ADHESIVE

Abstract

Described herein is a two-part condensation curable adhesive composition suitable for adhering a front lens having an inner surface coated with an anti-haze coating to a lamp body to create a sealed lamp unit. In general, once cured in place, residual ingredients from the adhesive composition or by-products of cure reactions thereof do not visibly inhibit functionality of the anti-haze coating of the sealed lamp unit.

Claims

1. A two-part condensation curable adhesive composition for adhering a front lens having an inner surface coated with an anti-haze coating to a lamp body to provide a sealed lamp unit, the adhesive composition comprising a base part, Part A, and a catalyst package, Part B, wherein Part A comprises: (a) a siloxane polymer having at least two hydroxyl or hydrolysable groups per molecule or a silyl modified organic polymer having at least two (R.sup.5).sub.m(Y.sup.1).sub.3-m—Si groups per molecule, where each R.sup.5 is a hydroxyl or a hydrolysable group, each Y.sup.1 is an alkyl group containing from 1 to 8 carbons and m is 1, 2, or 3, and where the organic polymer is selected from the group consisting of polyethers, hydrocarbon polymers, acrylate polymers, polyesters, polyurethanes and polyureas; and (b) a reinforcing filler; and wherein Part B comprises: (i) a polydialkylsiloxane which is unreactive with polymer (a) in Part A, with the polydialkylsiloxane having the general formula:
R.sup.3.sub.3—Si—O—((R.sup.2).sub.2SiO).sub.d—Si—R.sup.3.sub.3 where each R.sup.2 is an alkyl group or a phenyl group, each R.sup.3 is independently selected from the group consisting of alkyl, phenyl, alkenyl, and alkynyl groups, and d is an integer which provides a viscosity of from about 5 to about 100,000 mPa.Math.s at 25° C.; (ii) optionally, a reinforcing filler; (iii) a tin based catalyst, and; (iv) a cross-linker having the structure Si(OR).sub.4 where each R is an independently selected alkyl group containing from 2 to 10 carbon atoms; and (v) an adhesion promoter of the structure
(R′O).sub.3Si(CH.sub.2).sub.nN(H)—(CH.sub.2).sub.mNH.sub.2 where each R′ is an independently selected alkyl group containing from 1 to 10 carbon atoms, n is from 2 to 10, and m is from 2 to 10; and wherein once cured in place, residual ingredients from the adhesive composition or by-products of cure reactions thereof do not visibly inhibit functionality of the anti-haze coating of the sealed lamp unit.

2. The two-part condensation curable adhesive composition in accordance with claim L wherein the reinforcing filler (b) in Part A is a precipitated calcium carbonate and the optional reinforcing filler (ii) in Part B is precipitated calcium carbonate or fumed silica.

3. The two-part condensation curable adhesive composition in accordance with claim 1, wherein Part B comprises cross-linker (iv) in an amount of from 1 to 30% by weight, and/or adhesion promotor (v) in an amount of from 1.0 to 10% by weight, each based on Part B.

4. The two-part condensation curable adhesive composition in accordance with claim 1, wherein two, three or all R groups in cross-linker (iv) are the same and have 2 to 6 carbon atoms, and/or adhesion promoter (v) is selected from (ethylenediaminepropyl) trimethoxysilane, (ethylenediaminepropyl) triethoxysilane, or a mixture thereof.

5. The two-part condensation curable adhesive composition in accordance with claim 1, wherein a pigment/non-reinforcing filler is present in an amount of from 1 to 30% by weight of Part B.

6. The two-part condensation curable adhesive composition in accordance with claim 5, wherein the pigment/non-reinforcing filler is carbon black.

7. The two-part condensation curable adhesive composition in accordance with claim 1, wherein Part B comprises: the polydialkylsiloxane (i) in an amount of from 30 to 70.5 weight %; the optional reinforcing filler (ii) in an amount of from 0 to 10 weight %; the tin based catalyst (iii) in an amount of from 0.01 to 3 weight %; the cross-linker (iv) in an amount of from 1 to 30 weight %; the adhesion promoter (v) in an amount of from 1.0 to 10 weight %; and colored filler or pigment in an amount of from 0 to 30 weight %; with the total weight % of Part B being 100 weight %.

8. The two-part condensation curable adhesive composition in accordance with claim 1, wherein polymer (a) is the siloxane polymer.

9. The two-part condensation curable adhesive composition in accordance with claim 1, wherein: the weight ratio of cross-linker (iv) to adhesion promoter (v) in Part B is at least 1.5:1, or optionally is from 1.5:1 to 2:1; and/or once Part A and Part B are combined, the adhesive composition has a tack free time of less than 60 minutes, or optionally less than 40 minutes, in accordance with ASTM 2377-94 using a polyethylene film.

10. A lamp having a lamp body defining a lamp chamber containing a light source and having a front opening, and a front lens to engage into the front opening, the front lens having an inner surface which further defines the lamp chamber, the inner surface being coated with an anti-haze coating, wherein the front lens is adhered to the lamp chamber by a cured adhesive formed from the two-part condensation curable adhesive composition according to claim 1.

11. The A-lamp in accordance with claim 10, wherein: the weight ratio of cross-linker (iv) to adhesion promoter (v) in Part B is at least 1.5:1, or optionally is from 1.5:1 to 2:1; and/or once Part A and Part B are combined, the adhesive composition has a tack free time of less than 60 minutes, or optionally less than 40 minutes, in accordance with ASTM 2377-94 using a polyethylene film.

12. The lamp in accordance with claim 10, wherein the lamp body is made from polybutylene terephthalate, cast aluminum, acrylonitrile butadiene styrene, polypropylene, ethylene propylene diene monomer rubber, polyphenylene sulfide, polyether ether ketone or a composites thereof, low density polyethylene, high density polyethylene, polyamide, acrylic-styrene-acrylonitrile, or polybutylene terephthalate or a composites thereof.

13. The lamp in accordance with claim 10, wherein the front lens is made from polycarbonate or poly(methyl methacrylate).

14. The lamp in accordance with claim 10, wherein the outer surface of the front lens is treated with a scratch resistant coating.

15. The lamp in accordance with claim 10, wherein minimal or no haze can be observed on the inner surface of the front lens subsequent to cure of the adhesive composition.

16. A method for making the lamp in accordance with claim 10, the method including the steps of: providing the lamp body and the front lens; engaging the front lens into the front opening of the lamp body to form a joint; and sealing the joint between the front lens and the lamp body with the adhesive composition by mixing Part A and Part B of the composition together to form a mixture, applying the mixture onto the joint between the front lens and the lamp body and causing or allowing the adhesive composition to cure.

17. The method in accordance with claim 16, wherein minimal or no haze can be observed on the inner surface of the front lens subsequent to cure of the adhesive composition.

18. The lamp in accordance with claim 10, further defined as at least one of an outdoor light, a decorative light, or a vehicle lamp.

19. The lamp in accordance with claim 18, further defined as a vehicle lamp selected from the group consisting of headlamps, brake lamps, running lamps, turn signal lamps, fog lamps, back-up lamps and parking lamps.

20. An adhesive comprising the reaction product of the two-part condensation curable adhesive composition in accordance with claim 1.

Description

EXAMPLES

[0157] All viscosities mentioned were measured at 25° C. using a Brookfield Viscometer Type DV2T extra with spindle No. 7 rotating at 10 rpm.

[0158] In the following examples a standard base material was used for all examples. This was of the formula depicted in Table 1 below:

TABLE-US-00001 TABLE 1 Base Composition Base Ingredient Weight % of Base Dimethyl hydroxy terminated 57.8 polydimethylsiloxane, viscosity 16,500 mPa .Math. s at 25° C. Calcium Carbonate 40.8 Titanium dioxide 1.4

[0159] The calcium carbonate used was stearic acid treated commercially available calcium carbonate sold under the name Calofort® S from Specialty Minerals Inc.

[0160] A series of comparatives and examples of the part B catalyst package composition were produced as indicated in Tables 2 and 4 below and these were mixed with samples of the base composition depicted in Table 1 above in a Base:Catalyst package ratio of 10:1 and the resulting compositions were cured and analysed for their properties. The latter are depicted in Tables 3 and 5 below. The treated silica used in the catalyst package examples was AEROSIL® 974 from Evonik. Comparative catalyst package 1 uses ingredients often used in current adhesive formulations for lamp adhesives.

TABLE-US-00002 TABLE 2 Comparative Part B catalyst compositions Comp. 1 Comp. 2 Comp. 3 Comp. 4 Ingredients (wt. %) (wt. %) (wt. %) (wt. %) Trimethylsilyl terminated 56.89 70.33 73.87 71.97 polydimethylsiloxane 60,000 mPa .Math. s Carbon black 12.99 16.06 16.87 16.44 Treated silica 0.65 0.8 0.84 0.82 DMDTN catalyst 0.23 0.46 0.65 0.65 reaction product of 25.064 aminopropyltrimethoxysilane with glycidoxypropyltrimethoxysilane and methyltrimethoxysilane methyltrimethoxysilane 4.18 Gamma aminopropyltriethoxysilane 4.68 Tetraethylorthosilicate (iv) 7.67 5.44 6.568 Ethylenediaminepropyltrimethoxysilane (v) 2.33 3.56 Weight ratio of (iv):(v) 2.33:1   1.84:1   Mix ratio of Part A:Part B (parts by weight) 100:14 100:9.5 100:9.51 100:9.75

[0161] For the avoidance of doubt Mix ratio of Part A:Part B is in parts by weight. Hence, when the ratio is indicated to be 100:14, this might be interpreted to mean 100 g by weight of component A and 14 g by weight of Part B. The Ethylenediaminepropyltrimethoxysilane used in the examples is commercially available under the XIAMETER® OFS-6020 Silane name from Dow Silicones Corporation. The above compositions were assessed for their physical properties as depicted in Table 3 below. A test was developed to measure the effect of the by-products and volatiles from the adhesive compositions in an enclosed space on anti-haze coatings. Substrates were coated with two commercial anti-haze coatings, referred to hereafter as Commercial AHC 1 and Commercial AHC 2. The test protocol is described below and was used for all examples and comparative examples.

Antihaze coating (AHC) compatibility Test Method—to determine the compatibility of a silicone adhesive to two commercial anti-haze Coatings (AHCs).

[0162] To determine if the adhesive composition being used was a satisfactory lamp adhesive composition able to adhere said front lens having an inner surface coated with an anti-haze coating to a lamp body to create a sealed lamp unit (either with or without pre-treatment) and to ensure that once cured in place, in use, residual ingredients from the above composition or by-products of cure reactions did not visibly inhibit functionality of said anti-haze coating the following anti-haze coating compatibility test was developed. For the avoidance of doubt compatibility with respect to this test was intended to mean the determination as to whether or not the water-film-forming-effect intended by the provision of the AHC on an internal closed surface is changed by the by-products and residual cross-linker materials from the silicone adhesive.

[0163] The adhesive under test typically a silicone based material, was first prepared by mixing part A and part B in a ratio of part A:part B of 10:1, using a Hauschild-Mixer Type AM 501 (Hauschild & Co. KG, Germany). Once mixed approximately 1.0 g of the resulting uncured adhesive product was placed on the bottom of an Alu-Cup (Alu-Kappen Art.-Nr. 3621313 (32×30 mm), from SCHUETT-BIOTEC GMBH (hereafter referred to as “Alu-Cup”). The open end of the Alu-cup was then covered and closed by placing a polycarbonate (PC) plate, which had been previously coated with an anti-haze coating thereon, ensuring full closure. The PC plate was fixed in place ensuring that the Silicone Adhesive and the AHC share the same atmosphere for a typical cure time of the Silicone Adhesive. The Alu-Cups were then left for a 7 day period to allow the adhesive to thoroughly cure. It is to be understood that during the cure process, given it is by way of a condensation cure process by-products and residual cross-linker will evaporate into the atmosphere within the cup and may contaminate and effect the AHC on the inner facing surface of the polycarbonate strip.

[0164] After the 7 day cure period, a 2nd Alu-Cup, was filled with water and heated on a laboratory hotplate up to 75° C. The PC plate was then removed from the original Alu-Cup and placed onto the opening of the second Alu-Cup with the AHC coating facing the water therein. The interaction between the hot water and the AHC coated surface was then observed to determine the effectiveness of the AHC with respect to hazing/fogging. So that the reaction of the AHC to the heated water when the AHC is in contact with water steam and its water-film-forming property can be evaluated [0165] 1. This analysis was carried out for a 30 s period. As an alternative to observation the results may be photographed. The observation may be recorded by camera or video. [0166] 2. The samples were then ranked as follows:— [0167] a. Hazy surface, alu-cup-bottom not visible=>AHC fully contaminated [0168] b. Clear surface, alu-cup-bottom not visible, fine water drops=>AHC is contaminated [0169] c. Clear surface, alu-cup-bottom visible, large water drops=>AHC might be contaminated [0170] d. Clear surface, alu-cup-bottom visible, water film=>AHC is not contaminated [0171] 3. Silicone Adhesives which are ranked with (c) and (d) (Pass criteria) can be rated as compatible.

[0172] A series of standard physical property test were undertaken to ensure the adhesive had the necessary physical properties to function as an adhesive. The results thereof, together with details of the standard test methods followed are also depicted in Table 3.

[0173] Lap shear testing was also undertaken as described below

Lap shear Tensile Strength

[0174] Samples of the base component and catalyst package were mixed in a ratio of 10:1 as previously indicated. Samples of a pre-determined amount of the composition were applied onto a pre-cleaned first substrate (polycarbonate) surface in a laminating apparatus. A second substrate (a previously plasma treated polypropylene) was then placed on top of the composition applied to the first substrate to give a pre-sized lap. The two substrates were compressed and excess composition was removed. The samples of composition in said pre-sized laps sandwiched between the two substrates were cured at room temperature for a period of seven days after which the lap shear tensile strength was determined by pulling the pre-sized laps apart by shear rather than peel (180° pull) at a rate of 2.0 cm/min.

[0175] Cohesive failure (CF) is observed when the cured elastomer/adhesive itself breaks without detaching form the substrate surface. It was considered that if the failure was not by CF it was by adhesive failure (AF). Adhesive failure (AF) refers to the situation when a sample detaches cleanly (peels off) from a substrate surface. In some cases a mixed failure mode has been observed: i.e. some areas peel-off (i.e. AF) while some remain covered with cured elastomer/adhesive (i.e. CF). In such instances the portion displaying CF (% CF) is recorded (bearing in mind % CF+% AF=100%). The results of all the tests on compositions made using comparative catalyst packages 1 to 4 are provided in said Table 3 below. Following the above, the adhesive material remaining on the substrates were subjected to a peel test whereby one end of each sample assessed is undercut on the square down to the surface with a clean razor blade or the like. A tab is produced on each sample which is then held between the fingers and thumb and then smoothly pulled at about 90 degrees until there is either adhesive or cohesive failure.

TABLE-US-00003 TABLE 3 Properties of Compositions made using Base (Table 1 and the catalyst package of Table 2 post mixing in a 10:1 ratio) Characteristic Comp. 1 Comp. 2 Comp. 3 Comp. 4 Commercial AHC 1 compatibility 7 d hazy hazy no haze no haze RT cond. cond. Commercial AHC 2 compatibility 7 d hazy hazy no haze no haze RT cond. cond. Tack free time (min) (ASTM 2377-94) >180 120 Shore A Hardness (ASTM D2240-97) 14 22 7 d RT cure time (tacky) (slight tack) Elongation (%) (ASTM D412-98a) 886 616 7 d RT cure time Tensile Strength (MPa) (ASTM D412-98a) 1.22 1.85 7 d RT cure time Lap Shear Strength Adhesion 1.38 1.51 PC/plasma PP after 7 days aging at RT (MPa) Cohesive Failure on polycarbonate (%) 50 100 Cohesive failure polypropylene (%) 100 100 Lap Shear Strength Adhesion 0.66 0.89 PC/plasma PP after aging at 60° C. and/ 90% RH for 14 days (MPa) Cohesive Failure on polycarbonate (%) 60 70 after lap shear Cohesive Failure on polycarbonate (%) 60 70 after subsequent peel test Cohesive Failure on polypropylene (%) 50 60

[0176] It was identified that both comparatives 1 and 2 failed to pass the anti-haze coating test. Given this they were discounted as unsuitable and no further analysis of these materials was undertaken. Comparatives 3 and 4 did however generate formulations which passed the anti-haze coating test and therefore were analysed further. However, compositions made using comparative catalyst packages 3 and 4 were considered unsuitable because they (i) cured too slowly for headlamp assembly processes as may be appreciated given they had a tack free time much greater than 60 minutes e.g. of at least 120 minutes and indeed were found to have remained “sticky” after a 7 day curing period; and (ii) had a lap shear strength of <1 MPa after a 14 day period at 60° C. and 90% relative humidity.

[0177] Examples of acceptable catalyst packages as described in accordance with the composition herein together with two further comparatives are depicted in Table 4.

TABLE-US-00004 TABLE 4 Ex. 1 Ex. 2 Comp. 5 Comp. 6 Ingredients (wt. %) (wt. %) (wt. %) (wt. %) Trimethyl terminated 70.21 68.53 65.28 62.51 polydimethylsiloxane 60,000 mPa .Math. s Carbon black 16.04 15.65 14.91 14.27 Treated silica 0.80 0.78 0.75 0.72 DMDTN catalyst 0.61 0.59 0.57 0.54 Tetraethylorthosilicate (iv) 7.64 8.687 10.58 12.29 Ethylenediaminepropyltrimethoxysilane (v) 4.70 5.77 7.91 9.67 Weight ratio of (iv):(v) 1.63:1   1.5:1   1.34:1   1.27:1   Mix ratio of Part A:Part B (parts by weight) 100:10 100:10.25 100:10.74 100:11.23

[0178] Compositions made from the base material depicted in Table 1 together with example catalyst packages 1 and 2 and comparative catalyst packages 5 and 6 were prepared by mixing the base with each catalyst package in a 10:1 weight ratio. The resulting compositions were tested for their physical properties as depicted in Table 5 below.

TABLE-US-00005 TABLE 5 Characteristic Ex. 1 Ex. 2 Comp. 5 Comp. 6 Commercial AHC 1 compatibility 7 d RT no haze no haze hazy hazy cond. cond. Commercial AHC 2 compatibility 7 d RT no haze no haze hazy hazy cond. cond. Tack free time (min) (ASTM 2377-94) 39 23 10 6 Shore A Hardness 1 h (ASTM D2240-97) 14 22 24 22 Lap Shear Strength Adhesion 1.47 1.37 1.23 1.19 PC/plasma PP after 7 days aging at RT (MPa) Cohesive Failure on polycarbonate (PC) 100 100 100 100 (%) after lap shear and subsequent peel test Cohesive failure on polypropylene (PP) 100 100 100 100 (%) after lap shear and subsequent peel test Lap Shear Strength Adhesion 1.02 1.08 1.21 1.17 PC/plasma PP after aging at 60° C. and/ 90% RH for 14 days (MPa) Cohesive Failure on polycarbonate (%) 80 100 100 100 after lap shear Cohesive Failure on polycarbonate (%) 80% CF 0 0 0 after subsequent hand peel Cohesive Failure on polypropylene (%) 50 CF 100 100 100 Shore A Hardness (ASTM D2240-97) 28 30 31 31 Elongation (%)(ASTM D412-98a) 545 490 380 312 Tensile Strength (MPa) (ASTM D412-98a) 2.31 2.31 2.06 1.83

[0179] As will be observed in the above both examples 1 and 2 passed the anti-haze coating test described above unlike comparatives 5 and 6. It will be seen that compositions made using the catalyst packages of comparatives 5 and 6 gave hazing subsequent to the anti-haze testing and therefore were deemed unacceptable for the current need. Examples 1 and 2 also had an acceptable tack free time however the composition of example may require to be applied on a pre-treated surface to enhance adhesion on some substrates.