Method for producing silicone elastomer molds

Abstract

Silicone compositions are described for the production of negative molds that include a silicone elastomer. The molds can be used in the production of molded articles.

Claims

1. A method of preparing a negative mold MN produced from silicone elastomer for use in the manufacture of molded articles produced from different reproduction materials, the method comprising the following steps a) to d): a) preparing a polyorganosiloxane composition X that can be cured to produce an elastomer by polycondensation reactions, which does not contain a metallic catalyst, and comprising: a silicone base B comprising at least one polyorganosiloxane oil A that can be cured by a polycondensation reaction, and catalytic quantity of at least one polycondensation catalyst C, which is an organic compound having a general formula (I):
(R″).sub.2NH in which the symbols R″, which are identical or different, represent aliphatic hydrocarbon radicals containing 1 to 30 carbon atoms, b) applying said polyorganosiloxane X to a master to be duplicated, optionally already covered with a release agent, c) curing said polyorganosiloxane composition X in the presence of moisture supplied by ambient air or by a prior addition of water, in order to form the negative mold MN produced from silicone elastomer, which is an impression corresponding to the exterior contour of the master to be duplicated, and d) separating the negative mold MN produced from silicone elastomer from the master to be duplicated, wherein: a) the polyorganosiloxane composition X has a pot life of between 20 and 200 minutes, b) the curing of said polyorganosiloxane composition X, as measured by the Shore A hardness (SAH) of the negative mold MN, i) when measured at 4 days and 14 days after mixing, the the difference in the SAH polyorganosiloxane composition X, is less than 2, and ii) when measured 24 hours and 14 days after mixing, the, the Shore A hardness is at least 68% of the SAH measured at 14 days, and c) the negative mold MN produced can be used in greater than 37 successive molding/demolding cycles when used in demolding polyurethane replicas.

2. A method of molding replicas R, the method comprising steps a) to d) as claimed in claim 1, followed by the following steps e) to h): e) filling the negative mold MN produced from silicone elastomer with a reproduction material, f) allowing the reproduction material to harden inside the negative mold MN produced from silicone elastomer, in order to produce a replica R of the master to be duplicated, g) separating the replica R from the negative mold MN produced from silicone elastomer, and h) optionally, submitting the negative mold MN produced from silicone elastomer to steps e) to g) again, in order to form a new replica R, and the number of cycles of steps e) to g) that can be carried out with the negative mold MN is more than 37, when demolding polyurethane replicas.

3. The method as claimed in claim 1 wherein during step a), the polycondensation catalyst C has the general formula (I):
(R″).sub.2NH in which the symbols R″, which are identical or different, represent aliphatic hydrocarbon radicals containing 6 to 10 carbon atoms.

4. The method of claim 1, wherein the homogeneity of curing, as determined by measuring the Shore A hardness above and below the indenter and the difference is 2 or less.

5. The method of claim 1, wherein the at least one polyorganosiloxane oil A comprises a reactive α,ω-dihydroxydiorganopolysiloxane polymer having the general formula: ##STR00002## in which the substituents R.sup.1, which may be identical or different, each represent a monovalent C.sub.1 to C.sub.13 hydrocarbon, which may or may not be saturated, which may or may not be substituted, aliphatic, cyclic or aromatic, and n has a sufficient value to provide the α,ω-dihydroxydiorganopolysiloxane polymer with a dynamic viscosity at 25° C. of 10 to 1000000 m Pas.

6. The method of claim 5, wherein the at least one polyorganosiloxane oil A has a dynamic viscosity at 25° C. of from 50 to 200000 m Pas.

7. The method of claim 6, wherein at least 60% by number of the radicals R.sup.1 are methyl radicals.

8. The method of claim 7, where the radicals R.sup.1 that are not methyl radicals are phenyl and/or vinyl radicals.

9. The method of claim 1, wherein the polyorganosiloxane composition X comprises: (a) a silicone base that is capable of hardening into a silicone elastomer in the presence of a catalyst by polycondensation reactions, comprising: for 100 parts by weight of at least one α, ω-dihydroxydiorganopolysiloxane A, 0.1 to 60 parts by weight of at least one curing agent AR, and 0.001 to 10 parts by weight of water, and (b) a catalytically effective quantity of a polycondensation catalyst C.

10. The method of claim 9, wherein the curing agent AR is: a) a silane with the general formula (2):
R.sup.2.sub.kSi(OR.sup.3).sub.(4-k)  (2) in which the symbols R.sup.3, which may be identical or different, represent alkyl radicals containing 1 to 8 carbon atoms, or C.sub.3-C.sub.6 oxyalkylene radicals, the symbols R.sup.2 representing a saturated or unsaturated, linear or branched aliphatic hydrocarbon group, a saturated or unsaturated and/or aromatic, monocyclic or polycyclic carbocyclic group, and k is equal to 0 or 1; and b) partial hydrolysis and condensation products of a silane with formula (2).

11. The method of claim 10, wherein 0.1 to 6 parts by weight of curing agent AR are used per 100 parts by weight of the at least one polyorganosiloxane oil A.

12. The method of claim 9, wherein the compositions further comprises reinforcing fillers, semi-reinforcing fillers or packing fillers CH.

13. The method of claim 12, wherein the reinforcing fillers are fumed silicas or precipitated silicones having a specific surface area, measured using a BET method, of at least 50 m.sup.2/g, a mean primary particle dimension of less than 0.1 μm (micrometers) and an apparent density of less than 200 g/liter.

14. The method of claim 12, wherein the semi-reinforcing fillers or packing fillers are selected from ground quartz, calcined clays and diatomaceous earth and have a particle diameter of more than 0.1 μm.

Description

EXAMPLES

(1) 1) Starting Materials Used

(2) Paste preparation: Mixture of A200 fumed silica (supplied by Evonik—200 m.sup.2/g) treated with trimethylsilyl groups (approximately 30%) (CH1), 47V500 silicone oil (approximately 42%) (E1) and 48V14000 silicone oil (approximately 29%) (A1).

(3) Sifraco® E600 (supplied by Sibelco)=quartz=silica flour, crystalline silica, ground silica (CH2)

(4) Bluesil® FLD 48V14000 (α,ω-dihydroxydiorganopolysiloxane oil), viscosity 14000 mPa.Math.s—MW approx 48 kg/mol (A1)

(5) Bluesil® FLD 48V3500 (α,ω-dihydroxydiorganopolysiloxane oil), viscosity 3500 mPa.Math.s—MW approx 30 kg/mol (A2)

(6) Bluesil® FLD 48V750 (α,ω-dihydroxydiorganopolysiloxane oil), viscosity 750 mPa.Math.s—MW approx 15 kg/mol (A3)

(7) Bluesil® RP 120PA (α,ω-dihydroxydiorganopolysiloxane oil), viscosity 45 mPa.Math.s—MW approx 0.5 kg/mol (A4)

(8) Bluesil® FLD 47V50 (non-functional silicone oil) Viscosity 50 mPa.Math.s, MW approx 3-4 kg/mol (E1)

(9) Base Color 552 (supplied by Sioen)=white base color based on TiO.sub.2 (F1)

(10) Silane 51005—advanced or partially condensed ethyl silicate (SiOEt.sub.4), tetraethyl ester, hydrolyzed (AR1)

(11) Dynasilan® P (supplied by Evonik) or propyl silicate or tetra n-propylorthosilicate or tetrapropyl orthosilicate (AR2)

(12) Mediaplast® VP 5071/A (supplied by Kettlitz Chemie)—mixture of polyalkylbenzene and high molecular weight hydrocarbons (comprises between 25% and 50% of alkylbenzene (C10-C13)) (H1)

(13) Dimethyltin neodecanoate (supplied by Momentive)

(14) Decylamine CAS 2016-57-1 (supplied by Sigma-Aldrich) (C1)

(15) Dodecylamine CAS 124-22-1 (supplied by Sigma-Aldrich) (C2)

(16) Dibutylamine CAS 111-92-2 (supplied by Sigma-Aldrich) (C3)

(17) Dihexylamine CAS 143-16-8 (supplied by Sigma-Aldrich) (C4)

(18) Dioctylamine CAS 1120-48-5 (supplied by Sigma-Aldrich) (C5)

(19) Diisononylamine CAS 28454-70-8 (supplied by Sigma-Aldrich) (C6)

(20) Didodecylamine CAS 3007-31-6 (supplied by Sigma-Aldrich) (C7)

(21) Didecylamine CAS 1120-49-6 (supplied by Sigma-Aldrich) (C8)

(22) 2) Preparation of Examples in Accordance with the Invention and Comparative Examples:

(23) In all of the compositions, the percentages (%) mentioned are expressed by weight with respect to the total weight of all of the constituents of the formulation.

(24) The bicomponent precursors of the polyorganosiloxane compositions that can be vulcanized to silicone elastomers were composed of a part P1 and a part P2.

(25) Preparation of Parts P1

(26) The various constituents of part P1 were mixed using a DAC400 speed-mixer type appliance or using a propeller in a plastic pot.

(27) TABLE-US-00001 TABLE 1 Composition of parts P1 Composition Part P1-1 Part P1-2 Paste 60.2 60.2 Sifraco E600 18 18 48V3500 20 — 48V14000 — 20 Base Color 552 0.5 0.5 48V750 1 1 Bluesil RP 120PA 0.2 0.2 Water 0.1 0.1 Total 100 100

(28) Preparation of Parts P2

(29) The various constituents of parts P2 were manually mixed in a glass flask.

(30) TABLE-US-00002 TABLE 2 Part P2 for comparative examples Part P2 Part P2-C1 for Part P2-C2 for Part P2-C3 for comparative comparative comparative Reference test C1 test C2 test C3 Catalyst 6.6 2.11 2.49 Dimethyltin Decylamine Dodecylamine neodecanoate Silane 51005 40 35 35 Propyl silicate 5.3 5.3 Mediaplast VP 12.95 13.96 13.87 5071/A 47V50 40.45 43.63 43.34 Total 100 100 100

(31) TABLE-US-00003 TABLE 3 Part P2 for examples in accordance with the invention Reference P2-1 P2-2 P2-3 P2-4 P2-5 P2-6 P2-7 P2-8 P2-9 P2-10 Catalyst 3.62 3.62 3.24 3.47 2.49 4 9.5 1.74 2.49 4 Di- Di- Di- Di- Di- Di- Di- Di- Di- Di- isononyl- isononyl- octyl- butyl- hexyl- decyl- dodecyl- butyl- hexyl- decyl- amine amine amine amine amine amine amine amine amine amine Silane 40 35 35 40 35 40 40 35 40 35 51005 Propyl 5.3 5.3 5.3 5.3 5.3 silicate Mediaplast 13.67 13.6 13.69 13.7 13.87 13.58 12.24 14.06 13.94 13.5 VP 5071/A 47V50 42.71 42.48 42.77 42.83 43.34 42.42 38.26 43.9 43.57 42.2 Total 100 100 100 100 100 100 100 100 100 100

(32) Preparation of Mixtures P1+P2

(33) The parts P1 and P2 employed in the comparative bicomponent systems denoted Ck, in which k is 1 to 3, and the bicomponent systems in accordance with the invention, denoted Ex.m, in which m is from 1 to 11, are detailed Table 4.

(34) TABLE-US-00004 TABLE 4 Composition of bicomponent systems Bicomponent reference P1 + P2 Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. C1 C2 C3 1 2 3 4 5 6 7 8 9 10 11 Part P1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-1 P1-2 P1-1 P1-2 Part P2 P2-C1 P2-C2 P2-3 P2-1 P2-2 P2-3 P2-4 P2-5 P2-6 P2-7 P2-8 P2-9 P2-10 P2-11

(35) Part P1 and part P2 were mixed with a spatula for three minutes, then with a speed mixer (planetary mixer) for twenty seconds at 1800 rpm. The mixture was then vacuum degassed so that there were no defects (bubbles).

(36) The weight ratio was 100 parts of P1 to 5 parts of P2.

(37) Preparation of Negative Molds Produced from Silicone Elastomer:

(38) Negative molds were produced by applying the pre-mixed formulation (mixture of part P1 and of part P2) to a master to be duplicated placed at the bottom of a pot.

(39) 45 g of part P1 and 2.25 g of part P2 were mixed with a spatula for three minutes then with a speed mixer for twenty seconds at 1800 rpm. The mixture was then degassed under a vacuum bell jar for 5 minutes so that there were no defects (bubbles, air incorporated during mixing with the spatula) in the negative mold.

(40) A master (parallelepipedal rectangle with a height of 8 mm; a width of 35 mm and a length of 35 mm) to be duplicated was placed and centered at the bottom of a plastic pot (which had been degreased with ethanol) with a height of 27 mm and an internal diameter of 63 mm.

(41) The master+pot were tared and between 40 and 42 g of the formulation P1+P2 was applied to the master.

(42) The control negative molds denoted MN Ck, in which k was from 1 to 3, and the negative molds in accordance with the invention, denoted MN m, in which m was from 1 to 11, were obtained after curing the mixtures P1+P2. The mixture was allowed to cure at 23° C. for 24 hours. The negative mold produced from silicone elastomer was separated from the master to be duplicated.

(43) TABLE-US-00005 TABLE 5 Reference for control negative molds and negative molds in accordance with the invention Reference negative mold MN MN MN MN MN MN MN MN MN MN MN MN MN MN C1 C2 C3 1 2 3 4 5 6 7 8 9 10 11 Reference C1 C2 C3 Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. mixture 1 2 3 4 5 6 7 8 9 10 11 P1 + P2

(44) Preparation of Replicas:

(45) The negative molds produced from silicone elastomer were filled first time with polyurethane casting resin (reproduction material).

(46) F190 Fastcast polyurethane resin from Axson was prepared in transparent plastic pots (so that the homogeneity of the mixture could be observed) with a height of 48 mm and an internal diameter of 51 mm. The polyol part was charged and underwent decantation; it was therefore mixed with a spatula prior to use (homogeneous color and appearance without sedimentation at the bottom of the receptacle). This operation was easy to carry out manually.

(47) 12.5 g±0.1 g of the polyol part (white color) and 12.5 g±0.1 g of the isocyanate part (brown color) were weighed out. The two parts were mixed with a spatula for one minute, checking the homogeneity of the mixture (a yellow colored mixture was obtained). Two negative molds were then filled with this preparation (the cavity corresponding to the master to be duplicated was filled to the rim).

(48) The reproduction material was allowed to harden for 90 minutes at ambient temperature inside the silicone negative molds in order to produce a first replica.

(49) The replica was separated from the silicone negative mold by detaching each rim of the negative mold. If no adhesion to the negative mold was observed, a new replica was prepared and so on until the negative mold produced from silicone elastomer deteriorated.

(50) 3) Characterization

(51) Characterization Tests for Mixture P1+P2

(52) The properties of the mixture P1+P2 allowing molds to be produced from silicone elastomers were characterized by a pot life and curing kinetics expressed in Shore A Hardness.

(53) In addition, the silicone elastomer must not adhere to the master in order to facilitate its removal from the mold. A large number of demolding operations is an indication of great durability of the silicone elastomer mold.

(54) Measurement of Pot Life (with a “Techne Gelation Timer GT3”) in Accordance with the French Standard NF T 77 107

(55) A 22 mm diameter plunger weighing 11.4 g immersed in a sample is actuated with an alternating vertical movement with a period of one minute. When the consistency of the product is sufficient to support the weight of the disk for a minute, the gel point has been reached. An electrical contact then stops the timer started at the beginning of the test. This time, expressed in minutes (min), is then taken to be the pot life. A pot life of between 20 and 200 min is desired.

(56) Measurement of Curing Kinetics

(57) The curing kinetics were evaluated using the Shore A hardness (SAH) in accordance with the standards DIN 53505 and ISO 868. This hardness is generally measured 24 hours then 4 days and then 14 days after mixing the parts P1+P2. A hardness after 24 h equal to at least 68% of the final hardness at 14 days was desired. Hardnesses above and below the indenter are measured in order to evaluate the homogeneity of curing. Preferably, difference of 2 Shore A or less is desired.

(58) Post-curing expresses the difference in hardness between 14 days and 4 days: a difference of 2 Shore A or less is desired for below the indenter.

(59) Tests for Adhesion of Silicone Elastomer Mold to Master to be Reproduced:

(60) Masters to be duplicated formed from different materials were used in order to evaluate the development of adhesion of the silicone elastomer during the preparation of the negative mold.

(61) The evaluated materials were: an organic plastic, namely polyurethane, and plaster. For each of the materials, the master used was a parallelepipedal rectangle with a height of 8 mm, a width of 35 mm and a length of 35 mm. The surface of this part was smooth.

(62) After 24 hours, adhesion of the negative mold to the master was evaluated qualitatively during demolding. Demolding of the master was carried out by detaching each rim of the negative mold, one after the other, in order to evaluate the resistance to demolding.

(63) If there was no resistance, the adhesion was evaluated at 0.

(64) If a slight force had to be applied in order to remove the master, the adhesion was evaluated as +.

(65) If a large force had to be applied in order to remove the master, but it was possible to remove the master without tearing the silicone mold, the adhesion was evaluated as ++.

(66) When it was not possible to demold the master without tearing the silicone mold, the adhesion was evaluated as +++.

(67) A mark of 0 or + was desired in order to use the negative mold for the preparation of replicas.

(68) Demolding Test:

(69) The master used was a parallelepipedal rectangle produced from metal with a height of 8 mm, a width of 35 mm and a length of 35 mm. The surface of this part was smooth.

(70) The test molds were produced in a method for casting the pre-mixed formulation (mixture of part P1 and of part P2) onto the metal part placed at the bottom of a pot.

(71) After 24 hours, the master was demolded.

(72) Six days after demolding the master, the negative molds were filled for the first time with polyurethane casting resin (reproduction material).

(73) The polyurethane resin used to evaluate the resistance of the silicone elastomer negative mold was Fastcast F190 resin from Axson. This resin is in the form of a bicomponent product which, once mixed at ambient temperature (1:1 mixture), has a pot life of 8 minutes and can be demolded after 90 minutes.

(74) Next, between 3 and 5 polyurethane replicas were produced each day, each time with approximately 12.5 of polyurethane resin. Each time, the replicas molded from resin were left in the silicone elastomer negative mold for a minimum of 1.5 hours in order to obtain complete polymerization.

(75) Demolding of the molded resin replicas was carried out by detaching each rim of the silicone elastomer negative mold, one after the other, in order to evaluate the resistance to demolding.

(76) The number of reproductions which were obtained without degradation of the silicone elastomer negative mold (i.e. without tearing off small pieces of silicone) is presented in one of the tables below. This enables the polyurethane resistance of the various silicone elastomer negative molds to be compared.

(77) The results of the various tests carried out were as follows:

(78) TABLE-US-00006 TABLE 6 The appearance of part P2 was observed visually. Reference Nature of catalyst Observations, part P2 P2-C1 Dimethyltin neodecanoate Transparent single-phase liquid P2-C2 Decylamine Transparent single-phase liquid P2-C3 Dodecylamine Liquid/solid, two-phase P2-1 Diisononylamine Transparent single-phase liquid P2-2 Diisononylamine Transparent single-phase liquid P2-3 Dioctylamine Transparent single-phase liquid P2-4 Dibutylamine Transparent single-phase liquid P2-5 Dihexylamine Transparent single-phase liquid P2-6 Didecylamine Transparent single-phase liquid P2-7 Didodecylamine Liquid/solid, two-phase

(79) TABLE-US-00007 TABLE 7 Curing kinetics Pot SAH SAH 24 h × Nature of life 24 h 4 days 14 days Post- 100/SAH Reference catalyst (min) Below Above Below Above Below Above curing 14 d (%) C1 Dimethyltin 193 19 23 27 28 28 28 +1 68 neodecanoate C2 Decylamine 669 Not NM Too Too 16 16 At 24 hrs, not cured soft. soft. yet cured NM NM C3 Dodecylamine 669 Not NM Too NM 14 14 At 24 hrs, not cured soft. yet cured Ex. 1 Diisononylamine 90 19 20 24 25 26 26 +2 73 Ex. 2 Diisononylamine 120 18 18 23 24 24 25 +1 75 Ex. 3 Dioctylamine 125 18 17 23 24 25 26 +2 72 Ex. 4 Dibutylamine 68 18 16 23 22 25 23 +2 72 Ex. 5 Dihexylamine 134 17 17 23 23 24 25 +1 71 Ex. 6 Didecylamine 109 17 18 23 24 25 26 +2 68 Ex. 7 Didodecylamine 92 19 20 24 25 25 26 +1 76 Ex. 10 Didecylamine 124 17 17 23 24 25 26 +2 68

(80) TABLE-US-00008 TABLE 8 Results of test for evaluating the adhesion of the silicone elastomer negative mold to different masters Composition Adhesion of silicone Reference employed Nature of negative mold for during catalyst used to to negative manufacture of in the polyurethane plaster mold negative mold composition (PU) master master MN C1 C1 Dimethyltin 0 0 neodecanoate MN C2 C2 Decylamine +++ +++ MN C3 C3 Dodecylamine +++ +++ MN 2 Ex. 2  Diisononylamine 0 0 MN 3 Ex. 3  Dioctylamine + 0 MN 5 Ex. 5  Dihexylamine + 0 MN 8 Ex. 8  Dibutylamine ++ +++ MN 10 Ex. 10 Didecylamine 0 0

(81) TABLE-US-00009 TABLE 9 Number of successive molding/demolding cycles (durability of silicone elastomer mold) Reference Composition Number of successive for employed during Nature of moldings/demoldings negative manufacture of catalyst used in of articles molded mold negative mold the composition from PU MN C1 C1 Dimethyltin 37 neodecanoate MN C2 C2 Decylamine Sticks to master - not evaluated MN C3 C3 Dodecylamine Sticks to master - not evaluated MN 1 Ex. 1  Diisononylamine 46 MN 2 Ex. 2  Diisononylamine 41 MN 3 Ex. 3  Dioctylamine 47 MN 8 Ex. 8  Dibutylamine 58 MN 9 Ex. 9  Dihexylamine 52 MN 11 Ex. 11 Diisononylamine 54

(82) In conclusion, the catalysts employed in the silicone compositions used during the preparation of silicone elastomer molds in accordance with the invention can be used to simultaneously obtain: a sufficiently long pot life to use the part P1+part P2 mixture (between 20 and 200 min), “fast” curing (post-curing a maximum+2 and SAH ratio of 24 h×100/SAH 14 days>68%), silicone elastomer molds obtained using the method in accordance with the invention which can be used to mold a large number of parts, for example from polyurethane (number of successive molding/demolding cycles>37), and all this in the absence of tin-based compounds.

(83) In order to satisfy the supplemental conditions that the part containing the catalyst must be homogeneous (transparent single phase) and that the silicone elastomer negative molds obtained by the method in accordance with the invention must not adhere to the master even in the absence of release agent applied to the master to be reproduced, the polycondensation catalysts C satisfy the general formula (I)
(R″).sub.2NH
in which the symbols R″, which may be identical or different, represent aliphatic hydrocarbon radicals containing 6 to 10 carbon atoms.