HOLT MELT TYPE SEAL AGENT FOR A LAMP

Abstract: The present invention relates to the hot melt type seal agent for adhering and sealing a head lamp of a vehicle, wherein a lens and a housing are integrally one unit. The necessary component materials of the hot melt type seal agent of the present invention include a mixture produced by butyl rubber, SEBS block copolymer and olefin with high softening point. The hot melt type seal agent of the present invention withstands temperature changes in the head lamp and the gas pressure that is filled therein. Consequently, good adhesion, waterproof and high gas-tight performances are achieved.

Description: This invention relates to a hot melt type seal agent for use as an adhesive seal between a lens and a housing for an incandescent lamp such as a head lamp of a vehicle. Prior art Formerly, a lamp unit and a housing of a head lamp were separate units of an assembly, whereas recently the lamp unit and the housing have become integrally one unit for the purpose of weight reduction of a vehicle and the trend to reduce the complexity of design. In the integral head lamp, a hot melt type seal agent began to be used for adhering and sealing the glass or plastic lens to the plastic of FRP housing. The hot melt type seal agent is produced by kneading a polymer, a tackifier, a softener, a filler and other miscellaneous materials. As the polymer component of the hot melt type seal agent, a simple substance or mixture of such thermoplastic resin or thermoplastic elastomer as ethylene-vinyl acetate copolymer, polyamide resin, polyethylene, ethylene-propylene rubber, styrene-isoprene-styrene (SIS) block copolymer (Kraton® 1107), styrene-butadiene-styrene (SBS) block copolymer (Kraton® 1102), acrylic rubber, polyisobutylene rubber, polyester elastomer and so on and have been generally used. Especially the use of Kraton® 1102 is known from US-A 4,169,822. As the softener, a simple substance or mixture of olefin with low molecular weight, atactic polypropylene, polybutene, polyisobutylene with low molecular weight, paraffinic oil, naphthenic oil and straight chain aliphatic acid ester have been used. As the tackifier, a simple substance or mixture of terpene resin, terpene-phenol resin, rosin, hydrogenated-rosin resin, various petroleum resin and so on have been used. The hot melt type seal agent produced by kneading the above components, however, did not always give satisfactory results in adhesion, weather resistance under severe conditions and physical characteristics at high or low temperature and wet conditions though these results are necessary for the seal agent. For example, internal temperature of a lamp rises as high as 120 - 130°C, partially rising around 140°C when the lamp is lighted. In case of a halogen sealed beam lamp, the seal agent needs a greater sealing performance as it must withstand both the pressure of the sealed gas and a higher temperature than in ordinary incandescent lamps. For example SBS polymers (Kraton® 1102) according to US-A 4,169,822 or SIS polymers (Kraton® 1107) are not suitable for hot melt type seal agent according to the present application because these polymers are not compatible with butyl rubber (isobutylene or isoprene rubber) and an olefin wax having a high softening point. However, both butyl rubber and olefin wax are indispensable constituents of the seal agent according to the present application. Therefore if SBS polymers or SIS polymers would be used in the hot melt according of the present application they will cause separation during melting. Furtheron according to the present invention the hot melt seal is intended for a lamp to be used outdoor. Because double bonds exist in the molecules of SBS and SIS the heat stability and the weather resistance would be very low. Finally, the SBS polymers and SIS polymers have a low heat resistance and therefore not suitable for the present application for a lamp. An object of the present invention is to provide a hot melt type seal agent for a lamp which can withstand under the above-mentioned severe conditions. The object is realized by a hot melt type seal agent for a lamp comprising butyl rubber, styrene-ethylene-butylene-styrene (SEBS) block copolymer and olefin wax with a softening point higher than 110°C, the seal agent having a softening point of higher than 110°C measured by the ring and ball method (JIS-K-2531; ASTM D36), wherein the weight ratio of the butyl rubber:the SEBS block copolymer is between 90:10 to 40:60 and wherein the weight ratio of the butyl rubber plus the SEBS block copolymer in the seal agent is 20 to 50%, the weight ratio of the olefin wax in the seal agent is 5 to 30% and the weight ratio of the other materials (tackifier, softener, filler, antioxidant, coupling agent and/or colorant) in the seal agent is 20 to 75%. The butyl rubber as one of the necessary component materials of the present invention is preferably a copolymer of isobutylene and diene-hydrocarbon (mainly isoprene). For example, it may be Butyl Rubber 065® (product of Japan Butyl Rubber Corp., Isoprene Isobutylene Rubber = IIR), AID #10®, Chlorobutyl 1066®, Polysar-XL-20® or EXXON Butyl 365®. The SEBS polymer may be, for example, Kraton G-1650 (a styrene-ethylene-butene-styrene block copolymer), G-1652 or G-1726. The olefin wax is an olefin comprising a carboxyl group with an equivalent molecular weight preferably less than 6,000 whose melt viscosity is low and the softening point is preferably higher than 130°C measured by the ring and ball method. Oxidized type olefine whose molecule has a few carboxyl groups is more compatible with polar materials than non-oxidized type olefin. The olefin wax may be, for example, A-C316 by Allied Signal Co. with a softening point of 140°C. In addition to these necessary components, various resins as the above-mentioned tackifier are optionally added and kneaded. In this case, 100 to 150 weight parts of the resins are appropriate to be added per 100 parts of the polymers including the butyl rubber and the SEBS, which leads to good results of wetting and adhesion to the adherent. In addition to the above-mentioned olefin wax, the well-known softener as mentioned above may be comprised. 50 to 100 parts of the softener, in this case, are appropriate to be added per 100 parts of the polymer, which leads to good results of wetting of the adherent owing to its low melting temperature and low viscosity. The silane coupling agent is effective as the tackifier characterized by its adhesion to glass, especially a waterproof adhesion. The addition of 0.5 to 5 percentage by weight of the silane coupling is appropriate to be added; also pigment may be added as a colorant. In the present invention, the butyl rubber gives good adhesion, elongation and gas barrier characteristcs, while the SEBS gives good elasticity, cohesion and better weather resistance than the SIS and SBS. The oxidized type olefin wax with a high softening point gives high compatibility, adhesion by polar group, heat resistance and anticreep performance by its high softening point. Since the synergistic effect of these three component materials occurs, the softening point is over 110°C and their heat resistance is high, they are utilized as the hot melt type seal agent for a lamp of a vehicle, especially for a halogen sealed beam lamp which requires heat resistance and a gas barrier resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The examples of the hot melt type seal agent of the present invention and comparative examples are produced as in Table 1. COMPOSITION OF TEST MATERIALS (weight parts) Examples Comparative examples 1 2 1 2 3 Butyl rubber 065® 35 12 40 30 10 SEBS (G-1650) 5 18 0 0 20 Wax AC-316® 20 10 0 0 0 Wax APP® 0 0 20 10 10 Petroleum resin 30 40 30 40 40 Naphthenic oil 10 20 10 20 20 Silane 0.5 0.5 0 0 0 Here, * Butyl rubber 065® : by Japan Butyl Rubber * G-1650 : Kraton G-1650® by Shell Chemical * Wax AC-316®: by Allied Signal Co., softening point = 140°C * APP : atactic polypropylene, softening point = 100 °C * Petroleum resin : Escorez 5300® by EXXON Chemical * Naphthenic oil : Shellflex 371JY® by Shell Chemical * Silane : Silane coupling agent by Japan Unicor A-1100®. The examples are evaluated according to the following test methods: softening point is measured by the ring and ball method of JIS-K-2531 (ASTM D36); viscosity (x 10² poise) at 190 °C is measured by JIS-K-6838 (ASTM D2556-67T); tensile strength and break elongation between glass panes are measured at 20 °C, 80 °C and 110 °C by H type method of JIS-A-5758; and the resistance to hot water is evaluated by tensile strength and break elongation by the H type method at 20°C after the examples are immersed in water of 40°C for 120 hours. The results are given as shown in Table 2. The terms EXXON, Kraton, Escorez and Shellflex used in the above specification are registered trade marks.

Claims: A hot melt type seal agent for a lamp comprising butyl rubber, styrene-ethylene-butylene-styrene (SEBS) block copolymer and olefin wax with a softening point higher than 110 °C, the seal agent having a softening point of higher than 110 °C measured by the ring and ball method (JIS-K-2531; ASTM D36), wherein the weight ratio of the butyl rubber:the SEBS block copolymer is between 90:10 to 40:60 and wherein the weight ratio of the butyl rubber plus the SEBS block copolymer in the seal agent is 20 to 50 %, the weight ratio of the olefin wax in the seal agent is 5 to 30 % and the weight ratio of the other materials (tackifier, softener, filler, antioxidant, coupling agent and/or colorant) in the seal agent is 20 to 75 %. The hot melt type seal agent according to claim 1, wherein the softening point of the olefin wax is higher than 130 °C. The hot melt type seal agent according to claim 1, wherein the seal agent comprises at least one material selected from the group consisting of terpene resin, terpene-phenol resin, rosin and hydrogenated-rosin resin. The hot melt type seal agent according to claim 1, wherein the olefin wax is an olefin comprising a carboxyl group with an equivalent molecular weight of less than 6.000. The hot melt type seal agent according to claim 1, wherein the seal agent further comprises 0,5 to 5 weight % of silane coupling agent. The hot melt type seal agent according to claim 1, wherein the butyl rubber is a copolymer of isobutylene and dienehydrocarbon. The hot melt type seal agent according to claim 6, wherein the diene-hydrocarbon is isoprene. Production process for the hot melt type seal agent according to any of the preceeding claims, wherein the seal agent is producted by kneading a mixture of the component materials.

Inventors: SUMI, HIDEKATSU C/O AICA KOGYO CO., LTD., TOMITA, ATSUSHI C/O AICA KOGYO CO., LTD.
Applicants: AICA KOGYO CO., LTD.
Application year: 1989
Main classification: C09K3
IPC codes: C09K3, C09J153, F21S8, C09J123, F21V17