Injection Molding and Molding Compositions Therefore

Abstract

A method of combining rubbers and plastics when injection molding, and compositions usable in injection molding, are shown and described. Comminuted rubber from waste tires and waste plastics including any of high density polyethylene, polyethylene terephthalate, and polypropylene are combined and heated to melt at least the plastics. In one optional approach, both are melted. Plastics comprise from twenty to eighty percent by weight of the mixture, with rubber accounting for the balance. The mixture may be fortified with bonding, compatibilizing, and strengthening agents. The compositions may be cooled and pelletized for immediate use in injection operations.

Claims

1. An injection molding product resulting from the following steps: comminuting waste rubber into solid particles of dimensions sufficiently small to pass through an injection nozzle; melting plastic comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene; once the plastic is melted, adding the comminuted solid waste rubber to the melted plastic, thereby minimizing the time that the waste rubber is exposed to high temperatures and generation of volatile organic compounds; blending the comminuted waste rubber with the melted plastic; maintaining temperatures greater than a maximum melting point temperature of the plastic, whereby the waste rubber remains in a solid state; and injecting the blended solid waste rubber and the melted plastic into an injection mold, wherein the resulting molded product is a homogeneous mixture of the plastic and the waste rubber, and wherein the time that the waste rubber is exposed to high temperatures and the generation of volatile organic compounds is minimized.

2. The injection molding product of claim 1, further comprising the step of limiting a proportion of the constituent injection material to waste rubber in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being the plastic.

3. The injection molding product of claim 1, wherein the step of blending the comminuted waste rubber with the melted plastic, further comprises the step of blending in less than 2% Type F fly ash.

4. The injection molding product of claim 3, wherein Type F fly ash has an average diameter between 100 and 200 μm.

5. The injection molding product of claim 4, wherein the fly ash meets ASTM standard C618.

6. The injection molding product of claim 1, wherein the waste rubber comprises wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber.

7. The injection molding product of claim 1, wherein the plastic is waste plastic from discarded consumer articles.

8. A composition for a pellet of a constituent injection material comprising rubber particles and a plastic matrix material, the composition comprising: waste rubber particles; and plastic comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene, wherein the waste rubber particles and the plastic have been melted and blended, cooled, and formed into pellets.

9. The composition of claim 8, wherein a proportion of waste rubber in the constituent injection material is in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being the plastic.

10. The composition of claim 8, further comprising blending a bonding agent, a compatibilizing agent, and a strengthening agent with the constituent injection material.

11. The composition of claim 10, wherein the strengthening agent comprises majority fly ash, wherein the fly ash is type F fly ash meeting ASTM standard C618.

12. The composition of claim 8, wherein the waste rubber comprises wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber, and the plastic is waste plastic obtained from discarded consumer articles, and is comminuted.

13. A composition for a pellet of a constituent injection material comprising waste rubber particles and waste plastic matrix material, the composition comprising: waste rubber particles; and plastic comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene, wherein the waste rubber is blended with and encapsulated within the plastic, wherein the plastic has been melted prior to adding the waste rubber particles in order to minimize the time that the waste rubber is exposed to high temperatures and the generation of volatile organic compounds, and in order for the melted plastic to blend with and encapsulate the waste rubber particles, cooled, and formed into pellets, wherein the resulting pellets are a homogeneous mixture of the plastic and the waste rubber, and wherein the time that the waste rubber is exposed to high temperatures and the generation of volatile organic compounds is minimized.

14. The composition of claim 13, wherein melting temperatures have been maintained above a maximum melting point temperature of the plastic, whereby the waste rubber remains within the waste plastic as discrete particles encapsulated in a plastic matrix material.

15. The composition of claim 13, wherein a proportion of waste rubber within the constituent injection material is in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being the waste plastic.

16. The composition of claim 14, further comprising less than 2% Type F fly ash.

17. The composition of claim 16, wherein the Type F fly ash has an average diameter between 100 and 200 μm.

18. The composition of claim 13, wherein the waste rubber comprises wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber, and the plastic is waste plastic obtained from discarded consumer articles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Various objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:

[0021] FIG. 1 is a block diagram showing steps of a method of injection molding, the steps shown in abbreviated form;

[0022] FIG. 2 is an exploded schematic rendition of materials and apparatus used in injection molding, according to at least one aspect of the invention;

[0023] FIG. 3 is a schematic cross sectional view of one type of pellet, according to at least a further aspect of the invention; and

[0024] FIG. 4 is a schematic cross sectional view of another type of pellet, according to still another aspect of the invention.

DETAILED DESCRIPTION

[0025] FIG. 1 shows steps of a method 100 of injection molding. FIG. 2 shows materials and apparatus used in method 100 and to produce pelletized injection material. Steps of method 100 use 100-series reference numerals, and are shown in abbreviated form in FIG. 1. Apparatus and materials use 200-series reference numerals and are shown in FIG. 2. According to at least one aspect of the invention, there is shown a method 100 of injection molding, using an injection nozzle 200 (FIG. 2) having an orifice transverse dimension 202, and using a constituent injection material comprising rubber particles 204 and a plastic matrix material made from waste plastic 208. Method 100 may comprise a step 102 of comminuting waste rubber 204 having a melting point temperature into particles of dimensions sufficiently small to pass through injection nozzle 200, a step 104 of melting waste plastic 208 comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene, a step 106 of blending waste plastic 208 (after blending, waste plastic matrix material 208) with the comminuted waste rubber 204, a step 108 of maintaining temperatures greater than a maximum melting point temperature of waste plastic 208 and lower than the minimum melting point temperature of waste rubber 204. Thus waste rubber 204 remains in a solid state. Method 100 includes a step 110 of injecting blended waste rubber 204 and melted waste plastic 208 into an injection mold 210. Molding apparatus includes injection nozzle 200 and a heater 212 to melt waste plastic 208 or to maintain waste plastic 208 in a melted condition.

[0026] Method 100 may further comprise a step 112 of limiting a proportion of the constituent injection material to waste rubber 204 in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being waste plastic 208.

[0027] It will be appreciated that constituent materials including at least waste rubber particles 204, waste plastic 208, bonding agent 214, compatibilitizing agent 216, and strengthening agent 218 are initially received in a processor 206 to prepare a functional injectable mixture for injection into injection mold 210. Apparatus for handling the functional injectable mixture and its precursors may be conventional, and therefore will not be described in greater detail. This apparatus is shown in schematic form only in the Drawing Figs.

[0028] Preferably, the constituent injection material includes certain additives to improve performance. Method 100 may further comprise a step 114 of blending a bonding agent 214, a compatibilizing agent 216, and a strengthening agent 218 with the constituent injection material. Step 114 may be modified such that strengthening agent comprises majority fly ash. More particularly, step 114 may be modified such that the fly ash is type F fly ash meeting ASTM standard C618 (mainly consisted of SiO.sub.2 (51.4%), Al.sub.2O.sub.3 (22.4%), and Fe.sub.2O.sub.3 (10.86%), with a total percentage over 70%).

[0029] Step 102 of comminuting waste rubber may be modified such that waste rubber 204 comprises wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber.

[0030] Method 100 may further comprise a step 116 of obtaining waste plastic 208 from discarded consumer articles (not shown), and comminuting the discarded consumer articles.

[0031] The invention may also be thought of as a composition for providing pellets of constituent injection material fabricated from recycled products, the pellets being immediately usable in injection molding apparatus. Two generally similar compositions are proposed, noting that there exists a difference between the two.

[0032] Conventional pellet forming apparatus may be employed to heat and mix ingredients, and to extrude, cool, and pelletize the mixed ingredients. This conventional pellet forming apparatus is not shown. Resultant pellets are shown in FIGS. 3 (showing pellets according to a first option) and 4 (showing pellets according to a second option).

[0033] In the first option, a composition for a pellet 220 of a constituent injection material comprises rubber particles 204 and a plastic matrix material 208. The composition comprises waste rubber particles 204 and waste plastic 208 comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene, wherein waste rubber particles 204 and waste plastic 208 have been melted and blended, cooled, and formed into pellets 220.

[0034] In the first option, a proportion of waste rubber 204 in the constituent injection material is in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being waste plastic 208.

[0035] In the first option, the composition may further comprise bonding agent 214, compatibilizing agent 216, and strengthening agent 218 with the constituent injection material. Strengthening agent 218 may comprise majority fly ash, wherein the fly ash is type F fly ash meeting American Society for Testing and Materials (ASTM) standard C618.

[0036] Bonding agents and compatibilizing agents are known in the art of combining rubbers and plastics. Hence any known such agents may be employed. Known strengthening agents could be employed. Known strengthening agents may include ZnO, TiO.sub.2, and CaO. However, it is preferred to use fly ash to provide ceramics (e.g., metal oxides), which ceramics may include silica (Si0.sub.2), alumina (Al.sub.2O.sub.3), and iron (III) oxide Fe.sub.2O.sub.3).

[0037] In the first option, waste rubber 204 may comprise wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber. Waste plastic 218 may be obtained from discarded consumer articles, and is comminuted.

[0038] In the first option, waste rubber 204 and waste plastic 208 are both melted and blended to the point that the constituent injection material, apart from additives, is homogeneous. In the second option, waste rubber 204 is not melted. In the final pelletized product, discrete particles of waste rubber will be discernible and although entrained within waste plastic matrix material 208, remain apart therefrom.

[0039] To this end, in the second option, a composition for a pellet 222 of a constituent injection material comprising rubber particles 204 and plastic matrix material 208 may comprise waste rubber particles 204 having a melting point temperature, and waste plastic 208 comprising at least one of high density polyethylene, polyethylene terephthalate, and polypropylene. Waste rubber 204 is blended with and encapsulated within waste plastic 208. Waste plastic 208 has been melted to blend with and encapsulate waste rubber particles 204, cooled, and formed into pellets 222.

[0040] In the composition producing pellets 222, melting temperatures have been maintained above a maximum melting point temperature of waste plastic 208 and below the melting point temperature of waste rubber particles 204. Waste rubber 204 remains within waste plastic 208 as discrete particles encapsulated in plastic matrix material 208.

[0041] In the composition producing pellets 222, a proportion of waste rubber 204 within the constituent injection material is in a range of twenty to eighty percent by weight, with a remainder of the constituent injection material being waste plastic 208.

[0042] The composition producing pellets 222 may further comprise a bonding agent, a compatibilizing agent, and a strengthening agent with the constituent injection material. The same agents used to produce pellets 220 may be employed to produce pellets 222.

[0043] In the composition producing pellets 222, the strengthening agent may comprise majority fly ash, wherein the fly ash is type F fly ash meeting ASTM standard C618.

[0044] In the composition producing pellets 222, waste rubber 204 may comprise wheeled transport vehicle tire waste and ethylene propylene terpolymer rubber, and waste plastic 208 may be obtained from discarded consumer articles, and is comminuted.

[0045] Formulations which have been practiced are shown in tables 1 and 2 below.

TABLE-US-00001 TABLE 1 Exemplary Formulation Scrap—(ground or pulverized rubber tire buffings), 46% or (comminuted black ethylene propylene diene monomer rubber, a synthetic M-Class rubber via sulfur vulcanization under ASTM standard D-1418) Scrap—(ground black or colored high-density poly- 46% ethylene (HDPE/PEAD), a thermoplastic chemical formula generalized as (C.sub.2H.sub.4)n), or (ground black or colored low-density polyiethylene (LDPE/PEBD), a thermoplastic made from monomer ethylene (C.sub.2H.sub.4). Silicon dioxide  2% Cinnamic acid (C.sub.9H.sub.8)x)    0.05% Alumina (Al.sub.2O.sub.3)  2%

TABLE-US-00002 TABLE 2 Exemplary Formulation Rubber (EPDM & tire): 48% Plastic (HDPE, PET & PP) 48% Bonding agent 01% Compatibilizing agent 01% Fly Ash (Type F): 01%

[0046] In Tables 1 and 2, where ingredients do not add up to 100%, ingredient quantities may be adjusted to add up to 100%.

[0047] Rubber buffing made from 100% recycled rubber. Rubber buffings having maximum dimensions of 1 mm to 7 mm may be used.

[0048] Carbon black (having mass of 12.011 g/mol.), having at least 97% elemental carbon arranged as acini-form carbon particulate, as a coloring agent for non-black materials, quantity as necessary for color control.

[0049] Processing aids, lubricating, and homogenizing agents can be added to enhance bonding and mold release characteristics.

[0050] Most of the powders used as strengthening agents are metal oxides and their use has long before proved beneficial in rubber tire manufacturing as there are ZnO, TiO2, CaO. The mechanical static properties are modified by adding the powders and the effect primarily depends on the strength of the organic-inorganic interface, thus on the composition, specific surface area and surface charge of the powder, along with the processing parameters: temperature, duration, etc.

[0051] ZnO is the formula for zinc oxide, an inorganic compound. ZnO is a white powder that is insoluble in water. It is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first aid tapes. Although it occurs naturally as the mineral zincite, most ZnO is produced synthetically.

[0052] TiO2 is the formula for titanium dioxide, also called titania. TiO2 is a white, opaque, naturally occurring mineral existing in a number of crystalline forms, the most important of which are rutile and anatase. These naturally occurring oxide forms can be mined and serve as a source for commercial titanium. TiO2 is odorless and absorbent. TiO2 protects from ultraviolet radiation because of its property to absorb ultraviolet light. The photocatalytic activity of TiO2 results in thin coatings exhibiting self-cleaning and disinfecting properties under exposure to ultraviolet radiation. Alloys are characterized by being lightweight and having very high tensile strength (even at high temperatures), high corrosion resistance, and an ability to withstand extreme temperatures, and thus are used principally in aircraft, pipes for power plants, armorplating, naval ships, spacecraft, and missiles.

[0053] CaO is the formula for calcium oxide, commonly known as quicklime or burnt lime, a widely used chemical compound. It is a white caustic, alkaline, crystalline solid at room temperature. The broadly used term “lime” connotes calcium-containing inorganic materials, in which carbonates, oxides, and hydroxides of calcium, silicon, magnesium, aluminum, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound CaO, CaO that survives processing without reacting in building products such as cement is ailed free lime Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide, of which quicklime is the base anhydride) are important commodity chemicals.

[0054] Replacing these powders with fly ash represents an available and sustainable alternative; fly ash has a large specific surface, and, according to the coal and burning conditions, it may have variable composition; usually, fly ash has a negative surface charge due to the predominant oxidic composition. A significant problem is that the ionic fly ash surface has a high wetting behavior, while rubber (and plastics) is hydrophobic, with very low surface charge. Therefore, building up interfaces based on electrostatic attraction is highly unlikely and thermal linking should be considered. The thermal process must be well controlled; targeting strong interfaces (visco-elastic regimen) without decomposing the polymeric compounds.

[0055] Fly Ash (Type F) mainly consisted of SiO2 (51.4%), Al2O3 (22.4%), and Fe.sub.2O.sub.3 (10.86%), with a total percentage over 70%, therefore, according to the ASTM standards, the fly ash is of type F. The unburned carbon (loss of ignition) amounts to 3.6%. The fly ash should have an activated nano-surface (by alkali treatment) in order to develop uniform interfaces, with significant effect on the compression resistance and on impact. The effect of fly ash addition is correlated with the surface energy, targeting further applications.

[0056] Class F provides strength and lessens permeability I the long run. ASTM standard C618 provides information on the physical, chemical, and mechanical properties of the fly ash classes. Applications include PVC pipe, recycled plastic lumber, and binding agents and fillers in plastic products.

[0057] For reproducible composites obtained by embedding the inorganic powder in the organic polymer matrix, fly ash should have a constant surface property. Yet, the fly ash composition, crystalline structure and surface morphology significantly depend on the coal batch. Therefore, a conditioning process was applied for leveling these properties. The fly ash was washed under stirring for 24 hours in alkali solution (NaOH 2mo VL). During this process some oxides are removed (e.g. sodium and potassium oxides) and other oxides undergo a solubilization/reprecipitation process as SiO.sub.2 does. The fly ash with conditioned surface was dried at 1.20° C. for two hours, sieved, and the fraction with average diameters between 100 and 200 μm was selected for composite preparation.

TABLE-US-00003 TABLE 3 Properties Izod Flexural Impact Flexural Mod- Flexural Strength Pro- ulus, Strength @ ft .Math. lb/in perties psi 5%, psi 1 3.39 1 148160 3931 2 3.39 2 151583 3914 3 3.56 3 150931 3916 4 3.73 4 147877 3915 5 3.39 5 148738 3915 6 3.56 Average 11.6 11.6 7 3.05 Std. Dev. 8 3.56 9 3.73 10 3.22 Average 3.46 Std. Dev. 0.22 Tensile Tensile Elon- Strength gation Tensile Tensile Tensile @ @ Strength Elon- Pro- Break, (Break, @ gation @ perties psi % Yield, psi Yield, % 1 2119 62.0 2558 3.54 2 2241 24.8 2549 3.45 3 2159 36.9 2541 3.88 4 2096 72.4 2576 3.71 5 2133 47.9 2549 3.80 Average 2150 48.8 2555 3.68 Std. Dev. 56 19.1 13 0.18 Heat De- Com- flection pressive Tem- Rate, Strength peratures, g/10 Density @ Yield ° C. min g/cm.sup.3 1 3884 1 95.5 0.955 7.954 2 3847 2 95.6 0.955 8.232 3 3848 Average 95.6 0.955 8.09 4 3814 5 3824 Average 3843 Std. Dev. 27

[0058] Formulations may be further modified to include impact modifiers, fillers (also known as extenders), chemical rubber modifiers, e.g., to influence hardness, flexibility, friction characteristics, and bonding ability (for e.g., bonding to fiberglass reinforcement).

[0059] The above formulations and method 100 may be employed to produce many different products by injection molding. These products may include by way of non-limiting examples, roofing materials, building siding, flooring, fencing, below grade drain conduit and conduit components and accessories, in-ground support posts and poles, doors, furniture, storage and transport containers, motor vehicle parts, boats, recreational equipment such as skateboards, and ground mounted surfacing (e.g., tiles, also known as pavers).

[0060] While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is to be understood that the present invention is not to be limited to the disclosed arrangements, but is intended to cover various arrangements which are included within the spirit and scope of the broadest possible interpretation of the appended claims so as to encompass all modifications and equivalent arrangements which are possible.