CA1048699A - Polyisocyanate foam having isotropic cells and method and apparatus therefor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

A polyisocyanate foam having isotropic cells is manufactured by foaming operation in an apparatus comprising a mould composed of side walls capable of extending and retrenching or folding and unfolding perpendicularly to free rising direction, a detecting means, if desired, and a mould extending means provided on the respective side wall which operates to spread out the mould perpendicularly to free rising direction. Foaming in the free rising direction proceeds in a creamy state up to the position of the means in the unopened mould and then, foaming perpendicularly to free rising direction continues during a period of time from a creamy state to a tack-free state while the mould is spreading out, whereby isotropic cells are formed.
The so-manufactured foam has high dimensional stability and is suitably for insulating materials, especially low temperature insulating materials.

Description

` 1~48699 ~ his invention relates to a method of manufacturing a polyisocyanate foam having isotropic cells which has physical properties homogeneous in all the directions irrespective of foaming direction and good diMensional stability a~ an appropriate apparatus for carrying it into effect. Moreover this invention relates to a foam product having a homogeneous physical propertieq.
` There have heretofore been Icno~n1 and been put into practice various many arts on a method for shaping a polyurethane foam and an apparatus thereof, accordin`g to which the thus shaped ~0 foam has usually elliptic cells having a long diameter in the foaming direction, as known well. It is also well known that different physical properties of a polyurethane foam varying dependent upon foaming direction are ascribable to the cell structure.
~ ecause of this, various investigations have been conducted concerning alteration of such cellular structure, namely a method and apparatus for shaping a polyurethane foam to be isotropic cell structure, and for example, USP 3,249,486 and -Japanese Patent Publication 28,781/1973 are proposed as such.
However, according to those methods above in which a moulding container for a foam is provided with a lid on it or a flat plate for pressing the top face of a foam is placed, whereby the foam is extended also in a side wall direction of the container by compulsory pressing of the top portion of the foam and thus, isotropic cells are formed, a foaming pressure imposed upon the entire moulding container is naturally great, so that problems to be overcome in respect of construction of a moulding container in respect of construction of a moulding container and of mold releasing persisted.
In view of the above, the present invention prov~des a novel method of manufacturing polyisocyanate foam ha~ing an isotropic cell structure, in ,, ~ .

1~4~f~99 which the foam i5 obtained with a simple and light weight molding container and in a shortened mold~releasing time.
This method comprises the steps of placing a charge of a liquid polyisocyanate foamable composition into a mould cavity, allowing the composition to rise freely in one direction Z in the mould cavity by expansion during foaming and, while the composition is still fluid and rising, positively extending the size of the mould cavity in two mutually perpendicular directions X and Y perpendicular to said direction Z of free rising of the composition, to an equal extent in the two direc-tions X and Y and in rQsponse to the rising height and/or to the foaming rate of the composition in said free rising direction, so as to permit the composition to expand in said three direc-tions X, Y and Z to form an isotropic cell structure.
The present invention is also concerned with the polyisocyanate foam obtained by the method according to the invention, which foam is characterized by having substantially isotropic cells and physical properties; an apparent density of 0.025 - 0.015 g/cm , and a dimensional change index in every direction referred to ASTM D-2126 of within 5% at 70C, 95RH after 48 hrs. and that of within 1.5% at -20 C after 48 hrs.
Accordingly, the first aspect of this invention resides in the production of a foam having homogeneous physical properties.
The second aspect of this invention resides in the foam per se.
A third aspect of this invention resides in the construction of an apparatus for carrying out the method according to the invention.
Polyisocyanate foam as used in this specification means polyurethane foam, polyisocyanurate foam, polycarobodiimide foam etc. including isocyanate group as starting material of foam product. However, the present invention will only b~ explained with reference to the polyurethane foam, as below.
~ - 2 -B

1~48~99 The manufacturing process will be explained below wherein polyurethane foam having isotropic cells is obtained by positively spreading out the mould in X and Y directions.
In general, a polyurethane foam irrespec:tive of rigid or semirigid is produced as follows: after a foaming composition is mixed and stirred, it commences to foam in a creamy state in a few seconds to a few minutes; the composition is gradually increased in viscosity to be a so-called tack-free state in which even if a hand is touched on the foam surface the foam .s no more sticky in a few minutes to several tens of minutes; and thereafter, '

- 2 a -.

1~48~99 the fca~ing process is completed in a further few seconds to a few minutes. Here, the cell form of a foam is determi~ed during a period of time when the foam becomes from a creamy state to a taclc-free state, but it is almost not influenced during a period of time when the foa~ becomes from a tack-free state to a completea product since the foam volume is increased only in a few per cent~.
For this reason, it is essential in this invention to alter the cell form of a foam during a period of time when a foaminO
composition has fluidity before it becomes tack-free, for the pu~l)ose of which the cells of a foam are modified so that a pressure ~ay not be almost exerted upon around a foaming foam while the four sides X and Y directions of a moulding container are made free.
~hus, since the upper part o the moulding container is opened and the foam has fluid~ty as mentioned above, the foaming pressure of the foam during this time is very low and is of only a self-weight of the foaming composition, with the result that it is possible to obtain easily a polyurethane foam comprised of isotropic cells while making the four sides of the mould nearly free with a simple ~ig. :-The foam having isotropic cells thus obtained according to this invention has an appearance nearly similar to the prior art foams, but superior physical properties to them and can be manui`actured in a very short time, which fact leads to enhancement of productivity. It is noteworthy that the foam obtained in this invention has a good dimensional stability and accordingly, it is possible to lower greatly specific gravity of the foam in response to object for use. Consequently, great reduction of cost can be expected owing to the reduction in specific gravity, coupied with shortening in time of mould releasing.
In this invention, the idea of making the cells of a foam nearly completely isotropic form is based on the ground that foaming process, namely foam rising is carried out in the lateral 1~)48~99 direction as well as in the longitudinal direction, with the rat o of both the foaming directions being appropriately regulated, and an effective means for it is thus proposed.
The invention will be further described in greater detail by way of example with reference to the accompanying drawings in which: -Fig. 1 shows the sectional view of the free rising direction in conventional foam;
Fig. 2 shows the sectional view of the free rising direction of the foam in the present invention;
Fig. 3 is a perspective view showing schema of an outer mould of a foaming container in one example of this invention;
Fig. 4 and Fig. 5 are a perspective view showing portions of an inner mould, the essential part of this invention in which Fig. 4 is an inner mould and Fig. 5 is a bottom plate;
Fig. 6 is a perspective view of an inner mould after -foaming is completed and ~ig. 7 is a perspective view showing a situtation of an inner mould before a foaming composition is poured therein;
Fig. 8 is a plan view showing a situation that an inner mould is unopened or contracted and put in an outer mould;
Fig. ~ is a fragmentar~ sectional view showing a situa-tion when an inner mould and an outer mould are fitted just before a foaming composition is poured; and Fig. 10, Fig. 11 and Fig. 12 are views showing process steps of manufacturing a foam according to this invention in that order.
Fig. 13 and ~ig. 14 are perspective view of the mould used in the present invention and which show the other examples.
~ig. 15 is an outlined plan of the mou].d used in the present invention and which shows the other example. ~
In the preferred embodiments of this invention a~ herein~ -- 4 - ~

~ 6~4~99 a~ter described, a double mould in which outside the essenti.al moulcl of this invention an outer ~lould i5 used will be sho~m.
Howe~er, in this invention, the outer mould need not be necessarily used bu-t is inessential. It goes without saying that use o an outer mould is included in a scope of thls invention.
As shown in Fig. 1, the profile of the conventional ce'l is an ellipse with ~ajo- axis in Z direction due to the insufficient expansion in X and Y directions compared to that in ~ direction.
~i~. 2 shows the profile of isotropic cell of the foam manufactured in accordance with the present invention wherein the expansion in X and Y directions are the same level as in Z direction.
Now, referring to Fig. 3, one example of an outer mould (A) is shown, whereas in Fig. 4 one example of a mould (B) essential in this invention (hereinafter designated to as an inner mould) is illustrated in which Fig. 4 and Fig. 5 are a side wall (3) and a bottom plate (4), respectively.
` ~he outer mould (A) is so formed that side plates (1) can be opened outwards, for exa~ple in the arrow direction of the figure, and inside the outer mould is provided a roller conveyor (2) for making possible to readily put and remove the inner mould (~) hereinafter disclosed.
On the other hand, the inner mould (~) is co~posed of a main body having side walls (3) capable of being folded and retrenched as shown in Fig. 4 and a bottom plate (4) having a spacer (5) projected thereon which conforms to the bottom opening when the main body was folded and contracted, that is to say it became a state of Fig. 7 lest a foaming composition should not leak therethrough. In one example of construction that the main body is folded and contracted, pieces of the side wall are ~0 mutually fixed with hinges (7) as shown in Fig. 6.
~ he reference nu~ber (8) shown in Fig. 6 is ~etal fittings capable of disjointing the side walls (3) of the inner :

1~4~99 m~ d (~) in order to re~ove them from a foam produced after finls:n of the foaming process.
~ hen the inner mould (B) thus constructed is put in the outer mould (~), the former is folded and contracted in such a state as shown in ~ig. 7. ~his situation that the inner mould is put in the outer mould is sho~m in ~ig. 8, in which in the center part is formed a space a for injecting and holding a foaming composition therein and in the periphery thereof is formed a space b having a distance marked in the arrow of the figure and necessary to make the foam cells isotropic. In this connection, it is preferred and suitable that the central space a has an area of about 1/3 to 1/4 of the area of the space shoYn in ~ig. 6 from the viewpoint of formation of isotropic cells and of opening and contracting operation of the inner mould (B).
~ ig. 9 shows a construction of apparatus for carrying out foaming operation by the use of both the outer mould (A) and the inner mould (B) hereinabove described. Here, a cushoning material (9) having a thickness of ca. 5 to 10 mm is preliminarily sticked on the bottom plate (4), on which the spacer (5) is mounted and a mould-releasing paper (10) is further covered on the side walls (3) and the bottom plate (4) for the convenience of repeated use of the inner mould (B).
A suitable material which may be employed as the side wall (3) or the bottom plate (4) includes for ex~mple, a pl~Yood of a thickness of ca. 15 mm and a metal plate of the s~me strength.
~he tickness of the spacer (5) will suffice to be in the neighbor- -hood of 5 mm.
Besides, as shown in ~ig. 9, a holding plate (12') is pro~ided in contact with the outside of the side walls (3) of the inner mould (B) and Joined to a mould extending means (12) ~hich is operated to inform the timing for spreading out and shifting the inner mould (B) in the opening direction.
.

~ he mould extending means (12) is fixed picrcing through a side piece of the outer mould (A) in the iigure, but the outer mould (A) may be only a side frame capable of supporting the means.
~he means may be used in oil pressure system or screw system.
Operation of the mould extending means (12) is connected to a height detecting means (11) of contact-detecting type like limit switch, for detecting the height of the foam surface which is disposed in a specified position above the pouring space a, and by the operation of it the side walls (3) are opened and unfolded out~ards, namely in X and Y directions.
It i9 preferred that the detecting means (11) is so constructed that it is interlocked with the mould extending means (12) and operates automatically to spread the inner mould (B) out and that it can be pivoted or moved up and down so as to be removed immediately after the foam hardened.
The method of this invention is carried into effect by the use of the outer mould (A) and the inne~ mould (~) thus constructed. ~he invention will be hereinafter disclosed more concretely concerning manufacturing process of a polyurethane foam having isotropic cells.
First of all, as shown in ~ig. 10, a foaming composition for polyurethane in an amount sufficient to fill a space of the final volume as shown in ~ig. 12 is mixed, agitated and poured into the space a. Soon after a few seconds to a few minutes, the composition thus mixed commences to foam in a creamy state.
A foam comes to expand up to the height of the detecting means (i1) such as a limit switch which is located above the space a.
~his step so far is not particularly different from the conventional procèss of manufacturing a foam and the cells being thus formed are eiliptical, with the liquid composition having still fluidity.
~en the foam expanded up to the height of the detecting means (11), as shown in Fig. 11, the mould extending means (12) slide ~ 4 ~ ~ 9 9 ~
outwards, in response to which the side ~alls (3) of the irmer mould (~) go to open arld unfold in the X and Y directions gradually while ascertaining the height of the foam by the detecting means (11) and retaining it homogeneous, whereby the previous foaming in Z direction is changed to the foaming in X
and Y directions as mar~ed in the arrow and at the same time, the cells of the foam begin to be formed isotropic.
~ }le foaming in X and Y directions continues to proceed till the side walls (3) become the state of ~ig. 6 (cf. ~ig. 12).
~hus, when the foam beca~e a state that foa~ing no more occurs ~udging by appearances with the naked eye, it is released from the mould as a~ finished product.
~ ~hus, according to this invention, the foam product can be obtained that is composed of nearly isotropic cells and has homogeneous physical properties in all the directions because the subsequent foaming in X and Y directions takes place by auto- -matic actuation of the mould extending means interlocked to the height detecting means. ~urthermore, mould-releasing time of the foam can be exceedingly shortened since the foaming pressure is difficult to be exerted upon the foam itself at the side face. In this con~ection, the conventional foam was cracked when released -from mould owing to an inner stress occured in the side foam if it had not been kept to stand in a moulding container for 20 to 60 minutes at room temperature after finishing of the foaming process.
In contrast, according to this invention, even if mould-releasing is conducted in one or two minutes after foaming was finished, the foam thus obtained is not cracked Accordingly, it is advantageous in this invention that number of the foaming container to be required may be less than 1/10 in comparison with container number of the conventional methods.
hs a mould in the apparatus in this invention other moulds than those described so far and sho~n in ~ig. 4 and ~ig. 8 1¢3 4~99 ~ay be available, for example, the mould having bellow side wall (refer to Fig. 13 and Fig. 14) or one with four foldable corners (refer to Fig. 15). In such cases, mould extending means are preferably secured to the four corners and the process comprises pouring the foaming composition into the mould when it i9 shrinked indicated by line (21) and (23) and then spreading out the mould to the desired position (shown by line (22) and (24))in X and Y directions in response to the operation of height detecting means (11) (not sho~m on the Fig.) in Z direction; thereby poly-urethane foam having isotropic cells can be obtained.
~ he present invention will be further illustrated by the following non-limitative examples.
Example 1 Five kinds of compositions ("A" solution) were prepared as in the following table:

Ingredient 1 2 3 4 5 Polyether (sucrose delivertive: OH 60 60 60 60 60 value of 450) Polyether (sucrose delivertive: OH 40 40 40 40 4o value of 550) . .. .
Surface Active Agent (silicone) 2 2 2 2 2 , . . . . .. _ _ Amine Catalyst 0.4 0-.4 0.5 0.7 1.0 . . _.
Foaming Agent (Freon 11)~ 41 41 4~ 54 60 . _ ~otal 143.4 143.4 150.5156.7 163 lhen, to the respective "A"solution above is added 130 parts of prepolymer (sucrose polyether isocyanate), and the respective mixture is stirred. Five kinds of polyurethane foams were thus produced having different specific gravities.
trademark , _ 9 _ .~.''~.

` ` 1~48699 ~ he comparative test results of physical properties on them are shown in Table 1 given below. In the table, No. 1 is a polyurethane foam manufactured by the conventional art whereas No. 2 to No. 5 are polyurethane foams manufactured according to this invention. Size of the sample foam is 500 x 1000 x 2000 mm Table 1 ~o. Specific Direction !Compressiv~ _ Dimensional Change %
Gravityof Measure- Streng~h100~C 70C I -20C
of the ment (Kg/cm )48 hr. 95~ RH 48 hr Foam Core . 48 hr.
(g/cm3) 1 0,0291 L 0.88 +2.44 +4.63 _0,30 // 2.13 -1.20 -1.09 -0.45 . ,, , 2 0.0284 l 1.38 +0.~4 +2.49 -0.29 // 1,42 +0.50 +1.23 -0.30

3 0.0270 l 1.29 +0.7~ +2.70 -0.23 /t 1.35 -tO.83 +2.00 -0.23 ~ '.

4 0.0250 1 1.10 +0.96 +3.55 -0.10 // 1.15 +0.96 +2.30 _0.12 _ 0.0214 L 0.80 ~1.61 +4.67 -1.50 _ // 0.85 ~1.32 +3.40 -1.10 I ~:

Remark : Direction l : horizontal direction in Fig. 10 - 12 Directionll : up-and down direction in Fig. 10 - 12 Example 2 First, a composition solution was prepared in the following formula:
Polyether (aromatic series : OH value of 380) 30 parts Polyether (sucrose series : OH value of 450) 70 "
Surface Active Agent (silicone) 1 "
Amine Catalyst 1 "
Water 3 Foamin~ A~ent (Freon 11) 175 ,trademark ~ ,1 1~48699 Thereafter, to the compo~ition solution above was mixed and stirred 162 parts of prepolymer (sucrose-polyether isocyanate) to produce polyurethane foams both accordin~ to conventional method and the method of the invention. Comparison between both the polyurethane foams in physical properties was made and the results are sho~m in the following table:
Table 2 .. - . ~
Physical Properties Conventional Art This inve~ion ~pecific Gravity of the Foam Core 0,0170 0.0163 (g/cm3) Compressive 1 Strength 0.23 0.63 (kg/cm3) . Il O . 80 0.63 Dimensional -20C 1 -40.2 ~0.6 48 hr. Il -~.0 -0.6 70c 1 -2.0 +1.3 Change (~o) 95~oRH ~5.2 -0.7 . .
100C 1 ~3.5 ~0.8 4~ hr. ~' -2.1 -0.7 _ ~ ~ .
Water ab~orption 6.48 5.0 (vol. ~o) . _ Content of closed cens 76.3 _ .

rhermal Conductivity 0~0216 0.0190 (Kcal/mhrC) Remark : The directions 1 and ll are the same as in Example,l.
A9 will be seen from the tables below, the polyurethane foams obtained in accordance with this invention have superior physical properties almost equal both in the Z direction and in the X and Y directions to those of the conventionally manufactured foams~ that is to say it can be understood that the polyurethane 16)48~99 foa~ having i~otrnp c cell3 were obtained in thi~ inven-uion ~ he exa~lples ~o far show the methods of manufacturin~
polyurethalle foam having isotropic cells by ~preading out the mould in X and Y directions in response to the detecting means tvhich operates only when the foam rises to the specified height.in Z direction.
As mentloned above, the present invention compr ses spreading out the mould positively in X and Y directions in responsQ to the free rising height in Z dircction without recourse to the foaming pressure as in prior arts. In view of the philosophy of the present in~ention theObieCt can also be attained by positively operate the mould extending means in response to the foaming speed of foaming compo~ition. Thus it is a matter of course that the present invention comprises the modified examples as follows~
For an-~example, the mould extending means can be started to operate ~`~
in response to the operation of the rising height detecting means which starts simultaneously with or slightly a~ter-the begi-nning of expansion, In this case, the detecting means, unlike the case before mentioned, rises as the foam expands in Z direction up to the predetermined heigth with mould extending mean3 operating in response to it. After it reaches the predetermined height in Z
direction, it stops rising. It i8 possible to make mould extending means (12) continue to operate during the period of time when said height detecting means (11) is in contact with the foam sur~ace.
It may also be pO9 ~ible to make it a condition that the side ~a?l (3) of the mould is ~lightly bended inwards rather than completely opened at the finishing point of expansion as shoYrn in Fig 6, Furthermore, the mould extending mean~ can be independent-ly operated after the expansion begin~ under the condition pre-determined on the basis of preliminary -trial~ in response to - 12 - `

1~ 4 ~ ~ 9 ~
the rising height in Z direction and all of which can even be operated by programme restraint system, if desired. Although this method i9 inferior in accuracy to that mentioned before wherein the mould extending means operates by detecting directly the rising height in Z dlrection. It's possible to obtain the desired cell structure by proper control of the ambient temperature, humidity and quality of foaming compo~ tion.
~ he foam manufactured in accord~nce with the present invention i~ of low density and has improved physical property, especially high dimensional stability. Consequently the resultant ~oam is suitable for insulating material and yet the insulating exedution can be done economicaily. In sddition 'o that, the foam can take any form as in~ulating material such as plate, cube and circular arc-profiled form etc. and some other ~urface material can be laminated onto at leasts one surface of the foam such as paper, plastic sheet, ply~ood, asbestos, metal laminate etc.. Consequently, finished product will find so u3eful and wide ranged applications in the field of insulation industry.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of manufacturing a polyisocyanate foam having an isotropic cell structure, which comprises the steps of: placing a charge of a liquid polyisocyanate foamable composition into a mould cavity, allowing the composition to rise freely in one direction Z in the mould cavity by expansion during foaming and, while the composition is still fluid and rising, positively extending the size of the mould cavity in two mutually perpendicular directions X and Y perpendicular to said direction Z of free rising of the composition, to an equal extent in the two directions X and Y and in response to the rising height and/or to the foaming rate of the composition in said free rising direction, so as to permit the composition to expand in said three directions X, Y and Z to form an isotropic cell structure.

2. A method as claimed in claim 1, wherein the rising height in the free rising direction of the composition is detected.

3. A method as claimed in claim 1, wherein said extending of the size of the mould cavity is carried out during a period of time from the commencement of the tack-free state of the expansion of the foaming composition.

4. A method as claimed in claim 1, wherein said extending of the size of the mould cavity is carried out after the rising height in the free rising direction has reached a specified position.

5. A method as claimed in claim 1, wherein said polyisocyanate foam is a foam of polyurethane, polycarbodiimide or polyisocyanurate composition or mixture thereof.

6. A method as claimed in claim 5, wherein said foam is a rigid polyurethane foam.

7. A rigid polyisocyanate foam which is characterized by having substantially isotropic cells and physical properties:
an apparent density of 0.025 - 0.015 g/cm3, and a dimensional change index in every direction referred to ASTM D-2126 of within 5% at 70°C, 95RH after 48 hrs. and that of within 1.5% at -20°C after 48 hrs.

8. A foam as claimed in claim 7, wherein said foam is produced in accordance with claim 1.

9. A foam as claimed in claim 7, wherein said foam is a rigid polyurethane.