WO2018050707A1 - Solvent-free synthesis of silicone-polyurethane materials - Google Patents

Abstract

The invention relates to a method for the synthesis of a silicone-polyurethane material by means of the polyaddition of a pluri-isocyanate and a polysiloxane containing hydroxyl functions, of formula (I), in which: n is an integer greater than or equal to 1 and less than or equal to 70; R1 and R2 are hydrocarbon groups; R3, R4, R5 and R6 are hydrocarbon groups having between 1 and 18 carbon atoms.

Description

 Solvent-free Synthesis of Silicone / Polyurethane Materials

The invention relates to a process for synthesizing a silicone / polyurethane material by polyaddition, in particular for the encapsulation of electronic components.

 The encapsulation of electronic components generally aims to protect electronic components by covering them, enveloping them, or coating them with a suitable material, for their long-term operation under the conditions of their use, whether it is an individual electronic component or, a fortiori, a set of components integrated into an electronic module.

 To do this, the use of polymeric materials is appropriate for the simplicity of their implementation, which involves in-situ hardening of the material, by polymerization of the constituents of a monomer composition previously applied in covering the products to be protected.

 In order for the materials obtained to be of suitable quality for the encapsulation of electronic components, they are required to be resistant to operating conditions in terms of temperature and stability over time. The operating temperatures to be supported are in the temperature range above 150 ° C.

 Other qualitative requirements for these products include chemical resistance, water and moisture resistance, thermal and electrical insulation capacity.

 Polyurethane resins have the required mechanical properties, but their moisture recovery is too high for application as an encapsulant. In addition, their thermal stability is lower than that of silicone resins. The latter, for their part, are highly hydrophobic and have very good chemical and thermal stability. However, they are less impact resistant than polyurethane resins.

Materials combining Silicone and Polyurethane have already been synthesized to combine the properties of these two polymers while mitigating their defects. The synthetic route explored by Ebdon et al. is the development of architecture of interpenetrating networks of polymers (IP) associating a silicone network obtained from α, ω-dihydroxy-poly (dimethylsiloxane) crosslinked with tetraethoxysilane (TEOS) (polycondensation reaction giving rise to a release of ethanol) and a polyurethane network.

However, the immiscibility of the precursors does not make it possible to obtain homogeneous materials, since a significant phase separation is observed. Other RIPs were synthesized using poly (phenylmethylsiloxane) (PPMS) in place of a poly (dimethylsiloxane) (PDMS). In this case, the phase separation between the polyurethane and the polysiloxane is reduced, and more homogeneous materials have been obtained.

 These syntheses however require the use of solvent.

 Interpenetrated networks of polymers combining a polyurethane network (PUMA) and a Silicon (Si) network have also been synthesized by Vuillequez et al. The PUMA network is obtained by UV-initiated radical polymerization of a multi-methacrylate in the presence of the precursors of the silicone network. The silicone network is synthesized by polycondensation between α, ω-dihydroxypolydimethylsiloxane and ω-methacryloxypropyl trimethoxy silane (crosslinking agent). Due to the presence of the methacrylate functions on the crosslinking agent, the two networks are then linked to each other.

 The synthesized materials do not contain more than 6% silicone.

 The formation reaction of the silicone network leads to the release of alcohol during the synthesis. In addition, their synthesis is long (24h at 150 ° C).

 Another way to combine Silicone and Polyurethane in a material, is the synthesis of semi-interpenetrating polymer networks (semi-RIP). Byczynski et al. have immobilized a linear polyurethane in a siloxane material crosslinked with a diamine. Materials with higher thermal stability than polyurethane have been obtained.

 It is important to note that in all these works, the syntheses are carried out in the presence of solvent, which greatly facilitates the miscibility of the precursors. However, in the case of the encapsulation of electronic components, it is preferable not to use a solvent as this may damage the components to be encapsulated.

 Finally, recently, Byczynski et al have developed a material combining silicone and polyurethane, without using a solvent. Previously, the copolymer copoly (dimethyl) (methyl, hydroxypolyoxyethylene-propyl) siloxane (PSPEG) is prepared by a hydrosilylation reaction between polyoxyethylene allyl ether terminated by hydroxyl functions and a co-poly (dimethyl) (methyl hydrogen) siloxane). The silicone and polyurethane combining material is finally obtained by reacting PSPEG with different diisocyanate compounds.

However, these materials contain polyethylene oxide grafts that promote water recovery. In addition, their thermal degradation temperatures recorded at 5% mass loss is only 215 ° C. The properties of this material therefore do not allow its use as encapsulant of electronic compounds. The object of the present invention is to provide a solvent-free synthesis process of a silicone / polyurethane material that can be used as an encapsulant for electronic compounds.

The invention thus proposes a process for synthesizing a silicone / polyurethane material by polyaddition between a polyisocyanate and a polysiloxane containing hydroxyl functions of formula (I),

 in which :

 n is an integer greater than or equal to 1 and less than or equal to 70,

 R1 and R2 are hydrocarbon groups,

 R3, R4, R5 and R6 are hydrocarbon groups having from 1 to 18 carbon atoms.

Advantageously, the synthesis process according to the invention is simple, can be carried out directly in contact with the components to be encapsulated and makes it possible to obtain a silicone / polyurethane material whose physicochemical properties make it a good encapsulant.

The process according to the invention may also comprise one or more of the following characteristics, considered individually or in any technically possible combination:

 the multi-isocyanate is of formula (II),

dans lequel R7, R8 et R9 sont des groupements hydrocarbonés ; et/ou

wherein R7, R8 and R9 are hydrocarbon groups; and or

the process according to the invention is remarkable in that it is solvent-free, and / or the method comprises a mixing step in which the multi-isocyanate and the polysiloxane are mixed for a time t1, and a heating step in which the mixture undergoes a thermal program for a time t2 at a temperature T1; and or

the NCO function concentration ratio resulting from the polyisocyanate and the OH function concentration resulting from the polysiloxane is greater than or equal to 1 and less than or equal to 1.6; and or

n is greater than or equal to 8 and less than or equal to 21; and or

the mixing time t1 is determined so as to obtain a dynamic viscosity mixture of less than or equal to 1.5 Pa.s; and or

the mixing time t1 is greater than or equal to 1 min and less than or equal to 2h; and / or the temperature T1 is greater than or equal to 50 ° C and less than or equal to 90 ° C and the time t2 sufficiently high to obtain the temperature T1 at the heart of the mixture; and / or the time t2 is greater than or equal to 5min and less than or equal to 4h; and or

the heating program comprises a first part at a temperature T1A greater than or equal to 50 ° C and less than or equal to 70 ° C for a time t2A greater than or equal to 5min and less than or equal to 20min and then a second part a higher temperature T1B or equal to 70 ° C and less than or equal to 90 ° C for a time t2B greater than or equal to 1 min and less than or equal to 15 min; and or

the OH group of the formula (I) is terminal or located in the hydrocarbon groups RI, R2; and or

at least one, for example all, hydrocarbon groups R3, R4, R5 and R6 comprises an OH group of the formula (I) located at the end of the hydrocarbon groups; and or

 R3, R4, R5 and R6 are alkyls having 1 to 12 carbon atoms and / or aryls having 6 to 18 carbon atoms; and or

the groups R1 and R2 are hydrocarbon groups containing heteroatoms; and or

the groups R1 and R2 are hydrocarbon groups not containing heteroatoms; and or

the groups R7, R8 and R9 are hydrocarbon groups containing heteroatoms; and or

the groups R7, R8 and R9 are hydrocarbon groups not containing heteroatoms; and or the groups R 1 and R 2 are alkyls having 1 to 10 carbon atoms and / or ethers having 2 to 20 carbon atoms and / or esters having 2 to 20 carbon atoms; and or

 the groups R 1 and R 2 are propyls and / or ethers having 5 carbons; and / or - the groups R3, R4, R5 and R6 are methyls and / or phenyls; and or

 the groups R7, R8 and R9 are alkyls having from 1 to 12 carbon atoms and / or aryls having from 6 to 18 carbon atoms; and or

 the groups R7, R8 and R9 are alkyls having 6 carbons; and or

 the mixture of the polyisocyanate and the polysiloxane is carried out in the presence of a suitable catalyst for the synthesis of polyurethane; and or

 the catalyst used is dibutyl tin dilaurate (DBTDL); and or

 the concentration ratio of the catalyst adapted for the polyurethane synthesis relative to the OH function concentration of the compound (I) used is greater than or equal to 0.1% and less than or equal to 10%; and or

 the polyisocyanate is an oligomer of hexamethylene diisocyanate (PHMDI); and / or the mixture is poured into a housing having electronic components and associated link circuits before undergoing the thermal program.

The invention also relates to a silicone / polyurethane material, in particular intended for the encapsulation of electronic compounds, for example obtained by the process according to the invention.

 The Silicone / Polyurethane material may include one or more of the following features, considered individually or in any combination:

 the soluble fraction calculated after 72 hours of hot extraction with chloroform is greater than or equal to 1% by weight and less than or equal to 70% by weight; and / or the hardness expressed in Shore A is greater than or equal to 5 and less than or equal to 50; and or

 the humidity recovery expressed according to ISO 62 is less than or equal to 2%; and or

the degradation temperature in air expressed at 5% mass loss is greater than or equal to 240 ° C and less than or equal to 285 ° C. Finally, the invention relates to an electronic module obtained according to the method in which the mixture is cast in a housing comprising electronic components and associated link circuits before undergoing the thermal program.

The present invention will be better understood in the light of the following description which is given for information only and which is not intended to limit said invention, accompanied by the following figures.

 FIG. 1 is a representation of the various steps of the synthesis method according to the invention,

 FIG. 2 represents an exemplary structure of Silicone / Polyurethane material obtained according to a synthesis method according to the invention,

 FIG. 3 represents the influence of the number of siloxane groups (n) on the isothermal aging at 150 ° C. of the Silicone / Polyurethane material obtained, and FIG. 4 represents the influence of the nature of the spacer (R1 and R2). on the aging of the material Silicone / Polyurethane obtained.

The synthesis process according to the invention does not require the use of a solvent and makes it possible to obtain materials combining Silicone and Polyurethane.

 The reaction between the polyisocyanate and the polysiloxane is a step polymerization, more particularly a polyaddition. The polyaddition reaction does not release products during the reaction. The synthetic process consists in creating the polyurethane groups during the synthesis of the materials from the polyaddition between a polysiloxane containing hydroxyl functions and a polyisocyanate.

 As illustrated in FIG. 1, the polyaddition is a simple synthesis that can comprise a mixing step E1 in which the multi-isocyanate and the polysiloxane are mixed and a heating step E2 during which the mixture undergoes a thermal program.

 FIG. 2 is an exemplary structure of the silicone / polyurethane material obtained by the synthesis method according to the present invention.

 The polysiloxane used in the synthesis process according to the invention is of formula (I),

dans lequel :

in which :

 n is an integer greater than or equal to 1 and less than or equal to 70,

 R1 and R2 are hydrocarbon groups,

 R3, R4, R5 and R6 are hydrocarbon groups having from 1 to 18 carbon atoms.

According to one embodiment of the invention, the groups R3, R4, R5 and R6 are alkyls having from 1 to 12 carbon atoms and / or aryls having from 6 to 18 carbon atoms.

 According to a preferred embodiment, n is greater than or equal to 8 and less than or equal to 21.

 As illustrated in FIG. 3, it can be seen that the number of siloxane groups (n) has an influence on the aging of the silicone / polyurethane material obtained. Indeed, the higher n, the higher the thermal stability.

 The presence of the OH group in the polysiloxane is essential to allow the polyaddition reaction. The proportion of urethane in the silicone / polyurethane material can be modulated according to the number of OH functions in the polysiloxane, or the length of the chain when it is telechelic. A polymer is said telechelic when it is capable of undergoing a subsequent polymerization due to the presence of reactive groups at each of the two ends of the chain.

 The OH group of the formula (I) may be terminal or located in the hydrocarbon groups R 1, R 2.

 Alternatively, the OH group of the formula (I) may be located at the end of the hydrocarbon groups R3, R4, R5 and R6. The groups R1 and R2 are called "spacers". The groups R1 and R2 may be hydrocarbon groups containing or not heteroatoms.

 These same groups R 1 and R 2 can in particular be alkyls having 1 to 10 carbon atoms and / or ethers having 2 to 20 carbon atoms and / or esters having 2 to 20 carbon atoms.

 According to a preferred embodiment, the groups R 1 and R 2 are propyls and / or ethers having 5 carbons.

 As illustrated in FIG. 4, it can be seen that the nature and the size of these spacers have an influence on the aging of the Silicone / Polyurethane material obtained. Indeed, the spacers with an ether function are more stable than the spacers with an alkyl function.

The groups R3, R4, R5 and R6 may be methyls and / or phenyls. The multi-isocyanate used in the synthesis process according to the invention is of formula (II),

dans lequel R7, R8 et R9 sont des groupements hydrocarbonés.

wherein R7, R8 and R9 are hydrocarbon groups.

 The groups R7, R8 and R9 may be hydrocarbon groups containing or not heteroatoms.

 These groups R7, R8 and R9 can be alkyls having 1 to 12 carbon atoms and / or aryls having 6 to 18 carbon atoms.

 According to a preferred embodiment, the groups R7, R8 and R9 are alkyls having 6 carbons.

 The polyisocyanate used can also be an oligomer of hexamethylene diisocyanate.

 The polyisocyanate used is chosen so as to be soluble with the polysiloxane used.

The synthesis process according to the invention is a polyaddition reaction comprising the following steps:

 a mixing step during which the multi-isocyanate and the polysiloxane are mixed for a time t1,

 a heating step during which the mixture undergoes a thermal program for a time t2 at a temperature T1.

 The concentration ratio of NCO functions derived from the polyisocyanate and the concentration of OH functions derived from the polysiloxane may be greater than or equal to 1 and less than or equal to 1.6.

The duration of the mixture influences the homogeneity of the Silicone / Polyurethane material obtained. The homogeneity of the material is important for its use as an encapsulant of electronic components. The time t1 is therefore decisive with regard to the physical properties of the material obtained. The mixing time t1 is determined so as to obtain a mixture of dynamic viscosity less than or equal to 1.5 Pa.s. In the example described here, this viscosity is measured using a rheometer having a cone-plane type geometry.

 The mixing time t1 may be greater than or equal to 1 min and less than or equal to 2h. The heating temperature is decisive for obtaining the material

Silicone / polyurethane. Indeed, the polyaddition requires particular temperature conditions to take place.

 The temperature T1 may be greater than or equal to 50 ° C. and less than or equal to 90 ° C. and the time t 2 sufficiently high to obtain the temperature T1 at the heart of the mixture.

 The time t2 may be greater than or equal to 5min and less than or equal to 4h.

 According to a preferred embodiment, the heating program comprises a first portion at a temperature T1 A greater than or equal to 50 ° C and less than or equal to 70 ° C for a time t2A greater than or equal to 5min and less than or equal to 20min then a second portion at a TIB temperature greater than or equal to 70 ° C and less than or equal to 90 ° C for a time t2B greater than or equal to 1 min and less than or equal to 15 min.

The polyaddition reaction between the polyisocyanate and the polysiloxane according to the present invention can also be carried out in the presence of a suitable catalyst for the synthesis of polyurethane. The presence of a catalyst makes it possible to reduce the mixing time and the heating time required to obtain a silicone / polyurethane material.

 The concentration ratio of the catalyst suitable for the polyurethane synthesis relative to the OH function concentration of the compound (I) used may be greater than or equal to 0.1% and less than or equal to 10%.

 Said catalyst may be dibutyl tin dilaurate (DBTDL).

The invention also relates to a silicone / polyurethane material, in particular intended for the encapsulation of electronic compounds, for example obtained by the process according to the invention.

 The purified fraction of said Silicone / Polyurethane material calculated after 72 hours of hot extraction with chloroform may be greater than or equal to 1% by weight and less than or equal to 70% by weight.

The hardness of the Silicone / Polyurethane material expressed in Shore A may be greater than or equal to 5 and less than or equal to 50. The moisture recovery of the Silicone / Polyurethane material expressed according to the ISO 62 standard may be less than or equal to 2%.

 The degradation temperature of the Silicone / Polyurethane in air material expressed at 5% mass loss may be greater than or equal to 240 ° C and less than or equal to 285 ° C.

 The physicochemical properties of this material make it a suitable material for the encapsulation of electronic components.

Advantageously, the synthesis method according to the invention can be carried out directly in contact with the components to be encapsulated.

 Thus, according to a preferred embodiment, the mixture obtained after the mixing step is poured into a housing comprising electronic components and associated connecting circuits before undergoing the thermal program. The encapsulation of the electronic components and the polymerization of the material are then carried out simultaneously.

 The present invention also relates to the electronic module thus obtained.

The following synthetic method examples of a silicone / polyurethane material are given for information only and do not constitute a limitation.

Example 1

In the mixing step, 1.00 g (2.00 × 10 ^-3 mol OH) of polydimethylsiloxane terminated with hydroxyl ether functions (PDMS ether OH - n = 9), 0.40 g (2.2 × 10 ^-3 mol). NCO) of poly (hexamethylene diisocyanate) (PHMDI) and 0.13 g (2.00 × 10 ^-5 mol) of dibutyltin dilaurate (DBTDL) at 10% by weight in chloroform are placed in a pillbox and stirred with a magnetic stirrer during 5min During stirring, the reaction mixture is placed under dynamic vacuum.

 Then follows the heating step in which the mixture is poured into an aluminum cup to be placed 10 min at 60 ° C and 5 min at 80 ° C. After the thermal program, an opaque white material is obtained.

The material thus obtained is then characterized according to its physicochemical properties.

The soluble fraction of the material, calculated after 72 hours of hot extraction with chloroform is 5% by mass. The hardness of the material expressed in Shore A is 30.

 The moisture recovery of the material expressed according to the ISO 62 standard is 0.6%.

 The air degradation temperature of the material, expressed at 5% mass loss, is 280 ° C. with an air flow at 20 ° C./min of heating rate.

 The loss of mass of the material during its exposure time at a constant temperature of 150 ° C. in air is illustrated in FIG. 4 by the "Si 9 ether PU" curve.

Example 2: During the mixing step, 1.00 g (2.3 × 10 ^-3 mol of OH) of PDMS alkyl OH (PDMS alkyl OH - n = 9), 0.45 g (2.5 × 10 ^-3 mol of NCO) of PHMDI and 0.15 g (2.3.10 ^"5 mol) of 10% DBTDL) in bulk in chloroform are placed in a pill box and stirred with a magnetic stirrer for 5 minutes. dynamic vacuum.

 Then follows the heating step in which the mixture is poured into an aluminum cup to be placed 10 min at 60 ° C and 5 min at 80 ° C. After the thermal program, an opaque white material is obtained.

The material thus obtained is then characterized according to its physicochemical properties.

 The soluble fraction of the material, calculated after 72 hours of hot extraction with chloroform is 15% by weight.

 The hardness of the material expressed in Shore A is 30.

 The moisture recovery of the material expressed according to ISO 62 is 1.7%.

 The air degradation temperature of the material, expressed at 5% mass loss, is 245 ° C. with a flow of air at 20 ° C./min of heating rate.

 The loss of mass of the material during its exposure time at a constant temperature of 150 ° C in air is illustrated in Figures 3 and 4 by the curve "Si 9 alkyl PU". Example 3

During the mixing step, 1.00 g (1.1 × 10 ^-3 mol of OH) of PDMS alkyl OH (n = 18), 0.22 g (1.2 × 10 ³ mol of NCO) of PHMDI and 0.0734 g (1 1.10 ^"5 mol) of DBTDL at 10% by weight in chloroform are placed in a pill box and stirred with a magnetic stirrer for 5min. During stirring, the reaction mixture is placed under dynamic vacuum.

 Then follows the heating step in which the mixture is poured into an aluminum cup to be placed 10 min at 60 ° C and 5 min at 80 ° C. After the thermal program, an opaque white material is obtained.

The material thus obtained is then characterized according to its physicochemical properties.

 The soluble fraction of the material, calculated after 72 hours of hot extraction with chloroform is 15% by weight.

 The hardness of the material expressed in Shore A is 32.

 The moisture recovery of the material expressed according to the ISO 62 standard is 1.6%.

 The air degradation temperature of the material expressed at 5% mass loss is 265 ° C with an air flow at 20 ° C / min heating rate.

Example 4

In the mixing step, 5.0 g (1.0 × 10 ^-2 mol OH) of PDMS ether OH (n = 8), 2.0 g (1.1 × 10 ^-2 mol of NCO) of PHMDI and 0.33 g (5.0 × 10 ⁵ mol) DBTDL at 10% by weight in chloroform are placed in a pill box and stirred with a magnetic stirrer for 5 min During stirring, the reaction mixture is placed under dynamic vacuum.

 Then follows the heating step in which the mixture is poured into a power module which is then placed in an oven for 10 min at 60 ° C and then 5 min at 80 ° C. After the thermal program, an opaque white material covers all the electrical components of the power module.

The invention has been described above with the aid of embodiments without limitation of the general inventive concept.

Many other modifications and variations are suggested to those skilled in the art, after reflection on the various embodiments illustrated in this application. These embodiments are given by way of example and are not intended to limit the scope of the invention, which is determined exclusively by the claims below. In the claims, the word "comprising" does not exclude other elements or steps, and the use of the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are enumerated in mutually dependent claims does not indicate that a combination of these features can be advantageously used. Finally, any numerical reference used in the claims should not be interpreted as limiting the scope of the invention.

Claims

A process for synthesizing a silicone / polyurethane material by polyaddition between a multisocyanate and a polysiloxane containing hydroxyl functions of formula (I),

in which :  n is an integer greater than or equal to 1 and less than or equal to 70,  R1 and R2 are hydrocarbon groups,  R3, R4, R5 and R6 are hydrocarbon groups having from 1 to 18 carbon atoms. 2. Process for synthesizing a silicone / polyurethane material according to the preceding claim, in which the multi-isocyanate is of formula (II),

wherein R7, R8 and R9 are hydrocarbon groups. 3. Process for synthesizing a silicone / polyurethane material according to one of the preceding claims, in which the OH group of the formula (I) is terminal or located in the hydrocarbon groups R 1 and / or R 2. 4. A method of synthesizing a silicone / polyurethane material according to one of the preceding claims, wherein at least one of the hydrocarbon groups R3, R4, R5 and R6 comprises an OH group located at the end of said at least one hydrocarbon group. Process for the synthesis of a silicone / polyurethane material according to one of claims 1 to 3, in which R 3, R 4, R 5 and R 6 are alkyls having from 1 to 12 carbon atoms and / or aryls having from 6 to 6 carbon atoms. at 18 carbon atoms. 6. Process for synthesizing a silicone / polyurethane material according to one of the preceding claims, comprising the following steps:  a mixing step during which the multi-isocyanate and the polysiloxane are mixed for a time t1,  a heating step during which the mixture undergoes a thermal program for a time t2 at a temperature T1. 7. Process for synthesizing a silicone / polyurethane material according to one of the preceding claims, in which the NCO function concentration ratio resulting from the polyisocyanate and from the polysiloxane OH functional concentration is greater than or equal to 1. and less than or equal to 1.6. 8. A method of synthesizing a silicone / polyurethane material according to one of the preceding claims, wherein n is greater than or equal to 8 and less than or equal to 21. 9. A method of synthesizing a silicone / polyurethane material according to claim 6 or one of claims 7 to 8 taken together with claim 6, wherein the mixture obtained at the end of the mixing step has a viscosity. dynamic less than or equal to 1.5 Pa.s. 10. A method of synthesizing a silicone / polyurethane material according to one of claims 6 to 9, wherein the temperature T1 of the mixture is greater than or equal to 50 ° C and less than or equal to 90 ° C. 11. A method of synthesizing a silicone / polyurethane material according to one of claims 6 to 10, wherein the mixture is poured into a housing comprising electronic components and associated connecting circuits before undergoing the thermal program. 12. Silicone / polyurethane material obtained by the process according to one of the preceding claims.  13. Electronic module obtained according to the method according to claim 11.