Method of forming a protective article and 3D printer

Abstract

A method of forming a protective article includes feeding pellets (2) of different and immiscible first and second polymers and a blowing agent to an extruder (4) having a screw (6). The polymer is melted and mixed in the extruder screw (6). The mixture is extruded and ejected through a 3D printing nozzle (7) to create a pressure drop, thereby foaming the at least one polymer. An article is then printed from the foamed mixture. A 3D printer has two hoppers (1, 11) for feeding pellets to an extruder (4) having a screw (6).

Description

[0001] The present invention is directed to a method of forming a protective article.

[0002] In particular, the present invention relates to a method of forming an impact absorbing pad. Such a pad can be used in any application where impact protection is required. This can be used, for example, to protect electronic items such as phones, tablets and laptops, or can be used in protective clothing, such as industrial clothing or sportswear in applications such as cycling and motorcycling (e.g. protective gloves, helmets, jackets, pants, etc.). The present invention also relates to a 3D printer for making these pads and other articles.

[0003] Impact protection pads have conflicting requirements. They need to provide a high level of impact protection while still being light and flexible enough to allow them to be worn comfortably. Known techniques for forming impact absorbing pads include, for example, using foaming techniques or injection molding techniques. The different layers can be manufactured by different techniques to provide a layered structure with enhanced impact absorbing characteristics.

[0004] KR102355157 discloses a 3D printing technique for manufacturing various articles. This uses foamable and non-foamable filaments discharged from the same nozzle to produce a layered structure.

[0005] The present invention aims to improve the prior art.

[0006] According to a first aspect of the present invention, there is provided a method of forming a protective article according to claim 1 .

[0007] The present invention relies on the use of at least two immiscible or substantially immiscible polymers. However, from a processing perspective, immiscible polymers are compatible because they are able to form a consistent or substantially consistent polymer melt. In the present invention, immiscible polymer pellets are melted and extruded through a 3D printing nozzle along with a blowing agent or blowing agents. Upon exiting the 3D printing nozzle, the uniform polymer melt experiences a pressure drop, causing the polymer melt to expand and form a foam, which is then used to print the protective article.

[0008] Thus, the polymers used in the present invention are immiscible or substantially immiscible from a chemical standpoint, but compatible from a processing standpoint.

[0009] The present invention requires that the foam formed comprises (at least) two phases - a shrinkable phase and an elastic phase. The (at least) two phases enable the formed foam and protective article to achieve impact protection properties.

[0010] The first polymer and the second polymer typically have different (final) properties, such as different properties selected from one or more of density (e.g. measured according to ISO60), compression set (e.g. measured according to ISO1856), elasticity (e.g. measured according to ISO8307), storage and / or loss modulus (e.g. measured according to ISO6721). Preferably, the first polymer comprises or consists of a thermoplastic elastomer, and the second polymer preferably comprises or consists of a thermoplastic engineering polymer. Typically, the second polymer, such as a thermoplastic engineering polymer, will be harder, more rigid and have a higher dimensional stability than the first polymer, such as a thermoplastic elastomer.

[0011] Hardness may be determined in a conventional manner, for example according to ISO 1923. The measurement is usually made using a durometer, and may be expressed as a number on a suitable Shore scale (eg Shore OO, Shore A or Shore D).

[0012] The present invention provides a number of benefits. The final product is a foamed article formed from (at least) two different polymers, namely a first polymer and a second polymer. The first polymer is preferably relatively soft and resilient, so foams of the first polymer are well suited to absorbing low energy impacts and providing flexibility to the article. The second polymer preferably produces a harder foam, which provides enhanced high energy absorption because high energy impacts collapse the cells in the hard foam during use. The fact that the article, such as a pad, is 3D printed allows complex shapes to be formed in a single processing step.

[0013] The present invention provides significant advantages over KR102355157, which uses resin filaments driven through a nozzle. These filaments must be produced in a separate manufacturing step. In contrast, the present invention produces articles directly from pellets, thereby providing significant cost savings. Techniques using filaments can only be used with relatively hard materials, which limits their use. Filament technology is not intended to provide significant mixing of resins because the filaments are extruded side by side from the nozzle. In contrast, in the present invention, the pellets are mixed in the extruder screw so that the final product is substantially different from the product produced in KR102355157.

[0014] The relative amounts of the two polymers can remain fixed throughout the process and can be adjusted to meet the requirements of the article. However, by changing the amount of one or both polymers fed to the extruder and / or the amount of blowing agent, the method can be used to produce protective articles with properties that vary in different parts of the article. This is particularly useful for protective articles, where a high degree of protection can be concentrated in areas that are more likely to be subject to high impact. Higher amounts of the second polymer can be concentrated in these areas. These can be inserted into other areas with higher concentrations of the first polymer, which provides greater flexibility to the article.

[0015] The blowing agent can be selected to foam only one polymer, thereby forming a final material having foamed and unfoamed polymers. That is, foaming can occur in the first polymer or the second polymer. However, more preferably, the blowing agent foams both the first polymer and the second polymer.

[0016] The method may also include the use of one or more additional polymers having properties different from the first and second polymers. This may be used simultaneously with the first and second polymers, or one of the first and second polymers may be gradually removed prior to the introduction of the additional polymer. Four or more polymers may be used with the same technique. If desired, the blowing agent may be changed during the polymer change. The blowing agent may be selected to foam the one or more additional polymers in the same manner as the first and / or second polymers are foamed.

[0017] The polymer and blowing agent can be fed to the extruder from a single hopper. This represents the simplest form of the process. In this case, the properties of the article can be varied by changing the materials and / or the relative amounts of the materials in the hopper.

[0018] However, for greater flexibility, more than one hopper may be used, and the hoppers feed different materials to the extruder. This makes it easier to change the composition of the finished article during the printing process, as the feeds from the different hoppers can be varied to provide the desired blend. There may be one hopper for each different polymer, and one hopper for each different blowing agent, for maximum flexibility. Alternatively, one or more polymers and / or blowing agents may be combined in a single hopper, if desired.

[0019] According to a second aspect of the present invention, a 3D printer according to claim 9 is provided.

[0020] This provides a printer for producing 3D printed articles from a mixture of materials. When the printer uses a hopper for receiving pellets, it provides a simple and versatile way to produce a variety of 3D printing materials. Since it does not rely on filaments fed to the nozzle, it can be used with a variety of materials, especially softer materials that are not suitable for filament processes. The use of separate hoppers, each with its own conveyor, allows the properties of the materials to be changed during the printing process, and the presence of the extruder screw ensures that the materials are well mixed at the nozzle. In addition, if different materials are fed from the same hopper, there may be problems with material stratification in the hopper if the materials have different densities and / or particle sizes. This avoids the problem of them being fed from different hoppers because the pellets of different materials do not meet until they reach the extruder.

[0021] The printer may be used to form the foamed protective article of the first aspect of the invention, or to form any other article (foamed or non-foamed) requiring a well-mixed mixture of materials.

[0022] The first and second conveyors may be in the form of gravity feeds or conveyor belts, but are more preferably screw feeders.

[0023] Examples of the method and 3D printer according to the present invention will now be described with reference to the accompanying drawings, in which:

[0024] Figure 1 is a schematic diagram of the first method; and

[0025] Figure 2 is a similar schematic diagram of a second method and a 3D printer according to the second aspect of the present invention.

[0026] like Figure 1 As shown, a hopper 1 is filled with a premix 2 comprising pellets of a first polymer and a second polymer and a blowing agent.

[0027] This is initially formed as a premixed dry blend. There may be two or more polymers in the blend. At least one of the polymers, subsequently referred to as the first polymer, is suitable for forming a soft, resilient foam. The second polymer is suitable for forming a hard, collapsible foam. For processing purposes the polymers should be compatible, meaning that they need to form a blend that can be consistently extruded.

[0028] Preferred blends use a first polymer that is or includes a styrene ethylene butylene styrene (SEBS) thermoplastic elastomer (TPE) or a SEBS-based TPE. The second polymer is or includes high impact polystyrene (HIPS). Alternative blends may include, for example, combinations of EVA-based elastomers with HIPS or polyolefins, TPU with polycarbonate or PET.

[0029] Various blends of up to 100% of each of the first polymer or the second polymer may be used and provide the article with foams useful in different impact scenarios.

[0030] Typically a blowing agent is added to the dry blend in the hopper. The blowing agent (also referred to as a foaming agent) can be chemical, physical, or a combination of both. The concentration of the blowing agent can be adjusted and optimized to achieve a target foam density or article weight. In one embodiment, a chemical blowing agent can be added at a concentration of 1 to 2 wt.% (e.g., 1.5 wt.%). Alternatively or in combination, a physical blowing agent can vary, for example, between 5 and 15 wt.%, depending on the desired parts by weight.

[0031] Examples of conventional chemical blowing agents include one or more of sodium bicarbonate, citric acid, azodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide), 5-phenyltetrazole, and p-toluenesulfonylsemicarbazide. Typically, these substances decompose during the foaming process to produce nitrogen, carbon dioxide, or water.

[0032] Examples of conventional physical blowing agents include one or more of water, carbon dioxide, nitrogen, or hydrocarbons such as pentane. These substances can be added directly to the polymer melt. Another example of a physical blowing agent is a gas-containing expandable microsphere, which can be added to the polymer, for example, as a dry blend.

[0033] The dry mixture is then fed by a conveyor screw 3 into an extruder 4 mounted to the frame of the 3D printer. The dry blend is heated by a heater 5 in the extruder and propelled along the extruder toward the 3D printing nozzle 7 by an auger screw 6. The molten polymer and blowing agent exit the nozzle as a combined jet 8. The sudden pressure drop that occurs as the polymer exits the nozzle causes the polymer to foam. The extruded material falls onto the print bed 9, where the foaming can optionally continue for a short time in a controlled manner.

[0034] The method according to the present invention allows considerable variation in the final product depending on the choice of polymer and blowing agent. For example, the blowing agent can be selected so that it only foams the first polymer, resulting in a soft foamed polymer with a hard unfoamed polymer. In contrast, if the blowing agent only foams the second polymer, this will form a hard foamed polymer with a soft unfoamed polymer. If the blowing agent is selected to foam both polymers, this will result in an article having a mixture of a hard foamed polymer and a soft foamed polymer.

[0035] Variation of the ratio of the two polymers can produce a material with variable properties suitable for different impact protection situations. Figure 2 An apparatus particularly suitable for doing this is shown in . In this case, a first hopper 1 is provided with a premixed dry blend of polymers. A blowing agent 10 is provided in a separate hopper 11. Separate conveyor screws 12, 13 control the feed from the hoppers 1, 11 into the extruder 3 which is then operated as described above. Varying the premixed polymers and blowing agents allows different material properties to be achieved in different regions within the same article.

[0036] Instead of the blowing agent in the second hopper 11, one polymer may be provided, while the other polymer is provided in the first hopper. The blowing agent may also be provided separately via a third hopper.

[0037] Varying the feed rates of polymer and foaming agent during the printing process can produce materials suitable for different impact scenarios. A larger proportion of the harder second polymer will produce a product with lower overall flexibility but more suitable for high energy impact absorption. Conversely, a higher proportion of foam formed from the softer first polymer will result in a product that is more flexible overall but limited to low energy impacts. Generally, a material combination dominated by the softer foam will be suitable for multiple impact protection applications because the soft product provides resilience. A material dominated by the harder foam may be suitable for single use impact protection applications.

[0038] Using this approach, a product can be created where harder foams predominate in areas more likely to be subject to high impact, while softer foams can be used in other areas, making the overall product more conformable.

[0039] Additional components may be incorporated into the product in the same hopper and feeder or by, for example, adding additional hoppers and feeders.

[0040] Conventional additives may be added to the first polymer and / or the second polymer, and may also be added to any additional polymers that are present.

[0041] If a different product is formed in the 3D printer, the foaming agent may be omitted.

Claims

1. A method of forming a protective article, the method comprising the steps of: feeding pellets of a first polymer into an extruder; feeding pellets of a second polymer different from and immiscible with the first polymer to the extruder; feeding a blowing agent into the extruder; melting the polymer; mixing the polymers in an extruder screw; extruding the mixture of the polymer and the blowing agent through a 3D printing nozzle; ejecting the mixture from the 3D printing nozzle to generate a pressure drop, thereby foaming at least one of the polymers; and An article printed from the foamed mixture is formed.

2. The method according to claim 1, wherein: The second polymer is harder than the first polymer.

3. The method of claim 1 according to claim 2, further comprising: The amount of one or both polymers and / or the amount of blowing agent fed to the extruder was varied.

4. A method according to any preceding claim, wherein: The blowing agent causes two of the polymers to foam.

5. A method according to any preceding claim, further comprising: One or more additional polymers are fed to the extruder.

6. The method according to claim 5, wherein: Each or all of the one or more additional polymers are different from and / or immiscible with the first polymer and / or the second polymer.

7. A method according to any preceding claim, wherein: The polymer and blowing agent are fed to the extruder from a single hopper.

8. The method according to any one of claims 1 to 6, wherein: More than one hopper is used, and the hoppers feed different materials to the extruder.

9. A 3D printer, comprising: A first hopper, the first hopper is used for pellets of a first material: A second hopper, the second hopper is used for pellets of a second material: An extruder, the extruder comprising an extruder screw: a first conveyor for conveying pellets of the first material from the first hopper to the extruder; a second conveyor for conveying pellets of the second material from the second hopper to the extruder; a heater for melting the first material and the second material in the extruder; A 3D printing nozzle is located downstream of the extruder screw so that, in use, the extruder screw ejects melted and mixed material from the 3D printing nozzle.

10. The 3D printer according to claim 9, wherein: At least one of the first conveyor and the second conveyor is a screw feeder.

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