The detection of the anti-sheet strength of coated paint should pay attention to the discussion of the problem

0 Foreword
Nitrate cellulose produced by the mixture of nitric acid and sulfuric acid and cellulose esterification reaction, and esters, alcohols, aromatic hydrocarbons and other mixed solvents made of nitro coating on aircraft cloth, with fast drying, high viscosity, light transparency, stretch strength, flexibility and good extension performance characteristics. Brushing on the cloth has a good contraction force, so that the cloth is breathless, non-permeable, and can improve its mask strength and shrinkage. The strength of the coating film refers to the strength of the coating film resistance to the pull force, that is, when the free coating film is fractured or plasticed by the pull test, the load applied to the coating film of the unit cut-off area (the free coating film on the pre-test
mask) is applied

1 Test Part
1.1 Measurement Instruments and Materials Equipment
Electronic Balance: Sense 0.01 to 0.1 g, Beijing Analysis Instrument Factory; Wool Brush: Width 50 to 65 mm; Pull Tester: Measurement Range 0 to 200kg, Shanghai Textile Machinery Company; Wood Frame: 560 mm ×40 0 mm (on the inside), each side of the wood strip width of 25 mm, thickness of 35 mm; Mobu: 114 silk light flat cloth, Shijiazhuang Aircraft Manufacturing Company; metal needle pen; word change cone; glass plate: 500 mm ×400 mm; straight ruler: 20 cm, 0.5 mm, 500 mL stainless steel cup.
1.2 assay reagents
waterless ethanol (GB/T678), butanol (GB/T12590), ethyl acetate (GB/T12589), butyl acetate (HG/T3498), are pure analysis, Tianjin Northern Tian medicine chemical reagents, toluene (GB/T684), acetone (GB/T686), are pure analysis, Tianjin Kemio chemical reagents. The ratio of nitro-mixed thinners made by the above-mentioned reagents in different proportions is: n (toluene): n (ethanol) : n (butanol) : n (ethyl acetate): n (butyl acetate) - 50:7:10:11:22.
1.3 Measurement step
First, according to the length and width size of the wooden frame, crop a piece of cloth 3 to 5 cm larger than the outside of the wooden frame, tiled on the wooden frame, in the outside of the wood frame on both sides of the radial reduction of 4 mm, up and down Latitude to reduce 3 mm, each pull out a cloth, a total of 4 cloth wire, slightly force the wire seams aligned to the outer edge of the wooden frame, every 4 cm press a pushpin, tight cloth frame, the cloth should be loose and moderate, the center of the cloth can not collapse. The mask is framed and weighed on the balance, so that the mask and frame are heavy to W1(g) before painting, because the coating paint sticks through the high, the viscosity value measured with the coating-1 viscosity meter is usually more than 150 s In order to distribute the free coating film on the mask evenly, the appropriate amount of nitro thinner should be added for dilution and then brushing, but the dose of nitro dilution should not exceed 20% of the original paint amount, the amount of coating paint is still calculated according to the original paint. Painted under constant temperature and humidity conditions ( (25±2) , 50% ±5% ) for painting; Multiple moves, the amount of paint used per coating (in wet film meter) is 160 to 180 g/m2, the amount of paint per layer should be less than the actual weight gain after painting 18.75 g/m2 (in dry film). Each layer interval time is: the first, second, third, and fourth coating paint after the actual drying time is 20 to 30 min, 30 to 45 min, 45 to 60 min, 45 to 60 min. After painting, after coating the film drying 24 h under constant temperature and humidity conditions, the weighing amount is calculated as W2(g) after coating the mask and the frame mass, and the weight gain (g/m2) after coating the coating is calculated according to the 1.4.1 formula, i.e. the sum of the amount of paint per layer should be less than the actual weight gain of 75 g/m2 (with dry film meter) after painting 4 coatings.
After coating the film drying 72 h under constant temperature and humidity conditions, remove the mask from the frame, place it flat on the glass plate, strip it with a metal needle and pen, and use the longitude and latitude required by the pull test to take a 280 mm long, wide measure on the unpainted surface of the cloth. 52 mm cloth sample, and then with a metal stylus according to a good amount of size, along the mon cloth meriver and latitude will be coated cloth strip separate, separate cloth strip, accurate amount of 50 mm wide, the two sides of the excess lines from beginning to end, with scissors cut off the bristles. On the pull test machine, the distance between the lower two fixtures is adjusted to 20 cm, and the lower chuck drops at a rate of 100 to 110 mm/min. After calibrating the center of the test strip, stretch. When the test strip breaks, write down the pointer reading immediately. According to the same method, the pull test of the unpainted merichane and the latitude of the Monb bar are done respectively.
1.4 Calculation Method
1.4.1 Weight Gain Calculation method after mask painting
Weight gain X (g/m2) after mask painting
type (1): W1 - pre-painting mask and frame weight, g;
W2 - after painting cloth and frame weight, g;
S - Painted area, cm2.
1.4.2 After coating the mask, the amount of anti-sheet strength increase calculation method
(1) by increasing the amount of anti-sheet strength to the monb δ

F' - after painting by the test strip pull, kg;
b - test strip width (equal to 50 mm), mm.
F' is an arithmetic average of three similar values of the arithmetic of the pull force of the test strip, and the difference between the measured value and the average value of any one of them is not greater than 3% of the mean.
(2) latitude to Monb bracing strength increase of δ latitude (kg/m) by type (3) calculation:
medium: F-latitude - painted front latitude to Monb strip pull, kg;
F' latitude - painted after the latitude to test strip pull, kg;
b - test strip width (equal to 50 mm), mm.
Arithmetic average of the parallel strip pull force with three values, either of which measures the difference between the value and the mean, which is no greater than 3% of the mean.
(3) after coating the mask, the increase in the amount of anti-opening strength δ (kg/m) is calculated by type (4):
2 screening and analysis of the measurement data
the pull test is carried out on a pull test machine with a measuring range of 0 to 200 kg. Parallel test 5 sets of blank test pieces, taking 3 sets of 6 data with similar meriver and latitude values, calculated the average value, of which the difference between the measured value and the average value of any one, not greater than 3% of the average, see Table 1.
longitude, latitude blank test data
in this pull test machine after painting the test piece of the cloth to carry out a pull test. When the test strip is plastic to break, note the pointer reading, take the merith, latitude value similar to the 3 sets of 6 data, respectively, calculate the merichanical, latitude to Monb tensor strength increase (kg/m), and then calculate the total tensor strength (kg/m), in which any one measured the difference between the value and the mean, not greater than 3% of the average, see table 2.
meridial, latitude to Monb sheet strength increase volume data
after calculating merid, latitude to Monb sheet strength increase arithmetic average of 952.7, 922.7, Monb's total The arithmetic average is 1,875.3, and the difference between each result and the average is no more than 3% of the average, fully in line with the product standard Monb's total anti-zhang strength
degrees greater than 1,850 kg/cm.
3 Attention to the problems and preventive measures
based on years of user feedback and visits to large enterprises throughout the country, found that the testing process often appears the following problems, in response to the problems are now put forward corresponding preventive measures.
(1) after brushing free coating film in the mask paint surface has not been leveled there is a partial condensation, uneven distribution. The main reason for this is: because the coating paint belongs to volatile paint, table drying time is very short, the coating film has not been leveled on the table dry, coating paint product standards prescribed viscosity (coating-1 viscosity meter) for 120 to 180 s, due to the characteristics of the coating paint itself determines the paint In the storage process will appear in the phenomenon of resparation, in order to prevent the storage period viscosity reduced to the lower limit or below, the general offline coating paint viscosity will usually be greater than 160 s, so the testing process should be based on the viscosity size of the coating paint for the appropriate amount of dilution, but the added nitro dilution dose should not exceed 20% of the original paint amount.
(2) is white, speckled, and striped. The main reason for this is that the construction site is humid, the atmosphere contains more moisture, solvent evaporation is too fast, the surrounding temperature drops sharply, the water vapor condenses on the coating film, so that a small part of the nitric acid cellulose pre-emination forms white, speckled, the coating forms streaks; Point volatility of slow organic solvents, the construction site temperature should not be less than 12 degrees C, while paying attention to the construction site humidity and the volatile rate of solvents used, the relative humidity of the general construction environment should not be greater than 70%, otherwise there will be whitening phenomenon, and therefore will reduce the strength of the mask."
(3) the back of the cloth is a bit dripping, bubble phenomenon. The main reasons for this are: too much paint and thinner (volatile liquid) caused by low adhesion, brushing too much force, so that the glue through the low paint sample through the mask surface penetration to the back, forming a drop; Cloth, brushing speed is too fast, in the surface of the cloth to form a large number of bubbles, preventive measures: according to the size of the product viscosity to strictly control the addition of thinner, after adding diluent to fully stir evenly, do not make a small number of thinner floating on the coating paint sample.
(4) test mask strip has a twill. The main reason for this is: the draw line is not pumped, or there is a broken line exists, due to the presence of interrupted lines, can not find gaps, resulting in the tension of the wood frame when the longitude and latitude line appears twill, resulting in the coating of the cloth appears twill.
(5) to do the anti-zhang strength stretch test strip, sometimes in the early stages of the stretch suddenly appear a word break. The main reason for this is: because the mask test piece paint thick and thin uneven, usually coated with a lower content of film, generally around 10%, so the number of channels painted at least need to be evenly painted 4;
4 Conclusion
The test results of the anti-sheet strength are very strict for the use of coating paint, and the measurement results of the longitude and latitude-to-Monb anti-sheet strength will be affected by various aspects and produce errors. The error of the anti-sheet strength test is the error caused by the uneven use of coating paint on the cloth, the error of the size of the mask, the error of viscosity between the batch of coated paint, the error of the tightness of the cloth when the wood frame is on, the accuracy of the pressure test machine, the temperature and humidity of the test environment and the error brought about by the operation of the personnel. The standard size of the mask coating surface is 560 mm ×400 mm, while the size of the mask strip participating in the experiment is only 200 mm×50 mm, and these errors have a great impact on the results measured by such a small mask strip. In addition, the coating method of the cloth also determines that the upper reaches of the mask from the coating film is not the same uniform, uneven test pieces, it is difficult to represent the quality level of the sample sheet strength. This requires that by measuring the amount of dry film used per layer, the test pieces that do not conform to the test interval will be dropped, so that the effect of the comprehensive error is relatively reduced, so that the accuracy of the test is relatively improved.
above is the author over the years on the coating paint anti-zhang strength detection process of various problems. It is hoped that quality control personnel in the daily inspection, pay attention to the integration of standards, methods and actual inspection work, so that quality inspection work more scientific, inspection costs more economical, issued data more reliable.