GB2049542A

GB2049542A - Polyurethane mouldings

Info

Publication number: GB2049542A
Application number: GB8015206A
Authority: GB
Original assignee: Deutsche ITT Industries GmbH; ITT Industries Inc
Current assignee: TDK Micronas GmbH; ITT Inc
Priority date: 1979-05-14
Filing date: 1980-05-08
Publication date: 1980-12-31
Also published as: AR220050A1; IT1195027B; GB2049542B; AU538659B2; SE8003459L; FR2456601B1; ES491419A0; FR2456601A1; NL8002637A; DK188780A; DE3017981A1; ES8102904A1; KR830000947B1; CA1148710A; AU5820080A; IT8022025A0

Abstract

In a reaction injection moulding process for producing a coated polyurethane part, the surface of the mould is coated, prior to moulding, with a coating composition containing from 0.05 to 10% by weight of a polyurethane catalyst. The catalyst acts to bond the coating composition to the moulded part so that the shaped part upon removal from the mould contains a firmly adherent coating of the coating composition. The part may be rigid or flexible, porous or non-porous.

Description

SPECIFICATION Process for preparing polyurethane moulded part This invention relates to a process for producing a moulded polyurethane product having a firmly adherent coating and to the coated product so produced.

The reaction injection moulding process for producing elastomeric polyurethane parts is well known. In such a process, two separate liquid components are fed, under precise control, into a high pressure impingement mixer. One component is a polyol and may include a chain extender, catalyst and small amount of blowing agent; the other component is an isocyanate. After intimately mixing the components, they are injected into a metal mould at a pressure of from 1500 to 2500 psig. The heat of reaction volatilises the blowing agent, yielding a foam which exerts sufficient pressure to fill out the mould. The result is an integral skin microcellular elastomeric shaped part. The process is very economical and produces shaped parts of high quality for use, for example, as bumpers and frontfascias for automobiles.

Normally, after a part is prepared by the foregoing reaction injection moulding process and is removed from the mould, it is trimmed and post-cured at 250 F for about one half hour to complete the reaction. If the part is to be painted, as it normally is for automotive uses, the part must be intensively precleaned with a solvent and hot water detergent to remove the mould release, then coated with a primer composition, baked at 2500F for about one quarter hour, top coated and then baked again at 250"F for about one half hour to cure the paint composition. The process of cleaning, priming and painting the part requires considerable expenditure of energy and time and it would accordingly be desirable to simplify and thus reduce the cost of the post-moulding treatment of the polyurethane part.

According to the present invention there is provided a reaction injection moulding process for producing a coated polyurethane part, including coating the mould surfaces prior to moulding with a coating composition containing a polyurethane catalyst.

According to the invention there is further provided a process for producing a moulded polyurethane product by reaction injection moulding in which a polyol is mixed with an isocyanate to form a liquid mixture, including feeding the mixture to a closed mould where the mixture is reacted and moulded at elevated temperatures, and removing the moulded product from said mould, wherein the surface of said mould, prior to feeding the mixture into the mould, is coated with a paint primer containing from 1 to 10% by weight of the paint primer of a polyurethane catalyst, said catalyst acting to bond said paint composition to said moulded part so that the shaped product removed from said mould contains a firmly adherent coating of said paint primer.

The surface of the mould, prior to moulding the part, is coated with a coating composition containing from 0.05 to 10% by weight, advantageously 1 to 10% by weight, of the coating composition of a polyurethane catalyst. The catalyst has been found to provide active sites in the coating which act to bond the coating composition to the moulded part. The process may be used with a variety of protective or decorative coating compositions. In the case of a paint,coating, the primer may, for example, by applied in the mould while the top coat is applied externally ofthe mould. Such a process eliminates the intensive cleaning operation previously necessary before the paint composition is applied because no release agent is necessary in the mould.Furthermore, the amount of curing time and energy necessary for the paint is reduced because the paint is partially cured in the mould. Moreover, the quality of the paint or other coating is enhanced - it is more firmly adhered and more uniform than coatings placed on the part subsequent to moulding. An additional advantage is that the coating transfers completely with each moulding operation. Because no release agent is necessary, there is no build-up of wax or other release agent in the mould from successive moulding operations which periodically requires cleaning of the mould.

The coating process is substantially insensitive to film thickness, a sensitivity usually characteristic of this kind of process. Film thicknesses may range from 0.1 mil or even less to above 2.5 mil. The process is useful with a wide variety of metal mould surfaces, as for example, nickel plated steel, electroform nickel and kirkside (a zinc alloy). The process involves a very short flash off time - less than 15 seconds -.and hence is adaptable to production operations. The coatings are consistently uniform and thus coatings of controlled thicknesses can be obtained under production conditions.

Transfer coatings - that is, coatings applied to a mould and transferred to a shaped product during moulding - are known. However, such coatings have only been used with rubber moulds because there is no adhesion between such moulds and the coating. Rubber moulds are used for low pressure moulding and hence cannot be used for reaction injection moulding, which is a high pressure process. In the absence of an activator, the transfer coatings of the present invention will stick to the mould and will not adhere to the moulded part. Moreover, there will similarly be no adherence to the moulded part if the activator (the polyurethane catalyst) is added to one or the other of the reactant components fed to the mould rather than to the coating.If the activator is added to one of the reactant components, there will be no active sites available in the transfer coating on which the isocyanate and the polyol may react.

The transfer coating may be any decorative or protective coating of the type applied by conventional coating technology to reaction injection moulded parts. A preferred class of coatings are those based on urethane or acrylic polymers, either as protective coatings or with a pigment as a paint coating. A particularly preferred class of transfer coatings are paint primers. The paint primers may be applied within the mould and the moulded part thereafter top coated after removal from the mould.

In carrying out the process, the mould is brought to a temperature offrom 1 20" to 1500F, usually about 1 35 F. No wax is required to seal the mould surface, even in the case of kirkside moulds which normally require such treatment. Moreover, as previously indicated, no release agent need be sprayed onto the mould surface as the coating itself acts as a release agent. The primer may be a conventional urethane based resin primer or a modified acrylic resin based primer containing a polymethylmethacrylate type of resin. A preferred example is an acrylic based resin containing nitrocellulose, a polymethylmethacrylate resin, a plasticiser such as monoethyl ether acetate and a pigment.The primer will be mixed with a thinner, a particularly suitable example of which consists of a mixture of methyl ethyl ketone, methyl isobutyl ketone and toluol. Other organic solvents in which the primer is soluble may of course be used as a thinner. The transfer coat is mixed with from 0.05 to 10%, preferably 1-3%, by total weight of the transfer coating of an activator. The activator is a polyurethane catalyst which helps create a chemical bond between the transfer coat and the moulded part. Suitable examples of catalysts are stannous octate, 1,4-diazabicyclo (2,2,2) octane, phenyl mercuric propionate, triethylene diamine and N, N', N"-tris (dimethylamino-propyl)-symhexahydrotriazine. A particularly suitable activator is dibutyltin dilaurate.

Illustrative examples of other activators which may be used in the process are organometallic salts including cobalt, manganese, zinc and zirconium naphthenate; cobalt and lead benzoate; zinc, cobalt, manganese, lead and zirconium 2-ethyl-hexoate; cobalt octoate; stannous, lead and potassium oleate; zirconium toluene; sodium propionate; and lithium acetate. Metal chloride salts are also useful as activators such as stannous chloride and antimonytrichloride and pentachloride. Other amino activators are N4etramethylethylenedamine, N-tetramethyl-1 -3 butanediamine, tetramethyl guanidine, 4-dimethylaminopyridine, triethylamine, N-ethylmorpholine, N-N-dimethlbenzylamine, 1,2,4-trimethyl piperazine, N-ethylene diamine, dimethylamino ethyl piperazine and N-aminoethyl piperazine.

The following examples illustrate the invention. All parts and percentages, unless otherwise indicated, are by weight.

Example 1 The resin component was an ethylene oxide capped poly (oxpropylene) glycol containing 20 weight percent styrenelacrylonitrile copolymer and, ethylene glycol or 1,4-butane diol as a chain extender, dibutyltin dilaurate as a catalyst and Freon 11 (a registered trade mark for a fluorocarbon) as a blowing agent. The isocyanate was 4,4'-diphenylmethane diisocyanate. The resin and isocyanate were separately brought to 950F and then mixed at a pressure of 1600 psig in each feed line to the mixer. The ratio of isocyanate to resin was 0.72. Nucleation of resin by mixing with air brought the specific gravity of the reaction product to one. The high pressure recycle time was 5 seconds.

An automobile bumper was then reaction injection moulded with the foregoing reactants. The mould surface was initially sprayed with a clear grease release agent in toluene for the first moulding cycle.

Thereafter no further release agent was applied. The mould surface was then uniformly sprayed at 30 psig with a coating of the primer mixed with an equal part by weight of thinner. Thwe coating contained 6%, by total weight of the coating including thinner, of dibutyltin dilaurate. The primer consisted of nitrocellulose, a polymethylmethacrylate resin, monethyl ether acetate as the plasticiser and a pigment to impart the desired colour. The thinner was allowed to flash off for about 15 seconds. The mould was maintained at 1350F and the mixed reactants were injected into the mould after the mould was closed. The part was demoulded after two minutes. The part was wiped with a solvent to remove any dust, then post-cured at 250 F for 30 minutes to complete the cure of the polyurethane.It was then top coated by spraying with a polyurethane paint.

A number of samples of moulded bumpers containing a coating of primer and top coat produced in accordance with the foregoing example were subjected to a series of tests to determine the suitability of the paint coatings. All tests were performed in accordance with the specification of a major U.S. auto manufacturer for paint coatings on plastic parts for exterior use. The tests included hardness, adhesion, flexibility, serviceability, water resistance, weathering, resistance, thermal shock resistance, resistance to water and soap spotting and to acid spotting, gasoline resistance, chip resistance, oil resistance, resistance to scuffing, heat resistance and resistance to galvanic action.All results indicated that the in-mould paint samples, produced in accordance with Example 1, met or exceeded the specifications and were as good as parts painted outside the mould in accordance with standard procedures.

Example 2 Example 1 was repeated exceptthatthe mould surface was completely stripped of any mould release before the transfer coating was applied to the mould surface. No mould release was thereafter used. Release from the mould surface was excellent. A number of parts were moulded without any cleaning of the mould.

The parts exhibited substantially the same properties as those of example 1.

Example 3 A reaction injection moulded high modular urethane elastomer system was used for making in-mould coated parts. The system consisted of a resin component of a high molecular weight poly (oxypropylene) glycol grafted with a styrenelacrylonitrile copolymer, a chain extender of 1,4-butane diol and a urethane catalyst of dibutyltin dilaurate. The second component of the system was a polyisocyanate based on 4,4'-diphenyl methane diisocyanate and a small amount of Freon 11 as a blowing agent. The following processing conditions were used: Isocyanate Index 107 Resinilsocyanate wt ratio 1.0/1.0 Resin Temperature 55 C isocyanate Temperature 24 C Mould Temperature 700C Demould Time 60 seconds The mould was a flat plaque steel mould.The transfer coating was the same as that of Example 1 except that it contained 1% by weight of the activator-dibutyltin dilaurate. The transfer coating was sprayed onto the mould surface after completely stripping any mould release from the surface. The thinner was allowed to flash off for 10 seconds. The reaction mixture was injected into the mould after the mould was closed.

The part demoulded after one minute. The coating completely transferred to the part. A number of additional parts were made over the course of a day with excellent release and absolutely no cleaning of the mould between shots. Release was excellent even from the vertical areas of the plaque. Flash was easy to remove.

Example 4 Examples 1 and 2 were repeated but no activator was added to the coating. The coating did not adhere to the moulded part. In both experiments the coating stuck to the mould surface. Where a release agent was used, the coating could be peeled from the mould. Otherwise, it required a solvent to remove the coating from the mould surface.

Example 5 Example 2, in which flexible fascia material was used to make automobile bumpers, was repeated with different levels of the activator-dibulyltin dilaurate-in the coatings. The levels used were 0.05,0.1,0.15,0.25, 0.5, 1,2,3,4,5,6 and 10% by weight. In each case, the parts released from the mould and the coatings adhered to the parts. However, optimum results were obtained with between 1 and 3% by weight of activator.

Example 6 Examples 2 and 3 were repeated except that 3 and 6% respectively of each of the following activators were substituted for dibutyltin dilaurate: stannous octoate, 1, 4-diazabicyclo (2,2,2) octane (triethylene diamine), phenyl mercuric propionate and N,N"N"'-tris (dimethylamino-propyll-sym-hexahydrotriazine. Excellent release from the mould and adhesion of the coating to the part was observed in each case.

Example 8 The same procedure as in Example 2 was followed for preparing and spraying the transfer coating onto the mould surface. But in this example, a rigid urethane foam was used as a substrate material. The rigid urethane foam is supplied under the trade mark Baydur 722 and consists of an isocyanate component and a polyol component, the latter containing a chain extender and catalyst. A steel plaque mould was used. The resin temperature was 95 F, the mixing ratio of isocyanate to resin was 170/100. The mould was completely stripped of any mould release before the coating was applied to the mould surface. Excellent release from the mould surface was obtained. Adhesion of the coating to the part was excellent. The experiment was again repeated except that the Freon 11 blowing agent was omitted and a solid, non-porous part was produced. Again excellent release and adhesion of the coating to the moulded part was obtained.

The process is applicable to any polyurethane part produced by reaction injection moulding techniques from a two component system, one of which is normally an isocyanate and the other a polyol. The part may be rigid or flexible, porous or non-porous.

Claims

1. A reaction injection moulding process for producing a coated polyurethane part, including coating the mould surface prior to moulding with a coating composition containing a polyurethane catalyst.

2. A process for producing a moulded polyurethane part by reaction injection moulding in which the polyurethane reactants are mixed to form a liquid mixture, the mixture is fed to a mould where the mixture is reacted and moulded at elevated temperatures and a shaped part is removed from said mould, the improvement comprising coating the surface of said mould, prior to moulding said part, with a coating composition containing from 0.05 to 10% by weight of the coating composition of a polyurethane catalyst, said catalyst acting to bond said coating composition to said moulded part so that the shaped part removed from the mould contains a firmly adherent coating of said coating composition.

3. A process as claimed in claim 1 or 2 in which said coating composition is an acrylic or a urethane polymer.

4. A process as claimed in claim 1 or 2, in which said coating composition is a paint or a paint primer.

5. A process as claimed in claim 4, in which the paint primer is an acrylic polymer based primer.

6. A process as claimed in any one of claims 1 to 5, in which said coating composition is sprayed onto the surface of said mould.

7. A process as claimed in any one of claims 1 to 6, in which said coating contains from 1-3% by weight of the coating composition of the polyurethane catalyst.

8. A process as claimed in any one of claims 1 to 7, in which the catalyst is dibutyltin dilaurate.

9. A process for producing a moulded polyurethane product by reaction injection moulding in which a polyol is mixed with an isocyanate to form a liquid mixture, including feeding the mixture to a closed mould where the mixture is reacted and moulded at elevated temperatures, and removing the moulded product from said mould, wherein the surface of said mould, prior to feeding the mixture into the mould, is coated with a paint primer containing from 1 to 10% by weight of the paint primer of a polyurethane catalyst, said catalyst acting to bond said paint composition to said moulded part so that the shaped product removed from said mould contains a firmly adherent coating of said paint primer.

10. A reaction injection moulding process substantially as described herein with reference to the examples.

11. A reaction injection moulded polyurethane part prepared by a process as claimed in any one of claims 1 to 10.

12. A vehicle provided with one or more reaction injection moulded parts as claimed in claim 11.