DE102010025958A1 - Method for manufacturing modified surface of plastic component during molding in predetermined condition, involves molding plastic by extrusion, and solidifying body with substance mixture of plastic - Google Patents

Abstract

The present invention relates to a method for producing a plastic component with a predetermined surface quality, with polyolefins such as polyethylenes, polypropylenes or their blends being particularly suitable as plastics. The surface properties are such that the plastic component can be connected to other materials. The connection can take place, for example, by painting, printing, metallizing or gluing. The procedure consists of the following steps. A mixture of substances is applied to the surface of a tool. The substance mixture comprises a monomer with at least one free-radically polymerizable double bond and a free-radical initiator. A plastically deformable plastic is brought into contact with the substance mixture during shaping. The plastic substrate treated with the substance mixture solidifies so that it acquires a solid shape.

Description

The invention relates to a method for modifying plastic surfaces, in particular polyolefins. Suitable polyolefins are polyethylenes, polypropylenes and their blends. The invention can be used wherever semifinished products or components made of polyolefins are painted, printed, metallized, glued or otherwise connected, for. As body parts in the automotive industry or components that should have a corresponding surface conductivity, and where it depends on the receipt of the beneficial properties of the polyolefin in whole.

It is known and described in the relevant technical and patent literature to modify plastic surfaces by various methods. Since plastics are generally too hydrophobic on the surface because they have too few or no functional reactive groups, it is necessary to activate the polymer surfaces. Activation of the plastic surfaces is achieved predominantly by flaming, plasma treatment or irradiation by producing functional groups in monolayers at the outermost border of the plastic. This type of activation of polymer surfaces is performed as an additional technological step.

Conventional pretreatment methods, such as corona discharge, (low pressure) plasma modification, or flame treatment are generally suitable for surface modification; however, the effects that can be achieved are not permanent. These high-energy pretreatment processes generate surface-generated radicals which react in the presence of oxygen or water to form hydroxyl groups, keto groups or carboxyl groups. These groups contribute to increasing the surface energy. These reactions are supported by UV light and process gas radicals. In some polyolefins, such as PE, LLD, metallocene-catalyzed types or polyolefins with high additive contents, the effect is unsatisfactory.

Furthermore, it is disadvantageous that the stability of the pretreatment effect over a relatively long period of time is low. Therefore, a further processing of the surface-modified plastics without intermediate storage must take place, which is difficult to achieve in the industry.

Although the achievable surface energies can be very high, the adhesive strengths of subsequent coatings are often unsatisfactory. The reason for this is said to be layers of polar substances on the surface, so-called "weck boundary layer", which are not firmly bonded to the substrate. This layer consists of both additives and fragments of the polymer chain, which are generated by the high-energy pretreatment. A modification of the layer could be achieved by long-term etching with oxidizing reagents supported by ultrasound. The processes mentioned are based on unspecific reactions with the carbon atoms on the surface of the polymers. These modifications are usually not permanent.

Although the gas phase fluorination provides a lower increase in surface energy compared to plasma pretreatment and corona pretreatment; However, the achievable adhesive strengths for aqueous and radiation curable finishing systems and the long-term stability are better. However, there are also polyolefin types in these processes, which can only be modified slightly.

One way to achieve permanent surface modification is by grafting polar polymers onto the polyolefin surface. These reactions are initiated by radicals on the polyolefin surface, which are generated by ozone, plasma or UV irradiation. The fed from the liquid or vapor phase monomers are grafted onto the surface. The monomers used are usually acrylic derivatives, in some cases also silanes. As a result, in addition to the functional groups, such as carboxyl groups, hydroxyl groups or aldehyde groups, silane radicals are also bound to the polymer surface or plastic surface or SiO x deposits are produced, which are then likewise available as adhesion promoters. The disadvantage here is that the modification as an additional process step for shaping, preferably for planar surfaces, must be performed.

For example, in the German patent specification DE 199 02 948 A1 describes a method of modifying the surface of polymer substrates by radiation-induced or thermally-induced graft polymerization of a monomer and a property-determining polymer. In this case, the polymer substrate is pretreated prior to grafting with the polymer with a solution of at least one olefinically unsaturated monomer, at least one thermal initiator and / or a photoinitiator and optionally a solvent.

The European patent EP 0491 293 B1 deals with surface-modified polyolefin articles and a method for modifying the surface of these articles. The surface of the hydrophobic polyolefin is contacted with a copolymer material while the hydrophobic polyolefin is substantially melted and the copolymer material is heat-sealed with the hydrophobic polyolefin to provide a modified surface. The method is used in the production of fibers by extrusion.

In the German patent DE 100 42 566 A1 describes a method for modifying plastic surfaces, which can be used to activate or passivate the plastic surfaces. The modification takes place by bringing the plastic surface into contact with modifiers which react with the surface and / or wholly or partly penetrate the surface by interdiffusion and / or melt on the surface.

In the German patent DE 10 2005 011 594 describes an innovative process that enables surface modification of polymer surfaces in the injection molding process. The method is based on the initiation of radical reactions by the contact with the hot plastic melt, which finally couple a polymeric modifier to the plastic surface by radical reactions. However, the technical use is hampered by disadvantages, which are due to the application of the radical reactions. In particular, it must come in this process to a hydrogen abstraction in the polyolefin. However, suitable radical initiators are not sufficiently reactive in the thermal conditions in injection molding. Therefore, the achievable effects are still insufficient for many applications.

The use of primers has been proposed many times. The effect is based on the diffusion of a solution of functional compounds in the surface layer of plastics. The purpose of the solvent is to swell the surface layer and thus to allow the diffusion of the primer into the created open polymer structure. After evaporation of the solvent, the primer remains in the surface layer. As primers, both functional polymers [ DE-A1 43 16 585 ] as well as low molecular weight substances [ Primers for Adhesive Bonding to Polyolefins JIYUE YANC and ANDREW GARTON, Journal of Applied Polymer Science, Vol. 48, 359-370 (1993) ], like silanes [ De 600 23 430 ] proposed. Chemical reactions can lead to hydrolysis of the silanes and subsequent formation of siloxanes and crosslinking or anchoring of the siloxanes. The disadvantage is the use of solvents that pollute the environment and the most carried out by hand litigation.

All methods of surface modification of polyolefins have the disadvantage that the long-term stability of the surface modification is insufficient, i. H. is not permanent. Another disadvantage is that the methods according to the prior art are not suitable for all polyolefin types and must be carried out in separate, sometimes complex process steps.

It is therefore an object of the present invention to provide a method that allows a surface modification of a plastic component with long-term stability.

The object is solved by the subject matter of appended claim 1. Claim 1 relates to a method for producing a plastic component with a predetermined surface finish. The surface finish is such that a connection of the plastic component with other materials is possible. The bonding can be done for example by painting, printing, metallizing or gluing. The method comprises the following steps: A plastically deformable plastic substrate is brought into a predetermined shape. A substance mixture is applied to the surface of the plastically deformable plastic substrate. The substance mixture comprises a monomer having at least one free-radically polymerizable double bond and a free-radical initiator. The plastic substrate treated with the substance mixture solidifies so that it acquires a solid form.

The invention makes use of the fact that the plastic substrate has a lower density in the state of plastic deformability. This is especially true when the plastic substrate is liquefied by supplying heat. The substance mixture can consequently penetrate more easily into the surface of the plastic substrate. In addition, it is preferred to use free-radical initiators which are compatible with the polyolefin because of their chemical structure, favoring their diffusion. Therefore, the use of solvents to swell the surface is unnecessary.

Upon contact of the substance mixture with the hot plastic surface, two processes occur. On the one hand, the low-molecular components of the substance mixture diffuse very quickly into the outermost surface layer. The diffusion rate is increased by the high temperature and the low density of the melt, compared to the solidified plastic. On the other hand, the high temperature of the melt triggers the radical decomposition of the radical initiator. The resulting radicals initiate polymerization of the monomers or crosslinking when multifunctional monomers are used. As a result, the resulting functional polymers in the surface layer of the plastic parts anchored. After demolding, the surface layer of the moldings contains the firmly anchored substances which can lead to a surface modification.

Another process-integrated surface modification of polyolefins based on radical reactions involves coupling a so-called modifier to the polyolefin surface with the participation of radical reactions. However, since polyolefins are radically difficult to activate by hydrogen abstraction at the usual processing temperatures, the effect is low. In contrast, the effect with the proposed solution is far greater since the monomers only need to react with each other to anchor in the surface layer.

The application of the substance mixture takes place integrated into the molding process. The process modifies the surfaces of plastics for a wide range of tasks. In particular, the process is suitable for low reactivity, low glass transition temperature plastic substrates, such as polyolefins. Depending on the chemical composition of the substances, the surfaces may become more polar or nonpolar, chemically reactive or inert and thus form the basis for further surface treatment steps.

With the invention, a durable surface modification of plastic components with improved adhesion and wetting properties is achieved in the application. The process according to the invention makes it possible to improve the paintability with water-based paints or to improve the wettability with adhesive systems and to improve the adhesion of paints or to improve the adhesion of the bond. Due to the method according to the invention, the plastics processing industry is able to produce semi-finished products or components made of plastics, which are directly accessible to a surface finishing. With the method according to the invention additional investments, process costs and energy savings because the modification is carried out directly by the plastics processor and not only in the further processing. A surface pretreatment of the plastic products is eliminated. The plastic surface need not be treated with high energy and thus surface attacking compounds or jets. Technological steps in plastics processing can be made more flexible, i. H. the process chain becomes more flexible.

As a result, linear and / or branched polymers or a network are formed in the outermost surface layer of the plastic substrate. This network is firmly anchored and thus permanently determines the surface properties of the plastic component. The properties are determined by the nature and composition of the substance mixture. If desired, it is also possible to use monomers having further functional groups. However, such additional functionalization of the monomers is not required in most cases.

The aim is a very homogeneous wetting of the surface of the plastic substrate. Therefore, in particular, liquid substances for spraying or gaseous substances for vapor deposition are used.

A preferred embodiment of the present invention provides that the shaping takes place by injection molding of the plastic substrate into a mold with a predetermined cavity. The application of the substance mixture takes place in that the surface of the cavity is wetted with the substance mixture before the plastic substrate is introduced into the mold. Preferably, only a thin film of the substance mixture is applied to the cavity surface. In this case, for example, dissolved in a volatile solvent substance mixtures can be applied. As a solvent, for example, water can be used.

As an alternative process for shaping, the extrusion of the plastic substrate can be used. During extrusion, the plastic substrate is pressed through a specially shaped opening in a continuous process. It creates bodies with the cross section of the opening in any length. For this purpose, the plastic substrate is first melted by an extruder (also called screw press). Furthermore, in the extruder necessary for the flow of the nozzle pressure is built up. The surface of the plastic substrate emerging from the extruder is wetted with the substance mixture via a roller.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. Show it:

1 shows schematically an apparatus for injection molding, which is used in the preferred embodiment of the present invention;

2 shows a block diagram illustrating the process steps for producing a plastic component according to the preferred embodiment of the present invention.

In the 1 illustrated device for injection molding comprises two separate components. First, the device comprises a mold 60 . shown twice, and an injector 70 , Form 60 has a cavity 50 , which is intended to receive a liquid plastic substrate. The outer shape of the plastic component to be produced corresponds to the shape of the cavity 50 , As a plastic substrate, a polyethylene such as PE-HD (Moplen HF 500 N) is preferably used. There is also a heater 40 provided that regulates the temperature of the mold to a predetermined value. The process temperature for the mold can be preset to about 20 ° C, for example.

The injector 70 includes a funnel 20 for filling the plastic substrate. The plastic substrate is preferably introduced as granules into the injection device. Inside the injection device, a cavity is provided in which a so-called screw 10 is placed. The snail 10 conveys the plastic granules to a nozzle 30 , Furthermore, heaters are on the edge of the cavity 40 provided, which liquefies the plastic granules. The process temperature is usually above the melting temperature of the plastic substrate and is about 220 ° C for polyethylene. About a nozzle 30 and a channel 80 in the mold, the liquefied plastic substrate enters the cavity 50 , The screw conveys the plastic substrate, allowing the plastic substrate into the cavity under high pressure 50 is injected.

This in 2 Block diagram illustrates the process flow for the production of the plastic component according to the preferred embodiment of the present invention.

In the first step 100 becomes the surface of the cavity 50 wetted with the substance mixture. Preferably, a mixture of triethylene glycol dimethacrylate and lauroyl peroxide is applied to the cavity of the injection mold as a thin film. In the next step 200 the plastic substrate is shaped into the cavity 50 injected. The plastic substrate is granulated over the funnel 20 into the injection device and by means of the screw 10 over the nozzle 30 through the opening 80 injected into the cavity at high pressure. As a plastic substrate is preferably a standard type of polyethylene HD (Moplen HF 500 N) in the cavity 50 the closed form 60 injected. The injection is carried out using standard processing conditions, for example at a melt temperature of 220 ° C for the plastic substrate and a mold temperature of 20 ° C for the mold 60 ,

In step 300 solidifies the plastic substrate in the mold 60 until it is essentially a solid body. The mold is then opened and in step 400 the mold is opened and the finished plastic component removed. The measurement of the contact angle with respect to water gives values below 60 °.

LIST OF REFERENCE NUMBERS

10

slug

20

funnel

30

jet

40

heater

50

cavity

60

shape

70

sprayer

80

channel

100

Wetting the cavity surface with substance mixture

200

Injection of the plastic substrate

300

Freeze the plastic substrate

400

Removal of the plastic substrate from the mold

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 19902948 A1 [0008]
• EP 0491293 B1 [0009]
• DE 10042566 A1 [0010]
• DE 102005011594 [0011]
• DE 4316585 A1 [0012]
• DE 60023430 [0012]

Cited non-patent literature

• Primers for Adhesive Bonding to Polyolefins JIYUE YANC and ANDREW GARTON, Journal of Applied Polymer Science, Vol. 48, 359-370 (1993) [0012]

Claims (10)

Method for producing a surface-modified plastic component during shaping with a predetermined surface finish, which allows the plastic component to be joined to other substances, for example by painting, printing, metallizing or adhesive bonding, the method comprising the following steps: a) application ( 100 ) a mixture of chemical substances on the surface of a tool, wherein the substance mixture comprises a monomer having at least one radically polymerizable double bond and a radical initiator; b) shaping ( 200 ) a plastically deformable plastic by injection molding or extrusion, wherein the hot plastic surface comes into contact with the tool surface; and c) let it solidify ( 300 ) of the plastic mixture treated with the substance mixture until the plastic is a solid body. Process for producing a plastic component according to claim 1, wherein the shaping ( 200 ) by injection molding the plastic into a mold ( 60 ) with predetermined cavity ( 50 ) he follows; and applying ( 100 ) the substance mixture is applied to the surface of the mold by the surface of the cavity ( 50 ) is wetted with the substance mixture before the plastic is injected into the mold. Process for producing a plastic component according to claim 2, wherein the wetting ( 200 ) of the cavity ( 50 ) with the substance mixture by spray coating. Method according to claim 1, characterized in that the shaping ( 100 ) by extrusion of the plastic substrate, wherein the substance mixture is applied to a roller. A process for producing a plastic component according to any one of the preceding claims, wherein the monomer has polar groups. A process according to any one of the preceding claims, wherein the monomer has at least two polymerizable double bonds. A process according to any one of the preceding claims, wherein the radical initiator comprises alkyl groups. Method according to one of the preceding claims, characterized in that the radical initiator has a half-life of the decomposition at a temperature of 120 ° C of less than 1 min. Method according to one of the preceding claims, wherein the plastic comprises polyolefin. Plastic component with a predetermined surface texture, which allows a connection of the plastic component with other materials, for example by painting, printing, metallizing or gluing, characterized in that the plastic component can be produced by a method according to one of claims 1 to 7.

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