MXPA00007526A - Process for rigid polyurethane foams - Google Patents

Abstract

Process for preparing rigid polyurethane or urethane-modified polyisocyanurate foams comprising the step of reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive component in the presence of a blowing agent mixture comprising from 50 to 90%by weight of cyclopentane and from 10 to 50%by weight of a mixture comprising isopentane and/or n-pentane and isobutane and/or n-butane wherein the weight ratio of isopentane and/or n-pentane over isobutane and/or n-butane is between 5/95 and 95/5.

Description

PROCESS FOR PREPARING RIGID POLYURETHANE FOAMS This invention relates to processes for the preparation of rigid polyurethane or polyisocyanurate foams modified with urethane, to foams prepared in this way, and to new compositions useful in the process.

Rigid urethane-modified polyurethane and polyisocyanurate foams are generally prepared by reacting the appropriate isocyanate-reactive compound and polyisocyanate (usually a polyol) in the presence of a blowing agent. A use of these foams is a means of thermal insulation for example in the construction of refrigerated storage devices. The thermal insulation properties of rigid foams are dependent on several factors including, for closed cell rigid foams, the cell size and the thermal conductivity of the contents of the cells.

A class of materials that has been widely studied as the blowing agent in the production of urethane-modified polyurethane and polyisocyanurate foams are the Fully halogenated chlorofluorocarbons, and in particular trichlorofluoromethane (CFC-11). The exceptionally low thermal conductivity of these blowing agents, and in particular of CFC-11, has allowed the preparation of rigid foams having very effective insulating properties. Recent interest regarding the potential of chlorofluorocarbons to cause depletion of ozone in the atmosphere has led to an urgent need to develop reaction systems in which chlorofluorocarbon blowing agents are replaced by alternative materials that are environmentally acceptable and that they also produce foams that have the properties necessary for the many applications in which they are used. These alternative blowing agents proposed in the prior art include hydrochlorofluorocarbons, hydrofluorocarbons and especially hydrocarbons specifically alkanes and cycloalkanes such as isobutane, n-pentane, isopentane, cyclopentane, and mixtures thereof. Mixtures of cyclopentane and isobutane are preferred as described, for example, in EP 421269, and mixtures of cyclopentane and isopentane or n- pentane, as described, for example, in WO 94/25514. It is an object of the present invention to provide a mixture of hydrocarbon blowing agent that produces improved foam properties and at the same time allows for easy processing. These objects are satisfied by using in the process of making rigid foams of polyurethane or urethane-modified polyisocyanate from polyisocyanate and isocyanate-reactive components, a blowing agent mixture comprises from 50 to 90% by weight of cyclopentane and from 10 to 50% by weight of a mixture of isopentane and? or n-pentane and isobutane and / or n-butane wherein the weight ratio of isopentane and / or n-pentane and isobutane and / or n-butane is between 5 / 95 and 95/5. The use of this blowing agent mixture allows for easier processing than a mixture of cyclopentane and isobutane together with improved thermal insulation properties. Compared to the use of a mixture of cyclopentane and iso- or n-pentane, improved dimensional stability of the foams is obtained by allowing stable foams of lower density.

Preferably, the amount of cyclopentane in the blowing agent mixture is between 60 and 90% by weight, more preferably between 60 and 80% by weight, more preferably between 70 and 75% by weight, with the weight ratio of iso- and / or n-pentane and isobutane and / or n-butane which is preferably between 90/10 and 20/80, more preferably between 75/25 and 25/75, more preferably between 2/1 and 1/2. The use in the present mixture of isopentane blowing agent is preferred over n-pentane as is the use of isobutane with respect to n-butane. As examples of preferred blending agent mixtures for use in the present invention, the following may be given; a mixture containing 70% by weight of cyclopentane, 20% by weight of isopentane and 10% by weight of isobutane; a mixture containing 70% by weight of cyclopentane, 10% by weight of isopentane and 20% by weight of isobutane; a mixture containing 75% by weight of cyclopentane, 15% by weight of isopentane and 10% by weight of isobutane. Suitable isocyanate-reactive compounds to be used in the process of present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanate foams. Particular importance for the preparation of rigid foams are polyols and polyol blends having average hydroxyl numbers from 300 to 1000, especially from 300 to 700 mg KOH / g, and hydroxyl functionalities from 2 to 8, especially from 3 a 8. Suitable polyols have been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and / or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule . Suitable initiators include: polyols, for example glycerol, trimethylolpropane, tretanolamine, pentaerythritol, sorbitol and sucrose; polyamines, for example ethylene diamine, tolylene diamine (TDA), diaminodiphenylmethane (DADPM) and polymethylene polyphenylene polyamines; and aminoalcohols, for example ethanolamine and diethanolamine; and mixtures of these initiators. Other suitable polymeric polyols include polyesters obtained by the condensation of appropriate proportions of glycols and polyols of greater functionality with dicarboxylic or picarboxylic acids. Suitable further polymeric polyols include polyether terminated polyethers, polyamides, polyester amides, polycarbonates, polyacetals, polyolefins and polysiloxanes. Particularly preferred isocyanate-reactive compounds to be used in hydrocarbon blowing systems are amine-initiated polyether-polyols, especially aromatic amine-initiated polyols such as polyether-polyols initiated with TDA and DADPM, as described in WO 97. / 48748, the contents of which are incorporated herein. Organic polyisocyanates suitable for use in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, and in particular aromatic polyisocyanates such as diphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and 4,4 '-isomers and mixtures thereof, the mixtures of diphenylmethane diisocyanates (MDI) and oligomers thereof known in the art as "crude MDI" "or polymeric (polymethylene polyphenylene polyisocyanates), having an isocyanate functionality greater than 2, toluene diisocyanate in the form of its 2-, 4- and 2,6-isomers and mixtures thereof, 1,5-naphthalene diisocyanate and 1,4-benzene diisocyanate. Other organic polyisocyanates that may be mentioned include the aliphatic diisocyanates such as isophorone diisocyanate, 1,6-diisocyanatohexane and 4,4'-diisocyanatodicyclohexylmethane. The amounts of the polyisocyanate compositions and the polyfunctional isocyanate-reactive compositions to be selected will depend on the nature of the rigid polyurethane foam or urethane-modified polyisocyanurate to be produced and will be readily determined by those skilled in the art. Other known physical blowing agents for the production of rigid polyurethane foam can be used in conjunction with the hydrocarbon blowing agent mixture of the present invention. Examples of these include other hydrocarbons, dialkyl ethers, cycloalkylene ethers and ketones, fluorinated ethers, chlorofluorocarbons, perforated hydrocarbons, and in particular hydrochlorofluorocarbons and hydrofluorocarbons. Examples of suitable hydrochlorofluorocarbons include: 1-chloro-1,2-difluoroethane, 1-chloro-2,2-difluoroethane, 1-chloro-1, 1-difluoroethane, 1,1-dichloro-1-fluoroethane and monochlorodi luoromet anus. Examples of suitable hydrofluorocarbons include 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, trifluoromethane, heptaf luoropropane, 1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1 , 1,2, 2-pentafluoropropane, 1,1,1,3-tetrafluoropropane, 1,1,1,3,3-pentafluoropropane and 1,1,1,3,3-pentafluoro-n-butane. In general, water or other compounds comprising carbon dioxide are used in conjunction with physical blowing agents. When water is used as the chemical blowing co-agent, typical amounts are in the range of 0.2 to 5%, preferably from 0.5 to 3% by weight based on the isocyanate-reactive compound. The total amount of the blowing agent to be used in a reaction system to produce cellular polymeric materials will be readily determined by those skilled in the art. technique, but will typically be from 2 to 25% by weight based on the total reaction system. In addition to the polyisocyanate and the polyfunctional isocyanate reactive compositions and the blowing agent mixture, the reaction mixture forming the foam will commonly contain one or more conventional auxiliaries or additives to the formulations for the production of rigid polyurethane and modified polyisocyanurate foams with urethane. These optional additives include crosslinking agents, for example, low molecular weight polyols such as triethanolamine, foam stabilizing agents or surfactants, for example, siloxane-oxyalkylene copolymers, urethane catalysts, for example tin compounds such as as stannous octoate or dibutyltin dilaurate or tertiary amines such as dimethyl-cyclohexylamine or riet-ilen-diamine, isocyanurate catalysts, flame retardants, for example halogenated alkyl phosphates such as tris-chloropropyl phosphate and fillers or fillers such as black of coal. • In the operation of the process for making rigid foams according to the invention, they can use known pre-polymer or semi-prepolymer techniques of an injection, along with conventional mixing methods and the rigid foam can be produced in a form of planks, moldings, cavity fillings, sprayed foam, foam or laminated products with other materials such as hardwood veneer, plasterboard, plastics, p or metal. It is convenient in many applications to provide the components for the production of polyurethane in pre-mixed formulations based on each of the primary polyisocyanate components and isocyanate-reactive components. In particular, many reaction systems employ a polyisocyanate-reactive composition that contains the main additives such as the blowing agent in addition to the polyisocyanate-reactive component or components. Therefore, the present invention also provides a polyisocyanate-reactive composition comprising the present blowing agent mixture. The present invention is illustrated, but not limited by the following examples.

EXAMPLES 1-5 Refrigeration cabinets were filled with a polyurethane formulation containing the ingredients listed in table 1 below. The polyol is a polyol composition with an OH value of 390 mg KOH / g; the isocyanate is a polymeric composition of MDI. The reaction profile was followed with respect to the cream time (time taken by the reaction mixture to start foaming) and the chain time (time taken by the reaction mixture to reach the transition point from the fluid to the crosslinked mass). ). The free increase density of the foam was measured in accordance with ISO 845. The Flow Index was determined as follows: the height, a foamed reference formulation of certain height flows within a specified tube, is adjusted to 1.00; the height, the formulation of the sample foam of the same weight flows into the same tube, then it is determined in relation to this reference foam formulation. Blown foam of cyclopentane (Example 1) is used as the reference foam.

Lambda at 10 ° C was measured in accordance with ASTM C518. The level of foam is determined visually. The fill weight represents the weight difference between the foam-filled refrigerator cabinet and the non-filled cabinet and was determined for model 1 which is a single-volume refrigerator with thick walls and a simple flow pattern for the model 2 which is a type cabinet combined with a full flow pattern. The inverted thermal leak determines the loss of energy (heat transfer) through a cooling cabinet when a steady state speed (of energy loss) is reached. It is measured as follows: energy is given to a closed and conditioned refrigeration cabinet; the thermal flow is established from the internal and external surface; having established a stable state (thermal equilibrium) the energy is measured; the value -of RHL is the energy (in batios) necessary to maintain a difference at a predetermined temperature between the inside and the outside (in this case a temperature difference of 20 ° C was used). In Table 1, the RHL for the foams of sample is represented in relation to the reference foam (example 1) of which the RHL is set to 100. The RHL values were determined only for the refrigerators of model 1. The results are shown in Table 1 below.

Table 1 These results show that using a blowing agent mixture according to the invention (Examples 4 and 5) leads foams of lower density than those blown with cyclopentane only (Example 1); also the flow of the foam formulation has improved leading to lower fill weights of the refrigerator. Compared to foam blown with mixtures of cyclopentane / isopentane (Example 2) smaller filler weights are also obtained. Compared to foams blown with mixtures of cyclopentane / isobutane (Example 3), a better flow is obtained (smaller filler weights, especially for complex model refrigerators) and better insulation properties (lambda energy consumption).

Claims (8)

1. CLAIMS _ 1. Process for preparing rigid urethane-modified polyurethane or polyisocyanurate foams comprising the steps of reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive component in the presence of a blowing agent mixture comprising from 50 to 90% by weight of cyclopentane and from 10 to 50% by weight of a mixture of isopentane and / or n-pentane and isobutane and / or n-butane wherein the reaction by weight of isopentane and / or n-pentane with respect to isobutane and / or n-butane is between 5/95 and 95 /.
2. 2. The process according to claim 1, wherein the amount of cyclopentane in the blowing agent mixture is between 60 and 80% by weight and the mixing amount of the isopentane and / or n-pentane and isobutane and / or n- Butane is between 20 and 40% by weight.
3. 3. The process according to claim 1 or 2, wherein the weight ratio of iso- and / or n-pentane to iso- and / or n-butane between 75/25 and 25/75.
4. 4. The process according to claim 3, wherein the weight ratio of iso- and / or n-pentane with with respect to iso- and / or n-butane it is between 2/1 and 1/2.
5. The process according to any of the preceding claims, wherein the blowing agent mixture comprises cyclopentane, isopentane and isobutane.
6. The process according to claim 5, wherein the blowing agent mixture is selected from the group consisting of a mixture of 70% by weight of cyclopentane, 20% by weight of isopentane, and 10% by weight of isobutane; a mixture of 70% cyclopentane, 10% by weight of isopentane, 20% by weight of isobutane; a mixture of 75% by weight of cyclopentane, 15% by weight of isopentane, 10% by weight of isobutane.
7. 7. The rigid urethane-modified polyurethane or polyisocyanurate foam obtainable by the process as defined in any of the preceding claims.
8. 8. The isocyanate-reactive composition comprising a blowing agent mixture as defined in any of claims 1 to 6.