What is better; paints made from foraged natural pigments or mass-produced store-bought paints?
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Everything is derived from nature; unfortunately, today we are living in a world that is driven by consumerism. Imagine walking through a forest or climbing a mountain, and foraging for pigments to make your own paints just like how it was done in the bygone era, instead of going to an art supply store and purchasing a mass-produced tube of paint. It is indeed very convenient getting paint supplies from an art store, but is it as salubrious as what nature has to offer us? The answer is simply no!
The labels on paint tubes never provide us with information about how something was made, the origin of raw materials, who produced it and under which conditions, what it contains, and what impact it had on our environment during the manufacturing process! Honestly speaking, no one even thinks about any of this because modern society today has become disconnected from nature!
After dabbling with store-bought colors for a little while, I came to a realization that art supplies are notorious for remaining tight-lipped about the content of their paints. You don&#;t know what chemicals are in your paint unless they carry extreme health risks warning on the label or if you are a nerdy scientist like me who will go down to the bottom of it! These kinds of warning labels indicate they are toxic to you and should, therefore, be handled with care. I am yet to come across a label that indicates the toxicity of the contents of a paint tube to our environment and other life forms. This means, in art studios all across the world, artists often have no inkling of what they are using to produce art or the impact of those materials on the environment. Hence, I embarked on a creative journey of making my own watercolor paints from foraged pigments and practicing sustainability in creating art as well!
Making a connection with pigments in their wild habitat!
Working with natural pigments is a transformative journey that fosters a harmonious bond between oneself and the Earth. Becoming acquainted with pigments within their natural settings and learning to ethically gather them possesses the power to significantly alter one&#;s artistic approach.
The splendor of nature sparks a rekindling of our inner essence. It prompts an awakening of the senses, enabling us to delve into the sanctity of all that exists within nature and to acknowledge our interconnectedness with everything we encounter.
Given these realities, as a committed practitioner of sustainable art, I am on a journey to discover better ways to practice my craft &#; methods that do not involve consumption, pollution, or strain on our fragile ecosystems.
In this post, I will share with you my passion for making watercolor paints from foraged pigments. What is remarkable about this process is that each landscape is unique: your own land&#;s color palette will depend on its geological features.
As you forage for pigments and transform them into paints, you know exactly what goes into making a paint, where it came from, and lastly, they can all return back to the earth without having any destructive effect!
The ancient craft of Pigment Making
Natural pigments abound everywhere, and by immersing yourself in nature through travel and exploration, you can discover a diverse array of colors. Many of these hues originate from the earth itself: the rich tones of soil, clay, sand, or stone. Over the past couple of years, I&#;ve gathered a considerable collection of pigments from my travels. There&#;s a unique joy in crafting art using nothing but dust &#; art that fosters a deep connection with the materials themselves.
Foraging for natural pigments in the wild?
Any area with a significant amount of exposed rocks presents a potential opportunity to collect pigment stones. Since you&#;ll need pigments that are easy to process, especially when you&#;re just starting out, look for stones that are relatively soft. A simple test involves rubbing the stone against a hard surface. If it leaves behind a residue resembling paint or clay, it&#;s likely a suitable candidate for making paints.
For example, I&#;ve collected oxidized volcanic stones from Boca Cangrejo, Tenerife in , and paints made from various rocks gathered in Portugal and Austria.
While rocks such as sandstone, shale, and muscovite can also be processed, the effort involved is typically more labor-intensive. Harder stones may still be worth processing, especially if they offer unique colors. Clays have the potential to serve as good pigments, although not always. To prepare them, dig out the clay, allow it to dry, remove any large or hard rocks or organic matter, and grind it after levigation. Keep in mind that each geological formation and ecosystem presents its own nuances and challenges.
Rocks such as sandstone, shale, muscovite, etc. can also be processed, but the processing is a lot more tedious. Harder stones may be worth processing, especially if they have unique colors. Clays can make good pigments, but not always; you can dig them out, let them dry, remove any large or hard rocks or organic matter and grind them after levigation. Each geology and ecosystem has something different to offer you, and it requires a lot of experimentation.
Materials like soot and charcoal are excellent sources of pigments. Soot typically produces a warm black, while charcoal yields a cool black. Charcoal black, obtained through the carbonization or charring of wood, is highly stable, like all carbon blacks, and exhibits excellent lightfastness. It&#;s also compatible with other pigments. For instance, I collected some wood charcoal from a bonfire during a trail run in Upper Austria and transformed it into beautiful granular black paint. However, it&#;s important to remember that incomplete combustion of wood can result in the formation of toxic hydrocarbons. For more information on this topic, refer to [source link].
Among the best candidates for paint are ochres. Ochre is a term specifically used for pigments derived from iron oxides and iron-based minerals, clays, and soils. Essentially, ochres are common minerals found worldwide that contain varying amounts of iron and oxygen.
A short tutorial: Foraging for natural pigments.
How to make natural pigments
To prepare your pigments, you will need to ground the pigment candidates finely while not breathing in any dust. Before proceeding you must adhere to safety regulations. Connect with the energies of the earth during this process and embrace the time it takes to do this. I use the following approach:
1. Breaking rocks into smaller pieces
First, break the rocks into pieces that can be finely ground using a mortar and pestle. I use a hammer and a thick plastic sheet on which I break the rocks. Break the rocks as fine as you can using this method. This process must be carried outside and by wearing a respirator/NIOSH mask.
2. Grinding
Grind the pieces using a pestle and mortar until you have achieved a very fine powder. This process may be a bit difficult if you are not used to it. Therefore, before commencing make this process easy by breaking the pieces into smaller sizes with a hammer.
3. Sifting
Sifting is the most critical part of the pigment-making process. The goal is to attain the finest particles possible. You can sift multiple times to get a fine grind by using a sieve with very fine mesh. I use old pantyhose to get finer particles.
The process of grinding and sifting is really an art form in itself, some are easy to do, and some are quite difficult&#;depending on the material. It requires patience and is a very meditative process.
An alternative method of refining pigments is through the process of levigation. Read here for more information.
4. Make paints
Finally, paints are created by mixing pigments with different additives. Depending on the additives pigments can be transformed into oil paints, pastels, acrylic paints, watercolor paints, and/or tempera.
Handmade watercolor paints are made using a binder that is made from gum arabic, honey, glycerine (optional) distilled water, and clove oil (natural preservative). Read here about the safe working practice during the paint-making process. It is all about experimenting and figuring out what works best for you.
5. Make sustainable art
Once your paints are ready you can start creating art that expresses how you feel, something that you can connect with, art that makes you happy and is sustainable!
I am every bit enthralled by the process of making my own watercolor paints from the found treasures of the beautiful Earth. I hope this post has inspired you to pursue the same creative voyage!
If you want to learn more, check out my new online course, a comprehensive guide to foraging and making natural pigments.
Online Course: The Pigmentum
In this course, you will learn how to safely and ethically forage for natural pigments, how to identify, process, and transform an assortment of colored rocks and soils into beautiful and unique artist-grade pigments.
Disclaimer: Not every natural material is harmless. This includes mineral pigments and earth colors, which may contain hazardous components. When working with fine mineral dust, it is recommended to use a respirator or dust mask. It is advised that one must consult with the local authorities about the geological features of an area. The author may change the contents of this document at any time, either in whole or in part.
Reference links:
This is a continuation-in-part of now abandoned application Ser. No. 07/969,618 filed Oct. 30, and of now abandoned application Ser. No. 08/123,037 filed Sep. 20, , which is a continuation of application Ser. No. 07/698,776 filed May 13, , now abandoned.
The present invention relates to a process for the manufacture of pigments, especially a process for the manufacture of fluorescent pigments, and to certain pigments prepared.
BACKGROUND OF THE INVENTIONIt is known that when colored substances are subjected to polychromatic radiation such as, for example, daylight, they have the property of reflecting, transmitting or scattering only certain wavelengths and of absorbing the remainder of the luminous energy, which is dissipated by nonradiative processes. So-called daylight-fluorescent substances have the additional property of converting a proportion of the radiation absorbed at the blue end of the visible spectrum and in the near UV into light which is reemitted at longer wavelengths, also situated in the visible spectrum and equal to those of the light which these substances do not absorb. Through this process, they are capable of producing in the observer's eye an impression of color and of brightness which is up to four times greater than that of ordinary colored substances of the same color. It is also known that the intensity of the emitted fluorescent light is extremely sensitive to so-called fluorescence extinction phenomena and that it is a function especially of the concentration of the fluorescent substance itself (autoextinction phenomenon) and of the possible presence of other substances known as fluorescence inhibitors (which act, for example, by reabsorbing the emitted light or by nonradiative quantum deexcitation processes).
In most applications of colorants (for example paper coating, textile printing, plastic coatings) the colorant molecules must be prevented from migrating, diffusing or redissolving in a solvent. In the case of fluorescent colorants, furthermore, the fluorescence intensity is at a maximum (low autoextinction) in a precise concentration range and, if the other causes of extinction of fluorescence are to be limited, the colorant matter must be protected in an inert but transparent optical medium. A rigid polymer matrix in which the colorant molecule is soluble (solid solution) or dispersible meets these requirements of isolation, confinement and immobilisation. These colored polymers are employed in most cases in the form of finely ground particles, generally referred to as pigments.
The polymers employed for manufacturing fluorescent pigments belong to the classes of thermoplastic and thermosetting resins. Among those most commonly employed are aminoplastic resins resulting from the polycondensation of triazines, amines and formaldehyde. Other polymers, such as polyesters, polyamides and polyurethanes and polyvinyl chlorides can also form the carrier for colorant molecules. Depending on the degree of crosslinking obtained during the polymerisation, these resins are either thermoset or thermoplastic. Thermoset resins are employed in cases where good resistance to solvents and to plasticisers is required (absence of swelling and of colorant diffusion) and when softening under the effect of heat could create problems.
In known processes for the manufacture of these thermoset resins the above mixture is polycondensed in bulk, in noncontinuous batches. Such processes are described e.g. in U.S. Pat. No. 3,939,093, in GB 1,341,602 or in U.S. Pat. No. 3,812,051. On the average the reaction takes 2 hours, per batch, in the reactor. After complete polymerisation a hard, tough solid is obtained, whose texture often resembles that of horn. This solid must be taken out of the polymerisation reactor as a block. This can prove difficult and it is often preferred to complete the reaction by casting the reacting mass, which is still pasty, into troughs and finishing the polymerisation in an oven. The blocks are then crushed and then micronised. The micronisation of this solid presents some difficulties: it requires a pregrinding before a fine microniser is fed, it being necessary for the two items of equipment to be cleaned after each batch. Such conventional processes for the manufacture are also described in Chem. Brit., 335 (). The U.S. Pat. No. 3,972,849 proposes the use of known grinding equipment, such as a ball mill, as the reaction vessel in an attempt to avoid the dissadvantages of the conventional manufacturing process.
The inconvenience of the conventional manufacturing processes and the disadvantages of the pigment particles obtained by these processes have led some manufactures, on the other hand, to prefer the manufacture and the use of pigments based on thermoplastic resins each time that a high solvent and temperature resistance is not essential. U.S. Pat. No. 2,809,954, GB 869,801 and GB 980,583 describe the synthesis of pigments based on thermoplastic resins. These fusible, and hence heat-sensitive, resins do not lend themselves well to simple micronising by milling and hence to the manufacture of pigments of a fine and well-determined particle size. These resins generally require an additional stage of manufacture (dispersion, phase separation) to obtain pigment particles of well-determined particle size, which is described, for example, in U.S. Pat. Nos. 3,642,650 and 3,412,034.
The disadvantages of the two types of processes described above are avoided in the manufacture of amide (urea, melamine, and the like)/formaldehyde condensates of low molecular weight or of polyester alkyd resins, wherein to each type of said resins the colorant is attached by affinity. Such processes are described for example in GB 748,848, GB 786,678 or in GB 733,856. However, the applications of such pigments are in practice limited to inks and paints, because the colorant molecules are bound to the condensates only by affinity.
DESCRIPTION OF THE INVENTIONThe objective of the present invention is to manufacture pigments comprising a colored composition incorporated in a resin which isolates, confines and immobilises the colored composition, which pigments withstand the action of heat or of solvents, while avoiding the disadvantages of the processes of the prior art and especially the crushing and the difficulties of micronisation.
This objective is attained by a process for the manufacture of pigments, comprising a colored composition incorporated in a polycondensation resin by continuous bulk polycondensation of the reaction mixture, wherein the reactants for the formation of said polycondensation resin and the colored composition are introduced continuously into an extruder, preferably at a temperature of between 100° C. and 280° C., the mixture is caused to travel forward in the extruder, at the end of reaction the mixture is withdrawn continuously from the extruder, and is deposited continuously onto a conveyor belt, broken up into thermoset flakes, and cooled, said conveyor belt having means for cooling and means for detaching the said flakes from the said belt.
BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a process diagram of the process of the invention;
FIG. 2 is an IR spectrometry analysis of a crosslinked resin obtained by noncontinuous polycondensation according to the prior art; and
FIG. 3 is an IR spectrometry analysis of a crosslinked resin obtained according to the present invention.
Particularly suitable polycondensation resins to be used according to the instant invention are products which are inelastic, non-fiber-forming and brittle and which consequently may easily be converted into particulate form. The resins should moreover have a relatively high softening point, preferably of more than about 100° C., because otherwise at the temperatures which arise during milling the particles of resin may agglomerate and stick together. The resins should also have little or no solubility in the solvents conventionally used in processing, such as e.g. painters' naphtha, toluene and xylenes and also should not swell in these solvents. Furthermore, the resins should exhibit good transparency and adequate fastness to light. Resins meeting these requirements are generally known, and some of them have already been used for the preparation of daylight fluorescent pigments.
Suitable polycondensation resins are for example those, wherein the reactants for the formation of said polycondensation resins are
(a) at least one component A chosen from aromatic sulfonamides containing 2 hydrogens bonded to the nitrogen of the sulfonamide group,
(b) at least one component B chosen from substances containing 2 or more NH2 groups, each of the said NH2 groups being bonded to a carbon, the said carbon being bonded by a double bond to an &#;O, &#;S or &#;N, and
(c) at least one aldehyde component C.
A continuous process for the production of aqueous melamine-formaldehyde-precondensate solutions is described in the EP-A 355,760. This publication, however, neither discloses a continuous bulk polycondensation, nor the use of component A or of colorants as described in the instant application.
Among the substances capable of forming the component A according to the present invention, there will be mentioned especially benzenesulfonamide and benzenesulfonamide derivatives of general formula: ##STR1## where the groups R are hydrogen or alkyl groups. A particularly preferred substance A is para-toluenesulfonamide. ortho-toluenesulfonamide, or mixtures of aromatic sulfonamides, such as mixtures of ortho- and para-toluene-sulfonamide (e.g. a 50:50 mixture of these components), can also be employed and are available on the market. C1 -C4 alkyl-benzenesulfonamides, e.g. are also available commercially.
Among the substances which can be employed as component B according to the present invention there will be mentioned especially urea (NH2 CONH2), thiourea (NH2 CSNH2), guanidine (NH2)2 CNH, carbarnylurea (C2 H5 N3 O2), succinamide (C4 H8 N2 O2), among the noncyclic compounds; among cyclic compounds and more particularly among nitrogenous heterocyclic rings there will be mentioned the molecules containing a plurality of NH2 groups, each of these groups being bonded to a carbon of a heterocyclic ring, the said carbon being linked by a double bond to a nitrogen of the heterocyclic ring; these heterocyclic rings include the triazole, diazine, triazine and pyrimidine nuclei; there will be mentioned in particular the guanamine derivatives of general formula: ##STR2## where R' is hydrogen, an aliphatic radical, an aromatic radical, a saturated or unsaturated cycloaliphatic or alkoxyaryloxy radical. Benzoguanamine may be mentioned among the preferred compounds B.
A compound B which is particularly preferred when it is intended to obtain a thermoset resin is melamine (where R' is NH2). Diguanamines and triguanamines (whose synthesis from the corresponding nitrites and from dicyanodiamide is known, furthermore), or mixtures of the above substances can also be employed as component B according to the present invention, as well as the particular triazine compounds described in the U.S. Pat. No. 3,838,063. A certain amount of the component B according to the invention may be replaced by an isocyanuric ring containing compound, such as isocyanuric acid or its alkyl or aryl esters, respectively; pigment compositions comprising such resins are disclosed in U.S. Pat. No. 3,620,993.
The aldehyde or the mixture of aldehydes forming the component C according to the present invention are formaldehyde, acetaldehyde, propionaldehyde (higher aldehydes can be employed but do not offer any particular advantage within the meaning of the present invention). A particularly preferred compound is paraformaldehyde (CH2 O)n, because of its ease of use.
In the process according to the present invention the melamine concentration, which is preferably between approximately 13% and 40% by weight, of the weight of sulfonamide component A in the reaction mixture, can be taken to values which are markedly higher than those employed in the processes for the manufacture of thermoplastic resins. The concentration of component C in the mixture is preferably between 27% and 40% by weight of the sulfonamide.
A harder and more brittle material is thus obtained, which lends itself better to micronisation and which withstands better the action of heat and of solvents. In the case where the amine chosen as component B is melamine, a decrease in the cost of manufacture is also obtained when the proportion of B is increased, given the low cost of this product. The decrease in the cost of manufacture of the pigments according to the present invention also results generally from the replacement of processes using noncontinuous batches by a continuous reaction process. Surprisingly, it is therefore possible use this process according to the invention to obtain a thermoset resin.
IR spectrometry analysis of samples of crosslinked resin obtained according to the present invention (FIG. 3), when compared with a resin of the same initial composition, obtained by noncontinuous polycondensation according to the prior art (FIG. 2), shows differences in the absorption bands which are characteristic of these crosslinked structures (see FIGS. 2 and 3, in particular the - cm-1 region), and hence differences in the polymeric structures.
Further examples of suitable polycondensation resins are i.a. polyamide resins, polyester resins, polycarbonates or polyurethanes. Other suitable resins are polyester/polyamide resins prepared by the reaction of aminoalcohols or aminophenols with polycarbocylic acids, such as the resins described in U.S. Pat. No. 4,975,220.
Particularly suitable polycondensation resins are polyester resins and especially polyamide resins.
Among the preferred resins are crosslinked polyester resins from aromatic polycarboxylic acids or their anhydrides, particularly aromatic dicarboxylic and tricarboxylic acids, such as phthalic acid, isophthalic acid or trimellitic acid, and bifunctional or polyfunctional alcohols, such as ethylene glycol, glycerol, pentaerythritol, trimethylolpropane and neopentyl glycol. Especially preferred are polyester resins from phthalic anhydride and pentaerythritol. Such preferred polyester resins are described for example in DE 961,575 or in the above mentioned U.S. Pat. No. 3,972,849.
Other preferred polyester resins are partially crystalline thermoplastic opaque polyester resins which have a substantial numer of amorphous regions and which contain from 35 to 95 equivalent % of crystallinity-producing monomers and from 5 to 65 equivalent % of amorphous producing monomers. Such resins and their use for the preparation of fluorescent pigments are described in EP-A 489,482, especially on page 2, line 57 through page 4, line 40 which are hereby incorporated by reference.
Other preferred polycondensation resins to be prepared and used according to the invention are polyamide resins formed by the reaction of a polyfunctional amine with both a polycarboxylic acid and a nionocarboxylic acid, said polyamide being in the molecular weight range from about 400 to about . Such polyamide resins are substantially linear and have at least one carboxy group remaining on the majority of molecules, which permits a thermoplasitc resin to be formed which is extremely friable and grindable. The monocarboxylic acid may be added as such or may be formed in situ by reacting a monoamine and a dicarboxylic acid in sufficient quantity to form the desired corresponding monocarboxylic co-condensate to function as a terminator and control the molecular weight of the resin formed. Optionally, whether or not a monocarboxylic acid is added as such, or is formed in situ, a sufficient amount of stabilizing compound of an element from Groups IIA and IIB may be added to further stabilize the pigment. Such preferred polyamide resins are described in the U.S. Pat. No. 3,915,884, which document is incorporated herein by reference.
Preferred polyfunctional amines for the preparation of the instant polyamide resins are polyfunctional, preferably difunctional, primary amines. Particularly preferred are polyfunctional alicyclic primary amines, which form the most friable resins. Most preferred is isophorone diamine (1-amino-3-aminomethyl-3,5,5-trimethyl cyclohexane). Other suitable amines are aliphatic amines having an aromatic ring, such as the m- and p-xylylene diamines; aliphatic polyfunctional primary amines, such as ethylene diamine, diethylene triamine and the like.
Preferred monocarboxylic aromatic acids are benzoic acid and substituted benzoic acids, such as p-toluic, o-toluic, and 4-methoxy benzoic acid.
Preferred aromatic polycarboxylic acids are those which have carboxy groups on noncontiguous carbon atoms, such as isophthalic acid, terephthalic acid, trimesic acid and dicarboxy and tricarboxy naphthalene.
Other preferred polyamide resins are prepared by reaction of a diamine with an excess stoichiometric amount of a diacid. Such resins are described in U.S. Pat. No. 5,094,777, especially in column 2, line 13 through column 4, line 22, which are hereby incorporated by reference.
When a stabilizing compound of elements in Group IIA and Group IIB of the periodic table of elements is used, such compounds should preferably be compatible with the co-condensate and the coloring material. Suitable compounds are e.g. oxides, carbonates or organic acid salts of Group II elements, such as magnesium oxide, magnesium carbonate, zinc oxide, zinc stearate, calcium hydroxide and the like. Zinc oxide is preferred.
Other preferred polycondensation resins to be prepared and used according to the invention are epoxide resins based on bisphenol-A diglycidyl ethers and crosslinked with polyhydric phenols, such as bisphenol-A, with polycarboxylic acid anhydrides, with Lewis acids and particularly with dicyandiamides and related compounds; hybrid polyesters, such as solid saturated polyester resins having free carboxyl groups and being crosslinked with epoxide resins; polyesters, such as solid saturated polyesters having free carboxyl groups and being crosslinked with triglycidylisocyanurate (TGIC); polyurethanes, such as solid saturated polyesters with free hydroxyl groups being crosslinked with polyisocyanates.
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The polycondensation resins to be used according to the instant invention may, if appropriate, also contain other stabilizing compounds, such as UV-adsorbers or light stabilizers as e.g. the hindered amine light stablizers (HALS). Such stabilizers are well known in the art.
The U.S. Pat. No. 3,915,884 and U.S. Pat. No. 5,094,777 discloses, as mentioned above, the preferred polyamides and their use for the manufacture of fluorescent pigments. However, according to that reference the resins are synthesized in a non-continuous batch process over a prolonged period of time. Such a process is characterized by all the disadvantages discussed above for similar prior art processes.
Surprisingly, with the process of the instant invention a much faster, simpler and more convenient synthesis of the above polycondensation resins and of the pigments, particularly fluorescent pigments, is provided.
The pigments according to the invention comprise preferably at least one substance which is fluorescent in daylight, the preferred concentration of said substance being between 1% and 5% by weight of the pigments. When non-fluorescent dyes, e.g. solvent dyes are used, the preferred concentration may be up to 10% by weight of the pigments.
Colorants capable of forming a solid solution in a resin and capable of fluorescing in daylight are furthermore known and are, in general, listed in the Colour Index. Rhodamines, coumarines, xanthenes, perylenes and naphthalimides will be mentioned by way of example, no limitation being implied. Examples of appropriate colorants are also compounds described in GB 1,341,602, U.S. Pat. No. 3,939,093, U.S. Pat. No. 3,812,051, DE 3,703,495 and in EP-A 422,474.
Other suitable colorants are diketo-pyrrolo-pyrroles (DPP), especially those which are soluble or at least partially soluble in the resins used. Such DPP compounds are known and are described e.g. in U.S. Pat. No. 4,415,685; U.S. Pat. No. 4,810,802; U.S. Pat. No. 4,579,949 and especially in U.S. Pat. No. 4,585,878.
Preferred DPP colorants are compounds of the formula I ##STR3## wherein R1 and R2 independently of one another are hydrogen, C1 -C18 alkyl, C1 -C4 alkoxy, phenyl, cyano or halogen and R3 and R4 independently of one another are hydrogen, C1 -C18 alkyl, C3 -C12 alkenyl, C3 -C5 alkinyl, C2 -C5 alkoxycarbonyl, carbamoyl, C2 -C13 -alkylC1 -C4 alkoxycarbonyl, phenyl or phenyl substituted by chlorine, bromine, C1 -C4 alkyl, C1 -C4 alkoxy, trifluoromethyl or nitro. The substituents R1 and R2, if any, in each of the phenyl rings are preferably in the 3-position, most preferably in the 4-position. The alkyl and alkoxy groups, respectively can be straight chain or branched, such as methyl, ethyl, n- and isopropyl, n-, sec-, teit- and isobutyl etc. C3 -C12 alkenyl can be e.g. allyl, methallyl, 2-butenyl, 2-hexenyl, 3-hexenyl, 2-octenyl or 2-dodecenyl and C3 -C5 alkinyl e.g. propargyl, 1-butinyl, 2-butinyl or n-1-pentinyl. Particularly preferred are compounds of formula I, wherein R1 and R2 are hydrogen, 4-chloro or 4-tert-butyl and wherein R3 and R4 are hydrogen, methyl or 4-chlorophenyl. Also preferred are solubilizing groups R1 to R4.
When the above DPP compounds are used as colorants, the preferred concentration of said compounds is in the range of 0.01-5%, particularly 0.1-1%, by weight of the pigments.
Surprisingly, the pigments obtained when DPP colourants are used, are characterized by an unexpectedly increased light stability, when compared to the above soluble DPP colorants as such (i.e. not incorporated in a polycondensation resin according to the invention), and even more so when compared to the pigments obtained by using the other non DPP colorants defined above.
The compositions obtained by incorporating the above DPP colorants into the preferred polycondensation resins defined above are new. Consequently, another object of the invention are compositions comprising a diketo-pyrrolo-pyrrole colorants and a polycondensation resin selected from the group of crosslinked polyester resins from aromatic polycarboxylic acids or their anhydrides, particularly aromatic dicarboxylic and tricarboxylic acids, and bifunctional or poylfunctional alcohols, such as resins from phthalic anhydride and pentaerythritol, and polyamide resins formed by the reaction of a polyfunctional amine with both a polycarboxylic acid and a monocarboxylic acid, said polyamide being in the molecular weight range from about 400 to about . Preferred such polyester of polyamide resins are defined above.
The above compositions according to the invention can be prepared by mixing the reactants for the formation of said polycondensation resin and the DPP colorant in a reaction vessel and, if appropriate, heating the mixture obtained a temperature of between 100° C. and 280° C., preferably at a temperature of between 170° C. and 280° C., until the polycondensation resin is formed. The above process for the preparation is another object of the instant invention. The brittle polycondensation resin comprising the DPP colorant can then be micronised to the desired pigment particle size in any general manner known to the person skilled in the art. The viscous mixture obtained after the condensation reaction can for example be poured into a shallow pan, and after cooling down and solidifying it can be broken Lip into flake size particles and subsequently micronised.
The present invention is particularly adapted to the manufacture of daylight fluorescent pigments, that is to say pigments whose colored composition comprises one or more substances which are fluorescent in daylight and/or optionally one or more common colored substances. However, it is not limited to pigments of this type: by including in a resin according to the invention a compound which does not absorb in the visible but which fluoresces when it is excited by UV radiation, "transparent" pigments are obtained, which can be employed for particular applications such as invisible inks.
The pigments of the invention are suitable for a wide variety of applications, such as paper coating, textile printing, preparation of paints, plastisols, pastes, inks, markers, toners for non-impact printing or cosmetics.
The instant pigments are characterized by high heat stability and high light stability. Therefore they are particularly suitable for the mass coloration of polymers, particularly of those thermoplastic polymers in which the instant pigments can easily be dispersed. Suitable such polymers are e.g. polyesters, polyamides, PVC-polymers, ABS-polymers, styrenics, acrylics or polyurethanes. Particularly suitable polymers are polyolefins, especially polyethylene or polypropylene. It is particularly convenient to use the instant pigments for the preparation of fluorescent polymer, especially polyolefin masterbatches. The instant pigments, particularly those prepared with basic dyes or with solvent dyes, can also advantageously be used in printing inks, e.g. for textile printing.
The present invention also makes it possible to manufacture common, nonfluorescent colored pigments.
The concentration of the fluorescent substances in the mixture which is to be polycondensed may be adjusted so that the intensity of fluorescence is maximised. After polycondensation and micronisation the local microconcentration of fluorescent substances dissolved in the polymeric matrix remains constant whatever the subsequent overall dilution of the pigment powder, according to its use.
In the continuous process according to the present invention the polycondensation of the reaction mixture is preferably performed in a temperature range lying between 100° C. and 280° C.
When said polycondensation resin is a polyester resin, a hybrid polyester resin, a polyamide resin, an epoxide resin or a polyurethane resin, the temperature is more preferably between 170° C. and 280° C., especially preferred between 190° C. and 260° C.
When said polycondensation resin is a melamine formaldehyde resin obtained by the polycondensation of components A, B, and C described above, the reaction is preferably performed in a temperature range lying between 105° C. and 190° C.
The continuous polycondensation process is carried out in a particularly convenient and simple manner, wherein the colored composition and the reactants for the formation of the polycondensation resin are introduced continuously into a reactor, are melted and mixed, the mixture travels forward in the reactor and at the end of reaction the mixture is continuously withdrawn in a pasty state from the said reactor. The residence time of the mixture in the reactor is less than 10 min; on the average it is 1-4 minutes, particularly 2-3 minutes.
This process period which is short, when compared with the processes of the prior art (i.e. minutes vs. several hours) offers the additional advantage of making it possible to include in the resin matrix heat-sensitive colored substances and compositions (on condition that they withstand being heated to the reaction temperature for a few minutes), which would have been destroyed in the processes of the prior art.
Another advantage of the process according to the present invention is that it is possible to cast or drop the mixture at the end of reaction onto a conveying device on which it breaks up, cools and forms brittle flakes, and this makes it possible to do without a stage of crushing a solidified reaction mass. The flakes thus formed can be easily detached from the conveying device and are easy to micronise after cooling. The flakes are preferably micronised to a particle size of between 0.5 and 20 μm. The particularly preferred mean particle size is between 3 and 7 μm. An extruder has been found particularly suited as a reactor for implementing the process according to the present invention. In a particularly preferred manner use is made of an extruder whose endless screw is responsible both for mixing the components and propelling the reaction mixture in the reactor, and also for its extrusion. It is particularly advantageous to recover the reaction mixture at the outlet of the extruder on a conveyor belt which has means for cooling and means for detaching the said flakes from the said belt. The conveyor belt may be e.g. cooled by air or by water. The mixture leaving the extruder in the form of a pasty lace breaks up on the conveyor belt into droplets which spread and cool, forming flakes. At the other end of the conveyor belt these flakes are easily detached from the belt and are taken to the micronisation.
The characteristics and the advantages of the present invention will be understood better with the aid of the process diaigram (FIG. 1) and of the examples below.
EXAMPLE 1 Manufacture of Colored MixturesA range of shades extending from yellow to orange shades and to red can be produced by mixing e.g. the following colorants, listed in the Colour Index:
Solvent yellow 43
Solvent yellow 44 (C.I. No. )
Solvent yellow 172
Basic yellow 13
Basic yellow 19
Basic yellow 45
Basic red 1 (rhodamine 6G, C.I. No. )
Basic violet 10 (rhodamine B, C.I. No. )
Basic blue 7 (C.I. No. )
Pigment green 7 (C.I. No. ).
Pinks and mauves can be produced from rhodamine mixtures; in the case of mauve, the latter may be obtained e.g. by tinting basic violet 10 with basic blue (in small quantity, to minimise the fluorescence extinction). Green shades can be obtained with the aid of e.g. pigment green 7 and of yellow colorants.
A fluorescent whitening agent may be added.
EXAMPLE 2 Manufacture of Colored Melamine Formaldehyde FlakesA mixture comprising, by weight, 57% of para-toluenesulfonamide, 25% of paraformaldehyde and 15% of melamine (filled with 3%, relative to the total mixture, of yellow 43 colorant) is introduced (overall how rate 30 kg/hour) via the feed hopper (2) of an extruder (1) of coaxial type. The internal temperature of the compression zone (3) and of the extrusion zone (4) of the extruder are maintained at 175° C. (heater elements 7). The components of the reaction mixture are mixed with the aid of an extrusion screw (5) with a cylindrical core, which propels them through the compression zone. The average residence time, from the feed hopper to the extrusion head, is 2' 30". An extrusion head (6) for solid beam profiles can be employed. The extruded pasty lace falls, breaking up, onto a conveyor (11) with a water-cooled endless belt (12). The resin forms flakes on the belt and has set when it reaches its end.
EXAMPLE 3 Flake MicronisationThe flakes recovered at the end of the belt are fed into a mill (111) of the air jet microniser type.
The operating conditions are: dry air at 7 bars, room temperature, 25 kg/hour flow rate.
The table below gives the particle sizes of the pigments obtained.
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Colorant name Average Standard deviation
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Fuchsia pink 4.7 μm
3.3 μm
Fire orange 5.2 μm
3.4 μm
Yellow 5.3 μm
4.0 μm
Green 5.4 μm
3.7 μm
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For all these samples more than 99% of the micronised material is between 0.9 and 14 μm in particle size.
EXAMPLE 4According to the process of example 2, a fluorescent pink pigment is prepared from a mixture having 70% by weight of para-toluene sulfonamide, 18% by weight of paraformaldehyde, 9% by weight of melamine (dyed by 1.5% by weight of basic red 1 and 1.5% by weight of basic violet 10, the amount of colorant being relative to the total mixture).
By means of a latex (latex BASF SD 215®), a fluorescent pigment composition is prepared to be used for coating paper comprising:
25 parts of pink fluorescent pigment
25 parts of Carbital 95®
25 parts of latex BASF SD 215®
25 parts of of water
A fluorescent pink coated paper is obtained.
EXAMPLE 5A fluorescent pink pigment composition called masterbatch (cylindrical granulate forms--length: 5 mm-diameter: 2 mm) is obtained by including 35 g of pink fluorescent pigment of example 4 in 65 g of a polyvinyle chloride mixture composed of 55% of polyvinyle chloride, 31% of dioctyl phthalate and 2% of an organo-tin stabilizer, and passing said mixture through an extruder at 125° C. The filaments obtained are cooled at room temperature and passed through a grind-mill.
EXAMPLE 6 Manufacture of Colored Polyester Resin FlakesA mixture comprising, by weight, 68.5% of phthalic anhydride (flakes), 30.6% of pentaerythritol and 0.9% of rhodamine B is introduced (overall flow rate 30 kg/hour) via the feed hopper (2) of an extruder (1) of coaxial type. The internal temperature of the compression zone (3) and of the extrusion zone (4) of the extruder are maintained in a temperature range of 190 to 260° C. (heater elements 7). The components of the reaction mixture are mixed with the aid of an extrusion screw (5) with a cylindrical core, which propels them through the compression zone. The average residence time, from the feed hopper to the extrusion head, is 2'. An extrusion head (6) for solid beam profiles can be employed. The extruded pasty lace falls, breaking up, onto a conveyor (11) with a water-cooled endless belt (12). The resin forms flakes on the belt and solidifies while it reaches its end.
EXAMPLE 7 Flake MicronisationThe flakes recovered at the end of the belt are fed into a mill (111) of the air jet microniser type. The operating conditions are: dry air at 7 bars, room temperature, 20 kg/hour flow rate. The average particle size of the pigments obtained depends on the flow rate and ranges from 1 to 15 μm for more than 99% of the micronised material.
EXAMPLE 8 Manufacture of Colored Polyamide Flakes and their MicronisationAccording to the process of examples 6 and 7, a fluorescent yellow pigment is prepared from a mixture having 35.3% by weight of isophorone diamine, 34.5% by weight of isophthalic acid, 25.3% by weight of benzoic acid, 3.3% by weight of zinc oxide and 1.6% by weight of Hostasol® Yellow 3G (Hoechst AG; solvent yellow, C.I. No. ).
EXAMPLE 9 Preparation of a MasterbatchA fluorescent pink pigment composition called masterbatch (cylindrical granulate forms--length: 5 mm-diameter: 2 mm) is obtained by including 30 parts of pink fluorescent polyester pigment of example 6 and micronised as described in example 7 in 70 parts of a polyethylene mixture composed of 32 parts of low density polyethylene (Escorene® 600 BA G20; Exxon Chemicals), 32 parts of low density polyethylene (Escorene® RQ G50; Exxon Chemicals), 5 parts of polyethylene wax AC 540® Allied Chemical Co.) and 1 part of zinc stearate, and passing said mixture through an extruder at 155° C. The filaments obtained are cooled at room temperature and passed through a grind-mill.
EXAMPLE 10 Preparation of a MasterbatchA fluorescent yellow pigment composition called masterbatch is obtained as described in example 9 above by using 30 parts of the yellow fluorescent polyamide pigment prepared in example 8 and micronised as described in example 7.
EXAMPLE 11-12 Manufacture of Colored Polyamide Flakes and their MicronisationExample 11
According to the process of Examples 6 and 7 a fluorescent pink pigment is prepared from a mixture having 14.9% by weight of benzoic acid, 41.5% by weight of isophorone diamine, 40.5% by weight of isophthalic acid and 3.1% by weight of Flexo red 540 (BASF AG; rhodamine B, C.I. No. ).
EXAMPLE 12According to the process of Examples 6 and 7 a fluorescent yellow pigment is prepared from a mixture having 10.5% by weight of benzoic acid, 43.7% by weight of isophorone diamine, 42.7% by weight of isophthalic acid and 3.1% by weight of fluorescent yellow AA 216 (Holidays, Huthersfield, GB; C.I. Basic yellow 40).
EXAMPLE 13According to the process of example 6 fluorescent pink pigments are prepared from mixtures having the following compositions.
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A B C
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Benzoic acid 8.1% 24.9% 10.5
Isophorone diamine
44.9% 34.8% 43.7%
Isophthalic acid
43.9% 33.9% 42.7%
Flexo red 540
3.1% 3.1% 3.1%
Zinc oxide -- 3.3% --
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EXAMPLE 14
Flake Micronisation
The flakes recovered at the end of the belt from sample 13B above are fed into a mill of the air jet microniser type (Alpine 200 AFG, Augsburg). The particle size of the pigments obtained as analyzed by Sympatec Helos is given below.
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Velocity (rpm)
Flow (kg/h)
d.sub.50 d.sub.97
d.sub.10
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48 2.4 7.5 0.9
72 2.8 9.3 0.9
100 3.0 10.4 0.9
154 4.2 23.8 1.0
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EXAMPLE 15
Manufacture of Colored Poyester Resin Flakes and their Micronisation
According to the process of examples 6 and 7, but replacing the rhodamine B with 0.1% by weight of the pigment produced of a diketo-pyrrolo-pyrrole of the formula I ##STR4## wherenin R1 -R4 is hydrogen (prepared according to example 1 of U.S. Pat. No. 4,579,949), a fluorescent yellow-orange pigment is prepared.
EXAMPLE 16 Manufacture of Colored Polyamide Flakes and their MicronisationAccording to the process of example 8, a fluorescent yellow-orange pigment is prepared from a mixture having 35.3% by weight of isophorone diamine, 34.5% by weight of isophthalic acid, 26.85% by weight of benzoic acid, 3.3% by weight of zinc oxide and 0.05% by weight of a colorant of formula I above, wherein R1 and R2 are 4-chloro and R3 and R4 are hydrogen (prepared according to example 6 of U.S. Pat. No. 4,579,949).
EXAMPLE 17 Batch Preparation of Colored Polyamide and the Micronisation ThereofIn a round bottom flask a mixture of 36% isophorone diamine, 35% of isophthalic acid, 25% of benzoic acid, 3% of zinc oxide and 1% a colorant of formula I above, wherein R1 and R2 are hydrogen and R3 and R4 are methyl (prepared according to example 1 of U.S. Pat. No. 4,585,878) is heated to 250° C., held at this temperature for 10 minutes, cooled to room temperature and micronised according to example 3 to form a orange-yellow fluorescent pigment.
EXAMPLE 18 Manufacture of Colored Polyamide Flakes and their MicronisationA fluorescent orange-yellow pigment is prepared as described in example 8 but using a compound of formula I, wherein R1 and R2 are 4-tert-butyl and R3 and R4 are hydrogen as colorant (prepared according to example 20 of U.S. Pat. No. 4,579,949), instead of the Hostasol® Yellow 3G.
EXAMPLE 19 Manufacture of Colored Polyamide Flakes and their MicronisationA fluorescent yellow pigment is prepared as described in example 8 but using a compound of formula I, wherein R1 and R2 are 4-chloro and R3 and R4 are 4-chlorophenyl as colorant (prepared according to example 10 of U.S. Pat. No. 4,579,949).
EXAMPLE 20-23 Manufacture of Colored Polyester Flakes and their MicronisationExamples 16-19 are repeated by using the mixture of phthalic anhydride and pentaerythritol described in example 6 as reactants for the preparation of the polycondensation resin.
EXAMPLE 24According to the process of examples 6 and 7 a fluorescent pink pigment is prepared from a mixture having 29.2% by weight of glyderol, 69.8% by weight of phthalic anhydride flakes and 1.0% by weight of rhodamine B.
EXAMPLE 25Example 24 is repeated by substituting phthalic anhydride by an equivalent amount of butanedioic acid.
EXAMPLE 26According to the process of examples 6 and 7 a fluorescent pink pigment is prepared from a mixture having 29.2% by weight of ethylene glycol, 69.8% by weight of phthalic anhydride and 1% by weight of rhodamine B.
EXAMPLE 27According to the process of examples 7 and 8 a blue pigment is prepared from a mixture having 14.9% by weight of benzoic acid, 41.5% by weight of isophorone diamine, 40.5% by weight of isophthalic acid and 3.1% by weight of Fliso Blue 630® (BASF AG).
EXAMPLE 28A blue pigment composition for coating paper is prepared from the following components:
25 parts of blue pigment prepared in example 27
25 parts of carbital 95
25 parts of latex BASF SD 215®
25 parts of water
The composition can be used for coating paper.
EXAMPLE 29Preparation of a Printing Ink
A fluorescent pink ink is prepared from a mixture having 100 parts of binder (Ecocryl® , W. SIPPO Co., Villers Saint Paul, France), 20 parts of a fixer (fixer 99HD®, W. SIPPO Co.), 10 parts of emulsifier (ATEPRINT E®, Dr. Th. BHOME, Germany), 820 parts of water and 20 parts of the pink pigment obtained in example 9. The fluorescent ink is used for application by the screen process (or any similar process) on cotton fabric, which is then heated (dry heat) for 3 minutes at 150° C.
EXAMPLE 30 Manufacture of Colored Polyamide Flakes and their MicronisationAccording to the process of examples 6 and 7 a fluorescent pink pigment is prepared from a mixture of 44% by weight of isophorone diamine, 27% by weight of isophthalic acid, 25% by weight of azelaic acid, 3% by weight of ZnO and 1% by weight of rhodamine B.
EXAMPLE 31 Manufacture of Colored Polyamide Flakes and their MicronisationAccording to the process of examples 6 and 7 a fluorescent orange pigment is prepared from a mixture of 22% by weight of isophorone diamine, 20% by weight of 2-methyl-pentamethylenediamine, 29% by weight of isophthalic acid, 25% by weight of azelaic acid, 3% by weight of ZnO and 1% by weight of rhodamine 6G.
EXAMPLE 32 Manufacture of Colored Polyester Flakes and their MicronisationAccording to the process of examples 6 and 7 a fluorescent yellow pigment is prepared from a mixture of 60% by weight of phthalic anhydride, 31%, by weight of 1,4-cyclo-hexanedimethanol, 3% by weight of ethylene glycol, 4% by weight of glycerol and 2% by weight Hostasol® Yellow 3G (Hoechst AG).
EXAMPLE 33 Batch Preparation of Colored Polyamide Flakes and Micronisation ThereofAccording to the process of example 17 a fluorescent orange-yellow pigment is prepared from a mixture of 45% by weight isophorone diamine, 28% by weight of isophthalic acid, 25% by weight of azelaic acid and 2% by weight of the colorant in example 17, by heating the mixture to 270° C. for 5 minutes.
EXAMPLE 34 Batch Preparation of Colored Polyester Flakes and Micronisation ThereofAccording to the process of example 17 the following mixture is heated to 280° C. for 15 minutes: 57% by weight of terephthalic acid, 12% by weight of ethylene glycol, 30% by weight of 1,4-cyclohexanedimethanol and 1% by weight of the colorant used in example 19 to produce a fluorescent yellow pigment.
EXAMPLE 35 Batch Preparation of Colored Polyester Flakes and Micronisation ThereofAccording to the process of example 17 the following mixture is heated to 280° C. for 5 minutes: 29.8% by weight of terephthalic acid, 20% by weight of isophthalic acid, 50% by weight of 1,4-cyclohexanedimethanol and 0.2% by weight of the colorant used in example 18 to produce a fluorescent orange-yellow pigment.
The above examples are given merely by way of illustration. Other devices and operating conditions can be employed by a person skilled in the art without departing from the continuous polymerisation process forming the subject of the present invention.
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