Development and application of coatings for edible lard steel drums (2)

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Development and application of coatings for edible lard steel drums (2)

Gong Qingpei, Zhangzhou Chemical Factory, Ministry of Weapons Industry

(3) Improve coating performance and appearance quality

This test decided to add two factors: the amount of film-forming material added and the amount of pigment added.

In view of the problem of poor color hiding power of the coating, titanium dioxide (Ta) was selected as the color-increasing pigment, and the impact resistance, oil resistance, heat resistance and appearance of the new formulation were examined to determine the most mature formula. Develop the factor level table 3.

Table 3 factor level table

factor
Component usage %
H
PAM
SE
LC
HD
Tai
Bit level 1
16
27
30
8
5
5
Bit level 2
17
29
32
9
6
7
Bit level 3
18
30
35
10
7
10

This time, the orthogonal test method is still used to determine the test plan as:

L168(36)

The test conditions and results are shown in Table 4:

Table 4 Orthogonal test plan and test result table

Test number\factor
H component addition amount (%)
PAM addition amount (%)
SE addition amount (%)
LC addition amount (%)
HD addition amount (%)
Tai addition amount (%)
test results
Adhesion (level)
Impact resistance (kgf/cm2)
Oil resistance (100 ° C, 6 h, 0.5% moisture)
Oil resistance (100 ° C, 6 h)
Exterior
1
1
3
2
2
1
2
2
45
Yellowing
Yellowing
White, strong hiding power
2
2
1
1
1
2
1
1~2
50
Yellowing
Rust point
3
3
2
3
3
3
3
1
50
Yellowing
Yellowing
4
1
2
1
2
3
1
1~2
50
Yellowing
Yellowing
5
2
3
3
1
1
2
1~2
50
Yellowing
Yellowing
6
3
1
2
3
2
2
1
50
Yellowing
Yellowing
7
1
1
3
1
3
2
3
45
Yellowing, slightly falling off
Rust point
8
2
2
2
3
1
1
1
50
Yellowing
Yellowing
9
3
3
1
2
2
3
1
50
Yellowing
Yellowing
10
1
1
1
3
1
3
2
50
Yellowing
Yellowing
11
2
2
3
2
2
2
1
50
Yellowing
Yellowing
12
3
3
2
1
3
1
1
50
Yellowing
Yellowing
13
1
3
3
3
2
1
1~2
50
Yellowing
Yellowing
14
2
1
2
2
3
3
1~2
45
Yellowing
Rust spots turn yellow
15
3
2
1
1
1
2
1
50
Yellowing
Yellowing
16
1
2
1
1
2
3
2
50
Yellowing
Yellowing
17
2
3
3
3
3
2
1
50
Yellowing
Yellowing
18
3
1
2
2
1
1
1
50
Yellowing
Yellowing
-
I
12,290
10,300
8,300
10,295
8.5,295
7.5,300

Total adhesion = 25.5

Total impact resistance = 815

(Note: I, II, and III represent the adhesion of the bit level 1, 2, 3, and the resistance and the sum; R represents the range R = the maximum - the minimum)

II
7.5,295
7.5,300
8.5,290
8,290
8,300
9,290
III
6,300
8,295
9,295
7.5,300
10,290
9,295
-
R
6,10
2,5
1,10
2.5,10
2,10
1.5,10

It can be seen from the table that the tests on the 3rd, 5th, 6th, 9th, 10th, 11th, 15th, 16th and 17th are better. The surface of the test coupons produced is milky white, the surface is smooth, and there is no impact on the impact. Up to 50kg/cm2 has reached the best level of adhesion, and there are also two grades that meet the national requirements for food packaging coatings. The color is beautiful, no odor, no blistering, no falling off, etc. From the test, we have obtained an ideal formula, the content of each component is as follows:

H component 29%

PAM component 17%

SE component 32%

LC component 10%

HD component 7%

Tai component 5%

We repeated this test with more than 10 tests using this formula, and the results were very good. We sent the oil samples tested for oil resistance to the Ganzhou Health and Epidemic Prevention Station for inspection. The results were in line with the national standard GB9686--88 issued by the Ministry of Health.

Through a large number of tests, the formula for the anti-corrosion coating of the inner surface of the edible lard barrel - polyamide epoxy resin coating was found.

Third, the problems in the production of paint barrels and solutions

After the coating is selected, there are mainly the following problems in the production process:

1. Premature curing of the coating. Through analysis of the reasons, it was found that when the coating was prepared, the one-time ingredients were too much, the viscosity was too large, and the heating temperature was too high during the batching, which accelerated the curing of the coating. The coating has not yet been applied and the coating has solidified. This has brought difficulties to the construction and wasted raw materials. To solve the problem of premature curing of the coating, the key is to control the curing time. From the performance of the coating curing agent and the curing process: the PAM curing agent can be cured at room temperature. It has a fast curing speed and is a commonly used room temperature curing agent. The disadvantage is that the heat is released during curing and the use period is short. Due to the exothermic effect, the viscosity of the coating is continuously increased, which affects the quality of the coating and often blocks the nozzle. Therefore, when formulating the paint, batching is required. So as not to affect the quality of the spray. To reduce the viscosity of the ingredients, increase the amount of diluent and control the viscosity within a certain range. At the production site, it is also necessary to add a cold water tank to absorb the heat released during solidification, and to achieve the purpose of controlling the viscosity by controlling the temperature, thereby prolonging the curing time.

2. Coating peeling problem. The main factors causing the coating to fall off are: before the steel drum is sprayed, the surface of the barrel is stained, scaled, rusted, etc., the surface treatment is not thorough, the coating adheres poorly, the coating is peeled off, the drying temperature is not enough, and the drying is performed. The time is too short, resulting in incomplete curing, poor mechanical strength; too high drying temperature, too long, will make the coating yellow, brittle, and impact resistance. Therefore, in the production process, it is necessary to pay attention to the surface treatment of the steel drum before spraying to eliminate oil stains, scale and rust spots. To master the drying conditions, it is best to spray in the drying tunnel after drying at the appropriate temperature for a suitable time. Avoid hand-sticking the coating during handling. In addition, uneven thickness of the spray will also cause the spray to fall off. As long as the thickness of the coating can cover the substrate, it is better to be thinner. When the thickness of the coating is increased to a certain extent, the adhesion is lowered, so that the substrate is not used when spraying.

3. Rough paint problem. Mainly due to the poor precision of manual screening, the quality of raw materials for coatings is unstable, and it is not evenly stirred before spraying. Therefore, when coating ingredients, it is necessary to filter with silk screen to improve the fineness.

4. Hygiene guarantee during production. Since the polyamide epoxy resin coating is used for the coating of edible lard, the hygiene of the steel drum and the sanitation of the coating are ensured during the production process.

In the selection of coating materials, we first considered the non-toxic problem. The epoxy resin we chose is non-toxic and PAM is also hygienic. The diluent SE is a volatile solvent and is non-toxic. LC, HD and Tai are all non-toxic. All of these materials are hygienic and meet national health standards.

In the production process, measures should be taken to ensure hygiene: firstly, the spraying operation personnel should be inspected, and those without infectious diseases can be put into operation. Before the spraying, the steel drum should be subjected to necessary sanitary treatment. Before sealing, the inner surface of the steel drum should be applied. Carry out hygienic inspection, remove dirt and dust, and keep the inner surface of the barrel clean. The operator should wear special gloves. Wear protective clothing and masks.

Through a year of hard work, we have achieved certain results. We produced steel barrels for edible lard and shipped them to the Soviet Union in Yunnan, Guizhou and other places to solve the packaging problem of food lard. Through the actual inspection with the users to Yunnan and other places, we proved that our coatings are successful. This product fills the gap in the packaging of food lard in Sichuan Province.

Fourth, the conclusion

Polyamide epoxy resin coating has strong anti-corrosion ability, high adhesion and simple process. It is a good anti-corrosion coating for edible lard steel drum. The paint can also be used for anti-corrosion of the inner wall of the wine, soy sauce fermented food storage tank, tank truck and the like.

In the commodity market, the corrosion performance of many chemical products requires our barrel industry to provide a suitable steel drum package. At present, the technology of the domestic steel drum industry in this area is not very mature, so we have put forward higher requirements. In the future, we will apply synthetic organic polymer coatings and natural coatings to steel drums to solve the packaging corrosion problem of many chemical products.

references

(1) "Coating Process" Chemical Industry Press

(2) "Epoxy resin production and application" Petrochemical Industry Press

(3) GB9686-88 "Sanitary Standard for Polyamide Epoxy Resin Coatings on Inner Wall of Food Containers"

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