WO2006007364A2

WO2006007364A2 - Heat-stable colorant compositions for polymers

Info

Publication number: WO2006007364A2
Application number: PCT/US2005/020772
Authority: WO
Inventors: Mohammed Kamruzzaman; David Lee
Original assignee: Degussa Corporation
Priority date: 2004-06-10
Filing date: 2005-06-10
Publication date: 2006-01-19
Also published as: WO2006007364A3

Abstract

A heat-stable pigment dispersion for use in providing uniform and reproducible colors in polymers and polymer compositions subjected to high-temperature processing at temperatures in the range of 200° to 800°F during processes such as extrusion, calendaring and molding, consists of one or more heat-stable pigments, a solvent that evaporates during the high-temperature processing, one or more surfactants and an anti-settling agent. The physical properties and performance characteristics of the finished products show no adverse effects from the addition of the pigment dispersion, and polymers containing the pigment dispersion can be processed in the same manner as polymer compositions containing none of the pigment dispersion.

Description

HEAT-STABLE COLORANT COMPOSITIONS FOR POLYMERS

Field of the Invention

This invention relates to colorant compositions that are added to polymer compositions prior to or during processing of the polymers at high temperatures, such as those experienced during mixing, extrusion, calendeing and molding operations.

Background of the Invention

Polymers and polymeric compositions are often subjected to elevated

temperatures during manufacturing processes that employ extruders, calenders and various types of mixing, blending and molding equipment. The processing temperatures can range from 200⁰F to 800⁰F, depending upon the type of polymer or polymer blends, as well as the additives present in the composition.

Conventional pigment dispersions of the prior art typically contain one or. more polymeric resins and significant amounts of dispersants and surfactants as additives that remain in the polymeric compositions to which they have been added. As a result, these pigment dispersion additives can adversely effect the physical properties

and performance characteristics of the finished polymer products. Furthermore, it has

been found that the inclusion of the pigment dispersions of the prior art can also have

a negative impact on the processing and processability of the colored polymeric composition as compared to a similar composition to which no pigment dispersion has been added.

In the case of polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene

(FEP) resins and related fluorocarbon polymers, processing must be performed at a relatively high temperature in the range of 800⁰F . Conventional pigment dispersions

of the prior art cannot be used in these high-temperature polymer processing applications due to the occurrence of the thermal degradation of the vehicle resins, additives and/or the pigments themselves, all of which have a deleterious effect on the polymer composition and/or the processing,

It is also well known in the art that the addition and processing of dry pigments in a polymer composition that requires uniform color and color consistency from batch to batch is a difficult, time-consuming and therefore expensive undertaking.

In view of the above limitations and problems associated with the pigment

dispersions and colorants used to tint polymer compositions that are subjected to high

processing temperatures, an improved pigment dispersion that eliminates or reduces these problems would be of great benefit to the art.

It is therefore a primary objective of the present invention to provide a pigment dispersion that is heat stable at the elevated temperatures encountered in processing

polymers and polymer compositions, the addition of which pigment dispersion has little or no adverse effect on the physical properties of the colored plastic or the end

products which are fabricated from the tinted polymer composition. It is another object of the invention to provide in liquid form a pigment dispersion or colorant composition that is easy to measure and dispense and which is readily mixed with the polymer or polymer composition to provide a uniform and reproducible color in the end product.

A specific object of the invention is to provide a pigment dispersion that is resin-free and that contains a minimal quantity of additives to thereby eliminate or reduce the effect of the added pigment dispersion on the physical properties and performance specifications of the polymer or polymer composition to which the pigment dispersion is added.

Yet another object of the invention is to provide a line of liquid pigment dispersions for tinting polymers and polymer compositions that are stable when the

polymer is processed at high temperatures.

Summary of the Invention

The above objects and further advantages are achieved with the liquid pigment dispersion of the present invention that comprises one or more of the following components: a heat-stable pigment or blend of pigments, a hydrocarbon solvent, an

anti-settling agent and a surfactant. The liquid pigment dispersion contains no resin.

As will be understood by those of ordinary skill in the art, the hydrocarbon solvent component serves as a carrier or a coalescent agent for the pigment component. Since the inorganic pigment component is not soluble in the hydrocarbon

compositions(s), the physical mixture is in the nature of a slurry. The term "solvent" or "solvent carrier" is used herein for convenience and as a term of art in the context of describing the invention as it relates to the use of inorganic pigments.

The hydrocarbon solvent component is selected from aliphatic hydrocarbon solvents, mineral oil, mineral spirits, glycol ether, polypropylene glycol monomethyl ether acetate. A particularly preferred solvent is mineral spirits. Mixtures of solvents can also be used. During the high-temperature processing of the polymer compound or blend, all or substantially all of the carrier solvent will be driven out of the

polymer by the heat.

The heat-stable pigments are preferably selected from the class of inorganic pigments that includes metal oxides and metal trans-oxides, and those derived from the transition metals, such as compounds of iron, titanium, zinc, cobalt and chromium. Other inorganic pigments include carbon black, lead chromates and the

so-called natural earth colors, being the families of the siennas, ochers and umbers. Organic pigments that are heat stable at a lower end of the 200⁰F to 800⁰F temperature range can be used selectively for tinting polymer compositions that are to be processed at temperatures that do not exceed the pigments' maximum temperature stability range. The identification and selection of such pigments are within the

capability of those having ordinary skill in the art.

Any of the anti-settling or suspending agents known in the art to be useful in

the preparation of pigment dispersions can be used, so long as it remains stable at the processing temperature of the polymer for which the pigment dispersion is intended

for use. A particularly preferred pigment suspending agent is fumed silica. Alternatively, bentonite compounds and specifically the hydrous magnesium aluminum silicate sold under the trademark BENTONE^® can be used as the anti-settling or suspending agent for the pigments. The amount of anti-settling agent is in the range of 0.5% to 2.5% by weight of the dispersion.

A preferred dispersant or surfactant for use in the pigment dispersion is the class of compounds of hydroxy-functional carboxylic acid esters. The surfactants can be of the anionic, cationic or non-ionic type. The amount of the dispersant/surfactant required in the formulation is relatively small, typically in the range of 1-3.5% by weight, and as little as 0.1% can be used. As will be apparent to one of ordinary skill in the art, the effective amount of the dispersant selected will be based upon the pigment or pigments used in formulating the color dispersion, and that determination is well within the abilities of one having ordinary skill in the art.

The amount of pigment dispersion of the invention that is added to the polymer composition will be determined by the processor in order to achieve the desired color of the end product to be fabricated from the polymer. The pigment dispersions can be added in the range of from 0.1 % to 30%, by weight, and a preferred range is from 1 % to 20%, by weight.

Detailed Description of Preferred Embodiments

The invention will be further described and specific referred embodiments illustrated by the following series of general and specific examples. The pigment dispersions of the invention are formulated from the four components in the ranges set forth below, which ranges are expressed in weight percent: Solvent(s) 30-80

Pigment(s) 10-60

Dispersant 0.1 - 3.5

Anti-settling Agent 0.2 - 3.0

In a preferred embodiment, the following range of components are employed, again expressed in weight percent:

Solvent(s) 50-70

Pigment(s) 20-50

Dispersant 1 - 2

Anti-settling Agent 0.5 - 2.5

The following examples of pigment dispersions compositions are provided in accordance with the present invention and employ from one to three different high- temperature, heat-stable pigments. In each of these examples, the solvent is mineral spirits and the dispersant is a hydroxy-functional carboxylic acid ester.

Example 1:

Solvent 60.75 Dispersant 1.75 Titanium Dioxide 35.00 Fumed Silica 2.50

Example 2:

Solvent 66.88 Dispersant 1.45 Pigment Yellow 53 28.98 Fumed Silica 2.69

Example 3:

Solvent 60.87 Dispersant 1.74 Pigment Green 50 34.78 Fumed Silica 2.61

Example 4:

Solvent 59.77 Dispersant 3.50 Pigment Blue 28 35.00 Fumed Silica 1.73

Example 5:

Solvent 55.00 Dispersant 2.00 Pigment Black 12 40.00 Fumed Silica 3.00

Example 6:

Solvent 60.00 Dispersant 1.75 Pigment Black 12 20.70 Red Iron Oxide 14.19 Pigment Black 7 1.36 Fumed Silica 2.00

Example 7:

Solvent 65.70 Dispersant 2.00 Pigment Brown 24 30.00 Fumed Silica 2.30

Example 8:

Solvent 56.44 Dispersant 1.65 Pigment Green 17 39.51 Fumed Silica 2.40 Example 9:

Solvent 75.00 Dispersant 2.00 Carbon Black 20.00 Fumed Silica 3.00

In the preceding examples, the numbers associated with the pigments refer to the color index, a commonly used industry standard that is well known in the art.

Preparation of the pigment dispersions in accordance with the invention utilizes

conventional processing equipment well known in the art. A variable high-speed disperser of conventional design can be utilized. In the following example, the disperser used was sold under the trademark DISPERMAT by Byk Instrument Company. The method includes the following steps:

1. The solvent and surfactant are added to the mixer and blended at

low speed, e.g., 1500 rpm, for five minutes.

2. The pigment or pigments are added with continuous agitation at the same low speed.

3. The anti-settling agent is then added with continued agitation at the same speed.

4. The four ingredients are then mixed in the disperser at high speed, e.g. , 3000 rpm, for approximately thirty minutes. The resulting pigment dispersions are highly stable products that are non-

settling, or exhibit only a slight tendency to settle and can be returned to a uniform mixture by hand-stirring or with mild agitation using a conventional power mixer. The pigment dispersions of the invention are added to plastics to provide the desired degree of tinting during the mixing and/or blending stages of preparation of

the polymer compositions prior to molding, extrusion, calendaring or other processing to produce the desired end products. The colorant dispersions of the invention are easily handled as pourable liquids and can be precisely metered at the time of the mixing of a resin that is to be tinted. The solvent component of the pigment dispersion evaporates or is driven off at the elevated polymer processing temperature.

The evaporated solvent is preferably recovered to prevent release into the environment

and can be condensed for reuse. Such recovery equipment is well known in the art.

As a result of the relatively small quantities of the residual components making up the pigment dispersion, its presence in the resin formulation has little or no effect on the subsequent processing of the polymer or polymer blends and/or the end

products produced from the tinted resin compositions. The pigment dispersions of the invention provide a particular advantage to the polymer processing industrial user

because no significant changes to processing conditions following addition of the pigment dispersion need be developed and employed to produce the desired tinted polymeric end products.

The pigment dispersions of the invention are useful for tinting polymers that

undergo processing temperatures that range from 200⁰F to 800⁰F. At the high end of the range are fluoropolymers sold under the trademark TEFLON^® and the polyamides, including nylon 6 and nylon 66. Other high-melting temperature thermoplastic polymers include the polyamide group, polycarbonates, polybutylene, terephtalates, polyphenylene oxide, polyphenylene sulfide, sulfone polymers and silicone polymers.

Pigment dispersions produced in accordance with the invention were mixed in

TEFLON^® fluoropolymer (PTFE) powder and processed at 700° F on a calendar to produce uniformly and consistently tinted gasket sheet material. The physical properties of the tinted gaskets met the same performance specifications as the untinted gaskets containing no pigment dispersion component.

As noted above, the pigment dispersions of the invention are stable at

processing temperatures in the range of 200⁰F to 800⁰F. The polymers and polymer compositions to which the pigment dispersions of the invention are added achieve a uniform and reproducible color when processed. Furthermore, the physical properties

of the finished polymer compositions are not degraded by the presence of the pigment

dispersion as evidenced by the favorable comparison of the respective physical

property specifications and performance characteristics with those of the same polymer or polymer compositions to which no pigment dispersion has been added.

While the invention has been described and its preferred embodiments illustrated by reference to specific functional compounds and examples, the full extent

and scope of the protection accorded the invention is not to be so limited, but rather is

to be determined by the claims which follow.

Claims

I claim:

1. A heat-stable liquid pigment dispersion for use in coloring polymers and polymer compositions to provide a uniform and reproducible color in the finished polymer product following processing at temperatures in the range of 200° F to 800⁰F, the pigment dispersion comprising:

a. a solvent; b. one or more heat-stable pigments;

c. a surfactant dispersant; and d. an anti-settling agent.

2. The pigment dispersion of claim 1, wherein the solvent is selected from

the group consisting of mineral spirits, aliphatic hydrocarbon compounds, mineral oil, glycol ether, propylene glycol monomethyl ether acetate, and mixtures thereof.

3. The pigment dispersion of claim 1, wherein the one or more heat-stable

pigments are selected from the class of inorganic pigments.

4. The pigment dispersion of claim 1, wherein the dispersant is selected from the group consisting of hydroxy-functional carboxylic acid esters.

5. The pigment dispersion of claim 1, wherein the anti-settling agent is

selected from the group consisting of fumed silica and hydrous magnesium aluminum silicate.

6. The pigment dispersion of claim 1, wherein the solvent is mineral spirits, the one or more pigments are inorganic pigments, the surfactant dispersant is a hydroxy-functional carboxylic acid ester and the anti-settling agent is fumed silica.

7. The pigment dispersion of claim 2 that contains from 30% to 80% by weight of solvent.

8. The pigment dispersion of claim 3 that contains from 10% to 60% by weight of one or more heat-stable pigments.

9. The pigment dispersion of claim 4 that contains from 0.1 % to 3.5% by

weight of dispersant.

10. The pigment dispersion of claim 5 that contains from 0.2% to 3.0% by weight of anti-settling agent.

11. The pigment dispersion of claim 1 that contains, by weight, from 50%

to 70% of solvent, from 20% to 50% of one or more heat-stable pigments, from 1 % to 2% of dispersant and from 0.5% to 2.5% of anti-settling agent.

12. A method of preparing a heat-stable liquid pigment dispersion for use in coloring polymers and polymer compositions to provide a uniform and reproducible color in the finished polymer product following processing at temperatures in the range of 200°F to 800⁰F, the method comprising: a. mixing a solvent and a surfactant in a variable high-speed disperser at low speed; b. adding one or more heat-stable pigments with continuous

mixing at low speed to the mixture of step (a); c. adding an anti-settling agent with continuous mixing at

low speed to the composition of step (b); and d. mixing the mixture of step (c) at high speed until a uniform, highly stable pigment dispersion is obtained.

13. The method of claim 7, wherein the solvent is selected from the group consisting of mineral spirits, aliphatic hydrocarbon compounds, mineral oil, glycol

ether, propylene glycol monomethyl ether acetate, and mixtures thereof.

14. The method of claim 12, wherein the one or more heat-stable pigments

are selected from the class of inorganic pigments.

15. The method of claim 12, wherein the dispersant is selected from the group consisting of hydroxy-functional carboxylic acid esters.

16. The method of claim 12, wherein the anti-settling agent is selected from the group consisting of fumed silica and hydrous magnesium aluminum silicate.

17. A tinted polymeric composition to which was added the heat-stable pigment dispersion of claim 1 and then subjected to a temperature in the range of 200⁰F to 800°F during treatment by a process selected from the group consisting of molding, extrusion and calendaring.

18. A method of producing a uniformly tinted finished polymeric composition from an untinted precursor of the polymer that includes the steps of: a. blending the untinted polymer precursor with the heat-stable pigment dispersion of claim 1 to form a uniform mixture; and

b. processing the mixture of step (a) at a temperature in the range of 200⁰F to 800⁰F to thereby produce a uniformly tinted

finished polymer product.

19. The method of claim 18, wherein the mixture of step (b) was subjected to a process selected from the group consisting of molding, extrusion and calendaring.

20. The method of claim 18, wherein the polymeric composition is PTFE.