Method of manufacture of a foamed core class "a" article.

(54) Title: METHOD FOR THE MANUFACTURE OF A CLASS A FOAMED CORE ARTICLE

(54) Title: METHOD OF MANUFACTURE OF A FOAMED CORE CLASS A ARTICLE.

(57) Summary

The method of making an article having a surface, a crust and a core includes closing a first mold portion on a compressible seal. The seal is placed between the first and second mold portions. The portions define a pressurizable mold cavity that has a separate injection port and vent. The mold cavity is pressurized to a first pressure greater than atmospheric pressure. The molten plastic and a blowing agent that are injected form gas cells within the mix. Gas cells have an internal pressure that exceeds the first pressure. After waiting for a first period, the pressurized gas is vented for a second period at a rate sufficient to rupture the gas cells that form a scab adjacent to the wall of the mold cavity. The crust defines a core cavity filled with the foamed mixture, which solidifies. The mold portions are separated by releasing the article.

(57) Abstract

The method for manufacturing an article having a surface, a skin, and a core ineludes closing a first mold portion on a compressible seal. The seal is disposed between the first and second mold portions. The portions define a pressurizable mold cavity having a spaced apart injection port and a vent. The mold cavity is pressurized at a first pressure greater than atmospheric pressure. Molten plastic and a blowing agent are injected form gas cells within the mixture. The gas cells have an infernal pressure exceeding the first pressure. After waiting for a first period, the pressurizing gas is vented for a second period at a raff sufficient to rupture the gas cells which form a skin adjacent to the mold cavity wall. The skin defines a core cavity filled with the foamed mixture, which is solidified. The mold portions are separated releasing the article.

METHOD FOR THE MANUFACTURE OF A FOAMED CORE ITEM

A CLASS

CROSS REFERENCE TO RELATED REQUESTS

This application claims the benefit of the US provisional application Series No. 61 / 039,489 filed on March 26, 2008.

BACKGROUND OF THE INVENTION

one. Field of the Invention

The present invention relates to the method of manufacturing a foamed core article with a Class A visible surface and with integral structural reinforcements on the non-visible back surface in excess of current manufacturing capabilities.

2. Background Technique

Designers often use plastic parts as replacements for metal parts to take advantage of the greater design freedom that molded parts can give and reduce the weight and cost of the item. The injection molding process is used to produce such plastic articles. But when relatively large items such as heavy truck fascia are injection molded, the clamping force required to seal the mold and inject the amount of plastic material required to fill the mold cavity requires tremendous pressures to produce a usable part. The injection molds and molding machines that can produce these parts are very large and heavy and are extremely expensive to acquire and operate. These pieces of capital goods must be depreciated routinely through the number of pieces produced in them. To date, the costs have been higher than the heavy truck manufacturers have been willing to incur for their short-duration, low-volume programs. As a result, manufacturers have either limited the size of parts of injection molded parts or have opted for other less expensive processes to produce large parts.

In an effort to injection mold large parts without the overspending required for normal injection molds and machines, manufacturers have produced large parts of functional plastic by injecting a mixture of molten plastic and a blowing agent into the mold cavity. By adding a foaming agent to the plastic resin during the injection molding process, the foaming action creates localized pressure in the inner packing that forces the melt to fill the part cavity. The addition of the foaming agent to the molten resin expands the volume of the injected melt and thus reduces the amount of material used per casting cycle. By reducing the density of the melt, the weight of the article to be molded is also reduced. An additional benefit of adding the blowing agent to the melt, with the resulting foaming action in the cavity, is that the need for extreme external injection pressure and related clamping pressure is greatly reduced to maintain the closed mold. The net result is that the high pressure molding process now becomes a low pressure molding process. Despite these benefits, there are disadvantages that prevent the foamed plastic process from being widely used to manufacture Class A structural parts. These are:

The pressures of the inner packaging of the foamed plastic process do not always produce surfaces that are free of surface porosity and local shrinkage deformities, and due to the swirling of foam on the surfaces of the molded part, the foamed plastic process It is not capable of producing the desired Class A surface that is required for visual parts.

SUMMARY OF THE INVENTION

The present invention relates to a method of manufacturing a foamed core article with a Class A visible surface and with integral structural reinforcements on the non-visible back surface in excess of current manufacturing capabilities.

The method for use in manufacturing an article having a surface, a crust, and a core includes closing a first mold portion on a compressible seal. The seal is placed between the first mold portion and a second mold portion. The first and second mold portions each have a wall defining a pressurizable mold cavity. The pressurizable mold cavity has a mold cavity wall, an injection port, and a vent. Injection port and breather are separate.

The method further includes pressurizing the mold cavity using a pressurizing gas at a first pressure that is greater than atmospheric pressure. Through the injection port, a mixture of molten plastic and a blowing agent is injected. A blowing agent gas is generated to form gas cells within a mixture. Gas cells have an internal pressure that exceeds the first pressure. The method includes a first waiting period. For a second period after the first period, the pressurized gas is vented through the vent at a rate sufficient to rupture a portion of the gas cell to produce broken cells. The crust is formed adjacent to the wall of the mold cavity using the broken cells. The scab defines a core cavity that is filled with the

<td>mixture.</td><td>Mix then</td><td>I know</td><td>solidifies.</td><td>The</td><td>first</td>

<td>portion</td><td>mold is separated from</td><td>the</td><td>second portion</td><td>of</td><td>mold to</td>

<td>end of</td><td>release the item.</td><td></td><td></td><td></td><td></td>

<td></td><td>In another modality,</td><td>the</td><td>method includes</td><td colspan="2">close</td>

first mold portion on the second mold portion. The first and second mold portions define a pressurizable cavity having a mold cavity wall, an injection port, and a vent. Injection port and breather are separate. At least one mold portion further includes a flange having a width. The mold cavity is pressurized at a first pressure. A plastic composition is injected through the injection port into the mold cavity. A blowing agent is provided in the plastic composition to form a mixture. The blowing agent causes the plastic composition to foam. The foam has gas cells with an internal pressure that exceeds the first pressure. The method includes waiting for a first period. The mold cavity is vented to a second pressure that is less than the internal pressure of the gas cells. The second pressure is reduced at a predetermined rate by forming a crust that contacts the wall of the mold cavity. The scab is thick. The ratio of the width of the rim of the mold cavity to the thickness of the crust varies from 50% to 300%. The crust defines the core cavity that is filled with the plastic composition and mix. of blowing agent gas. The mixture solidifies. The first mold portion is separated from the second mold portion in order to release the article.

In another embodiment of the invention, the method includes counter-pressurizing a mold having walls defining a mold cavity using a first gas having a first pressure. The first gas is provided in the mold cavity before injecting the plastic composition containing a decomposable blowing agent. The blowing agent decomposes creating a second gas that has a second pressure. The first pressure exceeds the second pressure. The plastic composition expands in the mold cavity by reducing the first pressure to a third pressure. The third pressure varies from atmospheric pressure to less than the first pressure.

DETAILED DESCRIPTION OF THE PREFERRED MODE (S)

Except in the examples of operation or where it is expressly indicated otherwise, all the numbers in this description that indicate amounts of material, reaction conditions or uses should be understood as modified by the word approximately when describing the broader scope of the invention. . Practice established within numerical limits is generally preferred. Also, unless expressly stated otherwise:

percentage and proportion values ​​are by weight;

A group or class of materials described as suitable or preferred for a given purpose in conjunction with the invention implies that any one of two or more of these materials may be mixed and equally suitable or preferred;

the constituents described in chemical terms refer to the constituents at the time of addition to any combination specified in the description and do not prevent chemical interactions between the constituents of the mixture once mixed; and the first acronym definition or other abbreviation applies to all subsequent uses hereof of the same abbreviation and mutatis mutandis (changing what has to be changed) to normal grammatical variations of the initially defined abbreviation.

One embodiment of a method of forming a relatively large molded foam structural article includes injecting a molten plastic having a blowing agent additive into an attached metal mold. To minimize shrink-related surface depressions and reduce the amount of clamping force required, the item is made of foamed plastic. The foaming action substantially eliminates the need for the external packing of the injected plastic to completely fill the mold cavity. Reducing or eliminating the need for external packing significantly reduces the clamping tonnage required to injection mold the part. Lower clamping tonnage means items with larger surface areas can be molded with less machine clamping pressure.

The example of a relatively large item is a vehicle component, especially a truck body component, such as a fender fascia. Such a piece has a surface area that can be more than 2000 square inches (12, 900 cm²). The standard injection molding process for such a part, without any blowing agent, would require the use of an expensive steel mold that is capable of withstanding repeated and extreme clamping pressures and an injection molding machine that has a clamping tonnage that it varies from at least 500 tons (44,500 kilo Newtons (kN)). So the advantage of the foamed plastic molding process is to allow the fabrication of large structural parts without the need for a more expensive steel mold and without the need for extreme clamping pressures. It should be understood that this combination of process and materials is suitable for manufacturing articles that have areas of at least 100 square inches (650 cm²), 500 square inches (3225 cm²) and 1000 square inches (6450 cm²) or more.

One embodiment of the inventive process is based on the use of a particularly advantageous material blend of a plastic matrix including a casting resin, such as thermoplastic polyolefin (TPO), such as LYONDELLBASELL SEQÜEL # 1715, which has a production number from # 198OH1. The mixture includes a chemical blowing agent such as an exothermic blowing agent having an azo-type nucleating agent. The mixture may optionally include a mechanically injected blowing agent such as a gaseous or liquid fluid. The blowing agents serve to generate gas bubbles in the melt stream of the process. The degree to which these components interact to form a foamed melt stream depends on the concentration of the foaming agent in the molten resin. To achieve the physical properties for this modality, a concentration of 1% of the foaming agent was used and produced a complete material density of 97%. By increasing the amount of the chemical that can decompose or the mechanical blowing agent that is introduced into the casting residue, it is possible to influence the degree of nucleation and the resulting internal packing pressure in order to reduce the amount of casting resin in the cavity of the mold to achieve a wide range of material densities in the molded part. It should be understood that an endothermic solid or binary solid blowing agent may also be suitable.

In this embodiment, the 97% total part density is achieved with a molding process that has an injection extruder temperature profile of 400/410/420/410 ° F (204/210/216/210 ° C ) for four zones starting from the zone adjacent to a nozzle to the zone adjacent to the mold with a nozzle temperature of 400 ° F (204 ° C) and a mold temperature of 125 ° F (52 ° C). The test mold is run on a 500 ton Van Dorn press with a 60 fl.oz barrel. (1775 cm³) which is equipped with an interrupting nozzle that has a flow channel one inch (1.9 cm) in diameter. In order to establish a clamping pressure baseline for this mold, Sequel # 1715 molding resin, without the foaming agent, is injected into the mold cavity to verify that a full clamping pressure of 500 tons is required ( 445 kN) to mold a completely compact depression-free part without burrs on the parting line. A typical dimensional calculation for a part that has a mold line spacing of approximately 7.0 inches (18 cm) by 23.5 inches (60 cm), using a clamping factor of 3.0 tons per square inch (41 mega Pascals (MPa), confirms that a 500 ton (4450 kN) clamping machine is required to contain the standard injection process for a part of this size.

With the addition of 1% by weight of the exothermic foaming agent Ampacet # 701039-H to the Sequel # 1715 TPO resin, the machine clamping pressure can be reduced to 100 tons (890 kN) and the same part can be achieved without burr-free depressions as previously produced with 500 tons (4450 kN) of clamping pressure; an 80% reduction. The fill or boost pressure is purposely kept at zero or very low pressure to allow the foam nucleation cells to expand as freely as possible within the walls of the part cavity. In one embodiment, the fill pressure is between 1 psi (12 Pa) and approximately 75 psi (936 Pa). Although the fill pressure is zero or very low, the injected thermoplastic foam mixture continues to fill the cavity because the external pressure applied by the effervescent gas from the blowing agent causes the thermoplastic foam mixture to continue to expand until it reaches the wall of the part cavity.

The reduced clamping pressure requirement for the foamed resin molding process further reduces the strength of the compressive force required for the mold construction material. As a result, the mold building material can be changed from tool steel to a lighter weight and / or lower cost material, such as an aluminum or magnesium based material. Aluminum, for example, has the added benefit of a relatively higher thermal conductivity than tool steel. Increased thermal conductivity reduces process cooling time through better heat dissipation and serves to reduce overall process cycle time. For example, using aluminum means that the molds are lighter to handle and are more easily machined. Improved handling and machining has a very beneficial impact on the economy of the molding process. Therefore, foamed resin molding processes provide substantial tooling advantages over standard injection molding processes.

Another benefit of the foamed resin molding process is its ability to minimize surface deformities in injection molded articles that are commonly known as shrinkage depressions. The article often has two opposite surfaces. A surface A that is the surface shown that can be aesthetic. A surface B often does not need a good appearance relative to surface A. In articles that are produced by a standard injection molding process using solid thermoplastics, these deformities can typically occur on a flat surface that may be a class A surface. These deformities may not be aesthetically acceptable. Deformities are typically located on the opposite surface from a feature that makes the cross section of the article somewhat thicker and consequently has greater mass. In the case of articles that are molded from solid resin, these areas of higher mass also tend to cool relatively slower when compared to the thinner wall areas that surround them. Without wishing to join any particular theory, deformities such as surface depressions can occur because areas of higher mass contain more heat and therefore cool more slowly than areas of relatively thinner walls. The molding resin is able to continue to contract for a relatively longer period of time and for a relatively longer distance as it seeks thermal and dimensional balance with its surrounding plastic mass.

By adding the foaming agent to the molding resin, the molecular chains of the resin are disrupted by nucleated cells with their relatively thin cell walls. Nucleated cells can result in decreased shrink resistance in the casting resin. The thinner wall section has less mass and contains less heat than thicker wall sections. The faster the wall section cools, the less time is available for the wall to continue to contract. In addition to disrupting molecular contraction forces, nucleated cells provide an additional impediment to contraction, since the generated nitrogen gas that forms the bubbles to foam, provides for example a minuscule amount of internal gas pressure that tends to expand the newly formed cells in the molten resin matrix. A combined effect of the newly formed adjacent cells can generate enough outlet pressure to counteract the contraction forces of the cell walls. Counteracting contraction forces in a nucleated cell layer can limit surface depressions on the adjacent surface.

The foam injection molding process does not depend on mechanically filling the resin into the cavity to achieve the fully developed article,

ie, without depressions. Eliminating the mechanical stress on the resin and using only normal pressure to expand the resin foam can reduce or eliminate the related stress gradients that normally exist from the injection point to the point of last fill. As a result of localized filling of the part through the nucleation of the expanding cell, the article has minimal stress gradients. The molded article often exhibits no kink due to minimal stress on the foam material. The article also tends to contract less along the material's flow paths and is therefore dimensionally more stable.

Although the foamed resin injection molding process typically serves to make an article without depressions, by applying considerably less clamping pressure to a more efficient and less costly thermal injection mold, the resulting article exhibits the foam-filled resin matrix on its surface and cannot be considered to achieve a class A visual surface. The same cell structure that disrupts the tendency of the casting resin to contract also serves to compromise some of the physical performance properties of the casting resin. The inherent physical properties of a thermoplastic resin are based on the molecular proximity of one molecule to another in the resin matrix. However, both of these problems, the porous surface and reduced physical properties can be overcome, to some degree, by pressurizing the mold cavity with a gas that has a higher pressure than the internal pressure of the foam cells.

In at least one embodiment of this invention, compressible seals are applied to the mold at the parting line and at any other notches, cores, hook spatulas, ejector nails that penetrate the mold block, as needed, to prevent leakage of gas from the sealed mold cavity having a pressure greater than atmospheric pressure. The sealed mold cavity receives a pressurizing gas to increase the pressure within the mold cavity above atmospheric pressure. Injection of the foamed molten resin is delayed until the mold cavity reaches a pressure in the independently determined range and is selected from 50, 80, 90 psi (625, 1000, 1125 Pa) to 120, 150 and 200 psi (1500, 1875 and 2500 Pa) to suit the application. During injection of the molten plastic and blowing agent into the pressurized mold cavity through a gate, the expansion of the blowing agent gas into the resin foam in the mold cavity remains relatively minimal and closely controlled by the extruder of the injection unit and then by means of the counter pressure of the pressurizing gas. The pressurizing gas can be released or removed after a waiting period, such as the ventilation delay, lasting more than 1.5 seconds, 5 seconds, or 7 seconds during which the pressurized gas breaks the cell walls that are directly exposed to This pressurized gas and allow the molten resin to flow together and form a relatively thin wall of solid resin on top of the underlying foamed resin. As the crust thickness of the molding resin increases, the pressurized gas in the mold cavity is less able to reach the new underlying cells to break its walls, allowing these cells to form and grow. Once the desired crust thickness has been reached, the release or removal of gas from the pressurized mold during a period of depressurization may be either a controlled process such as through a pressure relief valve or a non-process. controlled such as through an atmospheric vent or into a recovery container. Once the gas pressure has been reduced to an ambient level, the underlying foamed resin is then free to nucleate and expand to fill the mold cavity. It should be understood that the article may have scabs on more than one side. The crusts can occur adjacent to any wall of the mold or insert cavity.

The retention time range can be independently selected from 1 second, 5 seconds, 10 seconds, 16 seconds and 20 seconds to 20 seconds, 30 seconds, 40 seconds or 50 seconds, depending on the desired distribution of the crust and the foam core structure. After a retention time in which the article is completely solidified, the mold can then be opened and the molded foam core article, such as the relatively large part for an automobile body, can be removed. The foam body has a relatively thick crust layer and a foam core layer. The thickness range of the foamed core layer can be selected from more than 1mm, 2mm and 3mm to less than 50mm, 40mm, 30mm, 20mm, 10mm and 5mm as required by the design of the piece. The crust layer is thick enough to prevent the cells of the foamed core layer from being visible or evident in the crust layer. The range of weight reduction can be independently selected from greater than, 2 and 3% by weight up to 5, 7, 10, 20 and 30% by weight to suit the needs of the molded article.

In at least one embodiment, the back pressure gas vent is delayed for a period ranging from about 1.5 seconds to about 10 seconds after the charge has been fully injected into the mold. In another embodiment, the ventilation delay is from about 3 seconds to about 8 seconds. A ventilation delay profile, a period of pressurizing gas ventilation, and / or a graph of the counter pressure pressure in the mold during the ventilation period helps to assess the structure of the resulting article, especially for the thickness of the scab and foam core. The higher the pressure of the counterpressure pressurizing gas, the thicker the crust. The longer the waiting period until ventilation, the thicker the crust. The profile can be used to adjust the gradient of the properties in the articles through the control of the diameters and amounts of voids generated. The profile may need to be developed in conjunction with the cooling properties of the mold and part design. By applying gas back pressure to the foamed resin injection molding process, it is now possible to manufacture an article that has a low pressure molded foam core with a solid crust on each side to improve the aesthetics of the article to a class A level and to impart most of the original physical properties of the non-foamed original thermoplastic to the overall structure of the article.

In addition to recovering almost all of the physical properties of the unfoamed resin, the new laminated crust / foam core / crust structure is capable of obtaining additional strength from the geometric nature of the laminated section. This type of structure is capable of achieving a higher flexural modulus than solid sections of equal weight to resin, but at a reduced material density. This flexural modulus can be calculated with the following formula:

flexural modulus of layered structure a (thickness of lamination)³

An example of the resulting article is the fender fascia of a truck that has a scab at least 1.5 mm thick adjacent and around a foamed core. The visible front crust is the surface shown, referred to as surface A, which is supported by the foamed central core, which also supports the rear side crust referred to as surface B, and typically provides bonding characteristics. The crust and foamed core in the present embodiment are injection molded with a 1% by weight mixture of the chemical foaming agent Ampacet # 701039-H and LYONDELL BASELL Sequel # 1715 TPO durable, which has the benefit of resisting damage from Typical spike impacts from debris originating from a highway. A further advantage of the combination of material and method arises from the fact that they are capable of forming mounting bosses and large structural ridges with a crust-foam-crust structure on the B-side of the fascia. But, the creation during the molding process of solid molding resin like the crust on the fascia can again produce depression problems related to contraction on the solid surfaces of the fascia, in opposite locations of the heavy structural ridges on the back of the fascia structure. Irregular shrinkage of the casting resin needs to be treated in order to produce a structural article having a class A surface with no depressions as opposed to large structural ridges and protrusion on surface B.

Most manufacturers of thermoplastic molding resin have published flange size recommendations for wall material of approximately 25% for TPO to avoid depression problems in standard molded articles. It should be understood that the ratio of thickness of the flanges to the wall material currently recommended can be as great as 45% depending on the plastic used. As that ratio increases beyond recommendations, the higher concentration of heat in the larger mass continues to cool more slowly at

<td>environment,</td><td>the</td><td>contraction</td><td>of the</td><td>material</td><td>continue being</td><td>plus</td>

<td>big in</td><td colspan="2">the sections</td><td>of</td><td>more to more</td><td>great than in</td><td>the</td>

<td>sections</td><td>plus</td><td>thin that</td><td>the</td><td>surround.</td><td colspan="2">The resulting delay</td>

to reach room temperature it allows the front surface to stretch longer and then inward thereby causing surface distortion, such as a surface depression.

The structural article with large B-surface structures, such as a Class 8 Heavy Truck Fascia can be molded using gas back pressure with foamed thermoplastic define or any other crystalline, semi-crystalline, or amorphous resin for molding. The resulting part has thicker than normal wall material of about 6mm but with an independently selected range of 1-10mm or about 6mm or greater. Large flanges that are well above the recommended flange size for the material to wall ratio for TPO can be molded in the same way. Proportional increases in proportion can be expected with the inventive process when other plastics are used.

With the combination of&gt; back pressure and foamed TPO, the ratio of the flange size to the wall material can be as large as 50%. Surprisingly, the combination of this method and this material, when combined with the use of edge trim and projections on surface B of the mold surface, results in the desired Class A surface for TPO when the ratio of the Flange width to wall material thickness is approximately 300% or more. The ratio of rim width to wall material thickness can vary from independently selected ratios of more than 25%, 50%, or 75% to 1000%, less than 1000%, or 100%. The addition of oversized flanges helps improve structural integrity, both strength and stiffness of the fascia. In addition, oversized flanges are also added to the rear side of the part to accept the joint clamps used to install the part to the truck chassis. This combination is advantageous in the Class A fascia which is designed in such a way that no additional reinforcing structures or braces are required beyond the mounting brackets. This saves manufacturers the cost of additional structures. It also helps designers to avoid using separate components such as support arms to install the fascia to achieve the necessary structural integrity. An additional advantage is that the dimensional stability of the fascia can be improved by eliminating molding-induced stresses. By reducing stresses, the structural durability of the fascia can be increased, especially with respect to the propagation of cracking and cracking. This is especially advantageous when an insert of foreign material such as metal, plastic, or non-plastic reinforcing components is over-molded in hollow mounting locations.

Many types of polymers and polymer compositions can be used as the plastic matrix for the crust and foamed core layers with this process. Non-limiting examples of the compositions can include thermoplastics, and lightly crosslinked thermoplastics. The plastics selected for the foam core article can be selected based on their physical properties and melting characteristics. For example, the truck fender fascia may have a relatively elastomeric material that has the advantage of being durable relative to the small tip impacts typical of debris hit on a road. Non-limiting examples of durable plastics can include structural foams comprising amorphous plastic, an olefin, thermoplastic polyolefin, and a thermoplastic elastomer.

It should be understood that these polymers can include mixtures of various plastics, as well as comprise reinforcements and additives such as plasticizers, rubber hardeners, grafts, fillers and fillers. Multiple injections of the same or different plastic and / or blowing agents can occur without opening the mold without violating the spirit of the invention.

In order to generate the plastic matrix having the number of voids, the blowing agent is typically added to the plastic before the plastic melts, although it may be added during or even after the melting of the plastic matrix. Blowing agents can include a chemical blowing agent such as an endothermic solid, an exothermic solid, and a binary solid and / or a physical blowing agent, such as a liquid that is infused or dissolved in the plastic matrix, a combination of core -covered with a blowing agent inside a plastic cover, and / or a gas injected or dissolved under pressure in the molten plastic. In one embodiment, the amount of the foaming agent added to the thermoplastic material is approximately 0.5% by weight or greater, depending on the application. In a further embodiment, the foaming agent is approximately 1% by weight or greater.

A non-limiting example of the exothermic blowing agent is an exothermic foam concentrate. A foam concentrate can include a heterogeneous nucleating agent. An example of the heterogeneous nucleating agent is an azo type nucleating agent, such as modified azodicarbonamide (ADC), which is sold as a chemical blowing agent such as product # 701039-H by Ampacet Corporation. The benefits of ADC come from the release of nitrogen gas against carbon dioxide. Nitrogen gas has a relatively low molecular weight, making it more reactive. Nitrogen's best foaming properties refer to the fact that the masterbatch of plastic and ADC only uses 20% by weight. ADC vs. 50% by weight more typical of chemical blowing agents that generate carbon dioxide. Chemical blowing agents and exothermic foam concentrates can also be used in conjunction with physical blowing agents. Other examples of nucleating agents include particulate solids such as talc or silica.

Nucleating agents generally lead to relatively finer cell structures than when no nucleating agents were used. The finer cell structure can result in a reduction of the absolute percentage of 1-15 in the density of the plastic matrix relative to the density that can be achieved using talc. ADC, when finely dispersed in the molten plastic, can produce a very fine cellular structure that includes a micro-cellular structure. An absolute weight reduction of 39% or less can be obtained using the azo-type nucleating agent. Typically, the average cell diameter, when ADC is used as the nucleating agent, can range from about 0.1mm to about 0.5mm. The cell diameter can be further reduced by suppressing cell growth by back pressure. The cell size range can be independently selected from 0.035mm, 0.050mm, 0.075mm, and 0.1mm to 0.3mm, 0.4mm, 0.5mm, 0.7mm, and mm.

When using a nucleating agent such as ADC, it is important to carefully monitor the temperature of the machine used to mix the molten plastic with the nucleating agent and the temperature of the mold. It is desirable that the nucleating agent be activated immediately prior to foaming. Premature activation can result in loss of effectiveness of the nucleating agent. A gas generation range from 165, 170, 180 or 200 ° C to 215, 200, 182 or 175 ° C can be independently selected. The maximum processing temperature can range from 230 ° C to 260 ° C or as high as 10 ° C below the degradation temperature of the plastic. The concentrate of the foaming agent or any other chemical blowing agent can be diluted in the plastic matrix (a decreasing proportion) in a range independently selected from

0.1, 1, 2, 5% by weight up to 10, 20, 30% by weight. The plastic in which the concentrate of the foaming agent or any other chemical blowing agent being mixed may be in the range of the degree of injection molding. As an example of the injection molding grade properties, the melt index before the addition of additives and blowing agents can range from 5 to 100 mg / 10 minutes when measured by ASTM D1238 condition L.

Example 1

A TPO resin, SOLVAY SEQUEL production number 1715, is used as the plastic resin matrix. This resin is based on SEQUEL number 1980HI, a designed polyolefin that has a low coefficient of linear thermal expansion. The polyolefin is mixed with 1% by weight of the exothermic chemical forming agent supplied by AMPACET number 701039-H, which comprises approximately 20% of a modified ADC.

Example 2

PHOENIX PLASTICS provides a masterbatch formulation that uses a polyolefin. CELL-SPAN 1000 uses a polyolefin polymer formulated with supramolecular chemicals that allow the formulation of directional hydrogen bonds that emulate the strongest covalent bonds. The foaming agent using in the CELL-SPAN product line includes the function of the nucleating agent. The descending ratio is 1%, but can be as little as 0.2% by weight. CELL-SPAN 1000 is an endothermic chemical foaming agent. It is intended to produce a small cell structure instead of a fine cell diameter structure.

Example 3

TPO SOLVAY SEQUEL resin production number 1980HI is mixed with 1% TRCEN40310ES type TECHMER TECHSPERSE to form the masterbatch.

Example 4

The TPO resin of SOLVAY SEQUEL production number 1980HI which is derived from SEQUEL number 1715, comprises the control material.

Example 5

The items in this example, six-inch-by-eight-inch plates (48 in.², 310 cm²), are molded from the materials used in Example 1, 2, 3 and 4 with the conditions and results provided in

Table 1.

Table 1

<td></td><td>TPO RESIN: Solvay Sequel # 1980Hl (Sequel # 1715)</td><td>TECHMER TRCEN40310ES</td><td>PHOENIX PLASTICS CELL- SPAN # 1000</td><td>AMPACET # 701039-H</td>

<td>Type and Size of the Press</td><td>300 ton Van Dorn</td><td>300 ton Van Dorn</td><td>300 ton Van Dorn</td><td>300 ton Van Dom</td>

<td>Force of Subjection:</td><td>300 tons</td><td>75 tons</td><td>75 tons</td><td>75 tons</td>

<td>Mold Temperature:</td><td>130 F</td><td>110 F</td><td>145 F cavity / 135 core</td><td>125 F</td>

<td>Melting Temperature by Zone:</td><td>400/410/420 / 400F</td><td>400/410/410 / 410F</td><td>400/410/420 / 410F</td><td>400/410/420 / 410F</td>

<td>Cargo Size</td><td>6.2 in.</td><td>5.6 in.</td><td>5.4 in.</td><td>6.0 in.</td>

<td>Loading Speed:</td><td>Fast</td><td> 4.1</td><td> 1.34</td><td> 10.59</td>

<td>Cycle Time:</td><td>90 sec.</td><td>80 sec.</td><td>80 sec.</td><td>120 sec.</td>

<td>Gas counter pressure</td><td>N / A</td><td>90 psi</td><td>50 psi</td><td>150 psi</td>

<td>Delay of Gas Release</td><td>N / A</td><td>3 sec.</td><td>3 sec.</td><td>3 sec.</td>

<td>Pressure increase</td><td> 2000/75</td><td> 2000/177</td><td> 2000/322</td><td> 2000/180</td>

<td>Maintained Pressure:</td><td>400 psi</td><td>25 psi</td><td>5 psi</td><td>50 psi</td>

<td>Retention time:</td><td>15 sec.</td><td>20 sec.</td><td>5 sec.</td><td>30 sec.</td>

<td>Against Pressure:</td><td>80 psi</td><td>80 psi</td><td>100 psi</td><td>100 psi</td>

<td>Curing time:</td><td>60 sec.</td><td>50 sec.</td><td>50 sec.</td><td>55 sec.</td>

<td>Compression RPM</td><td> 150</td><td> 150</td><td> 175</td><td> 175</td>

<td>Merger Control:</td><td>good</td><td>good</td><td>good</td><td>good</td>

<td>Problems of Pieces:</td><td>none</td><td>none</td><td>none</td><td>post blown trend</td>

<td>Weight of the piece:</td><td></td><td></td><td></td><td></td>

<td>5.0 mm</td><td>0.360 lib</td><td>0.335 lib.</td><td>0.355 lib.</td><td>0.356 lib.</td>

<td>% exchange</td><td> 0</td><td> -7.00%</td><td> -1,14%</td><td> -1.12%</td>

<td>7.0 mm</td><td>0.477 lib</td><td>0.447 lib.</td><td>0.465 lib.</td><td>0.466 lib.</td>

<td>% exchange</td><td> 0</td><td> -6.30%</td><td> -2.50%</td><td> -2.30%</td>

With the use of the fixing foaming agent it is reduced from 300 tons of chemical, the force force (2670 kN) to tons of force (667 kN) or up to approximately 75%. The filler size is reduced in a range of 3% by weight to 13% by weight when a foaming agent is added to the TPO relative to the original TPO control. However, the charging time increases to 10.59 seconds and ranges from 1.34 to 10.59 seconds. As a consequence, the cycle time is also increased by 30 seconds or up to 33%. Gas back pressure ranges from 50 to 150 psi (349-1034 kPa). It should be understood that additional combinations of charge size, charge speed, and gas back pressure can be used, depending on the resulting product and its specifications.

In this set of examples, the back pressure gas is removed over a period of about 3 seconds. The retention time that contributes to the cycle time is increased by as much as 15 seconds or 100% using the chemical blowing agents. The material of Example 1 tends to exhibit a tendency to foam beyond the retention time. The plate piece exhibits a reduction in weight of from about 1% to about 7%.

With the material from Example 1, it is surprising that additional gas back pressure is necessary to make the crust thick enough to hide the cell structure and provide a class A surface.

The increased back pressure ranges from an increase in

25% up to as much as a 300% increase over other chemically blown TOPs. The foaming agent surprisingly shows a drastic difference in the reactivity of the chemical foaming agent when Example 1 is used relative to Examples 2 and 3. The foam layer continues to foam well despite the relatively higher back pressure. This results in the plate sample having the desired relatively thick crust for durability and the relatively evenly distributed foam cells of a very fine cell diameter. The cells are desirably isotropic as well.

Example 6

A foam expansion test was carried out using the material from Example 1. In order to determine the limit of the expansive capacity of the foams, a -5.0 mm cavity was filled with enough resin and foam mixture to produce a plate acceptable. The same volume of the charge was injected into a 7.0 mm cavity and allowed to foam to its natural limits in the presence of gas back pressure of 150 psi (1034 kPa). If the resulting plate is of acceptable quality, the charge size is adjusted downward to the point where the foam achieves a minimum density and still produces an acceptable plate. If the resulting plate is not acceptable in terms of quality because it is a small charge, the charge size is adjusted to the point where the foam achieves a minimum density in acceptable plate productions. The degree of change in free lift is then calculated by comparing the deviation of the load with the original setting. Results are shown in table 2.

Table 2

<td colspan="2">Test Process: Calculated load size for 5.0mm plate = (6.0 / 12) 5 = 2.5 inch segment.</td>

<td colspan="2">Calculated charge time for 5.0mm plate = (10.6 / 12) 5 = 4.42 seconds of charge</td>

<td colspan="2">Gas back pressure and all other machine settings remain as before.</td>

<td>Test results:</td><td>Plate Condition:</td>

<td>Weighed 5.0mm Plate from 0.356 Ib to 2.5</td><td>Full part with smooth, burr-free surface</td>

<td>inches load Weighing Plate 7.0 mm from 0.361 Ib to 2.6</td><td>Part incomplete filling with many</td>

<td>inches load</td><td>dimples in front and behind the piece</td>

<td>Weighing Plate 7.0 mm from 0.357 Ib to 2.7</td><td>Part incomplete filling with many</td>

<td>inches load</td><td>dimples in front and behind the piece</td>

<td>Weighing Plate 7.0 mm from 0.387 Ib to 2.8</td><td>Part filled with 1.13 in. Surface chamfer,</td>

<td>inches load</td><td>69 dimples in half</td>

<td>Weighing Plate 7.0 mm from 0.403 Ib to 2.9</td><td>Filled part with 0.87 inch surface chamfer,</td>

<td>inches load</td><td>70 dimples in half</td>

<td>Weighing Plate 7.0 mm from 0.419 Ib to 3.0</td><td>Part filled with 0.50 in. Surface chamfer,</td>

<td>inches load</td><td>63 dimples in half</td>

<td>Weighing Plate 7.0 mm from 0.423 Ib to 3.1</td><td>Filled part with surface chamfer of 0.038</td>

<td>inches load</td><td>in., 57 dimples halved</td>

<td>Weighing Plate 7.0 mm from 0.431 Ib to 3.2</td><td>Part filled without chamfer, 43 dimples in half</td>

<td>inches load</td><td>Of the surface</td>

<td>Weighing Plate 7.0 mm from 0.471 Ib to 3.3</td><td>Full part, smooth surface, no burr</td>

<td>inches load</td><td></td>

Δ In order to achieve a fully foamed 5.0mm plate that has a good surface after gas back pressure, the amount of the filled cavity is minimized to the point where the foam cell structure is maximized. At the point where the cell structure is maximized, the part should still have a good surface appearance and part integrity. As a result of this minimization effort, the potential for additional cell expansion is reduced to the point where introducing that same size of load into a larger cavity does not produce any additional expansion. Results include detection of quality problems associated with a small piece of cargo.

Table 4

<td>Molding</td><td>Material</td><td>Outcome</td>

<td>Without molding</td><td>Example 4</td><td>Superficial depression in the surface of side A</td>

<td>Without molding</td><td>Example 1</td><td>Less superficial depression in the surface of side A than in the Example 1 / test without molding</td>

<td>With molding</td><td>Example 4</td><td>Less superficial depression in the surface of side A than in the Example 1 / test without molding</td>

<td>With molding</td><td>Example 1</td><td>Class A surface</td>

Surprisingly, the combination of this method and this material, when combined with the use of edge trim and projections on the B side of the mold surface, results in the desired Class A surface on a relatively large article.

Although embodiments of the invention have been illustrated and described, these embodiments are not intended to illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it should be understood that various changes can be made without departing from the spirit and scope of the invention.