Viscoelastic body excellent in workability

Abstract

To solve the problem that conventionally, a silicone gel sheet has strong adhesive force so as to pursuit softness, a viscoelastic body is stuck to a blade during works such as punching work, cutting work and slit work, and many mounting operators perform manual mounting, workability is poor, and improvement is required.SOLUTION: A viscoelastic body is formed by mixing and integrating a three-dimensional fiber structure formed of a non-woven fabric, an elastomer and fluororesin powder, and is excellent in workability. The elastomer constituting the viscoelastic body is silicone gel or urethane gel, and has Asker F hardness of 30 or less and penetration of 50 or more, and the three-dimensional fiber structure constituting the viscoelastic body has porosity of 51% or more and the thickness of 30 to 99% of the thickness of the viscoelastic body, and is arranged so as not to be exposed to the surface of the viscoelastic body.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a viscoelastic body having a non-adhesive cut surface and excellent processability. [Background technology]

[0002] Very soft viscoelastic bodies with a hardness of 30 or less as measured using an Asker F, such as silicone gel, have high vibration damping properties due to their high viscosity, but they also have the characteristics of being highly adhesive and stretchable with very little force.

[0003] When processing such a viscoelastic body, for example, when a square viscoelastic body is to be punched into a different shape using a punching machine, the viscoelastic body is prone to losing its shape due to its stickiness and stretchiness, making it difficult to set it into the punching machine in the correct square shape.

[0004] To solve this problem, the applicant has disclosed a viscoelastic body that is integrated with a three-dimensional fiber structure, has an Asker F hardness of 30 or less and a penetration of 50 or more, wherein the three-dimensional fiber structure is a nonwoven fabric, contains silicone gel or urethane gel, and has a porosity of 51% or more (see Patent Document 1).

[0005] Also disclosed is a three-dimensional thermally conductive molded body that can ensure sufficient gap filling and contact area for heat generating components such as IC chips and heat dissipating components such as heat sinks without applying excessive stress to these components. An embodiment of the three-dimensional thermally conductive molded body includes a thermally conductive material and a silicone-based material. However, the three-dimensional thermally conductive molded body has a substantially flat bottom surface and a three-dimensional shaped portion located inside the bottom surface, and the height of the three-dimensional shaped portion above the bottom surface is different at at least two points, resulting in a complex structure of the three-dimensional thermally conductive molded body and its manufacturing method (see Patent Document 2).

[0006] Also disclosed is at least one silicone sheet selected from a silicone gel sheet and a silicone putty sheet, the silicone sheet has a hardness of 75 or less on Shore 00, is cut in the thickness direction, the cut surfaces of the silicone sheet are adjacent to each other without any gaps, the cut surfaces of the silicone sheet are non-adhesive and separable at the cut surfaces, and the adhesiveness of the cut surfaces is 0.6 N or less when measured with a tackiness checker (see Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-125557 A [Patent Document 2] WO2018-078436 publication [Patent Document 3] JP 2019-169692 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in recent years, with the trend toward smaller devices and higher performance, silicone gel sheets etc. are required to be soft, have high thermal conductivity and are thin. Conventionally, silicone gel sheets etc. have been soft and have strong adhesive power in order to pursue vibration damping and impact resistance, and many mounting workers currently mount the devices manually, so there was a demand for improvements to be made to the poor workability. [Means for solving the problem]

[0009] The viscoelastic body of the present invention is a mixture of a three-dimensional fiber structure made of a nonwoven fabric, an elastomer, and a fluororesin powder, the elastomer being a silicone gel or a urethane gel. The elastomer has an Asker F hardness of 30 or less and a penetration of 50 or more. The three-dimensional fiber structure constituting the viscoelastic body has a porosity of 51% or more and a thickness of 30 to 99% of the thickness of the viscoelastic body. Effect of the Invention

[0010] The viscoelastic body of the present invention is made by mixing and integrating a three-dimensional fiber structure, an elastomer, and a fluororesin powder. Although an elastomer with an Asker F hardness of 30 or less and a penetration of 50 or more is used, the viscoelastic body is difficult to stretch and has high tensile strength because it is integrated with the three-dimensional fiber structure. In addition, due to the slipperiness of the fluororesin powder, the number of times that the material can be punched or cut without sticking to a blade is 10 times or more greater than that of conventional products. Therefore, the viscoelastic body of the present invention has excellent processability.

[0011] The viscoelastic body of the present invention has a predetermined thickness and is formed into a rectangular shape. Furthermore, even when the viscoelastic body is cut in the thickness direction, the cut surfaces are adjacent to each other without any gaps, and the cut surfaces are non-adhesive, so that the viscoelastic body can be easily separated into separate pieces at the cut surfaces. As a result, the cut surfaces do not come into contact with each other, and manual work can be easily performed, resulting in a significant improvement in workability compared to conventional work.

[0012] By adding fluororesin powder to the resin (silicone gel or urethane gel), the releasability from the punching blade was improved. Furthermore, by integrating the resin with a three-dimensional fiber structure (nonwoven fabric), the resin can be trapped between the fibers of the nonwoven fabric, preventing deformation. Furthermore, by integrating the gel with the nonwoven fabric, the adhesiveness of the resin can be utilized to increase the load-bearing capacity of the polymer, which is expected to improve vibration damping and shock absorption even for heavy objects. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view showing an example of an embodiment of the present invention. [Diagram 2] FIG. 1 is a plan view showing an example of an embodiment of the present invention. [Diagram 3] This is a micrograph of a portion of the cross section taken along line A-A in Figure 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The viscoelastic body 1 of the present invention is formed by filling and integrating a three-dimensional fiber structure 11 made of nonwoven fabric with a mixture of an elastomer 12 and a fluororesin powder 13, the elastomer 12 being a silicone gel or a urethane gel. The elastomer 12 has an Asker F hardness of 30 or less and a penetration of 50 or more.

[0015] The three-dimensional fiber structure 11 constituting the viscoelastic body 1 has a porosity of 51% or more. The three-dimensional fiber structure 11 has a thickness of 30 to 99% of the thickness of the viscoelastic body 1, and preferably has a thickness of 50 to 90% of the thickness of the viscoelastic body 1.

[0016] The elastomer in the present invention is a polymeric material that can recognize viscoelasticity at room temperature, and is a general term for polymeric compounds that have high elongation at room temperature and large breaking strain compared to other polymeric materials. The fluororesin powder in the present invention is an organic powder containing fluorine atoms in its molecular structure, and is also called an organic fluorine compound powder. Fluororesins include PTFE, PFA, FEP, ETFE, PCTFE, and PVDE. The powder diameter is 0.3 to 800 μm. PTFE powder includes molding powder for compression molding, fine powder that becomes fibrous when pressure is applied, and dispersion that is an aqueous dispersion.

[0017] In the present invention, the three-dimensional fiber structure 11 may be a nonwoven fabric, a woven fabric, a knitted fabric, or an open-cell structure such as a sponge, with the nonwoven fabric being preferred in terms of the uniformity of the void ratio when viewed three-dimensionally.

[0018] Here, uniformity means that in woven and knitted fabrics, the density is high at the points where the threads cross and overlap, resulting in variation in the void ratio, but in nonwoven fabrics, each fiber is mixed together, so no matter which part you cut out, the structure is roughly the same and there is less variation in the void ratio.

[0019] That is, the three-dimensional fiber structure 11 has a jungle gym-like structure, and in order to hold the elastomer 12 and the fluororesin powder 13 in sufficient space between the fibers, the porosity of the three-dimensional fiber structure 11 is preferably 51% or more, more preferably 70% or more, and even more preferably 90% or more. If the porosity is less than 51%, the elastomer 12 and the fluororesin powder 13 will not easily penetrate into the three-dimensional fiber structure 11, and interfaces will easily form between the three-dimensional fiber structure 11 and the elastomer 12 and the fluororesin powder 13.

[0020] When a nonwoven fabric is used for the three-dimensional fiber structure 11, the basis weight is not particularly limited, but is preferably 1 to 5,000 g / m 2 is preferable, and 1 to 500 g / m 2 More preferably, 1 g / m 2 Below 5,000 g / m, the number of fibers is small, making it difficult to control the void ratio. 2 If the thickness exceeds this range, the number of fibers increases and it tends to become difficult to control the void ratio.

[0021] The method for producing the nonwoven fabric 11 is not particularly limited, and any known method can be used. For example, the thermal bond method, the needle punch method, and the spunlace method can be mentioned. In the needle punch method, the fibers are opened by a carding machine, and then mechanically entangled with needles, and the void ratio is about 75 to 90% at most.

[0022] When the porosity is to be made higher than 90%, it is preferable to use a thermal bonding method in which the fibers are thermally bonded to each other using a binder fiber whose surface melts when heated at the contact points between the fibers, rather than entangling the fibers with a needle punch method, etc. Methods for fixing the fibers in the thermal bonding method include hot air, hot plate pressing, and hot calendaring.

[0023] The thermal bonding method can be used in combination with a needle punch method or the like. In this case, the mixing ratio of the binder fiber is not particularly limited. As a method that does not use binder fiber, a resin bonding method in which a resin is applied between the fibers of the nonwoven fabric 11 using a spray bottle or the like and dried, and the like is used as a binder, or a method in which a heat-melting powder is applied between the fibers of the nonwoven fabric 11 and melted therein can be used.

[0024] Conversely, if the void ratio is to be made lower than 75%, it is preferable to use a method in which the fibers are entangled by a needle punching method or the like, and then the fibers are further fixed together with binder fibers whose fiber surfaces melt when heated.

[0025] The thickness of the three-dimensional fiber structure 11 is not particularly limited, but is preferably 0.1 to 50 mm, more preferably 0.5 to 20 mm, and even more preferably 1 to 10 mm. If it is less than 0.1 mm, the strength will be weak, and if it exceeds 50 mm, it will be difficult to produce the three-dimensional fiber structure 11, and special equipment will be required.

[0026] There are no particular limitations on the fiber material constituting the three-dimensional fiber structure 11, and examples of the fiber material that can be used include organic fibers such as polyester, polyolefin, nylon, aramid, polyacrylic, polyether, polythioether, and polyimide, and inorganic fibers such as glass fiber, carbon fiber, and ceramic fiber. The fiber form is also not particularly limited, and examples of the fiber form include monofilament, multifilament, staple fiber, and short-cut fiber.

[0027] The fiber fineness is not particularly limited, but is preferably 1 to 100 dtex, and more preferably 3 to 18 dtex. If it exceeds 100 dtex, the fibers are thick and therefore have high rigidity, and the repulsive force between the fibers is strong, making it difficult to control the porosity to be low (to increase density), whereas if it is less than 1 dtex, the fibers are thin and therefore have low rigidity, and the fibers tend to overlap without repelling each other, making it difficult to control the porosity to be high (to decrease density).

[0028] The elastomer 12 is not particularly limited, and examples thereof include silicone gel, urethane gel, hydrogel, etc. Among them, silicone gel and urethane gel are preferred because the solvent is less likely to volatilize during long-term use.

[0029] Silicone gel can be obtained by reacting bifunctional organosiloxane with trifunctional or higher organosiloxane to crosslink. The siloxane gel forms a three-dimensional network structure, and silicone oil is supported between the three-dimensional network structure. As the siloxane gel, for example, a viscoelastic body composed of polydimethylsiloxane gel, polymethyltrifluoropropylsiloxane gel, polyphenylmethylsiloxane gel, etc. and silicone oil is particularly preferred. As the silicone oil, for example, dimethylsilicone oil, methylphenylsilicone oil, amino-modified silicone oil, epoxy-modified silicone oil, etc. can be mentioned.

[0030] Polyurethane gel can be obtained by reacting a difunctional or higher polyol with a difunctional or higher isocyanate. The polyurethane forms a three-dimensional mesh structure, and a plasticizer is inserted between the three-dimensional mesh structure. Examples of the polyurethane gel include polyether-based urethane, polyester-based urethane, polycarbonate-based urethane, polycaprolactone-based urethane, and polyolefin-based urethane. Examples of the plasticizer include phthalate esters, adipic acid esters, trimellitic acid esters, phosphate esters, citrate esters, sebacic acid esters, maleic acid esters, benzoic acid esters, and polyesters.

[0031] The three-dimensional fiber structure 11 being integrated means that it is not separated into individual layers, but is a composite of the three-dimensional fiber structure 11 made of nonwoven fabric 11, elastomer 12, and fluororesin powder 13. Here, the thickness of the three-dimensional fiber structure 11 is preferably 30% or more, and more preferably 50% or more, of the thickness made of the viscoelastic body 1. If it is less than 30%, the viscoelastic body 1 tends to stretch in the thickness direction, which tends to reduce handleability.

[0032] The method for integrating the three-dimensional fiber structure 11 is not particularly limited, but examples include a method in which the three-dimensional fiber structure 11 is impregnated with monomers or prepolymers that are the raw materials for the viscoelastic body 1 inside a mold and then cured. The size of the mold is appropriately adjusted according to the size of the viscoelastic body 1 to be produced. The curing time and temperature are appropriately set according to the type of elastomer 12 used.

[0033] The Asker F hardness of the elastomer 12 of the present invention is 30 or less, preferably 25 or less, and more preferably 20 or less. If the Asker F hardness exceeds 30, the viscoelastic body 1 becomes hard and difficult to stretch, reducing the benefits of using the three-dimensional fiber structure 11.

[0034] The penetration of the elastomer 12 of the present invention is at least 50, preferably at least 100, and more preferably at least 120. If it is less than 50, the viscoelastic body 1 becomes hard and difficult to stretch, reducing the benefits of having the three-dimensional fiber structure 11. The penetration is a value measured based on JIS K 2207.

[0035] The thickness of the viscoelastic body 1 of the present invention is not particularly limited, but is preferably 0.1 to 100 mm, and more preferably 0.5 to 50 mm. If it is less than 0.1 mm, it becomes too thin and sufficient viscoelasticity cannot be obtained, and if it exceeds 100 mm, processability such as defoaming during molding tends to deteriorate.

[0036] Applications of the viscoelastic body 1 of the present invention are not particularly limited, but include vibration damping materials, vibration isolation materials, soundproofing materials, heat shielding materials, electromagnetic wave shielding materials, cushioning materials, and impact absorbing materials. EXAMPLES

[0037] Examples will be described below, in which "%" is by weight unless otherwise specified.

[0038] Example 1 The three-dimensional fiber structure is made of nonwoven fabric, with a thickness of 3.0 mm and a basis weight of 300 g / m2, using polyester fiber (manufactured by HUVIS) with a fiber diameter of 16 dtex and polyester binder fiber (manufactured by HUVIS) with an adjusted blend ratio, and thermally bonded using the thermal bond method (after opening the fibers with a carding machine, they are thermally bonded through a dryer). 2 A polyester nonwoven fabric with a porosity of 90% was produced.

[0039] The polyester nonwoven fabric (three-dimensional fiber structure) thus produced was mixed with two liquids (LIQUID A and LIQUID B of SILGEL612 manufactured by Wacker Asahi Kasei Silicone Co., Ltd.) that serve as the raw materials for silicone gel, with the blending ratio adjusted. The fluororesin powder used was a mixture of molding powder 25μm (manufactured by Daikin Industries, Ltd.) and molding powder 6μm or fine powder 6μm (manufactured by Seishin Enterprise Co., Ltd.) in an appropriate ratio.

[0040] A viscoelastic body was obtained by impregnating 2% nonwoven fabric with 78% silicone gel and 20% fluororesin powder molding powder (25 μm) in a thermostatic oven (23°C, 24 hours) for crosslinking. The viscoelastic body sheet had a thickness of 3 mm and an Asker C hardness of 15.

[0041] Example 2 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 78% silicone gel and 20% fluororesin molding powder of 6 μm. The rest was the same as in Example 1.

[0042] Example 3 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 78% silicone gel, 12% 25 μm molding powder of fluororesin powder, and 8% 6 μm molding powder. The rest was the same as in Example 1.

[0043] Example 4 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 78% urethane gel, 12% 25 μm molding powder of fluororesin powder, and 8% 6 μm molding powder. The rest was the same as in Example 1.

[0044] Example 5 A viscoelastic body was produced by impregnating 15% nonwoven fabric with 65% silicone gel, 12% 25 μm molding powder of fluororesin powder, and 8% 6 μm molding powder. The rest was the same as in Example 1.

[0045] Example 6 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 88% silicone gel, 6% 25 μm fluororesin molding powder, and 4% 6 μm molding powder. The rest was the same as in Example 1.

[0046] Example 7 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 68% silicone gel, 18% 25 μm molding powder of fluororesin powder, and 12% 6 μm molding powder. The rest was the same as in Example 1.

[0047] Comparative Example 1 The viscoelastic body was prepared by mixing 100% silicone gel. The rest of the process was the same as in Example 1.

[0048] Comparative Example 2 A viscoelastic body was produced by impregnating 98% of silicone gel into 2% of nonwoven fabric. The rest was the same as in Example 1.

[0049] Comparative Example 3 A viscoelastic body was produced by impregnating 23% nonwoven fabric with 57% silicone gel, 12% 25μm fluororesin molding powder, and 8% 6μm molding powder. However, the silicone gel did not penetrate sufficiently into the nonwoven fabric, and a viscoelastic body could not be formed.

[0050] Comparative Example 4 A viscoelastic body was produced by impregnating 2% nonwoven fabric with 58% silicone gel, 24% 25μm fluororesin molding powder, and 16% 6μm molding powder. However, the silicone gel did not penetrate sufficiently into the nonwoven fabric, and a viscoelastic body could not be formed.

[0051] Comparative Example 5 A viscoelastic body was created by impregnating 2% nonwoven fabric with 78% silicone gel and 20% 6μm fine powder of fluororesin powder. However, the fine powder of fluororesin powder aggregated, and it was not possible to form a uniform viscoelastic body.

[0052] The viscoelastic bodies produced in Examples 1 to 7 and Comparative Examples 1 to 5 were evaluated by the methods described below. Table 1 shows the evaluation results of the Examples, and Table 2 shows the evaluation results of the Comparative Examples.

[0053] <Hardness> Hardness was measured with a durometer type E (Shore E) or an Asker C type hardness tester.

[0054] <Workability> They were produced in Examples 1 to 7 and Comparative Examples 1 to 5. The finished dimensions were 3.0 mm thick, 220 mm wide, and 220 mm long. ⊚: There are no gaps in the elastomer, no noticeable bubbles, and the sheet dimensions are stable. ◯: The fabrication was possible without any loss of elastomer or noticeable bubbles, but the permeability of the elastomer was low and it took a long time for the elastomer to be impregnated into the fiber structure. ×: A viscoelastic body could not be produced, so the following tests were not performed.

[0055] <Vibration damping> The dynamic viscoelasticity was measured using a rotational rheometer and tan δ was compared. ◎:tanδ≧0.4 ○: tan δ<0.4

[0056] <Load capacity> A 20mm x 15mm square specimen is placed on the top surface of the specimen with a force gauge and a pressure of 300g / cm 3 The thickness (mm) of the sample when subjected to the load was measured, and the percentage of deformation was confirmed. ◎: Thickness deformation rate 20% or less ○: Thickness deformation rate 30% or less ×: Thickness deformation rate 30% or more

[0057] Secondary workability: The specimens were punched into a φ30 mm round shape using a table continuous punching machine PAL500 manufactured by Sakamoto Zoki Co., Ltd. 100 test pieces were prepared, and the shapes after punching were visually observed. <Mold releasability> The releasability from the punching blade during punching was confirmed. Specifically, it was evaluated by how many consecutive punching shots could be performed without cleaning the blade after punching. ◎: 50 shots or more 〇: 10 or more shots ×: Less than 10 shots

[0058] <Shape stability> Dimensional stability when removed from the die after punching to φ30 mm. ◎: Dimensional tolerance is within ±5% and no distortion occurs. ○: Dimensional tolerance is within ±10%, or slight distortion of shape can be confirmed visually. ×: The dimensional tolerance was exceeded by ±10%, or the thickness or round shape was clearly deformed.

[0059] [Table 1]

[0060] [Table 2]

[0061] (evaluation) From the hardness and shape stability of Examples 1 to 7 and Comparative Examples 1 to 5, it can be seen that the viscoelastic body in which the three-dimensional fiber structures are integrated and composite is less likely to stretch due to the presence of the three-dimensional fiber structures, and thus has improved processability. In addition, by mixing 30 to 40 percent of the fluororesin powder with a small diameter of less than two-thirds of the main diameter, the viscosity during processing is reduced, making it easier to mold, and the hardness of the finished product is also reduced.

[0062] Comparative Examples 1 and 2 had poor releasability from the punching die during secondary processing, and in Comparative Examples 3 to 5, a viscoelastic body could not be produced. Compared with the viscoelastic bodies of Examples 1 to 7, the shape stability was poor, so the shape retention after punching was poor, resulting in poor processability. [Industrial Applicability]

[0063] The viscoelastic body of the present invention uses a highly flexible elastomer, which gives it high vibration damping (impact resistance) properties, yet is resistant to stretching and has high tensile strength and excellent processability, making it ideal for use as vibration damping materials, vibration-proofing materials, soundproofing materials, heat insulation materials, electromagnetic wave shielding materials, cushioning materials, shock absorbing materials, etc. [Explanation of symbols]

[0064] 1 Viscoelastic body 2 Cut surface 3 pieces 4 Adhesive layer 11 Three-dimensional fiber structures (nonwoven fabrics) 12 Elastomers (silicone gel, urethane gel) 13 Fluorine resin powder

Claims

1. A nonwoven fabric with a porosity of 51% or more is impregnated with a composition containing an elastomer and a fluororesin powder, and the composition is crosslinked to form a viscoelastic body. The fluororesin powder is a viscoelastic body having a diameter of 0.3 to 800 μm.

2. The viscoelastic body according to claim 1 , wherein the elastomer is a silicone gel or a urethane gel.

3. 3. The viscoelastic body according to claim 1, wherein the elastomer has an Asker F hardness of 30 or less and a penetration of 50 or more.

4. 3. The viscoelastic body according to claim 1, wherein the thickness of the nonwoven fabric is 30 to 99% of the thickness of the viscoelastic body.

5. A viscoelastic body as described in claim 1 or 2, wherein the fluororesin powder is a mixture of a main component powder having a diameter of 0.3 to 800 μm and a fluororesin powder having a smaller diameter than that of the main component, which is less than two-thirds of the diameter of the main component.

6. A viscoelastic body according to claim 1 or 2, wherein the fluororesin powder is PTFE (polytetrafluoroethylene) and is a molding powder, fine powder, or aqueous dispersion.

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