CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority upon US provisional application Serial No. 61/230,122 filed on July 30, 2009; and US provisional application Serial No, 61/260,922 filed on November 13, 2009, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a color concentrate or masterbatch for use in coloring plastics. More particularly, the present invention concerns a thermoplastic color masterbatch or concentrate that contains foaming or blowing agents for use in both coloring and foaming a thermoplastic polymer to which the color concentrate is added.

BACKGROUND OF THE INVENTION

[0003] Thermoplastic polymers are often colored in the molten state by the addition of color concentrates. Color concentrates are highly loaded dispersed colorants in a carrier polymer. Typically, the carrier polymer has either the same chemistry or it is compatible with the polymer to be colored. Color concentrates are generally used to ensure good dispersibility and incorporation of pigments and other additives into the polymer that is being colored. The use of color concentrates can also create a much cleaner environment for an end user who does not want to handle dusty colorants and other hard to handle materials. [0004] There are several methods for adding a color concentrate to a

thermoplastic polymer to be colored, However, the most common method involves a controlled metering of the color concentrate into the throat of a polymer extruder or injection molding machine using pellet feeders. In such applications, the concentrate is supplied in a solid pellet form.

[0005] The use of foaming or blowing agents in polymers is well known in the prior art. Foaming agents are used for a variety of reasons to create voids in the polymer thereby altering the density of the polymer. Materials formed from foamed polymers are used to reduce heat and/or noise transmission, as thermal insulators, and for liquid absorption. Foaming agents can also be used to alter the flow of the polymer during molding operations.

[0006] However, to date, the incorporation of blowing agents, such as

endothermic blowing agents which are typically unstable, into olefinic color concentrates has not been commercially viable. This is believed to be due to endothermic blowing agents tending to activate during production of the concentrate, and thus such agents are not available to perform their function when the

concentrate is added to the polymer that is being colored. For example, during production of a concentrate comprising NaHCCVcitric acid blends, temperatures of 16O ⁰ C are typically reached. And, during production of concentrates containing blends of citric acid/citrate, temperatures as high as 205 ⁰ C to 215°C are often reached. Exposure to such temperatures causes activation of many endothermic blowing agents. In addition, activation of blowing agents may result from mixing. Proper dispersion of the pigments within a polymer to be colored requires intensive mixing. The heat generated by this mixing (shear heating) frequently causes premature activation of the unstable blowing agents. SUMMARY OF THE INVENTION

[0007] The difficulties and drawbacks associated with previous-type systems are overcome in the present compositions and methods for a color masterbatch.

[0008] In one aspect, the present invention provides a color masterbatch comprising at least one pigment and at least one endothermic blowing agent.

[0009] In another aspect, the present invention provides a method of producing a color masterbatch. The method generally comprises providing a carrier polymer, at least one endothermic blowing agent, and at least one pigment. The method also comprises mixing the carrier polymer, blowing agent(s), and pigment(s) in an extruder such that there is no substantial degradation or reaction of the blowing agent to thereby form the color masterbatch.

[0010] As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the description is to be regarded as illustrative and not restrictive.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0011] The present invention provides a color masterbatch or concentrate and a method of incorporating otherwise unstable blowing agents into the masterbatch or concentrate that overcomes the deficiencies noted herein. As used herein, the terms "concentrate" and "masterbatch" are equivalent or interchangeable, and no special meaning is afforded to either term. A masterbatch in accordance with the present invention comprises from about 25% by weight to about 60% by weight of one or more endothermic blowing agents and from about 5% by weight to about 40% by weight of one or more pigments and/or like agents. In addition, the masterbatch may optionally further comprise from about 40% to about 50% of an olefinic carrier resin system. In addition, the masterbatch may also optionally further comprise from about 10% to about 15% of a iow density polyethylene (LDPE) having a relatively low melt flow index (MFI) ₁ such as about 20 g/min.

[0012] Preferably, combination or color masterbatches can be produced using an olefinic carrier resin system based on one or more Fischer Tropsch wax components and polybutene-1 copolymer. For such compositions, the preferred amount of Fischer Tropsch wax is from about 20% to about 25%, and the amount of polybutene-1 copolymer is from about 20% to about 25% based upon the weight of the masterbatch.

[0013] Fischer Tropsch waxes are synthetic waxes produced by a Fischer Tropsch process. Fischer Tropsch is a method for the synthesis of hydrocarbons and other aliphatic compounds from synthesis gas, a mixture of hydrogen and carbon monoxide in the presence of a catalyst.

[0014] Polybutene-1 (also known as polybutylene-1 , poly(i-butene), PB-1 ) is a polyolefin or saturated polymer with the chemical formulation (C ₄ H ₃ )n. It is produced by polymerization of 1-butene using supported Ziegler-Natta catalysts. Polybutene-1 is a high molecular weight, linear, isotactic, and semi-crystalline polymer.

Polybutene-1 combines typical characteristics of conventional poiyolefins with certain properties of technical polymers. Although the olefinic carrier resin system preferably includes one or more Fischer Tropsch wax components and one or more polybutene-1 polymers or copolymers, it will be appreciated that the invention includes the use of functionally similar components.

[0015] It will be appreciated that the exact composition of the masterbatch may vary greatly, depending upon the amount of pigment and blowing agent that is required. Representative preferred compositions for masterbatches made in accordance with the present invention are set forth beiow in Tables 1 and 2. All percentages are percentages by weight based upon the weight of the masterbatch.

Table 1 - Masterbatch Black Polyethylene

Table 2 - Masterbatch Brown Polyethylene

[0016] The preferred embodiment masterbatches can be prepared using a variety of different techniques and processes. However, a preferred strategy for forming the preferred masterbatches is to utilize an extruder and more preferably, an extruder modified as follows. Preferred conditions for production of the masterbatch using an extruder include split feeding of pigments and blowing agent into the extruder. At least two side feeders are preferred. Another preferred condition is application of shear forces only after pigment dosing. Yet, another preferred condition is that after the blowing agent addition, no further mixing takes place in the extruder. This can be accomplished by fitting screws with transport elements only. Although a preferred technique of preparing the preferred masterbatches involves the use of an extruder, it will be appreciated that other processing components could be used. [0017] As previously noted, subjecting relatively unstable endothermic blowing agents to excessively high temperatures can result in premature activation of the agents. In accordance with the invention, the use of particular components in the masterbatch serve to reduce temperature increases that may otherwise result during processing or mixing the masterbatch. Specifically, the addition of up to 25% by weight of the masterbatch of a Fischer Tropsch wax serves to reduce melt viscosity of the resulting masterbatch being prepared to such a level that processing temperatures can be significantly reduced as illustrated below in Table 3 wherein a Berstorf 25 mm, 48LD co-rotating twin screw extruder can be employed:

Table 3 - Reduction in Processing Temperatures in an Extruder

[0018] Although for preferred masterbatches using an olefinic carrier resin system, it is preferred to employ one or more Fischer Tropsch wax components, it will be appreciated that the invention is not limited to such. Thus, instead of using such components, the invention includes the use of other functionally similar components.

[0019] Table 4 is a further illustration of a preferred screw configuration suitable for use in preparing masterbatches in accordance with the present invention.

Table 4 - Preferred Screw Configuration For

Preparing Blowing Agent / Pigment Masterbatch

[0020] Suitable blowing agents for use with the present invention include agents that exhibit endothermic reactions upon activation such as for example sodium bicarbonate, citric acid, derivatives such as salts thereof, and combinations thereof. Preferably, the masterbatch contains less than 60% by weight blowing agents.

[0021] Nearly any type of pigment or combination of pigments can be used in the color masterbatch or concentrate. Nonlimiting examples of such pigments include but are not limited to the inorganic pigments listed in Table 5 and the organic (or biological origin) pigments listed in Table 6.

Table 5 - Inorganic Pigments

Table 6 - Organic and Biological Pigments

[0022] The preferred masterbatch may also optionally include anti-caking agents such as stearates, fatty acids and siiicas. Preferably, such anti-caking agents are present in the masterbatch in an amount of less than 5% by weight. Flow promoters such as silicas and tri-calcium phosphates may also be included in the masterbatch. Preferably, such flow promoters are present in the masterbatch at a concentration of less than 10% by weight of the masterbatch. Free flowing agents such as silicon dioxides and fumed silica may also be included in the masterbatch, preferably at a concentration of less than 2% by weight of the masterbatch.

[0023] It has been discovered that the present masterbatches can not be concentrated much higher than about 60% by weight blowing agent and about 40% by weight pigment, as higher loadings will induce higher shear, thereby causing premature blowing agent decomposition/activation.

[0024] Generally, the preferred masterbatches described herein are used by adding to a processing component as known in the art, during processing of a polymeric composition or polymeric melt to be colored.

Examples

[0025] The following is further illustrative of the production of a preferred black masterbatch using an extruder in accordance with the present invention.

[0026] The following components were pre-blended to form a masterbatch pigment portion:

15 - 25 % Black LDPE masterbatch containing 40% by weight carbon black,

20 - 25 % by weight poiybutene-1 copolymer, and

20 - 25% by weight Fischer Tropsch wax.

[0027] The masterbatch pigment portion blend was then dosed at the extruder hopper.

[0028] A masterbatch blowing agent portion was administered using a second side feeder for administering that portion to the extruder, The blowing agent portion comprised: ■ Encapsulated and modified (decomposition retarded) citric acid derivative,

NaHCθ ₃ and / or encapsulated and modified NaHCθ ₃ , Anti-caking agents such as stearates, fatty acids, and silicas, Flow promoters such as silicas and tricalcalciumphosphates, and Free flowing agents such as silicon dioxides and fumed siiica.

[0029] The screw configuration was configured such that after the second dosing station, no further mixing elements were present after the second dosing.

Accordingly, the blowing agent was blended into the melt at relatively low temperatures as shown below in Table 5.

Table 5 - Preferred Administration of Masterbatch Portions into Extruder

[0030] The masterbatch was prepared without prematurely activating the blowing agent. [0031] Many other benefits will no doubt become apparent from future application and development of this technology.

[0032] All patents, published applications, and articles noted herein are hereby incorporated by reference in their entirety.

[0033] It will be understood that any one or more feature or component of one embodiment described herein can be combined with one or more other features or components of another embodiment. Thus, the present invention includes any and all combinations of components or features of the embodiments described herein.

[0034] As described hereinabove, the present invention solves many problems associated with previously known compositions and methods. However, it will be appreciated that various changes in the details, materials and arrangements of components and/or operations, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the principle and scope of the invention, as expressed in the appended claims.