WO2001068734A1

WO2001068734A1 - A rigid polyisocyanurate foam

Info

Publication number: WO2001068734A1
Application number: PCT/EP2001/002895
Authority: WO
Inventors: Colin Nightingale
Original assignee: Kingspan Industrial Insulation Limited
Priority date: 2000-03-14
Filing date: 2001-03-13
Publication date: 2001-09-20
Also published as: GB2361700A; AU2001248351A1; GB0106320D0; GB2361700B

Abstract

A thermally stable polyisocyanurate foam, especially for pre-insulated pipes and fittings for carrying hot water or steam is formed from MDI and a tetrafunctional aliphatic caprolactone polyol in which the MDI index is from 300 to 1000, preferably 400 to 750 and ideally about 500. The tetrafunctional caprolactone polyol has a pentaerythritol backbone and contains only primary hydroxyl groups.

Description

"A RIGID POLYISOCYANURATE FOAM"

Introduction

The invention relates to a thermally stable polyisocyanurate foam, especially for use in relatively high temperature applications of typically up to 200°C. One use for such foam is in lining high temperature fluid pipes such as hot water or steam pipes.

Conventional systems for high temperature insulation- applications are generally of two types. One type is a polyimide foam such as that available under the brand SOLIMIDE from Inspec Foams. While this foam product has relatively high temperature stability it is expensive and its use is consequently restricted to specialised applications such as for the aerospace industry.

A cheaper more widely used alternative is a fiberglass based product which is difficult to manufacture and especially problematic in fitting to pipelines and pipeline fittings as it is difficult to cut, manipulate to a desired shape and leaves rough edges.

US 4,670,346 describes a process for preparing bifunctional or trifunctional polyisocyanurate polymer.

JP 60047013 A describes a method for producing a urethane-modifϊed polyisocyanurate foam having as essential components polyol, excess polyisocyanate compound, isocyanate trimerisation catalyst and foaming agent. The polyester polyol used comprises cyanuric acid ester which is aromatic and trifunctional. There is however still a need for an insulating material with relatively high temperature stability which will be relatively inexpensive and easy to use.

Statements of Invention

According to the invention there is provided a rigid polyisocyanurate foam formed from diphenylmethane diisocyanate (MDI) and a tetrafunctional aliphatic caprolactone polyol in which the MDI index is from 300 to 1000.

Preferably for improved thermal stability and physical properties the index is from 400 to 750.

Ideally for optimum balance between thermal and physical properties the index is approximately 500.

In a preferred embodiment of the invention the tetrafunctional aliphatic caprolactone polyol contains only primary hydroxyl groups.

Preferably the molecular weight of the tetrafunctional aliphatic caprolactone polyol is approximately 1000.

In one preferred embodiment of the invention the polyol contains carboxyl groups.

In one embodiment the polyol has a pentaerythritol backbone.

In another embodiment the polyol has an organic acid backbone. In this case preferably the organic acid is citric acid. In one aspect the foam includes an inorganic filler. Preferably the inorganic filler is present in an amount of up to 50% by weight of the foam.

In one embodiment of the invention the foam has a facing applied thereto.

The invention provides a rigid polyisocyanurate foam which has excellent high temperature properties.

It has surprisingly been found that the use of a tetrafunctional aliphatic caprolactone polyol provides a much enhanced foam with improved properties over conventional foams.

In particular the foam of the invention has been found to form a protective char layer when exposed to a high temperature in air, for example when placed in an oven at 200°C. Char formation is the partial oxidation of material when subjected to a high temperature environment which breaks down the molecular structure leaving a carbonaceous skeletal core. Once formed we have found that this char layer produces a protective layer insulating the inner material of the tetra functional aliphatic polyol foam from the outside environment thereby providing a foam having significantiy enhanced properties. This char formation allows the foam of the invention to be relatively unaffected by heat over long periods of time.

It was also found that the depth of foam discolouration when stored at 140°C over 25 weeks was substantially better than for polyisocyanurate (PIR) foam which was found to discolour completely over 8 weeks. In comparison the tetra functional aliphatic caprolactone polyol foam of the invention showed only a 32% depth of foam discolouration after 25 weeks. Thus the tetrafunctional aliphatic polyol foam has enhanced properties in less weight loss, volume change and a lower compression of change over time. In addition the foam has enhanced performance characteristics in comparison to conventional foams.

Such improved foam properties makes the foam of the invention very desirable for use in relatively high temperature applications.

We also found that using different fire retardants did not significantly effect the results.

The addition of up to 50wt% of an inorganic filler such as that available under the brand Fillite did not significantly adversely effect the temperature stability properties.

The invention also provides a pipe or pipe fitting having an insulating foam of the invention applied thereto. The invention applies especially to pre-insulated pipes and fittings. To form such pipes and fittings an annular space is created by an outer shell, for example a galvanised steel jacket, and the foam is injected into the annular space between the jacket and pipe. In this case because protection from atmospheric conditions is provided, the foam may be rated to up to 250°C.

Detailed Description

The invention will be more clearly understood from the following examples. Example 1

A foam was produced from the following formulation:

% parts by weight

Tetrafunctional aliphatic poly caprolactone polyol 15.9

(CAPA 316 from Solvay)

Fire Retardant 2.65 (REOFOS RDP from Great Lakes Chem Corp)

Surfactant 1.06

(B8404 from Goldschmidt)

Amine Catalyst 0.07

(Pentamethyldiethylenetriamine) Trimer Catalyst 0.27

(Potassium acetate)

Water 0.42

MDI using an MDI Index of 500 79.6

The polycaprolactone is first introduced into a vessel and all the other ingredients except the MDI are added at room temperature. The premix thus formed is then mixed with the MDI in a mixing head and the reactant mixture thus formed is laid down. Using either a continuous or discontinuous moulding production technique moulded sections of the required shape and size are then produced. Alternatively a free rise technique may be used to form a continuous or discontinuous block of foam. The block is cut to length and stored indoors at ambient temperature for about 24 hours and then stored outside from up to 5 days. The foam is then shaped as required, for example into the shape of two half tubes which are wrapped around a pipe for insulation of the pipe. The properties of the foam thus formed were tested. The foam was cut into sections which are typically 140mm x 100mm x 25 mm. The size of the cut foam was measured using vernier calipers and the weight was measured to an accuracy of O.Olg. The sample was then placed in a preheated hot air fan oven for a period of time during which the temperature in the oven was maintained substantially constant. The sample was then removed from the oven, left to stand for about 1 hour to cool and the weight dimensions re-measured.

To carry out compression tests a sample is maintained in an oven for 27 days and after removal and standing for one hour a compression test is carried out, the result being compared with a result from foam from the same block.

Comparative Example

For comparison, a conventional PIUR foam formulation was produced from the following:

% parts by weight Polyether/polyester polyol blend 30

Fire Retardant 2.65 Silicone Surfactant 1.06

Amine Catalyst 0.07

Trimer Catalyst 0.27

Water 0.42

MDI using an MDI Index of 220 65.53

The comparative foam was prepared and tested as described above.

The following results were obtained. % Weight loss at 8 days

Temperature 140°C 200°C 240°C

Example 1 @ 100kg/m³ 1.8 7.2 23.6

Comparative Example @100kg/m³ 2.6 14.8 37.1

% Volume Change at 8 davs

Temperature 140°C 200°C

Example 1 @ 100kg/m³ -0.6 -10.6

Comparative Example @ 100kg/m³ -1.8 -20

% Compression change after 27 davs

The results are plotted in Fig. 1.

Thermal Gravimetric Analysis (TGA)

This is a measure of the temperature at which % weight loss occurs.

% weight loss 5% 25% 50°/, Temperature (°C)

Example 1 300 450 540 Comparative Example 260 340 510

From the above test results it will be apparent that much greater temperature stability is achieved with the foam formulation of the invention than with conventional polyether /polyester (PIUR) foams. Percentage weight and dimensional changes using a hot plate at 215°C rather than a hot air oven produced similar results.

Example 2: % weight loss over 48 weeks

The weight loss of the tetrafunctional aliphatic caprolactone polyol foam of Example 1, the PIUR foam of the comparative example and PIR foam were measured over 48 weeks at 140°C, 200°C and over 43 weeks at 250°C as described in Example 1.

Figs 2 to 4 illustrate the results obtained. It is clear that the tetrafunctional aliphatic caprolactone polyol foam is significantly better at maintaining a lower weight loss especially at a temperature of 200°C. For example 30% weight loss at 200°C occurs after 5 days with the PIR foam and 10 days with the PIUR foam while it takes 31 days for the tetrafunctional aliphatic caprolactone polyol foam of the invention to show a 30% weight loss.

Example 3: Thermal Gravimetric Analysis (TGA)

As described in Example 1 the TGA is a measure of the temperature at which % weight loss occurs. Fig. 5 illustrates the results for five different foam types, phenolic, polyurethane (PUR), polyisocyanurate (PIR), PIUR and tetrafunctional aliphatic caprolactone polyol foam of the invention. The results show that the tetrafunctional aliphatic caprolactone polyol foam of the invention has a similar weight loss up to a temperature of 250°C but has a significantly lower % weight loss than the other foams as the temperature increases from 250 to 600°C. A comparison of the temperature at which % weight loss occurs for each type of foam is given in the following table <

% weight loss 5 25 50 Temperature (°C)

Phenolic (PF) 100 384 454

Polyurethane (PUR) 250 312 471

Polyisocyanurate (PIR) 200 351 482

Comparative example (PIUR) 260 340 510 Tetrafunctional Aliphatic Caprolactone 300 450 540

Example 4: Formation of protective char layer

Samples of tetrafunctional aliphatic caprolactone polyol foam (HT) and a known foam polyisocyanurate foam (PIR) were cut, weighed, measured and placed in an air filled environment at 200°C, such as an oven, for varying lengths of time.

To measure the extent of char formed the samples were cut in half, the extent of the black char layer measured by vernier calipers and recorded against the time the sample was subjected to the high temperature environment.

As the following table shows, there is a significant difference between char formation with the tetrafunctional aliphatic caprolactone polyol foam (HT) and the polyisocyanurate foam (PIR). The tetrafunctional aliphatic caprolactone polyol foam maintains a certain depth of char, not more than 20% of the foam layer over 48 weeks while with the polyisocyanurate foam char formation has passed through the whole foam layer, 100% depth, at 8 weeks.

Therefore the char layer formed with a tetrafunctional aliphatic caprolactone polyol foam of the invention exhibits insulation properties protecting the interior foam core from further oxidation. It maintains a stable protective layer on the outside of the foam. In comparison the char formed with the polyisocyanurate foam does not insulate the foam core allowing the whole depth of foam to be subjected to the oxidative polymer break down process.

Example 5: % of foam unaffected by heat

Samples of the tetra functional aliphatic caprolactone polyol foam of the invention and PIR foam were put in contact with a high temperature environment to mimic the situation wherein the inner side of a foam section is next to a hot pipe being insulated. The tetrafunctional aliphatic caprolactone polyol foam of the invention was found to form a protective char layer when put in contact with the hot pipe. The % of foam unaffected by the heat is measured as 100% foam depth minus the % of char depth.

As the following table shows, after 4 weeks at 200°C the % of tetra functional aliphatic caprolactone polyol foam (HT) unaffected by the heat was 87.5% and after 48 weeks at 200°C the % of unaffected foam was still above 80%. In comparison the PIR foam had 70.1% unaffected by the heat after 4 weeks while at 8 weeks the PIR foam was found to char to 100%) of its depth.

The foam of the invention may be used in a wide range of applications. For example, it may be used as insulation for a pipe or pipe fitting. The invention applies especially to pre-insulated pipes and fittings. To form such pipes and fittings an annular space is created by an outer shell, for example a galvanised steel jacket, and the foam is injected into the annular space between the jacket and pipe. In this case because protection from atmospheric conditions is provided, the foam may be rated up to 250°C.

The examples refer to specific polyols, fire retardants, surfactants and catalysts, however various alternatives on these components will be readily apparent to those skilled in the technology.

Many variations and modifications on the invention will be readily apparent and accordingly the invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims

1. A rigid polyisocyanurate foam formed from MDI and a tetrafunctional aliphatic caprolactone polyol in which the MDI index is from 300 to 1000.

2. A foam as claimed in claim 1 wherein the index is from 400 to 750.

3. A foam as claimed in claim 1 or 2 wherein the index is approximately 500.

4. A foam as claimed in any preceding claim wherein the tetrafunctional aliphatic caprolactone polyol contains only primary hydroxyl groups.

5. A foam as claimed in any preceding claim wherein the molecular weight of the tetrafunctional aliphatic caprolactone polyol is approximately 1000.

6. A foam as claimed in any preceding claim wherein the polyol contains carboxyl groups.

7. A foam as claimed in any preceding claim wherein the polyol has a pentaerythritol backbone.

8. A foam as claimed in any preceding claim wherein the polyol has an organic acid backbone.

9. A foam as claimed in claim 8 wherein the organic acid is citric acid.

10. A foam as claimed in any preceding claim including an inorganic filler.

11. A foam as claimed in claim 10 wherein the inorganic filler is present in an amount of up to 50% by weight of the foam.

12. A foam as claimed in any preceding claim having a facing applied thereto.

13. A pipe or pipe fitting having an insulating foam as claimed in any preceding claim applied thereto.