Development of high water resistant baking paint a

0.2

n-butyl acetate

3.0

cyclohexanone

2.0

BL 3175 Sn

9.0

adhesion promoter

2.0

byk-310

0.3

Red Colorant

3.5

coupling agent

2.0

diluent

xylene

51.0

ethyl acetate

27.0

n-butyl acetate

15.0

cyclohexanone

5.0

catacure KB

2.0

1.3.1 preparation of coating

first weigh and input thermosetting acrylic resin, amino resin, epoxy resin, defoamer, n-butyl acetate and cyclohexanone solvent according to the formula, The 1000 experimental results can be automatically stored at a speed of ~ 1200r/min and dispersed for 10~15min. Then, according to the formula, the closed isocyanate, adhesion promoter, surface control agent and red pigment are successively added, and dispersed at a speed of 600~800r/min for 5~6min. Finally, according to the formula, the coupling agent is added, dispersed at a speed of 600~800r/min for 3~5min, and the fineness of the coating is tested to be ≤ 15 μ M is enough

1.3.2 preparation of diluent

first put xylene, ethyl acetate, n-butyl acetate and cyclohexanone in sequence according to the formula, disperse them at the speed of 600 ~ 800r/min for 5~10min, then add accelerator catacure KB, and then disperse them at the speed of 600 ~ 800r/min for 3~5min

1.3.3 template preparation and drying process

take the prepared coating and diluent, mix the paint in the proportion of coating: diluent 1.0:0.8, spray it on the 304 stainless steel substrate for test with w-p gun (clean the substrate with 120 # white oil before spraying), then preheat it in the 90 ℃ electric blast drying oven for 5min, and then bake it in the 160 ℃ electric blast drying oven for 20min, Take it out and cool it naturally for 12h, and then test the film performance

1.4 film performance test

see Table 2 for film performance test results. It can be seen from table 2 that the main properties of the film are good and the boiling resistance is excellent

Table 2 film performance test results

Project

technical indicators

results

method/Standard

film color and appearance

meet the standard template, the surface is flat and smooth

through

visual

film thickness/μ M

15~20

19

gb/t 1764-1979

pencil hardness

≥ 2H

2H

gb/t 6739-1996

gloss (60 °)/%

agreed

qualified

gb/t 9754-1988

adhesion/grade

lattice method

0

gb/t 9286-1998

appearance after boiling (100 ℃ boiling water, 2h)

no blistering, gloss loss Wrinkle phenomenon

no abnormality

visual

adhesion after boiling (100 ℃ boiling water, 2h)/grade

0

0

GB/T

2 results and discussion

2.1 selection of resin

resin as the main component of the coating plays a major role in the performance of the coating (such as protective performance, mechanical performance, etc.). Amino baking varnish for household appliances, instruments, meters and appliances can generally be divided into alkyd amino baking varnish, acrylic amino baking varnish and polyester amino baking varnish; For the coating film painted on the stainless steel substrate that requires water boiling resistance, first of all, two basic requirements should be met: one is to have excellent adhesion to the stainless steel substrate that is difficult to adhere, so as to form a tight coating film that is not easy to be penetrated by water; the other is that the main resin should have excellent water boiling resistance; On the other hand, acrylic resin has good mechanical properties, weather resistance and chemical resistance. Based on the above considerations, thermosetting acrylic resin is selected as the main resin in this test. Five thermosetting acrylic resins from different manufacturers with good adhesion to stainless steel substrate were selected for comparative test. The test results are shown in Table 3

Table 3 Comparison Test of resin boiling resistance

Project

resin model

he3650

esb-1405

acr8688

tar-3358a-60

ac1066

conventional adhesion/grade

0

0

0

0

appearance after boiling (100 ℃ boiling water, 2h)

foaming, discoloration

foaming, discoloration

no abnormality

foaming, discoloration

foaming Discoloration

adhesion after boiling (100 ℃ boiling water, 2h)/grade

4

5

0

5

4

it can be seen from table 3 that the appearance of thermosetting acrylic resin esb-1405 and thermosetting acrylic resin tar-3358a-60 has blistering and discoloration after boiling test, and the film has no adhesion at the same time; Thermosetting acrylic resin he3650 and thermosetting acrylic resin ac1066 have serious paint drop after boiling, and the film has obvious blistering and discoloration, while thermosetting acrylic resin acr8688 has no abnormal appearance and good adhesion after boiling test. The reason may be that thermosetting acrylic resin acr8688 has high crosslinking density, good adhesion to stainless steel substrate, and few residual hydrolytic groups in the resin, Therefore, its coating has excellent boiling resistance on stainless steel substrate. Finally, thermosetting acrylic resin acr8688 was selected as the main resin of the formula

2.2 effect of the selection and dosage of amino resin on the boiling resistance of the film

as a crosslinking agent, amino resin improves the hardness, gloss, chemical resistance and drying speed of the matrix resin. Among amino resins, urea formaldehyde resin has poor comprehensive performance. Although butylated melamine resin has good performance in many aspects, it has poor adhesion and high brittleness. Compared with some amino resins such as methylated melamine resin and butylated melamine resin, the paint crosslinked with benzoic melamine resin has high gloss at the initial stage, and its alkaline resistance, water resistance and heat resistance have been improved. In order to meet the requirements of formula design, the benzene melamine resin uramex bf892 was selected as the main crosslinking agent

in amino baking varnish, the ratio between acrylic resin and amino resin has a crucial impact on the properties of the product. The crosslinking is insufficient, and the hardness and solvent resistance of the product cannot meet the requirements; If the crosslinking is excessive, the impact resistance and water resistance of the product cannot meet the requirements. It can be seen from table 4 that when the ratio of acrylic resin to amino resin is 1.2 ` 1.4, the water boiling resistance of the film is good

Table 4 Effect of the ratio of thermosetting acrylic resin to amino resin on the water boiling resistance of the film

Project

ratio of thermosetting acrylic resin to amino resin

1

1.2

1.4

1.6

1.8

conventional adhesion/grade

0

0

0

0

0 p>0

appearance after boiling (100 ℃ boiling water, 2h)

sporadic foaming

no abnormality

no abnormality

sporadic foaming

foaming

adhesion after boiling (100 ℃ boiling water, 2h)/grade

0

0

0

1

2.3 effect of epoxy resin and closed isocyanate on the boiling resistance of the film