Hollow body for toy applications and method for the production thereof

Abstract

The invention relates to a hollow body for toy applications which is chlorine-free and plasticizer-free and consists of at least 50% by weight of bio-based material, wherein the hollow body for toy applications has mutually different wall thicknesses in different regions and at least a portion of the hollow body has a hardness of < 75 Shore A.

Description

[0001] Hollow bodies for toy applications and methods for their manufacture

[0002] The present invention relates to a hollow body for toy applications produced according to a new method and to a method for its production, wherein the hollow body is, for example, a doll body part, in particular a doll head, which is characterized in particular by an improved haptic feel compared to previously known dolls or doll body parts, as well as an appealing appearance, which contribute to a more lifelike overall impression.

[0003] It has long been known from the prior art to produce hollow bodies such as dolls from cellophane using extrusion blow molding. In this process, thermoplastic materials are formed into a tubular preform and then blown into a hollow body in a closed, two-part mold. However, the resulting products exhibited very high stiffness and high flammability, which limited product safety. Since the mid-20th century, dolls based on PVC have been developed and further optimized. Due to plastisol technology, in which plasticizers gel in a thermal process, the hardness can be adjusted. However, this method has several disadvantages. First, the process leads to largely homogeneous wall thicknesses in large geometric sections, which do not allow for variation in mechanical properties across the molded part surface.The wall thickness cannot be precisely controlled and tailored to specific requirements. Furthermore, rotational molding results in increased wall thickness in areas where geometric elements protrude from the surface. Additionally, the mechanical properties of such gelled PVC plastisol materials are inferior to many thermoplastic materials in terms of strength, necessitating a greater wall thickness to adequately withstand tensile, tensile, and impact forces and ensure sufficient product safety. Finally, PVC is subject to considerable debate due to its harsh chemical manufacturing process, flammability, and carcinogenicity. The plasticizers used in the plastisol process also pose health risks, as they can enter the body through saliva or skin contact and are harmful to the liver and kidneys.Nevertheless, plasticizers are frequently used in toys because they are inexpensive and give the material desirable properties. However, this is particularly concerning in the case of dolls, as children touch them intensively with their hands and often their lips while playing, which further promotes the release of plasticizers through saliva and sweat.

[0004] Particularly with regard to the manufacture of doll heads, the existing state of the art is very extensive. For example, US 6,217,407 B1 and DE 1 038 964 describe the manufacture of doll heads obtained by joining two separate parts, with the resulting seam being covered by hair. Doll heads manufactured by injection molding are described, for example, in US 2,093,909 A and US 7037455.

[0005] WO 2008 / 137736 A1 describes the manufacture of two-part doll heads, wherein the two parts have coordinated areas for joining and, when joined, define a cavity between them.

[0006] DE 100 31 362 A1 and DE 199 54 239 A1 each describe a toy, in particular a doll, which, due to the possibility of oral contact, is made of plasticizer-free plastic, preferably polyurethane. The hardness of the molded parts is in the range between 40 and 90 Shore A, preferably 70 Shore A, and a uniform wall thickness distribution is desired.

[0007] DE 10031 362 A1 describes a plasticizable plastic material which contains a proportion of at least one natural polymer selected from polylactide, polyhydroxyalkanoates, cellulose esters, lignin and starch, as well as a polyamide based on dimer fatty acids.

[0008] Object of the invention

[0009] The object of the present invention is to provide an alternative method for manufacturing a hollow body for toy applications, in particular a doll body part and preferably a doll head, which overcomes the aforementioned disadvantages known from the prior art and is characterized in particular by the health safety of the doll body part obtained and by its appealing feel and appearance.

[0010] General description of the invention

[0011] The invention solves this problem with the features of the claims and in particular with a hollow body for toy applications which is chlorine-free, optionally halogen-free, and free of plasticizers and consists of at least 50 wt.% bio-based material, wherein the hollow body has different wall thicknesses in different areas and at least a part of the hollow body has a hardness of < 75 Shore A.

[0012] Bio-based thermoplastic polyurethane (TPU) or bio-based thermoplastic elastomer (TPE) are possible bio-based materials that are characterized by high flexibility and mechanical strength and are suitable for thin-walled structures with high perceived softness.

[0013] According to one embodiment, the bio-based material of which the hollow body for toy applications consists to at least 50 wt.% is preferably a biodegradable polymer according to DIN EN ISO 13432, in particular selected from the group comprising or consisting of polylactide, polyhydroxyalkanoate, thermoplastic starch, starch blends, polycaprolactones, polybutylene adipate terephthalate, polybutylene succinate, polybutylene succinate adipate, polysaccharide derivatives, lignin derivatives, protein derivatives and mixtures thereof.

[0014] Harmless additives for composting according to DIN EN ISO 13432, such as polyvinyl acetate or vinyl acetate-ethylene vinyl versate copolymer, can be added to the bio-based material.

[0015] In another embodiment, the bio-based material from which the hollow body for toy applications consists to at least 50 wt.% is a non-biodegradable thermoplastic polyurethane (TPU).

[0016] The mutagenicity and toxicity of aromatic isocyanates is considered a major disadvantage, especially for highly reactive toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI) with their conjugated benzene rings.

[0017] Despite the generally accepted biocompatibility of PU, some safety concerns remain regarding each step of PU synthesis, such as:

[0018] a) the toxic polyisocyanate synthesis pathway, in which, for example, phosgene, a highly toxic gas at room temperature, is used,

[0019] b) the impurities in the manufactured polyols and polyisocyanates, and

[0020] c) the remaining unreacted polyisocyanate monomers, catalysts and / or additives in the final product.

[0021] Therefore, the TPU polymers according to the invention will be completely safe for use in accordance with DIN EN 71-3 and DIN EN 71-9. Aromatic-free starting materials are preferably used, especially in the area of ​​isocyanates. Examples include hexamethylene diisocyanate (HMDI) or isophorone diisocyanate (IPDI).

[0022] The ingredients comply with DIN 71 regulations, specifically regarding:

[0023] DIN EN 71-3:

[0024] Testing for the presence of harmful heavy metals such as lead, mercury, cadmium and chromium, as these can pose health risks to children.

[0025] DIN EN 71-9:

[0026] The standard applies to toys or parts thereof that, during foreseeable or intended use, come into prolonged contact with the skin, are likely to be put in the mouth, can be ingested orally, can come into contact with the eyes, or contain organic compounds that could be inhaled. Although the standard has been withdrawn, it includes some chemical requirements not covered by other standards.

[0027] Preferably, the hollow body according to the invention for toy applications consists of more than 50 wt.% bio-based material, in particular at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.%, at least 95 wt.% or at least 99 wt.%.

[0028] According to the invention, the hollow body for toy applications has different wall thicknesses in different areas, with a portion or the entire hollow body having a hardness of < 75 Shore A. This was determined on a sample with a minimum thickness of 6 mm, which was not subjected to any mechanical stress, using the ZwickRoell 3114 / 15 device in accordance with DIN ISO 48-4:2021-02 (Elastomers or thermoplastic elastomers - Determination of hardness - Part 4: Indentation hardness by durometer method (Shore hardness)) (ISO 48-4:2018). A hardness of < 75 Shore A is not yet found in the prior art for bio-based materials; such materials are limited to hardness levels > 85 Shore A.Softer materials can generally only be achieved through the use of plasticizers. However, a perceived softness, which can be created by thin wall thicknesses, cannot be achieved with plasticized systems because the mechanical strength of the plasticized materials is not sufficiently high. Furthermore, as mentioned earlier, the active ingredients also migrate out of these materials.

[0029] It is very surprising that the present invention enables the provision of a hollow body for toy applications with a localized hardness of < 75 Shore A, even though it consists of at least 50 wt.% bio-based material. Furthermore, according to the invention, a different perceived softness is achieved by the hollow body having different wall thicknesses in different areas, with areas of thinner wall thickness being perceived as softer than areas of thicker wall thickness. The hollow body therefore has deliberately set, different wall thicknesses in different areas. Preferably, the hollow body has a first area with a first wall thickness and a second area with a second wall thickness, wherein the wall thickness in the first area is at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, or at least 60% less than in the second area.Optionally, there are also multiple first areas with the first wall thickness and / or multiple second areas with the second wall thickness.

[0030] According to a preferred embodiment, the hollow body according to the invention for toy applications is a doll body part and, in particular, a doll head, preferably a one-piece doll head. This preferably has a thinner wall in the area of ​​the lips than in the area of ​​the eyes, cheeks and / or nose, so that the doll's lips are perceived as softer to the touch than the eyes, cheeks and / or nose.

[0031] Alternatively, the hollow body according to the invention for toy applications can also be a toy animal or a part thereof.

[0032] The invention also relates to a method for manufacturing a hollow body for toy applications, comprising the following steps:

[0033] Providing a material that is chlorine-free, plasticizer-free and consists of at least 50% by weight of bio-based material; and

[0034] Forming the chlorine-free, plasticizer-free material, consisting of at least 50 wt% bio-based material, into a hollow body for toy applications, which has different wall thicknesses in different areas, wherein at least a part of the hollow body has a hardness of < 75 Shore A, determined on a sample with a minimum thickness of 6 mm, which is not subjected to any mechanical stress, using the ZwickRoell 3114 / 15 apparatus according to the standard DIN ISO 48-4:2021-02 (Elastomers or thermoplastic elastomers - Determination of hardness - Part 4: Indentation hardness by durometer method (Shore hardness) (ISO 48-4:2018).

[0035] According to one embodiment, the method according to the invention comprises a step of providing a 3D support structure which is arranged in an injection mold, wherein the shortest distance between the 3D support structure and the nearest inner wall of the injection mold is different at various locations of the 3D support structure, and wherein the forming of the chlorine-free material consisting of at least 50 wt.% bio-based material into a hollow body for toy applications includes overmolding the 3D support structure arranged in the injection mold with the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material, such that this fills the cavity between the 3D support structure and the injection mold, and wherein the forming of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material-% consisting of bio-based material also includes solidifying this material in the injection mold to form a hollow body for toy applications.

[0036] The 3D support structure used in the inventive method is preferably produced by 3D printing, preferably using a water-soluble or heat-soluble material. Heat-soluble materials are meltable at a temperature below the melting point of the material from which the hollow body for toy applications is formed, in order to prevent deformation or even destruction of the final product. This is because, after the material from which the hollow body for toy applications is formed has solidified in the space between the inner walls of the injection mold and the 3D support structure, the latter is dissolved again by melting through the application of heat, leaving behind the hollow body, which is preferably a doll body part and particularly preferably a doll head.

[0037] The 3D support structure is preferably arranged in the injection mold such that it is held in the desired position by a locking mandrel. The 3D support structure is then overmolded. The parting line of the injection mold is preferably curved and, if the hollow body is a doll's head for toy applications, corresponds to the doll's hairline. The parting line can be concealed, particularly by sewing in hair, but also by coloring or painting, so that it is no longer visible on the finished doll's head.

[0038] By selecting a suitable 3D support structure, this embodiment of the inventive method makes it possible to selectively adjust the material thickness of the hollow body for toy applications in any desired area. If the hollow body produced in the inventive method for toy applications is a doll's head, the smallest possible distance from the lips, which are formed as a negative mold in the injection mold, to the 3D support structure is preferably smaller than the smallest possible distance from other parts of the face, which are formed as negative molds in the injection mold, to the 3D support structure. In this way, the wall thickness of the doll's head in the area of ​​the lips is less than the wall thickness in other parts of the face, for example, in the area of ​​the eyes, cheeks, and / or nose.

[0039] In an alternative embodiment of the method according to the invention, the shaping of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material is carried out by means of blow molding, wherein the blow molding is selected from the group comprising injection blow molding and extrusion blow molding, and wherein the shaping of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material further includes solidifying this material in a mold to form a hollow body for toy applications.

[0040] In blow molding, a plastic tube is inflated and takes on a precise, predefined hollow shape within a metal mold. A subtype of blow molding is injection blow molding. This is a hybrid process between traditional injection molding and blow molding. In injection blow molding, plastic is first melted and injected into a metal rod containing a mold, creating a temporary blow mold blank. This blank is then inserted into another mold that corresponds to the shape of the final product. Using injected compressed air, the blank is shaped to reflect the hollow form.

[0041] A spatially resolved wall thickness distribution system enables variable (dynamic) adjustment of the wall thickness distribution along the length of the blow-molded blank. A dynamically flexible, deformable ring in the extrusion die is deformed by two servo-hydraulically or electrically driven actuators through pushing and / or pulling during extrusion of the blow-molded blank, according to the specifications of one or more profile curves. For each wall thickness point on the profile curve, the radial gap is partially adjusted around the circumference. The system allows for optimal adjustment of the blow-molded blank wall thickness both circumferentially and axially.In this way, a variable wall thickness distribution with areas of different wall thicknesses is obtained in the finally formed hollow body, wherein the hardness of the hollow body corresponds at least in certain areas to < 75 Shore A ("in certain areas" means in at least one area within the meaning of the present invention, whereby any number of further areas may also be included by this formulation).

[0042] With both embodiments of the inventive method, hollow bodies according to the invention are available for toy applications, in particular doll body parts, but also, for example, toy animals or parts thereof, which have different wall thicknesses in different areas and exhibit a hardness of < 75 Shore A at least in certain areas. The mechanical strength of a hollow body according to the invention for toy applications conforms to DIN EN 71. In addition, the doll body part according to the invention is colorable, sewable, and, in particular when the preferred method parameters explained in more detail below are observed, has a flash-reduced, i.e., burr-free, surface.

[0043] Detailed description of the invention

[0044] The invention will now be described in more detail with reference to exemplary embodiments and to Figure 1, which schematically shows a hollow body according to the invention for toy applications in the form of a doll body part.

[0045] Figure 1 shows a doll's head as a hollow body according to the invention for toy applications. According to the invention, this doll's head is chlorine-free, free of plasticizers, and consists of at least 50% by weight of bio-based material. The doll's head has different wall thicknesses in different areas, and at least a portion of the doll's head has a hardness of < 75 Shore A. According to the invention, areas with a thinner wall also exhibit less perceived softness, whereas areas with a thicker wall also exhibit less perceived softness. The bio-based material of which the doll's head consists of at least 50% by weight preferably conforms to DIN EN 71 and DIN EN 13432 with regard to its mechanical strength and biodegradability.

[0046] For example, the doll's head can consist of 80 wt% PBS, 5 wt% PLA and 15 wt% Vinnex (vinyl acetate ethylene copolymer).

[0047] Although the doll's head shown in Fig. 1 is molded in one piece, a curved parting line is clearly visible, running behind the ears and along the hairline. This line is created during demolding from the two-part injection mold. However, the parting line can be concealed by coloring or painting and / or by sewing in hair.

[0048] Demolding a doll's head from an injection mold is technically demanding, especially with complex geometries. The optimal choice of mold parting line and design is crucial for efficient production and high-quality final products. For an attractive design and optimal mold parting, it is recommended to make the doll's head as symmetrical as possible along the mold parting line. Furthermore, deep undercuts should be avoided, as they complicate demolding or necessitate additional tools such as slides. Reducing the depth of undercuts, taking into account the flexibility of the materials, is advisable, as these can stretch slightly during demolding.

[0049] Undercuts are geometric areas that make simple demolding from a two-part mold difficult or impossible. They occur when part of the geometry lies perpendicular to the demolding direction, so that the component cannot be pulled straight up or down out of the mold without being damaged or the mold being destroyed.

[0050] Preferably, within the scope of the present invention, CAD tools are used to simulate demolding and undercut analysis in order to identify problematic areas early on. Generous radii are provided at edges and transitions, and delicate details such as ears are positioned so that they are easy to demold along the parting line and / or accessible from both mold halves. In areas of the doll's head where a perceived softness is not desired, the wall thicknesses are made uniform to minimize material stresses and the risk of warping or flash formation. According to the invention, undercuts are preferably avoided or minimized.

[0051] The parting line is a crucial aspect of the doll's head's aesthetics and functionality. It is the visible line or seam that forms when two halves of a mold (e.g., in injection molding, die casting, or blow molding) meet during the manufacturing process. It marks the point where the two mold halves fit together and the material is injected into the mold. The parting line follows the geometry of the component and is determined by the workpiece design and the demolding direction. It may be visible as a thin edge or seam and depends on the precision of the mold and the material used. It enables the demolding of the component by separating the mold halves.

[0052] Visible parting lines can detract from the appearance of a component, especially in decorative or toy-like products such as dolls. Excess material escaping at the parting line creates unwanted burrs that require reworking. The parting line can also be a potential weak point, as an imperfect finish can disrupt the material homogeneity.

[0053] The parting line should run in less visible or aesthetically unobtrusive areas, such as transitions or natural edges. It should run along straight or slightly curved surfaces to facilitate the mold closure and be positioned in areas without undercuts to facilitate demolding.

[0054] Precise tool alignment and tight tolerances prevent burr formation at the parting line.

[0055] Especially in the production of dolls or doll body parts, a concealed positioning of the parting line is important. In the case of a doll's head, as shown in Fig. 1, this line preferably runs along the hairline, behind the ears, and at the neck, and not across prominent facial details such as the eyes or mouth, which, as complex areas, should lie entirely within one mold half to reduce demolding effort. The parting line should follow natural contours to visually conceal transitions. In the embodiment shown in Fig. 1, this is particularly the hairline, so that the parting line can be completely hidden by applying hair to it.

[0056] To prevent flash, it is crucial that the tool halves are precisely aligned to minimize gap formation. Tool gap dimensions must be kept tight, especially along the parting line, and high-quality guide and locking systems are required. Venting channels should be incorporated to prevent air bubbles, which can promote flash.

[0057] The design of the doll's head according to the invention is optimized for easy demolding, with a well-chosen parting line that is visually concealed and minimizes mechanical challenges. Flash can be largely avoided through precise tool manufacturing, tight gap dimensions, and optimized material flow. Early simulation of the manufacturing process and careful coordination of design and tooling are crucial for successful implementation.

[0058] The maximum undercut depth depends on the mechanical properties of the material used, the demolding conditions, and the geometry of the doll's head. For thermoplastic polyurethane (TPU) with a Shore hardness of A75 and a modulus of elasticity of 20 MPa, the following considerations and recommendations are relevant:

[0059] TPU with a modulus of elasticity of 20 MPa and Shore A75 exhibits moderate deformability. It can stretch elastically under moderate forces; however, deep undercuts are problematic due to limited elongation. Depending on the grade, TPU can stretch up to 300–500% of its original length before failure. This allows for moderate undercuts. For a component height of 80 mm, the undercut depth must not be so great that the tensile stress during demolding exceeds the material limit. In the area of ​​the doll's head, sharp undercuts or high material resistance should be avoided; conversely, rounded, smooth transitions minimize the force required for demolding. Undercuts can be overcome in elastic materials through local deformation. However, demolding must be performed uniformly to avoid damage.

[0060] The depth of an undercut can be mathematically described by the angle and geometry of the component relative to the demolding direction. An undercut occurs when a surface of the component has a region that runs perpendicular to or against the demolding direction in which the component is pulled out of the mold.

[0061] The undercut depth (h) is the maximum vertical distance between the outermost edge of an undercut area and the demolding direction plane.

[0062] The demolding angle (a) is the angle formed by the surface of the component relative to the demolding direction.

[0063] An undercut occurs when a > 90°, where a is the angle between the local surface and the demolding direction.

[0064] The maximum undercut depth is defined as follows:

[0065] , > ^max '

[0066] "max

[0067]

[0068] (j max Maximum tolerable tensile stress in the material, i.e., the point at which the material elongation is still within the elastic range and no plastic deformation occurs. For the TPU according to the invention, this is o max ~ 25% of the tensile strength: Effective material thickness (thickness of the delicate areas).

[0069] Thinner areas require smaller undercuts because the stress on the material increases.

[0070] E: Elastic modulus of the material (for TPU = 20 MPa).

[0071] The Shore A hardness (H) correlates with the elastic modulus E by

[0072] 0.0981

[0073] E = - (0.00254 - 0.0022 ■ H) 2

[0074] With H = 75, this results in E ~ 20 MPa (confirmed by the specification).

[0075] In intricate areas, the geometry of the component is additionally taken into account by the curvature r and the length of the undercut d. The following extended formula is used:

[0076] h max = ■ (t + r ■ (1 - cosö))

[0077]

[0078] E

[0079] The additional parameters are as follows:

[0080] • r: Radius of curvature in the undercut area

[0081] • 9: Angle between the demolding direction and the tangential line at the undercut (typically 6° = 15°-30° for moderate undercuts)

[0082] Example 1: Example calculation for a doll's head

[0083] The following values ​​are given:

[0084] • E = 20 MPa, t = 2 mm, r =5 mm, G = 20°, 0 max = 6 MPa (30% of 20 MPa)

[0085] Step 1: Calculating the undercut depth

[0086]

[0087] 1. First term ( V ^ E ) ':

[0088] 6 ■ 10 6 ■ 2 ■ 10“ 3

[0089] - — — — — = 0.6 mm

[0090] 20 ■ 10 6

[0091] 2. Second term ((r ■ (1 - cosd)

[0092] Min

[0093] 5 ■ (1 — cosl5°) = 0.1705 mm

[0094] Max

[0095] 5 ■ (1 — cos30°) = 0.65 mm

[0096] Total depth: -max = 0.77 mm up to 1.25 mm

[0097] For a TPU with the specified properties, the maximum undercut depth should be limited to 0.77 to 1.25 mm, depending on the exact geometry of the doll's head.

[0098] Example 2: Investigation of the different perceived softness of areas with different wall thicknesses

[0099] A key aspect of the present invention is the ability to selectively adjust the perceived softness of the toy by varying the wall thickness of the hollow body in different areas, even when using the same material. This varying perceived softness allows toys, particularly dolls, to be perceived as more lifelike, because certain body parts, such as the lips, which are softer on a real person than other body parts, such as the cheeks, are also softer on the doll.

[0100] To assess the locally perceived softness of an open hollow body made of thermoplastic elastomer, an instrumented indentation test is used.

[0101] Shore hardness describes only the material property and remains unchanged for an identical material. However, the perceived softness of the molded part is significantly determined by its geometry. The indentation force at a defined depth directly captures this component-specific compliance and allows for an objective evaluation of the perceived softness, even with a constant Shore hardness.

[0102] In the described test, the relationship between the applied force F and the indentation depth d is measured at a defined point on the component. This force-displacement relationship describes the local mechanical response of the component structure to a contact load. The measured response results from the interplay of the viscoelastic material behavior and the local geometry, in particular the wall thickness and the structural support.

[0103] The local indentation stiffness is derived as a physical parameter from the force-displacement relationship. It describes the force required to compress the component structure locally by a defined distance. The local indentation stiffness thus represents a direct measure of the component's structural compliance and correlates directly with perceived softness. Low indentation stiffness indicates high compliance and a soft feel, while high indentation stiffness corresponds to a stiffer and harder-feeling structure.

[0104] The characteristic value is location- and geometry-dependent and does not represent a purely material property. It is therefore particularly suitable for the comparative evaluation of different wall thickness ranges within a component or between geometrically comparable components.

[0105] The testing is carried out in accordance with established testing procedures according to ISO 2439, ISO 3386 and ISO 7619. The aforementioned standards are used as a methodological framework, without claiming formal conformity to the standards.

[0106] The testing principle is based on the perpendicular indentation of a defined punch into the surface of the component. During the indentation process, force and displacement are continuously recorded and plotted as a force-displacement curve. Characteristic parameters describing the local indentation softness are derived from this curve.

[0107] A uniaxial testing machine with integrated force measurement is used as the testing equipment. The displacement is measured at the punch. A round, flat punch with a diameter of ten millimeters serves as the indentation tool. The punch edge is slightly chamfered to prevent local damage to the surface. The component is supported stress-free on a rigid base.

[0108] The test is performed at room temperature. The measuring points on the component are clearly marked before the test. The distance of the measuring points to edges, openings, or webs is at least one punch diameter to avoid edge supports.

[0109] The indentation process is performed at a constant speed of ten millimeters per minute. The maximum indentation depth is two millimeters. For very thin-walled areas, a smaller indentation depth can be selected, provided it allows for reproducible measurement results. Before the actual measurement, each measuring point is preconditioned by five pre-cycles between zero and the maximum indentation depth to stabilize set effects and viscoelastic relaxation of the material. After pre-conditioning, the measurement cycle is performed. The punch is moved from zero to the defined indentation depth while force and displacement are continuously recorded. The indentation process is repeated three times for each measuring point. Average values ​​are calculated from the measurements, and the variance is documented.

[0110] For evaluation, the force at an indentation depth of two millimeters is determined from the force-displacement characteristic curve. Additionally, the indentation work is calculated as the area under the force-displacement curve up to the maximum indentation depth.

[0111] The assessment of softness is relative. Areas with lower force absorption and lower indentation effort are classified as softer than areas with higher force absorption.

[0112] The softness was measured at two points on a hollow doll head:

[0113] Regio frontalis: Forehead region on an extended vertical nasal line

[0114] Regio bucalis: Cheek region at mouth level

[0115] The bending stiffness is proportional to the modulus of elasticity multiplied by the wall thickness cubed.

[0116] > oc B xt®

[0117] (1)

[0118] D: Bending stiffness

[0119] E: Modulus of elasticity

[0120] t: wall thickness

[0121] We now assume a locally indented plate. The force required to indent to a defined depth is then proportional to the bending stiffness multiplied by the indentation depth divided by the geometric length squared.

[0122]

[0123] F: required indentation force

[0124] D: Indentation depth

[0125] a: geometric length or effective support length, as the area that bears the indentation (local effective span as the “clamped” zone with radius a around the contact point.

[0126] Substituting (1) into (2) yields:

[0127]

[0128] (3)

[0129] For an identical material with a Shore A hardness of 72 and a stiffness E = 50 MPa, the following indentation force F is required for d = 2.0 mm and the local effective span as a "clamped" zone with radius a = 15 mm around the contact point:

[0130] For a wall thickness of t = 4 mm, F = 28.4 N.

[0131] For a wall thickness of t = 10 mm, F = 444.4 N.

[0132] Therefore, if the wall thickness increases by a factor of 2.5, the indentation force increases by a factor of 15.

[0133] The features of the invention disclosed in the foregoing description, in the claims and in the figure can be essential for the realization of the invention in its various embodiments, both individually and in any combination.

Claims

Claims 1. Hollow body for toy applications, characterized in that it is chlorine-free and free of plasticizers and consists of at least 50 wt.% bio-based material, wherein the hollow body has different wall thicknesses in different areas and at least a part of the hollow body has a hardness of < 75 Shore A.

2. Hollow body for toy applications according to claim 1, characterized in that it has a first area with a first wall thickness and a second area with a second wall thickness, wherein the wall thickness in the first area is at least 10%, at least 20%, at least 30%, at least 40%, at least 50% or at least 60% less than in the second area.

3. Hollow body for toy applications according to claim 1 or claim 2, characterized in that it is a doll body part and in particular a doll head, which is formed in one piece.

4. Hollow body for toy applications according to one of the preceding claims, characterized in that the bio-based material is TPU or a polymer that is biodegradable according to DIN EN ISO 13432.

5. Hollow body for toy applications according to claim 4, characterized in that the at least one polymer biodegradable according to DIN EN ISO 13432 is selected from the group comprising polylactide, polyhydroxyalkanoate, thermoplastic starch, starch blends, polycaprolactones, polybutylene adipate terephthalate, polybutylene succinate, polybutylene succinate adipate, polysaccharide derivatives, lignin derivatives, protein derivatives and mixtures thereof.

6. Hollow body for toy applications according to any one of claims 3 to 5, characterized in that the hollow body is a doll's head and the first area with the first wall thickness is an area of ​​the lips and the second area with the second wall thickness is an area of ​​the eyes, cheeks and / or nose.

7. Method for manufacturing a hollow body for toy applications, comprising the following steps: Providing a material that is chlorine-free, plasticizer-free and consists of at least 50% by weight of bio-based material; and Forming the chlorine-free, plasticizer-free material, consisting of at least 50 wt% bio-based material, into a hollow body, wherein at least one area of ​​the hollow body has a hardness of < 75 Shore A.

8. Method according to claim 7, characterized in that the forming to form a hollow body includes the forming of a first area with a first wall thickness and the forming of a second area with a second wall thickness, wherein the wall thickness in the first area is at least 10%, at least 20%, at least 30%, at least 40% or at least 50% less than in the second area.

9. Method according to claim 8, characterized in that the shaping of the first area includes the shaping of lips and the shaping of the second area includes the shaping of eyes, cheeks and / or nose.

10. A method according to one of the preceding claims, characterized by the step of providing a 3D support structure, wherein the 3D support structure is arranged in an injection mold, wherein the shortest distance between the 3D support structure and the injection mold is different at different locations of the 3D support structure, and wherein the forming of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material into a hollow body for toy applications includes overmolding the 3D support structure arranged in the injection mold with the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material, such that the latter fills the cavity between the 3D support structure and the injection mold, and wherein the forming of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material-% of the material consisting of bio-based material also includes the solidification of this material in the injection mold to form a hollow body.

11. Method according to claim 10, characterized by a step following the solidification of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material in the injection mold, of releasing the hollow body from the injection mold and from the 3D support structure.

12. Method according to one of the preceding claims, characterized in that the shaping of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material is carried out by blow molding, wherein the blow molding is selected from the group comprising injection blow molding and extrusion blow molding, and wherein the shaping of the chlorine-free, plasticizer-free material consisting of at least 50 wt.% bio-based material further includes solidifying this material into a hollow body.

13. Method according to one of the preceding claims, characterized in that the bio-based material is TPU or a biodegradable polymer according to DIN EN ISO 13432, preferably selected from the group comprising polylactide, polyhydroxyalkanoate, thermoplastic starch, starch blends, polycaprolactones, polybutylene adipate terephthalate, polybutylene succinate, polybutylene succinate adipate, polysaccharide derivatives, lignin derivatives, protein derivatives and mixtures thereof.

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