uniform aspect which doe., not require trimming, an indis-

pensable operation in the process of the prior art.

The foam in formation runs through the first area, the

'reaction area situated upstream of the belt, in a previously determined time which varies from one foami to another. As has been indicated, in this area the surface of the endless belt is held at a constant temperature which also varies from

one foam to another. The time it takes the foam to traverse the consolidation

area depends on the predetermined time in the reaction area. The fundamental parameters constituting the object of the invention are defined as follows: TR Surface temperature of the reaction area. To= Surface temperature of the consolidation area. T= Surface temperature of the drying area. tR The time it takes an element of the endless belt, or the bottom part of the paper-lined block which rests on it, so 0: to traverse the reaction area; that is, from point A to point C represented in Figures 2 and 3 of the drawings.

@0 t= The time it takes the aforesaid element to traverse the 00 consolidation area; that is, from point C to point B 0

shown in Figures 2 and 3 of the drawings. *oo* tT =The tine it takes the mentioned e~ement to traverse the floor of the foaming tunnel; that is, from point A to *00 point B showrn in Figures 2 and 3 of the drawings. If it is borne in mind. that the floor of the foaming tun- nel traverses the reaction and consolidation areas, it is readily seen that tT =tR 4- t 0 i and sinace the value of t is predetermined for each type of foam, it is deduced that

to= t2 (2)

While the values tR and TR are fixed for a given foam, they vary from one foam to another, since as experts in the

art will understand the exothermicity of the reaction of polyurethane formation varies according to the nature of the principal ingredients, and of the ratio between them. As was indicated previously, the principal ingredients are polyol 00 and polyisocyanate. However, the percentage of water in the Smixture has an important role. A fundamental characteristic of the improvements obtained with the present invention is that the surface temperatures of the three areas fulfil the condition

TC TS

In general, the difference T. TR T ranges from between 10 and 152C, about 102C being preferable. A temp-

erature inside the fomning tunnel in the reaction area above a maximum limit can cause cracking of the foam, and even its combustion. Keeping in mind that this cracking temperature varies from one formulation to another,between approximately

•O o 45 and 8090, we have

TR TC 8020 SS

5: The temperature of the drying area T S can attain apparent- "250 ly high values, rangirg between 100 and 2502C, in very short periods of time. This is not in contradiction with what was said above with respect to cracking and/or combustion, if it is kept in mind that said surface drying temperature is pro- duced in an area outside the foaming tunnel, which is trav- ersed by the block in a very short time.

Although in the foregoing only one drying area has been

mentioned, the invention is not necessarily limited to only

one area of this type and several can exist, although practi-

cal reasons limit this number to three. Nevertheless, a single

drying area is the most preferable.

As a &onsequence of the difference in the mentioned three

thermic levels, once the drying area is passed and the paper

web is removed, a block is obtained having no densified bottom

and a smooth and uniform surface, a thin and uniform layer of

foam of a density similar to that of the rest of the block

having remained adhered to the paper web.

The length of the belt 1 which constitutes the reaction •@O area is represonted by AC, CB being the longitudinal edge of

the consolidation area. From the foregoing it will be seen g that the location of point C, although fixed for a given type o•0

*oo0 0 of foam, varies from one foam to another and can be to the *o •o right or to the left of the position shown in the Figure.

Beyond the foaming tunnel itself three drying areas can

be seen in Figure 2, represented by S 1 S 2 and S3. Said drying

areas -re generally narrower in width than the other two areas,

the width (or what is the same thing, the time it takes a cer-

tain element of the consolidated block to pass said drying area)

being related with the temperature in inverse ratio. That is.

a relatively narrow drying area (or its equivalent, a short time in passing that area) will require a high terperature and

vice versa. Figure 3 illustrates the temperature variation of a surface element of the foam block bottom with respect to time. In said

Figure 00' is the operation time of the belt of the foaming tun-

nel without any feeding of the components of the foam and 0'0" is

the stopping time of said belt, TR, and tR, t and Tt having

the previously indicated meanings.

It can be easily seen that the transition of the tempera-

ture between the reaction and consolidation areas is not sudden

and thus the inclined length of Figure 3 exists, point C being

at a temperature which can be considered as intermediate between

TR and T C Once the plate element of reference has reached the point of return, the part of the block bottom in contact with

said plate of reference undergoes, if the drying area S 1 exists,

SU a rise in temperature until the valrv TS1 is reached. If the 4 C' drying area lies downstream, for example at S 2 or S the tempera-

ture of the block commences to diminish, tending to equal that S of the atmosphere. The dotted line represented by BF would be

the variation of the temperature with respect to time if there

were no drying areas. It is also seen that the farther away the *0 foaming tunnel, the higher the temperature will have to be in 0 S the drying area to counteract the decrease of the consolidation *006

temperature. Naturally, once past the drying area the tempera- 6

.9. ture of the block surface will diminish from points D, E or G

C0 of Figure 3 to ambient temperature. S 2 The removal of the paper web being one of the important

aspects of the improvements obtained with this invention, it

must be noted that while in the foregoing reference has been made to paper as the most coimmon material used for the web inserted between the block of foaa in forma.tion and the rectangular hinged plates which form the endless conveyor

belt, any other weblike material can be used which fulfils the same function.

The following is an example of how commercial polyurethaie

foam can be obtained in accordance with the improved process of

this invention. This example is given only for the purpose of

illustration, and in no case must be considered limitative.

Feeding .is made from the mixing head, in an operation as co previously described, of a composition constituted by the foll- oo lO owing materials in the amounts as indicated in parts by weight:

Polyol 100

Toluenediisocyanate 51.3

Water 4.1 S000 I i 00 Dimethylaminoethanol 0.4

Silicone 1

Freon-11 6

0 Tin octoate 0.2

Dye 0.3

The temperature of thn reaction area is maintained at a

value TR= 41.52 120 and the temperature of the consolidation

area at a value T 51.59 4 120, with a time tR 2 to 3 min-

ute in the reaction area and a time t 3 to 2 minutes of 0 0O permanence in the consolidation area. A block is obtained which

after being subjected to a temperature of 1200C in the drying

area, and the continuous paper web having been removed from the

*bottom, has a substantially uniform density throughout its vol-

ume of 20 kg/m 3 that is, without any densification In the bot-

tom and without 'iregularities, and which does not need trimming.

The following shows, by simple calculation, the economic

advantages of the process of the invention.

An average-sized plant produces foam 200 days of te year and in each foaming produces a continuous block of 20 Tm, or in other words its yearly production is 20 x 200 4,000 Tm 4,000,000 Kg. Operating in accordance with the conventional process and supposing an average value of 4.5% in weight for the densified bottom, we have:

0 Yearly production of dense foam

4,000,000 X 0.045 180,000 Kg. St Yearly production of foam of uniform density

p 4,000,000 180,000 3,820,000 Kg. A plant of the same size working with the process of the

present invention, and estimating as 0.5% the percentage in weight of the thin layer of foam adhered to the paper web, would have a yearly production of foam of uniform density of:

S. 4,000,000 (4,000,000 x 0.005) 3,980,000 Kg. This means that with the process of the invention yearly output would increase: -3,980,000 3,820,000 160,000 kg/year It is deduced from this that the advantage of the system S

consists of manufacturing 160,000 kg of foam without any cost of raw mater.ials. Added to this saving would be the cost of power,.labor, etc. necessitated by the trimming, storage and sale of the dense foam.

Claims (9)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. Process for eliminating densification of the bottom

area during the manufacture of blocks of polyurethane foam, characterized in that: the endless conveyor belt of the

Sfoaming tunnel of the foam-producing installation is made to

co function for a period of time of between 15 and 90 minutes,

G at the same time as said endless belt is heated, so that the surface temperature of the upper portion of said belt, which @go

constitutes the floor of the tunnel, passes from room temp-

erature to a temperature Tp of between 60 and 802C; the 0 movement of the endless belt is stopped, a web of material, pre- ferably paper, is placed on the belt to be interposed between the

foam and the plates of the belt, and immediately feeding is

begun from the mixer-feeder head of the mixture of the react- ants constituting the foam upstream of said endless belt, the

temperature during this stopped period decreasing from the value T P to a value TR; at the moment the value TR is attained the

endless belt is again put into motion, operation is started of the devices for supplying and taking up the web of material, preferably paper, which covers the surface of said

endless belt, controlling at the same time the temperature of the surface of the upper portion of the belt forming the floor

of the tunnel so that in a first reaction area situated upstream

of said endless belt it acquires a constant value TR, and :Ln a

second consolidation area another constant value said temp- erature values being constant for each type of foam, and in that

the tirme said temperature is maintained for each type of foam

is detormined by the ratio tT tR 4 t t T being the total time of pormanence of the foam in the reactior. tunnel, tR being the time it takes a foam element to traverse the reaction area, a fixed value for each type of foam and t C being the time it takes a foam element to traverse the consolidation area; and in that after leaving the foaming tunnel the block in for-

5 mation undergoes, in at least one area located either before

the drawing conveyors, between them or after the last of said oo conveyors which constitute the drawing means, drying in the *0100 lower part of the block in a so-called drying area which is

c held at a constant temperature TS notably higher than TR and

**10 TC, after the passing of which removal is made of the web of material, preferably paper, to which is adhered a thin film 0

of foam, thus obtaining a block of polyurethane foam having no

densified bottom and a uniform surface which does not require

final trimming. 0

0

2. Process according to claim 1, characterized in that

the difference of temperature between the area of consolidation

and the area of reaction of the AT Tc TR is 152C maximum, preferably 100C. 0

3. Process according to the preceding claims, character-

ized in that the web of continuous material is selected from

among paper or other material which resists the high tempera-

tures of the drying area and has the necessary characteristics

of resistance.

I

4. A process for eliminating densification of the

bottom area of a block of urethane foam during manufacture,

substantially as hereinbefore described with reference to

the accompanying drawings.

0

5. Apparatus for use in eliminating densification of o0 the bottom area of a block of urethane foam during

manufacture, which apparatus comprises

a foaming tunnel the base of which is constituted by at

least a part of the upper portion or run of an endless .0 conveyor belt;

means for heating the endless conveyor belt;

means for feeding a web of suitable material on to the

endless conveyor belt;

means for feeding the reaction mixture on to the web at

a location upstream of the foaming tunnel; 0@

one or more drawing conveyors located downstream of the 6

foaming tunnel for drawing the block from the foaming

tunnel;

drying means located downstream of the foaming tunnel for

drying the block at a temperature which is higher than

the temperature in the foaming tunnel; and

means for regulating the temperature of the base of the

foaming tunnel so as to provie, in an upstream zone of

the tunnel, a lower temperature than the temperature in

a downstream zone of the tunnel, the upstream and

downstream zones corresponding to the reaction and

consolidation zones, respectively, of the block.

.9

6. Apparatus for use in eliminating densification of

the bottom area of a block of urethane foam during

manufacture, substantially as hereinbefore described with

reference to the accompanying drawings.

00

7. A block of urethane foam whenever produced by a 00 0*O process according to any one of Claims 1 to 4 or with the aid "0

0O 6 of apparatus according to Claim 5 or Claim 6. 00

*0

00

0 0000 0 *00

Dated this 20th day of DECEMBER, 1978 00 06*

*0 cV

TECFOAM S.A. 0 0

e

0*0

EDWD. WATERS SONS, Patent Attorneys, Queen Street, Melbourne, Vic., 3000, Australia.

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