Probelms with Latex Dipping of Vascular Catheters

Manufacturer:   I am an Engineer from a vascular catheters manufacturer. I found your blog (http://latexconsultants.blogspot.com) during my search for answers to the problems I am facing with my rubber manufacturing process and have found the information on the blog site very useful. However, I still have questions and I hope you will be able to give me some advice based on your technical expertise on rubber manufacturing and many years of experience. This is my first time working on rubber manufacturing and I have little knowledge in this aspect.

I am recently working on my own coagulant mixture of Calcium Nitrate plus Methanol and have used it to dip with natural dipping latex. However, I have been finding extremely bulky tip immediately after the formers have been removed from the latex tank. I have tried adjusting the dipping speed, only to find the same results. I have also adjusted the dipping duration for the coagulant, with similar end results. Is the Calcium Nitrate that I have added too little?

I am also facing balloon recovery issues on my balloon after inflation. What are the possible reasons for recovery problems?

John Woon (Senior Latex Consultant): 

Here's my comment and recommendation:
1) At first I thought what you meant by "bulky tips" was the effect of excessive pick up of either the coagulant or the latex at the tip on withdrawal for the formers from the two respective tanks. However, your photos show that it was the narrowing of the areas just below the tips making the tips appearing bulky and thicker.

2) Anyway, let's assume that it was in fact due to excessive pick up of either coagulant or the latex. To overcome this problem, you have to withdraw the former at a lowest possible speed.

3) Formers should be heated to higher temperature to ensure faster drying of the coagulant. You are now using 37C. Please try 45C. Faster drying of the coagulant would help to "set" it before it has a chance to flow back when the formers are inverted after withdrawal. Excessive flow back might result in thinning of the coagulant and hence latex pick-up as seen in the photos.

4) Ensure the formers are well cleaned (with detergent periodically) after each cycle of dipping. This is to ensure even coating of the coagulant.

5) Add about 0.1% of a non-ionic surfactant as a wetting agent in the coagulant. Triton X100 and Teric 320 are possible examples.

6) For health reason, do not use methanol which is highly toxic. It has been reported that workers who are repeatedly exposed to methanol could suffer from eventual blindness. Replace it  with ethanol or IPA (Isopropyl alcohol)

7) Poor recovery of the balloons after inflation and deflation could be due to insufficient drying of the balloons and also low modulus of the film. Prevulcanized latex is available commercially in three modulus ranges, namely low, medium and high modulus. I suggest you use either the medium modulus grade or a 50/50 blend of medium modulus and high modulus.