Method for promoting adhesion of plastic to oil-bleeding liquid silicone

Abstract

A method of manufacturing an electrical connector and an electrical connector having a layer or primer applied to a connector housing, the layer or primer having a free radical initiator dissolved in the layer or primer. An oil-bleeding liquid silicone is applied to the layer or primer. The layer or primer is crosslinked with the oil-bleeding liquid silicone to attach the oil-bleeding liquid silicone. The method includes applying a layer or primer having a free radical initiator dissolved therein to a housing; applying an oil-bleeding liquid silicone to the primer; and crosslinking the oil-bleeding liquid silicone to the layer or primer to attach the oil-bleeding silicone.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method of improving adhesion between a plastic and an oil-bleeding liquid silicone. In particular, the present invention relates to the use of a free radical initiator in a primer, a separate layer of oil-bleeding liquid silicone, or the oil-bleeding liquid silicone itself to improve adhesion to a plastic. It is believed that the free radical initiator promotes localized cross-linking at the interface between two adjacent layers without sacrificing the oil-bleeding properties of the liquid silicone. BACKGROUND

[0002] Connectors used in various industries such as automotive, electrical, and aerospace often benefit from the attachment of an oil-bleeding liquid silicone to the housing of the connector to provide both a bonding and lubricating function. While oil-bleeding liquid silicones can be applied to and directly attached to many connector housings or substrates, the oil-bleeding liquid silicones do not attach well to housings or substrates that can have acidic properties due to additives (e.g., flame retardant additives) added to the plastic housing.

[0003] Accordingly, it is desirable to develop an application method that allows an oil-bleeding liquid silicone to attach to a polymeric housing. Alternatively, it is desirable to use a primer in conjunction with a free radical initiator that allows an oil-bleeding liquid silicone to attach to a polymeric housing and allows the oil-bleeding liquid silicone to maintain its lubricating function. Alternatively, it is desirable to use a free radical initiator in the oil-bleeding liquid silicone itself to promote adhesion. SUMMARY

[0004] An embodiment relates to an electrical connector. The electrical connector has a housing comprising a polymeric composition having an additive. A primer having a free radical initiator dissolved therein is applied to the housing. An oil-bleeding liquid silicone is applied to the primer. The primer attaches to the housing, and the primer cross-links with the oil-bleeding liquid silicone at the interface between the primer and the oil-bleeding silicone, thereby attaching the oil-bleeding liquid silicone to the primer.

[0005] An embodiment relates to a method of manufacturing an electrical connector housing having a polymeric composition with an additive. The method includes applying a primer having a free radical initiator dissolved therein to the housing, attaching the primer to the housing, applying an oil-bleeding liquid silicone to the primer, and cross-linking the oil-bleeding liquid silicone with the primer at the interface between the primer and the oil-bleeding silicone so as to attach the oil-bleeding liquid silicone to the primer.

[0006] An embodiment relates to a method of manufacturing an electrical connector housing having a polymeric composition with an additive. The method includes dissolving a free radical initiator in an oil-bleeding liquid silicone and applying the oil-bleeding liquid silicone having the free radical initiator dissolved therein to the housing.

[0007] An embodiment relates to an electrical connector. The electrical connector has a housing having a polymeric composition with an additive. A primer with or without a free radical initiator is applied to the housing. A layer of an oil-bleeding liquid silicone with a free radical initiator dissolved therein is applied to the primer. An oil-bleeding liquid silicone without a free radical initiator dissolved therein is applied to the layer of the oil-bleeding liquid silicone with the free radical initiator. The primer is adhered to the housing and the layer of the oil-bleeding liquid silicone with the free radical initiator is adhered to the primer. The layer of the oil-bleeding liquid silicone with the free radical initiator is cross-linked with the oil-bleeding liquid silicone without a free radical initiator dissolved therein at an interface between the two layers to adhere the oil-bleeding liquid silicone without the free radical initiator to the layer of the oil-bleeding liquid silicone with the free radical initiator.

[0008] In yet another embodiment, an electrical connector has a housing having a polymeric composition with an additive. A primer is applied to the housing. An oil-bleeding liquid silicone with a free radical initiator is applied to the primer.

[0009] In yet another embodiment, an electrical connector has a housing having a polymeric composition with an additive. A primer is applied to the housing. An oil-bleeding liquid silicone with a free radical initiator is applied to the primer.

[0010] The principles of the application will be further explained with reference to the following illustrative embodiments, with reference to the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic cross-sectional view showing a primer and cross-linking of an oil-bleeding liquid silicone of the present application.

[0012] Figure 2 is a schematic view of a method of using a primer of the present application to bond an oil-bleeding liquid silicone to a surface of a housing.

[0013] Figure 3 is a schematic view of a method of bonding an oil-bleeding liquid silicone with a free radical initiator dissolved therein to a surface of a housing.

[0014] Figure 4 is a schematic cross-sectional view showing a primer, and a layer of an oil-bleeding liquid silicone mixed with a free radical initiator on the primer layer, and a layer of an oil-bleeding liquid silicone applied to the layer of the oil-bleeding liquid silicone mixed with the free radical initiator.

[0015] Figure 5 is a schematic view of a method of using a primer without a free radical initiator dissolved therein and a layer of an oil-bleeding silicone mixed with a free radical initiator to bond the oil-bleeding liquid silicone to a surface of a housing according to the present application.

[0016] Figure 6 is a schematic diagram of a method according to the present application for bonding an oil-bleeding liquid silicone to a surface of a housing using a primer in which a radical initiator is dissolved and a layer of an oil-bleeding silicone mixed with a radical initiator.

[0017] Figure 7 is a schematic cross-sectional view showing a primer on a housing and a layer of an oil-bleeding liquid silicone with a radical initiator applied to the primer. DETAILED DESCRIPTION

[0018] The description of illustrative embodiments according to the principles of the application is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the application disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present application. Relative terms such as "lower," "upper," "horizontal," "vertical," "above," "below," "up," "down," "top" and "bottom" as well as derivative thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated otherwise. Terms such as "attached," "fixed," "connected," "coupled," "interconnected" and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly, through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.

[0019] The term "locally cross-linked" or "cross-linked" / "cross-linking" refers to a situation where the radical initiator in a layer induces a chemical bond or linkage between two adjacent layers to form an interface between the two layers. The term "non-cross-linked" / "non-cross-linking" refers to a situation where no chemical bond or linkage is formed between two adjacent layers.

[0020] Furthermore, the features and benefits of the application are illustrated by reference to the preferred embodiments. Accordingly, the application expressly should not be limited to such preferred embodiments or the embodiments presented in this summary, which are intended to be illustrative only. Rather, the scope of the application is as set forth in the claims.

[0021] In various different applications, it is beneficial to provide an oil-bleeding liquid silicone to a housing of an electrical connector. The housing is formed from a polymeric composition with additives. The oil-bleeding liquid silicone provides both sealing and lubrication in order to reduce insertion force. This can be advantageous in various different environments or fields including, but not limited to, the automotive and aerospace industries.

[0022] In many applications, lipophilic liquid silicone can be directly bonded or adhered to the surface of a housing, which may be made of a plastic or polymeric composition containing additives. For example, for horizontal burn (HB) grade plastics typically used for housings (plastics that have already obtained an HB rating according to the UL 94 flammability standard), lipophilic liquid silicone will adhere adequately to the HB grade plastic to provide the required bonding and lubrication. However, in other applications where the plastic develops an acidic surface due to blooming in the plastic caused by additives (such as, but not limited to, flame retardant additives for V-0 grade plastics according to the UL 94 flammability standard), lipophilic liquid silicone may not adhere properly to the plastic. Therefore, a primer layer is required to provide proper bonding between the plastic housing and the lipophilic liquid silicone.

[0023] like Figure 1 As shown, a primer 10 is disposed between the housing 12 of the connector 14 and an oil-permeable liquid silicone 16. The housing 12 contains a polymer component containing additives. In the illustrated embodiment, the housing is made of V-0 grade plastic. V-0 plastic can be any desired plastic, including but not limited to: polyamides (PAs), such as PA6, PA66, PA66 / 6T, PA4T, PA9T, PA10T, PA11, PA610; and polyesters, such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). The V-0 grade plastic has one or more flame-retardant additives, such as, but not limited to, phosphonate-based flame retardants, which cause the surface of the housing to be acidic. The acidic surface has a pH less than 7.0.

[0024] The oil-bleeding silicone contains a small amount of uncured silicone in the cured silicone matrix that can migrate to the surface to provide lubrication. Another name for oil-bleeding silicone is self-lubricating silicone. The oil-bleeding liquid silicone 16 can be, but is not limited to, ELASTOSIL LR 3844 / 30 manufactured by Wacker Chemie AG. The oil-bleeding silicone can include, but is not limited to, 1% oil, 2% oil, 4% oil, 5% oil, 6% oil, such as from 1% to 6% oil, including from 4% to 6% oil. Other oil-bleeding liquid silicones include ELASTOSIL LR 3856 / 30 from Wacker Chemie AG, Silopren LSR 3596 / 30 from Momentive, and SILASTIC 9204-35 from Dow Inc. Other elastomers such as ethylene propylene diene rubber (EPDM), thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), and the like can also be used in the method. Many oil-bleeding silicones are platinum cure systems. Preferably, no free radical initiator is added to the oil-bleeding silicone itself because the addition of a free radical initiator tends to decrease the effectiveness of the oil-bleeding silicone.

[0025] The primer 10 has a free radical initiator mixed into the primer solution. In an illustrative embodiment, the primer matrix is a solution of reactive siloxane and silane in an organic solvent. The primer matrix can be, for example, Primer G 790 manufactured by Wacker Chemie AG.

[0026] In various embodiments, a free radical initiator is mixed into the primer solution. A free radical initiator is a substance that can generate free radical species and promote free radical reactions under mild conditions. Examples of free radical initiators include, but are not limited to, peroxides and azo radical initiators (e.g., azobisisobutyronitrile (AIBN)). In some embodiments, the free radical initiator is a peroxide dissolved in the primer 10 before the primer 10 containing the free radical initiator is applied to the housing 12. The primer 10 contains between about 0.3% and about 15% of the free radical initiator by weight, and preferably between about 1% and about 10% by weight. The primer 10 is applied to the housing 12 with a thickness between about 0.1 μm and about 100 μm, and preferably between about 1 μm and about 50 μm. If the free radical initiator is a peroxide, then the peroxide can be, but is not limited to, dicumyl peroxide, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, di-tert-butyl peroxide, tert-Butyl peroxybenzoate, etc.

[0027] The free radical initiator in primer 10 induces chemical bonding between primer 10 and the oil-soaked liquid silicone 16. The free radical initiator in primer 10 can also increase the crosslinking density at the interface 20 between the primer and the oil-soaked silicone 16. For example... Figure 1 As shown, the chemical bonding between the primer and the oil-permeable liquid silicone 16 occurs only at the interface 20 of the oil-permeable liquid silicone 16. As illustrated, interface 20 is located in the region between the primer 10 and the oil-permeable liquid silicone 16. This allows the oil-permeable liquid silicone 16 to adhere to the primer 10 and the housing 12 without adversely affecting the release of oil from the non-crosslinked regions 22 of the oil-permeable liquid silicone 16.

[0028] like Figure 2 As shown, a method 100 for bonding oil-permeable liquid silicone 16 to an acidic surface of a housing 12 made of polymer components includes: cleaning the surface of the housing 12 (step 102); dissolving a free radical initiator in a primer 10 (step 104); applying the primer 10 to the surface of the housing 12 (step 106); allowing the primer 10 to dry (step 108); and applying the oil-permeable liquid silicone 16 to the primer 10 (step 110).

[0029] The surface of the housing 12 to which the primer will be applied must be dry and free of grease, oil, wax, dirt, or other contaminants. The surface should be cleaned by physical cleaning such as plasma, corona, etc. or by chemical cleaning using solvents such as, but not limited to, isopropyl alcohol (IPA), acetone, or ethanol. Other surface treatment methods such as sandblasting, metal brushes, chemical etching, etc. can also be used to promote adhesion.

[0030] Once the surface of the housing 12 is cleaned and the primer is properly prepared with between about 0.3% and about 15% by weight of the primer of a free radical initiator, the primer 10 can be applied by spraying, dipping or immersion, blade coating or brushing or other suitable method. The primer 10 should be properly bonded to the housing 12 as thin as possible and free of air bubbles, but with sufficient thickness to crosslink with the oil- penetrating liquid silicone 16. The primer 10 is applied in a layer of between about 0.1 μιη and about 100 μιη in thickness, as previously described.

[0031] Drying of the primer 10 allows the primer 10 to firmly adhere to the surface of the housing 12. The length of the drying time depends on the application and the environment in which the drying occurs.

[0032] The oil-penetrating liquid silicone 16 is then applied to the primer after the drying process. The length of the drying time depends on the application and the environment in which the drying occurs. Initial adhesion immediately after curing of the silicone is strong in many cases.

[0033] The use of a free radical initiator dissolved in the primer 10 allows the oil-penetrating liquid silicone 16 to be bonded to the acidic surface of the polymeric component of the housing 12 without the need to change the composition of the oil-penetrating liquid silicone 16. This allows the same oil-penetrating liquid silicone 16 to be used for housings or substrates with acidic surfaces as well as for housings or substrates with non-acidic surfaces. The crosslinked region or interface 20 between the primer 10 and the oil-penetrating liquid silicone 16 also allows the oil-penetrating liquid silicone 16 to provide the proper lubricating function by releasing oil.

[0034] An alternative method of attaching the oil-penetrating liquid silicone 16 to the housing 12 is shown in Figure 3 In this method, the free radical initiator is dissolved directly in the oil-penetrating liquid silicone 16. No primer is used. The oil-penetrating liquid silicone 16 contains between about 0.01% and about 5% by weight of the free radical initiator and preferably contains between about 0.1% and about 2% by weight of the free radical initiator. The oil-penetrating liquid silicone 16 is applied to the housing 12 containing a polymeric component in the desired thickness required for that oil-penetrating liquid silicone 16 in order to provide sufficient protection and lubrication to the housing 12. The free radical initiator in the oil-penetrating liquid silicone 16 enhances the adhesion between the oil-penetrating liquid silicone 16 and the polymeric component of the housing 12.

[0035] As Figure 3 shown, the method 200 of incorporating the oil-bleeding liquid silicone 16 onto the acid surface of the housing 12 includes cleaning the surface of the housing 12 (step 202), dissolving a free radical initiator in the oil-bleeding liquid silicone 16 (step 204), and applying the oil-bleeding liquid silicone 16 having the free radical initiator dissolved therein onto the surface of the housing 12 (step 206).

[0036] The surface of the housing 12 to which the oil-bleeding liquid silicone 16 is applied must be dry and free of grease, oil, wax, dirt, or other contaminants. The surface should be cleaned as described above. Once the surface of the housing 12 is cleaned and the oil-bleeding liquid silicone 16 is properly prepared with between about 0.01% and about 5% by weight of the free radical initiator in the primer, the oil-bleeding liquid silicone 16 can be applied by spraying, dipping or immersion, blade coating or brushing, or other suitable method.

[0037] As Figure 4 shown, a layer 30 of primer 10 and oil-bleeding silicone mixed with a free radical initiator is provided between the housing 12 of the connector 14 and the oil-bleeding liquid silicone 16. In the illustrative embodiment shown, the housing is made of a V-0 rated plastic.

[0038] The oil-bleeding liquid silicone 16 can be, but is not limited to, ELASTOSIL LR 3844 / 30 manufactured by Wacker Chemie AG. The oil-bleeding silicone can include, but is not limited to, 1% oil, 2% oil, 4% oil, 5% oil, 6% oil. Many oil-bleeding silicones are platinum cure systems. In this embodiment, there are two layers of oil-bleeding liquid silicone. Only the layer that forms the interface between the primer and the oil-bleeding liquid silicone layer contains the free radical initiator.

[0039] The layer 30 is an oil-bleeding silicone having a free radical initiator mixed or dissolved in the oil-bleeding silicone. In various embodiments, the free radical initiator is dissolved in the ingredients used to form the layer 30 prior to applying the layer 30 containing the free radical initiator. The layer 30 contains between about 0.3% and about 15% by weight of the free radical initiator, and preferably between about 1% and about 10% by weight of the free radical initiator. The layer 30 is applied at a thickness of between about 0.1 pm and about 100 pm, and preferably between about 1 pm and about 50 pm.

[0040] The layer 30 is applied to the primer 10 after the primer is applied to the housing 12. As Figure 4As shown, the crosslinking between layer 30 and the oil-permeable liquid silicone 16 occurs only in the crosslinked region or interface 32 of the oil-permeable liquid silicone 16, which is located at the interface 32 between layer 30 and the oil-permeable liquid silicone 16. This allows the oil-permeable liquid silicone 16 to adhere to layer 30, primer 10, and housing 12 without adversely affecting the release of oil from the non-crosslinked region 32 of the oil-permeable liquid silicone 16.

[0041] In the above illustrative embodiments in which the intermediate layer 30 comprises an oil-permeable liquid silicone and a free radical initiator, the primer 10 does not have a free radical initiator mixed in solution. In other illustrative embodiments in which the intermediate layer 30 comprises an oil-permeable liquid silicone and a free radical initiator, the primer 10 also has a free radical initiator mixed in solution before being applied to the polymer shell.

[0042] like Figure 5 As shown, a method 300 for bonding oil-permeable liquid silicone 16 to a potentially acidic surface of a housing 12 includes: cleaning the surface of the housing 12 (step 302); applying a primer 10 to the housing 12 (step 304); dissolving a free radical initiator in a layer 30 of oil-permeable liquid silicone (step 306); applying the layer 30 of oil-permeable liquid silicone 16 containing the free radical initiator to the surface of the primer 10 (step 308) as a first oil-permeable silicone layer; and applying oil-permeable silicone 16, with or without a free radical initiator, as a second layer (step 310).

[0043] Or, such as Figure 6 As shown, a method 400 for bonding an oil-permeable liquid silicone 16 to an acidic surface of a housing 12 includes: cleaning the surface of the housing 12 (step 402); dissolving a free radical initiator in a primer 10 (step 404); applying the primer 10 to the surface of the housing 12 (step 406); allowing the primer 10 to dry (step 408); dissolving a free radical initiator in a layer 30 of oil-permeable liquid silicone (step 410); applying the layer 30 of oil-permeable liquid silicone 16 in which the free radical initiator is dissolved to the surface of the primer 10 (step 412) as a first oil-permeable silicone layer; and applying an oil-permeable silicone 16 with or without a free radical initiator as a second layer (step 414).

[0044] In yet another embodiment, such as Figure 7 As shown, a layer of primer 10 is applied to the polymer housing 12. An oil-permeable liquid silicone is mixed with a free radical initiator to form composition 18. Composition 18 is then applied to the primer 10. Composition 18 achieves improved adhesion to the polymer housing.

[0045] While the application has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the spirit and scope of the application as defined in the accompanying claims. It will be appreciated that those skilled in the art, on acquaintance with the principles underlying the present application, can use the present application for purposes other than those specifically described, and with modifications to the structures, arrangements, proportions, dimensions, materials and components, and in other embodiments, all without exceeding the scope of the application. Accordingly, the presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the application to be determined by the appended claims and equivalents thereof, and not limited to the above description or embodiments.

Claims

1. An electrical connector comprising a multi-layer with improved adhesion, the electrical connector comprising: a housing, the housing comprising a polymeric composition, the polymeric composition including an additive; a primer applied to the housing, the primer comprising a free radical initiator dissolved in the primer; and an oil-impregnated liquid silicone applied to the primer, wherein the free radical initiator allows the oil-impregnated liquid silicone to adhere to the housing and allows the oil-impregnated liquid silicone to maintain its lubricating function.

2. The electrical connector of claim 1, wherein, The primer has a thickness between 1 pm and 10 pm.

3. The electrical connector of claim 1, wherein, The primer contains 0.3% to 1% by weight of the free radical initiator.

4. The electrical connector of claim 1, wherein, The improved adhesion between the primer and the oil-impregnated liquid silicone only occurs at the interface of the primer and the oil-impregnated liquid silicone.

5. The electrical connector of claim 3, wherein, The free radical initiator is selected from the group consisting of peroxide and azo free radical initiators.

6. The electrical connector of claim 1, wherein, The matrix of the primer is a reactive siloxane and silane in an organic solvent.

7. The electrical connector of claim 1, wherein, The additive causes the housing to have an acidic surface.

8. The electrical connector of claim 1, wherein, The additive is a flame retardant additive.

9. The electrical connector of claim 8, wherein, The additive is phosphonate-based.

10. The electrical connector of claim 8, wherein, The housing with the flame retardant additive has a rating of UL 94 V-0 rating.

11. A method of manufacturing an electrical connector, the electrical connector having a housing, the housing comprising a polymeric composition, the polymeric composition including an additive, the method comprising: applying a primer to the housing, the primer having a free radical initiator dissolved in the primer; allowing the primer to adhere to the housing; applying an oil-impregnated liquid silicone to the primer; and cross-linking the oil-impregnated liquid silicone to the primer to adhere the oil- impregnated liquid silicone to the primer, wherein the free radical initiator allows the oil-impregnated liquid silicone to adhere to the housing and allows the oil-impregnated liquid silicone to maintain its lubricating function. cleaning a surface of the housing before applying the primer to the surface of the housing.

12. The method of claim 11, further comprising: allowing the primer to dry after applying the primer to the housing.

13. The method of claim 11, further comprising: allowing the oil-impregnated liquid silicone to dry after applying the oil- impregnated liquid silicone to the primer.

14. The method of claim 11, further comprising: applying the primer with a thickness between 1 pm and 10 pm.

15. The method of claim 11, wherein, The primer contains 0.3% to 1% by weight of the free radical initiator.

16. The method of claim 11, wherein, The primer and the oil-impregnated liquid silicone adhere to each other at the interface of the primer and the oil-impregnated liquid silicone.

17. The method of claim 11, wherein, The lubricating properties of the oil-impregnated liquid silicone are not affected by the interface.

18. The method of claim 17, wherein, The additive is a flame retardant additive that causes the housing to have an acidic surface.

19. The method of claim 11, wherein, 20. A method of manufacturing an electrical connector, the electrical connector having an additive in a housing, the method comprising: dissolving a free radical initiator in an oil-impregnated liquid silicone; and applying the oil-impregnated liquid silicone having the free radical initiator dissolved therein to the housing, wherein the free radical initiator allows the oil-impregnated liquid silicone to adhere to the housing and allows the oil-impregnated liquid silicone to maintain its lubricating function.

21. An electrical connector comprising: a housing, the housing having a polymeric composition, the polymeric composition including an additive; and ​ ​ an oil-impregnated liquid silicone applied to the housing, the oil-impregnated liquid silicone having a free radical initiator dissolved in the oil-impregnated liquid silicone; wherein the oil-impregnated liquid silicone enhances adhesion between the oil-impregnated liquid silicone and the polymeric composition of the housing, wherein the free radical initiator allows the oil-impregnated liquid silicone to adhere to the housing and allows the oil-impregnated liquid silicone to maintain its lubricating function.

22. The electrical connector of claim 21, wherein, The oil-impregnated liquid silicone contains between 0.1% and 5% by weight of the free radical initiator.

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