GB1589508A - Colour concentrates - Google Patents

Description

(54) COLOUR CONCENTRATESt (71) We, REED PLASTICS CORPORA~ TION, of Holden, Massachusetts 01520, United States of America, a company organized under the laws of the Commonwealth of Massachusetts, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: In the plastics industry, and in particular in connection with extruded plastics, it is both important and difficult to incorporate coloring materials in a uniformly distributed, finely dispersed form. Ordinarily plastic materials are colored by means of pigment, or finely divided solid particulate coloring materials, although a certain number of plastics may be colored by means of dyes or mixtures of dyes and pigments. In either case it is important to have the coloring material uniformly distributed so that the color of the plastics is uniform. In addition, it is also important to have the coloring materials dispersed in the plastic in a finely divided form, usually in the general range of sub-micron size and without significant quantities of large agglomerates. When a pigment is dispersed in a plastic as finely divided small particles it produces the desired color more efficiently and with the use of a smaller quantity of pigment. A greater uniformity of color is achieved, and the physical and mechanical properties of the plastic are better or not adversely affected.

The extrusion of fine plastic filaments is one of the more rigorous uses and applications of dye or pigment coloring materials in plastics or resins. These filaments may be relatively large, but they also may be as fine as one micron or even finer, with the result that agglomerates of pigment material may be as large as, or perhaps many times larger than, the filament diameter. Such agglomerates may seriously weaken the filament or may clog the screen pack, spinneret, extruder head or nozzle or the like. Generally speaking this means that the colored resin for an extruded filament should be virtually or completely free from particles larger than about one-half the filament diameter. One particular and very important problem to be solved, therefore, is the need for thorough dispersion and size reduction of a pigment material in a plastic for filament extrusion.

It has long been well known that finely divided particles, such as pigment particles, are different and difficult to disperse. When such particles are mixed in a suspending medium such as a plastic material, they tend to remain as clumps or as large agglomerates/aggregates. The difficulties accompanying agglomeration are known to require very powerful mixing procedures which are incompatible with the need to feed a plastic material rapidly and uniformly into processing equipment; such mixing may also impair the properties of the plastic itself. The art has partially solved this problem by accomplishing the mixing in two stages. In the first stage there is prepared a mixture of the plastic material and the coloring material, such as one or more pigments, to form a product generally known as a color concentrate or a masterbatch. The extremely difficult first step of properly dispersing the pigment in the plastic is separated from the extrusion process. Usually the color concentrate is made by another manufacturer or processor and sold to the party doing the extruding or other processing. It is usual in the industry to employ a color concentrate and to have this color concentrate prepared according to individual color specifications required by the customer. Subsequently the color concentrate is "let down" or diluted by mixing with the "natural" material or clear plastic, usually at a ratio between about 10 to 1 and about 100 to 1. A very common procedure is to let down the color concentrate by 25 to 1. The color concentrate and natural material mix together easily and the two can simply be fed simultaneously to the extruding equipment and mixed in the screw which feeds material to the extruding head or mixed in such other manner as the manufacturer may determine.

In effect the difficult problems associated with dispersing the pigment uniformly and free from agglomerates have not been solved but have merely been transferred from the extruding operation to a prior separate step of forming a satisfactory color concentrate.

The difficult job has been carved out and transferred to someone else for its solution.

One typical procedure for forming a color concentrate is shown in U.S. 3,755,244.

According to the procedures of this patent, a pigment and a polyolefin are thoroughly milled, after which the polyolefin is granulated and recovered. The recovered polyolefin becomes a color concentrate.

In methods heretofore employed it is usual to start with either a pigment in dry powder form, known in the art as dry color, or to start with what is known as press cake, which is a pigment mixed with water or some other liquid and pressed into the form of a moist cake or paste. Either dry color or press cake may have optional additives to impart specific properties or characteristics to the pigment. The pigment such as dry color or press cake is mixed with a polymer to produce a suspension or dispersion. This step of dispersing the pigment is ordinarily accomplished by very powerful mixing, such as high shear mixing such as in a pebble mill, a sand mill, a Bandbury mixer or the like. The product ordinarily resulting from such techniques mixes easily with the natural material at the extrusion machine. Unfortunately even with such rigorous mixing it is difficult to break up clumps or agglomerates of the pigment, and quite frequently a color concentrate may contain a relatively large population of agglomerates of at least several microns in diameter and in many cases in the range of 25 to 300 microns.

According to the present invention, there is provided a method of forming a color concentrate for use in coloring plastics materials, the method comprising: mixing a color material with a dispersion liquid, the mixing comprising the simultaneous application of high shear mixing and elastic wave energy, and acting to disperse and achieve size reduction of said color material into said dispersion liquid; mixing the resulting dispersion with a softenable polymer at a temperature at least as high as the softening point of the polymer, the latter mixing comprising high shear mixing, being carried out substantially in the absence of solvent for the color material or polymer, and resulting in flushing of the dispersed color material into said polymer; and recovering the resulting color concentrate.

For the avoidance of doubt it is pointed out that the term "color" as used herein includes the colors black and white. It is further pointed out that the term "elastic wave energy" as used herein in relation to applying energy to a medium means wave energy which is such that it is propagated into the medium with the performance of work therein, the mechanism whereby the waves of the wave energy are propagated in the medium involving elastic deformation of the medium.

It has been found that color concentrates can be produced by the method of the invention with a high degree of dispersion, more nearly approaching a perfect suspension of individual color material particles, each encapsulated in, or dispersed in, the resin material. The dispersed pigment particles generally are deagglomerated to produce particle sizes of approximately one micron or less. These is of course, a size distribution: the adequacy of dispersion of agglomerates in this art is judged by the maximum particle size, and dispersions having substantially no particles above one micron are readily attainable and are particularly valuable for extruded filaments; smaller particle sizes up to l micron maximum size can be achieved. The concentrates can be produced with a higher percentage of color while still equaling or exceeding quality standards.

To produce the desired product, a color material such as a dye or pigment as press cake, dry color or other form can be mixed with an inert dispersion (i.e. suspending) liquid which is stable at the mixing temperature and neither dissolves nor reacts with the pigment nor with the carrier, i.e. the softenable polymer, such as polymer or resin. The pigment or other coloring material being dispersed has greater affinity for the carrier than for the inert suspending liquid, so that it can be transferred from suspending liquid to carrier. The pigment can be suspended in water or other liquid such as glycerol or the like, and can be transferred or flushed to a resin, and neither pigment nor resin reacts with the liquid. If desired, a material which is solid at room temperature and either liquid or at least soft at operating temperature may be employed as the suspending liquid.

The pigment is mixed with the suspending liquid and preferably also a dispersing agent, with high shear mixing. Ultrasonic (i.e.

superaudible frequency) energy at the point of mixing may be used as the elastic wave energy to be used in combination with the high shear mixing.

The resulting suspension of pigment or other coloring material in the inert liquid may then be mixed with a quantity of the desired softenable polymer material at a temperature such that the polymer is well softened. Mixing and encapsulation of pig ment particles in polymer is accomplished by a procedure comprising high shear mixing, the procedure preferably comprising the simultaneous application of high shear mixing and elastic wave energy.

To accomplish combination mixing to disperse and reduce the aggregates/agglomerates the particles in the dispersion liquid or optionally to flush them to the resin, a generator of high frequency sound energy may be positioned as closely as practical to the point of mixing. At the end of a relatively short time, generally less than an hour, there is formed a product in which the pigment particles are as small as desired, optionally of sub-micron size, uniformly dispersed and encapsulated in the resin material, the encapsulation being sufficiently complete so that the particles remain suspended through- out reasonable shelf life. After suspension and encapsulation the inert liquid is removed, for example, by draining it off and washing or rinsing the colored resin. If the inert liquid is water or a water miscible liquid such as glycerol it can be washed out by water, leaving a color concentrate of plastic granules and encapsulated pigment essentially without contaminating impurities.

The concentrate granules can then be dried to remove moisture and optionally may be lightly ground to reduce the size of a few of the larger granules. Color concentrate granules may be utilized as the concentrate product, or they may be pelletized. Pelletized concentrates are easily formed by extruding the concentrate and cutting the extruded product into short lengths.

The present invention also comprehends a method of forming a colored extruded product having known cross-sectional dimensions, the method comprising mixing a color concentrate obtained by a method in accordance with the invention with an extrudable polymer, substantially all of the color particles of said color concentrate being smaller than the smallest of said dimensions, and extruding the resulting mixture to form said colored extruded product.

The color concentrate formed according to present invention can be employed for other uses and applications besides the coloring of extruded films or filaments of plastics.

For example, it can be used to form colored elastomers, resins for paints or coating compositions, inks and the like, and generally a full line of injection molded, blow molded or extruded plastic products.

In the production of color concentrates for plastics or resins there may be employed any of a wide variety of pigment or coloring materials. In this art it is usual for the supplier of color concentrates to match the color to the plastic producer's specifications of color by blending selected proportions of pigment and pigments. In producing such color matched color concentrates, various single and mixed pigments and dyes have been employed, and each and every pigment which the present inventor has employed has worked satisfactorily. It is presently believed that the pigments and dyes ordinarily used in the plastics industry are compatible with procedure of the present invention.

In the prior art, pigments have been dispersed with the assistance of dispersing agents or have been specially coated or otherwise treated to make them more easily dispersed. Such pigments or techniques may be employed in this invention but seem to be unnecessary at least with most pigments: the present invention can yield good dispersions without introducing additional ingredients. If the pigments have been coated or otherwise treated it may be desired to modify the effects thereof to ensure or increase the relative affinity of the pigment for the resin or carrier.

The present invention can result in substantially better dispersion of color materials in resins, elastomers and the like. Particle size and agglomerate size can be reduced to micron or sub-micron size and the reduced particle or agglomerate size can be maintained. The individual particles or agglomerates are encapsulated or at least partially surrounded by the continuous phase of the polymer of a color-concentrate. There can be substantial saving in time and cost by obtaining better dispersion in times as short as an hour or less, instead of inferior dispersion according to prior methods even with extended times of 24 hours or more.

The polymer is not degraded by long mixing times.

There is substantially improved flexibility, both in terms of a wider selection of color materials which may be included in a resin or similar product; and also in a much wider selection of materials which can be colored or treated. Not only can thermoplastic resins be colored and molded or extruded, but also color materials may be incorporated in polymers used in connection with surface coatings, inks, paints and the like.

The nature of the invention can be more fully understood with reference to the drawing, in which the Figure is a flow diagram illustrating a preferred embodiment in accordance with the invention.

In the figure, a first liquid 11 and a color material to be dispersed and encapsulated, identified in the drawing as dispersed material 12 are introduced into combined dispersion means 10 and processed with mixing means 13 and ultra-sonics energy 14 with suitable controls such as temperature controls 15. In actual practice the combined dispersion means 10 can be a tank, vat or other vessel or container having high shear mixing means 13 combined with ultrasonics energy means 14. Temperature controls 15 or other control means will be used to control operating or mixing conditions as desired.

The first liquid 11 may be a liquid such as glycerol or water which is presently preferred or one of the other materials into which the color material 12 is to be mixed.

After the material 12 has been dispersed into or suspended in the first liquid 11, the dispersion from combined dispersion means 10 is mixed with a softenable polymer 24 in flushing means 25, optionally with suitable temperature control means 26. Again as desired, flushing means 25 may be the same vat as used for combined dispersion means 10. In a typical and presently preferred embodiment of the invention a thermoplastic resin 24 of the same type which is intended for ultimate coloring or similar treatment is introduced to the flushing means 25 together with the dispersion of a pigment 12 in first liquid 11. The temperature is raised to the softening point of the resin, and the dispersed pigment is flushed to and encapsulated in the resin. If this temperature is above the boiling point of one of the components of the mixture, a pressurized vessel is used. After flushing, the mixture is cooled and transferred to liquid separation means 27 to separate out the first liquid for recovery and recycling or for discard.

The remaining product is purified in washing and drying means 28, and may be recovered as a granule product 30.

The granule product comprises the original dispersed color material 12 dispersed in and encapsulated in the resin 24. It generally is formed as granules which may if desired be lightly ground to reduce large particle sizes.

It may be treated by optional processing 31 to form tablets, pellets or a similar product.

It may be used directly in resin plastic processing 32 such as for example, plastic extrusion, or the like.

The present invention can achieve better results than prior methods. Agglomerates can be broken up more effectively, resulting in smaller sized particles and at the desired size range. The combination of high shear mixing and elastic wave energy breaks the agglomerates to form a stable dispersion in the first liquid. In this way, agglomerates which would otherwise resist deagglomeration are split apart and are kept deagglomerated until flushing takes place.

For a commercial operation according to this invention the color concentrate is generally made according to a batch system so that the desired balance of ingredients or materials can be achieved with the least problems and difficulties; but continuous rather than batch operation may be possible.

It is usually preferred to have twd or more sets of equipment in different sizes such as for example, a system employing 1000 gallon vats or tanks, a second system with 500 gallon vats or tanks, and a third system with 100 gallon vats or tanks. For the purpose of the description however, laboratory sized equipment is described with a capacity of 2.6 gallons so that a number of small runs could be made on a comparative basis.

The equipment employed included a Branson ultra-sonic cleaner with a stainless steel transducerized heated tank: Model 610-6 ATH (40 KHz) having internal dimensions of 6" x 10" x 10" (deep). The Branson cleaner was equipped with variable speed high shear mixer. A quartz glass immersion heater was employed as a supplemental heat source.

EXAMPLE I This Example discloses the preparation of a pigment color useful as a thermoplastic resin color concentrate. Into the Branson tank was placed four liters of glycerol. The homogenizing mixer was turned on and the ultra-sonic unit was turned on and set for 40 KHz. The desired quantity of a pigment press cake was added to the glycerol. Any of the usual coloring materials for resins or plastics may be used. In the specific example phthalo blue, G.S. was employed in the quantity to produce a 25% solids mixture in the final product. The combination of high shear and ultra-sonic mixing and dispersion was continued for one hour at room temperature.

The temperature in the tank reached about 1500F., the pH was adjusted to about 11 and there was added 375 grams of polyethylene. The combination of high shear mixing and ultra-sonics was continued while the mix was heated to 210 F. Heating was continued until granulation occurred at about 215 to 220"F.

The product was allowed to cool to until the granules became firm, for example at about 1700F. The contents of the tank were poured onto a screen and washed with water.

Granules of polyethylene containing the pigment were collected on the screen and after washing were pan-dried. The granule size was quite uniform but light grinding was employed to break up a few larger than average clumps of granules. The granules were of random shape, generally but not exactly spherical, averaging about a 1/ to 3/32 inch in diameter or of such size that they are retained on a 80/100 mesh screen.

EXAMPLE 2 The granule product of Example 1 was formed into pellets by extruding it into continuous strands 3/lug inch in diameter and cutting the stands when cooled into usual pellet size. The pellets are considered by some plastics processing operators to be a preferred physical form for a color concentrate. The pellets according to this Example were uniform in size and were uniformly colored. The pigment particle size in the pellet was 1 micron or less. The pellets are adapted to blend and mix uniformly with polyethylene in a film extruder, and can advantageously be added to natural materials entering the extruder at or prior to the screw feed. A sample of pellets prepared in this Example was fed to a natural polyethylene plastic, being let down in a ratio of 25:1 and the colored plastic extruded into a filament. Microscopic examination at 400 x magnification showed the particle size to be relatively uniformly dispersed with a maximum particle size acceptable for its intended application. The polyethylene pellets can also be used with polypropylene to make a film or filament.

EXAMPLE 3 The precedure of Example 1 was repeated employing nylon as the resin. The resin was added to the dispersion mix of pigment and glycerol at room temperature. Thereafter, the container was closed and an inert atmosphere (nitrogen) was maintained in the closed vessel. The product was mixed to the temperature required to melt/soften the resin.

The inert liquid in which the pigment is initially suspended is one which can be mixed with the pigment either in the form of dry powder or press cake. It should be substantially non-volatile at the working ranee of the plastic with which it is being used; at the present time most plastics with which it is being used; at the present time most plastics are extruded at a temperature between about 250 and about 550"F. The pigment particles should be capable of being dispersed in and should be held in suspension in the inert liquid. The particles should not be soluble in the liquid and should be releasable from said liquid, or capable of being flushed into with the desired resin.

The liquid should be easily separable from the resin, and thus not soluble in the resin and not a eood solvent for the resin. Desirably, the liquid may be water miscible and thus easily washed from the resin: a water miscible liquid appears to be well adapted for suspending pigment that is obtained in the form of press cake.

In addition to water itself, and glycerol, other materials include ethylene glycol, caprolactam, stearic acid and its salts, silicone fluids and the like, cellulose base materials, oils such as mineral oil, castor oil, peanut oil and the like, and various petroleum base oils. Where water is not detrimental, water with additives or dispersing agents or the like is preferred. In particular, materials of this sort are useful for special applications. If the suspending liquid is volatile at the operating temperature it may be employed in a closed, pressurized vessel in order to achieve the higher temperature.

For example, water can be used at temperatures in the range of 220 to 250"F at moderate pressure and at temperatures up to 500"F or 600"F at much higher pressures.

In general, however, for color concentrates for extruded plastics glycerol is at thistime considered to be the preferred liquid. From the foregoing it will be appreciated that the use, in accordance with the invention, of a combination of mechanical mixing and elastic wave energy can reduce the mixing and wetting time and/or improve the until mate product.

WHAT WE CLAIM IS: 1. A method of forming a color concentrate for use in coloring plastics materials, the method comprising: mixing a color material with a dispersion liquid, the mixing comprising the simultaneous application of high shear mixing and elastic wave energy (as herein defined), and of said color material into said dispersion liquid; mixing the resulting dispersion with a acting to disperse and achieve size reduction softenable polymer at a temperature at least as high as the softening point of the polymer, the latter mixing comprising hieh shear mixing, being carried out substantially in the absence of solvent for the color material or polymer, and resulting in flushing of the dispersed color material into said polymer; and recovering the resulting color concentrate.

2. A method according to claim 1, wherein said latter mixing comprises the simultaneous application of high shear mixing and elastic wave energy.

3. A method according to claim 1 or claim 2, wherein said elastic wave energy is ultrasonic energy.

4. A method according to any one of claims 1 to 3, wherein said color material is a pigment.

5. A method according to any one of claims 1 to 4, wherein said dispersion liquid is water containing at least one dispersing agent.

6. A method according to any one of claims 1 to 4, wherein said dispersion liquid is glycerol.

7. A method of forming a color concentrate, the method being substantially as described in either of the foregoing Examples 1 and 3.

8. A color concentrate whenever prepared by a method in accordance with any one of claims 1 to 7.

9. A method of forming a colored extruded product having known cross-sectional

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. a preferred physical form for a color concentrate. The pellets according to this Example were uniform in size and were uniformly colored. The pigment particle size in the pellet was 1 micron or less. The pellets are adapted to blend and mix uniformly with polyethylene in a film extruder, and can advantageously be added to natural materials entering the extruder at or prior to the screw feed. A sample of pellets prepared in this Example was fed to a natural polyethylene plastic, being let down in a ratio of 25:1 and the colored plastic extruded into a filament. Microscopic examination at 400 x magnification showed the particle size to be relatively uniformly dispersed with a maximum particle size acceptable for its intended application. The polyethylene pellets can also be used with polypropylene to make a film or filament. EXAMPLE 3 The precedure of Example 1 was repeated employing nylon as the resin. The resin was added to the dispersion mix of pigment and glycerol at room temperature. Thereafter, the container was closed and an inert atmosphere (nitrogen) was maintained in the closed vessel. The product was mixed to the temperature required to melt/soften the resin. The inert liquid in which the pigment is initially suspended is one which can be mixed with the pigment either in the form of dry powder or press cake. It should be substantially non-volatile at the working ranee of the plastic with which it is being used; at the present time most plastics with which it is being used; at the present time most plastics are extruded at a temperature between about 250 and about 550"F. The pigment particles should be capable of being dispersed in and should be held in suspension in the inert liquid. The particles should not be soluble in the liquid and should be releasable from said liquid, or capable of being flushed into with the desired resin. The liquid should be easily separable from the resin, and thus not soluble in the resin and not a eood solvent for the resin. Desirably, the liquid may be water miscible and thus easily washed from the resin: a water miscible liquid appears to be well adapted for suspending pigment that is obtained in the form of press cake. In addition to water itself, and glycerol, other materials include ethylene glycol, caprolactam, stearic acid and its salts, silicone fluids and the like, cellulose base materials, oils such as mineral oil, castor oil, peanut oil and the like, and various petroleum base oils. Where water is not detrimental, water with additives or dispersing agents or the like is preferred. In particular, materials of this sort are useful for special applications. If the suspending liquid is volatile at the operating temperature it may be employed in a closed, pressurized vessel in order to achieve the higher temperature. For example, water can be used at temperatures in the range of 220 to 250"F at moderate pressure and at temperatures up to 500"F or 600"F at much higher pressures. In general, however, for color concentrates for extruded plastics glycerol is at thistime considered to be the preferred liquid. From the foregoing it will be appreciated that the use, in accordance with the invention, of a combination of mechanical mixing and elastic wave energy can reduce the mixing and wetting time and/or improve the until mate product. WHAT WE CLAIM IS:

1. A method of forming a color concentrate for use in coloring plastics materials, the method comprising: mixing a color material with a dispersion liquid, the mixing comprising the simultaneous application of high shear mixing and elastic wave energy (as herein defined), and of said color material into said dispersion liquid; mixing the resulting dispersion with a acting to disperse and achieve size reduction softenable polymer at a temperature at least as high as the softening point of the polymer, the latter mixing comprising hieh shear mixing, being carried out substantially in the absence of solvent for the color material or polymer, and resulting in flushing of the dispersed color material into said polymer; and recovering the resulting color concentrate.

2. A method according to claim 1, wherein said latter mixing comprises the simultaneous application of high shear mixing and elastic wave energy.

3. A method according to claim 1 or claim 2, wherein said elastic wave energy is ultrasonic energy.

4. A method according to any one of claims 1 to 3, wherein said color material is a pigment.

5. A method according to any one of claims 1 to 4, wherein said dispersion liquid is water containing at least one dispersing agent.

6. A method according to any one of claims 1 to 4, wherein said dispersion liquid is glycerol.

7. A method of forming a color concentrate, the method being substantially as described in either of the foregoing Examples 1 and 3.

8. A color concentrate whenever prepared by a method in accordance with any one of claims 1 to 7.

9. A method of forming a colored extruded product having known cross-sectional

dimensions, the method comprising mixing a color concentrate in accordance with claim 8 with an extrudable polymer, substantially all of the color particles of said color concentrate being smaller than the smallest of said dimensions, and extruding the resulting mixture to form said colored extruded product.

10. A method according to claim 9, wherein said extrudable polymer is chemically the same as the softenable polymer of said color concentrate.

11. A method according to claim 9 or claim 10, wherein said extrudable product is in an extruded film.

12. A method according to claim 9 or claim 10, wherein said extruded product is an extruded filament.

13. A method according to claim 12, wherein said filament is less than one micron in thickness, and the color material of said color concentrate is a pigment.

14. A method of forming a colored extruded product, the method being substantially as described in the foregoing Example 2.

15. A colored extruded product whenever formed by a method in accordance with any one of claims 9 to 14.