Selection and application of cooking-resistant plastic ink pigments

The high-temperature retortability of ink mainly refers to the heat resistance of the ink, that is, the degree of discoloration of the ink layer under heat. The heat resistance of plastic ink mainly refers to the heat resistance of the package in the process of cooking, heat sealing and compounding, and the poor heat resistance is mainly manifested in the fading, discoloration, and unclear graphics. The heat resistance of the ink is mainly determined by the pigment and the binder. The heat resistance of the binder is poor and it changes from white to brown after heating. Therefore, the heat resistance of the light ink depends on the binder and the heat resistance of the colored ink. It depends on the pigment. This article will use red organic pigment ink as an example to analyze the heat resistance of the ink and the choice of pigment.

Organic pigment heat resistance test

The cooking-resistant plastic ink consists of a binder, a colorant, and an auxiliary agent (for example, a filler, a wetting agent, a viscosity reducer, etc.) composed of different resins. Organic pigments are insoluble in water and organic solvents. They are highly dispersed particulate colorants with bright colors, high color strength, and have good light resistance, weather resistance, heat resistance, solvent resistance, migration resistance, and dispersibility.

In the course of this experiment, four kinds of red pigments were selected as the colorants of plastics resistant cooking inks, because red pigments are commonly used pigments for printing inks, and the red organic pigments in solvent inks are the most common; furthermore, the heat resistance of red pigments is general. In four grades, it is colorful, and even slight discoloration can be distinguished.

1. Experimental pigments and instruments

1) Experimental pigments The four red pigments used in this experiment were:
1 Jin Guanghong C (Yellow Red) pigment, pigment index number: PR53:1, is a yellow powder, generally produced by CLT acid diazo coupling.
2 Permanent Red F4R (FR3560) pigment, pigment index number: PR8, is a bright red color powder, good alkali resistance, general light resistance, poor heat resistance, the case of concentrated nitric acid was blue and red, and concentrated sulfuric acid was yellow Everbright red, does not change color in case of sodium hydroxide.
3 Lisol Red BK (N53) pigment, pigment index number: PR57:1, is a dark red powder with blue light, bright color, high coloring power, insoluble in ethanol, golden red when dissolved in hot water, acid resistant Good alkalinity, general light fastness, heat resistance up to 150°C, concentrated sulfuric acid red, dilute to magenta precipitation, aqueous hydrochloric acid precipitation in the case of hydrochloric acid, the case of concentrated sodium hydroxide was brown.
4 Permanent red 2B (big red) pigment, pigment index number: PR48:2, purple-red powder, insoluble in water and ethanol, purple-red in case of concentrated sulfuric acid, blue-red precipitate after dilution, and reddish brown in case of concentrated nitric acid. Concentrated sodium hydroxide is red and has good heat resistance.
2) The main instrument KGZ-1A gloss meter; SM-II type sander; PB203-N type electronic balance; XXQG02 steam sterilizer; XD type scraper fineness meter; DMDE450 optical coating machine; D-8401 type multi-function Variable speed mixer.
3) Experimental raw materials and drugs Resin A solution, resin B solution, DCHP, low molecular wax, 4 pigments, toluene (analytical purity), butanone (analytical purity).

2. Preparation of experimental ink

First, the resin A liquid, low molecular wax, DCHP, toluene, butanone were mixed according to the formula, and after fully stirring for 10 minutes, it was used as the a part; then, an appropriate amount of the resin B liquid was further added and stirred for about 60 minutes as the b part to mix the components. Uniform.
1 The well-stirred ink is poured into a sand mill for grinding, so that the milled ink has various rheological properties and printability that the ink should have.
2 Place the prepared ink in a sample bottle, cap tightly, and label it for testing.
The formulation and the preparation process used in this test were performed according to the conventional method for industrial production of ink.
The inks formulated with the same quality of raw materials are gold light red C, permanent red F4R, Lisol red BK, and permanent red 2B in descending order of volume. Among them, the volume of the Jinguanghong C ink is about 3 times that of the permanent red 2B ink. The formulated permanent red 2B ink is very thick and difficult to filter. Therefore, when testing, use a solvent to dilute the permanent red 2B ink to the appropriate concentration.

3. Preparation of experimental samples and heat resistance test

1) Preparation of samples The prepared inks were screen-printed on a PET film, a BOPA film, and an ion bombarded BOPA film. The performance of the ink is tested according to the standard requirements. For the heat resistance test, reference is made to the heat resistance test standard for metallic inks. Several pieces of 20mm×100mm PET film and BOPA film are cut for use.
2) Content of pigment heat resistance test 1 Dry the pigments in 4 kinds of pigments under the conditions of 100°C and 40 minutes, compare them with the standard samples after cooling, and investigate the color changes.
2 Samples of 8 inks were dry-baked under 5 conditions at 100°C for 40 minutes. After cooling, they were compared with the standard samples to investigate their color changes.
3 Eight kinds of four kinds of inks were steamed and tapped in tap water under three conditions of 100°C and 40 minutes. After cooling, they were compared with the standard sample. The color change, fading, and water color of the sample were examined. Changes.
4. Experimental Standards This experiment was conducted in accordance with the national standards for gravure plastic ink inspection methods, glossiness test, fineness test, primary dryness test, adhesion fastness test, anti-blocking test, color inspection standard, and ink flow test standard. .

Experimental results and discussion

1. The effect of dry baking on the properties of inks and pigments

1) Discoloration of ink after dry-drying 1 Evaluation of standard inks and pigments The heat-resistance evaluation uses 5 levels: 5 levels, the same as the standard color pattern; 4 levels, slight discoloration; 3 levels, lighter discoloration; 2 levels, Discoloration is heavier; Grade 1, severely discolored.
2Experimental methods and results The three thin film specimens and the pigment were placed in a constant temperature oven at the same time. After baking at a predetermined time, two specimens were taken out. After cooling, they could be touched by hand and were not sticky, and they could be compared with standard samples. . Table 1 lists the discoloration of inks and pigments after dry baking under different conditions.

2) Analysis of the results When the heating temperature is below 135°C, the temperature has little effect on the discoloration of the film ink. The discoloration of the golden light C ink is slightly more serious than the other three inks. When the heating temperature is higher than 135°C, discoloration of the ink increases. Taken together, the heat resistance of Everlast Red 2B ink is slightly better than that of Everfix Red F4R and Lisol Red BK. Simply from the heat resistance of the pigments, the Everlasting Red F4R is better than the Lisol Red BK, and the Lisol Red BK is slightly better than the Everlast Red 2B.

2. The effect of boiling on ink performance

1) Discoloration of ink after boiled 1 Evaluation criteria and conditions Heat resistance of boiled water The evaluation criteria and sampling methods are the same as those for dry baking. In the experiment, distilled water was used for the boiling experiment, and the boiling temperature was 100°C. 120 to 121°C.
2 Experimental results After boiled at 100°C, there is almost no change in the color of Yongzhuhong 2B after boiled; the other 3 pigment inks fade more seriously, and the water color appears orange-yellow; the order of discoloration is golden light red C/PET film> permanent Red F4R/PET Film > Lisol Red BK/PET Film. Table 2 shows the discoloration of the samples under different boiling conditions.

2) Analysis of results After boiled in distilled water at 100°C, the effect of Everlast Red 2B is best, and other inks are slightly discolored. After boiled at 121 °C, the golden red C ink is severely discolored, so it is possible to eliminate the possibility of golden red C as a colorant resistant to cooking ink. Everlasting Red 2B's high temperature cooking performance is slightly better than the other two inks. After BOPA film cooking, there is a phenomenon of yellowing, and the discoloration of the ink on the film is worse than that of the PET film. This shows that the discoloration of the substrate can also affect the hiding effect of the colorant.
After boiling and dry baking experiments, the possibility of using golden red C pigment as a colorant for plastics resistant to cooking ink has been substantially eliminated. Therefore, in the following ink performance testing experiments, the relevant properties of the Golden Red C ink are no longer tested.

3. Determination of ink properties

1) Ink adhesion fastness test 1 The reference standard is GB/T 13217.7-91 GB/T 13217.1-91, and the test is carried out at a temperature of 25±1°C and a humidity of 65%±5%.
2 Test results and analysis The BOPA film was subjected to ion bombardment treatment with a vacuum coating machine for 3 minutes to increase the surface tension of the film. After the comparison experiment with the PET film (see Table 3), the following conclusions can be drawn:
a. The printing materials are different, and the adhesion fastness to the ink is different. Lisolol Baohong BK ink is the most affected by the material, and the fastness of 3 materials such as Everlast Red 2B is relatively close, and the attachment fastness is less affected by the material.
b. The fastness of permanent red 2B is better, and the permanent red F4R is the worst.
c. After the ion-treated film material, the attachment fastness to various inks has been significantly improved.
2) Determination of Ink Luster 1 Reference Standard: GB/T 13217.2-91. The test was performed at a temperature of 25±1°C and a humidity of 65%±5%.
2 Test results and analysis The experimental results show that the order of the glossiness of the three inks is: Yongkanghong 2B> Yongguhong F4R> Lithol Baohong BK. It can also be seen from the table that the glossiness of the ink is not related to the printing material. Some deviations in the data in the table are relatively large. The main reason may be that the ink on the film is not uniform, resulting in different reflectivity to light.

3) Determination of ink fineness 1 Reference standard: GB/T 13217.2-91. The test was carried out at a temperature of 25±1°C and a humidity of 65%±5%.
2 Test results and analysis Take 3 samples of each ink, and the measurement of fineness is: the average value of the fineness of Lisol's Borel BK ink is 4μm, and the fineness of the permanent red F4R ink.