Definition of wetting tension

It refers to that when the plastic surface is just completely wetted by the liquid (that is, the contact angle is equal to zero), the surface tension of the liquid is defined as the wetting tension of the plastic. At present, the film is mainly treated by EDM to improve the wetting tension of the film, so it is commonly known as corona value, which is hereinafter referred to as corona value.

Standard regulations on corona value

Gb/t 10003-2008 biaxially oriented polypropylene (BOPP) film for general use stipulates:

Wetting tension ≥ 38mn/m;

Among them, in the referenced documents, the test standard of corona value is specified as:

Gb/t 14216-2008 'determination of wetting tension of plastic films and sheets' stipulates the test solution and formula, test environment, test method, etc.

Testing in actual production

1. The ≥ 38mn/m specified in the above standard is based on the value measured with the configured test solution under the standard test method, and more points to the manufacturer's post production offline test.

(in view of the need for accurate proportioning of test fluid and the frequency of replacement, the manufacturer usually proportioned the test fluid once a week and stored it in the refrigerator)

2. However, in the use of the manufacturer's test, the simplified corona pen is used for testing:

Different from the standard test method, the corona pen (and the use time of the corona pen) and the storage time of the film, the test effect will be different to varying degrees.

According to the current industry recognized standards, the matte surface ≥ 38mn/m, the smooth film double-sided and matte film smooth surface, and the corona value ≥ 36mn/m can meet the paper plastic coating requirements and post process requirements.

From the experimental results, the value measured by the corona pen is about 2n/m lower than the actual value of the film

3. Remarks:

A. At present, there are many categories of test pens, including Sherman in Britain, acotest in Germany, Pacific in Japan, sun in the United States, corona-Plus in Taiwan, etc., and the test results are also different.

For the same test pen, because the volatility of ethylene glycol ether in the test solution in the pen is greater than that of formamide, the ratio of the two components changes with the use time and frequency, which will affect the test effect, that is, uncertainty.

Suggestions on the use time of corona pens. The frequently used corona pens should be updated no more than three months, and the infrequently used ones should be no more than six months.

4. The test method for the incoming products of our company: place the sample in the test environment [in the air-conditioned environment in summer (about 25 ℃) / indoors in winter (about 15 ℃)] for about 15 minutes, and test it with the corresponding corona pen (Sherman corona pen in the UK is recommended, and the most standard test pen is recommended by many manufacturers). The test fluid painted for 2 seconds or nearly 2 seconds does not shrink is the standard to determine whether it is qualified.