DE102010025862B4 - Process for modifying plastic surfaces and the plastic component produced with them - Google Patents

Abstract

A method for producing a surface-modified plastic component during shaping with a predetermined surface quality which allows the plastic component to be connected to other materials, for example by painting, printing, metallizing or gluing, the method comprising the following steps: a) applying (100 ) a chemical substance on the surface of a tool, the chemical substance comprising hydrolyzable silanes, in particular alkoxysilanes, chlorosilanes or silane esters, or mixtures of hydrolyzable silanes; b) shaping (200) of a plastically deformable plastic by injection molding or extrusion, the hot plastic surface comes into contact with the tool surface; c) allowing (300) the plastic treated with the substance to solidify until the plastic is a solid body; and d) applying (400) water to the surface of the solidified plastic.

Description

The invention relates to a method for modifying plastic surfaces, in particular polyolefins. Polyethylene, polypropylene and their blends are suitable as polyolefins. The invention can be used wherever semi-finished products or components made of polyolefins are painted, printed, metallized, glued or otherwise connected, e.g. body parts in the automotive industry or components that should have a corresponding surface conductivity, and where the maintenance of the advantageous basic properties is important of the polyolefin arrives in its entirety.

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 mainly achieved by flame treatment, plasma treatment or irradiation by creating functional groups in monolayers at the outermost limit of the plastic. This type of activation of polymer surfaces is carried out as an additional technological step.

The conventional pretreatment processes, 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. With these high-energy pretreatment processes, radicals are generated on the surface, which react in the presence of oxygen or water to form hydroxyl, keto or carboxyl groups. These groups help to increase the surface energy. These reactions are supported by UV light and radicals in the process gas. With some polyolefins, such as PE, LLD, metallocene-catalyzed types or polyolefins with high additive contents, the effect is unsatisfactory.

Another disadvantage is that the stability of the pretreatment effect is low over a relatively long period of time. For this reason, the surface-modified plastics must be processed further without intermediate storage, which is difficult to achieve in industry.

Although the surface energies that can be achieved can be very high, the adhesive strengths of subsequent coatings are often unsatisfactory. This is said to be caused by layers of polar substances on the surface, so-called “weak boundary layers”, which are not firmly attached to the substrate. This layer consists of additives as well as fragments of the polymer chain that are created by the high-energy pretreatment. A modification of the layer could be achieved by long-lasting 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 either.

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

One way to achieve permanent surface modification is to graft polar polymers onto the polyolefin surface. These reactions are started by radicals on the polyolefin surface that are generated by ozone, plasma or UV radiation. The monomers supplied from the liquid or vapor phase are grafted onto the surface. Acrylic derivatives and sometimes also silanes are used as monomers. As a result, in addition to the functional groups such as carboxyl, hydroxyl or aldehyde groups, silane residues are also bonded to the polymer or plastic surface or SiO _x deposits are produced, which are then also available as adhesion promoters. The disadvantage here is that the modification has to be carried out as an additional process step for shaping, preferably for planar surfaces.

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

The European patent specification 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 essentially melted and the copolymer material with the hydrophobic one Polyolefin is heat-welded so that a modified surface is created. The process is used in the manufacture of fibers in the extrusion process.

In the German patent specification 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 in that the plastic surface is brought into contact with modifiers which react with the surface and / or completely or partially penetrate the surface by interdiffusion and / or melt on the surface.

In the German patent specification DE 10 2005 011 594 A1 an innovative process is described that enables the surface modification of polymer surfaces in the injection molding process. The process is based on the initiation of radical reactions through contact with the hot plastic melt, which finally couple a polymeric modifier to the plastic surface through radical reactions. However, technical use is made more difficult by disadvantages which are justified by the use of the radical reactions. In particular, this process must lead to hydrogen abstraction in the polyolefin. However, radical initiators suitable for this purpose are not sufficiently reactive under the thermal conditions in injection molding. Therefore, the achievable effects are not yet sufficient 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 into the surface layer of plastics. The solvent has the task of swelling the surface layer and thus enabling the primers to diffuse into the open polymer structure created. After the solvent has evaporated, the primer remains in the surface layer. Both functional polymers [ DE 43 16 585 C1 ] 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 T2 ] suggested. Chemical reactions can lead to hydrolysis of the silanes and subsequently to the formation of siloxanes and to crosslinking or anchoring of the siloxanes. The disadvantage is the use of solvents that pollute the environment and the process management, which is usually carried out by hand.

After U.S. 6,352,658 B1 a method is known for shaping a decorative component with an outer elastomeric layer and an inner foam layer connected to it. A polyurethane mixture is produced by combining polyisocyanates and polyol and applied to the surface of a mold by spraying the two components, creating an elastomeric layer. During the further application of the polyurethane mixture to the surface of the mold, a stream of water is added to the polyurethane mixture, whereby a polyurethane mixture is formed that contains a blowing agent. By applying the polyurethane mixture with the blowing agent in the direction of the mold surface, an inner foam layer is formed which bonds with the outer elastomer layer. Finally, the component is removed from the mold.

According to the DE 101 13 272 A1 a method for producing decorative coated molded parts is known. For this purpose, the decorative materials are placed in a tool and back-injected with a molten plastic and then the decorative-coated molded parts are stored in water or sprayed with water and then dried.
The treatment in water is carried out in order to maintain the natural appearance of the decorative surfaces without any structural measures.

From the GB 2 300 587 A a substrate coated with a thermoplastic material is known, the thermoplastic material consisting of a thermoplastic alloy and at least one substance selected from infusible materials, UV stabilizers and antioxidants. This thermoplastic material can contain recycled material.

Furthermore, from the EP 0 625 418 A1 discloses a process for the manufacture of coated resin products which are coated during melting. This invention makes it possible to uniformly cover the outer surface of a molded resin product as a whole with a coating material.

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

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

The object is achieved by the subject matter of the attached claim 1. Claim 1 relates to a method for producing a surface-modified plastic component with a predetermined surface quality during the shaping process. The surface quality is 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 method comprises the following steps: A plastically deformable plastic substrate is brought into a predetermined shape. A chemical substance is applied to the surface of a tool. The chemical substance comprises hydrolyzable silanes, in particular alkoxysilanes, chlorosilanes or silane esters, or mixtures of hydrolyzable silanes.

A plastically deformable plastic is then shaped by injection molding or extrusion, the hot plastic surface coming into contact with the tool surface.
The plastic substrate treated with the substance solidifies, so that the plastic is a solid body. Finally, water in liquid or gaseous form is applied to the surface of the solidified plastic.

The invention takes advantage of the fact that the plastic substrate has a lower density in the state of plastic deformability. This is particularly true when the plastic substrate is liquefied by the supply of heat. The silanes can consequently penetrate more easily into the surface of the plastic substrate. Therefore the use of solvents to swell the surface is unnecessary.

Low molecular weight, in particular monomeric or olygomeric, silanes are preferably used because these silanes can diffuse particularly easily into the surface of the plastic substrate.

Conventional methods are based on post-treatment of a hardened plastic surface. These are additional process steps that are associated with complex logistics, additional energy and working hours. Since the method according to the invention is integrated into the shaping process, there is no post-treatment.

As a final step, the application of water to the surface leads to the fact that silanes lying on the surface and silanes diffused into the surface combine with one another. This creates a complex network of connections which is firmly anchored to the surface due to the diffused molecules. Linear and / or branched networks arise in the outermost surface layer of the plastic substrate. This network is firmly anchored and thus determines the surface properties of the plastic component permanently. The properties are determined by the type and composition of the silanes. If desired, silanes with further functional groups can also be used.

If, for example, alkoxysilanes are used as the chemical substance, the water molecules react with the alkoxysilanes to form silanol groups. When two silanol groups meet, they can condense, the silicon atoms being bonded to one another via siloxane groups. These reactions can occur several times per silicon atom. As a result, linear or branched siloxane polymers or a siloxane network are formed in the outermost surface layer. These siloxanes are firmly anchored and thus permanently determine the surface properties of the molded part. The properties are determined by the type and composition of the alkoxysilanes.

The method provides for a network of chemical substances based on siloxane bonds to be formed in the outermost surface layer of plastic parts or sheets. The application of the substances is integrated into the shaping process. With the help of this process, the surfaces of plastics are modified for a wide range of tasks. The process is particularly suitable for less reactive plastics, such as polyolefins, but also for plastics that would break down easily in contact with reactive substances, such as POM. Depending on the chemical composition of the substances, the surfaces can become more polar or non-polar, chemically reactive or inert and thus form the basis for further steps in surface finishing.

With the invention, a permanent surface modification of plastic components with improved adhesion and wetting properties is achieved in the application. The process according to the invention enables an improvement in the paintability with water-based paints or an improvement in the wettability with adhesive systems and better adhesion of paints or improved adhesion of the bond. On the basis of the method according to the invention, the plastics processing industry is enabled to manufacture semi-finished products or components from plastics that are directly accessible for surface finishing. The method according to the invention saves additional investment, process costs and energy, since the modification is carried out directly by the plastics processor and not only during further processing. Surface pretreatment of the plastic products is not required. The plastic surface does not have to be high-energy compounds or rays that attack the surface are treated. Technological steps in plastics processing can be designed more flexibly, ie the process chain becomes more flexible.

A preferred embodiment of the present invention provides that the shaping is carried out by injection molding the plastic substrate into a mold with a predetermined cavity. The chemical substance is applied by wetting the surface of the cavity with the substance before the plastic substrate is introduced into the mold. Preferably only a thin film of the substance is applied to the cavity surface. For example, substances dissolved in a volatile solvent can be used. When the cavity surface comes into contact with the molten plastic substrate, the silanes diffuse very quickly into the outermost surface layer of the plastic substrate.

The diffusion speed is increased by the high temperature and the low density of the melt compared to the solidified plastic. After removal from the mold, water molecules diffuse into the surface layer of the plastic substrate, favored by the low glass transition temperature.

The water molecules can come from the humidity. It is also possible to accelerate this process by evaporating with water vapor or by dipping the solidified plastic substrate in a water bath. In some cases, this process step is unconstrained, e.g. if the further processing of the surface is planned by painting with water-based paints.

The method according to the invention provides in particular to use alkoxysilane monomers as modifier substances and to apply these to the surface of the cavity of an injection molding tool in a thin film. For this purpose, the silanes can also be used in solution in a volatile solvent. On contact with the hot melt, the alkoxysilanes diffuse very quickly into the outermost surface layer.

The extrusion of the plastic substrate can be used as an alternative process for shaping. During extrusion, the plastic substrate is pressed through a specially shaped opening in a continuous process. Bodies with the cross-section of the opening in any length are created. To do this, the plastic substrate is first melted using an extruder (also known as a screw press). The pressure required to flow through the nozzle is also built up in the extruder. The surface of the plastic substrate emerging from the extruder is wetted with the chemical substance via a roller.

• 1 zeigt schematisch eine Vorrichtung zum Spritzgießen, die in der bevorzugten Ausführungsform der vorliegenden Erfindung eingesetzt wird;
• 2 zeigt ein Blockschaltdiagramm, das die Verfahrensschritte zum Herstellen eines Kunststoffbauteils gemäß dem bevorzugten Ausführungsbeispiel der vorliegenden Erfindung darstellt.

Preferred exemplary embodiments of the present invention are described below with reference to the accompanying figures. Show it:

• 1 Fig. 3 schematically shows an injection molding apparatus used in the preferred embodiment of the present invention;
• 2 FIG. 3 shows a block circuit diagram which illustrates the method steps for producing a plastic component according to the preferred exemplary embodiment of the present invention.

In the 1 The illustrated device for injection molding comprises two separate components. On the one hand, 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 external shape of the plastic component to be produced corresponds to the shape of the cavity 50 . A polyethylene such as PE-HD (Moplen HF 500 N) is preferably used as the plastic substrate. There is also a heater 40 provided which regulates the temperature of the mold to a predetermined value. The process temperature for the mold can be preset to approx. 20 ° C, for example.

The injector 70 includes a funnel 20th for filling the plastic substrate. The plastic substrate is preferably introduced into the injection device as granules. Inside the injection device a cavity is provided in which a so-called screw 10 is placed. The snail 10 conveys the plastic granulate to a nozzle 30th . There are also heaters at the edge of the cavity 40 provided that liquefy the plastic granulate. The process temperature is usually above the melting temperature of the plastic substrate and is approx. 220 ° C for polyethylene. Via a nozzle 30th and a channel 80 the liquefied plastic substrate enters the cavity in the mold 50 . The screw conveys the plastic substrate so that the plastic substrate enters the cavity under high pressure 50 is injected.

This in 2 The block diagram shown represents the process sequence for producing the plastic component according to a preferred exemplary embodiment of the present invention.

In the first step 100 becomes the surface of the cavity 50 wetted with the chemical substance. Aminopropyltrimethoxysilane (APTMS) is preferably applied as a thin film into the cavity of the injection molding tool. In the next step 200 the plastic substrate is used for shaping in the cavity 50 injected. The plastic substrate is as granules over the funnel 20th into the injector and by means of the screw 10 over the nozzle 30th through the opening 80 injected into the cavity at high pressure. A standard type of HD polyethylene (Moplen HF 500 N) is preferably inserted into the cavity as the plastic substrate 50 the closed form 60 injected. Injection takes place using standard processing conditions, for example a melt temperature of 220 ° C for the plastic substrate and a tool temperature of 20 ° C for the mold 60 .

In step 300 the plastic substrate solidifies in the mold 60 until it is essentially a solid body. The form is then opened and in step 400 the application of water takes place. After demoulding, the plastic substrate is stored in water for a few minutes or in air for a few days. The measurement of the contact angle with respect to water results in values below 60 °, so that painting with water-based paints is possible.

According to a further exemplary embodiment of the present invention, 1- [3- (trimethoxysilyl) propyl] urea is used as a chemical substance and applied to the surface of the injection molding tool as a thin film. The other materials and process steps correspond to those in embodiment 1. When measuring the contact angle with respect to water, a value of less than 60 ° results.

According to a third exemplary embodiment of the present invention, 3- (2-aminoethylamino) propyl-methyldimethoxysilane is used as the chemical substance and the procedure is otherwise as in Example 1. The contact angle after modification in injection molding is less than 60 °.

List of reference symbols

10

slug

20th

funnel

30th

jet

40

heater

50

cavity

60

shape

70

Spray device

80

channel

100

Wet the cavity surface with chemical substance

200

Injection of the plastic substrate

300

Allow the plastic substrate to solidify

400

Application of water to the surface of the solidified plastic substrate

Claims (9)

A method for producing a surface-modified plastic component during the shaping process with a predetermined surface quality which allows the plastic component to be connected to other substances, for example by painting, printing, metallizing or gluing, the method comprising the following steps: a) applying (100) a chemical substance to the surface of a tool, the chemical substance having hydrolyzable silanes, in particular alkoxysilanes, chlorosilanes or silane esters, or mixtures of hydrolyzable silanes; b) shaping (200) a plastically deformable plastic by injection molding or extrusion, the hot plastic surface coming into contact with the tool surface; c) allowing the plastic treated with the substance to solidify (300) until the plastic is a solid body; and d) applying (400) water to the surface of the solidified plastic. Method for producing a plastic component according to Claim 1 wherein the shaping (200) takes place by injection molding of the plastic in a mold (60) with a predetermined cavity (50); and the substance is applied (100) to the surface of the mold by wetting the surface of the cavity (50) with the substance before the plastic is injected into the mold. Method for producing a plastic component according to Claim 2 , wherein the wetting (100) of the cavity (50) with the substance takes place by spray coating. Procedure according to Claim 1 , characterized in that the shaping (200) takes place by extrusion of the plastic substrate, the substance being applied to a roller. Method for producing a plastic component according to one of the preceding claims, wherein the substance to be applied contains polar groups. Method according to one of the preceding claims, wherein the substance to be administered contains hydrolyzable groups. Procedure according to Claim 6 , the hydrolyzable groups being alkoxy groups, in particular methoxy groups or ethoxy groups. Method according to one of the preceding claims, wherein the plastic comprises polyolefin. Plastic component with a predetermined surface quality which allows the plastic component to be connected to other substances, for example by painting, printing, metallizing or gluing, characterized in that the plastic component is produced by a method according to one of the Claims 1 to 8th is made.

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