How to use temperature change powder in paints and inks and precautions

Date:2018-09-26 Author: Click:

1. The effect of binder (resin) viscosity and solid content on color density and surface gloss:

The choice of resin in the varnish has a significant influence on the color density and surface gloss of the thermochromic ink, and this effect is more pronounced for black ink. Since the content of the pigment in the color-changing ink is much higher than that of the ordinary ink, if the color-changing ink is prepared by using the resin of the ordinary ink, the ink may be unusable due to the high viscosity. Therefore, when the ink is adjusted, the amount of the resin can be reduced and the amount of the solvent can be increased to lower the viscosity of the ink. The consequence of this is that when the ink layer of the printed product is dried, since the resin content is small, it is not enough to fill the gap between the pigments, so that the surface of the ink layer is uneven and has no luster, thereby forming a diffuse reflection on the light. Therefore, the ink layer has a low apparent color density and a high gray scale. For black ink, it looks gray and not black. (If the surface of the printed product is covered with a layer of transparent varnish, the blackness can be obviously improved.) Therefore, the preparation of the thermochromic ink must use a resin with a high solid content and low viscosity (low polymerization degree or low molecular weight). This will get good results.

2. The relationship between the type of binder (resin) and its refractive index and the color density of the color-changing ink (paint) and the transparency after decolorization:

Thermal achromatic series (D series) color-changing pigments are often used in printing “cover-display” patterns, requiring the color-changing ink layer on the surface of the printed product to completely cover the underlying pattern during color development, and to be as transparent as possible after reaching the decoloring temperature, so that the lower layer The pattern is clearly displayed. In such applications, if the resin is improperly selected, the "white fog" will be generated after the ink layer is discolored, making the underlying pattern unclear. The basic reason is that the selected resin and the optical refractive index of the color change pigment microcapsule wall material are inconsistent. Numerous microcapsules are dispersed in the ink layer to form a large number of optical refractive interfaces, just like the white opacity formed by pulverizing a piece of transparent glass. Proper selection of resin can greatly reduce the color change ink layer

This phenomenon of refraction makes the achromatic ink layer more transparent. In general, the transparency of the alkyd resin and the acrylic resin is better, and the transparency of the polyamide resin and the nitrocellulose is the worst.

3. Solvent selection and effects on color change performance:

a. The effect of the refractive index of the solvent on the color density of the color-changing ink (coating):

The optical refractive index of the color-changing pigment microcapsule material is between about 1.50 and 1.54. When the refractive index of the solvent is the same or similar, the ink has a higher color density, such as toluene, xylene and benzyl alcohol (the optical refractive indices thereof are respectively It is 1.496, 1.493 and 1.540). On the contrary, when the refractive indices of the two are largely different, the apparent color density of the ink is low. For example, n-propanol (1.386), isopropanol (1.377), acetone (1.359), ethyl acetate (1.372), butyl acetate (1.394), ethylene glycol diethyl ether (1.392).

However, the effect of the solvent on the color density of the color changing ink is temporary. After the printing is completed, this effect will gradually disappear as the solvent in the ink layer evaporates.

b Effect of solvent on pigment discoloration performance:

Thermochromic pigments have different tolerances to different solvents. Soaking in some solvents for 6 months does not affect their discoloration properties, but other solvents can erode the microcapsule surface and penetrate into it within hours to weeks. Internally, the discoloration performance of the pigment is faded or even completely disappeared. After the solvent is volatilized, some of the discoloration properties are partially recoverable, and some are completely unrecoverable. In general, a solvent containing three or less carbon atoms is more destructive to the color-changing pigment, and a solvent containing six or more carbon atoms has little effect on the pigment. In addition, the erosion of the solvent is more pronounced at higher temperatures. The following is the approximate time required for the thermochromic pigment to soak in a different solvent at a temperature of 20 ° C until the discoloration performance fades.

Because the solvent resistance of different colors and different batches of products is not the same, the specific data is subject to actual measurement. The following data is for reference only.

Methanol

DMF

Ethanol

acetone

N-propanol

Isopropanol

Ethyl acetate

Butanone

Ethylene glycol diethyl ether

Butyl acetate

Within 5 hours

Within 2 days

10~60 days

20~90 days

1~6 months

2~5 months

3~6 months

3~10 months

Water (PH2-8)

Toluene

Cyclohexanone

Benzyl alcohol

gasoline

Mineral oil

turpentine

Plasticizer DOP

Xylene

Cyclohexane

More than 36 months

More than 12 months

For the above reasons, the following measures should be taken when formulating inks and coatings:

---Use as little or no alcohol solvent as possible under C4, and replace it with other solvents. For example, cyclohexanone can be used instead of propanol.

---When a solvent such as propanol must be used, the ink (paint) should be used as needed to avoid storage.

Since the color-changing pigment produced by our company is easily dispersed in the resin liquid, all the inks (paints) other than the color-changing pigment can be distributed, and a predetermined amount of color-changing pigment is added before printing, and the mixture can be added to the ink fountain after being uniformly stirred. print. It is also possible to dispense inks other than propanol, isopropyl alcohol, etc. (including color-changing pigments), and to add a predetermined amount of the above solvent before use, and to start printing after stirring. Note that the amount of ink to be dispensed at one time should not be too much.

Special Note: Finished diluents/mixtures and some resin solutions commonly used in the ink industry may contain components such as ethanol, acetone, and propanol which impair the performance of color-changing pigments. Even if the amount of harmful components is extremely small, it will have a serious impact.

4. Reduce the residual color of color-changing prints:

Black thermal achromatic color-changing pigments are often used for covering/display printing, such as color changing cups. This kind of application requires that the color changing ink layer completely cover the printed pattern of the bottom layer before the color is removed, and the residual color is minimized after the heat is removed, so that the underlying pattern is clearly displayed. In order to meet the above requirements, the following points should be noted in the operation:

(1) The thickness of the ink layer should be appropriate

When the pigment level is the same, the thickness of the ink layer plays a decisive role in the amount of residual color. The color is additive, taking glass as an example: a 1 mm thick glass is colorless and transparent, while a 100 mm thick glass is green. The same is true for the residual color, and the thicker the ink layer, the more obvious the residual color. Therefore, the ink layer should be thinned as much as possible while satisfying the covering requirements.

(2) Choosing the appropriate varnish and ink method

Some varnishes contain chemical components such as phosphate or chlorine/bromine. When a small amount of microcapsule pigment is broken during the ink adjustment process, these substances will irreversibly react with those broken pigments, making the residue The color is obviously increased. Therefore, the use of this varnish should be avoided.

5. Modification process and equipment for color changing ink (paint):

The color-changing pigment is a spherical type of microcapsule pigment having an average particle diameter of 3 to 7 μm. It is important to uniformly disperse the microcapsule pigment in the ink during the preparation process, and to avoid cracking of the microcapsule. It is forbidden to use a sander ball mill or other high-shear dispersion grinding equipment to disperse the pigments. They will completely destroy the microcapsule shell and cause irreparable damage to the discoloration performance of the pigment!

6. Dispersion operation in low viscosity systems:

The color-changing pigments produced by our company have a lipophilic surface and are easily dispersed in an oily medium. In the case where the system viscosity is less than 50 seconds (coating 4 cups), the dispersion operation can be carried out using a general dispersion stirring apparatus.

a dispersion mixing equipment:

ood dispersing effect can be obtained by using a toothed disc type dispersing agitator with strong shearing ability. The diameter of the toothed disc is about 1/3 of the diameter of the drum, and the height of the tooth is 1/10 of the diameter of the toothed disc, and is bent upward and downward by 30°. The tooth surface must be rounded to remove sharp angles. The stirring speed should be appropriate when adjusting the ink; if it is too low, it is difficult to achieve single particle dispersion. Too high will cause friction of the material and cause the outer wall of the microcapsule to rupture, and the discoloration performance is lost. For example, when the diameter of the sprocket is 100 mm, the stirring speed is 600 to 900 rpm, and the stirring time is 5 to 15 minutes.

b Dispersion mixing method:

Most of the solvent is first added to the color changing pigment so that the surface of the pigment is sufficiently wetted by the solvent. Then slowly add the resin solution while slowly stirring (if the resin is solid, it must be dissolved beforehand). After the initial agitation, the rotation speed is continuously increased for 5 to 15 minutes. Note: If a color-changing pigment is directly added to a resin having a high viscosity, a case where a plurality of pigment particles are encapsulated by a resin is formed, and even if a solvent is diluted, it is difficult to form a single particle dispersion by stirring.

The use of a dispersing agent contributes to the dispersing operation of the color changing pigment, but the specific variety and amount are determined after testing according to different inks or coatings.

c Dispersion operation in high viscosity systems

When the viscosity of the system is high, the stirring and dispersing operation becomes difficult, and the stirring also causes a large amount of bubbles which are difficult to eliminate in the system. At this point, the three-roller can be used to loosen the grinding ((0.8-1.5 mm)) for the dispersion operation. The specific method can refer to the following modulation process of the offset ink.

d Modulation of offset color change ink:

The reversible thermochromic pigment for offset printing is a variety of color-changing pigments developed by the company for the thinner characteristics of the offset ink layer. It is characterized by finer pigment particles (2-4 microns) and higher color development. Under the same conditions of pigment usage, the ink color concentration can be increased by 15-20% to adapt to the thinner ink layer of the offset printing process.

Compared with silk screen and gravure ink, the modulation of color-changing offset ink is more difficult. Please refer to the following points when adjusting ink:

A. The amount of color-changing pigment in the ink is 28-33%, the content is too low, the color concentration of the printed product is low, the content is too high, the ink is not good, and it is difficult to use.

B. The color-changing pigment particles for offset printing are fine and have high surface energy, so they are easy to aggregate and are difficult to disperse evenly. The high-speed stirring and dispersing method using modulation gravure and silk screen printing is easy to cause damage to the surface layer of the color-changing pigment microcapsule due to the high viscosity of the ink body. Loss of discoloration. It is recommended to use a low-speed mixer for preliminary preparation, then use a two-roller to loosen the grinding (0.5-1.0 mm) at low speed until the ink is even. Remember not to clamp the grinding grinding!

C. Select a varnish with high solid content and low viscosity (low molecular weight of polymer) and good fluidity. The smaller the average particle diameter of the color-changing pigment, the larger the specific surface area and the larger the amount of adsorption to the solvent. Therefore, the ink of the fine pigment is more dry than the crude pigment, and the fluidity is poor. Therefore, varnish with high solid content, low viscosity and good fluidity should be selected. This can still have better ink and printability after adding 33% color-changing pigment.

D. Try to use UV (ultraviolet-curing) varnish to prepare offset color-changing ink, because UV varnish contains almost no volatile solvent, high solid content, and good ink and printability after adding a high proportion of color-changing pigment.

E. It is recommended to add fumed silica with a 2-3% color change pigment content (requires a particle diameter of 4-6 microns) in the formulation. The hard particles can withstand the pressure during the ink adjustment and printing process, reducing the external force. Destruction of color-changing pigment microcapsules.

F. When possible, try to choose the color form of “Colored A” → “Colored B”. For example: try to use "red" → "yellow" instead of "red" → "colorless". Because the former is composed of a small amount of [about 3%--5%} yellow ordinary offset ink in the "rose red" → "colorless" offset ink, the composite color of the two forms a red color. After being heated, the red part of the rose becomes colorless, showing only the yellow color of the ordinary offset ink. Since the coloring density of ordinary offset ink is much higher than that of color changing ink, this form of color-changing offset ink has a higher coloring rate.

7. Aqueous color change ink and PH value

Thermochromic pigments can also be used to modify aqueous color shifting inks. When the system does not contain C4 or less solvent and PH=2.5~7.5, long-term protection from light (2~5 years) has no effect on the discoloration performance of color-changing pigments. However, when PH≥8 and long-term placement, it may damage the performance of the color-changing pigment. The addition of a small amount of nonionic emulsifier makes the color changing pigment easier to disperse in aqueous systems.