Video display of sodium alginate in flat screen printing equipment

　

　　The viscosity of the paste used for rotary screen printing should be low, and it should have excellent rheology and permeability, while the viscosity of sodium alginate is high, so appropriate substances can be added to adjust its viscosity, which not only improves the printing performance, but also reduces the production cost. At present, one of the most studied methods is to replace sodium alginate with denatured products such as starch and cellulose, such as sodium carboxymethyl starch. Starch carboxymethyl sodium can achieve satisfactory results in reactive dye printing, but its permeability and washability are poor, and it has some shortcomings such as hard handle and poor uniformity when used as printing paste. Therefore, the content of sodium carboxymethyl starch should not be too high, otherwise it will affect the printing effect. The optimum blending ratio of sodium carboxymethyl starch and sodium alginate was found through exploration, and their viscosity and application performance were studied. In addition, a low molecular weight viscosity regulator S was selected to modify sodium alginate, and its influence on the viscosity and printing effect of sodium alginate paste was studied.

Video display of sodium alginate in flat screen printing equipment



　

　

　　1 Experiment 1.1 Drugs and materials

　　Sodium alginate, sodium carboxymethyl starch, sodium hexametaphosphate, sodium carbonate, baking soda, urea, reactive brilliant red K22BP, reactive turquoise blue K2GL, pure cotton bleaching cloth, viscosity regulator S and protective agent F (all prepared by various compounds themselves).

　　1.2 Instruments and equipment

　　Hot air tentering setting machine, steaming machine, NDJ201 rotary viscometer, Y571B friction fastness tester.

　　1.3 Test conditions and methods

　　Viscosity test: Weigh a certain amount of sodium alginate (or sodium carboxymethyl starch and low-molecular viscosity regulator S with a certain mixing ratio), add it into 400m l water, dissolve it and paste it, and after standing for half an hour, measure the viscosity with a rotary viscometer at a temperature of 20 0 0.5℃ (in the test of the influence of temperature on the viscosity of paste, the temperature condition is T 0.5℃). Friction fastness test: It is determined according to "GB415278 Test Method for Friction Fastness of Printed and Dyed Cloth", which is divided into dry rubbing and wet rubbing, and the staining grade is rated by "GB25121995 Gray Sample Card for Evaluating Staining".

　　1.4 Original paste, color paste prescription and printing process

　　

　

　　

　

　　Note: Protective agent F is an organic sulfonate, which has the functions of solubilization and anti-agglomeration. X is 0g, 1g and 3g respectively.

　　Printing process:

　　Printing → Drying (80-90℃ for 10 min) & rarr; Steam (100℃,5min) or bake (150℃,5m in)→ Washing → Soaking → Washing → oven-dry

　　Results and discussion 2.1 Viscosity properties of mixed paste of sodium alginate and sodium carboxymethyl starch

　　2.1.1 Relationship between paste concentration and viscosity

　　Beat sodium alginate and sodium carboxymethyl starch into original paste, and measure its viscosity. The change rule is shown in Figure 1:

　　

　

　　Note: The relative viscosity is based on the viscosity (47mPa.S) when the sodium alginate concentration is 1%, and the viscosity of pastes with other concentrations is compared with it, the same below.

　　As can be seen from the above figure, the viscosities of sodium alginate and starch carboxymethyl sodium both increase with the increase of paste concentration, while the viscosity of sodium alginate is higher than that of starch carboxymethyl sodium, and the viscosity of sodium alginate increases more with the increase of paste concentration.

　　2.1.2 Viscosity properties of mixed paste of sodium alginate and sodium carboxymethyl starch.

　　Mixing sodium alginate and sodium carboxymethyl starch in different proportions, and measuring their viscosity values respectively, it is found that the viscosity change law is shown in Figure 2:

　　

　

　　As can be seen from the above figure, when sodium alginate is added with about 10% starch carboxymethyl sodium, the viscosity of the original paste is basically unchanged, but with the further increase of starch carboxymethyl sodium, the viscosity of the original paste decreases, and its viscosity decreases to the lowest when the content of starch carboxymethyl sodium is 80%. It can be seen that the appropriate content of starch carboxymethyl sodium is 10%, which basically does not reduce the viscosity of the original paste, and the viscosity is stable, but the production cost can be obviously reduced.

　　2.2 Viscosity properties of various pastes

　　2.2.1 Relationship between paste concentration and viscosity

　　The relationship between paste concentration and viscosity is shown in Figure 3:

　　

　

　　As can be seen from Figure 3, the viscosity increases with the increase of paste concentration. When the paste concentration is small, the viscosity increases slowly, and when the concentration exceeds 4.7g/400g of water, the viscosity increases sharply. Among the above five pastes, the viscosity of unmodified sodium alginate is the highest, while the viscosity of sodium alginate paste with viscosity regulator S and starch carboxymethyl sodium is obviously reduced, especially starch carboxymethyl sodium. For the modified paste, the viscosity decreases with the increase of the dosage of viscosity regulator S, but its viscosity is still higher than that with starch sodium carboxymethyl.

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　　2.2.2 Relationship between dosage of viscosity modifier S and viscosity

　　Dissolve sodium alginate (4.7 g) containing viscosity regulator S with different weight ratios in 400m l water to make a paste, and then measure its viscosity. The viscosity change is shown in Figure 4:

　　

　

　　

　

　　As can be seen from Figure 4, the viscosity regulator S has obvious viscosity reduction effect, while the viscosity of modified sodium alginate paste decreases linearly with the content of viscosity regulator S. When the content of viscosity regulator is 10%, the viscosity of modified sodium alginate paste decreases to the range of low viscosity sodium alginate, so it can be seen that the dosage (weight percentage) of viscosity regulator cannot exceed 10% at most.

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　　2.2.3 Relationship between temperature and paste viscosity

　　See Figure 5 for the influence of temperature on paste viscosity (paste concentration is 4.7g/400g of water): From Figure 5, it can be seen that the influence of temperature on the viscosity of all kinds of pastes is the same, that is, it decreases with the increase of temperature, and the trend of decrease is basically the same.

　　2.2.4pH Effect of pH value on paste viscosity

　　See Figure 6 for the relationship between pH value and viscosity of various pastes (paste concentration is 4.7g/400g water). As can be seen from Figure 6, the viscosity of the original paste is greatly influenced by the pH value, and the variation law of the viscosity influenced by the pH value is different for different pastes. For the unmodified sodium alginate and sodium carboxymethyl starch, the viscosity of the original paste first decreased with the increase of pH value, and reached the maximum when pH value was 9. Then, with the further increase of pH value, the viscosity increased slightly, but not much, which indicated that the viscosity of the two pastes basically tended to be stable in alkaline environment. It can be seen that when these two pastes are used in reactive dye printing, the most suitable pH value is about 9-11, especially when the pH value is 9, the fluidity is the best. However, the viscosity of sodium alginate paste with viscosity regulator S first increases with the increase of pH value, reaches the maximum when pH value is 7, and decreases with the further increase of pH value. After pH value reaches 9, its viscosity basically tends to be constant. It can be seen that the viscosity of modified paste is very unstable in acidic and neutral environments, but it tends to be stable in alkaline conditions. The optimum pH value of modified paste for reactive dye printing is about 9.

　　

　

　　2.3 Printing effect

　　2.3.1 Color light, brightness and color yield

　　It can be seen from the printed samples that the color of sodium alginate paste with viscosity regulator S and starch carboxymethyl sodium is basically the same as that of unmodified sodium alginate paste, and the color of printed samples with starch carboxymethyl sodium paste is the most vivid. The color of the sample with viscosity modifier S decreased slightly, and the color depth decreased more with the increase of viscosity modifier S. However, when the protective agent F is added to the color paste, the color of the printed sample becomes darker. With the increase of the dosage of the protective agent F, the color of the printed sample becomes darker. When the dosage of the protective agent F reaches 3%, the color of the printed sample is basically similar to that of other samples, which shows that the protective agent F has obvious protective effect on reactive dye printing. For different fixation processes, the color of the sample with steaming fixation is darker than that with baking fixation.

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　　2.3.2 Friction fastness

　　See Table 1 and Table 2 below for the rubbing fastness (staining) of printed samples of various pastes:

　　

　

　　

　

　　From the above table, it can be seen that the dry and wet friction of the printed samples of modified paste and unmodified paste are very high, except for a few which are grade 4, most of them are grade 4-5, and some are even close to grade 5, which shows that the modified paste has little effect on the fastness.

　　2.3.3 feel

　　The printed samples of all kinds of pastes feel similar and are soft. The printed sample with starch carboxymethyl sodium paste feels a little harder, because starch carboxymethyl sodium is not easy to be removed from the fabric, so the washing of the fabric should be strengthened after printing.

　　　　3 Conclusion 3.1 It is feasible to directly print reactive dyes by partially replacing sodium alginate with sodium carboxymethyl starch. The mixing ratio of sodium alginate and sodium carboxymethyl starch is 9∶1, and the viscosity (rheology, temperature and pH value) and printing performance of the mixed paste are basically the same as those of sodium alginate.

　　3.2 Replacing sodium alginate with viscosity regulator S can obviously reduce viscosity. When the concentration of viscosity regulator S reaches 8%-10%, the viscosity of modified sodium alginate paste is similar to that of low viscosity sodium alginate paste, which is basically suitable for rotary screen printing.

　　3.3 It is feasible to directly print reactive dyes by replacing sodium alginate with viscosity modifier S. After printing, the color shade and rubbing fastness of the products are basically unchanged, but the color depth is slightly reduced, and it is also slightly reduced when it is added for a long time. However, the adverse effect on color can be alleviated by adding the protective agent F. When the concentration of the protective agent reaches 3%, the color depth of the printed sample is basically the same as that of the unmodified and starch-added sodium carboxymethyl. Generally speaking, the printing effect of modified paste can basically reach the printing level of sodium alginate.

　　3.4 Replacing sodium alginate with starch carboxymethyl sodium and viscosity regulator S can obviously reduce the production cost. The appropriate dosage of starch carboxymethyl sodium is 10%, the appropriate dosage of viscosity regulator is 8%-10%, and about 3% of protective agent F is added.