WO2000000355A1

WO2000000355A1 - Production of abrasion-resistant printed silicon shaped parts

Info

Publication number: WO2000000355A1
Application number: PCT/EP1999/004362
Authority: WO
Inventors: Thomas Naumann; Stephan Kirchmeyer
Original assignee: Ge Bayer Silicones Gmbh & Co. Kg
Priority date: 1998-06-27
Filing date: 1999-06-23
Publication date: 2000-01-06
Also published as: DE19828639A1

Abstract

The present invention relates to a method for producing abrasion-resistant printed silicon shaped parts and the silicon shaped parts obtained using said method.

Description

Manufacture of abrasion-resistant, printed silicone molded parts

The present invention relates to a method for producing abrasion-resistant printed silicone molded parts and the silicone molded parts obtainable by this method.

It is known that moldings made of silicone rubber, so-called silicone moldings such. B. Switch and keyboard mats, which have been printed with printing pastes based on silicone rubber, have a low abrasion resistance. For this reason, so-called top coats based on silicone rubbers, polyurethanes or other organic binders are often applied by spraying and hardened by thermal treatment.

The main disadvantage of the spraying process is that only small parts of the topcoat get to the desired location during application and large parts are lost as so-called overspray. This is undesirable for cost reasons. In addition, the spraying process has the disadvantage that it can only be automated in a very complex and costly manner.

Screen and pad printing processes can be automated with relatively low investment costs. So far it has been considered disadvantageous that with the help of the previous topcoats only small layer thicknesses could be realized, which have only a low abrasion resistance.

There was therefore great interest in a process for the production of printed silicone molded parts, which can be automated easily and with little investment, and which at the same time delivers printed silicone molded parts with high abrasion resistance. It has now surprisingly been found that by a three-stage process with the following process steps

1. surface activation of the molded silicone part, 2. printing on a printing paste based on polyurethanes and 3. thermal treatment

printed silicone moldings with high abrasion resistance can be obtained.

This was surprising since, based on previous experience, it had to be assumed that only by applying films with a high layer thickness can molded articles with sufficient abrasion resistance be produced, which then have an undesirable hard handle, i.e. when touched, the print feels uncomfortably hard. However, this is not the case. The molded parts produced by the process according to the invention are extremely resistant to abrasion and also have an excellent grip. The process is also easy to automate and requires little investment.

The invention therefore relates to a method for producing abrasion-resistant printed silicone molded parts, a printing paste based on polyurethanes being printed on a silicone molded part after surface activation, and the molded part then being thermally treated.

All silicone molded parts known to the person skilled in the art can be used in the process according to the invention. Such silicone moldings are e.g. B. producible from compositions containing as base polymers polyorganosiloxanes, preferably polydiorganosiloxanes such as polydimethyl and polydiphenylsiloxanes, and additionally have accessible groups for crosslinking reactions. Such groups are predominantly H atoms, hydroxyl and vinyl groups, which can be located at the chain ends, but can also be incorporated into the chain. The masses often contain fillers and reinforcing materials such. B. silica and other additives, the type and amount of which can influence the mechanical and chemical behavior of the masses to be crosslinked.

Further additives are preferably crosslinking catalysts such as organic peroxides and metal compounds (for example platinum compounds such as hexachloroplatinic acid or tin compounds such as dibutyltin dilaurate), anti-aging agents, bactericides, fungicides, processing aids such as lubricants, inorganic and organic pigments. The silicone moldings are usually made from the masses by methods known to those skilled in the art by heating in suitable devices, for. B. heated molds, injection molding machines or extruders.

The silicone moldings which can be used in the process according to the invention can be surface-modified, for example by applying coatings or printing on the basis of silicones. The materials or coatings on which the coatings are based are in principle the same as those on which the moldings are based. You can colorants and additional tools such. B. flow, wetting and dispersing aids or solvents for setting desired viscosities, for. B. alcohols such as methanol, ethanol, n-propanol, isopropanol and butanol, ketones such as acetone and butanone, esters such as butyl acetate and methoxypropyl acetate, aromatic solvents such as toluene and xylene and aliphatic solvents such as hexane and white spirit.

The first step in the process, surface activation, mainly serves to increase the surface roughness of the silicone molded part - and thus also the binding force between the silicone molded part and the printing paste. The activation can e.g. B. by treatment with solvents; Treatment with alkaline solutions such as B. sodium or potassium hydroxide in water or suitable organic solvents; Treatment with oxidizing agents; mechanical roughening z. B. by grinding; and treatment with flame, plasma or corona discharges. Preferred surface activation methods are treatment with flames (gas flames) and corona discharges. Printing pastes based on polyurethanes in the sense of the invention are printing pastes which contain, in addition to hydroxyl-functional components, isocyanate-functional components. By reacting the hydroxyl groups with the isocyanate groups, urethane groups are formed.

The reaction of hydroxyl groups with isocyanate groups is known to the person skilled in the art and is known, for. B. in Houben-Weyl Methods of Organic Chemistry, Volume E 20 "Macromolecular Substances", published by H. Bartl, J. Falbe, Georg Thieme Verlag, Stuttgart, New York.

Printing pastes based on polyurethanes are preferably crosslinking compositions

a) 5 to 95 wt .-%, preferably 10 to 90 wt .-%, polyols with an average molecular weight (Mn) of 200 to 5000, which on average (by "means" in the present invention is to be understood as the number average) have at least 2 hydroxyl groups per molecule, b) 95 to 5% by weight of polyisocyanates, which on average have at least 2 isocyanate groups per molecule, (number average) c) 0 to 5% by weight of matting agent, d) 0 to 50% by weight % organic solvent and e) 0 to 5% by weight of further customary auxiliaries.

The polyols a) used in the printing paste based on polyurethanes have an average molecular weight (Mn) of 200 to 5000, preferably 500 to 2000 and on average at least 2 hydroxyl groups per molecule. The average molecular weight can be determined by means of gel permeation or particle exclusion chromatography. graph can be determined. Preferred polyols are hydroxyl-containing polyesters, polyethers, polycarbonates, polyester amides, polyacrylates and Polyacrylate polyols used. Polybutadienes containing hydroxyl groups are also suitable.

Suitable polyesters are e.g. B. the reaction products of polyhydric, preferably dihydric alcohols, which may optionally additionally contain trihydric alcohols, with polyhydric, preferably dihydric carboxylic acids or their esterifiable derivatives. The polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic and / or heterocyclic in nature and they can be substituted by halogen atoms and / or unsaturated.

As examples of such carboxylic acids and their derivatives are succinic acid, adipic acid, phthalic acid, isophthalic acid, phthalic anhydride, anhydride tetrahydrophthalic anhydride, hexahydrophthalic anhydride, Terachlorphthalsäureanhydrid, ene domethylentetrahydrophthalsäureanhydrid, maleic acid, maleic anhydride, marsäure fu, dimerized and trime catalyzed unsaturated fatty acids (optionally in admixture with monomeric unsaturated fatty acids) called dimethyl terephthalate and bisglycol terephthalate.

Suitable polyhydric alcohols are e.g. B. ethylene glycol, 1, 2- and 1, 3-propanediol, 1, 4- and 2,3-butanediol, 1, 6-hexanediol, 1, 8-octanediol, 2,2-dimethyl-1, 3-propanediol, 1st , 4-bis (hydroxymethyl) cyclohexane, 1, 1, 1-Tπ ^' s- (hydroxymethyl) propane, 1, 1, 1-tris (hydroxymethyl) ethane, di-, tri-, tetra- and higher polyethylene glycols, di - and higher polypropylene glycols and di- and higher polybutylene glycols. Lactone polyester, e.g. B. ε-caprolactone, or from hydroxycarboxylic acids, e.g. B. ω-hydroxycaproic acid can be used. However, the hydroxyl-functional polyesters known from oleochemistry, such as, for. B. castor oil and its transesterification products can be used.

Suitable polyethers can e.g. B. by polymerization of epoxides (such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide or epichlorohydrin) or of tetrahydrofuran with itself, preferably in the presence of Lewis catalysts such as Boron trifluoride. Suitable polyethers can furthermore be obtained by addition of the epoxides mentioned, preferably of ethylene oxide and propylene oxide, optionally in a mixture or in succession, to starting components with compounds containing reactive hydrogen atoms, such as water, alcohols, ammonia or amines, for. B. ethylene glycol, 1, 2- or 1, 3-propanediol, water, 4,4'-dihydroxydiphenylpropane, aniline, ethanolamine or ethylenediamine.

The polycarbonates containing hydroxyl groups are those which are known in the art, for. B. by reacting the above-mentioned diols, in particular 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol or thiodiglycol, with diaryl carbonates, e.g. B. diphenyl carbonate, or phosgene can be produced.

Suitable polyester amides and polyamides are e.g. B. the predominantly linear condensates obtained from polyvalent saturated or unsaturated carboxylic acids or their anhydrides and polyvalent saturated or unsaturated amino alcohols, diamines, polyamines and mixtures thereof.

Polyacrylates suitable for the present invention are polymers of compounds having ethylenically unsaturated groups, preferably esters of acrylic acid and methacrylic acid, eg. B. methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and hexyl acrylate or methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate and hexyl methacrylate. Other compounds containing ethylenically unsaturated groups are e.g. B. styrene, acrylonitrile, acrylamide,

Methacrylamide, acrylic acid, methacrylic acid, esters of maleic acid and fumaric acid such as. B. dimethyl maleate or dimethyl fumarate, esters of itaconic acid, methyl styrene and styrene sulfonic acid.

The polyacrylate polyols for the purposes of the present invention are hydroxyl-bearing, ethylenically unsaturated group-containing compounds (the ethylenically unsaturated groups as defined above), in particular hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxylethyl methacrylate and hydroxypropyl methacrylate. In addition, it is also possible to modify polymers containing carboxylic acid groups with compounds containing epoxy groups, one hydroxyl group being obtained per converted carboxylic acid group. It is also possible to polyacrylate polyols by etherification, for. B. with ethylene oxide or propylene oxide, or esterification, for. B. with caprolactone to further modify.

It is important that the compounds have an average molecular weight (Mn) of 200 to 5000 and at least 2 hydroxyl groups per molecule.

Particularly preferred polyols for printing paste based on polyurethanes are polyester polyols which have an average molecular weight between 500 and 2000 and 2 to 7 hydroxyl groups per molecule.

As polyisocyanates b), aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates or any mixtures of these polyisocyanates can be used, as described, for. B. in Houben-Weyl "Methods of Organic Chemistry", Volume E20 "Macromolecular Substances", editor H. Bartl, J. Falbe, Georg Thieme Verlag, Stuttgart, New York, 1987, pp. 1587-1593 . These are e.g. B. ethylene diisocyanate, 1, 4-tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate, 1, 12-dodecane diisocyanate, cyclobutane-1, 3-diisocyanate, cyclohexane-1, 3- and -1, 4-diisocyanate and any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 2,4- and 2,6-hexahydro-toluenediisocyanate and any mixtures of these isomers, hexahydro-1, 3 and / or -1, 4th -phenylene diisocyanate, perhydro-2,4'- and / or -4,4'-diphenylmethane diisocyanate, norbomane diisocyanates (e.g. US Pat. No. 3,492,330), 1,3- and 1,4-phenylene diisocyanate, 2, 4- and 2,6-tolylene diisocyanate and any mixtures of these isomers, diphenylmethane-2,4'- and / or -4,4'-diisocyanate. Modification products from the aforementioned isocyanates are also suitable. According to the present invention, “modification” is understood to mean the production of derivatives of simple polyisocyanates, in particular diisocyanates, containing derivatives of uretane, allophanate, uretdione and / or isocyanurate groups. Suitable modifiable diisocyanates are, for example Hexamethylene diisocyanate, cyclohexane-1, 3- and -1, 4-diisocyanate and any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 2,4- and 2,6-hexahydro toluenediisocyanate and any mixtures of these isomers, perhydro-2,4'- and / or -4,4'-diphenylmethane diisocyanate, 2,4- and 2,6-tolylene diisocynanate as well as any mixtures of these isomers, diphenylmethane-2,4'- and / or - 4,4'-diisocyanate and naphthylene-1, 5-diisocyanate The monoisocyanates which may be used include 1-isocyanatohexane, 1-isocyanatoctadecane, cyclohexyl isocyanate, phenyl isocyanate, the isomeric tolylene diisocyanates, benzyl isocyanate and 1-naphthyl isocyanate.

Particularly preferred modifiable diisocyanates are the technically important polyisocyanates such as 2,4-diisocyanatotoluene; whose technical mixtures with up to 35 wt .-%, based on the mixture, of 2,6-diisocyanatotoluene; 4,4'-diisocyanatodiphenylmethane, its technical mixtures with 2,4'- and 2,2'-diisocyanatodiphenylmethane; 1,6-diisocynatohexane; 1,4-diisocyanatobutane; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; 1-Isocyanato-3 (4) -isocyanatomethyl-1 - methylcyclohexane or mixtures of these diisocyanates.

For the purposes of the invention, isocyanates based on hexamethylene diisocyanate and isophorone diisocyanate modified by trimerization, biurization and allophanatization are very particularly preferred.

The quantitative ratios of polyols a) to polyisocyanates b) are preferably chosen so that 0.8 to 3.0, preferably 1.0 to 1.5, isocyanate groups of the polyisocyanate component fall per hydroxyl group of the polyol component. Organic solvents d) can be present in the printing paste in an amount of up to 50% by weight, preferably from 0 to 2.5% by weight. The viscosity of the printing pastes is adjusted on the one hand and the miscibility of the individual components is improved on the other hand. Suitable organic solvents are those solvents or solvent mixtures which contain no groups (such as hydroxyl, amino and carboxylic acid groups) which can react with isocyanate groups of the polyisocyanates b).

Suitable solvents or solvent mixtures in the sense of the invention are, for. B. acetone, 2-butanone, cyclohexanone, isobutyl methyl ketone, tetrahydrofuran, methyl acetate, ethyl acetate, butyl acetate, acetonitrile, chlorobenzene, chloroform, dichloromethane, perchlorethylene, carbon tetrachloride, trichlorethylene, trichloroethane, dichlorobenzene, dimethylformamide, dimethylformamide pyrrolidone, dimethylacetamide, dimethyl sulfoxide, dioxane, hexane, heptane, isooctane, ligroin, washing, soldering, light, varnish or test gasoline, petroleum ether, petroleum, turpentine oil substitute, cyclohexane, toluene, xylene, aliphatic or aromatic paint solvent mixtures, methylcyclohexane , Methylglycol acetate, methoxypropylacetate or mixtures thereof.

Toluene, xylene, butyl acetate and methoxypropyl acetate are preferred.

Matting agents c) for the purposes of the invention are particulate agents which are suitable for changing the gloss of the printing pastes, such as natural inorganic agents (for example talc and silica) or organic agents (for example polyolefin waxes). Matting agents can be present in the printing paste in an amount of up to 5% by weight, preferably 0.1 to 2% by weight.

The printing pastes which can be used in the process according to the invention can contain up to 5% by weight, preferably from 0.1 to 2% by weight, of conventional auxiliaries e). The tools within the meaning of the invention are, for. B. catalysts (such as catalysts which catalyze the reaction between polyisocyanates and polyols), additives which improve the adhesion of the printing paste, such as silanes (e.g. amino, epoxy, (meth) acrylate, Hydroxyl-, carboxyl- and thio-functional alkoxysiiane), surface-active additives, colorants, leveling agents, wetting agents, dispersing agents, stabilizers against aging and weathering, plasticizers, fungistatic and bacteriostatic substances and fillers.

Catalysts which catalyze the reaction between the polyisocyanate and the polyol, for example, are. B. tertiary amines (triethyiamine, N-methylmorphoiin, N, N, N'-tetramethylene diamine, 1, 4-diazabicyclo [2.2.2] octane, N-methyl-N'-dimethylaminoethylpiperazine and N, N- Dimethylcyclohexylamine) and organic metal compounds, in particular organic tin compounds such as tin (II) salts of carboxylic acids (tin (II) acetate, tin (II) actoate, tin (II) ethylhexoate and tin (II) laurate) and tin (IV) - Compounds (dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate). The catalysts mentioned can also be used as mixtures. Further representatives of usable catalysts as well as the details of the mode of action of the catalysts are in the plastics handbook, volume VII, edited by Vieweg and Höchtlen, Carl-Hanser-Verlag, Munich, 1966, e.g. B. on pages 96 to 102.

The colorants in the sense of the invention are organic or inorganic dyes and pigments such as azo, anthraquinone, thioindigo or other polycyclic organic pigments, carbon black, titanium dioxide, zinc sulfide, ultramarine, iron oxide, nickel or chromium antimony dioxide, cobalt blue, chromium oxide and Chromate pigments. The printing pastes which can be used in the process according to the invention preferably contain carbon black and no colorants.

In principle, all printing processes are suitable for applying the printing pastes to the silicone moldings in the process according to the invention. The screen printing method and the pad printing method described in DE 36 36 962 are preferably used. The thermal treatment is expediently carried out directly after the printing and serves to dry and crosslink the applied printing pastes. The thermal treatment can e.g. B. by heating the molded body to 50 to 200 ° C, preferably 70 to 150 ° C, in an oven or by irradiation with suitable lamps such as infrared radiators. However, the thermal treatment can also be carried out at temperatures lower than 50 ° C. if the printing pastes based on polyurethanes have suitable high crosslinking speeds for this. However, the use of printing pastes with high crosslinking speeds is not preferred since these usually have short processing times at processing temperature.

The layer thickness of the applied printing paste after the thermal treatment is preferably 5 to 20 μm.

Another object of the invention are abrasion-resistant printed silicone molded parts obtainable by the process according to the invention.

The following examples serve to illustrate the invention, but without being restrictive.

embodiments

example 1

Production of the molded silicone part; Blank sample: A plate with the dimensions 50 x 50 x 2 mm made of addition-crosslinked silicone rubber was coated with a commercially available black printing ink based on addition-crosslinking silicone rubber using a tampon printer (type Hermetic 61, available from Tampophnt) with a print image test area of 5 x Printed 10 mm three times in succession, wet on wet and then crosslinked with hot air at 180 ° C for 10 minutes.

Example 2

Production of the Printed Shaped Body by the Process According to the Invention: The surface of a blank was flamed with a gas burner. Immediately after the flame treatment, a transparent matt printing ink based on polyurethane, consisting of the homogeneously stirred mixture of 74 g polyol component (modified polyester based on isophthalic acid, hydroxyl number 70.2 mg KOH / g) and 26 g isocyanate component ( modified aliphatic isocyanate, isocyanate content 14.2%) with the pad printer from Example 1 applied three times in succession wet in wet and then crosslinked with hot air at 80 ° C. for 60 minutes.

Example 3

Production of the Printed Shaped Body by the Process According to the Invention: The printed surface of a blank was subjected to a corona treatment (type CG06 from Arcotec, activation ten times with a rolling speed of 100 mm / s, setting 10 kV, 300 watts). Immediately after the corona treatment, the printing ink from Example 2 was made using the tampon printer from Example 1 applied three times in succession, wet in wet and then crosslinked with hot air at 80 ° C. for 60 minutes.

Example 4

Comparison, production of the printed molded article without superficial activation: The printed surface of a blank sample was printed three times in succession, without flaming, with the printing ink from example 2, wet on wet using the pad printer from example 1, and then crosslinked with hot air at 80 ° C. for 60 minutes.

Example 5

Comparison, use of a printing paste based on silicone: The printed surface of a blank sample was immediately after the flame treatment from Example 2 with a transparent printing ink based on an addition-crosslinking silicone rubber, consisting of the homogeneous mixture of a vinyl group-containing silicone component, an Si-H Component having a group and a component having a platinum catalyst (100 parts by weight of dimethyl vinyl end-stopped polydimethylsiloxane with a viscosity of 1 Pa · s, 0.09 part by weight of ethynylcyclohexanol, 4.6 parts by weight of polydimethylsiloxane containing methylhydrosiloxy groups and an Si — H group content of 7 mmol / g, 0.022 silicone-platinum complex) printed three times in succession wet on wet using the same pad printer from Example 1 and then crosslinked with hot air at 80 ° C. for 60 minutes.

Example 7

Assessment of the printed moldings: The moldings from Examples 1 to 7 were tested. The adhesion of the topcoat was judged to be poor if the topcoat with simple means such as. B. removed with the help of a fingernail could or the layer showed clear cracks when the molded body was bent. To determine the abrasion, a test device RCA Abrasion Wear Tester (manufactured by Norman Tool, Inc., USA) was used in the setting 175 g contact weight, abrasion medium paper, continuous operation. The higher the cycle number, the better the abrasion resistance. From the table it can be seen that molded silicone articles with high abrasion resistance and good grip can be produced by the process according to the invention.

Claims

claims

1. A process for the production of abrasion-resistant printed silicone molded parts, characterized in that a printing paste based on polyurethanes is applied to the silicone molded part after surface activation and subsequently the silicone molded part is thermally treated.

2. The method according to claim 1, characterized in that ais surface activation, a corona treatment or a gas flame is carried out.

3. The method according to claim 1 or 2, characterized in that containing a printing paste

a) 5 to 95% by weight polyols with an average molecular weight of 200 to 5000, which have on average at least 2 hydroxyl groups per molecule, b) 95 to 5% by weight polyisocyanates, which have on average at least 2 isocyanate groups per molecule, c) 0 to 5% by weight of matting agent, d) 0 to 50% by weight of organic solvent and e) 0 to 5% by weight of further auxiliaries.

4. The method according to claim 3, characterized in that a polyester with an average molecular weight of 200 to 5000, which has an average of at least 2 hydroxyl groups per molecule, is used as the polyol.

5. The method according to claim 3 or 4, characterized in that one or more di- or polyisocyanates with an aliphatic or cycloaliphatic backbone or modification products thereof are used as the polyisocyanate.

6. The method according to one or more of claims 1 to 5, characterized in that the layer thickness of the applied printing paste after the thermal treatment is 5 to 20 microns.

7. The method according to one or more of claims 1 to 6, characterized in that the printing paste is applied by a pad printing process or a screen printing process.

8. The method according to one or more of claims 1 to 7, characterized in that the printing paste is applied by the wet-on-wet method with up to 10 cycles.

9. The method according to one or more of claims 1 to 8, characterized in that the thermal treatment is carried out by infrared radiation.

10. Abrasion-resistant printed silicone molded parts, obtainable by a process according to one or more of claims 1 to 9.