WEATHER STRIP

Abstract: Herein disclosed is a weather strip constructed of a rubber composition. The rubber composition comprises a mixture of 70 to 50 parts by weight of acrylonitrile-­ butadiene rubber and 30 to 50 parts by weight of polyvinylchloride, the acrylonitrile-butadiene rubber including not greater than 28 percent by weight of acrylonitrile; 10 to 40 parts by weight of dioctyl adipate relative to 100 parts by weight of the mixture; and not less than 0.1 part by weight of glycerin fatty acid ester, the glycerin fatty acid ester having a melting point not less than 45 o C and having a rational formula represented by:

Description: The present invention relates in general to a weather strip for automobiles, and more particularly, to a material of the weather strip, which eliminates or at least minimizes the uncomfortable squeak produced when the weather strip rubs against a glass pane, such as a door glass or the like. A conventional weather strip used in an automobile is outlined with reference to Figs. 2 and 3 of the accompanying drawings. In the drawings, particularly Fig. 3, there is partially shown a motor vehicle of the so-called "pillerless hardtop sedan type", to which a conventional weather strip is applied. Denoted by numeral 1 is the weather strip which is interposed between a front door glass 2 and a rear door glass 3. As is seen from Fig. 2, the weather strip 1 comprises a gripping portion 1a having a generally U-shaped cross section, a supporting wall portion 1b extending obliquely inward from an inboard side of the gripping portion 1a and a lip portion 1c extending outward from the leading end of the supporting wall portion 1b. The gripping portion 1a grips a front edge of the rear door glass 3. The lip portion 1c is contactable with the front door glass 2 to achieve a watertight sealing therebetween. Hitherto, as the material of such a weather strip 1, ethylene-propylene-diene-monomer (EPDM) has been widely used for its tolerable antiweatherability and reduced costs. However, the weather strip made of such EPDM, particularly when used for a long time, tends to produce an uncomfortable squeak when the door glass 2 rubs against the weather strip 1, more particularly, against the lip portion 1c of the same or vice versa. In order to solve this drawback, several measures have hitherto been proposed and put into practical use. One of the measures is to apply the weather strip with a surface treating agent to reduce the skin friction of the weather strip. Furthermore, Japanese Patent First Provisional Publication No. 61-238507 shows a measure of using acrylonitrile-butadiene rubber (NBR)/polyvinylchloride (PVC) as the material of the weather strip for reducing the friction. However, in the former measure, the durability of the surface treating agent is inevitably poor because the agent tends to peel off due to the repeated opening and closing movement of the door glass 2. Furthermore, the latter measure has failed to produce a satisfying result in minimizing the squeak. It is therefore the object of the present invention to provide a weather strip which is free of the undesirable squeak. According to the present invention, there is provided a weather strip constructed of a rubber composition which comprises a mixture of 70 to 50 parts by weight of acrylonitrile-butadiene rubber and 30 to 50 parts by weight of polyvinylchloride, the acrylonitrile-butadiene rubber including not more than 28 percent by weight of acrylonitrile; 10 to 40 parts by weight of dioctyl adipate relative to 100 parts by weight of the mixture; and not less than 0.1 part by weight of a glycerin fatty acid ester, the glycerin fatty acid ester having a melting point of not less than 45 °C and having a formula represented by: wherein R is a residue of a fatty acid. Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematically illustrated measuring device for measuring the coefficient of static friction of test samples; Fig. 2 is a horizontally sectional view of a conventional weather strip used in an automobile of the so-called "pillerless hardtop sedan type"; and Fig. 3 is a side, but partial, view of the pillerless hardtop sedan. In the following, the weather strip according to the present invention will be described in detail. The present invention is based on the fact that the undesirable squeak produced by the weather strip depends on the degree of the coefficient of static friction between the glass and the weather strip. As is known to those skilled in the art, there is an assured correlation between the coefficient of static friction and the so-called adhesion. That is, if the rubber substance has on its surface solid things bled out therefrom, the coefficient of static friction is reduced. Furthermore, it is known that there are bled-out solid things of a type which can reduce the coefficient of static friction to a sufficiently low level even though the amount of the bled-out things is relatively small. Furthermore, it is also known that liquid bled-out things increase the coefficient of static friction. Taking the above-mentioned facts into consideration, the inventors carried out various examinations and tests. The composition of the weather strip of the present invention preferably further comprises 70 parts by weight of carbon black; 5 parts by weight of zinc oxide; 1 part by weight of stearic acid; 3 parts by weight of a vulcanization accelerator; 1 part by weight of sulfur. Said weather strip preferably has a configuration which comprises a gripping portion having a generally U-shaped cross section, said gripping portion being adapted to be mounted to an edge of a glass pane; a supporting wall portion extending in one direction from said gripping portion; and a lip portion extending in the other direction from a leading end of said supporting wall. as a substitute for the glycerin fatty acid ester, a satisfying small coefficient of static friction was not obtained. When the amount of the glycerin fatty acid ester was less than 0.1 part by weight, the coefficient became too great. When the glycerin fatty acid ester having a melting point lower than 45 °C was used, the bleed-out thereof showed a liquid condition. When a plasticizer other than the dioctyl adipate was used, the use of the rubber substance (viz., weather strip) over a long time increased the bleed-out of the plasticizer and thus increased the coefficient of static friction. Furthermore, when the amount of the plasticizer was less than 10 parts by weight with respect to the polymer of 100 parts by weight, the hardness adjustment of the produced rubber substance became difficult making the kneading (or blending) of the rubber composition impossible. Furthermore, when the amount of the plasticizer was greater than 40 parts by weight, the liquid bled-out was increased causing an increase in the coefficient of static friction of the product. The reason of using a mixture of acrylonitrile-butadiene rubber (NBR) and polyvinylchloride (PVC) as the base was that they have small coefficients of static friction. However, when the mixing ratio fo NBR and PVC was higher than 70/30, the antiweatherability of the product became poor. Furthermore, when the mixing ratio of NBR and PVC was less than 50/50, the permanent set in fatigue of the product was increased to an unpractical degree. When the amount of nitrile in the acrylonitrile-butadiene rubber (NBR) was greater than 28 % by weight, the bled-out phenomenon was remarkable and thus the coefficient of static friction of the product was increased. In order to find out the above-mentioned facts, the following examinations were carried out by the inventors on both the invention and prior art. Test samples according to the present invention were constructed of a rubber composition having the following ingredients. Polymer (NBR/PVC) 100 parts by weight (mixing ratio varied) Carbon black (N550) 70 parts by weight Plasticizer kinds varied, amounts varied Zinc oxide 5 parts by weight Stearic acid 1 part by weight Vulcanization accelerator 3 parts by weight Sulfur 1 part by weight Lubricant kinds varied, amounts varied It is to be noted that the rubber composition was well kneaded and then pressed and heated at 160 °C for 15 min to mold each test sample. Test samples according to the prior art were constructed of a rubber composition having the following ingredients. Polymer (EPDM) 100 parts by weight Carbon black (N550) 70 parts by weight Paraffin oil 30 parts by weight Zinc oxide 5 parts by weight Stearic acid 1 part by weight Vulcanization accelerator 3 parts by weight Sulfur 1 part by weight It is also to be noted that the rubber composition was well kneaded and then pressed and heated at 160 °C for 15 min to mold each test sample. These test samples of the invention and the prior art were subjected to a friction test using a measuring device as shown in Fig. 1. In the drawing, numeral 4 denotes the test sample whose coefficient of static friction is to measured. The measuring device generally comprised a mushroom-shaped glass-made slider 5 (25 mm in diameter, 40 mm in length) which is slidably put on the test sample 4, a weight 6 of 200g which is put on the slider 5, a string 9 which pulls the glass-made slider 5 in a horizontal direction a load cell 7 which detects a load applied to the string 9 and a FFT analyzer 8 which derives the coefficient of static friction from the load detected by the load cell 7. The test samples which had undergone the friction test were all subjected to a 1000-times rubbing test under the same conditions and then they were subjected to the friction test again. Weather strips were also produced from the same rubber compositions of the invention and the prior art, and they were subjected to a road test wherein the weather strips are practically mounted on an automotive door glass in a manner as shown in Figs. 2 and 3. In the road test, it was examined whether, after a long drive on a rough road, an uncomfortable squeak was produced or not from the weather strip. The rubber composition of the invention and the test results of same are shown in TABLE-1 and those of the prior art are shown in TABLE-2. As is seen from these tables, the test samples and the molded weather strips according to the present invention show satisfying results compared with those of the prior art. In fact, the undesirable squeak was not produced by the weather strips of the invention. In practical use, only the lip portion 1c of the weather strip may be constructed of the rubber composition according to the invention.

Claims: 1. A weather strip constructed of a rubber composition which comprises: a mixture of 70 to 50 parts by weight of acrylonitrile-butadiene rubber and 30 to 50 parts by weight of polyvinylchloride, said acrylonitrile-butadiene rubber including not more than 28 percent by weight of acrylonitrile; 10 to 40 parts by weight of dioctyl adipate relative to 100 parts by weight of said mixture; and not less than 0.1 part by weight of a glycerin fatty acid ester, said glycerin fatty acid ester having a melting point of not less than 45°C and having a formula represented by wherein R is a residue of a fatty acid. 2. The weather strip of claim 1, in which said rubber composition is well kneaded and then pressed and heated at 160°C for 15 min to produce a molded product. 3. The weather strip of claim 1, wherein the composition further comprises: 70 parts by weight of carbon black; 5 parts by weight of zinc oxide; 1 part by weight of stearic acid; 3 parts by weight of a vulcanization accelerator; and 1 part by weight of sulfur. 4. The weather strip of claim 3, which has a configuration which comprises: a gripping portion having a generally U-shaped cross section, said gripping portion being adapted to be mounted to an edge of a glass pane; a supporting wall portion extending in one direction from said gripping portion; and a lip portion extending in the other direction from a leading end of said supporting wall.

Inventors: NAKAMURA, SHIGERU, SUGAWARA, HIROSHI
Applicants: NISSAN MOTOR CO., LTD.
Application year: 1989
Main classification: B60R13
IPC codes: C08L33, B60J10, C08L21, C08K5, C08L27, C08L9