Injection molded hydrophilic object and a method therefore

Abstract

Herein is detailed a method of injection molding a plastic object from a polymer composition comprising a polymer and a surfactant, and molded plastic objects resulting therefrom, by which method the molded plastic object obtains a surface coating of the surfactant after injection molding having a low contact angle.

Description

[0001] TITLE OF INVENTION

[0002] Injection molded hydrophilic object and a method therefore.

[0003] TECHNICAL FIELD

[0004] In the art of injection molding, there is herein detailed a method for obtaining injection molded hydrophilic objects, which are hydrophilic after injection molding without further processing, and injection molded hydrophilic objects resulting from the present method.

[0005] BACKGROUND

[0006] In the field of injection molded plastic objects it is a general problem that the plastic forming the object can have physical properties that are chosen for best performance of the structural properties of the formed object, but which may be problematic for the formed object when in use.

[0007] E.g., in injection molding of medical devices, plastics used for injection molding can in themselves be hydrophobic, but the intended use of the object can be in water or water-rich environments, such as tissue, requiring the molded object to be modified for improved compatibility with the desired target environment.

[0008] One such modification commonly employed is to treat the molded object with various chemicals that changes the surface properties of the molded object to improve the compatibility to the desired target environment, usually for changing the surface properties of the molded object from hydrophobic to hydrophilic . Often, this modification consists in providing an object molded from a hydrophobic polymer with a hydrophilic surface layer or coating, such that a desired compatibility to a water-rich environment is improved.

[0009] In the art, a surface of a plastic device can be made hydrophilic in numerous ways; however, a commonly employed method involves locating molecular components at the surface of the device, which are capable of modifying the surface hydrophilicity of the molded object, colloquially called making the surface hydrophilic using hydrophilic components. Such hydrophilic components generally fall in three groups: 1) Hydrophilic polymers, 2) Surfactants, or 3) Water soluble materials (e.g., sugars, polyols, salts etc.) . Commonly, such hydrophilic components are deposited on the device surface by a subsequent coating process after injection molding, or by in-mixing with the plastic material prior to injection molding of a desired plastic device from the plastic material in question.

[0010] When mixing the hydrophilic components with the plastic material in a compounding process and later injection molding devices, the hydrophilic components will (in some cases) migrate to the surface of the device and accumulate there thus indirectly forming a hydrophilic coating on the device and thereby rendering the device surface hydrophilic.

[0011] In the current state of the art, the mode of action is strongly linked to migration of the hydrophilic components through the polymer matrix. Without migration, molded devices do not become hydrophilic.

[0012] Migration of co-molded hydrophilic components is known to be affected by several aspects, such as: 1) Hydrophilic components can generally only migrate when the temperature is above the glass transition temperature of the plastic material used for molding the device in question. Devices therefore must often be tempered for days above the Tgof the plastic material in question for achieving proper migration, or the glass transition temperature of the material must be room temperature or below. 2) Migration is strongly affected by the molecular size of the hydrophilic components. Large molecules migrate slow or not at all, whereas small molecules migrate faster. 3) A suitable balance / imbalance between the plastic material and the hydrophilic components must exist. While chemical compatibility between plastic and hydrophilic components is essential to form a stable material, the compatibility must not be so good that the hydrophilic components are locked in place thus preventing migration. The standard solution to this is to add a chemically compatible hydrophilic component in a concentration above the solubility in the polymer. This ensures that at least a fraction of the hydrophilic component is free to migrate.

[0013] The most common molded plastic devices being hydrophilic are therefore molded from plastic materials formed by adding a relatively high concentration of a small hydrophilic component to a polymer with a low glass transition temperature .

[0014] The easiest plastic materials to make hydrophilic are the ones with a low glass transition temperature such as for example polypropylene (Tg= -20°C) , polyethylene (Tg= -110°C) and a range of elastomers. These low Tgmaterials are all relatively soft. Hard and structurally stable materials such as for example polystyrene (Tg=90°C) , polymethylmethacrylate (Tg= 100°C) and polycarbonate (Tg= 180°C) , generally have a Tgmuch higher than room temperature and cannot successfully be molded having hydrophilic surfaces to the extent of the present inventor' s knowledge .

[0015] Making hard plastic materials with a high Tghydrophilic, is often di f ficult or impossible . Adding a plastici zer to the compound material in a proper concentration will reduce Tgand permit migration of the hydrophilic components , but it will also make the molded obj ect softer than i f molded only from the pure plastic .

[0016] Of particular interest for medical devices are optically clear, transparent , color- free , and hard plastic materials . Hard compound plastic materials are as described above very di f ficult to make hydrophilic .

[0017] I f a device must be molded in a hard material due to product requirements , the only option currently is to use a hydrophilic coating . However, providing molded plastic products with hydrophilic coatings is procedurally complicated, time and labor extensive , and, consequently, expensive . A further complication is that due to supersaturation of additives in the plastic, such as e . g . hydrophilic additives , charging the polymer matrix with hydrophilic components in too high concentrations often cause precipitation in the polymer matrix . This precipitation generally makes the material hazy or opaque white , and consequently unsuitable for the intended purpose .

[0018] Due to these limitations for hydrophilic compound plastic materials , hydrophilic coatings are generally used for medical devices .

[0019] The present invention in a first aspect provides molded plastic devices having hydrophilic surface properties directly after molding, and in a preferred embodiment , the present invention enables optically clear, transparent , and hard plastic materials that , when inj ection molded, produces hydrophilic devices directly after inj ection molding .

[0020] DEFINITIONS

[0021] In the present disclosure there is distinguished between a polymer and a plastics material in that in the present disclosure a polymer refers to a macromolecule manufactured from connected, repeated monomers whereas a plastics material is a substance constituted from of one or more polymers in an amount suf ficiently for the resulting plastics material to exhibit macroscopic material properties , such as e . g . , melting and the ability to undergo flow under pressure when melted .

[0022] Further, the plastics material besides comprising an amount of one or more polymers suf ficient for providing the abovementioned macroscopic material properties may comprise a range of additives , such as e . g . plastici zers or, essential to the present invention, surfactants , suitable for the intended thermomolding of the plastics material into a plastics obj ect , but wherein the one or more polymers constitute the bulk of the total weight of the plastics material , such that the overall physical properties of the plastics material , e . g . , such as melting and flow under pressure is determined at least partially by fundamental physical properties of the constituting polymers .

[0023] Accordingly, and in general , at least 50 wt% based on total weight of a plastics material will be constituted by the one or more polymers for the plastics material in the sense of the present invention . Further, in the context of the present invention, a plastics obj ect is made from a plastics material in accordance with the above definitions but may contain further components added to the plastics material , such as e . g . , surfactants for creating a hydrophilic plastics obj ect after thermomolding in accordance with the below detailed invention .

[0024] In the context of the present disclosure , informally a plastics material can be described as soft , intermediate hard, or hard, which is merely intended as a tactile phenomenological scale and not as a characteri zing parameter of the invention . Soft plastics materials yield under tactile pressure and typically either contain an amount of plastici zer suf ficient to achieve this tactile impression and / or the plastics material presents a glass transition temperature which is below room temperature . Likewise , intermediate hard and hard refer to plastics material which under tactile pressure appear not to yield, typically because the plastics material does not comprise plastici zer or presents a glass transition temperature which is higher than room temperature .

[0025] In the context of the presently disclosed method of the invention, however, only polymer melts are concerned . The phenomenological characteri zations presented herein with respect to plastics materials are therefore for the illustration of the underlying technical problem solved by the present invention, but the invention itsel f concerns polymer melts . It is considered that the skilled person is able to determine when a plastics material is in a melted state , such that it is suitable for use in a thermomolding process . In the art, no fixed definition exists when a surface is considered hydrophilic. In the context of the present invention, a surface is considered hydrophilic if the static contact angle to water measured under ambient air using a contact angle goniometer is below 75°±5°, but preferably a surface is considered hydrophilic if the contact angle is below 65°±5°, measured over 5 different locations on a given test surface.

[0026] Commercially relevant hydrophilic surfaces generally have contact angles to water, which are below 45°±5°. As shown in the experiments of the present disclosure, such contact angles below can easily be obtained following the method of the present invention. It is a particular advantage of the present method, that contact angles of the hydrophilic surfaces after injection molding can reach below 35°±5°, below 25°±5°, and even below 15°±5°, which essentially corresponds to a surface, which is so hydrophilic that it is wettable by water.

[0027] Consequently, the present invention also concerns plastic objects which are hydrophilic after injection molding, particularly after injection molding in accordance with the herein disclosed method, which plastics objects have a contact angle to water below 65°±5°, preferably below 45°±5°, more preferably below 35°±5°, more preferably below 25°±5°, and even more preferably below 15°±5° after injection molding as measured at room temperature in ambient air using a contact angle goniometer measured over 5 different locations on a given test surface.

[0028] In the context of the present invention, a surfactant is to be understood in the common sense as a chemical compound decreasing the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid.

[0029] The surfactants studied herein present at least a hydrophilic part and a hydrophobic part spatially separated within the surfactant, such that the surfactant can lower the surface tension of water by preferential accretion at an interface of water either to air or to a surface. Most of the surfactants studied herein only have a single hydrophilic and a single hydrophobic part, but e.g., PEG-200 has intermittent sections of hydrophilic and hydrophobic parts.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] Figure 1 : Principle of invention la: As the polymer melt is injected in the mold cavity the surfactant evaporates from the melt. lb: The gas phase surfactant fills the cavity. Some of the surfactant will condense on the inside walls of the mold cavity; the rest will escape from the mold through gas vents. lc: The polymer melt fills the cavity and then solidifies as it cools.

[0032] Id: Aft er the molded device is ejected from the mold cavity, some of the surfactant is retained on the device surfaces thereby making the device hydrophilic .

[0033] Figure 2: Experimental setup for measuring vapor pressure.

[0034] Figure 3: Vapor pressure of LAD, GMS, and PMH vs temperature .

[0035] Figure 4: Polystyrene with 5% lauric acid diethanolamide. Contact angle of test devices injection molded at 240°C - 300°C (10 mm / s injection speed, 30°C mold temperature) .

[0036] Figure 5: Polystyrene with 5% lauric acid diethanolamide. Test devices injection molded at 10 mm / s - 150 mm / s injection speed (270°C, 30°C mold temperature) . Plots A and B show the same data but contact angle is plotted versus injection speed in B and versus Cavity filling time in A.

[0037] Figure 6: COC (Topas 8007S-04) with lauric acid diethanolamide. Test devices injection molded with 0.1% to 1% lauric acid diethanolamide at 270°C, 10 mm / s.

[0038] Figure 7: COC (Topas 8007S-04) with 0.5% and 1% lauric acid diethanolamide. Contact angle of test devices injection molded at 230°C - 290°C (10 mm / s injection speed, 30°C mold temperature) .

[0039] Figure 8: Polystyrene with 5% lauric acid diethanolamide. Test of injection speed vs. mold temperature.

[0040] It is to be understood, that the embodiments shown in the figures are for illustration of the present invention and cannot be construed as being limiting on the present invention. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

[0041] DETAILED DESCRIPTION

[0042] The present invention relates to molded plastic objects that are hydrophilic after molding (cf. Figure 1) , but in particular to plastic objects molded from hard plastic compound materials comprising a plastic material compounded with a hydrophilic component, molded into objects at specific molding conditions as detailed herein.

[0043] In general, for hard plastic compound materials the hydrophilic component does not migrate through the material to the device surface at room temperature but remain immobilized in the hard polymer matrix. When molded in a conventional manner, the molded devices thus in the general case do not become hydrophilic.

[0044] The present invention relies on the present inventor' s realization that in certain circumstances surfactants can be co-molded with a plastic composition and following the presently disclosed methods be made to deposit at least in part on the surfaces of the molded plastics objects, rendering these objects hydrophilic after injection molding, even when the plastic used for molding the object is otherwise hydrophobic.

[0045] In experiments of the prior art, a residual amount of the hydrophilic compound is sometimes observed on the molded surfaces, resulting from sublimation of the hydrophilic compound during injection molding. This effect is well known in the art, c.f. e.g. WO 2012 / 141336. However, as shown in the present experiments, if the same effect occurs in the present experiments, the amounts of hydrophilic compounds from sublimation would be too low to provide sufficient hydrophilicity to the molded surfaces, as sublimation would only affects hydrophilic compounds already present at the melt front.

[0046] The present experiments clearly show that the process of making the surfaces hydrophilic, in accordance with the method disclosed herein, involve evaporation of the hydrophilic compound from the polymer matrix, which evaporation is a process that requires a slower molding process than normally employed in the art, in order to allow the hydrophilic compounds to be replenished from the interior of the polymer matrix during the molding process. As such, the present invention deliberately requires that the molding condition are such that evaporation can take place (c.f. Figures 5 and 8 and the experimental discussion thereof) .

[0047] In the art, c.f. e.g. CA 870065 A, WO 2012 / 141336, ON 115386180 A, WO 99 / 64490 Al, JP 2018 / 048264, examples of polymer compositions are given, which correspond to the polymer compositions of the present experiments, which have been subjected to thermomolding under the same temperature conditions as herein discussed in the experiments. However, the examples of the prior art are silent on the molding times. In WO 2012 / 141336 the molding speed is discussed. It is stated therein (c.f. p. 17, lines 10-15, in conformance with the present art) that molding times disclosed therein are shorter than the sublimation speed of any additives contained in the plastics melt, for retaining purity of the molded objects.

[0048] In accordance with the above realizations and objectives, there is herein detailed in a first aspect of the present invention and disclosure a method of injection molding a plastic object (1) from a polymer composition comprising a polymer and a surfactant, the method comprising:

[0049] — providing the polymer composition as a polymer melt at an injection temperature to a mold (2) comprising a mold cavity (21) delimited by a mold surface (22) for molding the polymer composition to the plastic object (1) in the mold ( 2 ) ; wherein — the injection temperature is above a gas phase evaporation temperature of the surfactant at the gas temperature and pressure maintained inside the mold cavity (21) , and

[0050] — the mold (2) is maintained at a mold temperature, which is below the condensation temperature of the surfactant at the temperature and pressure maintained inside the mold cavity (21) , thereby

[0051] — causing surfactant evaporated from the polymer composition to condense on the mold surface (22) and, after the polymer composition has filled the mold cavity (21) forming the plastic object (1) , causing the condensed surfactant to transfer to the plastic object (1) as a surfactant layer on the plastic object (1) .

[0052] When a plastics object is formed by thermomolding as herein detailed, the present inventor has surprisingly discovered that enough of the surfactant is located on the molded device's surface by other mechanisms than migration, thereby rendering the molded object more hydrophilic than the molded object would have been if not molded according to the presently disclosed methods.

[0053] The inventor has determined that at raised molding temperatures, compared to normal molding temperatures, a fraction of the surfactant will evaporate from the molten polymer during injection in the mold cavity (Figure la) . The mold cavity is filled by the surfactant in vapor phase at a significant vapor pressure (Figure lb) . Some of the vapor will condense on the inside surfaces of the mold cavity, thus creating a deposition layer on the inside of the cavity before the molten plastic fills the cavity (Figure 1c) , which as the mold is filled, eventually comes into contact with the molten plastic . After filling the cavity and solidi fication of the plastic the devices are physically ej ected from the mold ( Figure Id) , and, surprisingly, enough of the deposition layer from the inside of the mold cavity is trans ferred to the plastic device , and the molded plastic devices thus become hydrophilic without migration due to the presence of a surfactant layer at the outer surface of the molded obj ect .

[0054] The present inventor has observed that this ef fect is negligible at normal molding conditions . Normally, molding is done at as low a temperature as possible to avoid discoloration, burning etc . of the molded obj ect , in combination with a fast inj ection speed to maximi ze production rate . At these conditions the vapor pressure of the hydrophilic component is low and the condensation time on the mold walls is very short . The resulting deposition layers on the surface of the molded devices of the prior art are much too thin to modi fy the surface hydrophilicity of the molded devices .

[0055] The present inventor now surprisingly has found that to maximi ze the resulting layer of a surfactant on a molded device , evaporation of the surfactant from the melt must be maximi zed and condensation on the inside mold walls must also be maximi zed . This is achieved in the method of the present invention by providing a high polymer inj ection temperature thereby sustaining a high vapor pressure and thus a fast evaporation, a slow inj ection speed for the matrix polymer into the mold cavity, which is therefore filled slowly permitting more of the surfactant time to evaporate from the polymer melt , and further by providing a lowered mold temperature for increasing the amount of a surfactant condensing on the mold walls.

[0056] Molding plastic devices at these unusual conditions using a compound plastic material comprising a polymer mixed with a low concentration (0.1% - 5%) of a surfactant, will produce the desired devices.

[0057] The combination of the compound material and unusual molding conditions in some embodiments enable optically clear and transparent devices that are hydrophilic after molding, even when the plastic material is constituted from polymers, such as e.g., polystyrene, otherwise considered hard, i.e., presenting glass transition temperatures well above room temperature, e.g., 80°C. This combination of properties, to the limit of the present inventor's knowledge, has so far not been possible.

[0058] The method of the invention relies on the determination of the evaporation temperature of the surfactant added to the plastics material before molding, since the injection temperature for the polymer melt into the mold must be above an evaporation temperature of the surfactant at the gas temperature and pressure maintained inside the mold cavity (21) such that the surfactant can evaporate from the molten plastics .

[0059] Generally, the determination of a suitable evaporation temperature is well known in the art and ubiquitously described in the relevant literature. In many cases, relevant data of partial pressure at a given temperature for a given surfactant can be found in the literature, but where this is not directly possible, the present inventor has determined relevant evaporation temperatures using the procedure detailed in OECD Guidelines for testing of chemicals #104, (https: / / doi.org / 10.1787 / 9789264069565-en, accessed 2024- 11-01) adopted 23 March 2006, using the equipment detailed in Figure 2, by measuring correlating values of temperature and partial pressure for the component investigated in accordance with the OECD Guidelines.

[0060] The results for partial pressures versus temperature (at atmospheric pressure) for three surfactants, Lauryl acid diethanolamide (LAD) , glycerol monostearate (GMS) , and polyalkyleneoxide modified heptamethyltrisiloxane (PMH) , c.f. Figure 3. For each of these surfactants, a suitable partial gas pressure of the molecule will build up in a mold chamber if the polymer melt is supplied to the mold chamber at a temperature giving rise to a detectable partial pressure of surfactant.

[0061] E.g., for PMH if the polymer melt is below 225°C, PMH has no detectable vapor pressure and therefore cannot be expected to transfer to the mold walls of the mold chamber by evaporation from the melt, whereas at 250°C or at 275°C, a measurable vapor pressure is observed. The experimentally established condensation temperature for PMH is therefore 225°C @ atmospheric pressure, within the accuracy of the OECD methodology .

[0062] As shown in the experiments, all three surfactants are suitable for use in the present invention, but from a manufacturing perspective, LAD is preferable as its vapor pressure varies linearly temperature over a 40°C span, i.e., from 240°C to 280°C, representing a suitable process window for this surfactant. By extrapolation, the condensation temperature for LAD is about 235°C @ atmospheric pressure, within the accuracy of the OECD methodology. The present experiments were in this respect conducted at atmospheric pressure , since most thermomolding is into a mold being in pressure equilibrium with the exterior, through vents from the mold cavity to the exterior, to prevent a pressure build-up inside the mold during thermomolding .

[0063] As such, determination of both the polymer melt temperature , which is necessary to evaporate a surfactant comprised in the polymer melt and the condensation temperature at least necessary to achieve surfactant condensation onto the sides of the mold cavity can be done by measuring the partial pressure of the surfactant versus temperature , also for establishing a process window for the surfactant versus melt temperature .

[0064] As disclosed, the mold ( 2 ) must be maintained at a mold temperature , which is below the condensation temperature of the surfactant at the gas temperature and pressure maintained inside the mold cavity ( 21 ) . For optimal ef fect , and for fastest obj ect formation inside the mold cavity, however, the mold will only very rarely be kept at a temperature close to the condensation temperature of the surfactant . Rather, the mold temperature will typically be determined by the solidi fication temperature of the plastic entering the mold, which is unrelated to ( and generally lower than) the condensation temperature of the surfactant .

[0065] In the method of the invention, the polymer melt will always enter the mold cavity at a temperature higher than the condensation temperature of the surfactant at the internal pressure of the mold in order to achieve evaporation . Thereby the two central temperatures necessary to be known for using the present invention, namely surfactant condensation temperature and melt temperature can be directly determined by knowledge of the P,T-diagram for the surfactant. Accordingly, the present method of the invention relies solely on thermodynamical equilibrium properties of the surfactant used, and not on intrinsic plastics properties, other than the plastic must be a melt at the injection temperature used.

[0066] In theory, the mold cavity can be kept at the condensation temperature of the surfactant, but for procedural economy, it is preferable to maintain the mold cavity at a temperature significantly lower than the condensation temperature of the surfactant for increased condensation of the surfactant onto the mold surface. However, and while the present invention does not concern such process optimization, as this will intricately depend on each given system of polymer and surfactant, unrelated to the present method, it is preferred in most embodiments that the mold shall have a temperature from 0°C to 80°C, preferably from 10°C to 70°C, more preferably from 20°C to 60°, and even more preferably from 30°C to 50°C. As can be seen from Figure 8, when the mold temperature and the injection speed are jointly optimized, the same polymer composition can result in molded objects with hydrophilicities ranging from not hydrophilic (i.e. above 75°±5°) to wetting (i.e. 5° and below) .

[0067] In accordance with the above realizations and objectives, there is herein detailed in a first aspect of the present invention and disclosure a method of injection molding a plastic object (1) from a polymer composition comprising a polymer and a surfactant, the method comprising:

[0068] — providing the polymer composition as a polymer melt at an injection temperature to a mold (2) comprising a mold cavity (21) delimited by a mold surface (22) for molding the polymer composition to the plastic object (1) in the mold ( 2 ) ; wherein

[0069] — the injection temperature is above a gas phase evaporation temperature of the surfactant at the gas temperature and pressure maintained inside the mold cavity (21) , and

[0070] — the mold (2) is maintained at a mold temperature, which is below the condensation temperature of the surfactant at the temperature and pressure maintained inside the mold cavity (21) , thereby

[0071] — causing surfactant evaporated from the polymer composition to condense on the mold surface (22) and, after the polymer composition has filled the mold cavity (21) forming the plastic object (1) , causing the condensed surfactant to transfer to the plastic object (1) as a surfactant layer on the plastic object (1) .

[0072] In consequence of the above, the present invention is solely concerned with surfactants, wherein a gas phase evaporation temperature of the surfactant, and a condensation temperature for the surfactant, at the gas temperature and pressure maintained inside the mold cavity (21) can be established. Preferably, although these values may be taken from the literature or relevant databases, the condensation temperature and partial pressure at ambient temperature and pressure is measured according to the OECD Guidelines for testing of chemicals # 104, adopted 23 March 2006.

[0073] For optimal use, for the surfactant it preferably is possible, over a temperature interval above the condensation temperature ( the operating window) , to establish a partial pressure of the surfactant in the gas phase in the mold, when the partial pressure is measured according to the OECD Guidelines for testing of chemicals # 104 , adopted 23 March 2006 .

[0074] As discussed herein, surfactants for which it is not possible to establish an operating window for surfactant evaporation, or where the surfactants do not evaporate at all , but rather degrade under influence of temperature , are not useful in the context of the present invention and are consequently excluded herefrom .

[0075] As mentioned, the present method relies solely on equilibrium properties of the evaporating surfactant . However, as shown in Example 3 , the feed rate of the polymer melt to the mold cavity ( and thus release rate of the surfactant from the polymer melt to the atmosphere ) will influence the outcome of the present method .

[0076] The present method does not as such concern optimi zation of the feed rate of a polymer melt comprising a surfactant to the mold cavity, but the skilled person can establish a maximum feed rate ( c . f . Figure 8 ) using the above method for the determination of vapor pressure in the OECD Guidelines for testing of chemicals # 104 , adopted 23 March 2006 , by measuring the time until equilibrium vapor pressure has been established, using instead of a pure sample of the surfactant , the polymer melt comprising the surfactant for a given amount of surfactant in the melt . I f the feed rate exceeds the time to achieve partial pressure equilibrium for the surfactant as measured, then the mold cavity will contain less than maximum surfactant possible available for subsequent condensation onto the cavity walls and as shown in the experiments, less reduction of the resulting contact angle is achieved.

[0077] Consequently, and in accordance with the present invention, in an embodiment thereof, there is herein detailed the method of the first aspect, wherein the plastic object (1) presents a plastic object surface (11) after injection molding to ambient air, having a contact angle to water which is lower than a comparative contact angle to water measured for the polymer or the polymer composition prior to injection molding. In an embodiment thereof, the contact angle to water of said plastic object (1) is below 75°±5°, more preferably below 65°±5°, preferably below 45°±5°, more preferably below 35°±5°, more preferably below 25°±5°, and even more preferably below 15°±5° after injection molding as measured at room temperature in ambient air using a contact angle goniometer preferably measured over at least 3, but preferably at least 5, different locations on said plastic object surface (11) .

[0078] In an embodiment thereof, there is herein detailed the method of the first aspect and any embodiment thereof, wherein the polymer comprised in the polymer composition is selected from polystyrene (PS) , polymethylmethacrylate (PMMA) , cyclic olefin copolymer (COC) , cyclic olefin polymer (COP) , cyclic block copolymers (CBC) , styrene methyl methacrylate copolymer (SMMA) , polyethylene terephthalate (PET) , or polycarbonate (PC) .

[0079] In an embodiment thereof, there is herein detailed the method of the first aspect and any embodiment thereof, wherein the surfactant is selected from a mono-, di-, or tri-substituted sorbitan fatty acid ester, monolaurin (ML) , glycerol monostearate (GMS) , Triton X-100, Poloxamer P188, lauryl acid diethanolamide (LAD) , or polyalkyleneoxide modified heptamethyltrisiloxane . In preferred embodiments thereof, the surfactants are lauryl acid diethanolamide (LAD) and glycerol monostearate (GMS) , or more preferably, lauryl acid diethanolamide (LAD) .

[0080] In an embodiment thereof, there is herein detailed the method of the first aspect and any embodiment thereof, wherein the surfactant is present in the polymer composition at a concentration of from 0.01 wt% to 10 wt%. Preferably, the surfactant is present from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 6 wt%, or even more preferably from 3 wt% to 5 wt% .

[0081] In a second aspect of the present invention and disclosure there is herein detailed a plastics object (1) injection molded according to any method of aforementioned first aspect and embodiments thereof.

[0082] In an embodiment of the aforementioned second aspect, the polymer is either a polystyrene (PS) or a cyclic olefin copolymer (COC) , and the surfactant is either lauryl acid diethanolamide (LAD) or glycerol monostearate, wherein the surfactant is present in the polymer composition in a concentration from 0.01 wt% to 10 wt%. In a preferred embodiment thereof, the surfactant is lauryl acid diethanolamide (LAD) .

[0083] Accordingly, there is herein detailed in an embodiment of the aforementioned second aspect, a plastics object (1) , wherein said polymer is a polystyrene (PS) and said surfactant is lauryl acid diethanolamide, and wherein said surfactant is present in said polymer composition in a concentration from 0.01 wt% to 10 wt%, preferably, from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 6 wt%, or even more preferably from 3 wt% to 5 wt%.

[0084] In an embodiment of the aforementioned second aspect, the polymer is polymethylmethacrylate (PMMA) and the surfactant is Triton X-100.

[0085] In an embodiment of the aforementioned second aspect, there is herein detailed a plastics object (1) according to any embodiment of said second aspect, wherein said plastic object (1) presents a plastic object surface (11) after injection molding to ambient air having a contact angle to water which is lower than a comparative contact angle to water measured for the polymer composition having undergone comparative injection molding without the surfactant.

[0086] In an embodiment of the aforementioned second aspect, there is herein detailed a plastics object (1) according to any embodiment of said second aspect, wherein the contact angle to water of said plastic object (1) is below 75°±5°, more preferably below 65°±5°, preferably below 45°±5°, more preferably below 35°±5°, more preferably below 25°±5°, and even more preferably below 15°±5° after injection molding as measured at room temperature in ambient air using a contact angle goniometer measured over 5 different locations on said plastic object surface (11) .

[0087] EXAMPLES

[0088] In accordance with the below experiments, the present inventor has succeeded in establishing that the following combinations of plastic materials and surfactants are of particular interest for the present invention. Plastic materials of particular interest

[0089] Optically transparent and hard polymer materials are of particular interest. These include polystyrene (PS) , polymethylmethacrylate (PMMA) , cyclic olefin copolymer (COC) , cyclic olefin polymer (COP) , styrene methyl methacrylate copolymer (SMMA) , polyethylene terephthalate (PET) , or polycarbonate (PC) .

[0090] Surfactants of particular interest

[0091] In accordance with the present inventor' s research, surfactants for use with the present invention must fulfill several criteria to function properly with this invention. a. They must be chemically compatible and miscible with the polymer material at the relevant concentration. b. They must be thermally stable at the high process temperature. Many hydrophilic components, including surfactants, will degrade and / or give discoloration before reaching temperatures where they have a useful vapor pressure. c. They must have a high boiling temperature, so the compound material can be molded at a temperature below the boiling temperature of the surfactant. Above the boiling temperature the vapor pressure is above atmospheric, and this will result in undesirable gas bubbles in the molded devices . d. It must be possible to evaporate the surfactant at the relevant molding temperatures 230°-330°C. e. They must have a relatively flat vapor pressure vs. temperature characteristic. As this allows tight control of a relatively high vapor pressure of the surfactant. f . At the highest stable process temperature of the polymer material , optimally the surfactant has a minimum 25 mbar vapor pressure , but preferably 100-200 mbar or even higher .

[0092] These criteria exclude most hydrophilic components . Sugars and polyols generally have very high boiling temperatures ( 400 ° C - 800 ° C ) and will carameli ze at much lower temperature than this . Salts have very high boiling temperatures ( 600 ° C - 1000 ° C ) . These high temperatures are incompatible with the relevant polymer materials . Likewise , hydrophilic polymers have so high molecular weight that they cannot evaporate .

[0093] Currently, the present inventor has identi fied surfactants as the only suitable class of chemical compounds for use in the present invention . As detailed below, numerous hydrophilic compounds have been tested (Experiment 1 ) and only a few of the tested substances were found to have the necessary properties , all of which are surfactants .

[0094] Surfactants

[0095] In the present research presented herein, the present inventor has evaluated numerous surfactants for their high temperature stability and evaporation characteristics . Most surfactants are not stable at the relevant polymer process temperatures and degrade , decompose , and discolor . Some of the surfactant molecules tested nevertheless evaporate and make the molded device hydrophilic, but the molded device becomes discolored, typically in yellow or brown colors , and will require co-molding with dyes and / or colorants to achieve market acceptance . The present research further has identi fied a selection of suitable surfactants and polymers which, when co-molded, result in both . Example 1 - Test of temperature stability of various surfactants . Samples were tested for heat stability in an open pan experiment . In turn, a respective test sample was loaded onto an open pan and heated under ambient pressure conditions while being monitored visually during the heating simultaneously with the temperature of the pan being measured . Results of the tests are reported below in Tables 1 and 2 .

[0096] Table 1 : Tested surfactants found to at least partially degrade at temperatures below their boiling points .

[0097] Most surfactants that were tested in the open pan experiment could not handle the high temperatures required for compounding with the relevant polymers during thermoplastics molding, but rather were found to degrade and discolor at temperatures below the process temperature of the relevant polymer and much below the boiling temperature of the surfactant . In general , for the results reported in Table 1 , no observable trends were found between the chemical composition of a tested compound and predictability of a potential thermal decomposition .

[0098] It was found that sorbitan fatty acid esters , traded as Span- X, were able to resist heating to some degree , with the higher weight fatty acids ester compounds degrading the least , and poly-substituted sorbitans performing better than their monosubstituted counterparts .

[0099] In subsequent tests , it was found that the members of the Span-X family of sorbitan fatty acid esters , such as those detailed in Table 1 , are suitable for use in the method of the present invention, and will yield a hydrophilic molded plastics obj ect after thermomolding, however due to the partial or strong discoloration under heating, they are not suitable for thermomolding of plastics obj ects which are intended to be clear and transparent after molding .

[0100] However, in embodiments of the present invention, the surfactant may be a mono- , di- , or tri-substituted sorbitan fatty acid ester, preferably a mono- , di- or tri-substituted sorbitan fatty acid ester having between 12 to 22 carbon atoms in at least one fatty acid residue , preferably a mono- , di- , or tri-substituted sorbitan fatty acid ester having between 16 to 20 carbon atoms in at least one fatty acid residue , more preferably a mono- , di- , or tri-substituted sorbitan fatty acid ester having 18 carbon atoms in at least one fatty acid residue . In preferred embodiments thereof , the surfactant is a tri-substituted sorbitan fatty acid . In preferred embodiments thereof , the tri-substituted sorbitan fatty acid is one or both of sorbitan tri-stearate ( Span- 65 ) or sorbitan tri-oleate ( Span- 85 ) , In Table 2 below are reported a few surfactants found to evaporate at temperatures below their degradation / discoloration temperature . These surfactants are relevant for use with this invention for molding plastics obj ects which are transparent and hydrophilic after molding .

[0101] Table 2 : Exemplary surfactants which evaporate with only minimal or even without thermal degradation .

[0102] Example 2 - Surfactant compatibility with polymers

[0103] While the select few surfactants in Table 2 have acceptable high temperature stability they may not be compatible with the relevant polymers . In the art , it is well known that chemical incompatibility between elements of the plastics composition usually give discoloration in the material and molded devices during thermomolding . E . g . , physical incompatibility between a surfactant and a polymer usually causes haze in the molded plastics obj ect caused by surfactant precipitation in the polymer matrix, wherein the physical incompatibility e . g . , can be caused by low solubility of the surfactant in the polymer with subsequent precipitation . And, while such precipitation can be avoided by reducing the concentration of surfactant in the compound, this also reduces the surfactant vapor pressure and thus the molded devices does not become hydrophilic .

[0104] Unfortunately, and to the day, it is an unsolved scienti fic question how to accurately predict solubility of a given compound in polymer solutions . To an extent , solubility can be predicted using semi-quantitative prediction systems such as Hansen solubility parameters , or using dedicated database systems , experimental confirmation of a predicted compatibility remains indispensable for veri fication of a predicted solubilities .

[0105] However, as detailed above , the present inventor' s research has provided the following general characteristics of the hydrophilic components suitable for being used as surfactants for co-molding with prospective polymers for yielding hydrophilic thermomolded plastics obj ects after thermomolding .

[0106] Example 3 - Identified polymer and surfactant blends suitable for co-molding for obtaining a transparent and hydrophilic plastics object after thermomolding . In the experiments below, contact angles were measured as static contact angles at atmospheric pressure and room temperature using a contact angle goniometer.

[0107] Polystyrene (PS) with lauryl acid diethanolamide (LAD) and / or glycerol monostearate (GMS) .

[0108] For PS the present inventor has experimentally identified lauryl acid diethanolamide and glycerol monostearate as excellent hydrophilic components that make the PS compound very hydrophilic. They are both chemically compatible with PS and have minimum discoloration of the compound material. 5% lauryl acid diethanolamide is best for PS as this compound is color and haze free. 1% glycerol monostearate has a little haze .

[0109] Polystyrene with 5% lauric acid diethanolamide (LAD)

[0110] Figure 4 shows contact angle of test devices injection molded at 240°C-300°C (10 mm / s injection speed, 30°C mold temperature) . As the molding temperature is increased the contact angle decrease and stabilize at 20° from 270° C and up .

[0111] Figure 5 shows contact angle of test devices injection molded at 10 mm / s - 150 mm / s injection speed (270°C, 30°C mold temperature) . As injection speed is decreased the contact angle decrease and stabilize at 20°.

[0112] Table 3 shows contact angle of test devices injection molded for 30°C and 60°C mold temperature (270°C, 10 mm / s) . Although the contact angle is slightly lower for 30°C mold temperature compared to 60°C, the difference is not statistically significant .

[0113] At normal molding settings for polystyrene (230°C, 30 mm / s) the contact angle is 80° as is normal for polystyrene. This compound will only give hydrophilic devices when molded at higher than normal temperature and injected at unusually slow speed .

[0114] Table 3: Polystyrene with 5% lauric acid diethanolamide. Test devices injection molded for 30°C and 60°C mold temperature at 270°C, 10 mm / s.

[0115] Polystyrene with 3% lauric acid diethanolamide (LAD)

[0116] In the experiment shown in Figure 8, an investigation of the dependency of the contact angle on mold temperature and injection speed, in accordance with the labels on the Figure. In the experiment, the injection speed was lowered in decrements of halves (approximately) from an originally 100 mm / s injection speed recommended by the manufacturer of the injection molding machine to 50 mm / s, 30 mm / s, and finally 10 mm / s injection speeds. The contact angle values for the 100 mm / s injection speed are not shown in the figure but tested essentially identical to the contact angle of pure polystyrene of about 90° irrespective of mold temperature. The experiments very clearly show how, for the same surfactant and polymer material , that without allowing for suf ficient time for the surfactant to evaporate from the polymer melt , no suf ficiently hydrophilic surfaces will result from the molding process .

[0117] As expected, lowering the mold temperature improves the availability of the surfactant on the mold surface by condensation, however ( and surprisingly) for the coldest mold surfaces , there is a slight trend towards increased contact angles between obj ects otherwise molded at the same inj ection speed . The inventor considers , without being bound by the considerations , that possibly some surfactant reorgani zation at the surface is necessary after deposition from the gas phase for the surfactant to obtain its maximum ef fect , which is helped by the mold surface not being too cold . And, oppositely, that when the mold is too hot , reorgani zation of the surfactant may become too rapid for an ordered surfactant layer to become established on the molded obj ect .

[0118] However, the merit of the present invention is very clearly shown in Figure 8 , namely that by allowing the surfactant time to evaporate during the molding process it is possible to obtain molded obj ects , which are hydrophilic ( even wettable by water ) directly after molding, where obj ects known from the prior art molded from the same starting materials and under the same temperature conditions of melt and mold are not . This , as shown, is caused by, in the molding methods of the prior art , the molding speeds having been selected for suppressing additive sublimation ( and consequently evaporation is never observed) , whereas the present invention actively utili zes the benefits of achieving surfactant evaporation in the methods of the present invention .

[0119] In this respect, the experiment disclosed in Figure 8 shows how a skilled person can easily determine an optimized injection speed for use with present method, such that surfactant evaporation is favored during molding, namely by stepwise lowering of the injection speed from an initial guess or known injection speed (e.g. a manufacturers recommendation) and performing a correlation test of injection speed to resulting plastics object contact angle to water measurement. In the present experiment the stepwise lowering is done by halving, and wetting surfaces were obtained after only three iterations.

[0120] Cyclic olefin copolymer (COC)

[0121] For COC we have used Topas 8007S-04 and for this we have experimentally identified lauryl acid diethanolamide and glycerol monostearate as excellent hydrophilic components that make the COC compound very hydrophilic. 1% glycerol monostearate is best for COC as this compound have a minimum color and haze (almost nothing) . Lauryl acid diethanolamide (LAD) works very well with COC but give the compound a faint yellow color.

[0122] Topas 8007 with LAD, PEG-200, or Poloxmer 188.

[0123] Figure 6. Test devices injection molded with 0.1% - 1% lauric acid diethanolamide at 270°C, 10 mm / s, i.e., unusually high temperature and slow injection speed for Topas 8007S-04. The higher the additive concentration the lower the resulting device contact angle. For reference, pure Topas 8007S-04 have a contact angle of 88°. Figure 7. Test devices injection molded with 0.5% and 1% lauric acid diethanolamide (LAD) . Contact angle of test devices injection molded at 230°C - 290°C (10 mm / s injection speed, 30°C mold temperature) . As the molding temperature is increased, the contact angle decreases.

[0124] Topas 8007 + 2% PEG-200

[0125] Molding Contact Visual appearance conditions angle

[0126] 250°C, 10 mm / s 77.8° Clear and almost without discoloration

[0127] 270°C, 10 mm / s 50.1° Minor yellow discoloration

[0128] 290°C, 10 mm / s 30.6° Hazy and orange / brown discoloration

[0129] Topas 8007 + 2% Poloxamer 188

[0130] Molding Contact Visual appearance conditions angle

[0131] 250°C, 10 mm / s 72.9° Almost without discoloration

[0132] 270°C, 10 mm / s 43.6° Some yellow discoloration

[0133] 290°C, 10 mm / s 37.3° Gas bubbles and brown discoloration

[0134] Cyclo-olef in-polymer (COP) COP (Zeonor 1060R) , cyclo-olef in-polymer with 2% lauryl acid diethanolamide. Devices molded in this compound become very hydrophilic at 250-270°C, 10 mm / s. Clear and transparent molded devices with a yellow tone. Cyclic block copolymers (CBC) :

[0135] CBC (Vivion 0510HFE) , cyclic block copolymers (CBCs) , which are fully hydrogenated polymers based on styrene and conjugated dienes via anionic polymerization with 1% lauryl acid diethanolamide. Devices molded in this compound become very hydrophilic at 270-300°C, 10 mm / s . Clear, transparent and color free molded devices.

[0136] Polymethylmethacrylate (PMMA)

[0137] For PMMA we have experimentally identified Triton X-100 as an excellent hydrophilic component that make a PMMA compound very hydrophilic. Minimum discoloration and haze. Unfortunately, as use of Triton X-100 in any context involving humans is forbidden due to its negative hormonal interference with the human body, the present example merely demonstrates the feasibility of the current method.

[0138] Poly (methyl methacrylate) (PMMA, Altuglas VM100) with 2% lauryl acid diethanolamide. Devices molded in this compound become very hydrophilic at 230-260°C, 10 mm / s, Clear, transparent and color free molded devices, but haze from 270°C.

[0139] CLOSING COMMENTS

[0140] Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. The term " comprising" as used in the claims does not exclude other elements or steps . The indefinite article "a" or "an" as used in the claims does not exclude a plurality . A single processor or other unit may ful fill the functions of several means recited in the claims . A reference sign used in a claim shall not be construed as limiting the scope .

Claims

CLAIMS1. A method of injection molding a plastic object (1) from a polymer composition comprising a polymer and a surfactant, the method comprising:— providing said polymer composition as a polymer melt at an injection temperature to a mold (2) comprising a mold cavity (21) delimited by a mold surface (22) for molding said polymer composition to said plastic object(1) in said mold(2) ; wherein— said injection temperature is above a gas phase evaporation temperature of said surfactant at the gas temperature and pressure maintained inside said mold cavity (21) , and— the mold (2) is maintained at a mold temperature, which is below the condensation temperature of the said surfactant at the temperature and pressure maintained inside said mold cavity (21) , thereby— causing surfactant evaporated from said polymer composition to condense on said mold surface (22) and, after said polymer composition has filled said mold cavity (21) forming said plastic object (1) , causing said condensed surfactant to transfer to said plastic object (1) as a surfactant layer on said plastic object (1) •2. The method according to claim 1, wherein said plastic object (1) presents a plastic object surface (11) after injection molding to ambient air having a contact angle to water which is lower than a comparative contact angleto water measured for the polymer composition having undergone comparative injection molding without the surfactant in accordance with the method of claim 1.

3. The method according to claim 2, wherein the contact angle to water of said plastic object (1) is below 75°±5°, more preferably below 65°±5°, preferably below 45°±5°, more preferably below 35°±5°, more preferably below 25°±5°, and even more preferably below 15°±5° after injection molding as measured at room temperature in ambient air using a contact angle goniometer, preferably measured over at least 3, but more preferably at least 5 different locations on said plastic object surface (11) .

4. The method according to any preceding claim, wherein said polymer comprised in said polymer composition is selected from polystyrene (PS) , polymethylmethacrylate (PMMA) , cyclic olefin copolymer (COC) , cyclic olefin polymer (COP) , cyclic block copolymers (CBC) , styrene methyl methacrylate copolymer (SMMA) , polyethylene terephthalate (PET) , or polycarbonate (PC) .

5. The method according to any preceding claim, wherein the surfactant is selected from a mono-, di-, or trisubstituted sorbitan fatty acid ester, monolaurin (ML) , glycerol monostearate (GMS) , Triton X-100, Poloxamer P188, lauryl acid diethanolamide (LAD) , or polyalkyleneoxide modified heptamethyltrisiloxane, preferably lauryl acid diethanolamide (LAD) or monolaurin (ML) , glycerol monostearate (GMS) , or more preferably lauryl acid diethanolamide (LAD) .

6. The method according to any preceding claim, wherein the surfactant is present in said polymer composition at aconcentration of from 0.01 wt% to 10 wt%, preferably, from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 6 wt%, or even more preferably from 3 wt% to 5 wt%.

7. A plastics object (1) injection molded according to any method of the claims 1 to 6.

8. A plastics object (1) according to claim 7, wherein said polymer is either a polystyrene (PS) or a cyclic olefin copolymer (COC) , and said surfactant is either lauryl acid diethanolamide or glycerol monostearate, wherein said surfactant is present in said polymer composition in a concentration from 0.01 wt% to 10 wt%, preferably, from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 6 wt%, or even more preferably from 3 wt% to 5 wt%.

9. A plastics object (1) according to either 7 or claim 8, wherein said polymer is a polystyrene (PS) and said surfactant is lauryl acid diethanolamide, and wherein said surfactant is present in said polymer composition in a concentration from 0.01 wt% to 10 wt%, preferably, from 0.5 wt% to 8 wt%, more preferably from 1 wt% to 6 wt%, or even more preferably from 3 wt% to 5 wt%.

10. A plastics object (1) according to claim 7, wherein said polymer is polymethylmethacrylate (PMMA) and said surfactant is Triton X-100.

11. A plastics object (1) according to any of the claims 7 to 10, wherein said plastic object (1) presents a plastic object surface (11) after injection molding to ambient air having a contact angle to water which is lower than a comparative contact angle to water measured for thepolymer composition having undergone comparative injection molding without the surfactant.

12. A plastics object (1) according to any of the claims 7 to 11, wherein the contact angle to water of said plastic object (1) is below 75°±5°, more preferably below 65°±5°, preferably below 45°±5°, more preferably below 35°±5°, more preferably below 25°±5°, and even more preferably below 15°±5° after injection molding as measured at room temperature in ambient air using a contact angle goniometer measured over 5 different locations on said plastic object surface (11) .

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