DE2442227C3 - 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 a coating agent, the consists of a substance having isocyanate end groups and a content of unreacted isocyanate groups and a substance with reactive hydrogen atoms, 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 containing coating composition to cure 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 coatings serve as protective coatings, for example for waterproof textile fabrics, and as adhesives for connecting metal with Metal. Wood with wood or metal with wood. Further the known coating compounds were used as binders suggested for various fillers, for example for vulcanized rubber to make railway coverings, for example for sprint places.

-, ο The invention is based on the object a To provide a method of applying a coating to a glass fiber reinforced polyester substrate to to obtain a surface quality in the case of a molded or injection-molded part made of polyester, as previously without

-, -> complex post-processing operations could not be achieved.

This object is achieved in that to eliminate surface defects on the already compression-molded or injection-molded, fully

M) dig thermoset polyester substrate in a mold and especially those in which the compression 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

h-, thickness of less than 0.5mm can be obtained that The mold is closed and enough pressure is exerted on the product so that the coating agent hits the surface of the substrate essentially covered and that

Coating agent cured in the mold under pressure will.

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 the need for manual editing operations, in accordance with 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 For a given resin composition, thicker areas 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, through the method according to the invention eliminates a third type of defect which does not necessarily consist of a surface defect, namely Microcracks, which generally occur in areas with low glass content or high filler content appear. These lead to local failure, the final cause of which is thermal or chemical shrinkage These cracks, which are open to the surface of the part, can cause painting problems similar to the Raise 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 covering 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 up and roll out where,; I let the composite and gel-like coating harden This process is based on the common cross-linking of the gel mass and the polyester resin at room temperature and is obviously not suitable for making one large number of compacts for the production of precision compacts. Among the commonly used Gel coating materials include thermosetting resins such as certain polyesters and amine / formaldehyde resins.

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

ι ο

It is also known in the pressing of thermoplastics, the compacts with a second thermoplastic Ma erial ^f to coat merely by heating and melting the materials. However, this method is not suitable for coating heat-cured objects, in particular high-strength materials such as fiber-reinforced plastics.

Further advantageous refinements of the method according to the invention are the subject of the subclaims.

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

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 of a cross section through a with a coating provided polyester substrate which has a rib

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

The preferred embodiment will now be explained

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, a conventional one 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 an article according to the invention is shown in FIG 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 Invention in the same way on other molding processes, e.g. B. the injection molding process apply.

As mentioned, the preferred molding method for practicing the invention is compression molding; The invention is in regard to this method explained In the production of a pressed composite part of a pressed heat-cured substrate and a coating based on isocyanate, the first working stage di.au that the part by conventional Formpreßmethoden are pressed Although the substrate of any by molding from If one can produce a large number of thermosetting resins, the polyester resins, especially the glass fiber reinforced types, have the greatest "" economic importance. Polyester resins generally represent mixtures of unsaturated polyester resins and crosslinkable monomers. Polyesters are produced by esterification (condensation) of polycarboxylic acids or their anhydrides with glycols, using known methods as well as acids and glycols. A recipe for the special substrate mostly used in the context of the invention is given below; The components and the respective parts by weight are listed:

component Parts 65% polypropylene fumarate solution in styrene 4000 35% polymethyl methacrylate solution with some carboxyl groups (Additive for low shrinkage) in styrene 2 240 J5% polymethyl methacrylate solution, no carboxyl groups (Additive for low shrinkage) in styrene 772 Calcium carbonate (filler) 10 520 tert-butyl perbenzoate; more peroxidic Initiator for the polyester-styrene- reaction 70 Zinc stearate 350 Mg (OH) ₂ 316 Fiberglass 7 830 26 098

The process step described below can optionally be carried out first. This stage consists in mixing the excess food, which because of the reactivity of the two components in the generally not more than a few minutes - or not more than half an hour before the application of the Coating agent should take place. To produce the coating agent, an isocyanate end group is mixed containing substance (optionally a prepolymer). which excess reactive isocyanate groups with a material which either has reactive hydrogen atoms (e.g. a polyhydroxyl compound) or one for trimerization represents the catalyst capable of terminal NCO groups. "Excess" here means that more cocyanate groups than reactive hydrogen atoms available. The isocyanate reacts with the under the action of heat and pressure Polyhydroxy compound or the catalyst, whereby an isocyanate-based coating is formed which, when applied according to the invention, closely adheres to the pressed part this is liable.

As mentioned, the porosity can be a result of air inclusions and / or poor distribution of the components of the molding compound. Since the in the form produced coating should generally have an improved surface quality, the Components of the coating agent can be distributed or dispersed more thoroughly by additional stirring. In addition, the coating agent is preferably degassed to remove trapped air. It should also Contain less filler than the molding compound used for the substrate, so that the coating is as homogeneous as possible. The recipe for the substrate comprises, for example, a total of 26,098 parts, of which 18,350 Parts (about 70%) represent filler and fibers, while typical coating agents which can be used in the form contain at most about 20 wt .-% (inorganic) 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 Applying the invention to compression molding, the mold must be opened sufficiently wide that the Filling of the coating agent in it on the surface

■ abandoned the thermoset 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

ι the coating 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 mold (either compression or 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.

.1 lUnn tirtA rln ^ t A \ n K i * tV * r · ' ri I 'il *. -., " Ti 1

carry out. In order to have as few operations as possible on the pressed substrate, it is generally advisable to carry out both pressing operations in the same compression molding press. 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 Toimulierungen "refer open the Fo ^r m" and "Ei '-2 ... ^e ben a filling in the form of" on both the form in which the substrate has been generated as used on a purely for pressing the coating special second progress. In each case, a filling of the coating agent is introduced into the mold, either on the surface of the FRP part to be coated or on the mold surface adjacent to this surface.

In the practical implementation of the erfindungsge MAESSEN method it was found that it nichi it is necessary to thoroughly clean the polyester substrate (for example, the surface with the help of a; Solvent from the mold release agent, oils, etc. zi) before you can use the coating agent in the Forrr brings up. Rather, all that is required is to remove any loose press burr that has remained on the part. Except it is no longer necessary to provide the polyester substrate with a primer before it is 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 is not made of polyester sub Strat expires, but when the i vesse is closed, it covers essentially the entire material to be coated Surface area in a generally uniform layer with a thickness of less than 0.5 mm preferably from 0.01 to 0.1 mm.

After the filling of the coating agent on there; Polyester substrate has been abandoned, can with derr second pressing cycle can be started by closing the mold. However, as mentioned, it is often | required to adjust the pressure again before the second Preßvor gear. When compression molding is dei The expression "closing the mold" is to be taken literally, while in the injection molding process the mold goes through; Injecting the mass filling the space between the mold and the pressed substrate Is "closed".

The pressure suitable for the second press cycle should be empirical for each shape of the part be determined that the surface of the font

produced coating where it has covered a surface defect, coherently and substantially is smooth; d. that is, the coating should essentially be the Shape correspond to the form generating the coating. This phenomenon is best illustrated in Fig.4 Fig. 4 illustrates in which the polyester substrate is not compressed by pressing a non-shrinkage reducing agent Additive-containing polyester resin was made to highlight the hollows. That The 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. ! i g. Fig. 3 shows the same type of sealing, but for the case of porosity, which, how mentioned, made the application of paints on plastic molded parts extremely problematic Has. It can be seen that the pores on the non-coating surface are generally in the range from about 1 to about 3 μm, while the surface having a coating itself in the 4000x magnification shows no visible pores or other defects. The one with a cover The visible lines on the surface are raised areas that indicate microscratches on the surface are due to the shape; given their width and height make up only a fraction of a micron, they affect the surface quality or the shine is not noticeable. Because of its porosity, the coating-free surface is too rough for such lines to appear train evenly.

The pressing of the coating applied in the mold apparently follows the same principle as on the the original problem of pits, d. H. the shrinkage of the resin composition on cooling after Hardening process, berul. "~ i a close investigation of the parts provided with a coating were raised areas of the coating agent above the Depressions were found immediately after the part was removed from the mold after the second pressing operation became. 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 Applying the correct pressing pressure (pressing the coating). If the pressure is too low, after the 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 unapproved state. Through this there is a raised point in that area where there would otherwise be a depression. While During cooling, the greater thickness of the mass over the troughs achieves the greater absolute degree of shrinkage of the base part and the mass in these areas compared to the rest of the surface. This ultimately results in an essentially smooth surface (i.e. corresponding to the shape of the die), 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 is limited to any particular working technique. In summary, it is about 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, is the compressibility of the polyester substrate not only on the respective polyester material, but also on the geometric dimensions depending on the part.

example 1

This example is intended to illustrate the interrelationship between the pressure for the second mold closing and the shape of the cavity after the in-mold coating is applied. A box-shaped, glass-reinforced polyester resin article having a plurality of internal reinforcing ribs and a cylindrical boss is used. The article was pressed like that in FIG. Figure 5 shows the cross section shown; the creation of a pressed part 10 between the punch 22 and the die 20 is illustrated. The pressing part 10 has a rib 12 and a surface 14 opposite the rib, au! which coating 16 (exaggerated) is to be applied to fill in any surface imperfections and generally improve the surface finish. Typical compression pressures for compression molding 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 mold is in the range from about 20.7 to about 68.9 bar, but generally in the range from about 27.8 to about 41.4 bar. Since the optimal pressure for the second closing of the mold appears to be related to the physical dimensions of the part, the ribs, etc., these dimensions are always given. Aside from the ridges and bumps, the bottom of the press part 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. that is, the part to which no coating has been applied. The "Surface" column shows the depth of the depression (negative sign) or the height of the raised area (no sign) after the pressing process has been completed and the part has cooled down. In addition, an estimated value for the pressure at which a surface measurement value of 0.0 mm (completely flat) would occur is given in the tabular measurement value overviews for each point. The example is meant to be in context

ίο

with F i g. 2, which shows a cross-section (either 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 235.24 0.0482

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.

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 ^ 9 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 2353 0.0396

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 merely as a supportive tendency the hypothesis should make it clear that by an increased pressure in the manufacture of the Cover in the form of the depth of the depression is reduced or the height of the raised point is increased. It also note that large areas of the molded parts 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 going into the chemical composition of the coating agent, the physical Properties that it must have are described. The coating agent must have certain characteristics possess which are common to all mullets. Uazu 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 drag agent is pushed out of the mold when the press is closed. Furthermore, the coating agent must be at the pressing temperature (generally about 149 ° C) a sufficient hardening state within an acceptable period of time reach. 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 Sometimes comes before the mold is completely closed. 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, is the ability to form a Film that adheres evenly to the polyester substrate without any pretreatment of the substrate surface takes place This adhesion must be such that the lowest possible interfacial failure occurs, Even if the surface of the part has defects or is damaged, the hardened part must also be Allow the coating to peel off easily from the chrome-plated surfaces of the mold.

One component of the coating agent is an isocyanate-terminated substance (hereinafter also referred to as "polyisocyanate"), which is available for the subsequent reactions has 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 having isocyanate end groups can also be a »semi-prepolymer« or a »quasi-prepolymer« whose manufacture is known

The term "isocyanate-terminated substance" includes any relatively low molecular weight containing (generally not solid) substances with terminal 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 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-4,4'-diisocyanate,

I, 5-naphthiline diisocyanate,

Cumo! -2,4-diisocyanate,

4-methoxy-1,3-phenylene diisocyanate,

4-chloro-1,3-phenylene diisocyanate,

Dicyclohexylmethane ^ / t'-diisocyanate,

4-bromo-1 3-phenylene diisocyanate,

4-ethox "-l, 3-phenylene diisocyanate,

2,4'-diisocyanatodiphenyl ether,

5,6-dimethyl-13-phenylene diisocyanate,

2,4-dimethyl-1,3-phenylene diisocyanate,

4,4'-diisocyanatodiphenyl ether,

Benzidine diisocyanate,

4,6-dimethyl-1,3-phenylene diisocyanate,

1,10-anthracene diisocyanate,

4,4'-diisocyanatodibenzyl,

simple or polymeric

Diphenylmethane diisocyanates, such as

3,3-dimethyl-4,4'-diisocyanatodiphenyl,

2,4-diisocyanatostilbene,

S.S'-DimethyM ^ '- diisocyanatodiphenyl,

1,4-anthracene diisocyanate,

2,5-fluoro diisocyanate,

1,8-naphthalene diisocyanate,

2,6-diisocyanatobenzofuran and

2,4,6-toluene triocyanate.

It should be noted that mixtures of two or more of these polyisocyanates are used can. Aromatic isocyanates are preferred, especially MDI (diphenylmethane-4,4'-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 into the trimerization of the terminal Caused isocyanate groups, in a known manner a trimer of the following general basic structure arises

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 | t

R OH + R ¹ NCO R -NC- C) -R

In view of this reaction, which takes place gradually even at room temperature, the polyisocyanate must or the polyhydroxyl compound until shortly before the point in time at which the coating agent is used will be kept separately. Of the types of processes described above, preference is given to the the latter, as the control of the trimerization reaction of the first method has proven more difficult.

The coating agent preferably contains a polyester which can be contained either in the polyisocyanate or in the polyhydroxyl compound or in both components. The polyester can be in the form of a solution of the unsaturated polyester in styrene which, after the addition of a suitable initiator, such as ¹ tert-butyl perbenzoate, forms a polymer with high molecular weight in a conventional manner by crosslinking.

The other main constituent (apart from the substance that supplies isocyanate groups) is the hydrogen atoms delivering substance, which is generally a polyhydroxyl compound (such as a polyol) or optionally is a polyester (saturated or unsaturated). 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 polyester 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 ι 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. Release agent like the natural product lecithin as well as an aliphatic phosphate have proven to be satisfactory proven. The polyisocyanate or the polyhydroxyl compound are generally in accordance with conventional pressing technology incorporates various other common 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 as well as a shiny, pigmented surface in one operation, so that the part after removal from the mold on End of the second pressing cycle without any further operations or manual repairs, Polishing, surface treatment or other such additional process steps, as previously required, is ready for use

The following example 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 intended to Do not limit 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, the relevant parts by weight being given for each constituent. 2 «

It provides a Ürethan-Vorpoiymeres prepared by mixing the following ingredients and heated for one hour at 105 ⁰ C:

component

Parts

Polypropylene 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 made with 2 parts of zinc tea rat and 2.9 parts of N, N-tris- (dimethylaminopropyl) -hexahydrotriazine, which trinierizes the isocyanate end groups of the prepolymer are added catalyzed. The mixture obtained is then used immediately after the prepolymer has combined with the triazine as usable in the form Coating agents. When the mixture cures, the trimer described above is formed.

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.

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

A mixture is also made from the following ingredients:

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 NJ4-Tris- {dimethylaminopropyl) -hexa- hydro triazine 1.50

Immediately before pressing, you mix there; Prepolymers with the aforementioned mixture. The! causes the crosslinked polyester and the styrofoam to form a linear polymer with the prepolymer whereby the excess isocyanate groups cause additional urethane formation, while there: Triazine trimerization of the end product as with / catalyzed

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

component

Parts

Polypropylene ether glycol, mgw. 1025 18.1 Polypropylene ether glycol, mgw. 425 163 Diphenylmethane-4-4'-diisocyanate 45.0

Talk 20.1

You also create a mixture of the following ingredients:

35 component Parts

Solution of an unsaturated polyester

in styrene 89.7

Zinc stearate 8.1

tert-butyl perbenzoate 2.2

N, N-Tris- {dimethylaminopropyl) -hexa-

hydrotriazine 1.0

The rest of the process and the implementation i are the same as in B, except that now diphenylmethane-4,4'-diisocyanate are followed by the formula is used:

OCN

// V

/ V

NCO

A urethane prepolymer is made by mat the following ingredients are mixed and the batch is heated to 100 ° C for 1 hour:

component

Parts

A polycaprolactone; H. one terminated by hydroxyl groups saturated polyester 24.7

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 as well as the excess diphenylmethane-4,4'-diisocyanate in a normal Urethane reaction converts to a highly crosslinked urethane coating agent

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

IO

component

Dear

One essentially out Diphenylmethane 4,4'-diisocyanate

existing liquid 18.01

Polyethylene butylene adipate (plasticizer)

(Mgw. About 2500) 10.81

Furthermore, one sets. a mixture of the following Components that are stored separately from the prepolymer:

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

35

40

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

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 Ethylenebutylenadtpat (Mgw. 2500) thixotropic agent

7.25 4.35 1.2

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 also polymerizes on its carbon-carbon double bonds itself while the prepolymer and the excess diphenylmethane-4,4'-diisocyanate with the terminal hydroxyl groups of both the propylene oxide adduct and the TMPTMA to form one cross-linked urethane coating agent react. If the experiment is modified, the proportion is increased of adipate and decreases 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 23 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 associated with the UV resistance of the MDI-urethane bond Problems to be overcome.

H,

OCN

Il H

NCO

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, impaired. Therefore, most commercially available unsaturated polyesters are suitable for this 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

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 produced in the absence of a catalyst Polypropylene fumarate having a molecular weight of about 1500 and a carboxyl number of 13, which is 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 835 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) 4.4

If it is applied according to the invention, it shows this coating agent has a permanent adhesion on the Polyester substrate

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 specific polyester formulation specified for the substrate is 116

Table I.

characteristic

Sample D

Tensile strength, kp / cm ² 480.9 408.8 426.4 Elongation at break,% 3 3 4.5 Hardness (Rockwell "R") 53 102 - Young modulus kp / cm ² 19 330 22 850 20 04

In addition to covering surface defects, the coating agents and coating methods described here can be used to improve and / or improve the surface properties of the polyester substrate this is given special properties by using certain additives One of the The most useful additive is carbon black, which not only serves as a black pigment, but also an electrical one can provide a conductive coating if one of the cohesive, networked conductive carbon blacks is used. Such a coating allows the polyester part to be electroplated or electrostatically coated with a paint provided (liquid or powder coated) or serve as an electromagnetic screen or reflector can.

The purpose of this example is to explain the use of a conductive additive. One hires in the form applicable coating agent from the following ingredients.

component

Parts

Test polyester in styrene (like E) 15.0
Propylene oxide adduct of pentaexythritol 4.25

Conductive carbon black ') 4.0

tert -butyl perbenzoate 0.225

Release agent 0.025

Diphenylmethane-4,4'-diiso-

cyanate / adipate ² ) 11.6

') With a coherent network structure and a coherent surface of 190 mVg.

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

After this covering 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.

Additives that are particularly suitable for automobile parts are metal flakes or other similar "incompatible" components, ie those that remain as a separate phase in the hardened coating agents.

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

in (generally 6.35 mm long or shorter) and make up no more than about 20% by weight of the coating composition. To the other physical properties, which can be modified by incorporating additives into the coating agent count

π the coefficient of friction, scratch resistance, 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 the person skilled in the art to apply the invention. From the description -. * Can of course be derived Derive modifications and changes of the preferred embodiments, which as in the invention

2 "> are to be viewed falling in accordance with the scope.

In addition 5 sheets of drawings

Claims (13)

Patent claims: U Method for applying a coating to a glass fiber reinforced polyester substrate, where ~. the substrate is a coating agent which consists of a substance containing isocyanate end groups with a content of unreacted isocyanate groups and a substance with reactive hydrogen atoms, is applied and cured, ι ο characterized in that to eliminate surface defects on the already compression molded or injection molded, completely heat-cured polyester substrate in a form and in particular that in which the compression or injection molding of the polyester substrate took place, the coating agent is applied to the polyester substrate in such an amount that a coating with a thickness of less than 0.5 mm can be obtained on the substrate, the mold is closed and sufficient pressure is exerted on the filling material so that the coating agent essentially covers the surface of the substrate and the coating agent is cured in the mold under pressure. 2) 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 has isocyanate end groups- i < > the substance with a content of tbluylene diisocyanate, diphenylmethane-4,4'-diisocyanate or dicyclohexyimethane-4,4'-diisocyanate is used. 4. The method according spoke 1. characterized in that the coating mitK. in such a r> 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 having isocyanate end groups w 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 the reactive hydrogen atom-containing substance is a polyester with terminal ends Hydroxyl groups is used. 7. The method according to claim 6, characterized in that a compound having polymerizable carbon-carbon double bonds is used as the reactive hydrogen atom-containing substance. 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 Enable electroplating or electrostatic spraying. 10. The method according to claim I _1, characterized in that a coating agent containing less than 20 wt .-% of an inorganic feed is used. 11. The method according to claim 1, characterized in that a sufficient amount of one Pigments used to achieve a smooth, pigmented surface containing coating agent will. 12. The method according to claim 7, characterized in that one reactive hydrogen atoms containing substance that also contains styrene, is used. 13. The method according to claim 1, characterized in that a coating center! is used, which also contains a mold release agent