Development and application of coatings for edible lard steel drums (1)
Gong Qingpei, Zhangzhou Chemical Factory, Ministry of Weapons Industry
Abstract: In this paper, polyamide epoxy resin coating was selected for the anti-corrosion and sanitation of packaged edible lard steel drums, and its formulation was developed. In the development, the orthogonal test was used to find out the best formula of the coating composition, and some solutions to the problems in the production process of the inner coating steel drum were analyzed.
Key words: development of steel barrel paint Shenghua lard
I. Introduction
At present, there are a series of problems in the currently used lard steel drums on the market. The quality of transportation and storage is a major issue to be resolved. The inner wall of the chemical lard steel barrel used in many meat joint factories has no paint, only some rapeseed oil is applied, which is easy to rust and pollute the oil, and the storage period cannot be guaranteed. Often due to the deterioration of edible oil, it is used as industrial oil, causing serious economic losses. In the past two years, we have developed a kind of anti-corrosion coating that meets the hygienic standard, which solves the problem of deterioration of edible lard storage and is welcomed by the meat joint factory. The situation we have developed is as follows for reference by peers.
Second, the choice of paint development formula
1. Performance and use of polyamide epoxy coatings
The epoxy resin (H) is a high molecular polymer containing an epoxy group. It is itself thermoplastic. In order to make epoxy resin a useful coating, it is necessary to react the epoxy resin with the curing agent to crosslink into a macromolecule of a network structure, in order to exhibit various excellent properties. Within the molecular structure of the polyamide (PAM), the low molecular weight polyamide resin contains an active amine group which can be crosslinked with an epoxy group in the epoxy resin to form a network structure. It has good adhesion and flexibility. It is not only a good curing agent for epoxy resins. It allows the epoxy to maintain its toughness for a long time. Therefore, after the epoxy resin and the polyamide are crosslinked together, the bulk structure becomes a high molecular polymer which is insoluble and hard to melt in water and fat. It has the advantages of strong adhesion, excellent chemical corrosion resistance, small shrinkage, good heat resistance, high mechanical strength and excellent electrical insulation performance. As a coating, it not only has unique properties in terms of corrosion resistance, but also greatly superior to other coatings in terms of mechanical properties, elasticity and gloss.
2. Develop formula:
Epoxy resin (H) is the main film-forming material of the coating. It is a thermoplastic, linear polymer resin. A simple uncured denatured epoxy resin is of no use value. When it is used, it is necessary to add a curing agent to crosslink the linear epoxy resin molecules into a large portion of the network structure, and to exhibit an excellent performance without dissolving the infusible epoxy coating. Therefore, curing agents and toughening agents are the most important auxiliary materials when epoxy resins are used. Since the polyamide (PAM) and the epoxy resin (H) have the above advantages after crosslinking, the polyamide resin is mainly selected as a curing agent and a toughening agent, and also serves as a secondary component of the film-forming substance.
When the oxygen resin is properly added during the curing process, the amount of the resin can be relatively reduced, the cost can be greatly reduced, and the physical and mechanical properties can be improved, and the adhesion of the coating can be enhanced. A certain amount of calcium carbonate (LC) and talc or white silica powder (HD) are used as inert fillers to adjust the mechanical strength of the coating film.
In addition, a special alcohol solution (SE) containing ethyl acetate or acetone is added to adjust the viscosity and fluidity of the coating, increase the film forming property of the coating, and make the film formation easy and easy to apply.
(1) Explore the best ratio of coating components:
In order to find out the best ratio of coating components, to evaluate the adhesion, impact resistance and oil resistance of the coating, it was decided to fix the amount of epoxy resin in the film-forming substance. The orthogonal test was mainly used to investigate the curing agent polyamide. The amount of addition, the amount of SE added, the amount of light filler LC added, the amount of heavy filler HD added, and other factors, and the drying temperature and drying time, are listed in Table 1.
Table 1 factor level table
Using the orthogonal table, the test plan was discharged. Because the amount of curing agent added is the key, so there are three levels in the row, and the mixed level is selected:
L18 (61×35)
Listing 2 is as follows:
Table 2 Orthogonal test plan and test result table
Total adhesion = 40.5
Total impact resistance = 815
(Note: I, II, III, IV, V, VI represent the adhesion of the bit level 1, 2, 3, 4, 5, 6, respectively, and the sum of the impact; R represents the range R = the maximum - the minimum)
Analysis of test results:
Comparing the results of the 18 batches of tests, it can be seen that the effects of the tests No. 10, 14, 16, and 18 are better; from the effect of the test coupons directly produced, the test film baked at 150 ° C has some yellowing.
From the calculation of the adhesion and the impact resistance, it can be seen that the lower the number of adhesion, the higher the level, so the smaller the adhesion, the better the bit level is, the better the impact resistance is, so the impact resistance The sum is the bigger the better.
It can be seen from the analysis of the experiment:
1 In the case of ensuring the performance of the coating, from the perspective of raw material cost. The amount of the curing agent added is about 16%.
2SE can adjust the viscosity of the coating after adding the coating, increase the use time and facilitate the construction, but too much addition will affect the properties of the coating and reduce the adhesion. Therefore, the amount of SE added is between 30 and 35%.
8 drying temperature and time have a greater impact on the properties of the coating. When the temperature is too high, the coating film becomes brittle, yellow, the temperature is too low, and the coating is not completely cured. Test results: drying temperature 120 ± 10 ° C, time selection 40 ~ 60 minutes is appropriate.
4 Appropriate addition of LC and HD can reduce the cost, enhance the adhesion of the coating, and facilitate construction.
By groping LC between 8-10%, HD does not exceed 8% at most.
A batch of steel drums was sprayed with the above-mentioned formula paint, and all performance indexes were met to meet the requirements. Because the whole paint is colorless and transparent, it can not cover the stain on the substrate after being coated on the inner surface of the steel drum, so that the inner surface of the steel drum is not uniform in color and the appearance is not beautiful. To this end, it was decided to add a white filler WF to make the paint consistent with the color of the lard.
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