DE102022000647A1 - Plastic and method for processing a plastic - Google Patents

Abstract

The invention relates to a method for processing a plastic, in which the plastic is processed with a laser and thereby modified or de-wetted. The plastic is then irradiated in order to at least partially achieve crosslinking of the plastic again. The invention also relates to a plastic, in particular an eye implant or an intraocular lens, which has at least one area in which the plastic has been vaporized with a laser and this area has been post-treated in order to crosslink the plastic again.

Description

The invention relates to a method for processing a plastic, in which the plastic is processed with a laser.

When material is removed above the evaporation threshold or a material modification below the evaporation threshold, depending on the type of plastic and the processing parameters, dewetting or depolymerization of the plastic can occur, which negatively affects the properties of the plastic. This applies to mechanical and chemical properties such as strength, elasticity, flexural fatigue strength, inertness and solubility. The invention also relates to a plastic, in particular an eye implant or an intraocular lens, which has at least one area in which plastic has been vaporized or modified with a laser.

It is known to treat plastics with a laser in order to remove material and/or polish the surface. An example of such processing of a plastic shows the DE 10 2017 002 986 B4 . Here, using the example of an intraocular lens, it is shown how a laser can be used to remove material and how the surface can also be polished with the laser.

However, the present invention relates not only to the treatment of intraocular lenses, eye implants, methacrylate plastics or thermoplastics, but in general to the processing of plastic, in which the plastic is processed with a laser.

The laser processing methods for evaporating plastic or just for modifying or melting plastic change the cross-linking of the molecules in the plastic. This also changes the properties of the plastic, at least in the area in which the plastic was processed. This applies in particular to the geometry during removal and melting. When melting and modifying, however, also the mechanical and chemical properties, in particular the refractive index on the surface or in the volume of the plastic.

In the context of the invention, a plastic is understood to mean a solid whose basic component is synthetically or semi-synthetically produced polymers with organic groups. Synthetic plastics are produced from monomers by polymerization (polyaddition, polycondensation, etc.).

The degree of cross-linking is reduced during the thermal treatment of plastics, such as in particular during melting and evaporation, or to change the refractive index in the material. This reduces hardness, toughness and melting point and increases solubility. This facilitates the processing of the plastic and makes it possible, for example, to further process a blank or a blank that has been pretreated with a laser with a polishing laser.

However, after the blank has been polished with a polishing laser, the plastic still has a lower degree of cross-linking than the untreated blank. This means that the plastic is no longer as hard and tough as the untreated blank.

The invention is therefore based on the object of processing or post-processing plastics in such a way that the disadvantages associated with the dewetting of the plastic are compensated for or at least minimized.

Fortunately, it turned out that this problem could be solved with a method having the features of claim 1, and the problem on which the invention is based is also solved with a plastic according to claim 14.

The invention is based on the finding that a variation of the method for removing, melting or modifying the plastic, even with the help of USP lasers with pulse durations of less than 1 ns and pulse energies of 0.1 μJ to 10 μJ, can adversely affect the processed lead plastic. Instead of continually optimizing the machining process, the invention is based on the knowledge that the plastic can be irradiated after laser machining in order to at least partially achieve cross-linking of the plastic again.

Particle radiation is suitable for the irradiation. Electron beams, gamma rays or also photons, in particular UV photons, can be used as particle radiation. The radiation activates the decrosslinked parts of the polymer chain in the form of electronic excitation or ionization, which then leads to increased crosslinking with other parts of the polymer chain. Experiments with a variation of the particle energy and the particle beam power with regard to the power introduced per area confirm the effect.

Contrary to previous approaches, no new method for reducing the dewetting of the plastic is used according to the invention laser processing is proposed, but the dewetting of the plastic during processing with the laser is accepted and the plastic is then irradiated in order to at least partially achieve crosslinking of the plastic again. As a result, the dewetting of the processed blank can be reduced, the plastic can once again have the properties of the blank after processing and it is even possible to achieve greater crosslinking than the degree of crosslinking of the blank in order to increase the hardness, toughness and melting point and the decrease solubility.

The plastic is thus cross-linked with the aim of polishing and reducing the viscosity by shortening the polymer chains. This can happen outside a lens on its surface, for example by laser ablation, but also inside the lens. Additional crosslinking is then usually only useful on the surfaces because of the polishability and the restoration of the extractability, and this can be achieved particularly advantageously with particle blasting.

One possible treatment of the plastic to increase crosslinking would be treatment with crosslinking agents. Such crosslinking agents are distinguished by at least two reactive groups. Crosslinkers with two identical reactive groups are called homobifunctional crosslinkers, while those with two different groups are called heterobifunctional crosslinkers.

The crosslinking of already existing polymers is referred to as crosslinking and can either take place via functionalities already present in the polymer through a skilful choice of the reaction conditions or through the use of multifunctional, low-molecular substances.

Depending on the degree of crosslinking, the crosslinking of polymers first produces elastomers and, with increasing crosslinking, thermosets.

According to the invention, however, no conventional crosslinking agent is used, but instead the plastic is irradiated after dewetting. The irradiation makes it possible to subsequently treat the plastic, which has previously been treated with a laser beam, with a special irradiation tailored to increase cross-linking.

While irradiation with the laser leads to dewetting of the plastic during ablation, melting, polishing or modification, irradiation with other beams or parameters leads to crosslinking of the plastic.

The method according to the invention thus makes it possible to process a plastic exclusively by irradiation and thus without contact, up to and including evaporation or polishing, and then to harden it again without contact or to improve the material properties.

These process steps can be carried out directly one after the other. They can also be carried out in parallel, with the dewetting occurring during the processing of the blank with the laser in a focused manner in the interior of the blank and/or on its surface and the radiation treatment with particle radiation counteracting this dewetting process. In order to be able to process plastic parts in a continuous process, they can be guided on a conveyor through treatment stations, such as inserting the blank, removing, polishing, crosslinking, final cleaning, final inspection, and packaging. However, a stationary blank can also be processed and irradiated with a laser. It is particularly easy here to define and vary the chronological sequence of the method steps.

The plastic parts can be heated by the radiation during processing to speed up the process. However, they can also be heated, for example, with infrared radiation, in particular to accelerate polishing and/or crosslinking.

Duroplasts and thermoplastics are particularly suitable as the plastic for the method according to the invention, but they can also be crosslinked by the irradiation in such a way that an elastomer or a duroplastic is formed.

An acrylate or methacrylate is particularly suitable as the plastic for processing with a laser and then with radiation for crosslinking.

The method described is particularly suitable for the production of implants. Laser processing makes it possible to produce a special implant from a blank, and preferably also an implant tailored to the special surgical treatment, and then to harden this implant again via the cross-linking of the plastic. The non-contact treatment of the plastic means that a plastic material that is suitable as an implant is dewetted and re-linked during processing, but ultimately has a similar cross-linking to the starting material. This avoids problems that could arise if a plastic approved for the manufacture of implants is damaged by treatment with the laser and the associated dewetting undergoes such a material change that it is no longer suitable as an implant.

Good experiences have been made with the use of the method for an eye implant and in particular for an intraocular lens.

Particularly suitable for processing a plastic according to the invention is the processing of the plastic with an ultra-short pulse laser (USP laser), since a particularly precise change in the plastic can be achieved in this way, which can range from a partial change in the material properties to an evaporation of material areas to a Polishing by melting material on the plastic surface is enough.

In order to be able to produce certain plastic bodies for use, for example as a mechanical component or as an implant, it is advantageous if part of the plastic is vaporized with the laser during processing or the refractive index is modified inside the blank. In addition, when processing the plastic with the laser, it can be polished by removing certain areas of the material or by liquefying it and thus increasing the effect of surface tension with regard to smoothing, in order to avoid microscopic structuring on the surface.

A simple processing of the plastic is achieved in that the plastic is processed with the laser on the surface of the plastic. However, machining the surface of the plastic also inevitably results in machining of areas of the plastic that lie below the surface in the interior of the plastic.

In addition to such processing close to the surface, the laser beam can also be used to process the plastic in a targeted manner inside the plastic. Here, in particular, plastic areas are addressed that are at least 0.2 mm away from the surface of the plastic.

By coordinating the de-wetting with the laser and the cross-linking with the irradiation, certain predefined material properties can be set on a surface area or in a volume area of the blank.

At the same point, an increase in dewetting can be offset by an increase in crosslinking, or the desired material properties are set through the interaction of a defined dewetting and a defined crosslinking.

However, the defined setting of material properties can also be used to provide different degrees of dewetting and crosslinking at different points, surface or volume areas. This gives the blank different material properties, depending on which area of the blank is being viewed.

For example, the blank can have outer surface areas that are particularly hardened by the irradiation and inner areas that are hardened to a lesser extent by the irradiation.

Thus, for example, a lens may have its refraction increased in one area and decreased or increased in another area on the path of a light ray passing through the lens to compensate for the change caused by machining of the blank or to achieve a specific refraction.

As with the laser, total duration, pulse duration, and intensity can be varied, these parameters can also be used to vary the effects of irradiation on material properties in the irradiated area.

In order to irradiate the plastic after dewetting in order to at least partially achieve crosslinking of the plastic again, irradiation with photons is proposed.

However, irradiation of the plastic with electrons, beta or gamma radiation has also proven to be advantageous.

The treatment of plastics with high-energy electron, beta or gamma radiation gives the plastic used the thermal, mechanical and chemical properties of high-performance plastics. This also makes it possible to use inexpensive mass-produced plastics for the process. Radiation crosslinking can take place after shaping as the last processing step in the process chain. The special processing, in particular the resulting hardness of the surface, makes it possible to pack the plastic parts loose in lattice boxes or cartons. The cross-linking can be precisely controlled with a precisely defined dose of radiation. The material properties can be precisely defined in advance and achieved through precise irradiation. With shielding, the degree of crosslinking can even be varied within a molded part. As a result, a plastic part can have different degrees of hardness.

Unlike chemical crosslinking processes, radiation crosslinking takes place at low temperatures; this makes editing easier.

Particularly good experiences have been made with the crosslinking of polyethylene (PE), polyamide (PA), polybutylene terephthalate (PBT) and polyvinyl chloride (PVC). In addition, the method according to the invention is suitable for thermoplastic elastomers (TPE) and polypropylene (PP).

According to the invention is therefore also a plastic, in particular an eye implant or an intraocular lens, which has at least one area in which the plastic has been processed with a laser, and dewetting of the plastic takes place with the laser and the plastic is after-treated at least in one area, to re-link the plastic. Such processing with a laser is, for example, the evaporation of part of the plastic or the polishing of the plastic by changing the surface of the plastic.

Particularly preferred plastics in this area have been polished after some of the plastic has evaporated and have been post-treated to re-crosslink the plastic.

Insofar as plastic is mentioned within the scope of this invention, any plastics are meant as raw materials, as molded parts or any plastic parts, such as mechanical elements or implants or also plastic surfaces or plastic areas within another component.

An exemplary embodiment according to the invention describes the production of an intraocular lens. This lens is made from a blank on which material is first removed using a removal laser. An area of the blank where the laser hits the blank is vaporized. This material removal of 0.01 to 10 µm/pulse is achieved with a laser with a pulse energy of 0.1 µJ to 10 µJ. The pulse duration of the UKP laser is less than 1 ns and the laser wavelength is preferably between 193 nm and 370 nm. A focus diameter of between 5 and 5 μm is advantageous.

The blank, which consists of an acrylate, is first deformed by evaporating surface areas so that it approximately reaches the predetermined end shape. The blank is then further processed with a polishing laser.

Since this leads to dewetting in the processing areas, the blank is then treated with electron, beta or gamma radiation, at least in these areas. The treatment lasts until the processed surface has at least reached the degree of crosslinking of the blank or even at least partially has a higher degree of crosslinking.

This makes it possible to produce plastic parts and, in particular, medical implants with a particularly hard and solvent-resistant surface.

The combination of a de-wetting process using a laser and a cross-linking process using radiation treatment makes it possible to produce the plastic part with different densities. For example, an intraocular lens produced using the method can have a harder, ie better crosslinked, plastic layer on the surface than on the inside for protection. Cross-linking gradients can be achieved in a cross-section through a plastic part, and the refractive index inside or inside the lens can be varied in a targeted manner through the predetermined cross-linking.

This makes it possible to influence the beam path of a light beam passing through the plastic body not only via the material properties and shape on the surface of the plastic body and in particular the lens, but also through the preset material density in the plastic and in particular through a density gradient within the plastic.

A preferred exemplary embodiment provides that a plastic blank is modified during laser processing and then irradiated in such a way that the plastic then has the material properties of the plastic blank again.

For processing the plastic with a laser are in particular in the DE 10 2017 002 986 A1 described method particularly advantageous.

An embodiment is shown in the figure and is described below.

It shows the only figure schematically a side view of a processing system.

That in the 1 Conveyor belt 1 shown carries lenses 2 (numbered only as an example) past several processing stations. An IR radiator 3, which heats the lens 2, is only shown as an example as the first processing station. The next processing station is a laser 4 that specifically changes the shape of the lens. Then comes a processing station with a laser 5 that marks the surface of the lens polished. The fourth station is a radiator 6 for high-energy electron, beta or gamma radiation. The last station is a packing station 7, where the lens 3 is packed in a sterile manner.

As an alternative, the lenses can also be positioned in a stationary position and different processing stations are guided past the lime trees. In addition, a combination of these two processing methods can also be carried out.

The irradiation, which is used for crosslinking, can be carried out with electron beams. An electron energy of E = 150 keV - 300 keV, in extreme cases up to 1.5 MeV, can be used. The mean power of the electron beam is then, for example, P=1-5 kW.

A reasonable dose rate can be PD = 50-500 kGy (kilo-grey). This dose can also be applied in several doses applied one after the other. For this purpose, the emitter can also run over the workpiece several times in order to ultimately apply the desired total dose in order to achieve the desired crosslinking.

In practice, the irradiated area A was 2×20 cm. This results in intensities I of 0.5 kW/cm2 - 3 kW/cm2. A feed rate of V = 3 - 10 cm/s is suitable for the surfaces mentioned above.

The data can be scaled up or down to achieve a corresponding intensity per area.

In the case of stationary irradiation, the corresponding intensities, irradiation durations and dose rates can be calculated.

The one in the DE 10 2017 002 986 A1 The methods described are values for conventional processing of a plastic blank with a laser. This results in dewetting, which should then be compensated for again. Or the material properties of the plastic blank are changed in a targeted manner on its surface and possibly also in its inner volume through a predetermined interaction of dewetting and crosslinking.

The special processing used in the DE 10 2017 002 986 B4 is described also describes the process step of de-wetting for the exemplary embodiment, which is followed by the process step of cross-linking described in this application.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017002986 B4 [0003, 0063]
• DE 102017002986 A1 [0052, 0062]

Claims (16)

Process for processing a plastic, in which the plastic is processed with a laser and at least partially modified, characterized in that the plastic is de-wetted and then irradiated in order to at least partially achieve cross-linking of the plastic again. procedure after claim 1 , characterized in that the plastic is a thermoplastic or a thermoset. Method according to one of the preceding claims, characterized in that the plastic is an acrylate and preferably a methacrylate. Method according to one of the preceding claims, characterized in that the plastic is an eye implant. Method according to one of the preceding claims, characterized in that the plastic is a visual aid such as in particular an intraocular lens or a contact lens. Method according to one of the preceding claims, characterized in that the laser is a UKP laser. Method according to one of the preceding claims, characterized in that part of the plastic is evaporated with the laser during processing. Method according to one of the preceding claims, characterized in that the plastic is polished with the laser during processing. Method according to one of the preceding claims, characterized in that the plastic is processed with the laser on the surface of the plastic. Method according to one of the preceding claims, characterized in that the plastic is processed with the laser at least also on the inside of the plastic. Method according to one of the preceding claims, characterized in that the plastic is irradiated with particle beams, in particular electron beams. Method according to one of the preceding claims, characterized in that the plastic is irradiated with photons. Method according to one of the preceding claims, characterized in that the plastic is irradiated with beta or gamma radiation. Method according to one of the preceding claims, characterized in that a plastic blank is modified during laser processing and is then irradiated in such a way that the plastic then again has the material properties of the plastic blank. Plastic, in particular an eye implant or intraocular lens, which has at least one area in which the plastic has been processed with a laser and thereby at least partially modified, characterized in that this area has been post-treated in order to crosslink the plastic again. plastic after claim 15 , characterized in that the plastic in this area has been polished after evaporating part of the plastic.

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