Raw materials and varieties of inks. Properties

1) Characteristics and types of pigment

Pigment is the coloring agent in ink, and it is the main raw material to express the color of ink. The difference between pigment and dye is that pigment is generally insoluble in water and linker, and most of them are suspended in solvent. Dyes, on the other hand, are soluble in the linker and can color all the objects. There are many kinds of pigments, and there are many ways to classify them. According to the general concept, they can be divided into inorganic pigments and organic pigments; according to the metal type, they can be divided into zinc pigments, cobalt pigments; according to the color characteristics, they can be divided into colored pigments and non-colored pigments, etc. Generally, they are classified internationally into:

a: pigment dyestuff (pigment dyestuff)

That is to say, it refers to the insoluble colored organism or carrier. Including azo pigment, phthalocyanine pigment, nitro pigment, nitroso pigment, reducing pigment.

b: Precipitated dyes (color precipitate-lake)

That is, organic pigments containing inorganic substances or carriers. Includes ordinary color precipitates, firm color precipitates.

c: Toner

This means water-soluble acid or basic dyes, which are organic pigments without inorganic substances or carriers. It is an organic colored body that is not washed out and has maximum coloring power.

2) Quality index of pigment

The quality of pigment directly affects the performance of ink, and generally there are the following indexes for evaluating the performance of pigment:

a: Color tone.

The color tone reflects the selective absorption characteristics of the pigment on the spectrum, which depends on the nature of the pigment itself, and is also related to the thickness of the ink film, the type of filler and linker used, and the characteristics of the paper. The more the pigment absorbs the main light waves, the less harmful the absorption.

b: coloring power.

The coloring power refers to the ability of a pigment mixed with other pigments to influence the color of the pigment mixture. The higher the coloring power of a pigment, the less quantity is needed to formulate ink with it.

c: covering power.

Covering power refers to the ability of the pigment to cover the surface of the object to be printed. That is, the ability of the color of the surface of the substrate not to pass through the pigment. The covering power of pigment depends on the difference between the refractive index of pigment and the refractive index of linker.

d: Apparent specific volume.

The apparent specific volume is the number of cubic meters of volume per kilogram of pigment. The apparent specific volume and the apparent specific gravity are the inverse of each other. The larger the apparent specific volume, the better.

e: oil absorption.

Oil absorption refers to the amount of oil that can be absorbed by a certain amount of pigment, calculated by the number of grams of linseed oil needed to make 100 grams of pigment stick together closely. The nature of printing ink is related to the oil absorption of the pigment, and the ink made of pigment with small oil absorption contains more pigment, which has strong ink coverage but poor stability. It is easy to produce heap plate and emulsification when printing. Generally speaking, the oil absorption of pigment should be large.

f: dispersion.

Dispersion reflects the size of pigment particles, the smaller the particles of the pigment the higher the dispersion. Generally improving the dispersion can make the color become vivid and improve the color brightness.

g: light resistance, sun resistance, penetration resistance and other corrosion resistance.

3)The basic requirements of offset printing ink on pigment.

a: The color performance requires very high coloring power, high color concentration, high transparency and small hue error.

b: Stability requirements for light, heat, acid and alkali corrosion resistance.

c: Printing performance requires fine and uniform particles, high dispersion and insoluble in water. Lipophilic than hydrophilic, does not contain harmful substances.

Two linking materials

1) The role of linking materials in ink

Linking materials are the basis of good or bad quality of ink, and its role in ink is as follows:

a: carrier and dispersing agent of pigment

b: determining the ink properties of ink

c: giving the ink a certain luster, abrasion resistance, solvent resistance, and impact resistance and other physical properties. Impact resistance and other physical properties

d : Determine the drying type and drying speed of the ink

2) The basic reaction mechanism of linker

After transferring the pigment to the substrate according to the need, in order to make the pigment firmly and stably fixed on the substrate, the linker needs to undergo the curing and cross-linking reaction from the small molecule to the large molecule. This reaction is carried out with the help of external heat and light energy or the removal of solvent. The basic reaction types are as follows:

a: polymerization

b: oxidation

c: condensation

d: isomerization

e: esterification and ester cross-linking

3) Types and characteristics of commonly used linkers

1) Dry linkers

This kind of linkers is mainly based on unsaturated vegetable oils (linoleum). This type of linker is mainly made of unsaturated vegetable oil (linseed oil, tung oil, castor oil, etc.), which is polymerized into a certain degree of viscous liquid at a suitable temperature. Its drying is the use of oxygen in the air on the unsaturated double bond oxidation crosslinking to form macromolecules. The ink made of this linker has better gloss, but the oxidized drying speed is very slow, and the addition of drying oil speeds up the drying speed, but makes the ink quality unstable. Moreover, the molecular weight of this linker is not very large, in the presence of water in the offset printing is easy to emulsify. Now simply use this linker to do ink has been a few, and often mix it with polymer resins or polymer resins modified with the vegetable oil to improve its application.

② solvent-based linker

This linker is made of solid resin dissolved in a solvent, generally used in the permeability of larger substrates such as newsprint.

3 reaction-type linker

The use of external energy to make the resin cross-linking curing effect of the linker, such as UV drying, EB (electron beam) drying, infrared drying and so on.

④ Resin-type linker

The linker using solid polymer synthetic resins dissolved in vegetable oils, petroleum series of high-boiling solvents, made of high-viscosity phase, and then add a low-viscosity ink oil dilution, when they come into contact with the substrate paper, the surface tension of the ink oil immediately penetrated into the paper that is, the initial drying ink - -Fixation. Thereafter, the remaining high-viscosity phase, due to the loss of mobility and crosslinking occurs curing and stay on the paper, that is, the completion of the ink adhesion drying. This linker can be made into a fast-drying type, glossy type and fast-drying glossy ink, which is determined by the nature of the resin and its content in the ink. In the selection of resin, it is generally necessary to consider its molecular structure and molecular weight, solubility and release of solvents, the stability of the resin and so on. Resin molecule is large, the content of ink is good; solvent solubility and release is opposite aspects, poor solubility and strong release, ink fixation is fast, and vice versa is slow. Common types of resins are:

1> solid resins made from synthetic solid resins dissolved in dry vegetable oil or high boiling petroleum solvents. Commonly used are:

a:Rosin esters include glycerin, pentaerythritol and their dimerized rosin esters.

b:Phenolic resins include phenolic resins and pure phenolic resins modified with rosin or dimerized rosin and based on phenol, bisphenol or alkylphenols (e.g., tert-butylphenol).

c:Rosin esters modified with maleic anhydride include rosin modified with maleic anhydride and dimerized rosin glycerol or pentaerythritol esters.

d:Petroleum resins include modified petroleum resins.

2> Liquid synthetic resins

a:Alkyd resins o-, m-, and terephthalic anhydride system of alkyd resins and so on.

b:Oil-modified phenolic resin dry vegetable oil modified phenolic resin.

c:polyurethane resin

The resin is used in large offset printing ink with good brightness, good mobility, good film, good wettability of the pigment and so on, but the dosage is too much curing speed is slow.

3> Gum oil to aluminum soap or acid aluminum compounds and their derivatives and resin oil made of elastic gel. Its commonly used ingredients

as follows:

a: aluminum stearate most of the two aluminum stearate, this substance is easy to make the gelatinous oil in high-speed printing is not stable, and the printing dot is poor.

b:Aluminum low carbonate commonly used aluminum isooctanoate, no disadvantages of aluminum stearate, better quality.

c:Aluminum isopropoxide and its derivatives are beneficial to ink gloss, printing performance, into a colloid stable, not easy to destroy at high speed.

Colloidal oil used in ink can make the ink to increase the viscosity without increasing the viscosity, in offset printing with de-sticky, improve the body bone, dots and other characteristics.

Three fillers

1) Filler in the ink role

Filler is a kind of white powder can be evenly dispersed in the linker, its dosage in the ink is based on the amount of ink pigment and ink requirements to adjust. Its role in the ink is as follows:

a: Reduce the cost of ink

b: Adjust the inkiness of ink

c: Adjust the color concentration of ink

2) Types and characteristics of common fillers

a: Aluminum hydroxide used in aluminum hydroxide inks are precipitated, which is commonly used as fillers in oil-based inks. It and the appropriate viscosity of the ink blending oil (dry linseed oil polymerized at a certain temperature) made of printing commonly used in the Veli oil. The amount of aluminum hydroxide in the ink can not be too much, otherwise it will inhibit the drying of the ink, but also weaken the gloss of the ink.

b: barium sulfate ink with barium sulfate is also made by precipitation. Its specific gravity, poor transparency, oil absorption, used alone in the ink will make the ink liquidity weakened, and the dosage can not be very high, otherwise there will be a heap of ink in the printing phenomenon. It can be used together with pigments with small specific gravity, fine particles, and not too high requirements of ink after grinding, in order to improve the fluidity of ink.

c: Aluminum barium white This filler is the precipitate of barium sulfate and aluminum hydroxide. Its luster is better, made of ink paste printing performance is also better, but if not used properly, will make the ink gelatinization or coarsening. Selected with ink blending oil can be ground together to obtain good fluidity and gloss.

d: Calcium carbonate ink used in calcium carbonate is obtained by precipitation of calcium hydroxide and sodium carbonate. The calcium carbonate obtained by this method has good transparency and gloss. And calcium carbonate particles can be very small (0.02-0.1μm), can reach the range of colloidal particles, so it is sometimes called colloidal calcium carbonate. Colloidal calcium carbonate in ink according to a certain proportion of deployment, can be very good to improve the fluidity of the ink, gloss, transparency, etc., and generally does not produce bad printing faults. Offset printing ink, especially resin-based offset printing ink, often selected calcium carbonate gum as a filler to replace other types of filler.

Four auxiliaries

Auxiliaries are added to the ink to improve some of the special properties of the ink or the requirements of the additives, can be pigments, linkers, and finished ink auxiliaries. Its purpose is to change the pigment, linker wettability, compatibility and ink itself, or some special requirements of the performance changes. The content of auxiliaries in ink is very small, generally not more than 10%. Ink often auxiliary agents are as follows:

1) desiccant mainly refers to the promotion of dry oil-type linker polymerization and drying substances. Mostly metal cobalt, manganese salts or soaps.

2) to remove the viscosity of this auxiliary agent can effectively reduce the viscosity and basically does not change the body of the ink bone. Commonly used waxes and grease (gel oil) class. Waxes to remove the viscosity of the agent in addition to the role of sticking, there are ink rubbing and increase the role of slippery; and gelatinous oil has a viscous and maintain the consistency and the role of the body bone.

3) thickening agent used to increase the viscosity of the ink and link material, improve the thixotropy of the ink, to prevent the deposition of pigments, and to improve the luster of the graphic and dot reproducibility.

4) Anti-scuffing agent is used to prevent scuffing of prints, generally starch is dispersed in the ink blending oil, and then mixed into the ink.