Molded thermoplastic articles.

(54) Title: MOLDED THERMOPLASTIC ARTICLES. (54) Title: MOLDED THERMOPLASTIC ARTICLES.

(57) Summary

An injection molded foam article that includes a frame and a projection that projects from the frame. The thickness of the projection is greater than 25% to 40% of the thickness of the structure, depending on the material of the article, and the front surface of the structure opposite to the projection has a Class A surface.

(57) Abstract

An injection molded foam article including a structure and a projection projecting from the structure. The thickness of the projection is greater than 25% to 40% of the thickness of the structure, depending on the material of the article, and the front surface of the structure opposite the projection has a Class A surface.

MOLDED THERMOPLASTIC ARTICLES

BACKGROUND OF THE INVENTION

The present invention relates to thermoplastic molded articles, and more specifically to thermoplastic foam articles molded by the invention.

Conventional injection molding typically involves injecting a molten thermoplastic at high pressure into the cavity of a closed mold. Injection pressure can vary anywhere from 140.6 10 kg / cm² at 703 kg / cm² (2,000 to 10,000 psi.), Depending on the item being made. After the thermoplastic has cooled sufficiently to a hardened condition, the mold is opened and the molded article is removed.

In conventional molding processes, a frequently encountered problem is the formation of sump marks or distortions on the surface of the molded article opposed to a projection, such as a rib, protrusions, bracket or return. A sink mark is a visually perceptible indent or recess on the surface of the article that is created largely as a result of shrinkage of uneven material during the curing segment of the injection molding process.

The formation of sump marks can cause a variety of factors, such as insufficient injection usage and unpacking pressure during the molding process. One of the major contributing factors 5 to the formation of sump marks on the surface of molded articles is the ratio of the thickness of the projection to the thickness of the structure or wall material from which the projection extends. It is well known that when conventional injection molding is used to make a molded thermoplastic article that a sink mark will form on the surface of the article when a thermoplastic olefin is used and the thickness of the projection is greater than about 25% of the structure thickness.

Furthermore, when certain other thermoplastic materials are used, such as for example crystalline, semi-crystalline or amorphous materials, a sink mark will form on the surface of the article when the projection is 40% or greater than the thickness of the structure. While a projection greater than 25% the thickness of the framework is not always required, there are many cases when a projection greater than the above ratio is highly desirable and beneficial. For example, a larger projection can provide greater structural integrity to the article and can provide a greater attachment area for attaching the molded article to other objects.

Figures 1-3 illustrate three different examples of conventional injection molding configurations.

Referring to Figure 1, a molded article 10a includes a front surface 12a and a rear surface 14a. The front surface 12a is a Class surface

A. As used herein a Class A surface is intended to refer to a surface that is visually decorative and uniform to the eye unaided or, in other words, is visually free of unintentional distortions, such as sink marks. , dimples, rebates, divotes or the like. Such Class A surfaces include non-textured or purposefully textured surfaces, such as hair cell surfaces and the like, and are visually free of unintentional distortion.

Molded article 10a also includes a wall structure or material 16a and a projection 18a. Structure 16a includes a front wall 20a that is defined by a portion of the front surface 12a and a rear wall 22a defined by a portion of the rear surface 14a. Projection 18a includes a first side wall 24a and a second side wall 26a, both of which are defined by portions of the rear surface 14a. Projection 18a also includes an end wall 28a defined by a portion of the rear surface 14a.

Furthermore, the molded article 10a also includes a gasket 30a between the structure 16a and the projection 18a. The joint 30a is also defined by portions of the rear surface 14a and blends with the side walls 24a and 26a of the projection 18a and the rear wall 22a of the structure

16a.

The side wall 24a and the side wall 26a of the projection 18a are separated by the distance T_p, which defines the thickness of the projection 18a. Additionally, the front wall 20a of structure 16a and the rear wall 22a of structure 16a are separated by distance T₃, which defines the thickness of structure 16a. It is well known in the industry that providing a Class surface

A using thermoplastic olefins (TPO), the distance T_p must be 25% or less than distance T₃ and the joint 30 should be around 90 degrees angle. If using certain other thermoplastic materials, such as those mentioned above, the distance T_p must be 40% or less than distance T₃.

Comparing Figures 2 and 3 with Figure 1, it is also generally well known that in the conventional injection molding industry the joint 30b between structure 16a and projection 18b is curved (as shown in Figure 2) or thickness T_p projection 18c is greater than 25% to 40% (depending on the material) of the thickness T₂ of structure 16c 8c (as shown in Figure 3), a visible distortion, such as sink mark 32, will form on the front surfaces 12b (Figure 2) and 12c (Figure 3) of the structure during the molding process. injection. Distortions are believed to occur due to the relatively large mass of thermoplastic material placed in the area of ​​the wall joint, in combination with the rest of the structure, it cools at a relatively slower rate compared to the thinner portions of the structure. As the greater concentration of heat in the larger mass continues to cool in the environment, the shrinkage of material continues longer in larger sections of mass than in the surrounding thinner sections.

The resulting delay in bringing to room temperature allows the front surface to be stretched longer and further inward thereby causing surface distortion, such as a sink mark.

While surfaces with unintentional distortion can be tolerated for low-end, non-visible products, when products are required to have a high-quality appearance, such as a Class A exterior surface and interior auto parts, distortions are not Intentionals are highly undesirable and frequently make the molded article inappropriate for use. It is desirable to have Class A surfaces on auto parts, such as fenders, sun visors, cab extenders, side trims, hoods and fenders.

Therefore, a need remains for molded articles having relatively large projections and a Class A surface on the opposite side thereof, said surface being visibly free of sump marks or distortions.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a molded article that includes a wall or frame material having a Class A front surface and a projection extending from the back surface of the frame.

The projection has a thickness that is greater than 25% to 40% the thickness of the structure (depending on the material of the article), and the front surface of the structure opposite

Ί the projection is a Class A surface.

One aspect of the present invention relates to an injection molded thermoplastic article having a front surface, a back surface, and a first distance between the front and rear surfaces. The article also includes at least one projection extending from the posterior surface of the structure.

The projection has a first side wall and a second side wall that is separated by a second distance that is greater than 40% of the first distance. The opposite front surface of the projection is a Class A surface.

Additionally, a fair mix is ​​placed between the frame and the projection.

Another aspect of the present invention relates to an injection molded thermoplastic article that includes a structure having a front surface and a rear surface separated by a first distance. The article also includes at least one projection extending from the rear surface of the structure, which may be a mixed joint between the projection and the structure.

The projection has a first side wall and a second side wall that is separated by a second distance, which is greater than 40% of the first distance, and a portion of the front surface that is opposite to the projection is a Class A surface. In addition, the item includes an outer solid skin layer and an inner foam core.

In a further aspect, the present invention is directed to and with a molded article comprised of TPO including a wall or structure material having a Class A front surface and a projection extending from the rear surface of the structure. The projection has a thickness that is greater than 25% of the thickness of the structure, and the front surface of the opposite structure the projection is a Class A surface.

BRIEF DESCRIPTION OF THE DIFFERENT VIEWS OF THE DRAWING

Throughout this description, reference will be made and reference has been made to the accompanying views of the drawing where as the invention has similar reference numbers, and where:

Figure 1 is a cross-sectional view of a prior art molded article made by conventional injection molding techniques;

Figure 2 is a cross-sectional view of another prior art molded article made by conventional injection molding techniques;

Figure 3 is a cross-sectional view of yet another prior art molded article made by conventional injection molding techniques;

Figure 4 is a front perspective view of a molded article constructed in accordance with the principles of the present invention;

Figure 5 is a rear plan view of the molded article of Figure 4;

Figure 6 is a cross-sectional view of a first embodiment of a molded article constructed in accordance with the principles of the present invention, as taken along the AA lines of Figure 5;

Figure 7 is a cross-sectional view of another embodiment of a molded article constructed in accordance with the principles of the present invention as taken along the AA lines of Figure 5;

Figure 8 is a cross-sectional view of still another embodiment of a molded article constructed in accordance with the principles of the present invention, as taken along lines Aa of Figure 5;

Figure 9 is a cross sectional view of a further embodiment of a molded article constructed in accordance with the principles of the present invention as taken along the Lines of Figure 5;

Figure 10 is an enlarged view of one of the mixed joint portions of Figure 9;

Figure 11 is a cross sectional view of yet another embodiment of a molded article constructed in accordance with the principles of the present invention as taken along lines Aa of Figure 5; and

Figure 12 is a cross sectional view of a mold that can be used in the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

<td></td><td colspan="5">Figures 4 and 5 illustrate an article or part 34</td>

<td>molded</td><td colspan="2">thermoplastic.</td><td>Article</td><td colspan="2">34 molded is intended</td>

<td>to be</td><td>a</td><td>Article</td><td>molded from</td><td>built example</td><td>of</td>

<td colspan="4">in accordance with the present invention</td><td>and can be used in or</td><td>in</td>

<td colspan="2">virtually</td><td>any</td><td>product.</td><td>In one modality,</td><td>the</td>

Molded article 34 is an interior or exterior automotive part, such as, for example, bumpers, sun visors, cab extensions, side fairings, roofs or fenders. Molded article 34 includes a wall structure or material 36 and at least one integral projection 38, such as a rib, boss, bracket, or return, projecting from the structure. Molded article 34 also includes a front surface 40 and a rear surface 42. The front surface 40 is a Class A surface. As mentioned above, as used herein, a Class A surface is intended to refer to a surface that is visually decorative and uniform to the eye without assistance or, in other words. , is visually free of unintentional distortions, such as sump marks, dimples, recesses, divots or the like. These Class A surfaces include non-textured or purpose-textured surfaces, such as hair cell surfaces and the like, that are visually free of unintended distortion.

Referring to Figure 6, the thermoplastic molded article 34 also includes an inner foam layer or inner core 46 and an outer skin layer 44, which preferably, but not necessarily, completely surrounds the foam layer 46. Foam layer 46 can be a layer of thermoplastic material that can be foamed by using a chemical foaming agent or by mechanically injecting a gas into the molten thermoplastic resin as it is being heated and extruded before being injected into the cavity printed. As shown, the foam layer 46 has small cells 48, which are formed by the foaming agent during the molding process. The average cell diameter scale can be independently selected from 0.035mm, 0.050mm, 0.075mm, 0.1mm,. 0.3mm, 0.4mm, 0.5mm, 0.7mm. and 1 mm. The density of the foam layer 46 is between about 75% and about 95% of the density of the solid base thermoplastic material from which the foam layer is made.

As discussed above, the outer skin layer 44 preferably surrounds the foam layer 46 and is comprised of a substantially solid layer of thermoplastic material, having few or no cells therein.

The skin layer 44 has an outer surface 50 that is defined by the front surface 40 and an inner surface 52. The outer surface 50 and the inner surface 52 are separated by a distance D, which defines the thickness of the skin layer 44. Distance D is greater than about

1.1 and can be between 1.1 and 2.5 or greater than 2.5.

Additionally, molded article 34 is comprised of about 85% by weight or more of solid thermoplastic material and about 15% by weight or less of foamed thermoplastic material. In one embodiment, the solid thermoplastic material is about 90% by weight and the foamed thermoplastic material is about 10% by weight.

Additionally, the total composite density of article 34, which is defined by skin layer 44 and foam layer 46 is between about 93% and about 97% of the density of the solid thermoplastic material from which the article is made.

Structure 36 includes a front wall 54 defined by a portion of front surface 40 and a rear wall 56 defined by portions of a rear surface 42. In the illustrated embodiment, structure 36 is shown as flat. However, structure 36 can also be curved in that it could have a concave or convex shape. The external surfaces of the front wall 54 and the rear wall 56 are separated by a distance T₈, which defines the thickness of the structure. In one modality, the distance T_s it is about 6mm or larger. In other modalities, the distance T_s It can be between about 1mm and about 12mm or greater than about 12mm. Distance T₃ it can be measured at any point immediately adjacent to the projection and in the immediate surrounding area along the structure, except in the area immediately opposite the projection.

Projection 38 extends from structure 36 and includes a first side wall 58, a second side wall 60, and an end wall 62, all of which are formed by portions of rear surface 42. Furthermore, the external surfaces of the first side wall 58 and second side wall 60 are separated by the distance T_p, which defines a thickness of the projection 38. The distance T_p it can be measured at any point along the root of the projection. In an embodiment where the molded article is made of TPO, the distance T_p is greater than 25% of the distance T₂. In an alternative embodiment where the molded article is made of TPO or other thermoplastic materials, such as, for example, crystalline, semi-crystalline or amorphous materials, the distance T_p can be greater than 40% of the distance T_s. In still further embodiments and regardless of whether the molded article is made of TPO or some other suitable polymer material, the distance T_p is about 50% or more than the distance T₂, about 75% or greater than distance T_to, or about 100% or greater than the distance T₂, In still other modalities, the distance T_p is between about 100% to about 200% of the distance T_s, between around

200% and about 1000% of the distance T₂, or around

1000% or greater than distance T_s. Even though the distance T_pis greater than 25% or 405 of the distance T₃ (depending on the polymer of the molded article), the front surface 40 of the molded article 34 is a Class A surface. In particular, the portion 64 of the front surface 40 opposite to the projection 38 is a Class A surface that is visually free. of distortions qu4 are due to shrinkage of uneven material resulting from uneven cooling of the mass of thermoplastic material.

In one modality, the distance T_s is about 6 mm or greater and the distance T_p is greater than 25% or 40% of the distance T₃. In yet another embodiment, the distance T₃ is about 10 mm or greater and the distance T_p is greater than 25% of the distance T₂ or greater than 405 of the distance T_s.

In Figure 6, the rear wall 56 of structure 36 is mixed with the first side wall 58 and the second side wall 60 to define a mixed joint 66 between projection 38 and structure 36. In the embodiment shown, joint 66 it is a curved joint. As used herein, the term "mixed joint" is intended to mean a joint other than one at a 90 degree angle.

These mixed joints may include, for example, curved joints, joints that include fillets, joints at angles greater than 90 degrees, bevels, and joints that include multiple angled or flat portions. Mixed joints provide several benefits. For example, molded articles that have mixed gaskets have a distance T_smore uniform between the outer surface 50 and the inner surface 52 of the skin layer 44, that is, an even thickness of the skin layer 44, especially in the area of ​​the joint. The even skin layer reduces the risk of sink marks and other distortions during the manufacturing process.

Thermoplastic materials that can be used to make articles in accordance with the present invention can include, for example, all crystalline, semi-crystalline, and amorphous thermoplastics. In one embodiment, the thermoplastic material used is an 8TPO thermoplastic polyolefin, such as Solvay Sequel # 1980 or Sequel # 1715, commercially available from Solvay Engineered

Polymers. Additionally, the thermoplastic material may contain additives, such as fire retardants, elastomers, talc fillers, pigments, and fiber reinforcements.

Figure 7 illustrates another embodiment of an article 20 68. In this embodiment, the joint 70 mixed between the structure 72 and the projection 74 includes bevels 76. The ratio of the distance T_p between the first and second side walls 78 and 80 of the projection 74 at the distance

T₃ between the front and rear walls 82 and 84 of structure 72 is any of the relationships described above and the front surface 86 of molded article 68 is a Class A surface.

Figure 8 illustrates yet another embodiment of a molded article 88. Molded article 88 includes a non-uniform projection 90 in which second side wall 92 extends at an angle from structure 94. Article 88 includes a first mixed joint portion 95 and a second mixed joint portion 96. The first joint portion 95 is a rounded joint, similar to the rounded joint shown in Figure 6. The second molded joint portion includes an angled joint and has an angle that is greater than 90 degrees, and more particularly, about 170 degrees. The ratio of the distance T_p between the first and second side walls 98 and 92 of the projection 90 at the distance T_s between the front and rear walls 100 and 102 of structure 94 is any of the relationships described above and the front surface 104 of the molded article 88 is a Class A surface.

Figure 9 illustrates a further embodiment of molded article 106 having a Class A surface even though distance T_p between the first lateral wall 108 and the second lateral wall 110 of the projection 112 is of the order of about 10 times (1000%) greater than the distance T, between the front and rear walls 114 and 116 of the structure 118. Additionally, article 106 includes a first mixed joint portion 107 and a second portion

109 joint joint between structure 118 and projection

112. The first and second mixed joint portions 107 and 109 may be any of the various types of mixed joints described herein. In the embodiment shown, the first gasket portion 107 includes a bevel generally similar to that described above with respect to the

Figure 7. Referring to Figure 10, the second joint portion 109 includes a plurality of planes, or generally straight surfaces, that are connected at angles 113 greater than 90 degrees.

Figure 11 illustrates yet another embodiment of a molded article 115 having a front surface 117 of

Class A. Similar to the previous modalities, the relation of the distance T_p between the first lateral wall 119 and the second second wall 121 of the projection 123 in relation to the distance T_s between the front surface 125 and the rear surface 127 of structure 129 can be any of the relationships described above.

Additionally, article 115 includes a gasket 133 mixed. In this mode, in an area adjacent to the board

133, the rear surface 127 of structure 129 has relatively large rounded curved portions 137. The curved portions 137 of the posterior surface 127 intersects the first and second lateral walls 119 and 121 of the projection 123, respectively, at an angle 1321 that is greater than oO degrees, and preferably about 135 degrees, to form the joint 133 mixed.

As previously mentioned, several different factors of the molding process have an effect on whether sump marks are formed on the front surface of the structure. Without being limited to any theory, it is believed that the skin layer / foam layer construction and mixed joint configurations described herein significantly reduce the formation of sump marks and other distortions on the front surface of the structure, especially when The molded article includes a projection with a thickness that is greater than 25% or 40% of the thickness of the structure, depending on the material of the molded article.

Foam articles molded in accordance with the present disclosure can be manufactured using the following gas counter pressure injection foam injection molding process. The gas counter pressure can be used with an injection mold that has a specially sealed cavity to hold the injected counter pressure gas, which is mounted on a conventional injection molding machine that typically includes a resin hopper, a fusion injection unit, a clamping unit, and a counter pressurized gas source.

In one embodiment of the process, a conventional injection molding machine is fitted with a mold, the cavity of which has been specially sealed and prepared for gas injection and ventilation. For example, compressible seals are applied to the mold at the parting line and any other sliders, cores, lifters, ejector pins that penetrate the mold block, as needed, to prevent gas leakage from a sealed mold cavity that it has a pressure in excess of atmospheric pressure. The sealed mold cavity receives a pressurizing gas to increase the pressure within the mold cavity above atmospheric pressure.

Figure 12 illustrates one embodiment of a mold 122 having an upper portion 124 and a lower portion 126 that are detachable for opening and closing. When closed, the upper portion 124 and the lower portion 126 form a cavity 128. The cavity 128 includes a projection sub-cavity 130 and a structural sub-cavity 132. The subcavity

130 Projection and structure subcavity 132 are such that they form a shape configured to mold an article having a structure and a projection projecting from the structure. In particular, the shape of the cavity is configured so that the ratio of the thickness of the projection to that of the structure is within the scales described above, and in any case the thickness of the projection is greater than 25% or greater than 40% of the thickness of the structure. The cavity 130 also includes a mixed gasket portion 137 that is configured to mold an article having any of the mixed gaskets described herein.

Foaming of the thermoplastic resin can be accomplished either by mechanical gas injection or by adding a chemical foaming agent to the molding resin. In the mechanical method, the foaming gas, such as nitrogen or other appropriate gas, is introduced directly into the melt stream between the extruder barrel of the injection unit and the mold cavity so that the gas dissolves inside and is contained by the pressurized function. During one shot injection, the gas is allowed to expand into the mold cavity to make a foam part structure.

When a chemical foaming agent (CFA) is used, the chemical granules are mixed together with the thermoplastic material granules and the mixture is then fed into the machine through the hopper. The chemical foaming agent is reacted by the heat of the extruder, thereby generating gases within the molten thermoplastic material to create a thermoplastic / gas mixture. The chemical blowing agents can be any suitable chemical blowing agents, such as for example TRCEN40310ES, which is commercially available from TechmerPM, Cell-Span # 1000, which is commercially available from Phoenex Plastics, and Ampacet # 701039-H, which is commercially available. from Ampacet. In one embodiment, the amount of foaming agent added to the thermoplastic material is about 0.5% to 2% by weight, and in another embodiment, the foaming agent is about 1% by weight or greater.

In one embodiment, the blowing or foaming agent is added to the plastic material before the plastic material is melted in order to generate a plastic matrix having a number of voids. In alternative embodiments, the foaming agent can be added during or even after melting the plastic matrix. Foaming 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 core-shell combination of a blowing agent within a plastic shell, and / or a gas injected or dissolved under pressure towards the molten plastic.

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 the aforementioned Ampacet # 701039-H. ADC benefits from releasing nitrogen gas against carbon dioxide. Nitrogen gas has a relatively low molecular weight, making it more reactive. The best 20 nitrogen foaming properties means that the ADC and plastic master batch uses only 20% by weight. ADC vs. the most typical 50% by weight for 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 a relative finer cell structure than when no nucleating agent is used. The finer cell structure can result in a 1-15 percent absolute reduction in density of the plastic matrix relative to the density that can be achieved using talc, ADC, when it is finely dispersed in the molten plastic, it can produce a very fine cell structure including a microcellular 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 vary 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 scale 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 control the temperature of the machine used to mix molten plastic with the nucleating agent and the temperature of the mold. It is desirable that the nucleating agent be activated immediately before foaming is desired. Premature activation can result in loss of effectiveness of the nucleating agent. A gas generation scale can be independently selected from 165, 170, 180, or 200 ° C to 215, 200, 182, or 175 ° C. 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. Foaming agent concentrate or any other chemical blowing agent can be diluted in the plastic matrix (a drop ratio) on an independently selected scale of 0.1

1, 2, 5% by weight to 10, 20, 30% by weight. The plastic into which the foaming agent concentrate or any other chemical blowing agent mixes can be on the injection molding grade scale. As an example of injection molding grade properties, a melt index before the addition of additives and blowing agents can range from 5 to 100 gm / 10 min when measured by the method of

ASTM D1238 condition L.

After or as the thermoplastic material is transformed into a molten state and gases are dissolved therein, the mold is closed and pre-pressurized with a back pressure gas, such as nitrogen or dried ambient air. The mold is pre-pressurized to a scale that is independently determined and selected from 6215, 100, 1125 Pa (50, 80, 90 pee) to 1500, 1875, and 2500 Pa (120, 150 and

200 psi) to be appropriate to the application. In one embodiment, the mold is pressurized to around 10,545 kg / cm²(150 psi). As explained in more detail below, The back pressure gas will provide a pressure to the molten thermoplastic / gas mixture, which is greater than the vapor pressure of the foaming gas, to prevent the gas within the thermoplastic from fizzing or foaming the thermoplastic. as the mixture is injected into the mold cavity.

After the mold has been pressurized, the molten thermoplastic / gas mixture is injected or fired through a door and into the mold cavity. The injection pressure at which the thermoplastic / gas mixture shoots into the cavity is highly dependent on the cavity size and shape, and can range from about 21.09 to about 140.6 kg / cm² (about 300 psi to about 2000 psi). As the thermoplastic / gas mixture enters the cavity, the natural tendency is for the gas within the mixture to fizz, that is, form gas bubbles that foam the thermoplastic. However, gas back pressure within the mold suppresses gas effervescence, allowing a substantially solid outer skin layer to form around the outside of the thermoplastic / gas mixture. The substantially solid skin layer does not contain or have a very small number of cells.

As or after the thermoplastic / gas mixture has been injected, the previously pressurized back pressure gas is vented from the mold. Ventilation may occur as the thermoplastic / gas mixture is injected or ventilation may be delayed until after the mixture has been injected. In one embodiment, the back pressure gas vent is delayed for a period that lasts for more than about 1.5 seconds, 5 seconds, 7 seconds, or between about 1 second to about 10 seconds after the shot has been fully delivered to mold. In another embodiment, the ventilation delay is about 3 seconds to about 8 seconds. The ventilation delay is directly proportional to the thickness of the thin layer, that is, the longer the ventilation delay, the thicker the skin layer. Once the desired layer thickness has been achieved, the release or removal of gas from the pressurized mold during a period of depressurization may be a controlled process, such as through a 5 pressure release valve, or an uncontrolled process such as through atmospheric ventilation or into a recovery container. After the back pressure gas has been vented and the solid skin layer is formed, the gas fizzles to form cells within the thermoplastic material, creating a foam layer or inner core below the skin layer.

In addition to venting the back pressure gas, after the thermoplastic gas mixture has been injected, the gasket off or pressure rise is maintained on purpose at zero or very low pressure. In one mode the packing pressure outside is between about 0.0703 kg / cm² and around 5,273 kg / cm² (1 psi and around 75 psi). Even when the packing pressure outside is zero or very low, the thermoplastic / gas mixture continues to fill or pack out of the cavity due to the outward pressure applied by the gas in the fizzy gas inside the thermoplastic / gas mixture causing the mixture grows or enlarges. For carrying or packing out of the mold cavity.

After the thermoplastic material has cooled to a substantially hardened state, the mold is opened and the molded article is removed. The retention time scale 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 a skin and core structure distribution of desired foam. After a retention time in which the article fully solidifies, the mold can then be opened and the molded foam core article can be removed. The foam body has a skin layer and a foam core layer. Foam core layer thickness scale can be selected from greater than 1mm, 2mm, and 3mm to less than 50mm, 40mm, 30mm, 20mm, 10mm, and 5mm as dictated by design of part. The skin layer is thick enough to prevent cells in the foamed core layer from being visible or evident in the skin layer. The weight reduction scale can be independently selected from greater than 1, 2, and 3% by weight to 5, 7, 10, 20, and 30% by weight to be appropriate to the needs of the molded article.

The following examples provide different embodiments of foam injection molding methods that can be employed to manufacture the molded thermoplastic articles of the present invention. It should be understood that various other methods can also be used to manufacture such molded thermoplastic articles and that the molded thermoplastic articles of the present invention are not intended to be limited by the following Examples.

Examples

Example 1

A TPO resin, SOLVAY SEQUEL production number 1980HI, is used as the plastic resin matrix.

This resin is based on SEQUEL number 1715, an engineered polyolefin, which has a low coefficient of linear thermal expansion. The polyolefin is mixed with 1% by weight of the exothermic chemical forming agent supplied by AMPACETAQ number 701039-H, which comprises about 205 of a modified ADC.

Example 2

PHOENIX PLASTICS provides a master batch formulation using a polyolefin. CELL-SPAN 1000 uses a polyolefin polymer formulated with supramolecular chemistries that allow the formulation of directional hydrogen bonds that emulate stronger covalent bonds. The foaming agent used in the CELL-SPAN product line includes the function of the nucleating agent. The drop ratio is 1%, but it could be as little as 0.25 by weight. CELL-SPAN 1000 is an endothermic chemical foaming agent. It is intended to provide a small cell structure rather than a fine cell diameter structure.

Example 3

TPOI resin blends WSOLVAN SEQUEL production number 1980HI with 1% TECHMER TECHSPERSE type

TRCEN40310ES to form a master batch.

Example 4

TPO resin from SOLVGAY SEQUEL production number 1980HI, which is derived from SEQUEL number 1715, comprises the control material

Example 5

Items in this examples, 15.24 cm x 20.32 cm (six inch by eight inch (310 cm) plates² (48 in²)) are molded from materials used in Example 1, 2, 3 and 4 with conditions and results provided in Table 1

Table 1

<td></td><td>TPO RESIN</td><td>TECHMER</td><td>FPHOENIX</td><td>AMPACET</td>

<td></td><td>Solvay</td><td>TRCEN</td><td>PLASTICS</td><td># 701039-H</td>

<td></td><td>Sequel</td><td>4030ES</td><td>CELL-SPAN</td><td></td>

<td></td><td># 1980 HI (Sequel # 1715</td><td></td><td> #1000</td><td></td>

<td>Type y</td><td>399 toin</td><td>300 ton</td><td>300 ton</td><td>300 ton</td>

<td>size of press</td><td>Van dorn</td><td>Van dorn</td><td>Van dorn</td><td>Van dorn</td>

<td>Force of</td><td> 300</td><td> 75</td><td> 75</td><td> 75</td>

<td>Subjection</td><td>tons</td><td>tons</td><td>tons</td><td>tons</td>

<td>Temperature printed</td><td>130 F</td><td>110 F</td><td>145 F Cavity/ 135 core</td><td>125 F</td>

<td>Temperature</td><td> 400/410/</td><td> 400/410/</td><td> 400/410/</td><td> 400/410/</td>

<td>of fusion by Zone</td><td>420/400 F</td><td>410/410 F</td><td>420/410 F</td><td>420/410 F</td>

<td>Size of Shooting</td><td>6.2 in</td><td>5.6 in</td><td>5.4 in</td><td>6.0 in</td>

<td>Time of cycle</td><td>90 sec</td><td>80 sec</td><td>80 sec</td><td>120 sec</td>

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

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

<td>Increase Pressure</td><td> 2000 / 75</td><td> 2000 ¡ 177</td><td> 2000 / 322</td><td> 2000 / 180</td>

<td>Pressure of</td><td>400 psi</td><td>25 psi</td><td>5 psi</td><td>50 psi</td>

<td>Retention</td><td></td><td></td><td></td><td></td>

<td>Time of</td><td>15 sec</td><td>20 sec</td><td>5 sec</td><td>30 sec</td>

<td>Retention</td><td></td><td></td><td></td><td></td>

<td>Pressure</td><td>80 pee</td><td>80 psi</td><td>100 psi</td><td>100 psi</td>

<td>Later</td><td></td><td></td><td></td><td></td>

<td>Time of</td><td>60 sec</td><td>50 sec</td><td>50 sec</td><td>55 sec</td>

<td>Cured</td><td></td><td></td><td></td><td></td>

<td>Tor RPM</td><td> 150</td><td> 150</td><td> 175</td><td> 175</td>

<td>nillo</td><td></td><td></td><td></td><td></td>

<td>Control of</td><td>good</td><td>good</td><td>good</td><td>rare</td>

<td>Fusion</td><td></td><td></td><td></td><td></td>

<td>problems</td><td>none</td><td>none</td><td>none</td><td>Trend</td>

<td>Part</td><td></td><td></td><td></td><td>Post-</td>

<td></td><td></td><td></td><td></td><td>blown</td>

<td>Weight of</td><td></td><td></td><td></td><td></td>

<td>Part</td><td></td><td></td><td></td><td></td>

<td>5.0 mm</td><td>0.360 Ib</td><td>0, .335 Ib</td><td>0.355 Ib</td><td>0.356 Ib</td>

<td>% Change</td><td> 0</td><td> -7,00%</td><td> -1.14%</td><td> -1.12%</td>

<td>7.0 mm</td><td>0.477 Ib</td><td>0.447 Ib</td><td>0.465 Ib</td><td>0.466 Ib</td>

<td>% Change</td><td> 0</td><td> -6.3%</td><td> -2.5%</td><td> -2.30%</td>

With the use of chemical foaming agent, the clamping force is reduced from 300 tons of force (82670 kN) and tons of force (667 kN) or up to around 75%. The shot size is reduced on a scale of 3% by weight to 13% by weight when a foaming agent was added to the TPO relative to the original TPO control. However, the firing time increases to 10.59 seconds and scales from 1.34 to

10.59 seconds. As a consequence, the cycle time also increases by 30 seconds or up to 33%. Gas back pressure ranges from 349-1034 kPa (50 to 150 psi). It should be understood that additional combinations of shot size, shot speed, and gas back pressure could be used depending on the resulting product and its specifications.

In this example set, the back pressure gas is removed over a period of about 3 seconds. The retention time contributing to the cycle time 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 parts exhibit a reduction in weight of about

1% to about 7%.

With the material of Example 1.1 it is surprising that additional gas back pressure is necessary to make the skin thick enough to hide the cell structure and provide a Class A surface. The increased back pressure varies from a 25% increase to as much as 300% increase relative to other chemically blown 5 TPOs. The foaming agent shows a surprising drastic difference in chemical foaming agent reactivity when Example 1 is used relative to the

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 relatively thick skin desired for durability and the foam relatively uniformly distributed in my cell diameter and fine. The cells are desirably isotropic in shape, too.

Example 6

A foam expansion test is performed using the material from Example 1. In order to determine the limit of the foam's expandability, a 5.0mm cavity is filled with enough resin and foam mix to provide an acceptable plate. The same firing volume is then injected into a 7.0 mm cavity and allowed to foam to its natural limits in the presence of gas back pressure of 1034 kPOa (150 pis). If the resulting plate is of acceptable quality the shot size adjusts to the point where the foam reaches the minimum density and still provides an acceptable plate. If the resulting plate is not acceptable in terms of quality because it is a short shot, the shot size is adjusted to the point where the foam reaches a minimum density in acceptable plate yields. The degree of free elevation change is then calculated by comparing the trigger deviation to the original setting. The results are shown in Table 2.

Table 2

Test Process

Calculated shot size for 5.0mm plate = 6.0 / 12) = 2.5inch hit

Calculated firing time for 5.0mm plate = (10.6 /

12) 5 = 4.42 sec. Shot +

Gas back pressure and all other machine settings remain as before

<td>Test Results</td><td>Plate Condition</td>

<td>5.0mm plate 0.356 weight</td><td>Complete part with surface</td>

<td>Ib at 2.5 inch shot</td><td>smooth, burr-free</td>

<td>7.0mm plate 0.361 weight</td><td>Incomplete Part Filling</td>

<td>Ib at 2.6 inch shot</td><td>with many holes in front and posterior part</td>

7.0mm plate 0.457 weight

Ib at 2.7 inch shot

7.0mm plate 0.387 weight

Ib at 2.8 inch shot

7.0mm plate weight

0.0.403 Ib at 2.9 inch shot

7.0mm plate 0.419 weight

Ib at 3.0 inch shot

7.0mm plate 0.423 weight

Ib at 3.1 inch shot

7.0mm plate 0.431 weight

Ib at 3.2 inch shot

7.0 mm plate 0.471 Ib at 3.3 inch shot

Part incomplete filling with many front and rear part holes

Fills with 1.13 in surface bevel 69 holes in the middle

Part filled with 0.87 in surface bevel, 70 holes in the middle

Part filled with 0.50 in bevel

<td colspan="2">superficial,</td><td> 63</td><td>holes</td><td>in</td>

<td>means, medium</td><td></td><td></td><td></td><td></td>

<td>Part</td><td>full</td><td>with</td><td> 0.038</td><td>in</td>

<td>bezel</td><td colspan="2">superficial,</td><td colspan="2">57 holes</td>

<td colspan="2">in the middle</td><td></td><td></td><td></td>

<td>Part</td><td>full</td><td>without</td><td>bezel,</td><td> 43</td>

holes in the middle of the surface

Full part, smooth surface, no burr

In order to achieve a fully foamed plate of

Having a good surface area after gas back pressure of 5.0mm, the amount of cavity fill is minimized to the point where the foam cell structure is maximized. At the point where the cell structure is maximized, the parts should still have good surface appearance and part integrity. As a result of this effort to minimize, the additional cell expansion power is reduced to the point where introducing that same shot size into a larger cavity provides no additional expansion. Results include detection of quality problems associated with a short-shot part.

Table 3

<td>Fillet</td><td colspan="2">Material</td><td colspan="2">Outcome</td>

<td>No fillet</td><td>Example</td><td> 4</td><td colspan="2">Sink marks</td>

<td></td><td></td><td></td><td colspan="2">on a surface</td>

<td></td><td></td><td></td><td>side A</td><td></td>

<td>No fillet</td><td>Example</td><td> 1</td><td>Fewer brands</td><td>of</td>

<td></td><td></td><td></td><td>sink</td><td>in</td>

<td></td><td></td><td></td><td>surface of</td><td>side</td>

<td></td><td></td><td></td><td colspan="2">Because Example 1 /</td>

<td></td><td></td><td></td><td>no proof</td><td>of</td>

<td></td><td></td><td></td><td>fillet</td><td></td>

<td>Fillet</td><td>Example</td><td> 4</td><td>Fewer brands</td><td>of</td>

<td></td><td></td><td></td><td>sink in</td><td>the</td>

<td></td><td></td><td></td><td>surface of</td><td>side</td>

<td></td><td></td><td>Because Example 1 / no proof of fillet</td>

<td>Fillet</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 fillets on the ribs and projections on the B side of the mold surface, results in the desired Class A surface on a relatively large article.

While this invention has been described with reference to certain illustrative aspects, it will be understood that this description will not be considered in a limiting sense.

Rather, various changes and modifications can be made to the illustrative embodiments without departing from the true spirit and scope of the invention, as defined by the following claims. Furthermore, it will be appreciated that any of these changes and modifications will be recognized by those skilled in the art as equivalent to one or more elements of the following claims, and will be covered by such claims to the fullest extent permitted by law.