14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS T•E LECTURER: I would not say that the 50% level is the only realistic one that one can make, but it is probably the only practical one because of the quantity of bottles necessary. If I wanted to find a level at which 1% broke, I would use the technique described here as the probit technique in order to estimate the spread, but if we think about 1%, it means that for every 100 bottles dropped, one will break at that height, and a single bottle breaking does not give a very good estimate. It means that 5,000 bottles must be dropped. In order to answer your question scientifically I would have to drop several thousand bottles by a probit method and plot the results. MR. C. D. RENFREW: I could perhaps offer another explanation for the very low impact figure you have obtained with the cylindr'cal bottle. In early work on PVC bottles we found that its notch sensitivity was very important in impact testing and that when setting up moulds for blow-moulding, if the two faces of the mould were deliberately offset as little as 0.127 mm this had the same effect as removing ten parts of impact modifier, i.e. if you had a ten parts impact modified material this would reduce the impact strength of the bottle to the unimpact-modified state. I wonder if the mould was not properly aligned in your tests on the cylindrical bottle because it is a dramatically low figure. T•E LECTURER: This is very interesting. Mr. Renfrew, what is a satisfactory temperature for cold drop testing? I have done a certain amount of testing at 10 ø because it is at a low temperature that the difference between an impact modified grade and a non-modified grade really shows up. I have chosen 10 ø as being not too cold to be unrealistic. MR. C. D. RENFREW: I completely agree with you. The effect is even more dramatic at 5 ø where the effect of the impact modifier allows it to give a very significant effect - it is perhaps unrealistic to test at 5 o MR. P. G. S•.TON: We use an injection-moulded polystyrene talc container with a welded bottom. Initial evaluation by drop tests at 1 m in the laboratory gave no failures at the weld, but in use the bottoms dropped off. Do you feel that this should have been predicted by drop tests? T•E LECTURER: It depends how you drop them. We had some problems with a similar container, and we investigated its strength not by drop testing, but by an impact test on the side of the container. We found that the bases popped off very neatly if they were not stuck on very well. I should think in a drop test you are holding the base fairly firmly while it takes the shock. We filled our bottle with talc and dropped it on one corner so that it dropped at roughly 45 o. MR. D. R. CRABTREE: Surely dropping it on its base is the most critical situation because you get the most hydraulic effect which is reduced by dropping it on the corner. T•E LECTURER: I do not see why the hydraulic effect should differ with the point of impact. You are still getting a shock wave through the liquid in fact, you are funnelling it into the corner if you drop it on to its corner. The problem with dropping it on to its corner is the difficulty to avoid imparting rotation and some of the force is lost as rotational energy on impact. By dropping onto the base you get a better

DROP TESTING OF PLASTIC CONTAINERS 15 shock. If you could drop them so that they hit firmly on the corner you would prob- ably get a good result. MR. C. E. Hm•s: In relation to orientation of drop, I am absolutely convinced that there is a major difference between dropping onto the bottom and dropping onto the flat - I do not accept that dropping onto the bottom is the most severe condition. I am surprised that nobody has referred to dropping on the cap because the shoulders are so frequently a source of potential problem. I would like to suggest that when one drops a bottle which has a pronounced difference between the minor and major axis onto its large, flat face, one gets, what I believe is called in America, 'hydronamic hammer', and one imparts a shock to the liquid which encourages it to flow violently at right angles to the plane of impact. Thus one will tend to knock out the face and knock off the shoulder, and one is therefore imparting a shock to the bottle which is diametrically opposed to the shock that it received when dropped onto its face. In relation to viscosity of the product I entirely endorse what you have said. I believe that it is unconforming to test with water, because one always suspects that one should test with the product, but whenever I have tested in strictly comparable series, between product and water, I always come to the conclusion that it was very reasonable to use water. I believe that 10 ø is very reasonable for testing, but I believe it is important to remember that bottles are frequently stored in quite a cold cellar and might be brought on to the production floor very cold. They can be well below 5 ø, and when first being filled in these conditions there is little doubt that they are probably in their most sensitive state. '['}•, Ll,:cTum,zu: Your comments are very useful indeed. Our bottles are closed with a long polythene top which would cushion the impact quite well, and it would therefore be unrealistic to drop them onto the top. Our factory storage is heated so we do not have that problem which you mention. Mm R. J. Fom.•t•s: I believe that in Scandinavia they use higher impact grades (luring the winter. MR. L. G•T•D: [ think it is important to remember that some people may be packing liquids with a very much greater density than water, and that the load inside a bottle can be very high. I have experienced considerable problems of container breakage with a sugar syrup. The water drop tests did not reveal the problem but dropping with the product did. Admittedly we were not doing these in PVC bottles but the differ nee of the weight of the contents was a point that we had to note. MR. D. B. VI•c•: What part does the ullage play? I would rather have thought that the larger the ullage the more the liquid would be free to move, and the more the hammering effect at the time of impact. Yet you mention worse results with a gel? TH• L•C•URF. R: My comments on the gel are based on very little experience but we have looked at a few containers with gels and they did seem remarkably fragile, and they do transmit shock rather well. I have not studied ullage systematically on our container but when investigating sachel strength in the past, this was an important point and I see no reason why it is not here. I do not know, however, whether there is a critical level.