WO2001030880A1

WO2001030880A1 - Process for the preparation of a rigid polyurethane foam

Info

Publication number: WO2001030880A1
Application number: PCT/EP2000/008941
Authority: WO
Inventors: Philippe Etienne Zarka; Juergen Kellner; Patrick Robert Andre Rene Morton
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 1999-10-26
Filing date: 2000-09-13
Publication date: 2001-05-03
Also published as: AU7287300A

Abstract

Process for the preparation of a rigid polyurethane foam by reacting a suitable polyisocyanate with a polyol component comprising from 1 to 45 wt % of recycled polyol in the presence of water and a suitable urethane catalyst and optionally usual auxiliaries, characterised in that the urethane catalyst comprises benzyl dimethylamine in an amount of from 1 to 10 parts by weight per 100 parts by weight of polyol component.

Description

DESCRIPTION

PROCESS FOR THE PREPARATION OF A RIGID POLYURETHANE FOAM

The present invention relates to a process for preparing a rigid polyurethane foam suitable as pipe insulation material using a polyol component which partly consists of recycled polyol.

Recycled polyols are known in the art. Generally, they are obtained by glycolysis, hydrolysis or aminolysis of polyurethane foams. The most widely used process, however, is glycolysis of polyurethane foams. In such a process the polyurethane foam is reacted with a glycol. The reaction product containing the polyol also has a relatively high content of amine groups resulting from the urethane and urea groups present in the original polyurethane foam. These amine groups function as a catalyst in the reaction of a polyol component containing the recycled polyol with polyisocyanate, thereby significantly increasing the reactivity of the polyol component. Such high reactivity is undesired in applications where the foam formulation has to flow into a long cavity, which should be filled with polyurethane foam. If the reactivity is too high the foam mixture's flowability will be considerably reduced and the cavity will not be completely filled with foam or stretched foam cells are obtained at pipe extremities, so that inferior products are obtained. Particularly when pre-insulated pipes are made in a discontinuous way, where the foam mixture is injected into the cavity of a pre-assembled pipe and has to fill the cavity between inner pipe and outer casing pipe up to lengths of e.g. 16 metres per pipe, the flow properties of the foam mixture are extremely important. One suitable way of preparing recycled polyols is, for instance, described in EP-A- 0592952. The process described here involves the glycolysis of polyurethanes in the presence of glycidylethers, thereby reducing the content of aromatic amines in the end product. However, others amine groups that catalyse the urethane formation remain present in the recycled polyol, so that the problem of increased reactivity is not solved. In general, rigid foams to be used as thermal insulation material in e.g. pipes should have a closed cell content of at least 90% in order to keep the insulating gases captured in the cells thereby providing the necessary insulating properties. Specifically for pipe insulation the rigid foam should also have a certain free rise density depending on the technique used to manufacture the insulated pipes. If a discontinuous pipe filling technique is used the foam should typically have a free rise density in the range of 20 to 40 g/1, more suitably 25 to 35 g/1, while in case a continuous pipe filling technique is used the polyurethane foam should have a free rise density in excess of 40 g/1, typically from 45 to 60 g/1, more suitably from 50 to 55 g/1.

In EP-A-0 676 433 a process for the preparation of rigid polyurethane foams using recycled polyols is disclosed, wherein the rigid foam prepared has an increased content of open cells and exhibits reduced shrinkage. However, the rigid foams prepared are unsuitable to serve as pipe insulation material, as their open cell content is too high. As indicated herein before, polyurethane foams serving as pipe insulation material should certainly not have an open cell content above 10%. Furthermore, the amount of recycled polyol used according to EP-A-0 676 433 is so high that the flow properties of the foaming mixture are insufficient. The present invention aims to provide a solution to the aforementioned problem of increased reactivity and hence reduced flowability arising from the use of recycled polyols in polyurethane foams for pipe insulation. Furthermore, this solution should not affect any of the thermal insulation properties or any other property, like mechanical strength and heat resistance, of the foam. It was found that the above problem can be adequately solved by using benzyl dimethylamine as catalyst or as co-catalyst in the preparation of rigid polyurethane foams from polyol components containing recycled polyols.

Preparing rigid foams by reacting a polyol component containing a recycled polyol with a polyisocyanate in the presence of suitable catalysts, blowing agents and other auxiliaries is known in the art. In DE-A-19718018, for instance, such a process has been described. Although DE-A-19718018 discloses that the foams produced are particularly suitable as pipe insulation material, the problem of increased reactivity and resulting poor flow properties is not addressed. In the working examples of DE-A-19718018 the actual insulation of a pipe is also not described. Accordingly, the present invention relates to a process for the preparation of a rigid polyurethane foam by reacting a suitable polyisocyanate with a polyol component comprising from 1 to 45 wt% of recycled polyol in the presence of water and a suitable urethane catalyst and optionally usual auxiliaries, characterised in that the urethane catalyst comprises benzyl dimethylamine in an amount of from 1 to 10 parts by weight per 100 parts by weight of polyol component.

Benzyl dimethylamine as such is known as a urethane catalyst. However, up to now it has never been proposed to use this specific catalyst for preparing rigid foams by a method involving recycled polyols as part of the polyol component. It was never considered that this specific catalyst could improve the flow properties of foam formulations for rigid foams containing recycled polyols, which foams are useful for insulating pipes. In accordance with the present invention benzyl dimethylamine may be used as the sole catalyst, but may also be used as a co-catalyst, i.e. together with one or more other urethane catalysts. Suitable other polyurethane catalysts are those described in e.g. EP-A-0,358,282 and US-A-5, 011,908 and include tertiary amines, salts of carboxylic acids and organometallic catalysts. Examples of suitable tertiary amines are triethylene diamine, N,N-dimethyl cyclohexyl amine, N-methyl morpholine, diethyl ethanol amine, diethanol amine and dimethyl cyclohexyl amine. Suitable organometallic catalysts include stannous octoate, stannous oleate, stannous acetate, stannous laureate, lead octoate, nickel naphthenate and dibutyltin dichloride. Further examples of organometallic catalysts are described in US-A-2, 846,408. Of course, mixtures of two or more of the aforementioned catalysts may also be used in addition to benzyl dimethylamine. Of the above catalysts dimethyl cyclohexyl amine is particularly suitable to be used in addition to benzyl dimethylamine.

In case a discontinuous pipe filling technique is used, the amount of benzyl dimethylamine is suitably chosen such that the reactivity of the polyurethane reaction mixture is characterised by a cream time of at least 30 seconds, preferably from 35 to 50 seconds, and a fibre time of at least 140 seconds, preferably from 150 to 210 seconds. In case a continuous pipe filling technique is used, the amount of benzyl dimethylamine is suitably chosen such that the reactivity of the polyurethane reaction mixture is characterised by a cream time of at most 20 seconds, preferably at least 2 seconds, and a fibre time of at most 70 seconds, preferably from 20 to 65 seconds. Discontinuous and continuous pipe filling techniques are known in the art. Cream time is the time lapsing from pouring the mixed foam formulation from the mixing chamber into the space where the foaming reaction should take place and the moment at which the foam mixture becomes creamy. Fibre time is the time lapsing from pouring the mixed foam formulation from the mixing chamber into the space where the foaming reaction should take place and the moment at which fibres can be drawn from the foam. Cream time and fibre time give an indication about the reactivity of the foam formulation and hence about the flow properties. A longer fibre time means that the foam system has more time to fill the cavity in the pipe. Once the fibre time is exceeded, the foam flow properties are considerably reduced, i.e. a proper filling of a cavity is no longer possible. As a general rule for the discontinuous filling of pipes up to a length of about 20 metres, it is known that the foam system used should fill the cavity completely well within the fibre time, i.e. the foam should arrive at both pipe extremities within 80-85% of the fibre time at the latest.

It is considered to be part of the routine skills of those skilled in the art to adjust the content of benzyl dimethylamine in accordance with the reactivity ranges indicated. When adhering to the ranges for cream time and fibre time indicated above for both discontinuous and continuous pipe filling techniques, the actual amount of benzyl dimethylamine will suitably be in the range from 1 to 5 parts by weight, preferably from 1.5 to 3.5 parts by weight, per 100 parts by weight of polyol component. The total amount of catalyst if benzyl dimethylamine is used as cocatalyst will normally range from 1 to 15 parts by weight. When benzyl dimethylamine is present in its preferred amount, the total amount of catalyst including benzyl dimethylamine will preferably be at most 8 parts by weight, per 100 parts by weight of polyol component.

The polyol component suitably comprises at least 5 wt% and preferably at least 10 wt% of recycled polyol, based on total weight of polyol component. Suitably not more than 40 wt%, preferably not more than 35 wt% of recycled polyol is present in the polyol component. The recycled polyol can be obtained from rigid polyurethane foams by any means known in the art, i.e. by hydrolysis, aminolysis or glycolysis of rigid polyurethane foam. One example of suitable glycolysis method is the method disclosed in EP-A-0 592 952. The recycled polyol, thus, may be a polyester polyol or a polyether polyol depending on the rigid polyol from which it is obtained. However, the use of a recycled polyether polyol is preferred. Generally, such recycled polyether polyol will have a functionality of from 1.7 to 8, suitably from 3 to 6, a molecular weight of up to 3000, suitably up to 2000 and more suitably from 250 to 1000, and a hydroxyl value of at least 120 mg KOH/g, suitably at least 200 mg KOH/g and more suitably from 300 to 600 mg KOH/g. The remainder up to 100 wt% of the polyol component consists of one or more polyols normally used to prepare rigid polyurethane foams. The remainder of the polyol component, accordingly, may be any polyether polyol or polyester polyol known to be applicable in rigid polyurethane and urethane-modified polyisocyanurate foams. The term "polyether polyol" as used in this connection refers to polyols comprising poly(alkylene oxide) chains, which polyols are normally obtained by reacting a polyhydroxy or polyamine initiator compound with at least one alkylene oxide and optionally other compounds. The term "polyester polyol" refers to polyols comprising ester bondings in the polymer chain. One way of preparing such polyols is, for instance, reacting a polycarboxylic acid or carboxylic acid anhydride with a polyhydroxy compound. The term "molecular weight" as used throughout this specification refers to number average molecular weight. Suitable polyester polyols are, for instance, described in EP-A-0 676 433 and include polyester polyols, which are typically produced from organic dicarboxylic acids or derivatives thereof (like anhydrides and esters) having from 2 to 12, preferably 4 to 6, carbon atoms and polyfunctional alcohols having from 2 to 12, preferably 2 to 5, carbon atoms. Suitable dicarboxylic acids include both aliphatic and aromatic acids like adipic acid, phthalic acid, fumaric acid and terephthalic acid, while the most preferred polyfunctional alcohols are diols like ethanediol, 1 ,4-butanediol and diethylene glycol. One category of suitable polyester polyols are the polyester polyols produced from phthalic anhydride and diethylene glycol. Another category uses either the heavy residue of the production of dimethyl terephthalate or scraps of recycled polyethylene terephthalate (PET) as the feedstock.

Suitable polyether polyols typically have a functionality of from 2 to 8, suitably from 3 to 6, a molecular weight of up to 3000, suitably up to 2000 and more suitably from 250 to 1000, and a hydroxyl value of at least 120 mg KOH/g, suitably at least 200 mg KOH/g and more suitably from 300 to 600 mg KOH g. Such polyether polyols are well known in the art and typically are alkylene oxide adducts of initiators, such as sucrose, sorbitol, pentaerythritol, glycerol, bisphenol A and blends of two or more of these. The alkylene oxides most frequently used are propylene oxide and ethylene oxide. The polyol component may also consist of a blend of two or more of the aforementioned polyols whereby the average functionality, hydroxyl value and molecular weight are in the ranges specified above. The polyisocyanate component may be any polyisocyanate known to be suitable in rigid polyurethane foams. Suitably, aromatic polyisocyanates are used and any di-, tri-, tetra- and higher functional aromatic polyisocyanate may be used. In EP-A-0,778,302, for instance, a list with suitable polyisocyanates is given. Preferred polyisocyanates are 2,4- and 2,6- toluene diisocyanate as well as mixtures thereof; 4,4'-diphenylmethane diisocyanate (MDI); polymethylene polyphenylene polyisocyanate and polymeric MDI, a mixture of polyisocyanates with MDI as the main component.

The polyisocyanate is generally used in such quantity that the isocyanate index is at least 100 and does not exceed 300, preferably from 110 to 250, more preferably from 120 to 200. As is well known in the art, the isocyanate index is defined as 100 times the equivalence ratio of isocyanate groups to active hydrogen atoms, such as those present in the polyol component and water.

Water is used as a (chemical) blowing agent: it reacts with isocyanate groups according to the well known NCO/H2O reaction, thereby releasing carbon dioxide which causes the blowing to occur. Water is suitably used in an amount of from 1 to 5 parts by weight per 100 parts by weight of polyol component.

In addition to water other blowing agents may be used as well. Suitable additional blowing agents are those conventionally applied in rigid polyurethane production and include partly halogenated alkanes, aliphatic alkanes and alicyclic alkanes. Fully halogenated hydrocarbons may also be used, but are less preferred due to their ozone depleting effect. Concrete examples of suitable blowing agents include l-chloro-l,l-difluoroethane, cyclopentane, cyclohexane, n-pentane, isopentane and mixtures of two or more of these. The use of n-pentane or cyclopentane in addition to water has been found particularly useful. The amount of additional blowing agent used may range from 0 to 30, preferably 5 to 20, parts by weight per 100 parts by weight of polyol component. Furthermore, low boiling blowing agents which give a frothing effect can also be used. Examples of such blowing agents include liquid carbon dioxide, HFC-134a (1,1,1,2-tetrafluoroethane) and HFC- 152a ( 1 , 1 -difluoroethane). The auxiliaries, which may be used, are those normally applied and may include foam stabilisers, flame retardants, colouring agents and fillers used in the usual amounts. For instance, organosilicone surfactants are often used as foam stabilisers. A large variety of such organosilicone surfactants is commercially available. Usually, such foam stabiliser is used in an amount of up to 5 parts by weight per 100 parts by weight of polyol component. The process according to the present invention can be carried out by conventional methods for preparing rigid polyurethane foams. Typically, these methods involve first mixing all components but the polyisocyanate component, so that a homogeneous mixture is obtained, and subsequently adding the polyisocyanate under continuous stirring. Immediately after the stirring has stopped the foaming mixture (or foam formulation) is poured into the reaction space where the urethane formation reaction takes place. As stated herein before in case the rigid polyurethane is used as pipe insulation material, the foaming mixture may be poured into the space between an inner pipe and an outer casing. The foaming mixture then has to flow through said space, thereby filling the space before the foaming reaction has proceeded to such a stage that the foaming mixture has become too stiff or hard to flow any further (indicated by the fibre time). If the foaming mixture has filled the space then the foaming reaction can be completed, so that the resulting foam entirely fills the reaction space.

The invention is further illustrated by the following examples. In these examples the following components are used:

Polyol A: an aliphatic, propylene oxide-based polyether polyol having an OH value of 470 mg KOH/g, an average molecular weight of 500 and an average functionality of 4.1; Polyol R: a recycled polyol having an OH value of 570 mg KOH/g and a functionality of about 3, which was obtained via glycolysis of a rigid polyurethane foam in accordance with the method described in EP-A-0 592 952;

SUPRASEC 5005: polymeric MDI, equivalent weight 133.33 eq/g, average nominal functionality of 2.7 and NCO content between 30 and 32% (ex Huntsman; SUPRASEC is a trademark);

DMCHA: N,N-dimethylcyclohexylamine catalyst;

BDMA: benzyl dimethylamine catalyst;

Polycat 41 : tris(dimethylaminopropyl)triazine ex Air Products (Polycat is a trademark);

B8404 - refers to TEGOSTAB B8404 - a silicone surfactant ex Goldschmidt (TEGOSTAB is a trademark). Example 1

Polyol A (66 pbw) and Polyol R (30 pbw) were mixed in a plastic beaker with water, BDMA, Polycat 41 , B8404 and cyclopentane in the amounts indicated in Table 1 at ambient temperature using a mechanical stirrer at a speed of 3000 r.p.m. by means of a stirrer. The polyisocyanate was subsequently added in five seconds and the mixture was stirred for another five seconds before pouring it into the polyethylene bag. Cream time (CT) was determined by recording the time from pouring the reaction mixture into the polyethylene bag and the instant at which this mixture showed the first signs of reaction, i.e. the instant at which the surface of the liquid reaction mixture becomes lighter in colour due to the formation of very fine gas bubbles.

Fibre time (FT) was determined by repeatedly inserting a 70 mm wooden stick approximately 10 mm into the surface of the rising foam at a distance of 30 to 40 mm from the side wall of the bag. The insertions started about 10 to 15 seconds before the expected fibre time and were repeated at a rate of about one insertion per second. The moment at which the wooden stick pulls out a fibre from the foam for the first time, is recorded as the fibre time. The starting point of the time recording is the same as for the cream time. Both cream time and fibre time were measured at 20 °C with the materials having been preconditioned at 20 °C. The free rise density (FRD) of the foams was determined according to ISO 845. The flow index, defined as the height per unit mass (in cm/g), is determined as follows. The reaction mixture is injected into a cast aluminium mould having a length of 200 cm, a width of 20 cm and a cavity thickness of 5 cm. The mould is provided with water-jacketing to keep the temperature at 40 °C and air vent holes at the upper end. The mould is mounted on a stand which allows it to be held in both horizontal and vertical positions. Prior to injecting the reaction mixture into the mould the inner walls of the mould are treated with a releasing agent (Tegotrenn LR808/877; Tegotrenn is a trademark) to facilitate the removal of the foam formed. When actually injecting the reaction mixture into the mould, the mould is arranged in an angle of 60° relative to the vertical, with the injection point at the low side of the mould. The amount of reaction mixture is such that an expected height of the foam is about 190 cm. After injection of the reaction mixture the injection hole is sealed and the mould is placed in an angle of 45° relative to the vertical with the injection point at the lower end of the mould. The foam is allowed to rise and to cure for 10 minutes. Then the height of the foam is determined while being in the mould. Hereafter the foam is removed from the mould and its weight is determined. The flow index is the quotient of the height and weight. The composition of the foam formulation and the results are indicated in Table 1.

Comparative Examples A and B

Example 1 was repeated except that DMCHA was used in stead of BDMA in an amount of

0.5 pbw (Comparative Example A) and in an amount of 2.0 pbw (Comparative Example

B).

The results are indicated in Table 1 (C-Ex. stands for Comparative Example).

Table 1 Formulations and foam formation

* of the foam in the mould for determining flow index ** not determined, because the reactivity was too high All foams listed in Table 1 had a closed cell content in excess of 92%, which is essential for making them suitable as insulating material. The density of the foams in all cases was in the range for pipe insulation foams to be applied in a discontinuous pipe filling technique. The results in table 1 show that the use of BDMA indeed results in a more retarded reactivity when using recycled polyols resulting in appropriate flow properties. It is well known that a reduction of the catalyst amount in order to increase the cream and/or fibre time of a foaming mixture can lead to an unacceptably low curing rate which in return leads to inferior foam properties, in particular to coarser cells, increased foam friability, poor mechanical properties and reduced insulation properties.

As can be seen from Table 1 the use of only 0.5 pbw DMCHA resulted in a reasonable reactivity, but its flow behaviour and appearance were much worse than when using 2.0 pbw of BDMA in accordance with the present invention. Using 2.0 pbw of DMCHA, on the other hand, resulted in a reactivity which was much too high for application in pipe insulation when applying a discontinuous pipe filling technique. The foam of Comparative Example B is also not suitable for application in a continuous pipe filling technique because of its density being too low to be applied in such a technique. Thus, the examples show that the use of BDMA as catalyst in a system containing recycled polyols results in an optimum combination of reactivity and flowability.

Claims

1. Process for the preparation of a rigid polyurethane foam by reacting a polyisocyanate with a polyol component comprising from 1 to 45 wt% of recycled polyol in the presence of water and a urethane catalyst and optionally usual auxiliaries, characterised in that the urethane catalyst comprises benzyl dimethylamine in an amount of from 1 to 10 parts by weight per 100 parts by weight of polyol component.

2. Process according to in claim 1, wherein the amount of benzyl dimethylamine is such that the reactivity of the polyurethane reaction mixture when used in a discontinuous pipe filling technique is characterised by a cream time of at least 30 seconds and a fibre time of at least 140 seconds.

3. Process according to claim 1, wherein the amount of benzyl dimethylamine is such that the reactivity of the polyurethane reaction mixture when used in a continuous pipe filling technique is characterised by a cream time of at most 20 seconds and a fibre time of at most 70 seconds.

4. Process according to claim 1, wherein the amount of benzyl dimethylamine is from 1 to 5, preferably from 1.5 to 3.5 parts by weight per 100 parts by weight of polyol component.

5. Process according to any one of claims 1 to 4, wherein the polyol component comprises from 5 to 40, preferably from 10 to 35 wt% of recycled polyol.

6. Process according to any one of claims 1 to 5, wherein water is used in an amount of from 1 to 5 parts by weight per 100 parts by weight of polyol component.