Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-08-31
2001-09-04
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06284814
ABSTRACT:
FIELD OF THE INVENTION
A method for introducing relatively large quantities of liquid additives into polymer-containing compositions can be used to provide a masterbatch composition suitable for use in a variety of polymer-containing compositions. For example, the masterbatch compositions can be used in molded resin articles, nonwoven fabrics and paints. The masterbatches find particular usefulness as a method for introducing biocides and antimicrobials into these compositions.
BACKGROUND OF THE INVENTION
Over the years, polymers have been widely used in both household and industrial applications. For example, the surface appearance, physical and mechanical properties of polystyrene resins have made them popular in a variety of fields including electronics, automobiles, as well as sundry and sanitary items. Similarly, polyolefins such as polyethylene and polypropylene, have been widely used in extrusion and injection molding applications.
The art has long sought to introduce additives, both liquid and solid, into polymers. To this end, masterbatches, e.g., solid dyes and pigments in a polymer matrix, have been used to introduce solid additives, e.g., a desired color, into a polymer.
Alternatively, liquid active ingredients have been introduced into the polymer compositions in order to provide or enhance a desired property of polymer compositions. Examples of “active” liquid agents include bactericides, perfumes, insectifuges, rust preventatives, mildew-proofing agents, and antimicrobials, among others.
One particularly significant problem faced in producing extruded or molded articles from resin materials has involved bacterial and microbiological fouling. This problem can be particularly pronounced since resins are often used in high moisture and humidity environments that serve as excellent breeding grounds for unwanted microorganisms such as bacteria, mold, fungi and mildew.
In an attempt to address this problem, a variety of processes have been developed each of which seek to introduce an antimicrobial or biocide agent into a molded resin article. In this regard, it has been proposed to mix the desired agent into the synthetic resins material prior to formation of the molded articles. Alternatively, processes have involved introducing the agent during or subsequent to formation of the articles. Examples of such process include applying the desired active agents onto the surface of the synthetic resin product, injecting the agent into a “space” within a formed resin product or laminating the agent between layers or sheets of the resin(s).
Specific techniques for introducing antimicrobial agents and/or biocides into polymer resins have been disclosed in U.S. Pat. No. 3,531,433, to Elmer, U.S. Pat. No. 3,987,007, to Kalogris, U.S. Pat. No. 4,725,657 to Shibanai, U.S. Pat. No. 4,938,955 to Niira et al., U.S. Pat. No. 5,205,016 to Ohmae et al., U.S. Pat. No. 5,358,979 to van Hoboken et al., U.S. Pat. No. 5, 482,989 to Koskiniemi, U.S. Pat. No. 5,516,814 to Trotoir, and U.S. Pat. No. 5,614,568 to Mawatari et al.
These techniques, however, have suffered from a variety of disadvantages. For example, attempts to introduce the active agents into the resins themselves have been faced with problems such as poor heat stability, toxicity, and a short life. Thus, these techniques have not proven entirely effective in providing a polymer product having the desired antimicrobial effect.
Moreover, these techniques are often severely limited in terms of the types and amounts of antimicrobial agents that may be introduced into the resin. For example, conventional processes using extruders to mix a polymer with an additive are significantly limited in terms of the polymers and additives that can be used. That is, where melting point for a resin is greater than the boiling point for a liquid additive, the components are said to be incompatible because the temperatures needed in the extruder would prevent the additive from becoming mixed with the resin.
One solution to this problem has involved the modification of the extruder so as to introduce certain additives immediately preceding the point where the polymer exits the extruder. While this arrangement has only worked for certain lower boiling point additives, it is also extremely limited in terms of the amounts of additive that may be introduced into the polymer. Moreover, it requires the use of very specialized equipment that increases production costs.
Even in those situations where the polymer and additive may be “compatible”, the amount of additive is typically limited to 5 weight percent or less, although as much as 10 weight percent has been suggested under certain limited conditions.
Recent attempts to increase the amount of the liquid additive have focused on the use of carriers, e.g., plasticizers such as those disclosed in U.S. Pat. No. 5,358,979, for the active agent, in this case, microbiocides. However, such carriers have introduced their own set of problems regarding the use and handling of the resulting masterbatch.
Accordingly, the need still exists for a method which is capable of providing increased amounts of liquid active component in a polymer without the need for carrier materials.
SUMMARY OF THE INVENTION
Among other factors the present invention is based on the surprising discovery that the suitable relaxation of a polymer can allow for the introduction of relatively large amounts of liquid additives without the need to employ a carrier material. This method makes possible the manufacture of a masterbatch that is easy to store, use and transport, and that can be used in a variety of polymer-containing compositions.
In one preferred aspect, the present invention relates to a method for making a masterbatch composition containing a polymer and one or more active agents present in an amount not less than 10% by weight of the composition. Moreover, the masterbatch is preferably at least substantially free of any carrier component for the active agent. This method preferably comprises the steps of:
(1) increasing the free volume between the chains of one or more polymers by, e.g., relaxing the desired polymer(s);
(2) introducing one or more liquid additives into the polymer(s) under conditions effective to provide a homogeneous mixture of the polymer(s) and the additive(s); and
(3) providing a sufficient residence time for the mixture, with optional gentle mixing, to allow the additive to enter the voids in the polymer(s).
Typically, step (1) involves melting of the polymer(s) while step (2) involves mixing of the polymer(s) and additive(s). In addition, Steps (2) and (3) can be repeated at least once, and preferable two or more times, depending on the nature of the polymer and the additive as well as the quantity of additive which is desired.
A preferred device for practicing this method is a twin screw extruder, and in particular, an extruder which employs a sequence of kneading (dispersive mixing) elements as well as turbine (or distributive mixing) elements in connection with step (2).
This method can be employed with a wide variety of polymers, active agents that, at ambient temperatures, are in either liquid or solid form. One example of a masterbatch produced by the inventive process comprises, as the polymer, a polyolefin, e.g., polyethylene, polypropylene, or copolymers thereof a polystyrene or a polyester and, as the active agent, an antimicrobial agent that is at least substantially free of heavy metals, arsenic, halogens, phenyls and formaldehydes, such as INTERSEPT® microbial agent.
Moreover, one or more non-carrier additives can be introduced into the polymer, prior to (2), in order to modify the melting point of the polymer mixture. This will increase the capability of the polymer(s) and allow for a more widely varied group of additives.
Other aspects of this invention include masterbatch compositions themselves as well as polymer-containing compositions produced from these masterbatch compositions.
REFERENCES:
patent: 3531433 (1970-09-01), Elmer
patent: 3942773 (1976-03-01), Csonger
patent: 3976608 (1976-
Alston & Bird LLP
Michl Paul R.
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