Shock Absorbing Material and Method for Producing the Same

Abstract

To provide an impact absorber that is light in weight but suitably retains its shape against impact and restores its shape after compression, and a method for producing the same.SOLUTION: An impact absorber contains gel and resin foam beads with an average particle size of 0.8 mm or more and has a density of less than 0.3 g / cm3. Preferably, the resin foam beads have a specific gravity of 0.15 or less. Preferably, the gel is silicone gel. Preferably, the impact absorber further contains a gas of 1-40 vol.%. Preferably, the gel is interposed between the resin foam beads.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a shock absorber and a method for manufacturing the same.

Background Art

[0002] There is known a shock absorber in which foamed beads are dispersed and mixed inside a gel to reduce the density, having light weight, flexibility, followability, and impact resistance, and it is used in electric and electronic devices, computers, automobiles, vibrating mechanical instruments, mat and cushion products, body protection pads, packaging cushioning materials, and the like.

[0003] Patent Document 1 discloses a shock absorber in which polystyrene foamed beads or polypropylene foamed beads are dispersed in a polyurethane gel. However, since the resin foamed beads have a large specific gravity and a small average particle size, and the density of the shock absorber is not sufficiently small, the weight reduction is not sufficient. When a large amount of foamed beads are blended for weight reduction, there are problems that the shape cannot be maintained against impact and the resilience after compression is poor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a shock absorber and a method for manufacturing the same, which are lightweight and have excellent shape maintainability against impact and resilience after compression.

Means for Solving the Problems

[0006] The inventor has found that by using resin foam beads with a large particle size and a small specific gravity, an impact absorber can be obtained that is lightweight yet excellent in shape retention against impact and resilience after compression, thus completing the present invention. Also, increasing the proportion of resin foam beads can enhance the lightweight property, but it is difficult to reduce the weight to be less than 0.6 of the specific gravity at the closest packing ratio. However, by incorporating air or pre-coating the resin foam beads, it has been found that an impact absorber with excellent shape retention and resilience after compression can be produced even when the specific gravity is 0.3 or less, thus completing the present invention.

[0007] That is, the present invention relates to an impact absorber containing a gel and resin foam beads with an average particle size of 0.8 mm or more and having a density of less than 0.3 g / cm 3 ³.

[0008] It is preferable that the specific gravity of the resin foam beads is 0.15 or less.

[0009] It is preferable that the gel is a silicone gel.

[0010] It is preferable that the impact absorber further contains 1 to 40% by volume of a gas.

[0011] It is preferable that the gel is interposed between the resin foam beads.

[0012] Also, the present invention relates to a method for producing an impact absorber having a density of less than 0.3 g / cm 3 ³, the method comprising a step of foaming a raw material of the gel and a step of filling a mold with the foamed raw material of the gel and heating and curing it together with resin foam beads.

[0013] In the above production method, it is preferable to further include a step of coating the resin foam beads with a part of the raw material of the gel.

[0014] In the above production method, it is preferable that the average particle size of the resin foam beads is 0.8 mm or more.

[0015] In the manufacturing method, it is preferable that the specific gravity of the resin foam beads is 0.15 or less.

Advantages of the Invention

[0016] Despite being lightweight, the shock absorber of the present invention is excellent in shape retention against shock and resilience after compression, and exhibits an excellent buffering effect especially for particularly fragile objects. Further, according to the manufacturing method of the shock absorber of the present invention, a shock absorber excellent in shape retention against shock and resilience after compression can be manufactured despite being lightweight.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] The shock absorber of the present invention contains a gel and resin foam beads having an average particle diameter of 0.8 mm or more, and is characterized in that the density is less than 0.3 g / cm 3 and less.

[0019] The gel is not particularly limited, and examples thereof include silicone gel, polyurethane gel, and hydrogel. Among them, silicone gel or polyurethane gel is preferable in that the volatilization of the solvent hardly occurs during long-term use. Further, since the temperature dependence of tanδ is smaller than that of polyurethane gel, silicone gel is more preferable.

[0020] Examples of silicone gels include those obtained by reacting a bifunctional organosiloxane with a trifunctional organosiloxane to effect crosslinking, and those in which a siloxane gel forms a three-dimensional network structure and a silicone oil is carried between the three-dimensional network structures are preferred. For example, viscoelastic bodies composed of polydimethylsiloxane gel, polymethyltrifluoropropylsiloxane gel, polyphenylmethylsiloxane gel, etc. and silicone oil are particularly preferred. Examples of silicone oils include dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, etc.

[0021] Examples of polyurethane gels include reaction products of polyether polyols and isocyanate compounds.

[0022] The Asker C hardness of the gel is preferably 20 or less, more preferably 15 or less. If it exceeds 20, since the gel is hard, the gel may inhibit the deformation of the beads and tend to cause a decrease in the impact absorption capacity. The Asker C hardness can be measured with an Asker C hardness meter.

[0023] The average particle diameter of the resin foam beads is 0.8 mm or more, preferably 1 mm or more. If it is less than 0.8 mm, the amount of deformation per bead is small, which causes a decrease in the impact absorption capacity in the final form. On the other hand, the upper limit of the average particle diameter is preferably 10 mm or less, more preferably 5 mm or less. If it exceeds 10 mm, the voids become large with only a single foam bead, so it is often mixed with beads having an average particle diameter of less than 10 mm, and tends to cause variations in weight and hardness in the final form due to mixing unevenness.

[0024] The specific gravity of the resin foam beads is 0.15 (0.15 g / cm 3The following is preferable, and 0.10 or less is more preferable. The lower limit is not particularly limited, but 0.01 or more is preferable. If it exceeds 0.15, the specific gravity tends to be high in the final form, and if it is less than 0.01, the strength of a single resin foam bead becomes weak, which tends to cause a decrease in strength in the final form.

[0025] The resin foam beads are a hollow body or a foam having an elastic outer shell. The material of the resin foam beads is not particularly limited, and examples thereof include polyethylene, polystyrene, polypropylene, EVA (ethylene vinyl acetate copolymer), polyphenylene ether, and copolymers of these homopolymers. Among these, polyethylene is preferable from the viewpoint of softness, and polypropylene is preferable from the viewpoint of heat resistance.

[0026] The contained volume ratio of the resin foam beads is preferably 0.9 to 9 of the resin foam beads with respect to 1 of the gel, and more preferably 2 to 5. If it is less than 0.9, the specific gravity becomes high in the final form, and if it exceeds 9, the amount of gel required for maintaining the structure in the final form tends to be insufficient.

[0027] The density of the shock absorber of the present invention is less than 0.3 g / cm 3 and preferably 0.25 g / cm 3 or less. If it exceeds 0.3 g / cm 3 , the superiority as weight reduction decreases when compared with other materials. The lower limit is not particularly limited, but 0.17 g / cm 3 or more is preferable.

[0028] In the shock absorber of the present invention, the content of the gel is preferably 15 to 30% by volume, and more preferably 17 to 25% by volume. Also, the content of the resin foam beads is preferably 40 to 80% by volume, and more preferably 45 to 75% by volume. If the content of the gel is less than 15% by volume, the amount of gel required for maintaining the structure in the final form tends to be insufficient, and if it exceeds 30% by volume, the superiority as weight reduction tends to decrease when compared with other materials.

[0029] The shock absorber of the present invention preferably further contains a gas. The gas content is preferably 1 to 40% by volume, more preferably 2 to 35% by volume. If it is less than 1% by volume, it becomes the level of contamination, and if it exceeds 35% by volume, the amount of gel and foam beads necessary for maintaining the structure in the final form tends to be insufficient. The gas content can be calculated by the following formula. {1 - (weight per unit volume of gel ÷ specific gravity of gel + weight per unit volume of resin foam beads ÷ specific gravity of resin foam beads)} × 100 (%) The gas referred to here means a gas other than the gas included inside the resin foam beads and the outer shell, etc.

[0030] The contained volume ratio of the gas is preferably 0.02 to 4 with respect to 1 of the gel, more preferably 0.05 to 3. If it is less than 0.02, it is the level of contamination, and it is difficult to obtain the effect of including air. If it exceeds 4, the amount of gel and foam beads necessary for maintaining the structure in the final form tends to be insufficient.

[0031] The gas is not particularly limited, and examples include air, nitrogen, helium, etc.

[0032] The shape of the shock absorber is not limited, and it may be appropriately selected according to the product and part where the shock absorber is used. For example, a square sheet shape, a block shape, a disk shape, a donut shape, a spherical shape, etc. can be mentioned.

[0033] The thickness of the shock absorber is not limited, but it is preferably 1.2 to 100 times the average particle diameter of the resin foam beads, more preferably 2 to 40 times. If it is less than 1.2 times, the shock absorption capacity of the shock absorber may decrease. If it exceeds 100 times, the amount of deformation per bead with respect to the overall thickness is small, so it tends to cause a decrease in the shock absorption capacity. Also, the specific thickness depends on the particle diameter of the resin foam beads, but is preferably 1.2 to 100 mm, more preferably 4 to 50 mm. If it is less than 1.2 mm, it will not function as a shock absorber, and if it is thicker than 100 mm, it tends to be inconvenient for use as a shock absorber.

[0034] In the shock absorber of the present invention, it is preferable that a gel is interposed between the resin foam beads. When using beads with a large average particle size, since the gel content is small, the gel may not be interposed between the beads. However, by previously coating the beads, the gel can be interposed between the resin foam beads, and the shape retention and deformability can be improved. The proportion of the volume of the part where the gel is not interposed is preferably 35% or less, and more preferably 10% or less.

[0035] The method for manufacturing a shock absorber having a density of 0.3 g / cm3 or less according to the present invention includes a step of foaming the raw material of the gel, and a step of filling the foamed raw material of the gel into a mold and heating and curing it together with the resin foam beads.

[0036] In the step of foaming the raw material of the gel, the raw material of the gel (main agent, curing agent, catalyst, etc.) is foamed by a stirrer or the like to include air bubbles in the raw material of the gel. As the gel, those described above can be used.

[0037] Subsequently, the foamed raw material of the gel is filled into a mold and heated and cured together with the resin foam beads. As the resin foam beads, those described above can be used. A mold release agent may be applied to the mold.

[0038] The resin foam beads may be filled into the mold in advance, or may be filled together with the foamed raw material of the gel.

[0039] The resin foam beads are preferably coated with a part of the raw material of the gel. Especially when a large amount of resin foam beads are used or when resin foam beads with a large average particle size are used, by coating, the gel can be sufficiently interposed between the resin foam beads, and the resin foam beads are fixed by the gel. Therefore, when receiving forces such as shock, compression, and vibration, the shape of the shock absorber can be maintained. The raw material of the gel used for coating does not necessarily need to be foamed.

[0040] The heating temperature and heating time may be appropriately selected according to the raw materials of the gel. For example, in the case of a silicone gel, it is preferably heated at 60 to 150 °C for about 5 to 15 minutes.

[0041] The use of the shock absorber of the present invention is not particularly limited, and examples include members for absorbing shock in electric and electronic devices, computers, automobiles, vibrating mechanical instruments, etc., mats and cushions, nursing care products such as body protection pads and wheelchairs, and packaging cushioning materials.

Examples

[0042] Hereinafter, examples will be described, but the present invention is not limited to only these examples.

[0043] (Example 1) 6.125 g of liquid A of silicone gel (specific gravity 0.98, Asker C hardness 5, SILGEL-612, manufactured by Asahi Kasei Wacker Silicone Co., Ltd.) and 6.125 g of liquid B containing a curing agent were mixed and stirred to prepare 12.25 g of the raw material of the gel. After coating half of this amount (6.125 g) sufficiently on the surface of 0.363 g of polyethylene foam beads (average particle size: 2.0 mm, specific gravity: 0.01, manufactured by Kaneka Corporation), it was filled into a mold with air holes having a width of 10 cm, a length of 10 cm, and a depth of 7 mm. Next, the remaining raw material (6.125 g) was foamed with a stirrer and then poured into the mold, and a drop lid with a thickness of 2 mm was put on. Then, it was heated using a press plate at 70 °C, demolded after 5 minutes, and a shock absorber with dimensions of 10 cm × 10 cm × 5 mm was produced.

[0044] (Example 2) A shock absorber was produced in the same manner as in Example 1, except that 8.13 g of a raw material composed of 4.065 g of liquid A of silicone gel and 0.465 g of liquid B containing a curing agent, and 0.25 g of polyethylene foam beads were used.

[0045] (Comparative Example 1) 0.25 g of the same polyethylene foam beads as those used in Example 1 were filled into a mold with a width of 10 cm, a length of 10 cm, and a depth of 5 mm. Subsequently, 12.25 g of Liquid A of the silicone gel and 12.25 g of Liquid B containing a curing agent were mixed. After degassing the bubbles in the obtained gel raw material, 24.5 g of it was filled into the mold. After filling, it was heated using a press plate at 70 °C, demolded after 5 minutes, and an impact absorber with dimensions of 10 cm × 10 cm × 5 mm was produced.

[0046] (Comparative Example 2) An impact absorber was produced in the same manner as in Comparative Example 1, except that 16.17 g of a raw material consisting of 8.085 g of Liquid A of the silicone gel and 8.085 g of Liquid B containing a curing agent, and 0.34 g of polyethylene foam beads were used.

[0047] (Comparative Example 3) 0.25 g of polyethylene foam beads (particle size: 0.5 mm, specific gravity: 0.01, manufactured by Kaneka Corporation) were filled into a mold with a width of 10 cm, a length of 10 cm, and a depth of 5 mm. Subsequently, 20.8 g of the main agent of a polyurethane gel (specific gravity 1.04, manufactured by Hiraizumi Yoko Co., Ltd.) and 5.2 g of the auxiliary agent containing a curing agent were mixed and stirred to prepare a gel raw material. After degassing the bubbles in a vacuum, it was filled into the mold. After filling, it was heated using a press plate at 70 °C, demolded after 30 minutes, and an impact absorber with dimensions of 10 cm × 10 cm × 5 mm was produced.

[0048] Using the impact absorbers produced in each example and comparative example, the following evaluations were carried out. Each evaluation was performed at 25 °C.

[0049] <Weight reduction> The density of the sample was measured, and the density was evaluated according to the following criteria. The results are shown in Table 1. A: The density is less than 0.3 g / cm 3 Less than B: The density is 0.3 g / cm or more and less than 0.5 g / cm 3 0.3 g / cm or more 3 Less than C: The density is 0.5 g / cm or more 3 Or more

[0050] <Shape maintenance> A 2-kg iron ball was dropped from a height of 10 mm (impact velocity: 0.47 m / sec), and the deformation of the sample after dropping was visually confirmed. The results are shown in Table 1. 〇: It was once deformed after dropping but returned to its original shape. ×: It was deformed after dropping and did not return to its original shape.

[0051] <Deformability> An iron disk with a diameter of 5 cm was placed at the center of the sample, a force was applied from above the disk, and the sum of the width and length of the gel when compressed by 50% in the thickness direction was evaluated. The results are shown in Table 1. 〇: The width and length were 10.0 cm each (no deformation) ×: The width or length was greater than 10.0 cm (deformation occurred)

[0052] In addition, enlarged views of the samples of Example 2 and Comparative Example 2 are shown in FIG. 1.

[0053]

Table 1

[0054] The shock absorbers of the present invention produced in Examples 1 and 2 were excellent in all evaluation items. On the other hand, in Comparative Examples 1 to 3, weight reduction was insufficient.

[0055] In the evaluation of shape maintenance, in Comparative Example 2, it did not return to its original shape. As shown in FIG. 1, since there was no gel between the foam beads and there were many parts where the beads were in direct contact (not fixed), it is considered that when the shock was received, the beads shifted and did not return to their original positions.

[0056] In the evaluation of deformability, in Comparative Example 2, the width became 10.2 cm and the length became 10.6 cm after compression, and in Comparative Example 3, the width became 10.7 cm and the length became 10.8 cm. In Comparative Example 2, since the foam beads were not fixed to each other, and in Comparative Example 3, since the average particle diameter of the foam beads was small, the vertical force could not be sufficiently absorbed, the foam beads moved horizontally, and it is considered that the structure could not be maintained.

[0057] (Reference Example 1) 24.5 g of Liquid A of the same silicone gel as used in Example 1 and 24.5 g of Liquid B containing a curing agent were mixed and stirred, and the bubbles in the resulting mixture were degassed under vacuum. This was filled into a mold with a width of 10 cm, a length of 10 cm, and a depth of 5 mm, heated using a press plate at 70°C, demolded after 5 minutes, and a sample of 10 cm × 10 cm × 5 mm was prepared. Using a Thomson blade, it was punched out into a cylindrical shape with a diameter of 25 mm.

[0058] (Reference Example 2) 41.6 g of the main agent of the same polyurethane gel as used in Comparative Example 3 and 10.4 g of the auxiliary agent containing a curing agent were mixed and stirred, and the bubbles in the resulting mixture were degassed under vacuum. This was filled into a mold with a width of 10 cm, a length of 10 cm, and a depth of 5 mm, heated using a press plate at 70°C, demolded after 30 minutes, and a sample of 10 cm × 10 cm × 5 mm was prepared. Using a Thomson blade, it was punched out into a cylindrical shape with a diameter of 25 mm.

[0059] Regarding the samples obtained in each reference example, the temperature dependence of the loss tangent (tanδ) of elasticity and viscosity was evaluated. Specifically, using a viscoelastic rheometer (AR-2000, manufactured by TA Instruments Japan Co., Ltd.), measurements were taken at -30°C to 200°C under the conditions of a frequency of 10 Hz and a strain of 1%. The results are shown in Figure 2.

[0060] Near 25°C where the evaluation was conducted, the tanδ values of the silicone gel and the polyurethane gel were almost the same. However, in the range of -30°C to 200°C, the tanδ of the polyurethane gel had a greater temperature dependence compared to the tanδ of the silicone gel. This is considered to be because polyurethane is a material having a Tg. When tanδ changes, the balance of viscoelasticity changes, so the hardness changes. Therefore, it can be seen that when using a shock absorber in a wide temperature range, particularly in the range of -20°C to 80°C, it is preferable to use a silicone gel.

Claims

1. A shock absorber containing a gel and resin foam beads with an average particle size of 0.8 mm or more and having a density of less than 0.3 g / cm ３ is provided. Furthermore, the following formula [1 - (weight per unit volume of gel ÷ specific gravity of gel + weight per unit volume of resin foam beads ÷ specific gravity of resin foam beads)] × 100 (%) An impact absorber in which the content of gases other than the gases contained inside and in the outer shell of the resin foam beads, which can be calculated by the above formula, is 1 to 40% by volume.

2. The impact absorber according to Claim 1, wherein the specific gravity of the resin foam beads is 0.15 or less.

3. The impact absorber according to Claim 1 or 2, wherein the gel is a silicone gel.

4. The impact absorber according to any one of Claims 1 to 3, wherein the gel is interposed between the resin foam beads.

5. A step of foaming the raw material of the gel, and A method for manufacturing a shock absorber having a step of filling a mold with a raw material of a foamed gel and heating and curing it together with resin foam beads, with a density of 0.3 g / cm ３ or less.

6. A method for producing an impact absorber according to Claim 5, further comprising a step of coating the resin foam beads with a part of the raw material of the gel.

7. The method for producing an impact absorber according to Claim 5 or 6, wherein the average particle diameter of the resin foam beads is 0.8 mm or more.

8. The method for producing an impact absorber according to any one of Claims 5 to 7, wherein the specific gravity of the resin foam beads is 0.15 or less.

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