Patent Application
20230390976
The invention relates to the technical field of extrusion blow molding of plastic products. In particular, it relates to a master batch composition for a weight-reduced plastic product produced by blow molding.
Foamed plastic is usually prepared by extrusion foaming, foam injection molding, or bead foaming. The polymer resin is fed into an extruder or molding machine and undergoes a series of reactions to form the final product. When manufacturing foamed plastic products, uneven pores distribution can easily lead to flaws in the final plastic products, for example big pores and uneven thickness. These defects may result in lower mechanical strength and unappealing visual defects.
When additives, such as foaming agents, are added to the feeding mixture which includes the polymer resin, a different particle size is also introduced between the feeding mixture and agents. The additives usually come in the form of a powder. The broad size difference between the powder particles and the particles in the feeding mixture further increases the likelihood of defects in the final products. There is a need to provide a feeding mixture with a uniform particle size.
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some further embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the above-mentioned problems of the need of even particle size distribution in a master batch composition for a plastic product.
Accordingly, one aspect of the present invention provides a master batch composition for a weight-reduced plastic product includes a carrier resin, a core-shell foaming agent, and at least one lubricant. The core-shell foaming agent includes at least one outer polymeric shell and at least one inner foaming agent core. The outer polymeric shell encapsulates the inner foaming agent core. The inner foaming agent core includes alkane. The master batch composition is configured to be integrated into the weight-reduced plastic product by extrusion blow molding with a base plastic resin to create a foamed plastic having a foaming pore size from 10 to 80 μm.
In a further embodiment of the present invention, the carrier resin includes thermoplastic polymers and their blends which have a melting temperature in a range between 50 and 160° C.
In a further embodiment of the present invention, the thermoplastic polymers and their blends comprise one or more polyethylene (PE) and Ethylene Vinyl Acetate (EVA).
In a further embodiment of the present invention, polyethylene comprises one or more linear low-density polyethylene, low-density polyethylene, and high-density polyethylene.
In a further embodiment of the present invention, the content of carrier resin ranges between 40 and 90 wt %.
In a further embodiment of the present invention, the outer polymeric shell is selected from poly lactic acid (PLA), poly(lactic-co-glycolic acid)(PLGA), polystyrene (PS), poly methacrylate (PMA), poly methyl Methacrylate (PMMA), or polymers comprising one or more monomers of acrylonitrile, methacrylonitrile, 3-butene nitrile, methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, methyl ethyl acrylate, glycidyl methacrylate, or any combination thereof, and the inner foaming agent core is selected from pentane, butane, n-hexane, n-heptane, isooctane or any combination thereof.
In a further embodiment of the present invention, the thickness of the outer polymeric shell is approximately between 0.5 and 2 μm.
In a further embodiment of the present invention, the content of core-shell foaming agent ranges between 10 and 50 wt %.
In a further embodiment of the present invention, the content of lubricant ranges between 1 and 30 wt %.
In a further embodiment of the present invention, at least one lubricant includes one or more lubricant selected from paraffin oil, paraffin wax, stearic acid and their blends.
In a further embodiment of the present invention, the weight-reduced plastic product has a master batch composition ranging between 1 and 10 wt %.
In a further embodiment of the present invention, the base plastic resin includes one or more polyethylene and polypropylene.
Another aspect of the present invention provides a method of preparing a master batch composition for weight-reduced plastic includes mixing a master batch composition to form a melt mixture in an internal mixer at a first temperature ranging between 50 and 160° C. The master batch composition includes a carrier resin, a core-shell foaming agent, and at least one lubricant. The core-shell foaming agent includes at least one outer polymeric shell and at least one inner foaming agent core. The outer polymeric shell encapsulates the inner foaming agent core. The inner foaming agent core includes alkane. Then the melt mixture is single-screw extruded and pelletized at a second temperature ranging between 50 and 160° C. to form pellets.
In a further embodiment of the present invention, the master batch composition includes 40 to 90 wt % of the carrier resin, 10 to 50 wt % of the core-shell foaming agent, and 1 to 30 wt % of at least one lubricant.
In a further embodiment of the present invention, the method further includes mixing the master batch composition in a form of pellets with a base plastic resin to form a molding mixture in an internal mixer. Next, the molding mixture is single-screw extruded at a temperature ranging between 180 and 220° C. to form a product preform. Followed by the single-screw extruding, the product preform is blow molded to form a plastic product.
In a further embodiment of the present invention, the single-screw extruding includes a die temperature ranging between 170 and 230° C., a screw rotation speed ranging between 15 and 17 Hz, and a blow pressure ranging between 0.25 and 0.6 Mpa.
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise, in which:
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
The present invention provides a method of preparing a master batch composition for weight-reduced plastic. Turning to
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Referring back to
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In step 220, the molding mixture undergoes single-screw extrusion at a temperature ranging between 180 and 220° C. to form a product preform. Turning to
An air supply system 520 is connected to the die head 530, and its pipe goes through the die head 530. A blow pin 522 at the end of the pipe of the air supply system 520 has the same outlet as the die head 530. The air supply system also has a valve 510 that is capable of controlling the flow of the air.
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Table 1 shows foamed plastic with different compositions and their properties. In this example, foamed bottles are made without commercial foaming agent in B0 (control sample), with commercial foaming agent 1 (CFA 1) in B1 and commercial foaming agent 2 (CFA 2) in B2. In B3, the master batch composition which includes the core-shell foaming agent (CoreFA) is used. PE in Table 1 indicates polyethylene. In each bottle sample, if foaming agent is used, the foaming agent/master batch composition is approximately 3%, and no more than 3%, in the final foamed bottles. In Table 1, the ‘Weight Reduction’ column, B3, which uses the core-shell foaming agent, shows 17.5% weight reduction and a similar thickness as B0, which has 100% polyethylene. Although B1 shows similar weight reduction (17%) like B3 in comparison with B0, its thickness is more than one third (⅓) less than B0. B2 shows the most weight reduction of 20%. B2 has a thickness which is about one third (⅓) less than B0. However, B2 is prone to burst in its final form. The foamed plastic film of B2 also shows a distorted, wrinkled appearance. The results are calculated from a sample number of 3.
Table 2 shows foamed plastic bottles formed under different condition of blow molding. B0 is the control sample with 100% PE, B4 has 2.5% master batch composition (MBC), B5 and B6 have 3% master batch composition respectively. The blow molding conditions for each sample are also listed in Table 2. The temperature of the single-screw extruder is indicated as SSE. The temperature of the die head is indicated as Die. In this example, the screw rotation speed is maintained at 16.8 Hz, the period of time of blowing is 13 seconds, and the blow pressure is 0.3 Mpa. In this example, the addition of the core-shell foaming agent ensures weight reduction and a desirable thickness of the final foamed plastic bottle. By slightly increasing the temperature at the die head from 186 to 190° C., the weight is further reduced.
Table 3 shows a chart including 10 repeated cycles of manufacturing the sample bottles discussed in Table 2. Table 3 shows that the quality of the foamed plastic bottle using the master batch composition is consistent, and the goal of weight reduction can be achieved by adding the master batch composition.
The mechanical strength of the foamed plastic bottle formed with the master batch composition of the present invention is tested and shown in Table 4. B0 is the control sample made without the addition of the master batch composition but PE alone. According to Table 4, the mechanical strength (e.g., tensile) retention is greater than 85% in general. That is, the addition of the master batch composition in the foamed plastic bottle can reduce the product weight and at the same time retain similar thickness and at least 85% (in comparison with the control sample) of mechanical strength.
The pore size of the foamed plastic bottle is further investigated under SEM imaging and shown in Table 5. Referring back to
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The pore size of the foamed plastic bottle is further investigated under SEM imaging and shown in Table 6. Referring back to
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In general, when the master batch composition of the present invention is used, the foamed plastic product has lower weight compared to plastic products without the master batch composition. The weight-reduced plastic product maintains a smooth surface and small and even pore size smaller than 100 μm. The mechanical strength of the foamed plastic product retains at least 85% of a conventional PE plastic product without foaming agent. The weight-reduced plastic product can satisfy the existing food container standards. By the addition of the master batch composition for approximately 2 to 3% to the base resin, a significant weight reduction is observed with a similar durability.
As used herein, terms “approximately”, “basically”, “substantially”, and “about” are used for describing and explaining a small variation. When being used in combination with an event or circumstance, the term may refer to a case in which the event or circumstance occurs precisely, and a case in which the event or circumstance occurs approximately. As used herein with respect to a given value or range, the term “about” generally means in the range of ±10%, ±5%, ±1%, or ±0.5% of the given value or range. The range may be indicated herein as from one endpoint to another endpoint or between two endpoints. Unless otherwise specified, all the ranges disclosed in the present disclosure include endpoints. The term “substantially coplanar” may refer to two surfaces within a few micrometers (μm) positioned along the same plane, for example, within 10 within 5 within 1 or within 0.5 μm located along the same plane. When reference is made to “substantially” the same numerical value or characteristic, the term may refer to a value within ±10%, ±5%, ±1%, or ±0.5% of the average of the values.
