JPH0655292B2 - How to polish the lacquer surface - Google Patents

Description

The present invention relates to a method for polishing highly elastic lacquer surfaces, in particular lacquer surfaces on plastics, in which the lacquer surface to be polished has a temperature of up to 5 ° C. due to the flow of cold gas. It is directed to the above method which is kept at.

BACKGROUND OF THE INVENTION High-elastic lacquer coatings, for example high-elastic lacquer coatings of the type used for lacquering plastics, can no longer be repaired to a perfect finish once the coating has dried. Conventional methods used for lacquers on metal (eg in the automobile industry) to rub and polish defective areas of the lacquer film (must be done in the oven immediately after the film has dried). Is usually not possible for lacquers on plastic.

Plastic parts are used extensively, especially in the construction of motor vehicles, for example to reduce weight and thereby save fuel, to prevent small injuries and to be more freely designable. Has been. These parts generally provide sufficient resistance to weather or chemicals (fuels, detergents),
Also, lacquering is required to be scratch resistant. In addition, plastic body parts must be lacquered with the same paint as the car body.

Such plastic lacquers must meet stringent requirements. It is particularly important to dry at temperatures of 80 ° C. or lower (due to the limited thermal resistance of plastics) and to provide a fully flexible lacquer film. Already in the literature (eg ("M. Schonfelder
(M. Schonfelder), “Effects of polyurethane lacquers on the mechanical properties of plastics (Einfluss von Polyuretha
n-lacken auf die mechanischen Eigenschaften von Ku
nststoffen) ”, No. 2, 1979, pp. 59-64, Elvira Moeller Gmbh, Filderstadt,” described in some detail. When certain lacquer coatings are applied to flexible synthetic materials, the joints between them can be damaged by impact (eg in an accident) and dangerous debris can result. The mechanical properties of the part before it is lacquered are impaired by the hard lacquer film. Therefore, the coating systems conventionally used for lacquering metals are generally unsuitable for lacquering plastics. Instead, highly elastic lacquer materials that dry at low temperatures, usually flexible two-component polyurethane lacquers, are used in Europe. When "on-line lacquer" is applied to body parts that are manufactured by the composite construction method and thus consist of both plastic and metal parts, metal parts as well as plastic parts are necessarily made of high-elasticity lacquer material. Lacquered.

However, defects in such lacquers cannot be satisfactorily repaired by methods of scrubbing and glazing after drying, which are customary for metallic lacquer coatings used in the automotive industry. Has been known for a long time. As the flexibility of the lacquer film increases, the repair problem becomes more difficult.

If, for example, a high-modulus clear lacquer filk is rubbed, its surface can no longer be restored to its initial gloss even after a few minutes of glazing. Dull luster spots and sanding streaks remain on the surface. If the lacquer film is tinted, the film may be matte or discolored, reducing its value. The reason for these poor results is not entirely clear, but it is certain that the repair of the film increases with the flexibility of the lacquer film, which is essential for the reasons pointed out above. Is. Elastic films can be considered to divert mechanical forces exerted by polishing or polishing. It was also found that the lacquer on the plastic when it was glazing became more strongly heated than the lacquer on the metal (probably due to differences in chemical structure and poor thermal conductivity on the plastic).

Due to the unsolved problems mentioned above, the defects (granular particles and other scars) found in lacquers on plastic parts cannot be repaired later, but require complete lacquering again. This is very laborious and expensive, and results in a high reject rate.

Therefore, the difficulty of glazing such lucky systems is due to the more widespread use of plastics in the automobile industry and on-line lacquering of automobiles (ie the same (elastic) lacquer on metal parts and plastic parts on car bodies). It is one of the biggest obstacles to simultaneous lacquering in the system).

SUMMARY OF THE INVENTION The object of the invention is to provide a new method for the polishing of lacquer surfaces, which makes it possible to polish highly elastic lacquer films, especially lacquer films on plastics. A further object is to provide a method which can be used in particular for on-line lacquering (including lacquering of metal surfaces) of car bodies produced by the composite construction method.

Means for Solving the Problems These objects could be achieved by the method according to the invention described below.

The present invention relates to a gloss of a highly elastic lacquer surface selected from the group consisting of a clear lacquer film having an elongation at break of greater than 60% DIN 53 455 and a colored lacquer film having an elongation at break of greater than 30% DIN 53 455. In the polishing method, the surface to be polished is maintained at a temperature of at most 5 ° C with a cold gas having a temperature of -20 ° C to -60 ° C during the polishing operation. Be directed.

[Detailed Description of the Invention]

Polishing furniture lacquer with air cooling is a DE
-As is known from AS (German Patent Specification) 2,653,487, furniture lacquers are not high-elasticity coatings and therefore this publication does not really relate to the problem solved by the present invention. Absent. Furthermore, this publication does not make any mention of the low temperatures which are essential to the invention. The relatively high temperatures (uncooled air) used for applying the lacquer surface in the method according to this publication are quite unsuitable for solving the problem of the invention.

The lacquer surface to be polished by the method according to the invention is greater than 60%, preferably greater than 80% (clear lacquer) or greater than 30% (colored lacquer).
A highly elastic lacquer film with elongation at break according to DIN 53 455. This type of lacquer film is made of a high-modulus two-component polyurethane lacquer, such as "" Desmodur and Desmophen Urethane Copolymer for the painting of plastic body parts made of plastic.
ating Resins for the coating of plastic car body p
arts) ”, Mobay Corporation, Pittsburgh, USA, issued 1988 (Order No. 56-B70
20 (7.2) A "is obtained in particular when used in the known manner for lacquering plastics, in particular plastic parts of car bodies, as well as metal parts in the case of on-line lacquering of car bodies produced by the composite construction method.
In such a two-component polyurethane lacquer, the binder consists of a polyisocyanate component and a polyol component and the amount of these components is about 0.5: 1 to 2: 1, preferably 0.8: 1 to 1.5: 1. This corresponds to the NCO / OH molar ratio. Suitable polyisocyanates are the well-known "lacquer polyisocyanates", for example 2,4-diisocyanatotoluene or 2,6-diisocyanatotoluene.
Mixtures with diisocyanatotoluene and in particular biuret-, isocyanurate- or urethane-modified derivatives of simple diisocyanates such as 1,6-diisocyanatohexane, the said derivatives generally being about 10-25.
It contains by weight of isocyanate groups.

Suitable polyols are polyester polyols, polyether polyols or polyacrylate polyols.

Polyester polyols generally have a molecular weight of 500 to 5000 and at least 2 per molecule, preferably about 2
Contains ~ 6 hydroxyl groups.

The polyether polyol is generally 1000-2000.
And has about 2-3 hydroxyl groups per molecule.

Acrylate polyols have a molecular weight of about 500 to 5000 and generally contain 1 to 12% by weight of hydroxyl groups.

Two-component lacquers are customary additives such as catalysts, pigments
Solvents, leveling agents, fillers and the like may also be included.

The plastic may be based on polyurethane, polycarbonate, polypropylene or acrylonitrile-butadiene copolymer or mixtures thereof with polycarbonate.

Generally, a known glazing aid (glazing paste) is used for glazing.
For example, "" Rompus Chemical Dictionary / Ott Albrecht-
Neumler (Rompps Chemie-Lexikon / Otto Albrecht-Ne
umuller) ”, Volume 5, pp. 3296 et seq., Stuttgart,
1987, published by W. Keller & Co. ”.

Suitable glazing devices for the method according to the invention include compressed air glazing devices and electrically operated glazing machines of the known type. A suitable polisher is, for example, the Chicago Pneumatic Inc. Angle Polisher CP869P from D-6222 Geisenheim / Line. Polishing tools of the type described in DE-AS (German Patent Specification) 2,145,714 are also
It is suitable if the polishing disc described therein is replaced by a suitable polishing disc covered with lamb skin.

For carrying out the process according to the invention, a temperature of at most 5 ° C., preferably not more than −10 ° C., is maintained during the surface polishing operation to be polished by flowing a gas stream over the surface to be polished. Is essential. This is the case, for example, in DE-AS (German Patent Publication) in order to maintain a permanent supply of cold cold gas on the surface to be polished.
This can be done by using the tools described in No. 2,145,714. A modified version of the tool described in DE-AS 2,145,714 may be used in which the cold gas is introduced centrally in a direction parallel to the axis of rotation. The manner in which cold gas is applied is not essential to the invention per se, as long as cold gas maintains the lacquer surface to be polished at the above-mentioned maximum temperature or below during the polishing operation. The gas used for cooling is at a temperature of about -20 ° C to -60 ° C. For example, evaporating liquid air or evaporating liquid nitrogen may suitably be used as cold gas.

In order to ensure proper cooling during the glazing operation, it is advisable to keep the diameter of the glazing disc at a maximum of 30 cm, preferably about 15-25 cm.

The method according to the invention provides for the first time an economical method for lacquer repair in which the polishing and polishing operations are coordinated with one another.

So when it cools, the damaged lacquer film first
It can be rubbed with a special abrasive paper, such as the abrasive paper sold as the "Finesse-it" system by 3M Deutschland of Neuss. The grain size of the abrasive paper used should be a compromise between the requirement for a coarse grain size that rubs quickly and the need to avoid deep polishing scars (caused by the coarse grain size and difficult to polish). Is. This is about 800-2
000 (preferably about 1200-1500) can be achieved with an abrasive paper. To avoid severe damage, these abrasives should have a small diameter (about 3 cm) and should be punched rather than cut out. In that case, even highly elastic lacquer systems can be rubbed in within seconds. If even faster operation is required, a rotary polisher can be used.

When the lacquer surface is rubbed, it can be polished by the method according to the invention.

The method according to the invention repairs a highly elastic lacquer by rubbing and polishing it to restore its initial gloss and without other defects (for example occasional abrasive streaks left on the surface). To enable that. The method according to the invention enables highly elastic lacquer films on plastic parts to be repaired without the need for relacquering.

Examples The present invention is further described by the following examples, without intending to limit the invention thereto. In these examples, all parts and percentages are by weight unless otherwise noted.

Example The ability to polish different lacquer systems of different elastic grades
ABS Polycarbonate Alloy (Ray) for testing
Bayer Bi-Blend of Berkusen ( Bayblen
d)) firstly used two-component polyureta on boards made from
Undercoat (biuretized hexamethylene diisocyanate
Desmodur of Bayer ( Desmodur) N) and
And a polyhydride having a hydroxyl content of 5.2% by weight
Roxy polyester (Desmophen of Bayer ( De
smophene) 1200) base material)
And then Bupper Tarno Harberts commercial metal
Slackers (silver gray, permacroon dia
Cloak Silver Metallic ( Permacron Diamant Si
lber-metallic)). Preprocessed like this
The plate, then the solvent-containing binary system (biuret poly
Isocyanate and Bayer's design of Leverkusen
Smophen ( 670 and Desmophene) D
esmophene) A365 polyol) based clearer
The coater was applied. Desmophen ( Desmophene) A36
5 (inelastic with a hydroxyl content of 2.8% by weight
Polyhydroxy polyacrylate resin) and Desmofe
( Desmophene) 670 (4.3% by weight of hydroxyl
Slightly branched elastic polyester poly with content
The weight ratio of all) can be changed as shown in Table 1.
It was Formulation 1 is very hard, while Formulation 4 is
Very elastic (clear lacquer fill at room temperature
See the value of the elongation at break. Formulation 4 is practical (eg
For example, in a car where the risk of mechanical shock is high.
Used for plastic front and rear parts
The highest degree of elasticity used in clear lacquers)
Equivalent to

The amount of polyisocyanate component used in the clear lacquer was an amount corresponding to an NCO / OH equivalent ratio of 1.2: 1. The clear lacquer further contained the following additives (percentages are weight percentages based on the binder (solid resin)): The clear lacquer contained as solvent a mixture of ethyl acetate, butyl acetate, methoxypropyl acetate, methyl ethyl ketone and xylene in a weight ratio of 1: 1: 1: 1: 1. The solid content was 49.5% by weight. The clear lacquer was applied by compressed air atomization, the dry film thickness of the clear lacquer being about 30 μm.

After evaporating for about 15 minutes, the lacquer was dried at 80 ° C. for 45 minutes. The sample thus lacquered was then removed from the oven and, after only a few minutes, wet rubbed and polished.

The abrasive paper used is "Finesse-i
t) "abrasive paper (diameter 3 cm, grain size about 1500), the surface of which was rubbed by hand (time about 10-15 seconds, area of rubbed surface about 3 cm x 3 cm).

The surface was then glazing with a cold gas glazing device having a rotating glazing surface (this glazing device is D-62
The 22 Geisenheim / Line Chicago Pneumatic glazing device CP869P was technically modified to allow cold gas to be introduced centrally in a direction parallel to the axis of rotation. ).

Evaporating liquid nitrogen was constantly applied to the surface (temperature at outlet -40 ° C) to keep the surface below -10 ° C during polishing. The glaze device has the surface of lamb skin, the diameter of the turntable is 20 cm, and the rotation speed is 2
It was 500 times / minute.

The "Finesse-it" paste was used as a polish aid. The sensitization obtained after a lustering time of 30 seconds is shown below (Gardner gloss value at 60 ° C, values in parenthesis at 20 ° C).

The initial gloss was restored, and no traces of polishing or polishing were left. Therefore, even highly elastic formulations can be rubbed and polished immediately after drying in an oven.

For comparison, the results are shown in Table 2 for a conventional glazing of the same lacquer composition (i.e. glazing according to the state of the art; all conditions are the same except that constant cooling with cold gas is omitted).

As is apparent from these results, the lacquers with little flexibility (Formulation Nos. 1 and 2) can be polished with comparatively good results even by conventional methods, and therefore by using cold gas. No further improvement is generally obtained. However, even clear lacquers with moderate elasticity (elongation at break> 60-70% at room temperature) can no longer be polished by conventional methods. In high elasticity systems, the initial gloss cannot be restored even by long-term polish of a few minutes, which is in any case unacceptable in practice.

The same glazing experiments were performed with Formulations 1-4 on primed aluminum plates instead of primed plastic plates. The same results were obtained within the range of measurement accuracy (both with and without cold gas). That is, the surface of the lower layer had little effect on the results obtained for the polish of the multilayer lacquer system.

This means that when the elastic lacquer system conventionally used for lacquering plastics is applied to metals (for example on-line lacquering of automobiles made by the composite construction method), the invention It means that it is just as difficult to polish them as on other materials without using the method according to.

The same results are also obtained when elastic lacquer raw materials other than those mentioned above are used. That is, the glazing time is greatly reduced by using the method according to the invention, or (for very high elasticity) glazing is possible only with the method.

Other grades of abrasive paper can be used with equally good results when the cold gas method is used. A very rough paper (grain size of about 60
Only when 0) is used.

From these results, it is acknowledged that a new method has been found in which the elastic lacquers currently used for lacquering plastics can be quickly repaired by rubbing and polishing.

Although the present invention has been described in detail above for purposes of illustration, such details are for that purpose only, and the spirit and scope of the present invention, except as may be limited by the claims. It should be understood that various modifications can be made by those skilled in the art without departing from the.

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Claims (1)

[Claims] 1. A highly elastic lacquer surface selected from the group consisting of a clear lacquer film having an elongation at break according to DIN 53 455 greater than 60% and a colored lacquer film having an elongation at break according to DIN 53 455 greater than 30%. In the glazing method, the surface to be glazing is maintained at a temperature of at most 5 ° C during the glazing operation with a cold gas having a temperature of -20 ° C to -60 ° C. .