MXPA01001623A - Sprayable powder composition for use as underbody protection or sealant - Google Patents

Abstract

The invention relates to powdery thermoplastic polymer compositions on the basis of polymers with polar, functional groups, which are suitable for the preparation of sprayable powdery compositions for use as underbody protection or sealants. The compositions are substantially free of water, volatile organic solvents and/or liquid plasticizers and are deposited on the substrates to be coated or sealed using known powder-coating technology. The compositions are used in motor vehicle construction as underbody protection or as sealant for joint seams.

Description

- POWDER COMPOSITION PULVERIZARLE FOR USE AS PROTECTION OR SEALER FOR BODY BASKETS The present invention relates to a powdery powder composition based on thermoplastic polymer powders and also to its preparation and use as a protection or sealant for body underbody. In order for these to retain their convenience of use, articles that comprise metallic tools [sic] in the construction of vehicles, mechanical engineering and construction of appliances are usually provided with coatings that are resistant to abrasion. In the construction of vehicles, especially in the construction of automobiles, these articles contain, in particular, the lower region of the body and also the arches of the rims and the so-called stirrups. In addition, it is necessary to seal the seams welded by stitches or otherwise mechanically held against the penetration of dust and water. In vehicle construction, this has been done using mainly plastisols, ie, dispersions of organic polymers in plasticizers, which gel when heated to relatively high temperatures and harden upon cooling. The plastisols used for this purpose are dispersions based on homopolymers and copolymers of (meth) acrylate, copolymers of styrene and also, in particular, homopolymers and / or copolymers of polyvinyl chloride in plasticizers. Frequently, together with other constituents, these plastisol compositions contain the so-called extenders in the form of high boiling point hydrocarbons. Although the aforementioned plasticizers and extenders are of low volatility, gelling in the coating furnaces of the automotive industry is always accompanied by evaporation of a small fraction of both constituents. This gives rise to problems of emissions and condensation problems in coating furnaces. Furthermore, despite the control of the modern process, it is impossible to completely avoid what is known as overspray, that is, the pulverization of the plastisol in the vicinity of the application booth. This so-called overspray must be discarded or recycled the product circuit by means of complex reprocessing methods. Therefore, there is a need, especially for the construction of vehicles, to provide compositions for protection in the lower parts of the body or sealing materials that do not contain solvents or plasticizers. In the past, compositions based on emulsions or "aqueous dispersions have been proposed for this purpose," but these have given rise to problems of application in the sequence of normal production of vehicles, given that during the short drying times inherent in The process, the water is unable to evaporate by cpmpleto, or even evaporates but with the formation of bubbles in the layer. Furthermore, even aqueous dispersion and emulsion systems always still include small amounts of volatile organic solvents such as so-called leveling auxiliaries and / or film-forming agents. The objective was, therefore, to provide compositions for protection in the lower parts of the bodywork and / or a sealing composition that does not contain solvents or plasticizers and also no water. According to the invention, this objective is achieved by the provision of pulverized, powdered compositions based on powdery thermoplastic polymers, these compositions being practically without water, volatile organic solvents and / or plasticizers, which are liquid at temperature ambient. These compositions contain one or more thermoplastic powder polymers, at least one of the polymers containing polar functional groups. In addition, these mixtures may contain other organic or inorganic solids in powder form. These compositions can be sprayed by electrostatic methods on metal surfaces without treatment, or on metal surfaces that have been pre-treated or coated organically or inorganically. As a result of this loading, the particles adhere to these metals immediately also after a few hours, even on vertical surfaces. By exposure to high temperature, this powder layer melts and then provides a firmly adherent film on the substrate. Similar powdery compositions have already been described, in the form of so-called powder coating materials. For example, US-A-4865882 discloses a method for powder coating metallic articles. The powder coating composition contains from 80 to 97% of a modified polypropylene powder and from 20 to 3% of a very low density polyethylene powder. These materials are mixed in the melt and formed into pellets in an extruder, and these pellets are then crushed by criomolienda to obtain a powder with an average particle size of about 150 μ. The metallic articles that are going to be coated, such as baskets, boards or accessories for cars, are then preheated to approximately 200 to 250 ° C, and subsequently submerged for a few seconds to a few minutes in a fluidized bed containing the composition for powder coating. As a result, a layer of the powder composition is deposited on the hot metal article. After coating, the metal article is heated from 160 to 230 ° C for a prolonged period to effect uniform melting of the surface of the coating obtained. This document does not describe coatings and seam seals for the protection of the lower parts of the bodywork. US-A-5498783 discloses a powder coating composition which is thermally crosslinked and consists of a powdery mixture of a polyester resin containing two or more carboxyl groups, a first crosslinker, which is reactive to the carboxyl groups of the polyester resin, another reactive acrylate copolymer and a second crosslinker, the second reticulator being proposed to be reactive to the reactive functionality of the acrylate copolymer. Due to their strong thermal shrinkage, however, these compositions are suitable only for coating applications that demand high hardness. For protection applications in the lower parts of the body and for sealing seams, where high flexibility is required, these compositions are convenient. Similar comments apply to the powder coating materials described in EP-A-404960, based on ethylene copolymers, an epoxy resin and a curing agent for the epoxy resin. In this case, it is said that the ethylene copolymer contains from 0.5 to 10% by weight of structural elements that originate from a comonomer containing carboxylic anhydride and from 3 to 40% by weight of a structure which is constituted by a monomer of olefinically unsaturated carboxylic acid. According to the teaching of this document, the powder coating composition described therein is said to be suitable for protecting metal substrates against gravel-induced corrosion. According to the teaching of this document, normal thermoplastic resin compositions, which do not have a high degree of thermal crosslinking, are unsuitable for producing a coating for gravel protection, since according to this teaching, thermoplastic resins have a small effect of adhesion on the substrate. WO 87/02043 discloses a powder coating composition containing a solid, epoxy powder that has an average epoxide functionality per molecule of more than 2, and a solid curing agent for this epoxy resin. The solid epoxy resin is a polyfunctional polyglycidyl ether of a bisphenol compound, or a polyfunctional polyglycidyl ether of a bisphenol modified with polyglycol. It is described that the powder composition can be sprayed directly onto phosphatized steel, chromed or galvanized or on chromed aluminum to form a durable coating. No information is given about the suitability of this composition for protection applications to the lower parts of the bodywork. WO 95/0324 describes a process for the preparation of a plastic that can be used as a powder coating material and / or hot melt adhesive. For this purpose, the polyolefins are subjected to a treatment of low temperature plasma in a frequency range from 30 kHz to 10 GHz. According to the teaching of this document, a transparent coating of good adhesion can be applied to glass, a a processing temperature of 160 ° C, using powder coating materials produced in this way. It is further claimed that this composition is suitable for producing a coating for the lower parts of the body in the construction of automobiles or as a coating on ship hulls. However, materials of this kind possess adequate adhesion to the metal board only for a very short, limited time. The sust.ratos that are going to be coated in the construction of automobiles, or that are going to be sealed with seam seals, are steel panels, customary in the construction of automobiles, which may have been phosphated and / or chrome-plated for the corrosion protection, or that are galvanized steel panels, and also steel boards of the aforementioned type that have been covered with electro-deposition coatings, known as materials for electro-cathodic coating, currently made boards have also been used of aluminum, aluminum alloys and magnesium alloys, so that coating compositions or sealants are necessary to obtain good adhesion on all of these aforementioned substrates. The polymer powders for use according to the invention are thermoplastic. It is required that these thermoplastics have a melting range between 50 ° C and 180 ° C and that they have, at least in proportion, polar groups having a pronounced dipole character and low spherical volume, to effect sufficient adhesion on any present anterior coating, and / or on the metal surface. It has been found that coatings based on polymers containing polar groups with nitrogen, such as polyurethanes or polyamides, either as a base polymer or copolymer, such as epoxies as the main component or as mixtures for powder mixtures, provide Excellent adhesion to electro-coated substrates (cathodically) or other primers. In the same way good adhesion results are obtained with copolymers of (meth) acrylic acid or (meth) acrylate. In addition, base polymers or copolymers including vinyl acetate, such as polyvinyl acetate copolymers or ethylene vinyl acetate polymers, for example, - likewise, effect adhesion to the aforementioned substrates. As already mentioned, the compositions for the lower body parts or sealant compositions of the invention can be constructed based on a powdery thermoplastic polymer containing polar groups.; however, it is also possible to use mixtures of two or more thermoplastic polymers in which case at least some of the polymers must carry polar groups. The polar functional groups should be selected from hydroxyl, amino, epoxy, carboxyl, ester, amide, urethane, isocyanurate, biuret, halofanate, blocked isocyanate, silanol or alkoxysilane. It is easily possible to mix thermoplastic polymers containing a high fraction of the aforementioned polar groups with homopolymers and / or poly-α-olefin copolymers, in which case the poly-α-olefins should preferably have been prepared by means of a prepolymer. treatment in corona or plasma. In the baking process of the coatings of the invention it is necessary to obtain efficient and impermeable coalescence of the polymer particles; therefore, only the aforementioned thermoplastic materials are convenient. Where mixtures of powders are used, for example, mixtures of polyurethanes or polyamides plus epoxides, there are strong indications that the cross-linking reaction of the polymer matrix with one another is not the reaction of primary importance, but rather that the primary reaction takes place, for example, with the substrate for electro-cathodic coating (coating by cataphoretic deposition) or with the metal substrate. As a result, there is good adhesion of the compounds for the protection of the lower body parts of the invention for the substrate; in addition, this guarantees that the composition does not undergo too high a level of crosslinking for the protection of the lower parts of the body, since high-level crosslinking would give rise to embrittlement of the coating. Particularly suitable for the compositions of the invention, for the aforementioned reasons, are, for example, the main binder components of the powder coating materials, proportioned crosslinkers, which are normally vital for powder coating applications, which are not added to these, or that are added only in a very small amount. Examples of binder systems in this class are specified, inter alia, in D. A. Bate, "powder coatings, Chemistry, manufacture and applications", SITA technology. London 1990, especially Chapters 2 to 4. Particular resilience is possessed, for example, by one-component epoxy powder coating materials having a softening point above 50 ° C, binder for powder coating based of polyurethanes having a melting range between 80 and 100 ° C, a melt index (MFI 190-2.16 in accordance with DIN 53735) 30-40 g / 10 min, powders of the polyethylene-acrylate copolymer having a melt index of and 15 g / 10 min, thermoplastic polyurethanes, polyamide powders, having a melt index of between 15 and 40 g / 10 min, ethylene-vinyl acetate copolymer powders, and also pre-treated LDPE (low density polyethylene) . In addition to the aforementioned polymeric constituents, the compositions of the invention may also contain finely divided inorganic and / or organic (polymeric) fillers, pigments and / or inhibitors of aging. Examples of suitable inorganic fillers are finely divided calcium carbonates in the form of the different crushed or precipitated limestones, barium sulfate, aluminum oxides, silicates. The colored pigments that can be used are carbon black, iron oxides, titanium dioxide, zinc oxide and similar color pigments known per se. In this context it may be convenient, for filling materials and for pigments, to use materials with a pre-treated surface. The inhibitors of aging that can be used in this context are all traditional inhibitors of aging for polymers, from the class of UV stabilizers against light-induced degradation or oxidative photo-polymer, antioxidants against thermal and thermo-oxidative degradation and also stabilizers against hydrolytic degradation or ozone protectors against attack by ozone. The nature and quantity of inhibitors for aging is guided by the chemical structure of the polymers that are used. In order that the compositions of the invention can be pulverized without problems as powder coating materials, it is important that all the powder constituents have an average particle size below 700 microns, of; preference below 200 microns, and with very particular preference below 80 microns. It is also necessary to ensure that the powder constituents do not exhibit any surface tack at temperatures below about 30 to 40 ° C, to prevent the formation of some of the powder particles before spray application. Investigations have shown that there is a direct dependence on applicability by common application techniques on particle size. The applicability defines the quantity per unit time and adhesion to sufficient drying on the metallic substrate. For this, the compositions have to meet the following requirements: • Good fluidization in the fluidized bed • Low transport air consumption • High quantitative performance per unit time • Therefore short coating time A low level of air consumption of transportation it is a prerequisite for a uniform layer pattern and to prevent the already applied powder from falling off. The preparation of the powder mixtures is necessary to select a process that avoids the separation during the application and during the recovery of the powdered powder in excess. Such a convenient process is based on a fluidization of the powder components in a stream of hot air and slightly below the melting temperature of the main polymer. It is possible to choose different temperatures according to the adjuvants and the second polymer. One possibility is a process in which the fluidization is carried out between 2 and 20 ° C below the melting temperature of the main polymer. Better results are achieved at a temperature range between 5 and 10 ° C below the melting range. By lightly sintering the surface of the powder mixtures, stickiness of the polymer particles between; Yes, so that the polymer powders are easily fluidizable, transportable and sprayable. In the case of the preferred preparation process, the procedure is as follows: premixed powders are blown into a reactor and fluidized, where they are subjected to a stream of hot air: then, this powder / air mixture is discharged. from a nozzle and cooled in a cold air current. The use of polyolefins pre-treated with plasma or in crown as the only base polymer for powder coatings for the protection of the lower parts of the body gives unsatisfactory results, given that these polymers do not achieve sufficient adhesion of the powder, in a long relative term on the surfaces that are going to be covered. In addition, the adhesion of the film after the baking process is not satisfactory. It is assumed that, in the case of plasma treatment, only the polymeric surface chains of the particles are transported to polar functional groups and that these light charges are inadequate to effect some satisfactory or at least adequate adhesion of powders, and / or adhesion of the movie. However, it may be convenient to make a proportional use of polyolefin powders pre-treated in this form as adjuvants of other polymers. In addition to the immersion processes described in the beginning, the powder coatings are sprayed in the spraying process, by the corona charging method or by the tribo process. The compositions of the invention can be applied by both aforementioned application processes, where particular preference is given to the tribo process, given that by means of this process it is possible to obtain a better deposition power or cover on the edges and angles and thus a better coating. To maximize the efficiency of the application of the coating composition, the application device, the energy circuit and the quality of the energy must coincide optimally with each other so that there are no interruptions related to the system for the operation . In addition to the good fluidisability of the powder composition, previously mentioned, in the tribo process the dust must also generate a minimum frictional load at a certain air speed. There is convenient test equipment to determine the electric tribo load capacity, for example, a current-load-time meter (I-Q-T meter). The objective in this case is to obtain a minimum discharge current from 1.7 to 2.5 μ at an air velocity of 1.8 m3 / h (t.p.n) (cubic meters per hour at normal pressure and temperature). With this spraying process, as you know, air is the means of transport used: air is necessary not only to transport but also to dose and generate the electric tribo charge. For economic application, it must be ensured that the air velocity for transportation, dosing and electric tribo air is as small as possible. This must not exceed 7.5 m3 / h. For this total air velocity to be sufficient for transportation, spraying and powder loading, the final fraction of the powder, ie, the fraction below 8 μ, should be as small as possible. A reduction in air velocity, especially in the transportation air velocity is also desirable to minimize abrasive wear of the application devices. The uniform expulsion of the powder is the result of effective fluidization in the container for the supply of the powder. In direct comparison with the protection for the lower parts of the body, of very high quality, based on a plastisol of P fC, of the prior art, the coatings for the protection of the lower parts of the body according to the present invention it provides abrasion values that are well above the level known in the present. As a result, it is possible to reduce the thickness of the coating considerably. In addition, the coating compositions of the invention are remarkable for a significantly reduced specific weight compared to PVC plastisols, so that, by both factors, a different reduction in vehicle weight is obtained. In the case of the use of the aforementioned powder compositions of the invention as protection for the lower parts of the bodies, that is, in the region of the lower parts of the vehicle body, in the arcs of the wheels or as protection of the abutments, layer thicknesses between 100 μ and 900 μ, preferably between 150 and 430 μ are applied. These coatings are then converted into films in paint drying ovens, in the normal sequence of the vehicle manufacturing process. The process temperatures normally available here for the formation of the film are between 110 ° C and 180 ° C, preferably up to 160 ° C, in a period of between about 15 and 30 minutes. For the application as material for sealing seams, which is applied, inter alia inside the vehicle also, these seam seals can also be specifically cured with the help of lasers. The adhesion tests followed by the condensation tests or the saline spray test, and also the low temperature behavior according to the requirements of the present specifications for the compositions for the protection of the lower parts of the body, of the manufacturers of automobiles throughout the world are covered with the powder materials of the invention. The invention will now be further clarified by reference to different examples for its realization.

Example 1 A powder mixture was prepared from the following constituents.

Polyepoxide powder 49.7% by weight (ab andamiento interval> 50 ° C) low density polyethylene powder 48.5% by weight of carbon black, P.rintex XWE1 (Degussa) 0.1% by weight coated calcium carbonate, precipitate Winof il SPT 0.5% by weight Aluminum oxide powder 1% by weight The aforementioned powder mixture was crushed for different particle size ranges and then fluidized, fluidizing the powder components in a stream of hot air at a temperature slightly below the melting temperature of the main polymer, and was subsequently discharged to through a nozzle and cooled in a cold air stream. To determine the best applicability, the following particle size ranges were investigated.

It was found, with optimization of the lowest possible conveyor air with good performance than the particle size distribution of < 200 μ is adequate. Better results were obtained with particle sizes < 80 μ.

Comparative results of different coatings for protection in the lower parts of the body From these comparative results it is evident that a polyolefin powder pre-treated with plasma according to the prior art (analogue WO 95/03344) does not provide satisfactory results in any of the criteria that are important for protective coatings for the lower parts of the body, except for dry adhesion. A traditional powder coating material of the prior art is unsuitable for a composition for protecting the lower parts of the body with respect to the maximum thickness of the coating that can be achieved and with respect to the abrasion resistance and ccn with respect to the test of bending at low temperature. In the same way as for example 1, powder mixtures were prepared based on the different binders. These powder mixtures were then used to coat electro-coated, cathode and baked metal boards at 150 or 170 ° C. The quality of the film was subsequently evaluated with respect to the visual appearance, expansion and adhesion behavior. In addition, the abrasion resistance was measured. For comparison purposes, the same measurements were made on a high-quality PVC film plastisol, Terotex 3028 from Henkel Tereson. The results are established in the following table.

Parameters for the binders used: Example 7 polyurethane powder MFI: 35 g / 10 min. Example 8 polyethylene-acrylate copolymer MFI 8 g / 10 min. Example 9 Polyurethane powder 2, melting range (Kofler) 90-100 ° C. Example 10 polyethylene-acrylate copolymer powder, MFI 8 g / 10 min. Example 11 epoxide powder, melting range > 50 ° C (DSC method, differential scanning calorimetry). Example 12 copolyamide, MFI: 18 g / 10 min.

All the coatings provided a convenient continuous film for protection in the lower parts of the body, which in almost all cases was highly flexible and extensible. All the coatings showed excellent adhesion results (classification scale LO = very good, 0 = completely inadequate) not only after baking at 150 ° C but also after baking at 170 ° C and also after condensing weather tests (exposure to condensation, 14 d / 40 ° C). To determine the abrasion resistance by the BMW method, metal boards were produced with the coating compositions in the coating thickness stated in the table. The amount of gravel (one kg) required to penetrate the protective coating for the lower parts of the body was measured completely. From the abrasion values found it is evident that all the protection formulations for the lower parts of the body give very good values, which even at low coating thicknesses are at least equal to the high quality plastisol coatings.

Claims (7)

1. A composition for protection of low body films, powder, which can be sprayed, or sealant, based on thermoplastic powdered polymers, is characterized by being virtually free of water, volatile organic solvents and / or liquid plasticizers, powder constituents have an average particle size below 700μ, preferably below 200μ, and in particular below 80μ, and at least some of the polymers carry polar functional groups.

2. The composition according to claim 1, characterized in that the thermoplastic polymer has a melting range of between 50 ° C and 180 ° C.

3. The composition according to at least one of the preceding claims, characterized in that a mixture of thermoplastic polymers is used.

4. The composition according to at least one of the preceding claims, characterized in that the polymer or polymers contain polar functional groups, selected from the groups hydroxyl, amino, epoxy, carboxyl, ester, amide, isocyanurate urethane. , biuret, halofJanate, blocked isocyanate, silanol or alkoxysilane.

5. The composition according to at least one of the preceding claims, characterized in that in addition to the thermoplastic polymer (s) it contains finely divided filler materials, pigments and / or aging inhibitors.

6. The use of compositions based on thermoplastic powdered polymers according to at least one of claims 1 to 5 for coating the protective area in the lower parts of the body or as sealants for sealing seams and joints in construction of motor vehicles.

7. A process for coating motorized vehicles or parts of motorized vehicles in the area of the lower part of the bodywork or in the arcs of the wheels, is characterized by the following essential process steps: • A composition based on thermoplastic polymers in powder according to at least one of claims 1 to 5 on the substrate optionally pre-coated with electro-cathodic coating with the aid of crown or tribo coating units. • Followed by baking the coating at temperatures between 110 ° C and 180 ° C for 15 to 30 minutes. • To give a thickness of the coating layer from 100 μ to 900 μ of the film thickness.