The first in a series of articles about ink raw materials.

A basic knowledge of raw materials and their properties is an essential part of understanding inks. This series of articles is designed to cover some of the parts of this understanding. The basis for this series of articles will be about the three-part nature of almost all printing inks. The graphic below outlines these three key parts:

The Colorant is the most important part of the ink, as it is the only part that you see. The two types of colorants are used in printing inks: pigments and dyes. Generally, pigments are insoluble in water, whereas dyes are soluble in water or other solvents. In paste inks, pigments are our key colorants. In liquid inks, both types are used.

Pigments:

where & how are they used?

In recent years, there has been a greater move to standardize printing production and this has led to an increased use of 4-color "process" printing: particularly in publication and commercial areas. Packaging is still different and more demanding in terms of color and the properties of the colorants used, but it is moving towards a more uniform approach to color selection. 4-color process inks are based on single pigments. They are:

In the US, the ink hues for proofing and therefore process printing have been governed by SWOP (Specification for Web Offset Publication). Gravure publication printing has come into color compliance with the SWOP specification with the introduction of the so called halftone gravure, Group VI, and the use of SWOP-controlled separations and proofs for gravure magazine production. Any use of the old gravure process colors and 3 color systems has been dropped because they won't meet the new separation or color requirements of process printing.

We have also seen far greater use of color in the newspaper and no-heat areas with the efforts made by USA Today and the introduction of SNAP (Specification for No Heat Web Publications) to provide guidance and controls for the newspaper insert market. Both of these areas have the same color pigments used in SWOP in their specifications for color.

The major consumption of colored inks is centered on these three colors, but the packaging market is still growing and requires pigments with resistance properties that are often better than those of our process magenta and yellow. So far very little has been done in web offset heatset in the packaging market, primarily because no one has been able to develop a variable cutoff folder or sheeter; and re-reeling is still not a feasible proposition in heatset offset, although real progress has been made in handling heatset production pieces for off-line finishing. Packaging printing, in all its aspects, will therefore continue to be concentrated in sheet fed offset, gravure and flexography. Flexible packaging is the province of liquid inks, and the flexo and gravure processes utilize both pigments and dyes in their formulations.

More about pigments...

As many people only deal with pigments in the form of flushes a little background into the methods used to classify and describe pigments may not be remiss. All colorants used in the industry are listed in the Colour Index, which identifies a colorant in two ways:

1. Generic Name: (i.e.: C.l. Pigment Blue 15:3.)

2. Constitution Number: (i.e.: C.l. 74160.)

This data is for green shade Phthalocyanine Blue. The Constitution Number is only given to colorants where the chemical constitution has been disclosed. The Generic name tells whether the colorant is a pigment or a dye. With dyes the name is one of the four dye types: Acid, Basic, Solvent or Disperse. Thus we get the dye:

C.I. Basic Red 1, for Rhodamine 6G Red.

The CAS Registry Number (Chemical Abstract of Substances) and/or the CA Index Name (Chemical Abstracts) are often also used to identify our colorants in such documents as MSDS sheets and product technical data sheets.

Let's take this a bit further now. The full identification for Lithol Rubine is as follows:

Generic name: C.l. Pigment Red 57:1

Constitution no: C.l. 15850:1

CAS Registry Number: 5281-04-9

CA Index Name:

2-Naphthalenecarboxylic acid, 3-hyd roxy-4 [(4-methyl-2-sulfophenyl) azo]-, calcium salt (1:1)

As every chemical in use in industry has to be on the TSCA Inventory (named for the Toxic Substances Control Act of Congress), it has to be given a CAS (Chemical Abstract of Substances) Registry Number and CA Index Name for registration and identification purposes. Pigments fall into three major classes:

A. Organic Pigments

B. Inorganic Pigments

C. Carbon Blacks

These are the basic pigments of today's printing inks, and are the subject of the rest of this article. Organic pigments are based primarily on carbon but may contain metallic eIements necessary to "lake" dyes. Laking precipitates, or solidifies dyes, rendering them insoluble. Many attempts have been made to classify the organic pigments used in inks, none have been totally satisfactory.

For our purpose we can use a simple grouping of four types.

1. Pigment Dyestuffs

This class includes all of the insoluble azo pigment types such as Hansa Yellwos, Diarylide Yellows, Nitraniline Oranges, Napthol Reds and the Para and Toluidine Reds. This group covers a large segment of the pigments that are used for specialized properties, required usually in packaging printing.

2. Lakes and Toners

These are precipitated colors of either azo or non-azo types. The common azo types are Red 2B's, Lithol Rubiones, Red Lake C and the Lithols, all are derivatives of 2-Napthol Acids which have been laked with Calcium, Barium, Manganese or Strontium.

The second major group is the Basic Dye salts, comprising the Rhodamines and Triphenylmethane basic dyes laked with PMA (PhosphoMolybdic Acid) or PMTA (PhosphoMolybdoTungstic Acid). These are known by the trade name "Fanals" in Europe. These pigments are extremely strong, bright, clean colors and find applications in all types of ink. In liquid inks, their transparency makes them invaluable in foil inks.

Finally we have the Triphenylmethane inner salts group, comprising the Alkali or "Reflex" Blues. These are used as toners for blacks as well as for strong, bright, clean blues.

3. Phthalocyanines

The Phthalocyanine Blues and Greens sit in a class by themselves. Two crystal forms of the blue are available: alpha is a red shade, beta the green. The beta is the more resistant to flocculation (settling) in aromatic hydrocarbon solvent-based liquid inks, and there are special flocculation-resistant grades available that are specifically for use in these systems.

The Phthalo Greens are obtained by chlorination of the blue pigment. The greater the degree of chlorine used, the yellower the shade. Using bromine to replace part of the chlorine will move the shade even further to the yellow side.

4. Complex Organic Pigments

This group includes Quinacridones, Indanthrone, Perylene, Perinone and Dioxazine types which although rarely used in normal inks may find applications in inks where their special properties such as high heat or light stability and chemical resistance properties are required. This type of pigment is considerably more expensive than the conventional range of ink pigments. Only Dioxazine Violet finds fairly wide application in making resistant red shade blues, particularly in packaging inks.

My discussion of pigments is to be continued in the next issue, covering other pigment types and issues.

Spring 1995

Part 2 of a Multi-part Series.

In the last segment, I discussed the largest segment of the colorants market, organic pigments. Now, it's time to take a look at mineral-based, or "inorganic" pigments and dyes.

Inorganic Pigments

At the present time the inorganic pigments are not a real factor in the publication, commercial and packaging fields except for whites and extenders. The inorganic colors are much weaker than organic pigments and have far lower oil absorption, this results in dispersions that have higher pigment loading and higher specific gravity particularly with those containing heavy metals. Toxicity and environmental concerns have reduced the application areas in which these pigments were widely used in the past.

Inorganic Pigments can be broken down into a number of groups based primarily on their chemical constitution.

1. Lead Chromates

3. Iron Blues

5. Natural Oxides

7. Extenders

2. Cadmiums

4. Synthetic Oxides

6. Opaque Whites

7. Extenders

8. Metallics

Of these, only the Opaque Whites, Extenders and Metallics have any real significance in today's markets. I will limit my discussion to these pigments only.

Opaque Whites

Opaque whites are used to "cover" whatever they're printed on. Only one type of opaque white is used to any extent in inks today: Titanium Dioxide. Two forms are available, Rutile and Anatase. Rutile has the greatest opacity while Anatase is whiter. Most grades are surface treated to improve dispersion, gloss, flow characteristics and final film performance.

Zinc Oxide and Lithopone do find some limited specialized applications.

Extenders

These are cheap pigments that range from clays to synthetically produced materials. Their primary application is as cheapeners to reduce color strength but they do become an essential ingredient in tints to maintain the correct pigment loading. Calcium Carbonate is one of the most widely used in both its untreated and surface treated forms.

Clays are also widely used primarily because of their low cost. These are Aluminum Silicates occurring naturally as kaolin or china clay.

Magnesium Carbonate and Alumina Hydrate find some uses, the latter also being used to promote gloss and flow.

Metallics

Two types of metallic pigments are used: aluminum powders for silver inks and bronze powders for gold. Metallics are available in two forms: leafing grades to make inks where the particles are in a platelet form, which are called linings. The non-leafing grades are known as powders and are used for bronzing and for making metal sheen inks.

All of these materials have a fatty acid coating on the surface. This is applied to prevent the possibility of explosions in the hammer mills that are used in their manufacture.

Carbon Black

Carbon Blacks are considered as a separate class of pigment because of their very small particle size and structural complexity in relation to all of the other pigment types. The particle size range of the carbon blacks used in inks is about 10-30 millimicrons compared to about 500 millimicrons found with most organic pigments.

Printing inks are the second largest users of carbon black, tire manufacture being the largest. In the past channel blacks were used for inks, but today most blacks are oil furnace types with various surface modifications being used to improve the dispersion and flow characteristics.

Specialty Pigments

There are a number of specialty pigments which do not fit into any of the categories we have covered. Typically, there are the fluorescent colors which are not pigments but powdered solid resin-dye solutions. Nacreous, or pearlescent pigments which can be either fish scales or talcs that have been surface treated, or surface modified Titanium Dioxide.

DYES

The dyes that are used as colorants in printing inks as can be divided into four groups:

1. Acid Dyes

2. Basic Dyes

3. Azo Metal Complexes

4. Disperse Dyes

Each group has very different properties and applications. Dyes are generally used in liquid inks but can find some applications in other ink areas.

Acid Dyes

The Acid dyes are water soluble and have only limited applications in normal inks. They are found in some security inks where they show up very clearly any attempt to tamper with entries.

Basic Dyes

The basic dyes are one of the more widely used groups. They are extremely strong and these dyes were originally known as aniline or coal tar dyestuffs because they are derived from the aromatic compounds that used to be obtained from coal tar.

The basic dyes are soluble in alcohol and water but are usually made water insoluble with a laking agent such as tannic acid. These lakes are still soluble in alcohol. The original types of flexo inks were syrups containing dye, tannic acid and alcohol and used to print kraft and glassine bags. The lightfastness of the basic dyes is poor, but this is improved when a laking agent is used. Besides the dyestuffs themselves, there are three other groups of materials that are derived from them.

1. Basic Dye Bases

These are fatty acid soaps of the dyes and are classed as solvent dyes. Whereas basic dyes are soluble in alcohol, the bases are soluble in hydrocarbon solvents and oils. As a result these dyes find application as toners for blacks and as soluble colors for certain types of ball pen inks.

2. Fluorescent Pigments

The fluorescent pigments are solid resin solutions of the basic dyes in sulphonamide, amino, or other resins, which are then crushed and micronized. The fluorescent colors are weak and high loadings are necessary if maximum fluorescent effect is to be obtained. The selection of the type of pigment based on the resin used is important in liquid inks because the solvent in the ink should not dissolve up the resin in the pigment or else the fluorescent effect will be lost. They are widely used in all types of inks, but are most effective in silk screen and gravure inks because of the much thicker film that is possible, and the effect is dependent on the amount of color that you can put down.

3. PMTA and Copper Ferrocyanide complexes of Basic Dyes

These pigments, although having improved lightfastness, do bleed in alcohol and cannot be spirit varnished or solvent laminated and can give problems with aqueous coatings due to the presence of alcohol in most of these coatings. UV coatings will also cause bleed problems due to the presence of reactive diluents.

Disperse Dyes

The disperse dyes are dyes that have low molecular weight and sublime (evaporate) at relatively low temperatures. When used in inks, they are dispersed in the ink system rather than being dissolved as one would expect with other dyestuffs. They can be used in almost any vehicle system in all processes and the primary application is for heat transfer inks to decorate polyester cloth. Modern cloth printing is usually carried out using gravure preprinted paper with the pattern being heat transferred to the cloth. This method is primarily used for synthetic fibres such as polyester and polyester blends because the dye is dissolved into the fibre and is therefore permanent. With cloth that is primarily cotton, the dyes are only deposited on the application surface of the fibre and are easily washed off.

Azo Metal Complexes

The azo metal complexes are often referred to as the lightfast dyes. They have considerably better lightfastness than the other types of dyestuff and find wide application where the high transparency and bright color is required such as in foil decoration. Chromium is mainly used as the complexing metal. Some of these dyes will give different color solutions in different solvents. This type of dyestuff is rather expensive and is normally used only where others do not have the required properties.

The range of colorants available to us, although large, has been reduced over the years as different producers dropped certain lines. Some of the leading pigment producers such as DuPont and Cyanamid got out of the manufacture of pigments altogether. Since the market has changed radically, the need for many of the more exotic pigments for the printing ink industry has declined.

In the next issue, I'll start discussing resins used in printing inks and varnishes.

Summer 1995

Part 3 of a 5 - Part Series.

The basis of vehicle technology has historically been in rosin. This has always been the start point in modern ink technology, just as linseed oil has been a diluent for vehicles. I'll cover resin technology in two parts: first, reviewing rosin-resins, and the next part in a later issue, the wide range of other resins and polymers that are available today.

Rosin from trees was one of the key reasons the British colonized North America - they were looking for a source of pine pitch for caulking ships which was not controlled by Sweden. The Southern Atlantic States have continued to be that source of pine pitch even today. Originally, rosin was obtained by tapping live trees and collecting the sap which contained rosin, turpentine and water. Today, we still get rosin in this way but due to the labor intensive collection method, gum rosin mostly comes from abroad.

There are three sources of rosin production:

1. Gum Rosin from tapping pine trees.

2. Wood Rosin from stumps of pine trees aged in the ground.

3. Tall Oil Rosin from the chemical wood pulping process.

Of these three methods, wood rosin has ceased to exist due to a lack of stumps caused by the changed methods of tree harvesting for paper production. Hybrid trees have been developed with growth cycles of 5-10 years to maturity rather than the 20-25 years that older types of trees required. Now days, the stumps are removed directly after cutting, and new saplings planted instead of leaving them in the ground for 20 years. In this way, it is possible to grow three times as many trees as previously. Some of the "super resins" used in the past were obtained from dimerised wood rosin. This disappeared due to lack of stumps. Dimerised rosin is now produced from other rosin sources.

Tall Oil rosin has become a major source of rosin for most purposes today. Tall oil is obtained from the black liquor from the sulphate process for chemical pulping of wood for paper. The bulk of the tall oil rosin goes back into papermaking as paper size, but it is still where most rosin comes from today. Unfortunately recycling, besides making problems for the printer, makes problems for ink makers and others because it has cut down the amount of tall oil rosin available.

Rosin as it stands is too "soft" to be used in formulation of vehicles and inks and it must be modified. There are four basic modifications to rosins:

1. Metal Resinates come from the reaction of Calcium Oxide and/or Zinc Oxide give resins soluble in hydrocarbon solvents with extremely fast solvent release. This type of resin was used in heatset letterpress and is widely used in publication gravure inks as well as inks for gift wrap.

2. Ester Gums are made by reacting rosin with glycols, glycerol or pentaerythritol. The glycols make plasticisers, but the other two polyols give hard resins which are soluble in aliphatic and aromatic hydrocarbons. These are used widely in liquid and paste inks. Ester gums made from dimerised rosin have considerably higher melting points than from rosin and were the basis for heatset inks for many years.

3. Maleic Resins come in three varieties:

a. Rosin Maleic Adducts these have high acid values (300) and were used in the glycol based moisture set inks. Fumaric acid was used to give higher melting point resins.

b. Partially Esterified Rosin Maleics with acid values in the 150 range are soluble in alcohols and di and triglycols but not in ethylene glycol without amine solubilization. These resins are used in alcohol-based liquid inks, as well as water based flexo. They can also be used in the so called letterpress water washable inks.

c. Esterified Rosin Maleics have acid values of less than 25 and are soluble in aliphatics. They are made by reacting maleic anhydride with ester gums. Their solvent release is slower than the phenolics but they have better solubility and light stability. They are used in gravure inks for publication and catalogue inks. In paste inks, they are used in both heatset and sheetfed vehicles and overprint varnishes.

4. Phenolic Resins are prepared by reacting phenols and substituted phenols with rosins. Selection of the phenol will govern solubility and melting. The acid values of the esterified types are less than 25 and they are soluble in hydrocarbons and are widely used in paste inks. This same type is also used in better quality gravure publication and catalogue inks.

It can be seen that rosin-based resins find wide application in both paste and liquid inks and were long the only source of resins for inkmakers. In the continuation of this discussion in the next issue, we will deal with hydrocarbon resins and the film former resins that are so important in today's packaging ink business.

Fall 1995

Part 4 of a 5 - Part Series

This article is a continuation of a series of articles about ink raw materials. Now, we tackle the subject of synthetic resins and their use in printing inks.

There are vast numbers of synthetic resins available on the market but we will only cover the key ones that are used in the ink industry.

There are some facts that we need to understand when dealing with polymeric materials. Molecular weight is a factor in viscosity relationships, and this affects the solids content of an ink. Gloss is directly related to molecular weight and solids, so that low molecular weight materials allow us to formulate with high solids.

Acrylic Resins

The wrong molecular weight will cause misting and flying in paste inks and stringing and cob-webbing in liquid inks. In the latter, this is the reason why dispersions and latex materials have become an important aspect of formulation, because in this form we can use materials with very high molecular weight (1,0()0,C00) and not have these problems.

Generally, solution acrylics about 70(x) molecular weight will give problems. This is why we find emulsions and dispersions being used in coatings, and high speed inks which give good gloss from aqueous systems which could never be achieved with conventional solvent based systems.

Hydrocarbon Resins

The hydrocarbon resins have become extremely important in inks due to the increased cost of the rosin-derived resins. They are thermoplastic, low molecular weight polymers that are produced from a wide range of feedstocks. These range from coal tar through petroleum distillates to the monomer streams from petroleum cracking. The original feedstock was coal tar and its derivatives from coke ovens. Early production was centered in western Pennsylvania. Today the major source of feedstocks is the oil industry via "cracking" procedures. The average molecular weight of the hydrocarbon resins will normally be below 2000. These resins are used widely in inks and adhesives. They were originally used as extenders for more expensive resin types. One of the biggest applications is still in adhesives. Originally the properties of this type of resin were not considered good enough to be used alone and they were relegated to the role of extenders. With today's cost-conscious attitudes in formulation, their properties are more acceptable and these resins and their modified forms are used alone in commodity type offset no-heat and heatset publication inks. The fact that generally they are soluble at high solids levels is an asset in achieving gloss. The available materials range from viscous liquids to hard brittle solids. Normally they're only soluble in hydrocarbon solvents, but some types can be modified to make them water soluble or dispersible.

C5 Aliphatic Hydrocarbon Resins

The C5 Aliphatic resins have relatively low melting ranges that limit their application in paste inks. They do however find extensive use in the field of hot melt adhesives where their compatibility with waxes and EVA resins are advantages. They also cost a bit less and darken easily.

 

C9 Aromatic Hydrocarbon Resins

This type of hydrocarbon resin finds wide use in inks. They can give high resin loading so that higher solids will give better gloss. They have decent solvent release but resoftening can be a problem when used alone. These resins are neutral, so they're used in metallics without danger of tarnishing. Most of the C9 resins have Iodine Values around 100 which does not put them in the same range of drying possibilities of the C5 resins.

 

Modified C9 Hydrocarbons

In order to provide reactivity other than unsaturation, the hydrocarbons can be reacted with maleic anhydride to give sites for reaction with aluminum acylates or other gellants. They allow us to build vehicles with gel body so necessary in today's high speed ink formulations.

 

Cyclopentadiene Resins

Cyclopentadiene and dicyclopentadiene are used to prepare highly unsaturated resins the solutions of which will dry with the addition of cobalt and manganese driers. These are a subgroup of the C5 resins.

 

Terpene Resins

The terpene resins are made by the polymerization of beta-pinene or dipentene/allocimene mixtures. The terpene resins have pale color and can be reacted with maleic anhydride to give gel reactivity. The main application is in adhesives and hot melts but they also find application in paper sizes.

 

Sytrene Resins

We also have a whole range of resins derived from styrene and its various related monomers. These are of particular importance because styrene acrylic copolymers are the backbone of both liquid and dry copier toners.

The alpha methyl styrene resins, being water white find many uses in gravure inks and over print coatings because of color and light stability.

Styrene-derived emulsions also have an important place in aqueous coatings where again styrene acrylics are major types that are used.

The high molecular weight hydrocarbon resins such as polyethylene and polypropylene will be covered under additives in a later issue as their role is as a performance modifier.

The next major group of resins is the film formers which although having minimal use in paste inks are the backbone of liquid inks formulation. Of these the cellulose resins are a major group and these will be covered in the next issue.

Part 5 of a 5 - Part series.

This article is a continuation of a series of articles about ink raw materials. In this installment, I discuss the uses of film-forming resins like the cellulosics, acrylics, and polyamides.

Cellulosic Resins

Cellulose provides a whole range of very useful film former resins for liquid inks. The most important of these are the two Nitrocellulose resins, although others also have very useful areas of application

Nitrocellulose Resins

The nitrogen content of Nitrocellulose (NC) governs the properties of this type of resin: notably the solubility, molecular weight and viscosity. The nitrogen content of NC can range from 10.7-12.2%, the nitrogen content being controlled by the conditions of the nitration. The lower nitrogen grades are soluble in ethanol and are known as Ss Nitrocellulose. The medium nitrogen grades are soluble in esters are known as RS Nitrocellulose. The high nitrogen materials are only used in explosives.

Nitrocellulose-based inks find extensive application in inks for films and foils. Nitrocellulose is also a very good dispersing resin. In applications such as Acrylic NC heat resistant inks, the color is dispersed in the NC itself.

RS Nitrocellulose

The ester-soluble Nitrocellulose solutions are diluted with aromatic hydrocarbons and are used in 1~pe C Packaging gravure inks. Normally, they are plasticized with ester plasticizers, and can be modified with a range of other resin types

SS Nitrocellulose

SS Nitrocellulose is soluble in ethanol, but normally some ester solvent is included in the formulation. Ss Nitrocellulose has another useful asset: it is alkali-soluble, a necessary property for the removal of labels on returnable beverage bottles. Ss Nitrocellulose Is the main resin in E Type gravure inks and is also used as a modifier in alcohol type polyamide inks where it provides improved solvent release and film forming properties.

Ethyl Cellulose Resins

Ethyl cellulose is an extremely useful film former which is easier and safer to handle than Nitrocellulose. Two types are used in inks and are available in a range of viscosity grades.

N Type

The N Type Ethyl Cellulose is soluble in alcohol/aromatic hydrocarbon blends, the viscosity and solids content being adjustable by variations in the solvent blend ratios. These polymers have wide compatibility with other resin types and find wide use in gravure. They are particularly useful in improving film hardness.

 

T Type

This type is soluble in Toluene or other aromatic hydrocarbons and finds application in packaging gravure.

EHEC Resins

Ethyl Hydroxy Ethyl Celluloses (EHEC) are hydroxylated variants of ethyl cellulose which have an extremely useful property: they are soluble in aliphatic hydrocarbons like paste ink solvents. EHEC has compatibility with a range of resin types such as rosin modified phenolics and was used to replace Nitrocellulose-based screen inks. EHEC is also compatible with drying oils such as Linseed oil.

CMC

Carboy Methyl Cellulose (GMC) is water-dispersible resin and is used for viscosity control in water flexo inks. CMC also finds application in lithographic fountain solutions where it is used as a replacement for gum arabic. It is particularly used in neutral and alkaline fountain solutions as gum arabic kicks out under alkaline conditions.

Cellulose Acetates

Cellulose Acetate is not very soluble in many solvents and blends used in liquid inks. Therefore it is modified into the butyrate or propionate esters. The esters have greater solvent tolerance and compatibility with other resins. The normal materials available are listed below and they are used in film formation (making a hard, protective layer). The alcohol soluble types are soluble in lower alcohols.

CAB Cellulose Acetate Butyrate

ASB Alcohol Soluble Butyrate

CAP Cellulose Acetate Propionate

ASP Alcohol Soluble Propionate

Acrylic Resins

Acrylic resins are available in a wide range of types. The straight acrylics are rarely used as they have only limited solubility in inks. The Acrylic esters are the common types used for inks.

Acrylic Solution Resins

The solution resins, although they can be used as the main resin in a system, are very poor dispersion resins for pigments. It is often a better approach to use another compatible resin such as Nitrocellulose to carry out the color dispersion. These resins are esters of acrylic acid with lower alcohols, having solubility in alcohols. Styrene acrylic copolymer resins are widely used in toners for photocopiers. These are soluble in hydrocarbon solvents.

 

Acrylic Aqueous Emulsions

This type of material has become very important in the finishing coatings market. straight acrylics are too expensive for this application so that styrene acrylics are the general type.

 

Acrylic NAD

The acrylic Non-Aqueous Dispersions (NAD) have found a specific outlet in gravure as the carrier for fluorescent pigments.

Polyamide Resins

The polyamides are an interesting group of resins, being made from dimer fatty acids and amines. There are two types: reactive polyamides being used as curing agents for epoxies and having high amine values. The non-reactive polyamides we associate with inks having weird and wonderful solution behavior.

Reactive Polyamides

The reactive polyamides are used primarily in adhesives and two-component systems where the high amine material acts as a curing agent for epoxide resins.

 

Non-Reactive Polyamides

The non-reactive type can be divided into to two groups related to their molecular size, solubility; and compatibility characteristics. These resins are internally plasticized and therefore need additions of plasticisers only for specialty applications. Both types are used in formulation of polyolefin film inks. Two sub-types are discussed below:

 

Co-Solvent Polyamides

The cosolvent polyamides are soluble n-propanol and isopropanol but are normally formulated with a mire of isopropanol, toluene and water. This gives formulations that are less prone to gel and will have lower viscosity than with straight isopropanol. This type is compatible with rosin esters, rosin maleics and phenolics. This type made the original polyamide formulas, compatible with oil alkyds and used for non-drip paints. This type is also often used to correct gel structure in paste ink gelled vehicles.

 

Alcohol Soluble Polyamides

This type of polyamide is soluble in ethanol as well as n-propanol and isopropanol. This Is important as these resins are compatible with SS Nitrocellulose to give much faster drying than is possible with the cosolvent polyamide type of formulation.

END OF ARTICLE