DE2442227B2 - Process for applying a coating to a glass fiber reinforced polyester substrate - Google Patents

Description

The invention relates to a method for applying a coating to a glass fiber reinforced polyester substrate, wherein on the substrate a coating agent which consists of an isocyanate-terminated substance with a content of unreacted isocyanate groups and a substance with reactive hydrogen atoms exists, is applied and cured.

A method of the type mentioned is known from US-PS 37 03 426, the from this Patent known polyester compositions for the construction of plastic panels for the construction industry or are intended for automobile bodies or boat hulls.

It is also known from US Pat. No. 3,715,337, an isocyanate end group and reactive hydrogen atoms to cure containing coating composition by means of pressure and heat, with a substantially defect-free crosslinked isocyanate-based coating is produced, which is bonded to the substrate.

The known covers serve as protective covers, for example for waterproof textile fabrics, and as adhesives for bonding metal to metal. Wood with wood or metal with wood. Further the known coating compositions have been proposed as binders for various fillers, for example for vulcanized rubber to produce track surfaces, for example for sports fields.

The invention is based on the object of a method for applying a coating to a To create fiberglass-reinforced polyester substrate in order to have a molded or injection-molded part made of polyester Maintain surface quality that was previously not achieved without extensive post-processing operations could be.

This object is achieved in that to eliminate surface defects on the already compression molded or injection molded, fully heat-cured polyester substrate in a mold and especially that in which the compression or injection molding of the polyester substrate took place, the coating agent is applied in such an amount on the polyester substrate that a coating with a Thickness of less than 0.5 mm can be obtained, the mold closed and enough pressure on the product is applied so that the coating agent covers the surface of the substrate substantially and that

Coating agent is hardened in the form under pressure.

The surface quality obtained in compression or injection molding processes is achieved by the method according to the invention significantly improved in terms of their uniformity, without manual processing operations are necessary, according to the preferred method not even a removal of the polyester substrate from the compression or injection mold to carry out the process steps according to the invention is required

With the method according to the invention, surface depressions (depressions) can be eliminated which may occur as a result of uneven shrinkage of molded or pressed parts, with the self must then be expected if polyester resins with low shrinkage are used. the In practice, shrinkage occurs when a component cools after the hardening process and shows in the form of a trough compared to any other thicker section of the component, such as one Rib. This is in part due to the fact that a given percentage of shrinkage occurs in such thicker areas for a given resin composition result in greater overall shrinkage

Furthermore, an undesired porosity of the surface is eliminated by the method according to the invention, which is mainly due to air pockets and an insufficient distribution of certain components of the Molding compound, such as that of the filler or the reinforcing fibers, is caused, with the porosity at the occurs over the entire surface of the pressed part.

Finally, the method according to the invention eliminates a third type of error which is not necessary consists of only one surface defect, namely microcracks, which generally occur in areas with low glass content or high filler content occur. These lead to local failure, its final cause is thermal or chemical shrinkage. These cracks leading to the surface of the part open can pose paint problems similar to porosity.

The inventive method has compared to conventional methods for applying a cured resin coating on a thermoset part has considerable advantages. With a known yellow coating the coating material is applied to the mold surface and allowed to partially cure. The mixture of resin composition and glass fibers is then applied to the layer of gel-like coating on and rolled out, after which the composite and gel-like coating are allowed to harden. This process is based on the joint crosslinking of the gel mass and the polyester resin at room temperature and Obviously, it is not suitable for the production of a large number of compacts, nor for the production of Precision pressings. Commonly used gel coating materials include thermosetting ones Resins such as certain polyesters and melamine-formaldehyde resins.

According to a further coating method for a thermosetting substrate, a with a resinous material, e.g. B. a polyester, impregnated paper - generally in the press form - laminated. However, since the paper does not have good flowability, it tends to tear when it is is applied to non-horizontal surfaces where the distance between the joined metal molds is decreased.

It is also known in the pressing of thermoplastics, the compacts with a second thermoplastic Coating material by simply heating and melting the materials together. These However, the method is not suitable for coating heat-cured objects, especially high-strength materials such as fiber-reinforced plastics.

Further advantageous embodiments of the method according to the invention are the subject of the sub-claims.

The invention will then be explained with reference to the drawings

F i g. 1 is a flow diagram illustrating the preferred mode of operation of the invention. ι -, F i g. FIG. 2 shows a cross section through a typical pressed part having a rib or a hump and FIG explains the dimensions given in example 1,

F i g. 3 a photographic one made with the aid of a scanning electron microscope (4000x magnification) Comparison of an uncoated polyester surface and such a surface according to the invention has been provided with a coating,

Fig. 4 is a photographic perspective view a cross section through a coated polyester substrate having a rib having,

F i g. Figure 5 illustrates a cross section through a typical die assembly.

The preferred embodiment jo is explained below.

In the description of the invention, the term "in-mold coating" is used for two reasons Distinguishing this method from the gel coating used. First, can be a conventional gel-like coating have a thickness of about 0.38 mm or more, while that described herein The coating is preferably of the same thickness as a paint, i.e. in the range of about 0.013 to 0.127 mm. Second, the methods of application are different in that, according to the invention, an object in the mold in which it is produced is provided with a coating after it has hardened. Even though therefore, the coating agent and the coating method bring particular advantages with them, if of these is used in compression molding, the invention can be applied in the same way to other molding processes, z. B. the injection molding process apply.

As mentioned, the preferred molding method for practicing the invention is compression molding; the 5 «The invention is explained in terms of this method. When producing a pressed composite part from a pressed, thermoset substrate and an isocyanate-based coating is the first stage by pressing the part using conventional compression molding techniques. Though you get the substrate can make any of a variety of thermosetting resins by compression molding, have the Polyester resins, especially the glass fiber reinforced types, have the greatest economic importance. Polyester bo Resins generally represent mixtures of unsaturated polyester resins and crosslinkable monomers are. Polyesters are esterified (condensation) of polycarboxylic acids or their anhydrides with Glycols produced using known methods b5 as well as acids and glycols. Below will a recipe given for the special substrate mostly used in the context of the invention; cited are the components and the respective parts by weight:

component Parts 65% polypropylene futnarate solution in styrene 4000 35% polymethyl methacrylate solution with some carboxyl groups (Additive for low shrinkage) in styrene 2 240 35% polymethyl methacrylate solution, no carboxyl groups (Additive for low shrinkage)
in styrene
Calcium carbonate (filler) 772 tert-butyl perbenzoate; more peroxidic 10 520 Initiator for the polyester-styrene- reaction Zinc stearate 70 Mg (OH) ₂ 350 Fiberglass 316 7 830

26 098

The process step described below can optionally be carried out first. This stage consists in mixing the coating agent, which because of the reactivity of the two components in the generally no more than a few minutes or a maximum of half an hour before the application of the Coating agent should take place. An isocyanate end group is mixed in to produce the coating agent containing substance (optionally a prepolymer) which has excess reactive isocyanate groups with a material which either has reactive hydrogen atoms (e.g. a polyhydroxyl compound) or one capable of trimerizing the terminal NCO groups "Excess" means here that there are more isocyanate groups than reactive hydrogen atoms available. The isocyanate reacts with the under the action of heat and pressure Polyhydroxyl compound or the catalyst, whereby an isocyanate-based coating is formed which at application according to the invention to the pressed part closely this is liable.

As mentioned, the porosity can be a result of air inclusions and / or poor distribution of the Be components of the molding compound. Since the coating produced in the mold is generally improved Should have surface properties, the constituents of the coating agent should have additional Stir can be distributed or dispersed more thoroughly. In addition, the coating agent is preferably used for Removal of trapped air degassed. It should also contain less filler than that for the substrate molding compound used so that the coating is as homogeneous as possible. The recipe for the substrate includes For example, a total of 26,098 parts, of which 18,350 parts (around 70%) represent filler and fibers, while typical coating agents that can be used in the form are at most about 20% by weight (inorganic) Contain filler.

After the press cycle carried out for the substrate, the mold is opened. However, the opening takes place only after the substrate has cured completely, as the latter in the case of one before the complete Curing taking place pressure relief can break, either due to from inside The gas escaping from the substrate or as a result of the substrate surface sticking to the mold. at Application of the invention to compression molding, the mold must be opened sufficiently wide that the Filling of the coating agent therein applied to the surface of the heat-cured substrate to be coated can be. In another molding process, e.g. B. the injection molding process, but means »sufficient opening the mold to introduce the filling «that you can mold up to one of the desired thickness

ίο the cover opens to the appropriate degree To allow the filling material to be injected.

At this point in time, the coating agent can be filled onto the glass fiber reinforced polyester substrate in the same form (either pressed or

is injection mold) in which the polyester substrate is produced was applied. You can also take the part out of the first mold and put it in a second mold give and carry out the application of the coating agent there. In order to minimize the number of operations on To have to make pressed substrate, it is generally expedient to carry out both pressing operations in the same molding press. It can be used to increase productivity or for other reasons however, it can sometimes be advantageous to use a different press for the second press cycle. Therefore the terms "opening the form" and "putting a fill ... into the form" relate to both to the form in which the substrate was created, as well as to one only for pressing the coating used special second form. In each case, the coating agent is filled into the mold entered, either on the surface of the FRP part to be coated or on this Surface adjacent mold surface.

In practicing the process of the invention, it was found that it was not it is necessary to thoroughly clean the polyester substrate (for example, the surface with the help of a Solvent from the mold release agent, oil, etc.

free) before applying the coating agent in the mold. Rather, you just have to put everything on the part Remove any remaining loose press burr. In addition, it is no longer necessary to use the polyester substrate primer before putting it in the

The form is provided with the coating

During the development of the coating agents and coating processes described here, it was found that that the coating agent should preferably have such a consistency that it does not come from the polyester substrate expires that, however, when the press is closed, it covers essentially the entire surface to be coated Surface area in a generally uniform layer less than 0.5 mm thick preferably from 0.01 to 0.1 mm.

After the filling of the coating agent has been applied to the polyester substrate, the second pressing cycle can be started by closing the mold. However, as mentioned, it is common It is necessary to adjust the pressing pressure again before the second pressing process. When compression molding is dei The expression "closing the mold" should be taken literally, while in the injection molding process the mold is through there! Injecting the mass filling the space between the mold and the pressed substrate

b ^r > is »closed«.

The pressure suitable for the second pressing cycle should be empirical for each shape of the part be determined that the surface of the in the Forrr

produced coating where it has covered a surface defect, coherently and substantially is smooth; d. That is, the coating should correspond essentially to the shape of the mold producing the coating. This phenomenon is best illustrated in Fig.4 Fig. 4 illustrates in which the polyester substrate was made by pressing a non-shrinkage additive containing polyester resin to highlight the hollows. That Coating agent was pigmented dark to make it clear that the coating after cooling is thicker where a hollow has to be filled, while at the same time a flat, smooth surface (cf. the darker area above the hollow) is created. It is also found that the microcracks with the coating agent were filled, not only the cracks adjacent to the surface, but also the cracks located below the trough in the upper part of the rib, but open to the surface. F i g. Fig. 3 shows the same type of sealing, but for the case of porosity, which how mentioned, the application of paints on plastic molded parts has made extremely problematic so far. It can be seen that the pores on the coated surface are generally in the range of about 1 to about 3 μπι, while the one Coated surface no visible pores or even at 4000 times magnification shows another defect The lines that can be seen on the coated surface are raised areas that indicate microscratches on the surface are due to the shape; since their width and height are only a fraction of a micron, they do not noticeably affect the surface quality or the gloss. The coating-free surface Because of its porosity, it is too rough for such lines to be formed evenly.

The pressing of the coating applied in the mold apparently follows the same principle as on the the original problem of the pits, i.e. the shrinkage of the resin mass on cooling after The hardening process is based on a close examination of the parts provided with a coating Raised areas of the coating agent were found above the troughs immediately after the part after was removed from the mold during the second pressing operation. A later examination after the coating was allowed to cool showed that the shrinkage the coating composition takes place in such a way that when it cools down while taking on the permanent shape of the coating assumes the desired surface quality without any noticeable depressions or raised areas occur. However, this is apparently only the case when looking at the second press cycle (pressing the coating) is applying the correct pressing pressure. If the pressure is too low, after that When the part cools, there is still a depression, while if the pressure is too high, a raised area Based on these observations, it was assumed that during the second pressing operation the thicker parts of the cured polyester substrate are compressed to a greater extent, so that a larger proportion (thickness) of the coating agent covers the surface (and the troughs) at these points can. Then, when the pressure is released at the end of the second press cycle, the polyester substrate picks up its uncompressed form again, and the excess portion of the coating agent arrives also in an unstressed state. This results in a raised point in that area, where there would otherwise be a hollow. During the cooling process, the mass becomes thicker

■ -> above the troughs the greater absolute degree of shrinkage of the base part and the mass in this Area districts compared to the rest of the surface. This ultimately results in an essentially smooth one (i.e. corresponding to the shape of the die) surface

U) before, where previously there were depressions, waviness and other surface defects on the pressed part. It it is emphasized, however, that these considerations are merely theoretical in nature and that the invention is not in any way Way be in some special working technique In summary, it is limited to achieving one flat surface required, the depth of the hollow or other flaws, the compressibility of the Polyester substrate, the shrinkage behavior of the coating agent, the thickness of the coating and the pressing pressure for the second pressing cycle to be matched empirically. As in the example below As can be seen, the compressibility of the polyester substrate is not only dependent on the respective polyester material, but also on the geometric dimensions depending on the part.

example 1 This example aims to illustrate the interrelationship between

the pressing pressure for the second closing of the mold and the shape of the cavity after the one taking place in the mold Illustrate coating application. A box-shaped, glass-reinforced polyester resin article with several internal reinforcement ribs is used. pen and a cylindrical hump. The object was pressed, as the cross-section shown in Figure 5 shows; it becomes the production of a pressed part 10 illustrated between punch 22 and die 20 and a surface 14 opposite the rib on which the coating 16 (shown exaggerated) should be applied to fill any surface defects and the surface texture in general to improve. Typical compression pressures for compression molding sen are about 34.6 to about 138.4 bar. In this example the parts are pressed at a pressure of about 68.9 bar. The pressure for the second closing of the Shape is in the range of about 20.7 to about 68.9 bar, but generally in the range of about 27.8 to about 41.4 bar. Since the optimal pressure for the second closing of the mold apparently with the physical Dimensions of the part, ribs, etc. these dimensions are always given. Aside from the ribs and humps, the soil possesses of the compact has a generally uniform thickness of about 2.54 mm and a surface area of about 897 cm ² . In each part of the example, the information “0” in the column with the heading “bar” relates only to the comparative test piece, ie the part to which none

bo coating has been applied. In the "Surface" column are the depth of the depression (negative sign) or the height of the raised point (no sign) after the pressing process is complete and the part has cooled down specified. In addition, the tabular measurement Overviews of values for each part, an estimated one Value given for the pressing pressure at which a surface measurement value of 0.0 mm (completely flat) would occur. The example is meant to be in context

be evaluated with Fig. 2, which shows a cross-section (either of a rib or a hump), which illustrates the dimensions referred to in the example. The thickness of the in the form The average coating produced is about 0.05 to about 0.13 mm.

Rib # 1

This rib has a depth of 2.54 cm, a width of 0.254 cm and a "width + curves" 2.79 cm.

Pressure, bar Surface, mm 0 0.0304 9.85 0.0203 24.82 0.0203 31.71 0 44.12 0.0167 58.81 0.0190 98.59 0.0279 173.47 0.0406 2353 0.0482

Pressure, bar Surface, mm 0 0.0279 9.85 0.0088 24.82 0.0096 36.54 0 44.12 0.0147 58.81 0.0246 98.59 0.0147 173.47 0.0177 235.24 0.0246

humpback

The hump has a width (or diameter) of 2.54 cm, a depth of 6.1 cm and a "Width + curves" of 3.18 cm.

Pressure, bar Surface, mm 0 0.0231 9.85 0.0093 24.82 0.0106 33.09 0 44.12 0.0121 58.81 0.0177 98.59 0.0198 173.47 0.0426 235.24 0.0396

ι υ

Rib # 2

This rib also has a depth of 2.54 cm and a width of 0.254 cm, but a "width + curves" of 1.52 cm.

Because of the difficulty of accurately measuring the depressions and raised areas, it should be noted that the The above figures are not to be understood as absolute values, but are merely intended to show a tendency to support the hypothesis that the depth of the trough is reduced by an increased pressing pressure in the production of the coating in the mold or the height of the raised point is increased. It should also be noted that large areas of the molded parts that are expected to be are flat, actually appear wavy in the micro range.

The in-mold coating application method of the present invention has been found to provide a strong reduction of the surface waviness with it, whereby the surface quality and the Surface gloss can be improved.

The coating agent

The coating agent is an isocyanate-based material, with the isocyanate component providing the necessary adhesion on the polyester substrate, the remaining part, among other things, the hardness, tensile strength and surface quality result.

Before the chemical composition of the coating agent is discussed, the physical properties that it must have should be described will. The coating agent must have certain characteristics which are common to all molding compounds. In addition includes that the coating agent must be flowable under pressure to completely with the part to be coated to cover a homogeneous skin. However, the viscosity must not be so low that the coating agent is pushed out of the mold when the press is closed. Furthermore, the coating agent at the pressing temperature (generally about 149 ° C) must be within a reach a sufficient hardening state within a reasonable period of time. On the other hand, the curing rate must not be so fast that it leads to a Burning of the coating agent or incomplete wetting or incomplete coverage of the Partly before the mold is fully closed comes the integrity and durability of the hardened The coating must be such that it is not susceptible to scratching or abrasion during normal handling is, especially at the elevated curing temperatures. Another required property of the coating agent, which conventional molding compounds do not have the ability to form a film that adheres evenly to the polyester substrate, without a pretreatment of the substrate surface taking place. This liability must be such that the least possible interfacial failure occurs even if the surface of the part is imperfect or damaged. In addition, the hardened coating must easily come off the chrome-plated surfaces of the Let the mold peel off.

One component of the coating agent is a substance with terminal isocyanate groups (hereinafter also referred to as "polyisocyanate"), which is used for the later reactions available excess NCO groups.

This substance can be a urethane prepolymer (prepolymer), as can be achieved by reacting a organic polyhydroxyl compound with a polyisocyanate in such proportions that the number of available NCO groups exceeds those of the reactive hydrogen atoms, can be prepared. That The prepolymers obtained are free of reactive hydrogen atoms, but have a significant number isocyanate groups available for later implementation. The substance containing isocyanate end groups can also be a “semi-prepolymer” or “quasi-prepolymer”, the production of which is known.

The term "isocyanate-terminated substance" includes any relatively low molecular weight (generally non-solid) substance terminated with isocyanate groups, regardless

of whether the NCO groups complete the Form main chain (longest chain) or a shorter side chain. Furthermore, from the substance with Isocyanate end groups required that it has excess, unreacted NCO groups, which are necessary for the later implementation (e.g. trimerization or urethane formation) are available.

A variety of polyisocyanate compounds can be used. Examples of suitable organic Polyisocyanates are the isomers and mixtures of isomers of

Toluene diisocyanate,

Diphenylmethane 'M' diisocyanate,

1,5-naphthalene diisocyanate,

Cumene-2,4-diisocyanate,

4-methoxy-13-phenylene diisocyanate,

4-chloro-13-phenylene diisocyanate,

Dicyclohexylmethane-4,4'-diisocyanate,

4-bromo-13-phenylene diisocyanate,

4-ethoxy-13-phenylene diisocyanate,

2,4'-diisocyanatodiphenyl ether,

5,6-dimethyl-1,3-phenylene diisocyanate,

2,4-dimethyl-13-phenylene diisocyanate,

4,4'-diisocyanatodiphenyl ether,

Benzidine diisocyanate,

4,6-dimethyl-13-phenylene diisocyanate,

1,1O-anthracene diisocyanate,

4,4'-diisocyanatodibenzyl,

simple or polymeric

Diphenylmethane diisocyanates, such as

33-dimethyl-4,4'-diisocyanatodiphenyl,

2,4-diisocyanates tubes,

33'-dimethyl-4,4'-diisocyanatodiphenyl,

1,4-anthracene diisocyanate,

2,5-fluoro diisocyanate,

1,8-naphthalene diisocyanate,

2,6-diisocyanatobenzofuran and

2,4,6-toluene triisocyanate.

It should be noted that mixtures of two or more of these polyisocyanates are used can. Aromatic isocyanates are preferred, especially MDI (diphenylmethane ^ '- diisocyanate) and hydrogenated MDI.

In order to produce the coating agent, the polyisocyanate can be converted by several methods bring. The first method is to add a suitable catalyst to the polyisocyanate incorporated, which causes the trimerization of the terminal isocyanate groups, in a known manner a trimer of the following general basic structure is formed

The second method relies on a conventional urethane reaction of the type in which, for example a polyhydroxyl compound by thermally and / or chemically catalyzed reaction with a polyisocyanate a urethane polymer according to the following reaction equation gives:

HO

149 ° C I Il

R-OH + R '-NCO R'-N-C-O-R

H) With regard to this reaction, the self at Room temperature gradually expires, the polyisocyanate or the polyhydroxyl compound must be up shortly before the time at which the coating agent is used must be kept separately. From the above Process types described, preference is given to the latter, since it allows the trimerization reaction to be controlled the first method has proven more difficult.

The coating agent preferably contains a polyester either in the polyisocyanate or in the Polyhydroxyl compound or both components can be included. The polyester can be in the form of a Solution of the unsaturated polyester in styrene, which after adding a suitable initiator, such as tert-butyl perbenzoate, in a conventional manner Crosslinking forms a high molecular weight polymer.

The other main constituent (apart from the substance that supplies isocyanate groups) is the hydrogen atoms delivering substance, which is generally a

jo polyhydroxyl compound (such as a polyol) or optionally a polyester (saturated or unsaturated) is. For the end reaction it is expedient that approximately molar Equivalence in terms of the total number of isocyanate groups and hydroxyl groups (or reactive Hydrogen atoms).

Examples of suitable polyols are diols, such as glycols, triols, such as glycerol, trimethylolpropane, Butanetriols or hexanetriols, tetrols such as erythritol and pentaerythritol, pentols, hexols such as sorbitol and mannitol, as well as other various higher functional alcohols. Other suitable polyhydroxy compounds are unsaturated compounds that have polymerizable carbon-carbon double bonds, z. B. unsaturated polyesters dissolved in styrene, as well as methacrylates, ζ. B. partially esterified trimethylolpropane trimethacrylate, which contains residual hydroxyl groups.

A third main component of the coating agent is the mold release agent, which does not necessarily consist of the substances normally used for molding compounds must be selected. Metallic soaps such as zinc stearate and some of the other most common metallic soaps, act as catalysts for isocyanate polymerization and can shorten the curing time of the coating agent to an intolerable extent and thereby possibly preventing adequate wetting of the surface of the polyester substrate. One to short curing times can also impair the correct adhesion of the coating agent to the substrate. Separating

Medium such as the natural product lecithin and an aliphatic phosphate have proven to be satisfactory. Various other UbIi-

b5 before incorporating additives, e.g. B. talc, diluent, Plasticizers and colloidal silica. It has been found that the inventive method at Adding a pigment to the coating agent is the filling

of hollows and other imperfections and the sealing of the pores enables as well as a glossy, pigmented surface in one _; n operation so that the part is ready for use after removal from the mold at the end of the second molding cycle without any further operations or manual touch-up, polishing, surface treatment or other such additional process steps as previously required

The example below is intended to make it easier for the person skilled in the art to carry out the method according to the invention. The recipes given therein are not intended to restrict the invention either individually or in combination.

Example 2

This example shows the selection of a suitable coating agent that can be used in the form, whereby for the parts by weight are given for each constituent.

10

15th

component Parts Solution of an unsaturated polyester in styrene 97.56 Zinc stearate 1.98 tert-butyl perbenzoate peroxidic initiator for the Polyester / styrene conversion 1.50 N, N-Tris- (dimethylaminopropyl) -hexa- hydrotriazine 1.50

It provides a urethane prepolymer prepared by mixing the following ingredients and heated for one hour at 105 ⁰ C: 23 part

Immediately before pressing, you mix there! Prepolymers with the aforementioned mixture. This leads to the fact that the crosslinked polyester and the styrofoam form a linear polymer with the prepolymer, the excess isocyanate groups causing additional urethane formation, while there; Triazine catalyzes the trimerization of the final product as in A.

A urethane prepolymer according to B is provided Replacement of tolylene diisocyanate with diphenylmethane-4,4'-diisocyanate from the following recipe:

Parts

component

Parts

Poly propylene ether glycol, mgw. 1025 45

Polypropylene ether glycol, mgw. 425 42
80:20 mixture of 2,4- / 2,6-toluene

diisocyanate 69

Talc 37.4

This urethane prepolymer is mixed with 2 parts of zinc stearate and 2.9 parts of N, N-tris (dimethylaminopropyl) hexahydrotriazine, which catalyzes the trimerization of the isocyanate end groups of the prepolymer, The mixture obtained is then used immediately after the prepolymer has been combined with the triazine as a coating agent that can be used in the form. When the mixture cures it forms the trimer described above.

A urethane prepolymer is prepared in the same manner as in A, except that the Use ingredients in the following quantities. The letter following a listed ingredient indicates the sample or the test in which the component concerned appears first and through a footnote is explained.

Polypropylene ether glycol, mgw. 1025 18.1

Polypropylene ether glycol, mgw. 425 16.9

Diphenylmethane-4-4'-diisocyanate 45.0

Talk 20.1

You also create a mixture of the following ingredients:

33 component

component

Parts

Polypropylene ether glycol, mgw. 1025 23

Polypropylene ether glycol, mgw. 425 21.5
80:20 mixture of 2,4- / 2,6-toluene

diisocyanate 35.3

Talk 19.1

b5

A mixture is also made from the following ingredients:

Parts

Solution of an unsaturated polyester

in styrene 89.7

Zinc stearate 8.1

tert-butyl perbenzoate 2.2

N, N-Tris- (dimethylaminopropyl) -hexa-

hydro triazine 1.0

The rest of the process and the implementation are the same as in B, except that nunmehi Diphenylmethane-4,4'-diisocyanate with the following formula is used:

50

55 OCN

NCO

A urethane prepolymer is made by mixing the following ingredients and adding the Batch heated to 100 ° C for 1 hour:

Component parts

bO A polycaprolactone, ie a saturated polyester 24.7 having terminal hydroxyl groups

One essentially out
Diphenylmethane-4,4'-diisocyanate consisting liquid 41.1

Talk 15.1

Lecithin (release agent) 1.0

Immediately before pressing, the prepolymer is mixed with 18.1 parts of a propylene oxide adduct of pentaerythritol, which is in the form with both the prepolymer and the excess diphenylmethane-4,4'-diisocyanate in a normal Urethane reaction converts to a highly crosslinked urethane coating agent.

K)

A urethane prepolymer is prepared with a large molar excess of diphenylmethane-4,4'-diisocyanate analogous to D from the following components:

component

Parts

15th

20th

One essentially out

Diphenylmethane-4,4'-diisocyanate

existing liquid - 18.01

Polyethylene butylene adipate (plasticizer)

(Mgw. About 2500) 10.81

A mixture of the following ingredients is also prepared, which is separated from the prepolymer kept:

component

Parts

Trial polyester in styrene

(unsaturated, terminal

Containing hydroxyl groups

Polypropylene fumarate) (2500 mgw) 37.27

A propylene oxide adduct of

Pentaerythritol 10.56

Talk 20.75

tert-butyl perbenzoate 0.56

Release agent 0.06

Thixotropic agent 1.96

30th

J5

40

During the pressing process, the test polyester and the styrene crosslink as in B, and the prepolymer and the excess diphenylmethane ^^ '- diisocyanate settle with the polyester and the terminal Hydroxyl groups of the propylene oxide adduct after normal urethane reactions to form a crosslinked coating agent around.

It provides a urethane prepolymer prepared by mixing the following ingredients and the mixture heated for 1 hour at 100 ⁰ C:

component

Parts

One essentially out
Diphenylmethane-4,4'-diisocyanate

existing liquid
Ethylene butylene adipate (Mgw. 2500) thixotropic agent

60

7.25 435 1.2

b5

In addition, you make a mixture of the following ingredients:

component

Parts

Trimethylolpropane trimethacrylate
(TMPTMA) with residual hydroxyl groups and a hydroxyl number of 40 15

Propylene oxide adduct of pentaerythritol 8.35

Release agent 0.025

tert-butyl perbenzoate 0.075

10% isocyanate catalyst
(Dibutyltin dilaurate) in styrene 0.075

During the pressing process, the TMPTMA polymerizes in its carbon-carbon double bonds with itself, while the prepolymer and the excess diphenylmethane-4,4'-diisocyanate react with the terminal hydroxyl groups of both the propylene oxide adduct and the TMPTMA to form a crosslinked urethane coating agent. A modification of the experiment involves increasing the amount of adipate and decreasing the amount of TMPTMA; this gives a more flexible coating.

It can be seen that the formulation of F is very similar to that of E; the main difference is that in the case of F, instead of the polypropylene fumarate (test product), a commercial monomer mixture is used (TMPTMA) begins.

Analogously to Example F, a urethane prepolymer is produced from the following components:

component

Parts

Hydrogenated diphenylmethane-4,4'-diiso-

cyanate with the following formula 4.85

Ethylene butylene adipate (Mgw. 2500) 2.90

Thixotropic agent 1.20

A second mix is made from the following ingredients:

component

Parts

Trimethylolpropane trimethacrylate

(TMPTMA) 10.0

Talc 5.5

Propylene oxide adduct of pentaerythritol 2.9

Release agent 0.025

tert-butyl perbenzoate 0.15

2% benzoquinone in styrene (inhibitor for over free radicals
ongoing TMPTMA reaction) 0.1

10% isocyanate catalyst (dibutyltin dilaurate) in styrene 0.05

All reactions are the same as in F except that through the use of the hydrogenated diphenylmethane-4,4'-diisocyanate (MDI) those related to the UV resistance of the MDI-urethane bond Problems to be overcome.

H ₂

OCN

NCO

H H

H ₂ H

If the gel time (or hardening time) of the Coating agent is too short, the adhesion between the coating and the substrate, as mentioned, Therefore, most commercially available unsaturated polyesters are suitable for the present No purpose as they contain a condensation catalyst that also acts on the urethane reaction Certain polyesters have a catalytic effect, for example a solution of an unsaturated polyester in styrene, have a certain suitability at press temperatures of about 149 ° C, while this is the case with most

K)

is not the case with other commercially available polyesters

An unsaturated polyester similar to commercially available polyesters is produced by thermal condensation of maleic anhydride and 1,2-propanediol in the absence of a catalyst produced A polypropylene fumarate with a molecular weight of about 1500 and a carboxyl number of 13, which in Styrene (65% fumarate 35% styrene) is dissolved. A coating agent that can be used in the mold is then prepared by mixing the following approaches:

component Parts A. Polypropylene fumarate in styrene 15.00 A. Propylene oxide adduct of Pentaerythritol 4.25 Talk 8.35 tert-butyl perbenzoate 0.225 Release agent 0.025 An essentially composed of diphenyl B. methane 4,4'-diisocyanate existing liquid 7.2 Ethylene butylene adipate (Mgw. 2500) M.

When applied according to the invention, this coating agent exhibits excellent adhesion to Polyester substrate. J5

Although the term "isocyanate-based coating" as used in the description and claims is used, the trimer of experiments A, B and C as well as the real urethane of experiments D, E, F and G should include, the latter type of substance is preferred. In terms of the importance of physical Properties of the coating are shown in Table I below for selected properties Compositions, whereby the letters under the keyword "sample" represent the respective composition given according to Example 2. Regarding the hardness values, it should be noted that the hardness value for the above for the substrate has the specific polyester formulation indicated 116o.

Table I. sample
D. E. F. characteristic 480.9
3
53
19 330 408.8
3
102
22 850 426.4
4.5
20 040 Tensile strength, kp / cm ²
Elongation at break,%
Hardness (Rockwell "R")
Young modulus kp / cm ²

In addition to covering surface defects, the coating agents described here and coating methods that improve the surface properties of the polyester substrate and / or this is given special properties by using certain additives. One of The most useful additives are carbon black, which not only serves as a black pigment, but also an electrical one Can provide conductive coating if you have one of the cohesive network structure, conductive Types of soot used. Such a coating W) enables the polyester part to be electroplated or electrostatically painted (liquid or powder coated) or as electromagnetic shield or reflector can serve.

b ^r i This example explains the use of a conductive additive. A coating composition which can be used in the form is prepared from the following ingredients.

component

Parts

Test polyester in styrene (like E) 15.0

Propylene oxide adduct of pentaexythritol 4.25

Conductive carbon black ¹ ) 4.0

tert-butyl perbenzoate 0.225

Release agent 0.025
Diphenylmethane-4,4'-diiso-

cyanate / adipate ² ) 1 'J, 6

¹ J With a coherent network structure and a coherent surface area of 190 m ² / g.

² ) 10: 6 mixture of essentially liquid diphenylmethane-4,4'-diisocyanate and polyethylene butylene adipate

After this coating has been pressed onto the polyester substrate, the electrical resistance is measured between two spots 10 inches apart. The resistance is about 1000 ohms Compared to a resistance of more than 50 megohms over an analog range of a device according to the invention, but without using carbon black with an overcoated part.

In addition to the pigments or instead of them, other additives can be used for decorative purposes.

In particular, additives are suitable for automobile parts Metal flakes or other similar "incompatible" components, i.e. those in the hardened Coating agents remain as a separate phase.

j The physical properties (e.g. tensile strength, notched impact strength and modulus) can be improved by adding reinforcing fibers, preferably glass fibers.
Since the coating is thin, the fibers should be very short

ι «(generally 635 mm long or shorter) and not more than about 20% by weight of the coating agent turn off. As for the rest of the physical properties that result from the incorporation of additives into the Coating agents can be modified, count

ι -3 the coefficient of friction, the scratch resistance, the weather resistance, the resistance to certain types of radiation damage, such as UV rays, chemical and corrosion resistance as well as impact resistance

The above detailed description of the invention enables those skilled in the art to apply the invention. Of course, modifications and changes to the preferred ones can be derived from the description Derive embodiments that as in the invention

2 ^r ) are to be viewed falling in accordance with the scope.

In addition 5 sheets of drawings

Claims (13)

Patent claims: 1. A method for applying a coating to a glass fiber reinforced polyester substrate, wherein on the substrate is a coating agent composed of an isocyanate-terminated substance a content of unreacted isocyanate groups and a substance with reactive hydrogen atoms consists, is applied and cured, characterized in that for elimination of surface imperfections on the already compression molded or injection molded, completely thermoset polyester substrate in a form and especially that in which the pressing or Injection molding of the polyester substrate was carried out, the coating agent in such an amount on the polyester substrate is abandoned that on the substrate a coating with a thickness of less than 0.5 mm can be obtained, the mold is closed and sufficient pressure is exerted on the product, so that the coating agent essentially covers the surface of the substrate, and the coating agent is cured in the mold under pressure. 2. The method according to claim 1, characterized in that the pressure in the range from 21 to about 70 bar 3. The method according to claim 1, characterized in that one having isocyanate end groups Substance containing tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate or dicyclohexylmethane-4,4'-diisocyanate is used. 4. The method according to claim 1, characterized in that the coating agent in such Amount is applied to the substrate to a coating with a thickness of 0.013 to 0.127 mm form. 5. The method according to claim 1, characterized in that have as isocyanate end groups Γ) de substance is an isocyanate-terminated polyurethane prepolymer with a content of excess diisocyanate is used. 6. The method according to claim 1, characterized in that containing as reactive hydrogen atoms Substance a polyester with terminal hydroxyl groups is used. 7. The method according to claim 6, characterized in that having reactive hydrogen atoms Substance uses a compound with polymerizable carbon-carbon double bonds will. 8. The method according to claim 1, characterized in that a polyester substrate, which is additionally is crosslinked with styrene is used. 9. The method according to claim 1, characterized in that an electrically conductive material containing coating agent is used to carry out a coating in an additional stage Allow electroplating or electrostatic spraying. 10. The method according to claim 1, characterized in that a less than 20 wt .-% of one inorganic filler-containing coating agent is used. 11. The method according to claim 1, characterized in that that a sufficient amount of a pigment to achieve a smooth, pigmented one Surface-containing coating agent is used. 12. The method according to claim 7, characterized in that that a substance containing reactive hydrogen atoms which additionally contains styrene, is used. 13. The method according to claim 1, characterized in that that a coating agent is used which additionally contains a mold release agent