BOPP Film Quality Control
BOPP testing is very important for BOPP quality control. BOPP(Biaxially Oriented Polypropylene) cigarette film, with is excellent moisture barrier property, optical performances, heat seal property as well as high heat seal strength, reasonable shrinkage rate and good stiffness, is the first choice for cigarette film. The testing items of BOPP are the judgment for BOOP film performance. In order to better control the quality of BOPP cigarette film, Labthink, integrates the testing demand and introduces the relevant BOPP cigarette film testing methods and items, so as to bring useful helps for the cigarette companies.
A. Moisture Barrier Property Testing of BOPP Cigarette Film
High moisture barrier property performance is a must for cigarette package so as to avoid deterioration caused by moisture. At present, this factor is not fully noticed by the cigarette manufacturers. Labthink PARAM TSY-T1H is developed according to ASTM E96, ISO 2528 and other standards to test moisture transmission rate for materials. The lower WVTR the better. But, higher barrier property means more costs. Therefore, the common data is less than 10g/m2.day or 5g/m2.day.
B. Thickness of BOPP
Thickness of BOPP cigarette film is the basic film performance index. Uneven thickness would influence the tensile strength and permeability as well as the following procedures. Thicker cigarette film would have better stiffness with better visual performance. But, the cost would also be great. In order to find the balanced solution, high precision thickness tester is needed. Labthink PARAM CHY-C2 is the lab thickness tester with the precision up to 0.1um. When testing thickness in different directions, deviation must be controlled within 3% usually. Meanwhile, the edge thickness of BOPP film has to be measured.
C. BOPP Cigarette Film Tensile Strength, Elongation and Elastic Modulus
Cigarette package requires high tensile strength of BOPP films, which can greatly reduce the breakage during packaging process. Generally, 140N/mm2 vertically and 200N/mm2 crosswise are required. Elongation rate is for analysis of incision easiness of films. Cigarette packaging industry is different from other industries. Higher elongation rate is not better. Max. limitations of 200% vertically and 80% crosswise can guarantee easy incision and assembling smoothness. Other industries require those two indexes. But cigarette package requires more detailed requirements on incision easiness during high speed production. Therefore, Elastic Modulus testing is also put forward. Labthink PARAM XLW(PC) Auto Tensile Tester is the professional tester for film and its tensile strength with Elastic Modulus testing. Low Elastic Modulus would lead to worse stiffness, unsuccessful production procedure and inferior incision easiness as well as package breakage and film obstruction.
Commonly, Elastic Modulus is required to be above 2000N/mm2 for cigarette film. However, when testing Elastic Modulus, testing conditions and temperature must be emphasized. Otherwise, the results will fluctuate greatly. Therefore, testing condition must be stated.
D. The Heat Seal Strength of BOPP Cigarette Film
BOPP is required to have high heat seal strength and wider heat seal scope by the cigarette industry, so as to improve packing speed and proper operation. If the heat seal temperature is higher, it would lead to wrinkle because of increased BOPP film shrinkage. Therefore, proper heat seal temperature should be chosen so as to avoid unstable heat seal, wrinkle and other phenomena. The heat seal style of BOPP cigarette film is heat-pressure seal, that is, to heat seal at certain heat seal temperature, pressure and period. The heat seal testing is to test the minimum heat seal separating force after heat sealing. It is widely applied in the cigarette industry that Labthink PARAM HST-H3 Heat Seal Tester and PARAM XLW (PC) Auto Tensile Tester are used together. The heat seal strength of cigarette is normally required to be above 2.0N/15mm. Now, with the development of cigarette packing machine, low temperature heat seal film becomes more popular, which requires the heat seal strength above 1.5N/15mm.
E. BOPP Cigarette Film Coefficient of Friction Testing
The smoothness of BOPP cigarette film is one important index for BOPP films with is the testing requirements coming along with the high speed packing.
There are four kinds of situations that need coefficient of friction testing, namely, the coefficient of friction of the film and the metal side of the machine or the transfer belt; the inside side between films; the film inner side and the cigarette outer package; and the outer film side and the outer package. Of these four coefficients of friction, the first should be low so as to better transfer the cigarette package and improve packing speed.
The inside coefficient of friction should be a bit higher than that of the outer film and the machine metal side for precise location of film and cigarette package so as to improve heat seal quality and packing effects. The coefficient of film and outer paper box should be low for smooth insertion of cigarette packages. The testing speed is 100mm/min, or 150mm/min in US Standard. Labthink PARAM MXD-02 Coefficient of Friction Tester complies with many standards including US standards and international standards, and gets wide applications. Since the reference for cigarette film coefficient of friction varies, e.g., metal panel, cigarette box, inner and outer sides of films, etc., the coefficient of friction is normally between 0.2-0.6.
F. The Heat Shrinkage Testing for BOPP Cigarette Film
BOPP film heat shrinkage is mainly used for the evaluation of heat stability under different conditions or different factors. For rigid cigarette package, such rigid package has good support effect, around which high shrinkage film can be applied so as to achieve even and beautiful visual effects. Therefore, rigid package requires the heat shrinkage of BOPP cigarette film to be up to 8% to 12%.
But, deformation cause by high shrinkage rate is a problem for ordinary flexible cigarette package. Generally, the shrinkage rate is controlled within 3%-7%. For heat shrinkage testing of BOPP cigarette film, ASTM D 2732, or GB/T 13519 is applied. Take Labthink PARAM RSY-R2 Film Free Shrink Tester as an example; mark the vertical and crosswise lines on the specimen with clear indication of direction. Put the specimen in between the frame, and immediately emerge into 120±2C constant temperature medium for 20 seconds. Then, emerge the specimen into the prepared normal temperature bath for 5 seconds, and take it out. Lay horizontally and measure the vertical and crosswise size within 30 minutes. The measurement should be with accuracy up to 1 mm. At present, some companies heats 1 minute, 5 minutes or other conditions under 120C with different testing results.
G. BOPP Cigarette Film Abrasion Resistance Testing
With stricter requirements for abrasion resistance, inferior abrasion resistance performance would greatly influence the beauty of the cigarette package. The testing of abrasion resistance is to avoid scratch on the surface of the product caused by the contact of film surface and the machine; and to avoid wounds caused by film and outer package. Labthink PARAM MCJ-01A Rub Tester can be applied for the test. Take a piece of clean offset paper of 50mm width and 80g/m2 onto the rub tester. Cut a piece of BOPP cigarette of certain size and put on the rub platform. Set the rub times and start to see the abrasion.
Above all, there are many BOPP cigarette film testing items. When testing, relevant standards must be applied; or unified testing conditions for data comparison. Labthink, is willing to have further dialogues on BOPP film and its quality with professionals of the industry.