DE102019110124A1 - Reactive injection molding process with activation by UV radiation - Google Patents

Abstract

A reactive injection molding process for the production of molded parts (18) made of plastic with at least two areas (18, 28) of different properties, the reactive resin being cured with UV radiation (20, 36) in a cavity (10) of a tool (12) , whereby a duromeric plastic is obtained, is characterized in that the reactive resin of all areas (18, 28) is cured in a cavity (10) of the same tool (12) and the curing is carried out by irradiation with UV radiation (20, 36) done gradually.

Description

Technical area

The invention relates to a reactive injection molding process for the production of molded parts made of plastic with at least two areas of different properties, the plastic being cured with UV radiation in a cavity of a tool. The invention also relates to a tool for carrying out the method.

An activatable reactive resin is used in reactive injection molding processes. The activation can generally take place through heat or radiation. With activation, the networking process is set in motion and maintained. The reactive injection molding process differs from conventional thermoplastic injection molding processes, in which a thermoplastic material is melted, injected and then cooled down, among other things. through lower process temperatures and pressures.

The present invention relates to a method with activation by UV radiation in contrast to thermal reactive resin injection molding methods. In thermal reactive resin injection molding processes, a heat-activatable reactive resin is introduced into the injection molding tool at a relatively low temperature and then cured with the supply of heat. When activated with UV radiation, a reactive resin is introduced into the cavity of a tool and irradiated with UV radiation to cure.

State of the art

US 8 647 555 B2 discloses a multicomponent process in which, in a first step, the largest proportion of the volume of the molded part is cast. In a second step, the surface layer made of a different material is then applied in a second, somewhat larger cavity. The mechanical properties of the material applied last determine the surface properties of the workpiece. The disadvantage of the known method is that several expensive tool parts are required in order to produce the various cavities. A turntable injection molding machine on which the various tool elements can be arranged is required for automation. The production of small series with this method is correspondingly uneconomical.

Disclosure of the invention

The object of the invention is to create a more economical reactive injection molding process of the type mentioned at the beginning.

According to the invention, the object is achieved in that the plastic of all areas is cured in a cavity of the same tool and the curing takes place step by step by exposure to UV radiation.

The same tool is always used in the method according to the invention. The cavity formed by the tool, i. the cavity in which the molded part is produced has the same shape and the same volume throughout the process. Curing takes place gradually to create different areas. First of all, in a first step, the material is cured in a first area. Then the material is cured in further areas in further steps. It can be provided that the first area comprises at least part of the surface of the molded part that is in contact with the tool.

Differences in the material properties in the various areas in the molded part can then be produced in different ways. In one embodiment of the invention it is provided that the UV radiation in each of the irradiation steps has different radiation properties and / or takes place in different ways. Different radiation properties can be realized in particular with different wavelengths. However, alternatively or additionally, the dose, i.e. to vary the intensity and / or exposure time in such a way that the curing process can be controlled in a suitable manner.

Alternatively or additionally, however, it can also be provided that the plastic of an area in the cavity of the tool is cured by irradiation with UV radiation in an irradiation step, before further plastic is fed into another area in the cavity of the tool and cured in the next irradiation step becomes. For example, the surface of the tool can first be coated and cured. Then the remaining volume inside the cavity is filled and cured. This can take place in particular in that the resin of the first irradiated area is applied to a tool surface by roller application, spray application, dipping, injection molding or another coating technique.

Alternatively, it is provided that the entire cavity is filled in one step and the step-by-step irradiation follows.

It can be provided that different materials are introduced into the cavity, which, for example, with the same UV radiation Radiation leads to different material properties in the areas in different steps. The same material can also be used. The surface is then hardened at, for example, a short wavelength, while the bulk material remains liquid. The surface quality is good on the side facing the UV radiation. This surface is hard and hardened and the bulk material underneath is liquid because it has hardly reacted. With UV irradiation, there is strong shrinkage, especially in the case of large volumes. Then the surfaces deform. If the surface hardens first, the risk of it changing is significantly lower. According to the invention, the good, hard and hardened surface is produced first, and then the remaining volume is hardened. The shrinkage takes place, for example, in the area on the side of the molding tool facing away from the UV source. Since the material is still liquid before the second irradiation, shrinkage can again be partially compensated for.

The different properties of the areas can in particular include the material composition of the plastic, the strength, rigidity, toughness and / or the hardness of the hardened plastic.

The activation can be controlled in that the UV radiation has different wavelengths. It is also possible to use additional different intensities and / or different irradiation times for each irradiation step. Also the dose, i.e. the combination of intensity and duration can have an impact. It is important that a short wavelength has a lower penetration depth and that the surface is hardened as a result.

When controlling via a lower dose, an increased photoinitiator concentration is used to reduce the penetration depth.

A particularly preferred method is characterized in that the surface of the molded part in contact with the tool forms an area that is irradiated with UV radiation of a shorter wavelength with a defined dose, at which the UV radiation only penetrates into the surface area of the molded part and this cures and the remaining area of the molded part is then irradiated with UV radiation, the wavelength and intensity of which is designed in such a way that the remaining volume of the molded part is completely irradiated and hardens. The wavelength can be longer than in the first step. In this way, molded parts with a high level of surface accuracy can be achieved, which can also be produced inexpensively in smaller series. In particular, the method according to the invention allows the use of surfaces with a microstructure profile.

According to the invention, a cavity-forming tool is provided for carrying out the described method, characterized by at least one radiation source for generating UV radiation with which a reactive resin located in the cavity can be irradiated.

The radiation source can be controllable, so that the UV radiation is emitted at different frequencies, temporal emission profiles, intensities or other properties. Alternatively or in addition, it can also be provided that at least two radiation sources for generating UV radiation with at least two different radiation frequencies, radiation intensities or other different radiation properties are provided. The use of filters for wavelength selection in the case of broadband radiation sources can also be provided.

The tool can have a tool surface adjoining the cavity, through which the UV radiation can be conducted into the cavity. For this purpose, the tool surface can be at least partially transparent to the UV radiation.

The radiation source can be formed by one or more UV LEDs. These can be integrated directly into the tool. However, it is also possible to use a mercury vapor lamp or another radiation source for UV radiation, for example. These can be provided with filters. They can be integrated directly into the tool. But they can also be attached outside the tool. Then it makes sense if light guides are provided via which the UV radiation can be guided to the tool surface adjoining the cavity.

In particular, when the UV radiation source is integrated into the tool, it is advantageous if coolant is provided for cooling the radiation source and the tool. In particular, the cooling circuit that may already be present for cooling the tool can also be used for cooling the radiation source. But it is also possible that the radiation source has its own cooling.

In a further embodiment of the invention, a robotic arm or other controllable means for the automated application of uncured resin material to a tool surface is provided. Alternatively, a manual order can also be provided.

The surface of the tool adjoining the cavity can be at least partially provided with a structure or microstructure.

Refinements of the invention are the subject of the dependent claims. An exemplary embodiment is explained in more detail below with reference to the accompanying drawings.

Definitions

In this description and in the appended claims, all terms have a meaning familiar to the person skilled in the art, those of the specialist literature and standards in particular DIN EN 806-1 and DIN EN 1717 and the relevant Internet pages and publications, in particular of a lexical nature, for example www.Wikipedia.de, www.wissen.de or www.techniklexikon.net, the competitors, research institutes, universities and associations, for example VCH or the Association of German Engineers. In particular, the terms used do not have the opposite meaning to that which the person skilled in the art inferred from the above publications.

Figure list

• 1 shows an open tool with integrated UV LEDs with an applied hard layer according to a first embodiment.
• 2 shows the tool 1 in the closed state with applied hard layer and injected, volume-filling plastic material.
• 3 shows a detail of the hard layer with transition area.
• 4th shows a hardened workpiece with a hard layer surface.
• 5 shows a closed tool according to a second embodiment with a reactive resin that can be activated by UV radiation and has a low penetration depth for short-wave UV radiation and a high penetration depth for long-wave UV radiation.
• 6 shows the tool 5 when exposed to short-wave UV radiation and a hardened hard layer surface.
• 7th shows the tool 5 when exposed to long-wave UV radiation and fully cured.

Description of the exemplary embodiments

Embodiment 1:

For the production of a plastic molded part 18th an injection molding process is used. These methods have long been known in the field of mass production of plastic parts. A starting material 19th in the form of a resin becomes liquid in the cavity 10 an injection molding tool generally designated 12 and then cured. This is in 1 and 2 illustrated.

The cavity 10 is the cavity that forms when the tool parts are brought together 14th and 16 of the tool 12 arises. Shape and volume of the cavity 10 determine the shape of the plastic molded part produced 18th . One with the tool 12 manufactured plastic molding 18th is exemplary in 4th shown.

The aim is series production with low costs, good reproducibility, short cycle times and a high degree of automation. A reactive injection molding process is used here to achieve high heat resistance, mechanical strength and low shrinkage, as well as, if necessary, the introduction of a high content of reinforcing fibers. The gradual cross-linking results in a higher surface quality on the visible side of the component on the side from which the UV radiation enters. The total shrinkage is not reduced or only marginally reduced.

In the present embodiment, fillers such as reinforcing fibers, for example UV-transparent glass fibers, ceramics and metals, can be added to the starting material. The liquid starting material 19th can be enriched with higher proportions of fillers at low viscosity than with known processes. This enables the series production of plastic molded parts with improved properties for special applications.

The required process pressures in reactive resin injection molding are selected to be significantly lower than in thermoplastic injection molding due to the lower viscosity. As a result, the injection molding machines used can be made smaller. That is particularly economical.

Most reactive resins are characterized by lower purchase prices compared to high-temperature thermoplastics. The cycle times that result from the crosslinking time of the plastic are determined by the exposure to UV radiation explained in more detail below 20th kept low. UV-curing reactive resins are used in UV reactive resin injection molding 19th into the injection mold 12 brought in. The molded parts are used for curing 18th through transparent cutouts 22nd in the tool part 14th of the tool 12 with UV radiation 20th exposed. UV light emitting diodes (UV LEDs) 24 , 34 provided as radiation sources. UV LEDs 24 , 34 have high energy efficiency and a compact design with good controllability at the same time. Four UV LEDs are shown schematically in the figures. It goes without saying that the type, position and number of the radiation sources can be varied.

In the source material 19th To adapt the mechanical, physical or chemical properties, additives such as fillers, reinforcing materials, stabilizers etc. can be included in variable proportions.

In a first exemplary embodiment, the UV radiation source is 24 in the tool 12 integrated. This is in 1 and 2 illustrated. That in the cavity 10 introduced starting material 19th is through a UV transparent part 22nd of the tool 12 exposed. Examples of such UV-transparent materials are quartz glass and fluoropolymers. The remaining part 26th of the tool 12 consists in the usual way of metals, such as steel or aluminum. At low process pressures, it is also possible to use plastic tools.

The UV reactive resin 19th hardens quickly and therefore enables short cycle times. This is possible because the photopolymerization of reactive resins usually takes place much faster than thermal crosslinking.

Depending on the application, certain surface properties of a molded part 18th to be required. These are, for example, high abrasion resistance, good or low wettability and microstructured surfaces. The molded part is manufactured to achieve these properties 18th made of UV-curing reactive resins with hard layers 28 which in several steps in a single cavity 10 are manufactured

First, this is done on at least one part 32 the surface of an open tool 12 a UV-curing reactive resin is applied which, after curing, forms the hard layer surface 28 forms. This is in 1 illustrated. After closing the mold 12 the top layer is cured by means of short-wave UV radiation 20th . Roller application, spray application, dipping, injection molding and other relevant methods from coating technology can be suitable for applying the hard-layer resin. The coating can be automated. The resin for the hard layer 28 is applied to the surface with the help of a robotic arm (not shown) 32 of the open tool 12 applied.

The volume-filling material is then injected 19th . Known injection molding techniques are suitable for this. The volume filling material 19th consists of either the same or a different UV-curing reactive resin. It is made with long wave UV radiation 36 hardened. The wavelength of the UV radiation 36 is selected so that the molding 18th is completely penetrated. The long-wave UV radiation 36 can with uv leds 34 be generated. This is in 2 illustrated. Then the tool 12 opened and the molding 18th taken. This is in 4th illustrated.

For cooling the UV LEDs 24 is a heat sink 37 provided in 1 and 2 is easy to see. In the present embodiment, the heat sink 37 water-cooled. This is through arrows 38 illustrated. The water cooling is attached to the cooling circuit for cooling the tool 12 connected. The UV LEDs 24 are available in module form. These are in the first embodiment according to 1 and 2 directly on the back with the help of the tool cooling circuit and are as shown in the tool 12 integrated.

Embodiment 2:

In a method according to a further exemplary embodiment, no separate introduction of hard layer and volume-filling material is provided. In this embodiment, there are two different areas 18th and 28 achieved by placing a UV-curing reactive resin in the closed cavity 10 is injected and the material with successive exposure to UV radiation of short wavelength 20th and long wavelength 36 hardens. First is the surface 28 of the molded part 18th by means of short-wave radiation 20th cured, which has a low penetration depth. The remaining volume is then removed using long-wave UV radiation 36 cured with high penetration depth. One or more radiation sources are used for each wavelength 24 and 34 required, which each emit a suitable wavelength spectrum for both hardening processes. It is important that the irradiation takes place gradually, first with a shorter wavelength, then with a longer one, so that first one area and then another area cures. The wavelengths are chosen so that the penetration depth of the shorter ones occurs only superficially, in the desired thickness range typically a few μm or a few hundred nanometers, while the long wavelength is chosen so that the entire volume is penetrated by it.

One advantage of the technology is the ability to create molded parts 18th with very high accuracy of the surface geometry and high surface quality. Since the shrinkage of a polymer material depends on its volume, the accuracy can mainly be due to the thin layer thickness of the surface layer 28 be achieved. Due to the gradual curing, the area where precision is required, ie the surface is solidified first. There is little shrinkage there. The volume follows. This means that shrinkage is only possible on the side facing away from the surface. The surface is hardened first, allowing the remaining volume to shrink 18th has no influence on the accuracy of the surface geometry. Depending on the application, the surface can 32 the cavity 10 be provided with a structure or microstructure. This is during the manufacturing process of the molded parts 18th mapped into the surface of the hard layer. In this way, the functionality of the workpiece surface can be influenced in terms of its wettability, slip resistance, visual appearance and other relevant properties.

Another advantage is the realizable mechanical properties of the workpieces produced 18th . Such properties are, for example, a high hardness on their surface 28 . Among other things, this results in high abrasion resistance. The volume filling material 19th can, for example, be adjusted with the help of fillers such as glass fibers so that high strengths are achieved after curing. Due to the low viscosity of reactive resins compared to thermoplastics, the fillers can be added in significantly higher proportions. As a result, the resilience of the molded part increases 18th .

The hard layer 28 on the surface of the molded part 18th indicates after exposure to short-wave UV radiation 20th on the side facing the remaining volume of the cavity 40 a transition area 41 on. This area is characterized by a high proportion of functional groups. This is in 3 shown. During the subsequent hardening of the volume material 19th This enables a high level of cross-linking and good connections between the two areas 28 and 29 of the molded part 18th can be achieved. The good connection results in good mechanical properties of the molded part 18th and above all good adhesion of the superficial hard layer on the hardened volume material.

Compared to other methods that are used to apply a hard layer 28 are suitable, the invention allows the production times to be reduced significantly. The tool 12 must be used to apply the layer 28 cannot be opened and exchanged. The hardening of the surface 28 and volume 29 can run in one closing cycle.

For the production of a molded part 18th with different areas 28 and 29 accordingly only one tool set 14th , 16 with unchangeable cavity 10 needed. The tool costs are compared to that from the US 8 647 555 B2 known methods correspondingly lower. An injection molding machine with turntable equipment is not required.

By using UV-LED modules 24 and 34 the resulting heat loss can be reduced compared to mercury vapor lamps, which increases the service life of the tool 12 elevated. In addition, the UV LED modules 24 , 34 can be cooled directly on the back. As a result, there is no need for complex attachment of cooling elements in the beam path.

Details such as the sprue channel, tool cooling system, ejector pins or centering elements, which are typically required in injection molding processes, have not been shown here for the sake of simplicity.

Embodiment 3:

Another embodiment is shown in 4th to 6 shown. In this embodiment is a UV radiation source 124 outside of a tool 112 housed. This is in 4th to 6 illustrated. As an external UV radiation source 124 conventional mercury vapor lamps can be used. These generate both short-wave UV radiation 120 , as well as long-wave UV radiation 136 . By using different optical filters in the beam path 121 and 138 can either use short-wave or long-wave radiation for the gradual curing of the reactive resin 119 to be isolated.

The UV radiation 120 or. 136 is by means of optics 125 into one or more optical fibers 130 coupled. With the fiber optic cable 130 is first short-wave UV radiation 120 into the cavity 110 initiated. This is in 4th illustrated. With this radiation 120 first becomes the surface 128 of the resin 119 hardened. This is in 5 illustrated.

Then longer-wave UV radiation is used 136 into the optical fiber 130 coupled. The selection of the wavelengths can be made with a suitable filter or spectrometer in the optics 125 respectively. With the longer-wave UV radiation 136 the remaining resin will be in the cavity 110 to a molded part 118 hardened.

The exemplary embodiments explained above serve to illustrate the invention as claimed in the claims. Features that are disclosed together with other features can generally also be used alone or in combination with other features that are explicitly or implicitly disclosed in the exemplary embodiments in the text or in the drawings. Dimensions and sizes are only given as examples. The expert suitable areas arise from his specialist knowledge and therefore do not need to be explained in more detail here. The disclosure of a specific embodiment of a feature does not mean that the invention is to be restricted to this specific embodiment. Rather, such a feature can be implemented by a large number of other configurations familiar to the person skilled in the art. The invention can therefore not only be implemented in the form of the configurations explained, but rather by all configurations which are covered by the scope of protection of the appended claims.

The terms "above", "below", "right" and "left" refer exclusively to the attached drawings. It goes without saying that the devices claimed can also assume a different orientation. The term “containing” and the term “comprising” mean that further components not mentioned can be provided. The terms "essentially", "predominantly" and "predominantly" include all characteristics that a property or a content predominantly, i.e. have more than all of the other components or properties of the feature mentioned, that is to say more than 50% for two components.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed 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

• US 8647555 B2 [0004, 0043]

Non-patent literature cited

• DIN EN 806-1 [0024]
• DIN EN 1717 [0024]

Claims (20)

Reactive injection molding process for the production of molded parts (18) made of plastic with at least two areas (18, 28) of different properties, the plastic being cured with UV radiation (20, 36) in a cavity (10) of a tool (12), characterized in that the plastic of all areas (18, 28) is cured in a cavity (10) of the same tool (12) and the curing takes place step by step by irradiation with UV radiation (20, 36). Procedure according to Claim 1 , characterized in that the UV radiation (20, 36) in each of the irradiation steps has different radiation properties and / or takes place in different ways. Method according to one of the preceding claims, characterized in that one of the regions (28) comprises at least part of the surface (32) of the molded part (18) which is in contact with the tool (12). Method according to one of the preceding claims, characterized in that the plastic of an area (28) in the cavity (10) of the tool (12) is cured by irradiation with UV radiation (20) in one irradiation step, before further plastic is cured in another Area is fed into the cavity (10) of the tool (12) and cured in the next irradiation step. Procedure according to Claim 3 or 4th , characterized in that the plastic of the first irradiated area (28) is applied to a tool surface (32) by roller application, spray application, dipping, injection molding or another coating technique. Method according to one of the preceding claims, characterized in that the different properties of the areas (18, 28) include the material composition of the plastic and / or the hardness of the hardened plastic. Method according to one of the preceding claims, characterized in that the UV radiation (20, 36) has different wavelengths. Method according to one of the preceding claims, characterized in that the UV radiation (20, 36) has a different intensity, dose and / or different irradiation duration for each irradiation step. Method according to one of the preceding claims, characterized in that the surface of the molded part (18) in contact with the tool (22) forms an area which is irradiated with UV radiation (20) in a wavelength range between 280 nm and 330 nm and the remaining area of the molded part (18) is irradiated with UV radiation (36) between 340 nm and 440 nm. Tool (12) for performing a method according to one of the Claims 1 to 8th , containing a tool (12) forming a cavity (10), characterized by at least one radiation source (24, 34) for generating UV radiation (20, 36) with which material located in the cavity (10) can be irradiated. Tool after Claim 10 , characterized in that the radiation source (24, 34) is controllable, so that the UV radiation (20, 36) is emitted with different frequencies, temporal emission profiles, intensities or other properties. Tool after Claim 9 or 10 , characterized in that at least two radiation sources (24, 34) are provided for generating UV radiation (20, 36) with at least two different wavelengths. Tool after one of the Claims 9 to 11 , characterized in that at least two radiation sources (24, 34) are provided for generating UV radiation (20, 36) with at least two different radiation intensities or other different radiation properties. Tool according to one of the preceding Claims 9 to 13 , characterized in that the tool (12) has a tool surface (22, 32) adjoining the cavity (10) through which the UV radiation (20, 36) can be guided into the cavity (10). Tool (12) according to one of the preceding Claims 9 to 14th , characterized in that the tool surface (22) is at least partially transparent to the UV radiation (20, 36). Tool (12) according to one of the preceding Claims 9 to 15th , characterized in that the radiation source is formed by one or more UV LEDs (24, 34). Tool (12) according to one of the preceding Claims 9 to 16 , characterized by optical waveguides (130) via which the UV radiation can be guided to the tool surface adjoining the cavity. Tool (12) according to one of the preceding Claims 9 to 17th , characterized by coolant (38) for cooling the radiation source (24, 34) and the tool (12). Tool (12) according to one of the preceding Claims 9 to 16 , characterized by a robot arm or other controllable means for the automated application of reactive resin to a tool surface (32). Tool (12) according to one of the preceding Claims 9 to 17th , characterized in that the surface (32) of the tool adjoining the cavity (10) is at least partially provided with a structure or microstructure.

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