The characteristics and classification of rosin-modified phenolic resin and its application in offset printing inks

Prepared by: Shaoguan Derui Chemical Industry Co.

• General situation of rosin-modified phenolic resin for offset offset printing ink

Rosin modified phenolic resin (rosin modified phenolic resin, rosin denatured phenolic resin) is a rosin modified oil-soluble alkyl phenolic resin esterified with polyols, which is a light yellow or brown transparent solid with irregular shapes.

Rosin-modified phenolic resin is widely used in the printing ink industry.

The rosin-modified phenolic resin is further esterified with polyols to obtain resins with high melting point and any acid value; modified resins with high acid value have good alcohol solubility and can be used in the manufacture of gravure inks, etc.

Rosin-modified phenolic resin is also currently the most widely used offset printing ink resin, and its performance determines the quality of the ink.

With the continuous updating of printing equipment, rosin-modified phenolic resins of different specifications are also emerging.

One-step synthesis process of rosin modified phenolic resin:

The one-step method is characterized by mixing raw materials such as phenol and aldehyde with rosin and reacting directly.

Two-step synthesis process of rosin modified phenolic resin:

The two-step method is to first carry out polycondensation reaction between paraformaldehyde and alkylphenol.

The advantage of the one-step process is that the waste is removed in the form of steam, which is easy to environmentally friendly treatment, but the phenolic condensation reaction that occurs in the molten rosin is easy to produce many side reactions due to the high reaction temperature and uneven dissolution, so the detection and quality of the condensation products Adjustment is more difficult to control, and it is not easy to obtain stable resin products.

Modern printing speeds are getting higher and higher, and the temperature that the ink bears during printing is also getting higher and higher, and the rise in temperature greatly reduces the viscosity of the ink, making the ink easier to emulsify.

In order to develop inks suitable for high-speed printing, it is necessary to have an in-depth understanding of the resin properties used.

On the other hand, the better the solubility of the resin, the lower the solid content in the binder system, the smaller the structure of the resin in the binder; on the contrary, the worse the solubility of the resin, the lower the solid content in the binder system.

A more precise expression is that the structure of the resin is mainly determined by the polymer part in the GPC molecular weight distribution range, and is also related to the molecular shape, molecular weight distribution, and resin production process.

The mechanical relaxation phenomenon of polymers is defined as viscoelasticity, and viscoelasticity is an important characteristic of polymers.

Similarly, the purpose of gelling the resin binder is to make up for the structure of the resin and improve the viscoelasticity of the system, thereby reducing flying ink and adapting to high-speed printing.

2.
Application theory of rosin-modified phenolic resin in offset printing inks

No single resin can have all the best index requirements, so we often use two or more rosin-modified phenolic resins in the design of offset printing inks to meet the requirements of modern high-speed printing.
Rosin-modified phenolic resin can be widely used in offset offset printing inks.
In summary, at least because it meets the following performance requirements:

• Solubility (completely or partially) in ink solvents.
  These solvents include vegetable and high-boiling aliphatic solvents (12-16 carbon petroleum distillate).
  Generally, it can only be dissolved in mineral oil solvents within a certain range, and has good wetting and dispersing ability for pigments.
  This offset printing ink is the fundamental reason for the successful development from polymer oil-based inks to synthetic resin-based inks since the 1950s.
  
• Compatibility with other ink components (such as solvent oil, alkyd resin, wax, etc.
  ).
  
• High softening point, high tolerance, usually the softening point is in the range of 140℃-190℃, the higher the n-heptane value, the better the solvent release and solubility of the resin, and the low softening point resin can be used to increase the dispersion of the pigment.
  Has good spreading and leveling.
  
• Excellent pigment wetting and dispersing, excellent spreading and leveling performance.
  The resin can be made to contain a certain amount of polar groups (such as carboxylic acid groups) according to needs, which can be combined with the surface of the pigment particles to form a more uniform dispersed phase structure and have the rheological properties of a plastic fluid.
  The non-acid value of petroleum resin has very poor fluidity and must be modified by maleic acid before it can be used.
  
• The high viscosity and low viscosity of the resin, as well as excellent gelling properties (sensitive reactivity with aluminum chelate gelling agents).
  At present, the new development direction of offset printing ink is to use less or less gelling agent, and to increase the viscosity and cohesion of the rosin resin by increasing the structure and molecular weight of the rosin resin to meet the dual requirements of high printing and environmental protection.
  
• Good drying properties, excellent film-forming properties.
  Corresponding cross-linked network can be formed in the resin structure, with a certain molecular weight, and plasticization in the structure can be realized, so that the ink has the most suitable drying time, adhesion, abrasion resistance, weather resistance, high gloss and so on for printing.
  .
  
• Appropriate emulsifying ability.
  The hydrophilic polar groups in the resin (such as residual hydroxyl groups of polyols, etc.
  ) must be controlled within an appropriate range.
  If the content of the polar group is too high, the ink will easily absorb water and cause printing failures such as piling and paste, which will affect the quality of the printing.
  On the contrary, if the water resistance is too strong, the ink will take a long time to reach the emulsification equilibrium state on the printing machine, and it will be moisturized.
  It is difficult for the water width of the plate liquid to remain stable on the plate surface, and malfunctions such as uneven ink application may occur.
  
• Less Misting phenomenon.
  Flying ink is a unique phenomenon that occurs in the process of drawing and breaking when the ink layer is passed through the ink distribution roller on the printing machine for many times to form an ink layer, and when the ink layer is peeled off by a shearing force.
  Utilizing the extremely large molecular volume steric properties of rosin, it can increase the structural steric hindrance and branching degree of the resin, increase the cohesive energy and molecular weight of the resin, and control the appropriate degree of compatibility between the resin and the mineral oil solvent, which is beneficial to reduce Flying ink phenomenon.
  

In conclusion, the characteristics of rosin-modified phenolic resin with excellent performance are as follows: 1.
High molecular weight rosin-modified phenolic resin provides high binder viscosity, good gelling properties and body bones, and has excellent solvent release and fixation.
speed.
2.
Low molecular weight rosin modified phenolic resin provides good solubility and low solution viscosity, which can increase the amount of resin, good pigment wetting and dispersing, and excellent spreading and leveling.
3.
In addition to molecular weight, the chemical structure (aliphatic, aromatic linear, branched, cross-chain, etc.
) and functionality (number of carboxyl and hydroxyl groups) of rosin-modified phenolic resin can also explain the properties of many ink resins.
.

3.
The main technical standards of rosin-modified phenolic resin for offset printing inks

In the composition of printing inks, they are usually polymers or condensates of some organic compounds.
Ink resins with excellent performance often need to have the following properties:

(1) Solubility and release of resin

Because the printing process determines that the printing ink should have certain rheological properties, the resin in the printing ink is generally made into a liquid state, and even some resins that are already in a liquid state often require solvents or diluents due to excessive viscosity.
It can be used after reducing the viscosity.
Therefore, the solubility of the resin is very important.

1.
Solubility of resin

The so-called resin solubility refers to the ease with which the resin can be dissolved in various solvents.
Since resins are all materials with large molecular weight, it is generally impossible to dissolve in a true solution state.
Instead, solvent molecules penetrate into the macromolecular gaps of the resin, causing the resin to swell indefinitely, and then be dispersed in the solvent to become a colloidal dispersion state.
Solution.
And the ease of dissolution is relative to the solvent.
Resins with polar groups are easier to dissolve in polar solvents, and solvents with similar structures or groups to the resin are also easier to dissolve the resin; This kind of resin, the smaller molecular weight is easier to dissolve than the larger molecular weight.
In addition, it is also related to external factors such as temperature and stirring speed.
In ink manufacturing, resins are generally applied in liquid form, so solid resins must have a certain degree of solubility before they can be used.
Some resins that are already liquid can be applied after being dissolved in a solvent and lowered in viscosity due to excessive viscosity.
So solubility is an important property of resin.

Commonly used methods to determine the solubility of resins are as follows.

(1) Judging by the transparency, solubility and storage stability of the resin in the fixed solvent.
Poor transparency, insoluble matter, resin precipitation or jelly during storage, etc.
, indicate poor solubility.

(2) Judging by the solubility viscosity of the resin in the fixed solvent.
The lower the viscosity, the better the solubility.

(3) Judging by the tolerance of the resin to a certain solvent or diluent.
The resin is first dissolved in a strong solvent to become a uniform and transparent solution, and then titrated with a weak solvent or diluent until the resin precipitates out and becomes muddy in the solution.
The amount of weak solvent or diluent consumed is used to measure the resin’s Solubility.
The greater the consumption of the latter, the better the solubility.
This method is used to determine the n-heptane value of the resin used in offset printing inks.

2.
Solvent release of resin

Releasability refers to the ability to separate the solvent from the resin dissolved by the solvent.
After the ink is printed, the solvent separates from the resin to gel and dry the resin.

Because the resin is applied in printing in the conversion form of solid→dissolving into liquid→drying conjunctiva into solid state, the solubility of the resin is required to have an appropriate degree to ensure that its solubility and release properties are both very good.
balance.
Therefore, the solubility of the resin is not the larger the better, but an appropriate degree.

The release of the resin is related to the solubility.
The resin with too good solubility is not conducive to the separation of solvents or diluents from the resin, making the ink film dry and unsatisfactory, resulting in smearing, blocking and other defects in the printed product.
The release is poor.
Generally, a resin that is too soluble in a certain solvent has poor releasability to the solvent.
Due to the limitations of the printing process and the prevention of environmental pollution, the solvents and thinners used in the ink are often limited.
Therefore, while selecting solvents and diluents to adjust the solubility and release of the resin, the ink manufacturer must also focus on the choice of the resin itself.
It is necessary to choose the above two aspects to achieve a good balance of performance.
Resin.

(2) Softening point of resin

Most solid resins are amorphous substances, which gradually soften as the temperature increases, their plasticity increases, and finally become liquid.
The softening point refers to the specified temperature when the resin becomes a viscous liquid during the softening process.
This temperature is called the softening point (flow temperature).
The softening point of the resin is equivalent to the melting point of the crystal.
The softening point increases as the relative molecular weight of the resin increases.
Generally speaking, the higher the softening point of the resin, the stronger the release of the solvent.
Especially for resins with the same chemical composition, this feature is more prominent, but because the softening process of the resin progresses gradually, there is no obvious limit when it becomes a liquid.
Therefore, the level of softening point is affected by the measurement method.
The ring and ball method is a softening point determination method commonly used in the ink industry.
The softening point has a more direct relationship with the molecular weight of the resin.
The molecular weight is large, and the softening point is also high.
Therefore, the resins used in offset printing inks should have a higher softening point.

(3) Viscosity of resin

Generally speaking, the resin viscosity actually refers to the solution viscosity of the resin under specific conditions, or the solubility viscosity.
The viscosity of the resin is related to the relative molecular weight, solubility, temperature of the solution, and the amount of solvent of the resin.
It has two meanings: one is to indicate the molecular weight of the resin; the other is to indicate the solubility of the resin in the solvent.
Among the resins of the same series, those with high molecular weight have high viscosity, and among the resins of different series with poor solubility, the viscosity is also high.
Therefore, a resin with a large solubility viscosity does not necessarily have a large molecular weight.
On the contrary, a resin with a low solubility viscosity does not necessarily have a small molecular weight.
It depends on the specific situation and specific analysis.
In addition, when the temperature of the solution increases, the viscosity decreases, and when the concentration of the solution increases, the viscosity increases.
When the diluent is excessive, the viscosity sometimes increases.
This is a manifestation of poor solubility and increased viscosity.

Because the resin solution, especially when the concentration is high, is a fluid with a certain degree of plasticity, that is, a non-Newtonian fluid, the classic capillary method is not suitable for the determination of the viscosity of this resin.
The viscosity measurement methods actually used in today's production include laray, cone and plate viscosimeter, emila rotary viscometer (emila), and paint No.
4 ford cup (No.
4 ford cup).
, Hoppler, bubble viscosimeter, etc.
Knowing the solubility viscosity of the resin helps to understand the properties of the resin.
Skilled ink manufacturers can predict the performance of ink in many aspects.

(4) Acid value of resin

Acid value is also called acid value.
Many resins used in inks are made from organic acids such as resin acids, fatty acids, aromatic acids, and other compounds through condensation, esterification, and other reactions.
These resins have some unreacted carboxyl groups (-COOH).
), this carboxyl group gives the resin a certain acid value.
It is defined as the milligrams of potassium hydroxide consumed per gram of resin for neutralization.
The acid value has a certain influence on the performance of the ink.

When the acid value of the resin is too large, the properties of the ink will be unstable.
For example, the water resistance decreases, and the ink is easy to be hydrophilic and emulsified during printing.
If the acid value is too large, it will easily react with alkaline pigments, resulting in increased viscosity after the ink.
, And even gel; if the acid value is too small, the wettability of the resin and the pigment will be poor, the flowability of the ink will be poor, and there will be disadvantages such as low gloss.
Therefore, the acid value of the resin is not as low as possible.
Like other indicators, it should be controlled within an appropriate range.
The acid value of the resin used in water-based inks must be controlled to a very high value.
In short, the acid value is also an important indicator of the degree of reaction in the resin reaction process.
It is necessary to prevent one-sided pursuit of other quality indicators and allow the acid value to drop to an inappropriate limit.

(5) The color of the resin

The color of the resin is caused by a variety of pigment impurities, so the resin should be made as colorless or light as possible, and the hue of the color ink should be as little as possible.
The color of the resin is not only related to the nature and purity of the raw materials used to make the resin, but also has a lot to do with the resin synthesis process and equipment conditions.
For example, the color of alkyd resin produced by solvent method is much lighter than that produced by melting method, and it is inert.
The gas protection product prevents it from contacting with oxygen and can also effectively reduce the color.
The color index is particularly important for the manufacture of light-colored inks, such as iron-printing white inks, overprint varnishes, etc.
The rosin resin of sheet-fed offset printing inks is generally light yellow.

(6).
Transparency of resin

The transparency of the resin is observed visually.
In the above solubility, transparency is a reference for the solubility of the resin; at the same time, it is also a reflection of the completeness of the reaction of the resin.
For example, the isophthalic alkyd resin is often turbid when the reaction is not complete.
Transparency becomes completely transparent.
In addition, the water and other impurities mixed in the resin also affect the transparency, and the transparency affects the solubility of the resin, and the low-transparency resin has poor solubility.

(7).
Water resistance of resin

The water resistance of the resin directly affects the water resistance of the ink.
The water resistance of the ink has two meanings, namely the water resistance during the printing process and the water resistance after the ink film is formed.
The former, such as offset ink printing, requires sufficient resistance to printing syrup, otherwise the ink will have a series of problems such as emulsification, paste printing, and poor transfer.
The latter, such as retort-resistant printing ink for food packaging, has to withstand the test of boiling or steam sterilization as the finished product.
Resin molecules with many hydrophilic groups, such as hydroxyl—OH, carboxy—COOH, amine—NH2, sulfonic acid—SO3H, methoxy—OCH3, etc.
, have poor water resistance.
The water resistance of the resin is mainly related to the structure and molecular weight of the resin, and has little to do with the manufacturing process.

The latest national standard for rosin-modified phenolic resin is LY/T 1179-2013.
The inspection and testing of rosin-modified phenolic resin in the printing ink industry is also consistent with this.
At present, the main testing items and indicators of rosin-modified phenolic resin for offset printing inks are roughly as follows :

Rosin modified phenolic resin testing items and indicators for offset printing inks

Fourth, the application of rosin-modified phenolic resin in offset printing inks

Rosin-modified phenolic resin is used in lithographic inks, and the amount can reach 25-30% in sheet-fed lithographic inks, rotary lithographic inks and corresponding dry (anhydrous) lithographic inks.

It can be seen from Table 1 that web offset printing inks use more mineral oil solvents than sheetfed offset printing inks.
The main difference between the two is the solubility of the resin and the distillation range of the solvent.
It is necessary to choose a resin with high solubility and high softening point to be applied to the rotary ink, so that the ink has better fluidity and solvent release, so as to ensure that the solvent can quickly detach (permeate into the paper or partially evaporate) after printing to form a film.

After the sheet-fed lithographic ink is printed, although the drying performance is determined by the two stages of "fixing" and "oxidizing conjunctiva", the speed of "fixing" restricts the printing speed.
Generally, the balance between fixation and gloss can be obtained by adjusting the processing technology of the binder, but fundamentally, a resin with higher solubility and higher molecular weight and corresponding solubility (usually expressed in n-heptane value), specific distillation The mineral oil solvent in the range of low temperature can be used to obtain fast-fixing, high-gloss sheet-fed lithographic ink through the binder processing technology that dissolves at low temperature.
After the sheet-fed lithographic ink is printed, although the drying performance is determined by the two stages of "fixing" and "oxidizing conjunctiva", the speed of "fixing" restricts the printing speed.

Table 1 Offset printing ink formula composition

5.
Application of Derui Chemical Modified Rosin Resin in Offset Printing Ink

(1).
Quick-drying gloss offset printing ink and varnish: 2101, DCH2102, DCH2105, 5131, 5133, 6120, 6121, 8101, 8102, 8131, 8132, 8137, 8143;

(2).
Quick-drying resin offset printing ink: DCH2102, 5131, 5135, 8101, 8132, 8145, 8147, 6124, 6127;

(3).
Soybean environmental protection offset printing ink: DCH2102, DCH2103, DCH2105, 2101, 2106, 8131, 8132, 8143, 8147;

(4).
Offset printing hot and cold fixed web offset printing ink: DCH2102, DCH2103, DCH2105, 2101, 5107, 5131, 5132, 320, 323, 6120, 6124, 6127, 8101, 8131, 8134, 8145, 8155

(5).
Solvent-free offset printing ink (0 VOC offset printing ink): 2106, DCH2103, DCH2105, 5133, 8101, 8131, 8143, 6120, 6121, 8155;

(6).
Gel-free offset printing ink: 8103, 8133, 8134, 8145;

(7).
No phenolic offset printing ink: 4101, 4102, 4130, M-1110, 170;

(8).
Light-colored rosin modified phenolic resin: 2101, 5131, 6120, 6121, 8101, 8131, DCH2105;

(9).
Wear-resistant offset printing ink: 2101, DCH2102;

(10).
Waterless offset printing ink: 8155;