EP0990414A2 - Use of a method to improve the properties of a plastic material by fluorination or plasma treatment - Google Patents

Abstract

The invention relates to the use of the method to improve the wetting properties of plastic materials by subsequently activating their surfaces by means of fluorination or plasma treatment. The method is to be used for plastic parts of dishwashers or washing machines that are directly exposed to the washing or cleaning liquid. According to this process, components made entirely from a polymeric material, such as polypropylene, polyethylene, their copolymers, polyamide or from a regrind of these plastics or coated with this plastic and incorporated in the rinse water cycle are treated. This treatment results in a significant improvement in the dripping behavior on the items to be washed, such as cutlery drawers, crockery baskets, etc., without additional constructive measures, and discoloration of the components caused by lipophilic food dyes can no longer occur.

Description

The object of the invention relates to the application of the method, plastic materials by subsequently activating their surfaces using fluorination or plasma treatment to improve their properties for subsequent treatments.

Such methods are commonly used in surface cleaning and treatment of Plastic parts retrofitted to provide the indispensable pretreatments for one later processing, such as gluing, painting, printing, coating, etc. to reduce the various molded parts or to replace them entirely with safe processes. With these processes, the wettability of the workpiece surfaces is increased.

So z. B. by the low pressure plasma process (generally plasma process) in one In addition to gas chemical degreasing of the workpiece surface, a "dry process" also includes a Change in surface area achievable, for example, in a noticeable increase in Surface wettability expresses. Basically, plastics are treated in plasma are vacuum resistant and withstand a temperature load of at least 50 ° C. to Generation of a low-pressure plasma is in a vacuum chamber (process chamber) a gas or gas mixture is introduced at a pressure of 1 mbar and by applying a high-frequency AC voltage is ionized. This plasma with its highly active Particles are characterized by their strong reactivity and activate the workpiece surfaces. The process is used in electronics, in the automotive industry as well in the processing of molded parts for packaging. Plastic molded parts are predominantly used processed from polyethylene (PE), polypropylene (PP) and / or their copolymers. The plasma process is reprinted from "Adhäsion" issue 5, year 1989, article "Surface treatment using low pressure plasma" by Gerhard Liebel, described in detail.

When activated by fluorination, plastic surfaces are treated with elemental fluorine. This treatment also brings about a sustainable surface refinement by increasing it water wettability, which, however, affects the mechanical properties of the material unaffected. As a result, the plastic gains high-quality advantages, such as being easy to stick on Permeability of various solvents or gases, low coefficient of friction and high resistance to aggressive chemicals. In particular has this procedure is enforced in the production of plastic fuel tanks. The fluorinated After treatment, tanks are equipped with a barrier layer, which prevents fuel permeation reduced to a few percentages (see Kautschuk-Plastik-Zeitung, No. 421 of August 23, 1990, "It's your turn", fluorination of fuel tanks).

For water-bearing household appliances, such as dishwashers or washing machines, in particular however, in dishwashers, it is well known that with the washing or cleaning liquid molded parts and assemblies that come into contact, such as washware carriers, washware containers etc. made of a high quality polymeric plastic, such as. B. to manufacture polypropylene (PP) or at least the surfaces of the parts with a corresponding material (e.g. polyamide) to cover (see German utility model DE 73 29 899 U1 and DE 70 01 337 U1). On the one hand, these measures serve to protect the corrosion of the flushing or cleaning liquid parts that come into contact and, on the other hand, protect what is stored in the basket Dishes or cutlery.

However, the known covering of a crockery or cutlery basket with plastic can be due to the non-optimal draining properties of the plastic used, that there are still drops of water at the points of contact between plastic and dishes or hang cutlery on the rack, which is often the case in the "drying" program section cannot be completely eliminated. Inadequate drainage of water has an effect unfavorable with regard to the amount of water necessary for optimal rinsing and cleaning low water and heating energy consumption and favors negative water stains on the crockery and cutlery items. An optimal cleaning and rinsing result is therefore not always achievable. Furthermore, the total elimination requires getting stuck Drops of water an increased drying performance or an extended program duration.

To improve these negative properties of the baskets it has also become known To provide washware racks or cutlery drawers with additional drop arresters, or the Meshes and grids of the basket frames in the shape of a cutting edge or sawtooth to train (see EP-PS 0 186 157). However, these measures complicate and make production more expensive the washware carrier made of high quality plastic and only reduce the problem partially.

In addition, there is the problem that plastic-coated parts with in the washing process discolor over time, usually a yellow or reddish yellow discoloration is recognizable. The discoloration occurs practically on all plastic parts exposed to the washing liquid on in the rinse tank and outside the rinse tank in the conduit of the rinse water are arranged. The yellow discolouration is particularly noticeable in the plastic-coated Crockery baskets and cutlery baskets as well as cutlery drawers made of plastic; but essentially on PP plastic parts. As could be determined, the result Discoloration on the one hand from the fact that the detergent and dishwashing detergent are essential for the dishes have changed. Previous cleaning agents containing chlorine had a bleaching effect, which largely prevented discoloration of the plastic. Cleaners currently in use replace chlorine with oxygen, but oxygen bleaching prevents discoloration can. However, plastic discoloration is caused by carotene (beta-carotene), which is a fat-soluble natural dye in the food residues to be rinsed off the dishes accrues.

Starting from a method of the type mentioned in the introduction, the object of the invention based on a simple inexpensive improvement in draining behavior with the flushing or Cleaning liquid coming into contact with water-bearing household appliances To create plastic parts of the devices and these parts also discolored material in the prevent prolonged use.

The object is achieved according to the invention by using the method, Plastic materials through subsequent activation of their surfaces using fluorination or improve plasma treatment in their wetting properties on plastic parts of dishwashers or washing machines with the washing or cleaning liquid are acted upon directly.

The advantages achieved with the invention can be seen in particular in that without additional constructive measures on the washware containers, such as cutlery drawers, crockery baskets etc. with reasonable equipment program effort in terms of time and costs an essential Improvement in dripping behavior is achieved in the washware carriers. This is true also for dishwashing containers or plastic tubs made of plastic, if necessary, Water washing boxes or the like from washing machines. In addition to the improved The draining effect also increases the corrosion protection of the treated plastic parts reached.

Cutlery drawers or rinsing containers are usually molded parts from a high quality polymeric plastic material, e.g. B. made of polypropylene (polymer). Both Baskets of crockery, it is common to manufacture them as semi-finished products from metal wire and then to be coated with a polyamide (thermoplastic) for corrosion protection. Here are for the The cutlery and crockery holders as well as the basket bases are drained of water drops in a special elaborate profile. When using the method according to the invention to activate the surfaces of plastic, however, such constructive No measures are taken on the washware racks and the rinsing containers for draining off water or can be attributed to a simplified design. It has been shown that the known or usually plasma or deposited for a paint application on plastic Fluorination process surprisingly changed the treated plastic surface for water, that adhering water spreads out as a thin water film. In addition, in just as surprising and not obvious way achieved by the invention that the material discoloration caused by carotene, particularly in dishwashers no longer occurs on the plastic parts in the rinse water circuit. There is also when using fluorination or plasma treatment on plastic washware carriers the possibility of a less expensive replenishment of the high-quality plastic with success use, the environmentally friendly advantages are obvious. The advantages for practice can be seen in the fact that an inexpensive economical plastic with targeted improvements Surface properties can be used, which is also very durable.

The components in the dishwashing water circulation in dishwashers, such as dish racks, Cutlery drawers or cutlery baskets as well as sieves and the like have a different one Water wettability of the surfaces. For example, the products are fresh from the spray PP material (polypropylene) lipophilic and therefore water-repellent and fat-friendly. going one assumes that in the rinsing process hardened fats of the food residues are very readily fat-soluble Pick up beta-carotene dyes and transport them to the plastic components an untreated plastic due to the lipophilic (fat-friendly) character of the normal Attach the PP surfaces of the dye to the PP material and discolor it.

The discolouration that can be seen in households on untreated plastic components of dishwashers can differ from component to component. It was determined, that a strong discoloration z. B. is caused by tomato paste in food. Oils (e.g. olive oils) may have a lighter yellow color and hardened fats (e.g. frying fats) cause strong red discoloration. In all cases there is always a fat for the dye transport necessary.

Using the example of cutlery baskets or cutlery drawers used in dishwashers the effect of the advantage achieved with the method used according to the invention is said to be Improvement of water dripping behavior as well as color stability or avoidance a material discoloration are described in more detail.

To prevent water drops from forming, the finished cutlery drawer becomes one Subsequent surface treatment after the plasma process or by fluorination. This treatment makes the plastic surface of the cutlery drawer hydrophilic, So fat-repellent and water-friendly.

The hydrophilic surface property means that the contact angle of a drop is very different small or extremely flat. This increases the wetting properties of the surface. Drops of rinsing water can develop well over a large area and thin, which makes them quick Draining the rinsing liquid is concerned. With cutlery baskets or cutlery drawers treated in this way, which are exposed to the rinsing or cleaning liquid is therefore reduced also the amount of residual water bound in the mesh and grids of the basket opposite an untreated washware carrier by approx. 40 to 50 percent. The changed ones also have an effect Wetting properties save energy when drying dishes. Be too Avoid water marks or the like on the cutlery and glasses.

Because, on the other hand, the cutlery drawer after its treatment by the plasma process or the fluorination becomes hydrophilic, the fat-soluble natural dye beta-carotene cannot have a more discolouring effect because the plastic surface of the cutlery holder is grease-friendly is no longer present after treatment. So there is also the problem of material discoloration the plastic in the use of the dishwasher eliminated. One through lipophilic Coloring of the components caused by food coloring can no longer occur. In particular Carotene discoloration (based on beta-carotene) no longer occurs.

The method according to the invention is both new and already in use Plastic components (especially in the crockery baskets or the like) applicable. The method can also be used for plastic tubs or water inlet boxes from Washing machines can be used with the same advantages.

Claims (3)

Application of the process, plastic materials by subsequent activation of their Surfaces by means of fluorination or plasma treatment in their wetting properties improve on plastic parts of dishwashers or washing machines with the Flushing or cleaning liquid are directly applied. Application of the method according to claim 1,
characterized,
that completely from a polymeric material such as polypropylene, polyethylene, their copolymers, polyamide or from a regenerate of these plastics or coated with this plastic and included in the rinse water circuit components are treated. Application of the method according to claims 1 and 2, in particular to plastic parts of dishwashers,
characterized,
that washing containers or washware carriers in the form of cutlery baskets, cutlery drawers or crockery baskets are treated to improve the water dripping behavior and / or to avoid discoloration of the material.