Liquid color composition with cottonseed oil base

Abstract

A liquid colorant for use in molding or extruding plastic products comprises pigment dispersed in cottonseed oil.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention involves the use of cottonseed oil as the primary ingredient or a secondary ingredient for the liquid carrier when manufacturing liquid color for the plastics industry.

Description of the Prior Art

Plastic products are most often colored.

Color pigments begin in powder form. Because powder is messy and difficult to handle, it is almost always pre-dispersed into some “carrier” that is easier to handle.

Typically color pigment is pre-dispersed into pellets of plastic resin, with the pellets containing typically 50% pigment, by weight. In the United States, these pellets are referred to as “concentrate” and in Europe as “masterbatch”.

DESCRIPTION OF THE INVENTION

A better method to make the pigment easier to handle is to pre-disperse the pigment into a liquid carrier. This is the method to which this invention is directed.

The liquid carrier for the pigment must be compatible with the plastic resin to which it is to be added. Different resins may require different carriers. When selecting a liquid carrier, certain characteristics are desirable while other characteristics must be avoided.

Surfactants, or “soap-like” carriers can cause “slip” in the molding or extrusion process, which must be avoided.

The liquid carrier must not break down at the high temperatures required in the molding or extrusion process that melts the plastic resin.

Carrier liquid that impart an odor to the final part cannot be used when molding or extruding products to be used to contain food, such as plastic water bottles.

Cost and availability of the carrier liquid are always factors.

Heretofore, no single liquid carrier solves all these problems. However this invention is based on the discovery that cottonseed oil is superior to many other carriers in meeting a number of these requirements and solving many or the problems. Cottonseed oil has not previously been used as a carrier for pigment in making liquid color to be used in plastics molding or extrusion.

Cottonseed oil has a relatively high flash point, and a high smoke point, well above 400° F. Most other liquid carriers smoke below 400° F.

Cottonseed oil has very little odor. Cottonseed oil is known to be used as a cooking oil that does not impart any flavor to the food being cooked. This is a benefit when molding or extruding plastic products used for food packaging.

Cottonseed oil is high in antioxidants, providing an advantage in preserving products packaged in plastic that has been molded or extruded using a cottonseed oil carrier for the liquid color that provides color for the product packaging.

Cottonseed oil is high in vitamin “E”, an antioxidant, which is often required as an additive when using other carriers.

Cottonseed oil is available in bulk qualities, and is competitively priced.

In one of its aspects, this invention provides a method of fabricating a plastic article of pre-selected color where the method includes preparing a blend, where the blend comprises solid plastic resin pellets and liquid color of a hue and in an amount to impart the pre-selected color to the article to be fabricated, where the liquid color includes cottonseed oil, and thereafter forming the blend under pressure and heat into the plastic article. The method may be accomplished either by injection molding or by extrusion. In practice of this aspect of the invention, the liquid color preferably comprises at least one dispersion of a single pigment in cottonseed oil. Even more preferably, the liquid color may comprise a plurality of dispersions each of a single pigment in cottonseed oil.

The method may further include the liquid color comprising at least one additive to facilitate fabrication of the plastic article, where the additive may be selected from the group comprising lubricants, blowing agents, light stabilizers, nucleating agents, antistatic agents and antioxidants.

In another aspect of this invention, the invention provides a liquid colorant for use in molding or extruding plastic products where the colorant comprises pigment dispersed in cottonseed oil. In a more limited aspect of the invention, the invention provides a liquid colorant for use in molding or extruding plastic products consisting of only pigment and cottonseed oil.

In still another aspect, this invention provides a liquid colorant for use in molding or extruding plastic products where the colorant includes pigment, cottonseed oil, and at least one additive, with the additive desirably being dispersed together with the pigment in the cottonseed oil. In this aspect of the invention, the additive may be one or more lubricants, blowing agents, light stabilizers, nucleating agents, antistatic agents, and antioxidants.

In the preferred practice of this invention, a single pigment dispersion is prepared initially by dispersing pigment of a desired color in cottonseed oil to create a liquid blend. The pigment is initially introduced into a vat of cottonseed oil which acts as a liquid carrier. The pigment is stirred into the cottonseed oil. The pigment is added to the cottonseed oil in the known correct proportion. Typically the batch of pigment added to the cottonseed oil is from 50% to 70% by weight of the resulting pigment-cottonseed oil blend. That is the preferred range; the range can be as low as 25% by weight of pigment relative to the weight of the resulting pigment-cottonseed oil blend up to 80% by weight of pigment to the weight of the resulting pigment-cottonseed oil blend.

In general, it is desirable to put as much pigment into the cottonseed oil as is possible.

Next the dispersion of the pigment in the cottonseed oil is milled by passing the liquid through a mill that serves to break down any agglomerates of pigment that may remain in the single pigment dispersion, thereby reducing the particle size of the pigment to as small a size as possible. The resulting particles of pigment powder are very, very small, which produces the fullest, richest color. Milling the single pigment dispersion allows the use of less pigment to perform the particular coloring function thereby reducing costs. The milling may be done using a roller mill or a sand mill. Both roller mills and sand mills are common industrial mills.

In the practice of the invention, it is desirable at times to produce a color that is not one of the colors of the basic pigment. In such case, two or more single pigment dispersions, each dispersion being of a single pigment in cottonseed oil, are prepared. The two or more single pigment dispersions are then blended together to produce a resulting dispersion exhibiting the correct hue or shade of color as desired. The resulting dispersion is then milled. This two-step process allows milling of a larger quantity of pigment in the resulting dispersion at one time so that clean up between milling different colors is less frequent and avoids the expense of milling of each of the single pigment dispersions separately.

Use of cottonseed oil as the carrier for the single pigment dispersion or the blend of single pigment dispersion results in liquid color that is compatible with nearly all resins that are currently used in plastic molding and extrusion. The cottonseed oil-based pigment dispersion does not leach out of any finished product, nor does the cottonseed oil by itself leach out of any finished product. The cottonseed oil has been found to hold the pigment powder particles in suspension very well and accepts a high loading of pigment.

The pigment-cottonseed oil liquid colorant in accordance with the invention may be used to color most commercially used thermoplastics, whether processed by means of extrusion, injection molding or blow molding, as well as thermoplastics that are processed using less conventional processes. When properly formulated, the pigment-cottonseed oil liquid color according to the invention is not just compatible with a base resin, but frequently improves the fabricating process and/or the performance properties of the fabricated plastic parts.

Liquid color according to this invention may be formulated in various ways to provide various advantageous product characteristics. For example, commodity colorants may be formulated in accordance with the invention to maximize savings without sacrificing processability and cosmetic appearance of the final plastic parts. Such commodity colorants offer the processor economics of color and are suitable for mass manufacture of volume parts such as housewares, disposable goods, toys and the like.

The invention also has applicability to providing liquid color for use in fabricating articles designed for outdoor use, specifically for lawn and garden applications, for the toy and recreation industries. The liquid color in accordance with the invention may be formulated to meet very stringent requirements of heat stability and light fastness of the resulting fabricated color parts. Such parts may be used in applications requiring extended exposure to sunlight and/or unusually high temperatures during the fabrication process.

The liquid color according to the invention may be produced to provide special effects such as fluorescent, phosphorescent, pearlescent, and non-dispersing finishes, where such unconventional appearances dictated by the design of the parts.

Liquid color in accordance with the invention is typically from 20% to 40% cheaper than use of pelletized color concentrate.

In another method for practicing the invention, one may make liquid color for use in the course of molding or extruding plastic parts by initially providing a collection of pigments. Next, one selects a formula for the pigment(s) and liquid carrier that will provide liquid color in a desired hue for coloring plastic parts being molded or extruded. Selecting the formula may be a “trial and error” process, in that slight changes in hue as required by a customer require changes in the pigment constituency, thereby requiring experimentation as to the exact formula of pigments required to produce the required hue. Once the formula has been established for the amount of pigment(s) and the amount of liquid carrier, the pigments are selected in amounts required by the formula by the collection of pigments. A liquid carrier of cottonseed oil is provided in an amount according to the formula and the selected pigments are then blended, preferably but not necessarily all at once, into the cottonseed oil to produce a required liquid color. When this approach is used, the finished liquid color is generally not milled, as the mill would have to be cleaned after every color blend. However, such liquid color can be milled if necessary. This method of the invention avoids the two-step process of making the single pigment dispersions, milling single pigment dispersions individually, and then combining the single pigment dispersions to produce the required liquid color.

The processing of thermoplastic resin and/or the performance of the fabricated plastic parts can often be greatly enhanced through use of additives. Many commercial resins already include additives. However, significant benefits can be derived from further modification of such compounds in many cases. Moreover, use of additives affords a plastics processor the opportunity to tailor the plastic resin material to a specific application.

Processing aid-type additives improve productivity of the molding or extrusion machinery through reduction of internal friction; these additives are referred to as “lubricants.” Other processing aid-type additives change polymer morphology and are referred to as “nucleating agents.” Still other processing aid-type additives remove excessive heat and are in the form of endothermic blowing agents. Yet additional processing aid-type additives suppress thermal decomposition during processing and are generally referred to as “antioxidants.”

Other additives, such as blowing agents and optical brighteners, enhance aesthetics and/or performance properties of the final parts by, for example, providing antistatic properties or ultraviolent light stabilization characteristics to the product.

Modification of properties of thermopolymers through the addition of various chemical additives is economically preferable to the introduction of an entirely new resin. The most economical way to add these additives to the molding or extrusion process is through the use of liquid color in accordance with this invention.

As used in the claims below, “comprising” means “including” while “consisting of” means “having only”, and “consisting essentially of” means having the stated constituents plus trivial amounts of other reagents which do not materially affect the properties of the claimed product.

Claims

1. A method of fabricating a plastic article of preselected color, comprising: a. preparing a blend comprising solid plastic resin pellets and liquid color of a hue and in an amount to impart the preselected color to the article to be fabricated;b. the liquid color comprising cottonseed oil;c. forming the blend under pressure and heat into the plastic article; wherein the liquid color comprises at least one additive to facilitate fabrication of the plastic article and the additive is selected from the group comprising lubricants, blowing agents, light stabilizers, nucleating agents, antistatic agents, and antioxidants.