JPH0249225B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a bellows boot for a vehicle that houses and protects coupling members such as shock absorbers, constant velocity joints, and steering wheels used in automobiles and the like. Historically, conventional bellows boots for vehicles have generally been made of rubber, but while bellows boots for vehicles made of such rubber have flexibility, they do not allow stones to fly from the outside and collide with them. There is no bellows boot for vehicles that satisfies the required performance of a bellows boot for a vehicle, which is to prevent breakage by mitigating the impact of solid objects such as rubber boots, etc., and to have the strength to withstand repeated bending, high-speed rotation, etc. Therefore, in order to improve the defects of rubber bellows boots for vehicles, for example,
As disclosed in Japanese Utility Model Publication No. 56-72930, the outer surface of the boot body made of rubber is coated with a reinforcing layer made of a heat-shrinkable material or a wear-resistant material such as resin. However, even these products do not fully satisfy the boot performance required by the above-mentioned bellows boots for vehicles. This has the disadvantage that the manufacturing process becomes complicated and the cost becomes high. In view of the above-mentioned circumstances, the present inventors have fundamentally reviewed the historical fact that conventional bellows boots for vehicles are manufactured mainly from rubber, and have determined that the bellows boots for vehicles are When a load is applied to the bellows wall (hereinafter referred to as the bellows wall) to cause it to expand, contract, and bend, and then the load is removed, the bellows wall quickly recovers.In other words, the bellows wall has a high rebound modulus. The bellows wall must be flexible (low hardness), i.e., the bellows wall must not easily collapse or deform due to slight external force, i.e., the bellows wall must have shape retention (high hardness), and the bellows wall must have shape retention (high hardness). The bellows wall is heat resistant, oil resistant,
Bellows boots for vehicles maintain the above-mentioned performance including cold resistance, that is, the bellows wall maintains its strength over a long period of time, the manufacturing process of the bellows wall is simplified, and bellows boots can be provided at low cost. The present invention was completed as a result of extensive research in order to obtain a bellows boot for a vehicle that satisfies these strict required characteristics. In other words, if the manufacturing process was made mainly of rubber bodies that require a vulcanization process, the manufacturing process would be complicated and it would not be possible to manufacture them at a low price. When attempting to manufacture boots, he came up with the idea of using soft polyvinyl chloride (PVC) as the main material in order to provide flexibility to the bellows wall. Soft polyvinyl chloride (PVC) is flexible and inexpensive, so it partially satisfies the above-mentioned required properties, but one of the above-mentioned required properties is the shape retention of the bellows wall. As a result of various attempts to solve this problem, we have come to the conclusion that it is suitable to use a laminated layer of thermoplastic polyurethane elastomer (TPU). In bellows boots for vehicles, we realized that it is important for the bellows wall to have a high rebound modulus as mentioned above, so we decided to use the soft polyvinyl chloride (PVC) and thermoplastic polyurethane elastomer (TPU). We conducted various experiments to find out what factors are involved in achieving a high impact resilience modulus, and found that when using PVC with a high degree of polymerization as shown in Table 1 below as flexible polyvinyl chloride (hereinafter referred to as PVC), As shown in Figure 1, when the vertical axis is the rebound modulus and the horizontal axis is the shore A hardness (see the lower unit of Figure 1), it has the properties shown by curve A. As shown in the figure, when the vertical axis represents the impact elasticity modulus and the horizontal axis represents the average degree of polymerization, curve B
It has been found that the thermoplastic polyurethane elastomer (hereinafter referred to as TPU) has the properties shown in Table 1 below. When the elastic modulus is expressed in a table with shore A hardness (refer to the upper unit in Figure 1) on the horizontal axis, curve C is obtained.
It was found that it has the properties shown below. Therefore, based on the above-mentioned characteristics of the rebound modulus of PVC and TPU, we conducted various experiments on a laminate made of two layers consisting of the PVC as the main body and the TPU as the outer covering.
As shown in the figure, when the vertical axis shows the rebound modulus and the horizontal axis shows Shore A hardness, the curve E
We learned that it has the properties shown below. Based on the results obtained in this way,
For a laminate consisting of two layers of PVC and TPU, a rebound modulus of 70% or more in Figure 1 is considered suitable as a molded product, and the flexibility, shape retention, heat resistance, oil resistance, and cold resistance are An experiment regarding the strength included found that it was sufficiently satisfactory as a bellows boot for a vehicle. Therefore, the PVC with a rebound modulus of 70% or more in FIG.
Shore A hardness of TPU and a laminate thereof is an important requirement, and as can be understood from Fig. 2, the degree of polymerization of PVC is also taken into consideration in order to further increase the impact resilience. The first feature is that the average degree of polymerization is 1500 or more and the shore A hardness is
It has a two-layer structure: a main layer made of soft polyvinyl chloride with a hardness of 30 to 87, and a skin layer covering the outside of the main layer made of a thermoplastic polyurethane elastomer with a Shore A hardness of 81 to 99. The skin layer is laminated by coextrusion in an extrusion die, and the laminated wall surface is expanded by blow molding to form a bellows shape, and the formed laminated wall surface has a shore A hardness of 40 to 95. Bellows boots for vehicles , which is in . In the above case, the main layer is composed of two layers, the main layer and the epidermal layer covering the outside of the main layer, but even if an epidermal layer is added to cover the inner side of the main main layer and the structure is made up of three layers, the above-mentioned The second feature of the present invention is that the average degree of polymerization is 1500 or more and the shore A hardness is
It has a three-layer structure: a main layer made of soft polyvinyl chloride with a hardness of 30 to 87; and a skin layer covering the outside and inside of the main layer made of a thermoplastic polyurethane elastomer with a Shore A hardness of 81 to 99; The layer and the skin layer are laminated by co-extrusion in an extrusion die, and the laminated wall surface is expanded by blow molding to form a bellows shape, and the formed laminated wall surface has a shore A hardness of 40 to 95.For vehicles. These are bellows boots. The PVC has an average degree of polymerization (P) of
It is a mixture of 1,500 to 10,000 polyvinyl chloride and 30 to 220 parts of a plasticizer per 100 parts of the polyvinyl chloride, and other fillers, stabilizers, stabilizing aids,
Pigments and the like may also be appropriately blended. As the plasticizer, phthalate-based, epoxy-based, phosphoric ester-based, fatty acid ester-based, linear dibasic ester-based, or polyester-based plasticizers can be used, but in the present invention, the type of plasticizer is not particularly important. It is not limited. If the average degree of polymerization of the polyvinyl chloride exceeds 12,000, the surface appearance of the parison during molding will be poor and the moldability will be significantly poor. Also, if the plasticizer is less than 30 parts, it becomes inelastic,
If it exceeds 220 parts, the tensile strength will drop significantly. The above-mentioned TPU is obtained by polyadding various polyethers or polyester diols and glycols with diisocyanates, and also includes those in which triols, diamines, triamines, etc. are used in combination, for example, polyester-based TPUs. These are called polyurethane, polyether polyurethane, etc. Note that diisocyanates include 4-4'-diphenylmethane diisocyanate, 4-4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc., and glycols include ethylene glycol, 1,4- Butylene glycol, 1,4'-hexane diol, bishydroxyethoxybenzene, etc., and polyester diols include polyethylene adipate, poly-1,4-butylene adipate, poly-1,6-hexane adipate,
Examples of the polyether diol include polycaprolactone and polycarbonate, and examples of the polyether diol include polyoxytetramethylene glycol. As a means for further laminating, a multilayer blow molding method using coextrusion is used, and in particular, the overall thickness composition ratio of the TPU layer and PVC layer is 90:10 to 0.5:
99.5 Preferably in the case of 50:50 to 0.5:99.5, there is no drawdown of the parison and the parison itself can be molded into the mold cavity shape in good condition, resulting in a uniform wall thickness of the bellows and good elasticity. can be expected. Furthermore, the interlayer adhesion strength of the bellows wall was extremely high in all cases, and molded products that could not be peeled off were obtained. Note that blow molding refers to plasticized TPU and
PVC is coextruded into a multilayer tubular parison or multilayer sheet, and then molded into a three-dimensional shape using positive or negative pressure. Example 1 PVC-(1) and TPU-(1) shown in Table 1 were each made with a screw diameter of 50 mm and a screw length (L/
D) Melt and knead in a 22 extruder, and join the outer layer with TPU and the inner layer with PVC in an extrusion die.
40mm, total thickness 2mm (thickness composition ratio of outer layer and inner layer)
A bellows as shown in Fig. 3 is produced by co-extruding a cylindrical two-layer parison with a ratio of 20:80), closing the extruded parison in a split mold, and blowing compressed air into it for hollow forming. A molded product K having connection parts 2, 2 at both ends of part 1 was obtained. The molded product K has a length of 200 mm, a bellows ridge diameter of 60 mm, a valley diameter of 45 mm, an average wall thickness of 0.7 mm, and a pitch of 11.5 mm.
As shown in Figure 4, the inner layer 3 made of PVC and TPU
It is composed of two layers with an outer layer 4 consisting of. Example 2 PVC-(2) and TPU-(2) shown in Table 1 were melt-kneaded in an extruder, and joined in an extrusion die with PVC as the middle layer and TPU as the inner and outer layers. ,
The thickness composition ratio of the outer layer, middle layer, and inner layer is 10:80:10
A molded article L was obtained by coextrusion as a three-layer parison set to , and blow molding. The molded product L
The shape is substantially the same as the molded product K according to Example 1, and is composed of three layers: an inner layer 5 and an outer layer 6 made of TPU, and an intermediate layer 7 made of PVC. Note that the specifications of the extruder, the dimensions of the parison, and the shape of the molded product are the same as in Example 1 described above. Example 3 Using PVC-(3) and TPU-(3) shown in Table 1,
The thickness composition ratio of the outer layer, middle layer, and inner layer is 25:50:25.
A molded product M having the same shape as shown in FIG.
I got it. Comparative Example 1 Using PVC-(2) shown in Table 1, by extruding and blow-molding a single PVC parison, the third
A molded product N having the same shape as shown in the figure was obtained. still,
The specifications of the extruder, the dimensions of the parison, and the shape of the molded product are the same as in Example 1 above. Comparative Example 2 A molded article O was obtained using the same specifications and methods as in Example 1 above, except that PVC-(4) and TPU-(1) shown in Table 1 were used. Comparative Example 3 A molded product P was obtained in the same manner as in Example 2 above, except that PVC-(4) and TPU-(2) shown in Table 1 were used. Comparative Example 4 A molded product Q was obtained using the same specifications as in Example 3 above, except that PVC-(4) and TPU-(3) shown in Table 1 were used. The results of testing the characteristics of the molded products K to O obtained in Examples 1 to 3 and Comparative Example 1 were
Shown in the table. In addition, each of the above Examples 1 to 3 and each Comparative Example 1 to
Table 3 shows the results of testing the impact resilience modulus of each of the molded products K to Q obtained in 4.

【table】

【table】

[Piercing strength]

A part of the wall of the molded product obtained in Examples and Comparative Examples was cut out as a sample, and the periphery of the sample was fixed with a fixing frame having an opening of 10 mm in diameter. A needle formed into a round shape with a radius of curvature of 0.5 mm was heated at 20℃ and 65%RH for 50 minutes.
Pierce at a speed of ±5 mm/min., measure the maximum load until the needle penetrates, and divide the value by the wall thickness of the sample. This test method is practical as an evaluation method for molded products from which samples are collected under harsh conditions, for example, when the molded products are subjected to collisions with sharp pebbles. [Heat resistance] Fix the upper end of the molded product, suspend a weight with a constant load from the lower end, place it in a high temperature atmosphere for a certain period of time, and measure the change in length of the molded product. η (%) = l ₁ - l ₀ / l ₀ × 100 η: Rate of change of molded product, l ₀ : A 100 g weight is suspended at 20°C and 65%RH,
Length of the molded product after 1 hour, l ₁ : Length after 1 hour of hanging a 100g weight at 120℃, [Rebound modulus] One end of the molded product under the conditions of 20℃ and 65% RH Hold it in the chuck and place the other end on the load cell.
After compressing at a speed of mm/min. so that the peaks and valleys of the bellows part are completely in contact with each other, it is restored at the same speed, the load at this time is measured, and the load and amount of change are calculated as shown in Figure 6. Record the relationship as a hysteresis curve. ψ (%) = A ₁ / A ₂ × 100 ψ: Modulus of rebound elasticity of molded product A ₀ : Area surrounded by l ₁ and a by the X axis A ₁ : Area surrounded by l ₂ , a and the X axis Surrounded area As a completely elastic body, ψ approaches 100, or as a molded product that is used in a wide range of applications, excellent impact resilience is an important property and is a practical evaluation method for molded products. It is. As a result of comparing the characteristics of the molded products of the above-mentioned Examples and Comparative Examples, as shown in Table 2, the molded products according to the Examples of the present invention were compared to the conventional PVC shown in Comparative Example 1.
It can be seen that it has excellent mechanical strength such as tensile strength, tear strength, and puncture strength, which cannot be obtained with a single molded product, and excellent oil resistance against grease, gasoline, etc. Furthermore, as shown in Table 3, the molded product according to the present invention has an excellent rebound modulus that cannot be obtained with the molded products shown in Comparative Examples 3 and 4. As is clear from the above, the molded product according to the present invention, that is, the bellows boot for a vehicle, has a bellows wall that has a high rebound modulus, has flexibility and shape retention, and maintains strength over a long period of time. Moreover, it is simple and easy to manufacture, and can be provided at low cost.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between Shore A hardness and impact resilience modulus, Figure 2 is a diagram showing the relationship between PVC average degree of polymerization and impact resilience modulus, and Figure 3 is an elastic molded article according to the present invention. A front view showing an example, Fig. 4 is an enlarged sectional view of the main part, Fig. 5 is an enlarged sectional view of the main part of another embodiment, and Fig. 6 shows the load and amount of change when measuring the rebound modulus FIG.

Claims (1)

[Scope of Claims] 1. A main layer made of soft polyvinyl chloride with an average degree of polymerization of 1500 or more and a Shore A hardness of 30 to 87, and a thermoplastic polyurethane elastomer with a Shore A hardness of 81 to 99. It has a two-layer structure with a skin layer covering the outside of the main layer, and the main layer and the skin layer are laminated by co-extrusion in an extrusion die, and the laminated wall is expanded by blow molding to form a bellows shape. A bellows boot for a vehicle, characterized in that the formed laminated wall surface has Shore A hardness of 40 to 95. 2. A main layer made of soft polyvinyl chloride with an average degree of polymerization of 1500 or more and a Shore A hardness of 30 to 87, and an outer and inner side of the main layer made of a thermoplastic polyurethane elastomer with a Shore A hardness of 81 to 99. The main layer and the skin layer are laminated by co-extrusion in an extrusion die, and the laminated wall is expanded by blow molding to form a bellows shape. A bellows boot for a vehicle, characterized in that the shore A hardness of the laminated wall surface is 40 to 95.