Blowing Agent Composition for Preparing a Rigid Polyurethane Foam

The following Examples illustrate the present invention specifically.

A premix of the above formulation (about 125 g) was taken into an aerosol can (AE No. 180, tin plate can) and stored at 60.degree. C. for a period of 10 days, 20 days and 30 days. Samples after storage and a sample before storage were evaluated. The acid value was measured by using a mixture of Bromothymol Blue and Phenol Red as an indicator and titrating the samples with a 1/10 N ethanol solution of potassium hydroxide. The results are shown in Table 1.

The premixes obtained by using the mixed blowing agent of the invention had higher stability than the premix obtained by using Flon-11 as a sole blowing agent and were equivalent to the premix obtained by using Flon-11 with the stabilizer.

The compatibility test is to determine whether the premix can be stored as a solution without separation into the polyol and Flon. The specific test procedure was as follows:

A polyol and Flon were taken into a 150 ml cylindrical glass bottle so that the ratio between them was 75/25, 70/30, 65/35/ 60/40, 55/45, or 50/50 (by weight and the total amount was about 60 to 80% of the volume of the glass bottle. The compounds were mixed for 5 minutes by using a shaking device (Iwaki KF shaker) and left to stand at room temperature (about 23.degree. C.) for 1 hour, and then the mixed condition was observed.

When the polyol and Flon completely dissolved in each other, a clear one-layer mixture was obtained. When they were not dissolved in each other, the mixture separated into 2 or 3 layers. In this case, the lower layer was a colorless clear brown Flon layer and the upper layer was a clear brown layer composed mainly of the polyol. In the case of the three layers, the interlayer was an emulsion of the polyol and Flon. Since the mixing ratio of the polyol to Flon in premixes actually used is in the range of from 70/30 to 65/35, the following standards of evaluation were used.

Excellent: dissolved at a mixing ratio of 55/45

Good: dissolved at a mixing ratio of 60/40

Fair: dissolved at a mixing ratio of 65/35

Poor dissolved or separated at a mixing ratio of 70/30

A premix evaluated as "good" shows compatibility in an actually used mixing ratio range and can be normally used. It is however likely to separate at low temperatures, for example in the wintertime. It is difficult therefore to use it as a standard recipe.

PPG-NT-470 (to be referred to as polyol A) as an example of an amine-type polyol, PPG-SUI-460 (to be referred to as polyol B) as an example of a sugar-type polyol and PPG-LV-450LKA (to be referred to as polyol C) as an example of a sugar-type hydrophilic polyol (all of these compounds were products of Mitsui Toatsu Chemicals, Inc.) were each selected and mixed with Flon-11. The compatibility test was carried out on the mixture. Polyols A and B dissolved in any of the ratios, and evaluated as good. But polyol C had poor compatiblity with Flon-11. It dissolved at a ratio of 75/25, but the other samples having a low polyol content separated into three layers. The results are shown in Table 2.

The same compatibility test as in Run 1 was carried out except that a mixture of Flon-123 and n-pentane was used instead of Flon-11 in Run No. 1. The mixing ratio of Flon-123 to n-pentane was 95/5, 90/10 and 70/30. The compatibility of Flon-123 with the polyol was higher as the proportion Flon-123 became higher. The results are shown in Table 2.

To polyol A and polyol B, 5 % by weight of water was added to prepare hydrous polyols. The hydrous polyol/ Flon-11 premix was tested for compatibility between the hydrous polyol and Flon-11. The compatibility decreased in all cases. The results are shown in Table 2.

The compatibility test was carried out by using a mixture composed of the hydrous polyol, Flon-123 and n-pentane in Run 3. As the proportion of Flon-123 in the mixture became higher, the compatibility of the blowing agent mixture with the hydrous polyol was higher. The results are shown in Table 2.

Polyols, a catalyst, a silicone, a blowing agent and water were weighed as described in the following formulation, taken into a 500 ml plastic container (polyethylene cup) and stirred at a low speed by a fourblade labo-mixer to form a premix. Then, 128 parts by weight of an isocyanate was poured into the container and the mixture was immediately stirred at a high speed (for 5 seconds at about 2000 rpm). The mixture was quickly poured into a panel (an aluminum mold having a size of 400.times.35.times.600 mm) lined with kraft paper; surface temperature 40.degree. C.), and foamed.

The state of foaming was visually observed using the various blowing agents. The rise time (R.T.) which elapsed until the end of the rising of the foam and the tack-free time (T.F.T.) which elapsed until the upper part of the foam during foaming did not show tackiness when it was lightly touched by a polytetrafluoroethylene rod were measured. The density, the ratio of closed cells formed and the compression strength of each of the resulting foams were measured, and the results are shown in Table 3.

When n-pentane was mixed in a large amount, the state of foaming at the time of using the mixed blowing agent was such that the foaming speed (H.T. and T.F.T.) was improved as compared with the use of Flon-11. As the amount of n-pentane added increased, the density decreased, the ratio of closed cells increased, and the compression strength increased.