JP2013136661A - Foamed rubber molded product for seal material, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamed rubber molded product which is suitable for a seal material capable of improving sound insulating properties and cushion properties in spite of its reduced weight.SOLUTION: In the foamed rubber molded product for seal material including bubbles, the bubbles are at least partially formed by a foaming agent, and, as the bubbles, bubbles relatively large in diameter and bubbles smaller in diameter than the large-diameter bubbles are formed respectively as individual bubbles.

Description

  The present invention relates to a foamed rubber molded body for a sealing material and a method for producing the same.

  With the recent reduction in weight of vehicles, the sealing material is also required to be reduced in weight. Therefore, a sealing material made of a rubber molded body that is reduced in weight by enclosing bubbles, that is, a sealing material made of a foamed rubber molded body is used. A sealing material made of a foamed rubber molded body can be reduced in weight to some extent by increasing the number of bubbles while satisfying certain required performance as a sealing material.

  In relation to this, for example, Patent Document 1 discloses a weather strip in which a rubber material contains heat-expandable microcapsules for the purpose of weight reduction, and bubbles are formed by expanding the microcapsules with heat during vulcanization. Has been. According to Patent Document 1, bubbles can be formed more precisely, and the weather strip can be reduced in weight.

  Further, for example, Patent Document 2 discloses a foamed rubber molded body that is lightened by forming bubbles with a foaming agent. In Patent Document 2, when a rubber raw material containing a foaming agent is extruded to obtain a foamed rubber molded product having a specific gravity of 1.0 or less, a material having a specific gravity of 1.0 or less is stabilized when extruded at a high speed. In order to solve the problems, the upper limit of the foaming agent blending form and the particle size is specified. . That is, the pyrolytic foaming agent is added in the form of being supported by an inorganic powder, and the particle size of the inorganic powder is defined as 9 μm or less, and the particle size of the pyrolytic foaming agent is defined as 8 μm or less.

JP-A-6-183305 Japanese Patent No. 3507701

  By the way, sealing materials (so-called weather strips) that are installed around the doors and windows of vehicles not only prevent moisture and dust such as rain from entering the passenger compartment through the gap between the body and parts, but also cushions. It is desirable to have both sound and sound insulation properties. When the bubbles are formed only by the microcapsules as in Patent Document 1, the bubbles are formed more densely as the amount of addition of the microcapsules is increased, and the weight of the sealing material can be reduced. However, there is a tendency that the sealing material becomes harder and cushioning properties are harder to obtain than when bubbles are formed with a foaming agent.

  On the other hand, the foamed rubber molded body in which bubbles are formed by a foaming agent as in Patent Document 2 can be reduced in weight and increased in cushioning properties (impact absorption) as the amount of bubbles is increased. However, sound insulation tends to decrease as the amount of bubbles increases. This is considered to be caused by bubbles communicating with each other when the amount of bubbles is increased when bubbles are formed with a foaming agent. Therefore, we have earnestly studied whether it is possible to have sound insulation by forming each bubble independently, but when adding a foaming agent with a single particle size as in the past, if bubbles are made, It was not possible to avoid the bubbles communicating while increasing the amount. However, as a result of further investigation, the theory is not necessarily clear, but it is possible to form relatively large-sized bubbles and small-sized bubbles while forming at least part of the bubbles with a foaming agent. It has been found that each bubble becomes a single bubble that exists independently, and that it is possible to simultaneously improve the weight reduction and cushioning properties and sound insulation properties, which are conventionally in a trade-off relationship. The present invention has been completed based on such knowledge, and the object of the present invention is to provide a foamed rubber molded article suitable for a sealing material that is light in weight and can improve sound insulation and cushioning properties. It is to provide.

  The present invention is, first, a foamed rubber molded article for a sealing material enclosing air bubbles, wherein the air bubbles are at least partially formed of a foaming agent, and as the air bubbles, relatively large diameter air bubbles, It has a smaller diameter than a large diameter bubble, and each bubble is formed as a single bubble. The term “relative” refers to the relationship between the two types of bubbles in the rubber molding for sealing material, and is not related to the size of general bubbles.

  According to such a foamed rubber molded article for a sealing material, excellent cushioning properties can be ensured while reducing the weight because at least a part of the bubbles is formed of the foaming agent. In addition, the sound insulation can be improved by forming the bubbles as single bubbles.

  Here, it is preferable that the large-sized bubble has a bubble diameter of 300 to 500 μm, and the small-sized bubble has a bubble diameter of 50 to 140 μm.

  The foamed rubber molded article for a sealing material according to the present invention is different in that the raw material rubber has different particle sizes of a foaming agent having a relatively large particle size and a foaming agent having a smaller particle size than the foaming agent having a larger particle size. It can be obtained by mixing two kinds of foaming agents and foaming the two kinds of foaming agents. By using two types of foaming agents, a foaming agent having a relatively large particle size and a foaming agent having a small particle size, even in the same amount of addition as that of the single particle size additive, A relatively large-sized bubble and a smaller-sized bubble can each be formed as a single bubble. Thus, when forming both a large diameter bubble and a small diameter bubble with a foaming agent, it is preferable at the point which is easy to ensure cushioning properties.

  One or more of the group consisting of 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), azodicarbonamide (ADCA), and N, N′-dinitrosopentamethylenetetramine (DPT) as the blowing agent. Are preferably used in combination, and among them, OBSH is more preferable in that the odor of the generated gas is small.

  Moreover, you may form a large diameter bubble by a hollow body. Here, the hollow body includes a microballoon in which the internal cavity is directly formed into bubbles, and a thermally expandable microcapsule that forms bubbles by being expanded by heating during vulcanization. In this case, the size of the bubbles can be controlled more easily by mixing a hollow body with the raw rubber instead of the foaming agent having a large particle size.

  That is, it is desirable that the large-diameter bubbles are formed by at least one of a foaming agent or a hollow body, and the small-diameter bubbles are formed by foaming of the foaming agent.

  Moreover, as for the foamed rubber molded object for sealing materials of this invention, it is desirable that specific gravity is 0.3-0.7.

  As the rubber raw material, ethylene-propylene-diene rubber can be suitably used from the viewpoint of heat resistance and weather resistance.

  According to the present invention, it is possible to provide a foamed rubber molded article suitable for a sealing material that is lightweight and can improve sound insulation and cushioning properties.

It is a digital micrograph of the cut surface which shows the bubble form of the foaming rubber molding of Example 1. 2 is a digital micrograph of a cut surface showing a bubble shape of a foamed rubber molded body of Comparative Example 1. FIG.

  The foamed rubber molded article for sealing material of the present invention is particularly characterized by its bubble diameter and its bubble form. That is, the foamed rubber molded body for a sealing material of the present invention is a mixture of relatively large diameter bubbles and bubbles smaller in diameter than the large diameter bubbles, and each bubble is formed as a single bubble. Is.

  The large diameter and small diameter of the bubbles in the present invention are distinguished by the relative size of the diameter of the bubbles contained in the foamed rubber molded body for a sealing material. In practice, a difference in bubble diameter may occur due to variations in foaming, but this means that there are large-sized bubbles and small-sized bubbles that allow a certain variation. It is preferable that the small bubble has an average bubble diameter of half or less than that of the large bubble. The standard of the bubble diameter of a large diameter bubble is 300-500 micrometers from a viewpoint of cushioning property ensuring. The small-diameter bubble may be smaller than that, but is preferably 50 to 250 μm, more preferably 50 to 200 μm, and most preferably 50 to 140 μm.

  As a desirable embodiment of the foamed rubber molded article for a sealing material of the present invention, there is one in which all of large diameter bubbles and small diameter bubbles are formed of a foaming agent. In a conventional method for producing a foamed rubber molded body, it can be produced by using two types of foaming agents having different particle diameters. A conventional method for producing a foamed rubber molding is typically a rubber raw material in which a foaming agent and other additives such as sulfur are mixed, and heated to vulcanize the raw rubber and foam the foaming agent. And a method for producing a foamed rubber molded body. As a method for molding the rubber raw material, known methods such as an extrusion molding method and a casting method can be applied. As the heating means, known means such as hot air heating, microwave heating, steam heating, etc. can be applied, and a plurality of heating means may be combined.

  The main component rubber is not particularly limited, and various rubbers can be used. For example, ethylene-propylene rubber, that is, EPDM (rubbery copolymer of ethylene, propylene and diene) or EPM (rubbery copolymer of ethylene and propylene), CR (chloroprene rubber), SBR (styrene and butadiene) Rubbery copolymer), NBR (nitrile rubber) and the like. EPDM is preferred for sealing materials that require heat resistance and weather resistance, such as weather strips.

  As the foaming agent, various chemical foaming agents can be used. For example, 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), azodicarbonamide (ADCA), and N which are organic decomposition foaming agents. , N′-dinitrosopentamethylenetetramine (DPT) can be used. These foaming agents may be used alone or in combination. OBSH is preferable in that the odor of the generated gas is small. OBSH is also preferable in that it can easily form bubbles having different sizes by adding two kinds of foaming agents having different particle diameters, since it efficiently foams at a general vulcanization temperature.

Two types of foaming agents having different particle diameters are a foaming agent having a relatively large particle diameter (hereinafter referred to as “large foaming agent”) and a foaming agent having a smaller particle diameter than a large foaming agent (hereinafter referred to as “foaming agent”). It is described as “small foaming agent”). The theory is not clear, but when using a foaming agent with a single particle size, adjacent bubbles are connected and easy to form open cells. However, if two types of foaming agents with different particle sizes are used, large bubbles and small diameters are used. Are easily formed as individual bubbles. The total amount of foaming agent added to the rubber raw material can be appropriately adjusted in consideration of the specific gravity of the foamed molded rubber material for sealing material and the amount of gas generated by the foaming agent used. On the other hand, the total amount of the foaming agent is 1 to 5 parts by weight. If it is less than 1 part by weight, it is difficult to reduce the weight, and if it exceeds 5 parts by weight, the efficiency is poor. In this case, in order to obtain a large bubble having a bubble diameter of about 300 to 500 μm and a small bubble having a bubble diameter of about 50 to 140 μm, the particle size of the large foaming agent is 9 to 16 μm and the small foaming agent is used. The particle size may be 2 to 6 μm within a range where the particle size is less than half that of a large foaming agent. Moreover, it is preferable to add equally a large foaming agent and a small foaming agent with respect to the addition ratio (weight ratio) of a large foaming agent and a small foaming agent. The term “equivalent” here is not limited to the completely same amount, and may be, for example, approximately the same amount with a width of about 80 to 120 parts by weight of a small foaming agent with respect to 100 parts by weight of a large foaming agent. If it deviates from this, the balance between the large-diameter bubbles and the small-diameter bubbles is poor, and there is a possibility that both or one of the sound insulation properties and the cushioning properties are deteriorated. The density of the foamed rubber molded body for a sealing material manufactured as described above can be set to, for example, 0.3 to 0.7 g / cm ³ .

  The theory of such foamed rubber molded products for sealing materials is not clear, but the surface roughness is smaller than that of conventional foamed rubber molded products having substantially the same density, so that the hand feeling is good and the compressive load is high. Small and excellent cushioning. In addition, it has excellent sound insulation. Although the theory is not necessarily clear, since each bubble is formed as a single bubble, the bubble does not communicate with the front and back of the molded body, and the sound insulation is improved because air propagation of sound is suppressed. Inferred. Further, since the bubbles are formed as single bubbles, the water permeability is low. Therefore, it can be suitably used as various kinds of sealing materials including weather strips for vehicles.

  Further, as another desirable embodiment of the foamed rubber molded article for a sealing material of the present invention, there is one in which at least a part of large-sized bubbles are formed of thermally expandable microcapsules. In the said manufacturing method, it can manufacture by replacing part or all of a big foaming agent with the heat | fever expansible microcapsule expanded by the heating at the time of vulcanization. The thermally expandable capsule expands by heating during vulcanization to form bubbles.

  As the thermally expandable microcapsule, for example, a microcapsule that encloses a liquid that vaporizes before reaching the heating temperature during vulcanization (a liquid having a boiling point lower than the heating temperature) can be used. Examples of such microcapsules include those containing low-boiling hydrocarbons such as isobutane, n-pentane, and n-hexane with an acrylonitrile copolymer or vinylidene chloride copolymer as an outer shell. As the thermally expandable microcapsules, those that expand to the size of the target large-sized bubbles at the heating temperature during vulcanization are used.

  Such a foamed rubber molded article for a sealing material has an advantage that the size of bubbles can be easily controlled during production by using thermally expandable microcapsules. And since the thermally expansible microcapsule is used for formation of a large diameter bubble, while adding the said advantage, the addition quantity of a thermally expansible microcapsule can be suppressed and cushioning properties can be ensured. Therefore, it is lightweight and excellent in cushioning properties and sound insulation properties.

  In addition, the foamed rubber molded body for a sealing material of the present invention may be formed by adding at least a part of large-sized bubbles to a rubber raw material as a hollow body in which internal cavities become bubbles as they are. Examples of such hollow bodies include microballoons made of inorganic materials such as glass balloons and silica balloons, microballoons made of thermosetting resins such as phenol and epoxy, and the like.

  Using EPDM as a rubber raw material, using OBSH with a particle size (median diameter) of 14 μm and a particle size of 4 μm OBSH as a foaming agent, test pieces of foamed rubber molded articles of Example 1 and Comparative Examples 1 and 2 with the composition shown in Table 1 It was created. First, the materials are kneaded, then the kneaded materials are extruded into a substantially cylindrical shape with an extruder having a cylinder diameter of 90 mm, and the extruded body is heated and vulcanized by passing through a microwave tank and a thermal oven tank in order. At the same time, the foaming agent was foamed to obtain foamed rubber moldings of Example 1 and Comparative Examples 1 and 2. In addition, the feed rate of the foamed rubber molded body at the end point of the thermal oven was 10 m / min.

  When the cut surface of the obtained foamed rubber molded product was observed, the foamed rubber molded product of Example 1 had large-sized bubbles and small-sized bubbles, most of which were formed as single cells (see FIG. 1). ). The large bubble has a bubble diameter of 300 to 500 μm, and the small bubble has a bubble diameter of 50 to 140 μm. The foamed rubber molded article of Comparative Example 1 is an example in which only a conventionally used foaming agent having a particle size of 14 μm is blended, but bubbles having a cell diameter of about 300 to 500 μm were formed as open cells. However, smaller bubbles were also generated due to variations in the particle diameter of the foaming agent, variations in the amount of foaming gas, and the like (see FIG. 2). In Comparative Example 2, only a foaming agent having a particle diameter of 4 μm was blended, and bubbles having a bubble diameter similar to that of the small diameter bubbles in Example 1 were formed as open cells.

  The foamed rubber molded bodies of Example 1 and Comparative Examples 1 and 2 were measured for density, compression load at 50% compression, and surface roughness (Rz). The measurement results are shown in Table 2.

  As apparent from Table 2, the densities of the foamed rubber molded bodies of Example 1 and Comparative Examples 1 and 2 are approximately the same. However, there was a difference in compressive load and surface roughness. The compressive load was smaller in Example 1 in which two types of foaming agents having different particle diameters were blended compared to Comparative Examples 1 and 2 in which only one type of foaming agent was blended. In comparison with Example 1, Comparative Example 1 and Comparative Example 2, the surface roughness was the smallest in Example 1, and compared with the foamed rubber molded article of Comparative Example 1 in which only a conventionally used foaming agent having a particle size of 14 μm was blended. Even so, the surface roughness was almost half. In addition, Example 1 was better in sound insulation than others.

Claims (7)

  A foamed rubber molded body for a sealing material enclosing air bubbles, wherein the air bubbles are at least partly formed of a foaming agent, and as the air bubbles, a relatively large diameter air bubble and a larger diameter air bubble A foamed rubber molded article for a sealing material, characterized by having small-sized bubbles and each bubble being formed as a single bubble.   2. The foamed rubber molded article for a sealing material according to claim 1, wherein the large-sized bubbles have a bubble diameter of 300 to 500 μm, and the small-sized bubbles have a bubble diameter of 50 to 140 μm. The large-sized bubbles are formed of at least one of a foaming agent or a hollow body,
The foamed rubber molded article for a sealing material according to claim 1 or 2, wherein the small-diameter bubbles are formed by foaming of a foaming agent.   4. The foamed rubber molded article for a sealing material according to claim 1, wherein the specific gravity is 0.3 to 0.7. 5.   Two kinds of foaming agents having different particle diameters, that is, a foaming agent having a relatively large particle diameter and a foaming agent having a smaller particle diameter than the foaming agent having a large particle diameter are mixed with the raw rubber, A method for producing a foamed rubber molded article for a sealing material, comprising foaming a foaming agent.   One or more of the group consisting of 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), azodicarbonamide (ADCA), and N, N′-dinitrosopentamethylenetetramine (DPT) as the blowing agent. The method for producing a foamed rubber extruded body for a seal material according to claim 5, which is used in combination. The rubber raw material is ethylene-propylene-diene rubber;
OBSH is used as said foaming agent, The manufacturing method of the foaming rubber molded object for sealing materials of Claim 6 characterized by the above-mentioned.