Injection-molded part

Abstract

The invention relates to an injection-molded part (10) made of polyester, wherein the injection-molded part has a foamed structure and wherein a surface roughness Rz of all surfaces of the injection-molded part (10) is in a range of 1.00 µm to 5.00 µm.

Description

[0001] HOEFER & PARTNER

[0002] SCI260302PCT March 3, 2026 Applicant:

[0003] Schwan Cosmetics International GmbH

[0004] Schwanweg 1

[0005] 90562 Heroldsberg, Germany

[0006] Injection-molded part

[0007] Description

[0008] The present invention relates to an injection-molded part made of polyester having a foamed structure.

[0009] The production of injection-molded plastic parts enables the implementation of various molded components for diverse applications, including sleeves and protective caps for pencils. Due to their flow characteristics, some plastics, particularly acrylonitrile butadiene styrene (ABS), have proven to be especially well-suited for injection molding. ABS has a melt volume flow rate of 45 cm3 / 10 min (test standard ISO 1133-1:2018), so that it exhibits such high flowability that even the smallest cavities are filled reliably, enabling the easy implementation of thinner wall sections, e.g. in long cylindrical molded parts comprising challenging flow paths.

[0010] Due to its application-related and mechanical properties, polyesters have proven advantageous compared to ABS. However, polyesters, such as polyethylene terephthalate (PET), have a melt volume flow rate of approximately 20 cm3 / 10 min, making it difficult to injection mold polyesters using the same tools as for ABS. Especially thin-walled and cylindrical molded parts (injection-molded parts) of considerable length, as mentioned above, cannot yet be injection molded with the same tools suitable for ABS because the polyester injection molding compounds exhibit insufficient flowability.

[0011] Based on this prior art, it is an object of the present invention to specify an injection-molded part which is characterized by very good surface properties and mechanical properties and which may also be present in the form of complex structures free of short shots or defects. This object is achieved by the features of the independent claim. The dependent claims contain advantageous embodiments and configurations of the invention.

[0012] Thus, the object is achieved by an injection-molded part made of polyester, characterized by a foamed structure. According to the present invention, an injection-molded part made of polyester is understood to be an injection-molded part that comprises polyester as the polymeric material and consists substantially of polyester. This may be a single polyester ortwo or more polyesters in the form of a mixture. Copolyesters and mixtures thereof, including further polyesters, are also possible.

[0013] The foamed structure is a structure that introduces a certain porosity into the injection-molded part, which does not originate from the polyester. It results from the addition of a gas-releasing blowing agent or blowing agent mixture to an injection molding compound from which the injection-molded part according to the invention is obtained after the injection molding process. The specific gas-releasing blowing agent is not limited, but it is a chemical blowing agent that, upon decomposition, releases the gas that creates the foamed structure in the polyester. The foamed structure is also reflected on the surfaces of the injection-molded part according to the invention. The foamed polyester structure results in a lightweight yet mechanically sufficiently stable injection-molded part.

[0014] According to the invention, all surfaces of the injection-molded part have a surface roughness Rz in the range of 1.00 pm to 5.00 pm, and, in particular from 1.00 pm to 3.00 pm. A surface roughness Rz in the range of 1.00 pm to 5.00 pm results in a very good tactile feel with a matte finish. This also improves any decoration (screen printing, pad printing, and hot stamping) or the wetting of the injection-molded part with a substrate.

[0015] These properties are significantly improved for a surface roughness Rz of 1.00 to 3.00 pm. The surface is also somewhat more homogeneous without losing grip.

[0016] Without wishing to be bound by theory, it is assumed that the surface roughness in the range of 1.00 to 5.00 pm is caused by the gas released from the gas-releasing blowing agent during the injection molding of the injection-molded part according to the invention. The released gas creates gas streaks (silver streaks) that form scarring on the surface of the injection-molded part. This results from the fact that a critical pressure threshold is undershot behind the melt front, causing the gas bubbles formed during the injection of the injection molding compound into the injection mold cavity to begin to grow. Due to the fountain flow of the polyester at the flow front, the material is conveyed from the center to the outside during cavity filling. This causes the gas bubbles formed during the injection process to be smoothed out on the mold surface, creating irregularities that manifest as a surface roughness Rz of 1.00 to 5.00 pm. The surface roughness Rz in a range of 1.00 to 5.00 pm may be controlled by appropriately selecting the gas-releasing blowing agent(s) and also the quantity of these blowing agents in the injection molding compound to be processed to form the injection-molded part according to the invention. In particular, the gas-releasing blowing agent is selected in this case such that it decomposes as late as possible, i.e., shortly before or during the injection of the injection molding compound into the injection cavity, because, in this way, the gas formed has little opportunity to escape from the injection molding compound, and the gas bubbles that formsurface roughness Rz remain in the injection-molded compound, and, as described in detail above, grow and may be found on the surface of the injection-molded part in the form of surface irregularities. The gas-releasing blowing agent to be used is therefore preferably characterized by a moderate decomposition rate at the high temperatures of the injection molding process. In this case, two or more gas-releasing blowing agents may also interact "catalytically", i.e., shift decomposition of one gas-releasing blowing agent into the desired temperature range. Alternatively or additionally, higher concentrations of gas-releasing blowing agent or blowing agent mixture may be utilized if the gas-releasing blowing agent tends to decompose at lower temperatures in order to achieve the required surface roughness. However, this may be disadvantageous in terms of the cost of the injection-molded part and also the processing of the injection molding compound into the injection-molded part.

[0017] In particular, by means of an optimized proportion of gas-releasing blowing agent, the surface roughness Rz can be brought into a preferred range of 1.00 to 3.00 pm.

[0018] Surface roughness Rz is measured by means of a measuring device from Nanofocus, a confocal microscope. During the measurement with the confocal microscope, there is no contact between the sample and the lens. The sample rests on the sample stage without being fixed, so there is no contact pressure. The confocal microscope only displays focused points, filtering out blurred image information (including stray light) through an aperture effect. Thus, only light from the focal plane reaches the light sensor and contributes to the confocal curve signal. One thousand confocal images are acquired within a few seconds, and measurement software calculates a precise three-dimensional height image from the confocal image stack, from which the Rz value may be determined. Test standard DIN EN ISO 4287 from 1997 is used to determine surface roughness Rz. The maximum roughness profile height is determined, i.e., the sum of the height of the tallest profile peak and the depth of the deepest profile valley within a single measurement segment. Surface roughness value Rz therefore characterizes the foam structure of the injection-molded polyester, which in turn is important for the surface properties, tactile feel, and mechanical properties of the injection-molded part. The following polyesters are particularly well suited for the injection-molded part according to the invention: polyethylene terephthalate (PET), PBT (polybutylene terephthalate), glycol-modified PET (PETG), (glycol-modified) polycyclohexylenedimethylene terephthalate (PCTA). Due to its very good mechanical properties, good tactile feel, and optical properties, the polyester preferably comprises polyethylene terephthalate (PET). Furthermore, PET is characterized by very good compatibility with volatile hydrocarbons and volatile silicones, as well as high impermeability and thus low gas permeability to volatile hydrocarbons and volatile silicones, even at thin wall thicknesses of the PET material. This is particularly important when the injection-molded part is used as a storage container, such as a shaft and / or protective capand / or sleeve and / or cartridge of a pencil, such as a cosmetic pencil. Cosmetic compositions often contain volatile hydrocarbons and volatile silicones that may diffuse through the walls of a storage container, inevitably leading to a loss of properties in the cosmetic compositions. In addition, PET is also resistant to weak acids and alkalis, oils and fats, perchlorinated, aliphatic and aromatic hydrocarbons, carbon tetrachloride, neutral and acidic salts, alcohols, ethers and water at room temperature, resulting in a wide range of applications for the injection-molded part according to the invention.

[0019] The higher the proportion of PET in the polyester, the more pronounced the aforementioned properties are determined by PET. Therefore, the polyester comprises at least 50% PET by mass, based on the total mass of polyester. PET is particularly preferably contained in the injection-molded part as the sole polyester.

[0020] Due to its very good mechanical properties, its extremely low self-weight, not only compared to ABS but also overall, and also to achieve, for example, improved sharpenability by means of a conventional sharpener in injection-molded parts designed as pencil sleeves, the porous foam structure exhibits pores with a diameter of 50 to 200 pm. In this case, a pore size greater than 200 pm is disadvantageous with regard to the absorption of dirt and other substrates that may penetrate the surface of the injection-molded part. A pore size of less than 50 pm may not always achieve a sufficient improvement in the injection-molded structure.

[0021] A further advantageous embodiment provides for a pore volume of the injection-molded part in a range of 10 to 30%. This allows for significant weight reduction while simultaneously improving mechanical properties. In particular, very thin-walled injection-molded parts may be produced that are characterized by consistently good mechanical properties. In the case of sleeves, such as cosmetic or writing instrument sleeves, which must be able to be sharpened, a pore volume in a range of 10 to 30% also improves the sharpenability, i.e., reduces the sharpening force. The pore volume may be determined by means of density measurement (Archimedes' principle).

[0022] Due to an improvement in surface quality, the surface roughness Ra of all surfaces of the injection-molded part is preferably in a range of 0.10 pm to 0.40 pm and, in particular, in a range of 0.10 pm to 0.25 pm. The surface roughness Ra is determined as described in standard DIN EN ISO 4287 from 1997 and represents the arithmetic mean roughness value, i.e., an absolute value of the ordinate values of the roughness profile.

[0023] To improve printability, for example by screen printing or pad printing, the injection-molded part, according to an advantageous embodiment, has a free surface energy of at least 47 mN / m and, in particular, at least 50 mN / m. The free surface energy is understood to be the average free surface energy determined by contact angle measurement (determined via Young-Laplacedroplet contour analysis; for example, using a device from Kruss). The Kruss Mobile Agent device is utilized for contact angle measurement, and water and diiodomethane are used as test liquids, which are metered onto the substrate whose surface energy is to be determined. The free surface energy is determined from the contact angles of the test liquids. The contact angle indicates the degree of attraction between the material molecules and with molecules of other materials (substrate). In this case, the free surface energy may be adjusted to the desired range by selecting a suitable polyester. In this case, the degree of polymerization, and thus also the remaining free OH groups and / or ester groups, play a particularly important role. Furthermore, the gas-releasing blowing agent used may leave, for example, hydroxyl groups and / or carboxyl groups on the surface of the resulting injection-molded part, which scars during the injection molding process, and by which the free surface energy may be controlled.

[0024] Printability or application with a substrate may be improved in particular if the injection-molded part advantageously features a polar fraction of the free surface energy of at least 1.5 mN / m and, in particular, of at least 3 mN / m.

[0025] The mechanical stability of the injection-molded part may be improved, in particular, by the injected-molded part comprising at least a first outer layer, a second outer layer, and an inner layer located between the first and second outer layers. This inner layer may preferably be a wall comprising the three aforementioned layers in the specified order, as is the case, for example, with the wall of a sleeve. In this case, the injection molding process is carried out such that the sleeve is cooled at its outer and inner surfaces (these surfaces containing the outer layers) by cooling the injection molding cavity. According to an advantageous embodiment, the hardness of the outer layers is higher than a hardness of the inner layer located between the skin layers, where the hardness specified here is understood to be the Shore D hardness.

[0026] Without wishing to be bound by theory, it is assumed that the layers (outer and inner layers) form due to the gas-releasing blowing agent utilized in the injection molding compound used for the molded part. When, in this case, the polyester melt comes into contact with the injection mold cavity, which is at a much lower temperature than the polyester melt, a rapid decrease of the viscosity of the polyester melt occurs in the region of the cavity wall. The polyester melt cools quickly in this region. Also, gas bubbles form in the polyester melt due to the decomposition of the gas-releasing blowing agent, leading to expansion of the material. However, the increase in the viscosity of the polyester melt due to the cooling of the injection molding cavity prevents the material from expanding in this region. This results in a higher orientation of the polyester chains in the outer regions due to a semi-crystalline arrangement, which manifests as increased hardness of the outer regions compared to the inner region. Theinner region is cooled less intensely and therefore, due to the expansion and distribution of gas bubbles, has a less pronounced semi-crystalline arrangement and thus also a lower hardness. According to a further advantageous embodiment, a Shore D hardness of the first and / or second outer layer is at least 80, in particular at least 85 and, in particular, at least 88. This results in improved stiffness of the outer layer, which is advantageous with regard to mechanical stability, in particular, with respect to impact and shock.

[0027] The Shore D hardness is measured on a plate-shaped specimen having a thickness of 6 mm under a load of 50 N with a dwell time of 15 s. The applicable standard is ISO 868:2003. Ten measurements are taken and the mean value is calculated.

[0028] In the two preceding embodiments, it is also preferred that the outer layers comprise a nucleating agent. The nucleating agent is derived in particular from the gas-releasing blowing agent, which is preferably present in the form of a carbonate, such as, in particular, MgCO3and / or CaCO3, optionally in combination with monosodium citrate. The nucleating agent formed from the blowing agent is advantageously MgO and / or CaO.

[0029] It has been found that gas-releasing blowing agents, which leave behind a nucleating agent such as CaO or MgO after gas release, lead to a nucleation effect in the polymer structure of the polyester, resulting in the formation of crystalline regions in the outer layer(s) of the injection-molded part according to the invention. In this case, crystalline outer layers lead to increased stiffness, wherein a porous foam structure improves the elasticity of the injection-molded part.

[0030] As a result, the material's resilience is also improved, for example. This leads, for example, to a positive effect on the sealing system between a cap and a sleeve, or between a protective cap and a shaft of a cosmetic or writing pencil, which are present in the form of injection-molded parts according to the invention. The system seals better, and volatile components (fluids, hydrocarbons) cannot escape. Preferably, the particles of the gas-releasing blowing agent with nucleating effect have an average particle size of less than or equal to 0.08 pm, as this increases the crystallization rate of the polymer structure. The chemical nature of the nucleating particles may be verified by EDX.

[0031] According to an advantageous embodiment, the intrinsic viscosity of the injection-molded part is less than 0.700 dl / g, in particular, less than 0.600 dl / g, and, in particular, less than 0.560 dl / g. The intrinsic viscosity (in short: IV) is a measure of the average molecular weight of the polyester in the injection-molded part. In this case, shorter polymer chain lengths result in a lower IV. The lower IV of the injection-molded part according to the invention, compared to injection-molded parts injection-molded without a gas-releasing blowing agent, is due to the degradation of the polyester chain. It is assumed that this chain degradation, the so-calleddegradation of the polyester, is predominantly caused by the chemical blowing agent used in the injection molding compound for the production of the injection-molded part according to the invention. The IV of the injection-molded part according to this embodiment is reduced by more than 30% compared to an injection-molded part made from the same polyester but without a blowing agent.

[0032] If the IV is within the value range specified above, it may be assumed that the melt volume rate of the polyester during the injection molding process was so high that the injection-molded part is characterized by the fact that it has no short shots or defects, even with complex geometries, which is advantageous in terms of the mechanical properties and, of course, also the optical and tactile properties of the injection-molded part.

[0033] Advantageously, the IV of the injection-molded part is at least 0.400 dl / g. Below 0.400 dl / g, the material is usually very brittle, so the expected good mechanical properties are less easily achieved.

[0034] For example, degradation may be caused by the use of citrates as blowing agents, as the citrates locally lead to an increase in the COOH content in the polyester, which in turn is a measure of the hydrolysis of the polyester.

[0035] In particular, if monosodium citrate is used as one of the gas-releasing blowing agents, this salt may form NaOH and citric acidaq. Sodium hydroxide is a compound that saponifies polyesters, which also lowers the IV by breaking down the polymer chains.

[0036] The small amounts of water produced during the decomposition of citric acid may also promote hydrolytic cleavage of the polyester and thus reduce the IV.

[0037] Furthermore, carbonates, especially MgCO3and / or CaCO3, as gas-releasing blowing agents, also lead to a reduction in IV. This effect may be explained by the fact that the oxide (MgO or CaO) formed during the release of CO2from the carbonate reacts with small amounts of water to form the corresponding hydroxide (Mg(OH)2or Ca(OH)2). These hydroxides cause alkaline cleavage (saponification) of the polyester, reducing the IV.

[0038] In particular, when sodium monocitrate and CaCO3and / or MgCO3are utilized as a gasreleasing blowing agent mixture, a significant reduction in IV occurs. As a result, the free surface energy increases.

[0039] According to the invention, the IV is measured in accordance with DIN-53728-3 (1985).

[0040] Acid groups are formed at the cleavage sites of the polyester. Preferably, the COOH group content in the injection-molded part is greater than 52 mmol / kg, and, in particular, greater than 55 mmol / kg, based on the mass of the injection-molded part. The COOH group content is also a measure of the average molecular weight of the polyester in the injection-molded part. If theproportion of COOH groups is within the value range specified above, it may be assumed that the melt volume rate of the polyester during the injection molding process was so high that the injection-molded part is characterized by the fact that it has no short shots or defects, even with complex geometries, which is advantageous in terms of the mechanical properties and, of course, also the optical and tactile properties.

[0041] Preferably, the COOH group content in the injection-molded part is at most 70 mmol / kg and, in particular, at most 65 mmol / kg, as otherwise excessive chain degradation of the polyester occurs, which may negatively impact mechanical properties of the polyester.

[0042] The processing of the injection molding compound into the injection-molded part is also reflected in the crystallization temperature of the injection-molded part, which is preferably below 140 °C and, in particular, below 130 °C, whereas for the same injection-molded polyester, however, without the use of a gas-releasing blowing agent, it is above 135 °C. Advantageously, the crystallization temperature is at least 115 °C.

[0043] The crystallization temperature is determined by means of the following DSC method: (3 cycles):

[0044] A 7 mg sample of the injection-molded part is used according to the following measurement protocol:

[0045] 1. Heating from 25 °C to 280 °C [10 K / min], holding for 15 minutes.

[0046] 2. Cooling to 25 °C [10 K / min], holding for 15 minutes.

[0047] 3. Heating up to 280 °C [10 K / min]

[0048] Five measurements are performed for each material sample.

[0049] The measurement is taken against an empty crucible.

[0050] In this case, the crystallization temperature Tc is the temperature at which the polyester polymer begins to crystallize from the melt as it cools. The polymer chains arrange themselves in an ordered manner, releasing heat (exothermic). This exothermic peak may be measured by means of DSC. Tc thus indicates how well the polymer may crystallize and is therefore a measure of the molar mass distribution of the polyester in the injection-molded part.

[0051] A higher Tc indicates faster crystallization kinetics. Chemical foaming may slow down crystallization. This has an impact on the mobility of the molecules and alters the nucleation sites. A lower Tc value therefore indicates chemical foaming of the polyester.

[0052] Preferably, the crystallization temperature of the injection-molded part is also below the crystallization temperature of the polyester used for the injection-molded part.Furthermore, it is advantageous for a recrystallization temperature of the injection-molded part to be above 170 °C and, in particular, above 190 °C, and furthermore advantageously at most 210 °C.

[0053] The recrystallization temperature (Tr) may also be determined by means of the aforementioned DSC measurement. A recrystallization temperature occurs when, upon reheating the material sample, existing crystallites rearrange and form new, stable crystal structures. This effect occurs particularly in polyester polymers with slow crystallization or in semi-crystalline mixtures. A pronounced recrystallization peak may indicate that the polymer did not fully crystallize during the previous cooling phase. Higher Tr values indicate that the original crystals were less perfect and restructured upon reheating. Due to chemical modification resulting from the utilization of gas-releasing blowing agents in the injection molding compound from which the injection-molded part is formed, foamed polyester may exhibit a less stable crystal structure, leading to significant recrystallization upon heating, i.e., a different type of crystal structure.

[0054] Preferably, the recrystallization temperature of the foamed injection-molded part is also above the recrystallization temperature of the polyester utilized for the injection-molded part.

[0055] It is particularly advantageous in this case, if the temperature difference between a recrystallization temperature of the foamed injection-molded part and a crystallization temperature of the foamed injection-molded part is greater than 40 °C, in particular greater than 55 °C, and, in particular, greater than 70 °C, and preferably at most 95 °C.

[0056] The injection-molded part according to the invention is designed, due to its very good mechanical properties, its good tactile feel, its good printability, its impermeability to volatile hydrocarbons even at low wall thicknesses and its resistance to various chemicals, in particular, as a shaft and / or protective cap and / or sleeve of a cosmetic pencil.

[0057] Example

[0058] An example of the production of an injection-molded part according to an advantageous embodiment is given below. However, the present invention is not limited to this example. An injection molding compound is produced by mixing 96.0% by mass PET (Cuma PET L04040), 2.0% by mass black color batch (NG91050115-ZT RENOL-SCHWARZ), and 2.0% by mass CO2-releasing blowing agent mixture (Tecocell GT, from Trexel; a mixture of monosodium citrate and CaCO3) and heating the mixture to a temperature ranging from 265 °C to 290 °C (see below). The residual moisture content was 0.0022% (22 ppm) H2O.The raw materials were mixed after the PET had been pre-dried, after which the gas-releasing blowing agent mixture in the form of granules was metered in. The color batch was also metered in.

[0059] The injection molding compound produced in this way was injection molded at a constant injection speed and injection time and a constant back pressure of 50 bar under the following parameters:

[0060] Clamping force: 800 kN

[0061] Injection speed: 90 ccm

[0062] Injection time: 0.56 s

[0063] Maximum injection pressure: 2000 bar

[0064] Switching pressure: 2000 bar

[0065] Switchover points 11.00 bar

[0066] Holding pressure speed: 80.0 cm3 / s

[0067] Holding pressure: 1200; > 1200; > 250 bar

[0068] Holding pressure time: 0.25 sec; > 1.75 sec; > 0.2 sec

[0069] Metering delay: 3 s

[0070] Metering speed: 200 m / min

[0071] Back pressure: 80 bar

[0072] Metering volume: 53 ccm

[0073] Metering time: 3.55 s

[0074] Decompression stroke: 8 cm3at 20 cm3 / s

[0075] Cooling time: 22 s

[0076] Cycle time: 45.50 s

[0077] Cylinder temperatures: 50 / 285 / 285 / 280 / 275 °C (degressive temperature profile)

[0078] Tool temperatures:

[0079] Ejector side: 30 °C

[0080] Nozzle side: 60 °C

[0081] Core cooling: 20 °CThe drying conditions were as follows:

[0082] 60 °C to 160 °C for 2 to 6 hours.

[0083] A two-chamber dry air dryer TTM 2 / 50 EST was used in a temperature range of 60 °C to 160 °C (+ / - 2 °C).

[0084] Due to the expansion of the gas during the injection molding process, the viscosity of the PET material decreased. Compared to the identical PET component without a gas-releasing blowing agent mixture, a viscosity reduction of up to 55% was achieved, and an increase in MVR to 45% up to 55% was confirmed by a flow spiral test. This enabled long flow path lengths and thin wall thicknesses in the injection-molded part.

[0085] The dimensions of the flow spiral were as follows:

[0086] - Length: 1150 mm

[0087] - Width: 6 mm

[0088] - Thickness: 2 mm

[0089] The following table shows the measurement results for the MVR value depending on the amount of gas-releasing blowing agent:

[0090]

[0091] * The amount of gas-releasing blowing agent mixture is given in % by mass and was based on the mass fraction of polyester used.

[0092] The measured values in the table above were determined by means of a flow spiral test (dimensions and parameters are set forth above) and represent the mean value calculated from 20 individual measurements. A result of 0 represents the MVR value required for a satisfactory injection molding result. Furthermore, higher MVR values are advantageous for a high surface quality.In addition, the surface energy and topography of the resulting injection-molded part were determined.

[0093] The average surface free energy of the injection-molded parts resulting from the exemplary injection molding compound disclosed above was 47 mN / m and above. The values are summarized in the table below:

[0094]

[0095] The measured values in the table represent the average value resulting from 10 individual measurements.

[0096] A value of 0 corresponds to a standard ABS injection-molded part.

[0097] The printability of the injection-molded part surface may be controlled via the surface free energy.

[0098] Surface energy is crucial for decoration (screen printing, pad printing, and hot stamping) I wetting with a substrate. Here, the polar fractions play a particularly important role. The polar fraction of the surface free energy should be between 1.5 and 5 dyn (mN / m), and in particular between 3 and 5 dyn.

[0099] The surface energy may be determined, as set forth above, by means of a contact angle measurement (device: Mobile Agent by Kruss).

[0100] The measured quantity “contact angle” provides a measure of the cohesive forces between the material molecules themselves and the adhesive forces with molecules of other materials (substrate).

[0101] In addition, the roughness values Ra and Rz of the injection-molded parts resulting from the exemplary injection-molding composition described above were also determined. The results may be found in the table below:

[0102]

[0103] The measured values in the table represent the average value resulting from 10 individual measurements. The value 0 is the reference value for an ABS standard. The value

[0104]

[0105] represents a high-gloss “ABS” surface.

[0106] The roughness values Ra and Rz (2D parameters) describe the surface texture (topography), which is crucial for the tactile sensation of the injection-molded part. A rougher surface provides better grip. As mentioned earlier, Ra and Rz may be controlled by the composition of the injection molding compound used in the production of the injection-molded part.

[0107] Topographic measurements were taken on black components to obtain the above values. For comparison, a standard ABS grade was measured.

[0108] Ra is the arithmetic mean roughness value, which may be determined from the absolute values of the ordinate values of the roughness profile.

[0109] Rz is the maximum height of the roughness profile, calculated as the sum of the height of the tallest profile peak and the depth of the deepest profile valley within a single measurement segment.

[0110] The test standard used to determine surface roughness Ra and Rz is DIN EN ISO 4287 from 1997.

[0111] The IV and the COOH group content of the injection-molded part were also determined (according to DIN EN ISO 2114, August 2000). The measured values may be found in the table below:

[0112]

[0113]

[0114] It can be seen that the IV of the injection-molded parts, which were injection-molded using a gas-releasing blowing agent, is significantly reduced compared to the standards without gasreleasing blowing agent (Cuma PET L04040 and PET component after processing by injection molding, which corresponds to Cuma PET L04040 processed by injection molding).

[0115] Also, an average COOH group content of 59 mmol / kg injection-molded part was found in the Flex rPET sample and the Flex PET sample.

[0116] Also, the melting temperature Tm, the crystallization temperature Tc, and the recrystallization temperature Tr were measured according to the method described in the description. The results may be found in the table below:

[0117]

[0118] The mean values from 10 measurements were:

[0119] - Tc: 120 °C

[0120] - Tr: 200 °C

[0121] Shore A hardness was also determined in the outer regions of the injection-molded component. The mean value determined from 10 measurements was 90, whereas it was only 81 for an unfoamed injection-molded part made of the same polyester.Further details of the invention will become apparent from the following description and the figures.

[0122] In the figures:

[0123] Figure 1 shows a schematic cross-sectional representation illustrating the temporal progression of the injection molding process for an injection-molded part according to a first embodiment.

[0124] Figure 2 shows a cross-sectional area of a wall of an injection-molded part according to a second advantageous embodiment.

[0125] The figures show only the essential aspects or elements of the present invention. All other aspects / elements have been omitted for the sake of clarity. In the figures, identical reference numerals denote identical components / elements.

[0126] In Figure 1, reference numbers 101 and 102 show in detail a cross-sectional view of a cold (e.g., cooled to 20 °C) mold insert of an injection mold during the injection process of a molten injection molding compound 2 according to an advantageous embodiment of the method according to the invention, which comprised a polyester and a gas-releasing blowing agent mixture. Rather, a change in the flow front of a hot injection molding compound 2 over time is shown, wherein injection molding compound 2 moves in a cavity along mold inserts 101 and 102 of an injection mold, which are cold compared to injection molding compound 2.

[0127] As indicated by reference numeral 4, a fountain flow of molten injection molding compound 2 occurs in the cavity of the injection mold. Injection molding compound 2 is moved further along the small black arrows by the pushing melt, that is to say, from the center of the melt towards mold inserts 101, 102.

[0128] Reference numeral 3 exemplifies a gas bubble located in the melt front of the melt which gas bubble was released from the gas-releasing blowing agent mixture contained in injection molding compound 2 and initially migrates to the surface of molten injection molding compound 2. Behind the melt front, a critical pressure threshold is undershot, causing gas bubble 3 to begin to grow. Due to fountain flow 4 typical of thermoplastics at the flow front, injection molding compound 2 is conveyed from the center to the outside during cavity filling. This causes gas bubbles 3 formed during the injection process to be smoothed out on the surface of mold inserts 101, 102, creating irregularities that produce inhomogeneous light refraction. This phenomenon is also referred to as gas streaking. Injection molding compound 2 solidifies on cold mold inserts 101, 102, and the smoothed-out gas bubbles 3 are integrated into the surface of the resulting injection-molded part in the form of gas streaks.Gas streaks (also called silver streaks) cause scarring on the surface of the injection-molded part, which may be measured in the form of surface roughness (Rz and Ra).

[0129] Figure 2 shows in detail a cross-sectional area of a wall 1 of an injection-molded part 10 according to a second advantageous embodiment of the invention. Reference numeral 5 describes the inner layer of injection-molded part 10, which is surrounded by two outer layers 6 of higher hardness (Martens hardness) than inner layer 5. The gas streaks shown in Figure 1 have formed depressions on the surface of wall 1 , which are open to the surroundings of injection-molded part 10 and contribute to the tactile grip of injection-molded part 10. These depressions are also referred to as surface roughness, which may be determined as an Rz value and is in a range of 1.00 pm to 5.00 pm. This also results in a relatively matte surface of injection-molded part 10.

[0130] It was found that the use of a gas-releasing blowing agent mixture led to a nucleation effect (by MgO and / or CaO) in the polymer structure of injection-molded part 10, resulting in the formation of crystalline regions in outer layers 6 of injection-molded part 10. It should be noted that the base material is polyester (PET), which is amorphous. Higher crystallinity improved the resilience of the material.

[0131] This can lead to a positive effect on the sealing system between cap and sleeve or protective cap and shaft of the cosmetic pencil, provided injection-molded parts 10 are, for example, formed in the form of a cap, a sleeve, a shaft, or a protective cap for a cosmetic pencil. The system seals so that any volatile components (such as hydrocarbons) contained in the cosmetic composition within the cosmetic pencil cannot escape.

[0132] An increase in the crystallization rate in the macromolecular structure could be achieved by nanosized (<0.08 pm) particles made of CaCO3(calcium carbonate) which, in combination with monosodium citrate, released CO2and created microcellular structures in the polymer melt. The cell size of the foam structure was approximately 50-200 pm.

[0133] Crystalline outer layers 6 led to increased stiffness and an improved foam structure, thereby enhancing the elasticity and, as a result, resilience compared to pure injection-molded PET. In addition to the above written description of the invention, explicit reference is hereby made to the graphic representation of the invention in the figures for supplementary disclosure.

Claims

Claims1. An injection-molded part (10) made of polyester, wherein the injection-molded part has a foamed structure and wherein a surface roughness Rz of all surfaces of the injection-molded part (10) is in a range of 1.00 pm to 5.00 pm.

2. The injection-molded part (10) according to claim 1, wherein the surface roughness Rz of all surfaces of the injection-molded part (10) is in a range of 1.00 pm to 3.00 pm.

3. The injection-molded part according to claim 1 or 2, wherein the polyester comprises polyethylene terephthalate and is in particular polyethylene terephthalate.

4. The injection-molded part (10) according to any one of the preceding claims, wherein the pores of the foamed structure have a diameter of 50 to 200 pm.

5. The injection-molded part (10) according to any one of the preceding claims, wherein a pore volume of the injection-molded part (10) is in a range of 10 to 30%.

6. The injection-molded part (10) according to any one of the preceding claims, wherein a surface roughness Ra of all surfaces of the injection-molded part (10) is in a range of 0.10 pm to 0.40 pm, and in particular in a range of 0.10 pm to 0.25 pm.

7. The injection-molded part (10) according to any one of the preceding claims, wherein the injection-molded part (10) has a free surface energy of at least 47 mN / m, and in particular of at least 50 mN / m.

8. The injection-molded part (10) according to any one of the preceding claims, wherein the injection-molded part (10) has a polar component of the free surface energy of at least 1.5 mN / m, and in particular of at least 3 mN / m.

9. The injection-molded part (10) according to any one of the preceding claims, comprising at least a first skin layer (6) and a second skin layer (6) and an inner layer (5) located between the first and the second skin layer (6), wherein a hardness of the skin layers (6) is higher than a hardness of the inner layer (5).

10. The injection-molded part (10) according to claim 9, wherein a Shore D hardness of the first and / or second outer layer (6) is at least 80, in particular at least 85, and in particular at least 88.

11. The injection-molded part (10) according to claim 9 or 10, wherein the skin layers (6) comprise a nucleating agent.

12. The injection-molded part (10) according to any one of the preceding claims, wherein an intrinsic viscosity of the injection-molded part (10) is less than 0.700 dl / g, in particular less than 0.600 dl / g, and in particular less than 0.560 dl / g.

13. The injection-molded part (10) according to any one of the preceding claims, wherein a content of COOH groups in the injection-molded part (10) is more than 52 mmol / kg, in particular more than 55 mmol / kg.

14. The injection-molded part (10) according to any one of the preceding claims, wherein a crystallization temperature (Tc) of the injection-molded part (10) is below 140 °C, in particular below 130 °C.

15. The injection-molded part (10) according to any one of the preceding claims, wherein a crystallization temperature (Tc) of the injection-molded part (10) is below the crystallization temperature (Tc) of the polyester used for the injection-molded part (10).

16. The injection-molded part (10) according to any one of the preceding claims, wherein a recrystallization temperature (Tr) of the injection-molded part (10) is above 170 °C, in particular above 190 °C.

17. The injection-molded part (10) according to any one of the preceding claims, wherein a recrystallization temperature (Tr) of the injection-molded part (10) is above the recrystallization temperature of the polyester used for the injection-molded part (10).

18. The injection-molded part (10) according to any one of the preceding claims, wherein a temperature difference between a recrystallization temperature (Tr) of the foamed injection-molded part (10) and a crystallization temperature (Tc) of the foamed injection-molded part (10) is greater than 40 °C, in particular greater than 55 °C, and in particular greater than 70 °C.

19. The injection-molded part (10) according to any one of the preceding claims, designed as a shaft and / or protective cap and / or sleeve of a pencil, in particular a cosmetic pencil.

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