WO2015029860A1 - 発泡シート - Google Patents
発泡シート Download PDFInfo
- Publication number
- WO2015029860A1 WO2015029860A1 PCT/JP2014/071831 JP2014071831W WO2015029860A1 WO 2015029860 A1 WO2015029860 A1 WO 2015029860A1 JP 2014071831 W JP2014071831 W JP 2014071831W WO 2015029860 A1 WO2015029860 A1 WO 2015029860A1
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- WIPO (PCT)
- Prior art keywords
- strain
- foam sheet
- support member
- impact
- strain detection
- Prior art date
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/18—Telephone sets specially adapted for use in ships, mines, or other places exposed to adverse environment
- H04M1/185—Improving the rigidity of the casing or resistance to shocks
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/0004—Use of compounding ingredients, the chemical constitution of which is unknown, broadly defined, or irrelevant
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
- G02B3/02—Simple or compound lenses with non-spherical faces
- G02B3/04—Simple or compound lenses with non-spherical faces with continuous faces that are rotationally symmetrical but deviate from a true sphere, e.g. so called "aspheric" lenses
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/0202—Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets
- H04M1/026—Details of the structure or mounting of specific components
- H04M1/0266—Details of the structure or mounting of specific components for a display module assembly
Definitions
- the present invention relates to a foam sheet excellent in shock absorption, and an electric / electronic device using the foam sheet.
- an image display member fixed to an image display device such as a liquid crystal display, an organic electroluminescence display (hereinafter referred to as “OLE display”), a plasma display, a so-called “mobile phone”, “smart phone”, or “portable information terminal”
- OLED display organic electroluminescence display
- a plasma display a so-called “mobile phone”, “smart phone”, or “portable information terminal”
- a foam material is used as an impact absorbing material.
- a foam material As such a foam material, a polyethylene foam having a low foaming and an closed cell structure and a foaming ratio of about 30 times has been used. Specifically, for example, in the technique disclosed in Japanese Patent Laid-Open No. 2001-100216, a gasket made of a polyurethane foam having a density of 0.3 to 0.5 g / cm 3 is used. Further, for example, in the technique disclosed in Japanese Patent Application Laid-Open No. 2002-309196, a sealing material for electric / electronic devices made of a foam structure having an average cell diameter of 1 to 50 ⁇ m is used.
- the image display member 102 of the smartphone 101 is configured by laminating a cover glass 103, an adhesive 104, a panel glass 105, an OLE display 106, and a foam sheet 107, and is housed in a housing 108.
- the foam sheet 107 is attached to the entire back surface of the OLE display 106.
- the conventional foamed sheet 107 does not exhibit sufficient shock absorption when the thickness is reduced. Therefore, even if the area of the image display member 102 is increased, when the smartphone 101 is dropped on the ground or the like, the impact at the time of collision is absorbed and the OLE display 106 constituting the image display member 102 is deformed. There is a need for foam sheets that prevent breakage due to corrosion.
- the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a foamed sheet that exhibits excellent shock absorption even when the thickness is very thin. It is another object of the present invention to provide an electric / electronic device that is less likely to damage an image display member or the like due to an impact when dropped, even if it is reduced in size and thickness.
- the foam sheet of the present invention has a thickness of 30 to 200 ⁇ m, a density of 0.2 to 0.7 g / cm 3 and an average cell diameter of 10 to 100 ⁇ m.
- a sheet is configured to be able to hold the foam sheet sandwiched between a support member and a strain detection member, and strain of the strain detection member when an impact force is applied to the support member is measured by a strain gauge.
- the strain suppression rate represented by the following formula is 20% or more.
- Strain suppression rate (%) ⁇ ( ⁇ 0 ⁇ 1 ) / ⁇ 0 ⁇ ⁇ 100 (In the above equation, ⁇ 0 is the maximum strain of the strain detection member when an impact force is applied to the support member in a state where the foam sheet is not mounted between the support member and the strain detection member. And ⁇ 1 is the maximum strain of the strain detection member when an impact force is applied to the support member in a state where the foam sheet is mounted between the support member and the strain detection member.
- a foam sheet is formed of a foam having a density of 0.2 to 0.7 g / cm 3 and an average cell diameter of 10 to 100 ⁇ m, and a strain suppression rate of 20% or more.
- Strain suppression rate is configured to be able to hold a foam sheet sandwiched between a support member and a strain detection member, and measures the strain of the strain member when an impact force is applied to the support member by an impact test. It can be obtained using an apparatus.
- the impact test apparatus holds the foam sheet in a state of being sandwiched between the support member and the strain detection member, and the foam sheet in any thickness direction.
- Holding means for holding at a compressibility
- impact load means for applying an impact force to the support member held by the holding means, and an impact force applied to the foam sheet by the impact load means via the support member
- Strain detection means for detecting strain generated in the strain detection member by the strain gauge, and output means for calculating and outputting the strain suppression rate based on the strain detected by the strain detection means. You may do it.
- an impact test device can be used to hold a thin foam sheet with an arbitrary holding force and measure the strain of the strain detecting member when the impact force is applied to the foam sheet with a strain gauge. It becomes possible.
- the maximum distortion ⁇ 0 of the detection member when the foam sheet is not mounted between the support member and the strain detection member, and the detection when the foam sheet is mounted between the support member and the strain detection member By measuring the maximum strain ⁇ 1 of the member with a strain gauge, it becomes possible to obtain the strain suppression rate of the foam sheet.
- the holding means is fixed perpendicularly to the table so that one surface side of the strain detection member is in close contact, and a portion receiving the impact force of the strain detection member is a load.
- a fixing jig having a concave portion formed in the central portion so as to be deformable in the direction, and an opening formed in the central portion so as to be slidable in the direction toward the fixing jig, and Abutting on the surface of the support member in close contact with the foam sheet so as to cover the entire surface of the foam sheet fixed on the other side, the surface opposite to the surface in contact with the foam sheet;
- a pressing jig fixed to the table in a state of pressing to the foam sheet side, and a pressing pressure by which the pressing jig presses the support member is adjusted to arbitrarily set the compression ratio in the thickness direction of the foam sheet.
- the Pressure Adjusting means, and the impact load means applies an impact force to the support member that enters the opening of the pressing jig and covers the foam sheet, and the strain detection means is You may make it detect the distortion which generate
- the thin foam sheet is held at a compression rate in an arbitrary thickness direction, and the entire surface of the foam sheet is supported by impact loading means from the opening formed in the center part of the pressing jig. It becomes possible to apply an impact force to the entire surface of the thin foam sheet through the plate.
- the fixing jig fixed perpendicularly to the table is in close contact with one surface side of the strain detection member, and the central portion so that the portion receiving the impact force of the strain detection member can be deformed in the load direction. A recess is formed.
- the strain detection member can be freely deformed by an impact force, and the strain detection means reliably ensures the maximum strain generated by the deformation of the strain detection member inside the recess by the impact force via the strain gauge. Can be detected.
- the impact load means includes a pendulum-type hammer that is pivotally supported at one end and a hammer holding means that lifts and holds the hammer at a predetermined angle.
- the impact force may be applied by swinging down the hammer held by the hammer holding means.
- the strain detection member is constituted by two plate members being in close contact with each other, and the strain gauge is the first of the two plate members to which the foam sheet is in close contact.
- a single plate member may be attached to the surface opposite to the surface to which the foam sheet is in close contact, and laminated between the two plate members.
- a strain gauge is provided on a surface opposite to the surface of the first plate member to which the foam sheet is in close contact with the surface to which the foam sheet is in close contact. Is pasted.
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement, has a maximum value within a range from 500 Hz to 50000 Hz, and from 500 Hz
- the loss tangent (tan ⁇ ) at 3000 Hz may be 0.2 or more.
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement, has a maximum value in the range from 500 Hz to 50000 Hz, and the loss at 500 Hz to 3000 Hz.
- foamed sheet of the present invention may be used as an impact absorbing sheet for electric / electronic devices.
- foam sheet as an impact absorbing sheet for electrical and electronic equipment, even when the electrical and electronic equipment is downsized and thinned, it can absorb the impact when dropped and suppress damage. It becomes.
- the electrical / electronic device of the present invention is a foam sheet made of a foam having a thickness of 30 to 200 ⁇ m, a density of 0.2 to 0.7 g / cm 3 , and an average cell diameter of 10 to 100 ⁇ m.
- An impact test apparatus configured to be able to hold the foam sheet sandwiched between a support member and a strain detection member, and to measure strain of the strain detection member when an impact force is applied to the support member using a strain gauge.
- a foam sheet having a strain suppression rate represented by the following formula of 20% or more is used.
- Strain suppression rate (%) ⁇ ( ⁇ 0 ⁇ 1 ) / ⁇ 0 ⁇ ⁇ 100 (In the above equation, ⁇ 0 is the maximum strain of the strain detection member when an impact force is applied to the support member in a state where the foam sheet is not mounted between the support member and the strain detection member. And ⁇ 1 is the maximum strain of the strain detection member when an impact force is applied to the support member in a state where the foam sheet is mounted between the support member and the strain detection member.
- the foam sheet is made of a foam having a thickness of 30 to 200 ⁇ m, a density of 0.2 to 0.7 g / cm 3 , and an average cell diameter of 10 to 100 ⁇ m.
- the impact test apparatus holds the foam sheet in a state of being sandwiched between the support member and the strain detection member, and the foam sheet has an arbitrary thickness.
- Holding means for holding at a compressibility in the direction, impact loading means for applying an impact force to the support member held by the holding means, and the foamed sheet is loaded by the impact load means via the support member
- Strain detection means for detecting strain generated in the strain detection member by an impact force by the strain gauge; output means for calculating and outputting the strain suppression rate based on the strain detected by the strain detection means; You may make it provide.
- the electric / electronic device it is possible to measure in advance the strain suppression rate of the thin foamed sheet through an impact test device before mounting the thin foamed sheet on the electric / electronic device.
- the electric / electronic device can absorb the impact at the time of dropping and suppress the breakage by using the foamed sheet whose distortion suppression rate is measured in advance.
- the holding means is fixed perpendicularly to the table so that one surface side of the strain detection member is in close contact with the impact detection force of the strain detection member.
- the jig detects the distortion by providing a fixing jig having a concave portion formed in the central portion so as to be deformable in the load direction and an opening formed in the central portion so as to be slidable in the direction toward the fixing jig.
- the support member in contact with the surface of the support member that is in close contact with the foam sheet so as to cover the entire surface of the foam sheet that is fixed to the other surface side of the portion, the surface being in contact with the foam sheet.
- a pressing jig fixed to the table in a state where the foaming sheet is pressed to the foam sheet side, and a pressing pressure by which the pressing jig presses the support member is adjusted to arbitrarily adjust the compressibility in the thickness direction of the foam sheet.
- Set to Pressure adjusting means, and the impact load means applies an impact force to the support member that enters the opening of the pressing jig and covers the foam sheet, and the strain detection means is provided by the strain gauge. You may make it detect the distortion which generate
- the electric / electronic device it is possible to measure the strain suppression rate of the thin foam sheet with high accuracy through an impact test device before the thin foam sheet is mounted on the electric / electronic device.
- the electric / electronic device can absorb the impact at the time of dropping and suppress the breakage by using the foamed sheet whose distortion suppression rate is measured with high accuracy.
- the impact load means includes a pendulum-type hammer that is pivotally supported at one end and a hammer holding means that lifts and holds the hammer at a predetermined angle. And the impact force may be applied by swinging down the hammer held by the hammer holding means.
- the electric / electronic device before the thin foam sheet is mounted on the electric / electronic device, it becomes possible to conduct a comparative study of the strain suppression rate and the like for each thin foam sheet through an impact test apparatus. As a result, the electric / electronic device can use the foam sheet having the maximum distortion suppression rate, and can absorb the impact at the time of dropping and suppress the breakage.
- the strain detection member is configured such that two plate members are in close contact with each other, and the strain gauge is in contact with the foam sheet among the two plate members.
- the first plate member may be laminated on the surface opposite to the surface to which the foam sheet is in close contact, and laminated between the two plate members.
- a strain gauge is attached to the OLE display to which the foam sheet is closely attached in the image display member of the smartphone via an impact test device.
- an alternative evaluation of the actual machine test dropped on the ground or the like can be performed.
- the electric / electronic device can use the foam sheet for the image display member of the smartphone, and can absorb the impact at the time of dropping and suppress the breakage.
- the foamed sheet has a loss tangent (tan ⁇ ) that is a ratio of a loss elastic modulus to a storage elastic modulus by dynamic viscoelasticity measurement within a range from 500 Hz to 50000 Hz.
- the loss tangent (tan ⁇ ) from 500 Hz to 3000 Hz may be 0.2 or more.
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement, has a maximum value within a range from 500 Hz to 50000 Hz, and is from 500 Hz to 3000 Hz.
- the foam sheet may be used as an impact absorbing sheet for electric / electronic devices.
- the foam sheet as an impact absorbing sheet for electric / electronic devices, it is possible to further absorb the impact at the time of dropping and prevent damage. Further downsizing and thinning can be achieved.
- a housing and an image display member may be provided, and the foamed sheet may be sandwiched between the housing and the image display member.
- the impact test apparatus 1 includes a holding member 3 as a holding unit that holds a test piece 2 formed of a foam sheet with an arbitrary holding force, and a test piece 2.
- An impact load member 4 serving as an impact load means for applying an impact force to the load
- a strain gauge 6 for measuring the strain of the strain detection member 5 to which the test piece 2 is closely attached
- a strain of the strain detection member 5 from a signal of the strain gauge 6
- PC personal computer
- the holding member 3 that holds the test piece 2 with an arbitrary holding force includes a fixing jig 11 fixed to the table 10, a strain detection member 5, the test piece 2, and a support member facing the fixing jig 11. 9, and a slidable holding jig 12 so as to be held between them.
- the holding jig 12 has an opening 12A formed at the center, is slidably installed on a pedestal 13 that can slide on the table 10, and can slide on the table 10 together with the pedestal 13. .
- the pedestal 13 is provided with a lever 14 for sliding the pedestal 13 and a fixing member 15 that is slid by the lever 14 and fixed to the table 10 after the temporary position is determined.
- the pressing jig 12 is provided with a pressing pressure adjusting means 16.
- the pressing pressure adjusting means 16 is preferably provided with a digital gauge or the like interlocked with the pressing jig 12.
- the pressing pressure adjusting means 16 finely adjusts the pressing jig 12 on the pedestal 13 fixed at the temporary position with respect to the test piece 2 in the front-rear direction (the left-right direction in FIG. 1). This makes it possible to adjust the holding force acting on the test piece 2 sandwiched between the strain detection member 5 and the support member 9.
- the impact load member 4 for applying an impact force to the test piece 2 held by the holding member 3 is a shaft having one end 22 pivotally supported with respect to the column 20 and a hammer 24 on the other end side. 23 and an arm 21 for lifting and holding the hammer 24 at a predetermined angle.
- the arm 21 can be fixedly held at a predetermined angle.
- the hammer 24 uses a steel ball, so that the hammer 24 can be integrally lifted at a predetermined angle by providing an electromagnet 25 at one end of the arm 21.
- the hammer 24 is not limited to the electromagnet 25 as long as the hammer 24 can be lifted together with the arm 21 and the hammer 24 and the arm 21 can be easily separated. Further, the hammer 24 is not limited to a spherical shape, and may be a block shape, for example.
- the strain detection member 5 that is in close contact with the fixing jig 11 has two first plate members 5 ⁇ / b> A and a second plate member 5 ⁇ / b> B that are made of resin such as acrylic resin or polycarbonate. It is configured.
- the strain gauge 6 is a lower end portion of the surface on the fixing jig 11 side of the first member 5A to which the test piece 2 is in close contact, that is, a surface opposite to the surface to which the test piece 2 of the first member 5A is in close contact. Is stuck between the first plate member 5A and the second plate member 5B. Thereby, the strain generated by the impact force of the first plate member 5A can be detected by the strain gauge 6.
- the strain detection member 5 is in close contact with the fixing jig 11 so that the lower end thereof faces the position where the hammer 24 of the support member 9 collides. Further, on the surface of the fixing jig 11 to which the strain detection member 5 is in close contact, a portion from a lower end receiving the impact force of the strain detection member 5 to a predetermined height (for example, a height of 4 cm) is a load direction. A recessed portion 27 that is recessed by a predetermined depth (for example, a depth of about 5 mm) is formed so as to be deformable. In addition, by providing an adhesive or the like on the outer surface of the second plate member 5B of the strain detection member 5, the strain detection member 5 can be attached to the fixing jig 11, and can be reliably fixed to the fixing jig.
- the support member 9 is formed of a resin plate material such as acrylic resin or polycarbonate, is in close contact with the test piece 2 in close contact with the first plate member 5A of the strain detection member 5, and is pressed by the pressing jig 12.
- the strain detector 7 is electrically connected to the strain gauge 6 and the PC 8, detects the strain ⁇ of the first plate member 5 ⁇ / b> A from the signal from the strain gauge 6, and outputs it to the PC 8.
- the PC 8 sequentially stores the time data of the strain ⁇ input from the strain detection unit 7, calculates the time change of the strain, the maximum value of the strain amount, the strain suppression rate described later, and the like and displays them on the liquid crystal display or the like.
- test piece 2 corresponds to the foam sheet 107 of the smartphone 101 shown in FIG.
- the first plate member 5A of the strain detection member 5 corresponds to the OLE display 106 of the smartphone 101 shown in FIG.
- the second plate member 5B of the strain detection member 5 corresponds to the cover glass 103, the adhesive 104, and the panel glass 105 of the smartphone 101 shown in FIG.
- the support member 9 corresponds to the housing 108 of the smartphone 101 shown in FIG.
- the thickness of the test piece 2 is measured in advance.
- the holding pressure adjusting means 16 is adjusted, the holding jig 12 is moved from the reference point by the thickness of the test piece 2, and the test piece 2 is set between the strain detection member 5 and the support member 9.
- the thickness of the test piece 2 is taken into account while checking the gauge of the pressing pressure adjusting means 16.
- the electromagnet 25 provided at one end of the arm 21 is switched on, and the hammer 24 is fixedly held on the arm 21. Then, after the arm 21 is swung up to an arbitrary predetermined angle and fixed, the electromagnet 25 is switched off to cause the hammer 24 to collide with the support member 9 held by the holding member 3 (see FIG. 2).
- the strain of the first plate member 5 ⁇ / b> A of the detection member 5 at this time is measured by the strain gauge 6.
- the strain detection member 5 and the support member 9 are in close contact with each other, and are firmly fixed to the fixing jig 11, and the hammer 24 is caused to collide with the support member 9 in the same manner.
- the strain suppression rate [%] of the test piece 2 can be calculated by measuring the strain of the first plate member 5A of the detection member 5 and calculating the following equation (1).
- ⁇ 0 is the first plate member 5A when an impact force is applied to the support member 9 in a state where the test piece 2 is not mounted between the strain detection member 5 and the support member 9.
- ⁇ 1 is the maximum strain of the first plate member 5A when an impact force is applied to the support member 9 with the test piece 2 mounted between the strain detection member 5 and the support member 9. is there.
- the signal from the strain gauge 6 is input to the strain detector 7.
- the signal from the strain gauge 6 is converted into strain ⁇ and output to the PC 8.
- the PC 8 sequentially stores the time data of the strain ⁇ input from the strain detection unit 7, calculates the time change of the strain, the maximum amount of strain, the strain suppression rate, and the like, and displays them on the liquid crystal display or the like. Therefore, the impact test apparatus 1 has a time variation of strain generated in the strain detection member 5 and a maximum strain amount when an impact force is applied to the test piece 2 formed of a thin foam sheet having a thickness of 30 to 200 ⁇ m. A value, a distortion suppression rate, etc. can be detected and output.
- the drop test device 31 includes a drop table 32 that is formed of a thick metal plate such as a stainless steel plate and arranged horizontally, and a guide rail 33 that is erected vertically on the upper surface of the drop table 32.
- the chuck member 35 attached so as to be freely dropped along the guide rail 33 and the lower end of the guide rail 33 at a low height (for example, a height of 5 cm) and free-falling. It comprises a pair of stop members 36 provided so that the chuck member 35 abutted and stopped.
- the pair of stop members 36 are formed of a hard rubber plate or the like.
- a height detection device (not shown) that detects the height of each chuck member 35 from each stop member 36 is provided.
- the chuck member 35 is erected in a right-angled outward direction (the front side in FIG. 5) from both side edges in the horizontal direction perpendicular to the dropping direction P.
- a pair of plate-like arm portions 35A is provided.
- a pair of air cylinders 37 are attached to the opposing positions of the tip portions of the pair of arm portions 35A, and the pistons 37A of the air cylinders 37 protrude from the horizontal outer side to the horizontal inner side by a predetermined length. It is attached as possible.
- the drop test apparatus 31 can support the smartphone 101 horizontally by causing the piston 37 ⁇ / b> A of each air cylinder 37 to protrude inward in the horizontal direction.
- the chuck member 35 can be freely dropped from an arbitrary height while the smartphone 101 is horizontally supported.
- the chuck member 35 becomes a predetermined height (for example, a height of 5 cm) from each stop member 36 by a height detection device (not shown).
- the piston 37A of each air cylinder 37 is pulled in, and only the smartphone 101 is configured to fall freely horizontally.
- the strain gauge 6 is attached to the OLE display 106 of the smartphone 101, and the strain gauge 6 is electrically connected to the strain detector 7. As a result, a signal from the strain gauge 6 when the smartphone 101 is dropped horizontally from an arbitrary height is input to the strain detector 7, and the strain detector 7 detects the strain ⁇ of the OLE display 106 to detect the PC8. Output to.
- the PC 8 sequentially stores the time data of the strain ⁇ input from the strain detection unit 7, calculates the time change of the strain, the maximum amount of strain, the strain suppression rate, and the like, and displays them on the liquid crystal display or the like.
- the drop test device 31 projects the piston 37A of each air cylinder 37 inward in the horizontal direction, and horizontally supports the smartphone 101 with the same material and the same thickness of the foam sheet 107 as the test piece 2.
- the smartphone 101 can be freely dropped horizontally with respect to the drop table 32 from any height by freely dropping the chuck member 35 from any height.
- the PC 8 is the time variation of the distortion of the OLE display 106 and the amount of distortion when the smartphone 101 on which the foam sheet 107 of the same material and thickness as the test piece 2 is mounted is freely dropped horizontally from an arbitrary height. Can be calculated and displayed on a liquid crystal display or the like.
- the weight of the hammer 24 is set to 96 grams, and the angle lifted with respect to the column 20 of the shaft 23 (the swing angle ⁇ in FIG. 1) is set to 47 degrees. went.
- the actual machine test by the drop test apparatus 31 was performed by setting the drop height to 1.5 m.
- each impact test and each actual machine test of Examples 1 to 4 and Comparative Examples 1 and 2 which will be described later were also performed with the same settings.
- the reference strain characteristic curve 41 representing the reference strain characteristic by the impact test becomes a maximum value of “0.612” after about 0.3 msec after receiving the impact force of the hammer 24, and about 0
- the distortion becomes “ ⁇ 0.1” after 49 msec.
- an actual machine reference strain characteristic curve 42 representing an actual machine reference strain characteristic by an actual machine test has a maximum strain value of “0.607” about 0.3 msec after contact with the drop table 32, and the distortion after about 0.45 msec. Is “ ⁇ 0.1”.
- the reference distortion characteristic curve 41 and the actual machine reference distortion characteristic curve 42 substantially coincide. That is, an actual machine test by the drop test apparatus 31 in a state where the foam sheet 107 is not attached to the smartphone 101, an impact test in a state where the test piece 2 is not attached between the strain detection member 5 and the support member 9. It can be reproduced by an impact test with the device 1.
- the frequency (load speed) of the reference distortion characteristic curve 41 and the actual machine reference distortion characteristic curve 42 was approximately the same at about 1000 Hz.
- the foam sheet of the present invention is composed of a foam having a thickness of 30 to 200 ⁇ m, a density of 0.2 to 0.7 g / cm 3 , an average cell diameter of 10 to 100 ⁇ m, and a strain suppression rate of 20% or more. ing. Therefore, a desired impact absorbability can be exhibited.
- the thickness of the foamed sheet of the present invention is 30 to 200 ⁇ m.
- the lower limit is preferably 40 ⁇ m, more preferably 50 ⁇ m, and the upper limit is preferably 170 ⁇ m, more preferably 150 ⁇ m.
- the thickness of a foamed sheet is 30 micrometers or more, it can contain a bubble uniformly and can exhibit the outstanding impact absorption.
- the thickness of the foamed sheet is 200 ⁇ m or less, it can easily follow a minute clearance.
- the foamed sheet of the present invention is excellent in impact absorbency despite being as thin as 30 to 200 ⁇ m.
- the density of the foam constituting the foam sheet of the present invention is 0.2 to 0.7 g / cm 3 .
- the lower limit is preferably 0.25 g / cm 3 , more preferably 0.3 g / cm 3
- the upper limit is preferably 0.6 g / cm 3 , more preferably 0.5 g / cm 3 .
- the average cell diameter of the foam is 10 to 100 ⁇ m.
- the lower limit is preferably 15 ⁇ m, more preferably 20 ⁇ m, and the upper limit is preferably 90 ⁇ m, more preferably 80 ⁇ m.
- the average cell diameter is 10 ⁇ m or more, excellent impact absorbability is exhibited. Further, since the average cell diameter is 100 ⁇ m or less, the compression recovery property is also excellent.
- the distortion suppression rate of the foamed sheet of the present invention is 20% or more. Even if it is preferably 30% or more, more preferably 40% or more, excellent impact absorbability is exhibited. Since the strain suppression rate of the foamed sheet is 20% or more, even when the thickness is as thin as 30 to 200 ⁇ m, the strain can be suppressed and excellent shock absorption can be exhibited.
- the foamed sheet of the present invention has a loss tangent (tan ⁇ ), which is a ratio of loss elastic modulus to storage elastic modulus by dynamic viscoelasticity measurement, having a maximum value in a range from 500 Hz to 50000 Hz, and loss at 500 Hz to 3000 Hz.
- the tangent (tan ⁇ ) is formed to be 0.2 or more. For this reason, even when the thickness is as small as 30 to 200 ⁇ m, it is possible to exhibit even more excellent shock absorption during dropping.
- the foamed sheet of the present invention is formed so that the loss tangent (tan ⁇ ) from 500 Hz to 3000 Hz is 0.2 or more. It is desirable that the loss tangent (tan ⁇ ) at 500 Hz to 2000 Hz, more preferably 500 Hz to 1500 Hz, be 0.2 or more. That is, it is considered that the foam sheet having a loss tangent (tan ⁇ ) at a frequency close to the load speed (frequency) at the actual machine test of the smartphone 101 has a higher shock absorption at the time of dropping.
- the storage elastic modulus is a repulsive force with respect to the impact energy applied to the foam sheet, and when the storage elastic modulus is high, the impact is repelled as it is.
- the loss elastic modulus is a physical property that changes impact energy applied to the foam sheet to heat, and the higher the loss elastic modulus is, the more the impact energy is changed to heat, so the impact is absorbed and the strain is reduced. For this reason, a foam sheet having a large loss tangent (tan ⁇ ), which is a ratio of the storage elastic modulus and the loss elastic modulus, has a higher impact absorbability (distortion suppression rate). Presumed to be high.
- the initial elastic modulus of the foam is preferably low from the viewpoint of impact absorption.
- the initial elastic modulus (a value calculated from a slope at the time of 10% strain in a tensile test under a 23 ° C. environment and a tensile speed of 300 mm / min) is preferably 5 N / mm 2 or less, more preferably 3 N / mm 2. It is as follows.
- the lower limit value of the initial elastic modulus is, for example, 0.1 N / mm 2 .
- the foam constituting the foam sheet of the present invention is not particularly limited in its composition and cell structure as long as it has the above characteristics.
- the cell structure may be an open cell structure, a closed cell structure, or a semi-continuous semi-independent structure.
- the impact absorption can be adjusted by selecting the average cell diameter, density, etc., but when the thickness of the foamed sheet is very small (for example, a thickness of 30 to 200 ⁇ m). ), It is not possible to absorb the shock sufficiently by adjusting these characteristics. This is because when the thickness of the foam sheet is very thin, the bubbles in the foam are immediately crushed by the impact and the shock buffering function by the bubbles is lost.
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement of the foam, has a maximum value in the range from 500 Hz to 50000 Hz, Since the loss tangent (tan ⁇ ) from 500 Hz to 3000 Hz is 0.2 or more, even after the bubbles are crushed, the constituent material of the foam exerts the function of buffering the impact when dropped.
- the foam can be composed of a resin composition containing a resin material (polymer).
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement of the resin composition in an unfoamed state [resin composition when not foamed (solid)], is from 500 Hz. It has a maximum value in the range up to 50000 Hz, and the loss tangent (tan ⁇ ) from 500 Hz to 3000 Hz is preferably 0.2 or more. In the case of a material having two or more maximum values of the loss tangent, it is desirable that at least one of them falls within a range from 500 Hz to 50000 Hz.
- the maximum value of the loss tangent (tan ⁇ ) within the range from 500 Hz to 50000 Hz of the resin composition is preferably higher from the viewpoint of shock absorption.
- the initial elastic modulus (23 ° C., tensile speed 300 mm / min) of the resin composition (solid material) in an unfoamed state is desirably low, preferably 50 N / mm 2 or less, more preferably 30 N / mm 2. It is as follows.
- the lower limit value of the initial elastic modulus is, for example, 0.3 N / mm 2 .
- the resin material (polymer) constituting the foam is not particularly limited, and a known or well-known resin material constituting the foam can be used.
- the resin material include acrylic polymers, rubbers, urethane polymers, and ethylene-vinyl acetate copolymers. Among these, acrylic polymers, rubbers, and urethane polymers are preferable from the viewpoint of impact absorption.
- One type of resin material (polymer) constituting the foam may be used alone, or two or more types may be used.
- Tg of the resin material (polymer) can be used as an index or a standard.
- the resin material (polymer) has a Tg of ⁇ 50 ° C. or more and less than 50 ° C. (lower limit is preferably ⁇ 40 ° C., more preferably ⁇ 30 ° C., upper limit is preferably 40 ° C., more preferably 30 ° C.) It can be selected from resin materials (polymers) in the range.
- the acrylic polymer is preferably an acrylic polymer formed with a monomer having a homopolymer Tg of ⁇ 10 ° C. or more and a monomer having a homopolymer Tg of less than ⁇ 10 ° C. as essential monomer components.
- the loss tangent (tan ⁇ ) which is the ratio of the loss elastic modulus to the storage elastic modulus by dynamic viscoelasticity measurement, is 500 Hz.
- a foam having a loss tangent (tan ⁇ ) from 500 Hz to 3000 Hz of 0.2 or more can be obtained relatively easily.
- glass transition temperature (Tg) when forming a homopolymer means “glass transition temperature (Tg of homopolymer of the monomer)”.
- Tg of homopolymer glass transition temperature (Tg of homopolymer of the monomer).
- the Tg of a homopolymer of a monomer not described in the above document refers to, for example, a value obtained by the following measurement method (see JP 2007-51271 A).
- this homopolymer solution is cast-coated on a separator and dried to prepare a test sample (sheet-like homopolymer) having a thickness of about 2 mm.
- This test sample was punched into a disk shape having a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to a shear strain at a frequency of 1 Hz using a viscoelasticity tester (ARES, manufactured by Rheometrics). Viscoelasticity is measured in a shear mode at a heating rate of 150 ° C. and 5 ° C./min, and the maximum value (peak top) temperature of tan ⁇ is defined as the Tg of the homopolymer.
- the Tg of the resin material (polymer) can also be measured by this method.
- the Tg is, for example, ⁇ 10 ° C. to 250 ° C., preferably 10 to 230 ° C., more preferably 50 to 200 ° C.
- Examples of the homopolymer having a Tg of ⁇ 10 ° C. or more include, for example, (meth) acrylonitrile; amide group-containing monomers such as (meth) acrylamide and N-hydroxyethyl (meth) acrylamide; (meth) acrylic acid; methacrylic acid (Meth) acrylic acid alkyl esters having homopolymers such as methyl and ethyl methacrylate having a Tg of ⁇ 10 ° C. or higher; (meth) acrylic acid isobornyl; heterocycle-containing vinyl monomers such as N-vinyl-2-pyrrolidone; Examples thereof include hydroxyl group-containing monomers such as ethyl methacrylate.
- (meth) acrylonitrile (especially acrylonitrile) is particularly preferable.
- (meth) acrylonitrile (especially acrylonitrile) is used as a monomer having a Tg of -10 ° C. or higher for the homopolymer, the maximum value (peak top) of the loss tangent (tan ⁇ ) of the foam may be due to strong intermolecular interaction. The strength can be increased.
- the Tg is, for example, ⁇ 70 ° C. or more and less than ⁇ 10 ° C., preferably ⁇ 70 ° C. to ⁇ 12 ° C., more preferably ⁇ 65 ° C. to ⁇ 15 ° C. .
- Examples of the homopolymer having a Tg of less than ⁇ 10 ° C. include, for example, (meth) acrylic acid alkyl esters having a homopolymer Tg of less than ⁇ 10 ° C., such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc. Is mentioned. These can be used individually by 1 type or in combination of 2 or more types. Among these, acrylic acid C2-8 alkyl ester is particularly preferable.
- the content of the monomer having a Tg of -10 ° C. or more of the homopolymer is, for example, 2 to 30% by weight with respect to all the monomer components forming the acrylic polymer (total amount of monomer components), and the lower limit is preferably 3% by weight. %, More preferably 4% by weight, and the upper limit is preferably 25% by weight, more preferably 20% by weight.
- the content of the monomer having a Tg of the homopolymer of less than ⁇ 10 ° C. with respect to all the monomer components forming the acrylic polymer (total amount of monomer components) is, for example, 70 to 98% by weight, and the lower limit is preferably The upper limit is preferably 97% by weight, more preferably 96% by weight.
- the rubber may be natural rubber or synthetic rubber.
- examples of the rubber include nitrile rubber (NBR), methyl methacrylate-butadiene rubber (MBR), styrene-butadiene rubber (SBR), acrylic rubber (ACM, ANM), and urethane rubber (AU).
- NBR nitrile rubber
- MRR methyl methacrylate-butadiene rubber
- SBR styrene-butadiene rubber
- ACM acrylic rubber
- AU urethane rubber
- NBR nitrile rubber
- MRR methyl methacrylate-butadiene rubber
- MRR methyl methacrylate-butadiene rubber
- urethane polymer examples include polycarbonate polyurethane, polyester polyurethane, and polyether polyurethane.
- ethylene-vinyl acetate copolymer a known or well-known ethylene-vinyl acetate copolymer can be used.
- the foam constituting the foam sheet may contain a surfactant, a cross-linking agent, a thickener, and other additives as required in addition to the resin material (polymer).
- an optional surfactant may be included for the purpose of reducing the bubble diameter and stabilizing the foam.
- the surfactant is not particularly limited, and any of anionic, cationic, and nonionic surfactants may be used. From the viewpoint of finer bubble diameter and stability of foamed foam, anionic surfactants may be used. Particularly preferred is ammonium stearate.
- the addition amount of the surfactant is, for example, 0 to 10 parts by weight with respect to 100 parts by weight of the resin material (polymer), the lower limit is preferably 0.5 parts by weight, and the upper limit is preferably 8 parts by weight.
- an arbitrary cross-linking agent may be included.
- the crosslinking agent is not particularly limited, and any of oil-soluble and water-soluble may be used.
- examples of the crosslinking agent include epoxy, oxazoline, isocyanate, carbodiimide, melamine, and metal oxide.
- the addition amount of the crosslinking agent is, for example, 0 to 10 parts by weight with respect to 100 parts by weight of the resin material (polymer), the lower limit is preferably 0.01 parts by weight, and the upper limit is preferably 5 parts by weight.
- an optional thickener may be included.
- the thickener is not particularly limited, and examples thereof include acrylic acid type, urethane type, and polyvinyl alcohol type.
- the addition amount of the thickener is, for example, 0 to 10 parts by weight with respect to 100 parts by weight of the resin material (polymer), the lower limit is preferably 0.1 parts by weight, and the upper limit is preferably 5 parts by weight.
- any appropriate other component may be included within the range not impairing the shock absorption.
- Such other components may contain only 1 type and may contain 2 or more types.
- Examples of the other components include polymer components other than those described above, softeners, antioxidants, anti-aging agents, rust inhibitors, gelling agents, curing agents, plasticizers, fillers, reinforcing agents, foaming agents, Examples include flame retardants, light stabilizers, ultraviolet absorbers, colorants (such as pigments and dyes), pH adjusters, solvents (organic solvents), thermal polymerization initiators, and photopolymerization initiators.
- the filler examples include silica, clay (mica, talc, smectite, etc.), alumina, titania, zinc oxide, zeolite, graphite, inorganic fiber (carbon fiber, glass fiber, etc.), organic fiber, and metal powder. It is done.
- the foam sheet of the present invention can be produced by subjecting a resin composition containing a resin material (polymer) constituting the foam to foam molding.
- foaming method bubble forming method
- methods usually used for foam molding such as physical methods and chemical methods, can be employed.
- the physical method is to disperse a gas component such as air or nitrogen in a polymer solution and form bubbles by mechanical mixing.
- the chemical method is a method of obtaining a foam by forming cells with a gas generated by thermal decomposition of a foaming agent added to a polymer base. From the viewpoint of environmental problems, a physical method is preferable. Bubbles formed by physical methods are often open cells.
- the resin composition containing the resin material (polymer) to be subjected to foam molding a resin solution in which the resin material is dissolved in a solvent may be used. From the viewpoint of cellularity, it is preferable to use an emulsion containing the resin material. . As an emulsion, you may blend and use 2 or more types of emulsion.
- the solid content concentration of the emulsion is preferably higher from the viewpoint of film formability.
- the solid content concentration of the emulsion is preferably 30% by weight or more, more preferably 40% by weight or more, and further preferably 50% by weight or more.
- a method of producing a foam through a step of foaming the emulsion resin composition mechanically (Step A) is preferable.
- the foaming device is not particularly limited, and examples thereof include a high-speed shearing method, a vibration method, and a pressurized gas discharge method. Among these, the high-speed shearing method is preferable from the viewpoint of finer bubble diameter and production of a large capacity.
- Bubbles when foamed by mechanical stirring are gas (gas) taken into the emulsion.
- the gas is not particularly limited as long as it is inert to the emulsion, and examples thereof include air, nitrogen, carbon dioxide and the like. Among these, air is preferable from the viewpoint of economy.
- the foamed sheet of the present invention can be obtained through a step (Step B) in which the emulsion resin composition foamed by the above method is applied onto a substrate and dried.
- Step B a general method can be adopted as a coating method and a drying method.
- Step B includes a preliminary drying step B1 for drying the bubble-containing emulsion resin composition applied on the substrate at 50 ° C. or higher and lower than 125 ° C., and then a main drying step B2 for further drying at 125 ° C. or higher and 160 ° C. or lower. Preferably it is.
- the temperature in the preliminary drying step B1 is preferably 60 ° C. or higher and 100 ° C. or lower.
- the time of the preliminary drying step B1 is, for example, 0.5 minutes to 30 minutes, preferably 1 minute to 15 minutes.
- the temperature in this drying process B2 becomes like this. Preferably they are 130 degreeC or more and 155 degrees C or less.
- the time of the main drying step B2 is, for example, 0.5 minutes to 30 minutes, preferably 1 minute to 15 minutes.
- the average cell diameter of the foam can be adjusted by adjusting the type and amount of the surfactant and by adjusting the stirring speed and stirring time during mechanical stirring. Obtainable.
- the foam density can be adjusted to 0.2 to 0.7 g / cm 3 by adjusting the amount of gas (gas) component incorporated into the emulsion resin composition during mechanical stirring. .
- the foam sheet of the present invention may have an adhesive layer on one side or both sides of the foam. It does not specifically limit as an adhesive which comprises an adhesive layer, For example, any of an acrylic adhesive, a rubber adhesive, a silicone adhesive, etc. may be sufficient. Moreover, when providing an adhesive layer, you may laminate
- the foamed sheet of the present invention may be distributed on the market as a wound body (rolled material) wound in a roll shape.
- the foamed sheet of the present invention is excellent in impact absorption even if the thickness is small. Therefore, for example, in an electrical / electronic device, various members or parts (for example, optical members) are used for attaching (attaching) a predetermined part (for example, a housing) to a member for electrical / electronic devices, In particular, it is useful as an impact absorbing sheet.
- an image display member attached to an image display device such as a liquid crystal display, an OLE display, or a plasma display (particularly, a small image display member)
- Display members such as touch panels attached to mobile communication devices such as so-called “mobile phones”, “smartphones” and “portable information terminals”, cameras and lenses (particularly small cameras and lenses), and the like. It is done.
- the electrical / electronic device of the present invention uses the foam sheet of the present invention.
- Such an electric / electronic device is, for example, an electric / electronic device provided with an image display member, and the foam sheet is sandwiched between the casing of the electric or electronic device and the image display member.
- Electrical and electronic equipment having a specific structure. Examples of the electric / electronic devices include mobile communication devices such as so-called “mobile phones”, “smartphones”, and “portable information terminals”.
- Example 1 will be described.
- this invention is not restrict
- % representing the content means% by weight.
- Example 1 100 parts by weight of acrylic emulsion (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid Disperse (“ROBOMIX”) 5 parts by weight of polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28.7%) 2.5 parts by weight The mixture was stirred and mixed to produce foam. This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C.
- acrylic emulsion solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)
- fatty acid ammonium surfactant aqueous dispersion of
- Example 2 100 parts by weight of acrylic emulsion (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid 33%) 5 parts by weight, 4 parts by weight of oxazoline-based crosslinking agent (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content 24.9%), polyacrylic acid thickener (ethyl acrylate-acrylic acid co 1.5 parts by weight of a polymer (acrylic acid 20 wt%) and a solid content of 28.7% were stirred and mixed with a disper (“Robomix” manufactured by Primics) to foam.
- a disper (“Robomix” manufactured by Primics)
- This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes.
- a foam (foamed sheet) having a thickness of 150 ⁇ m, a density of 0.33 g / cm 3 , and an average cell diameter of 87 ⁇ m was obtained.
- Example 3 100 parts by weight of acrylic emulsion (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid 33%) 5 parts by weight, epoxy crosslinking agent (sorbitol polyglycidyl ether) 4 parts by weight, polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28. 7%) Part by weight was stirred and mixed with a disper (manufactured by “Robomix” Primex) to make foam.
- acrylic emulsion solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)
- fatty acid ammonium surfactant aqueous dispersion of ammonium stearate, solid
- This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes.
- a foam (foamed sheet) having a thickness of 150 ⁇ m, a density of 0.35 g / cm 3 , and an average cell diameter of 61 ⁇ m was obtained.
- Example 4 100 parts by weight of a synthetic rubber emulsion (“Lackstar 1570” manufactured by DIC, solid content: 42.4%, NBR), 5 parts by weight of a fatty acid ammonium-based surfactant (aqueous dispersion of ammonium stearate, solid content: 33%), 1.3 parts by weight of a urethane-based thickener (“Hydran Assister T10” manufactured by DIC, solid content 25.1%) was stirred and mixed with a disper (“Robomix” Primix) to generate foam. This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C.
- a synthetic rubber emulsion (“Lackstar 1570” manufactured by DIC, solid content: 42.4%, NBR)
- a fatty acid ammonium-based surfactant aqueous dispersion of ammonium stearate, solid content: 33%)
- a foam (foamed sheet) having a thickness of 150 ⁇ m, a density of 0.26 g / cm 3 , and an average cell diameter of 55 ⁇ m was obtained.
- Comparative Example 1 100 parts by weight of acrylic emulsion (solid content 60%, butyl acrylate-methyl methacrylate-acrylonitrile copolymer (acrylonitrile 5% by weight)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%) 5 parts by weight, 1.5 parts by weight of a polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28.7%) made by Disper ("Robomix” Primex) The mixture was stirred and mixed to form foam.
- a polyacrylic acid thickener ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28.7%
- This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes.
- a foam (foamed sheet) having a thickness of 140 ⁇ m, a density of 0.38 g / cm 3 , and an average cell diameter of 75 ⁇ m was obtained.
- Comparative Example 2 100 parts by weight of acrylic emulsion (solid content 60%, butyl acrylate-methyl methacrylate-acrylonitrile copolymer (acrylonitrile 5% by weight)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%) 5 parts by weight, 1 part by weight of polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28.7%) with Disper ("Robomix” Primex) The mixture was stirred and foamed.
- acrylic emulsion solid content 60%, butyl acrylate-methyl methacrylate-acrylonitrile copolymer (acrylonitrile 5% by weight)
- fatty acid ammonium surfactant aqueous dispersion of ammonium stearate, solid content 33%) 5 parts by weight, 1 part by weight of polyacrylic acid thickener (ethyl acrylate-acrylic acid copo
- This foam was applied onto a peeled PET film (thickness: 38 ⁇ m, trade name “MRF # 38” manufactured by Mitsubishi Plastics) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes.
- a foam (foamed sheet) having a thickness of 150 ⁇ m, a density of 0.45 g / cm 3 , and an average cell diameter of 69 ⁇ m was obtained.
- An average cell diameter ( ⁇ m) was obtained by capturing an enlarged image of the foam cross section with a low vacuum scanning electron microscope (“S-3400N scanning electron microscope” manufactured by Hitachi High-Tech Science Systems) and analyzing the image. The number of bubbles analyzed is about 10 to 20.
- a foam (foamed sheet) is punched with a 100 mm ⁇ 100 mm punching blade mold, and the dimensions of the punched sample are measured. Further, the thickness is measured with a 1/100 dial gauge having a measurement terminal diameter ( ⁇ ) of 20 mm. The volume of the foam was calculated from these values. Next, the weight of the foam is measured with an upper pan balance having a minimum scale of 0.01 g or more. From these values, the density (g / cm 3 ) of the foam was calculated.
- each foam (foamed sheet) was sandwiched between the strain detection member 5 and the support member 9 to perform an impact test.
- the strain characteristic of the strain detection member 5 was measured by setting the weight of the hammer 24 to 96 grams and the swing angle ⁇ of the shaft 23 to the support column 20 to be 47 degrees.
- each foam (foamed sheet) was attached to the smartphone 101, and a drop test (actual machine test) was performed. The drop height was set to 1.5 m, and the actual machine distortion characteristics of the OLE display 106 and the presence or absence of drop cracks in the OLE display 106 were measured.
- FIG. 8 shows a strain characteristic curve 47 representing the strain characteristics of the strain detection member 5 measured by mounting the foam sheet of Example 1 on the impact test apparatus 1.
- the strain characteristic curve 47 of the foamed sheet of Example 1 shows that the strain becomes the maximum value of “0.252” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0. 1 ”. Therefore, the distortion suppression rate is about 59% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- FIG. 8 shows an actual machine distortion characteristic curve 48 representing the actual machine distortion characteristic of the OLE display 106 measured by attaching the foam sheet of Example 1 to the smartphone 101 using the drop test apparatus 31.
- the actual machine distortion characteristic curve 48 of the foamed sheet of Example 1 shows that the strain becomes the maximum value of “0.240” after about 0.3 msec from the contact with the drop table 32, and the strain becomes “ ⁇ 0. 1 ”.
- the strain suppression rate when mounted on an actual machine was about 60%, which was almost the same as the strain suppression rate measured by the impact test apparatus 1. Moreover, the frequency (load speed) of the distortion characteristic curve 47 and the actual machine distortion characteristic curve 48 was substantially the same at about 1000 Hz. Further, no cracks due to dropping occurred in the OLE display 106, and “ ⁇ ” marks were written in the “actual machine falling crack” column of the evaluation result table 45.
- FIG. 10 shows a strain characteristic curve 49 representing the strain characteristics of the strain detection member 5 measured by mounting the foam sheet of Example 2 on the impact test apparatus 1.
- the strain characteristic curve 49 of the foamed sheet of Example 2 shows that the strain becomes the maximum value of “0.263” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0.0. 1 ”. Therefore, the distortion suppression rate is about 57% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- FIG. 10 shows an actual machine distortion characteristic curve 50 representing an actual machine distortion characteristic of the OLE display 106 measured by attaching the foam sheet of Example 2 to the smartphone 101 using the drop test apparatus 31.
- the actual machine strain characteristic curve 50 of the foamed sheet of Example 2 shows that the strain becomes the maximum value of “0.266” after about 0.3 msec from the contact with the drop table 32, and the strain becomes “ ⁇ 0. 1 ”.
- the strain suppression rate when mounted on an actual machine was about 56%, which was almost the same as the strain suppression rate measured by the impact test apparatus 1. Moreover, the frequency (load speed) of the distortion characteristic curve 49 and the actual machine distortion characteristic curve 50 was substantially the same at about 1000 Hz. Further, no cracks due to dropping occurred in the OLE display 106, and “ ⁇ ” marks were written in the “actual machine falling crack” column of the evaluation result table 45.
- FIG. 12 shows a strain characteristic curve 51 representing the strain characteristics of the strain detection member 5 measured by mounting the foam sheet of Example 3 on the impact test apparatus 1.
- the strain characteristic curve 51 of the foamed sheet of Example 3 shows that the strain becomes the maximum value of “0.324” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0. 1 ”. Therefore, the distortion suppression rate is about 47% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- FIG. 12 shows an actual machine distortion characteristic curve 52 representing the actual machine distortion characteristic of the OLE display 106 measured by attaching the foam sheet of Example 3 to the smartphone 101 using the drop test apparatus 31.
- the actual machine distortion characteristic curve 52 of the foamed sheet of Example 3 has a maximum strain value of “0.316” about 0.3 msec after contact with the drop table 32, and the strain becomes “ ⁇ 0. 09 ".
- the strain suppression rate when mounted on an actual machine was about 48%, which was almost the same as the strain suppression rate measured by the impact test apparatus 1.
- the frequency (load speed) of the distortion characteristic curve 51 and the actual machine distortion characteristic curve 52 was substantially the same at about 1000 Hz. Further, no cracks due to dropping occurred in the OLE display 106, and a “ ⁇ ” mark was written in the “actual machine falling crack” column of the evaluation result table 45.
- FIG. 14 shows a strain characteristic curve 53 representing the strain characteristics of the strain detection member 5 measured by mounting the foam sheet of Example 4 on the impact test apparatus 1.
- the strain characteristic curve 53 of the foamed sheet of Example 4 shows that the strain becomes the maximum value of “0.375” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0. 1 ”. Therefore, the distortion suppression rate is about 39% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- FIG. 14 shows an actual machine distortion characteristic curve 54 representing the actual machine distortion characteristics of the OLE display 106 measured by attaching the foam sheet of Example 4 to the smartphone 101 using the drop test apparatus 31.
- the actual machine strain characteristic curve 54 of the foamed sheet of Example 4 shows that the strain becomes the maximum value of “0.379” after about 0.3 msec after coming into contact with the drop table 32, and the strain becomes “ ⁇ 0. 03 ".
- the strain suppression rate when mounted on an actual machine was about 38%, which was almost the same as the strain suppression rate measured with the impact test apparatus 1.
- the frequency (load speed) of the distortion characteristic curve 53 and the actual machine distortion characteristic curve 54 was substantially the same at about 1000 Hz.
- a crack due to dropping occurred in the OLE display 106, and a “ ⁇ ” mark was written in the “actual machine falling crack” column of the evaluation result table 45.
- FIG. 16 shows a strain characteristic curve 55 representing the strain characteristics of the strain detection member 5 measured by mounting the foam sheet of Comparative Example 1 on the impact test apparatus 1.
- the distortion characteristic curve 55 of the foamed sheet of Comparative Example 1 shows that the strain becomes the maximum value of “0.511” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0.0. 1 ”. Therefore, the distortion suppression rate is about 16% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- FIG. 16 shows an actual machine distortion characteristic curve 56 representing the actual machine distortion characteristics of the OLE display 106 measured by attaching the foam sheet of Comparative Example 1 to the smartphone 101 using the drop test apparatus 31.
- the actual machine distortion characteristic curve 56 of the foamed sheet of Comparative Example 1 shows that the strain becomes the maximum value of “0.501” after about 0.3 msec from the contact with the drop table 32, and the strain becomes “ ⁇ 0. 1 ”.
- the strain suppression rate when mounted on an actual machine was about 16%, which was almost the same as the strain suppression rate measured by the impact test apparatus 1.
- the frequency (load speed) of the distortion characteristic curve 55 and the actual machine distortion characteristic curve 56 was substantially the same at about 1000 Hz.
- a crack due to dropping occurred in the OLE display 106, and an “x” mark was written in the “actual machine falling crack” column of the evaluation result table 45.
- FIG. 18 shows a distortion characteristic curve 57 representing the distortion characteristic of the distortion detection member 5 measured by mounting the foamed sheet of Comparative Example 2 on the impact test apparatus 1.
- the distortion characteristic curve 57 of the foamed sheet of Comparative Example 2 shows that the strain becomes the maximum value of “0.525” about 0.3 msec after receiving the impact force of the hammer 24, and the strain becomes “ ⁇ 0. 1 ”. Therefore, the distortion suppression rate is about 14% according to the above formula (1), and is described in the column of “distortion suppression rate” in the evaluation result table 45.
- the actual machine distortion characteristic curve 58 of the foamed sheet of Comparative Example 2 shows that the strain becomes the maximum value of “0.522” after about 0.3 msec after coming into contact with the drop table 32, and the strain becomes “ ⁇ 0.0. 1 ”.
- the strain suppression rate when mounted on an actual machine was about 14%, which was almost the same as the strain suppression rate measured by the impact test apparatus 1.
- the frequency (load speed) of the distortion characteristic curve 57 and the actual machine distortion characteristic curve 58 was substantially the same at about 1000 Hz.
- a crack due to dropping occurred in the OLE display 106, and an “x” mark was written in the “actual machine falling crack” column of the evaluation result table 45.
- the frequency (load speed) of the strain characteristic curve 47 and the actual machine strain characteristic curve 48 of the foamed sheet of Example 1 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “1.356”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “1.144”
- the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “1.369”.
- the loss tangent (tan ⁇ ) at the frequency of 2686 Hz was the maximum value “1.375”.
- the frequency (load speed) of the strain characteristic curve 49 and the actual machine strain characteristic curve 50 of the foamed sheet of Example 2 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “1.293”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “1.176”, and the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “1.328”. Further, the loss tangent (tan ⁇ ) at the frequency of 3216 Hz was the maximum value “1.329”.
- the frequency (load speed) of the distortion characteristic curve 51 and the actual machine distortion characteristic curve 52 of the foamed sheet of Example 3 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “0.837”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “0.801”
- the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “0.901”.
- the loss tangent (tan ⁇ ) at the frequency of 47406 Hz was the maximum value “1.039”.
- the frequency (load speed) of the strain characteristic curve 53 and the actual machine strain characteristic curve 54 of the foamed sheet of Example 4 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “0.605”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “0.524”, and the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “0.768”.
- the loss tangent (tan ⁇ ) at a frequency of 4026 Hz was the maximum value “1.263”.
- the frequency (load speed) of the distortion characteristic curve 55 and the actual machine distortion characteristic curve 56 of the foamed sheet of Comparative Example 1 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “0.101”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “0.100”, and the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “0.088”.
- the frequency (load speed) of the distortion characteristic curve 57 and the actual machine distortion characteristic curve 58 of the foamed sheet of Comparative Example 2 was about 1000 Hz.
- the loss tangent (tan ⁇ ) at a frequency of 1000 Hz is “0.167”, which is described in the column “tan ⁇ (1 kHz)” of the evaluation result table 45. did.
- the loss tangent (tan ⁇ ) at a frequency of 500 Hz was “0.192”, and the loss tangent (tan ⁇ ) at a frequency of 3000 Hz was “0.136”.
- the thickness is 30 to 200 ⁇ m, and the density Is 0.2 to 0.7 g / cm 3 , the average cell diameter is 10 to 100 ⁇ m, and the distortion suppression rate of the foam sheet measured using the impact test apparatus 1 is “20% or more”.
- the distortion suppression rate of the foam sheet measured using the impact test apparatus 1 is “20% or more”.
- the distortion suppression rate of the foam sheet is “20% or more”, and the loss tangent (tan ⁇ ) of the foam sheet has a maximum value in the range of 500 Hz to 50000 Hz, and further, 500 Hz to 3000 Hz, If the loss tangent (tan ⁇ ) from 500 Hz to 2000 Hz, more preferably from 500 Hz to 1500 Hz is “0.2 or more”, it is considered that cracks due to falling of the OLE display 106 can be more effectively suppressed in an actual machine test. .
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Abstract
Description
歪み抑制率(%)={(ε0-ε1)/ε0}×100
(上式において、ε0は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着していない状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みであり、ε1は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着した状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みである。)
前記発泡シートを支持部材と歪み検出部材との間に挟んだ状態で保持可能に構成され、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の歪みを歪みゲージによって測定する衝撃試験装置を用いた場合に、下記式で表される歪み抑制率が20%以上である発泡シートが用いられていることを特徴とする。
歪み抑制率(%)={(ε0-ε1)/ε0}×100
(上式において、ε0は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着していない状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みであり、ε1は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着した状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みである。)
図1乃至図4に示すように、本実施形態に係る衝撃試験装置1は、発泡シートから形成された試験片2を任意の保持力で保持する保持手段としての保持部材3と、試験片2に衝撃力を負荷する衝撃負荷手段としての衝撃負荷部材4と、試験片2が密着される歪み検出部材5の歪みを測定する歪みゲージ6と、歪みゲージ6の信号から歪み検出部材5の歪みを検出する歪み検出手段としての歪み検出部7と、歪み検出部7から入力された歪みデータに基づいて歪み抑制率[%]を算出して出力する出力手段としてのパーソナルコンピュータ(以下、「PC」という。)8と、から構成される。
まず、保持部材3の固定治具11及び押さえ治具12間に試験片2を挿入せずに、歪み検出部材5と支持部材9だけを密着させた状態で挿入する。そして、レバー14によって台座13を固定治具11側にスライドさせて支持板28におおよそ密着させて台座13を仮固定する。次いで、押さえ圧力調整手段16によって台座13を微調整し、固定治具11と支持板28とを密着固定する。そして、このとき押さえ圧力調整手段16に設けられているメモリをリセットし、押さえ治具12の位置を基準点とする。
試験片2のセット終了後、アーム21の一端に設けられている電磁石25のスイッチを入れ、ハンマ24をアーム21に固定保持する。そして、アーム21を任意の所定角度に振り上げて固定後、電磁石25のスイッチを切り、ハンマ24を保持部材3に保持されている支持部材9に衝突させる(図2参照)。
また、このときの検出部材5の第1板部材5Aの歪みを歪みゲージ6によって測定する。
ここで、試験片2を挿入する前に、歪み検出部材5と支持部材9だけを密着させた状態で、固定治具11に密着固定して、同様にしてハンマ24を支持部材9に衝突させ、この際の検出部材5の第1板部材5Aの歪みを測定しておき、下記(1)式で計算することによって試験片2の歪み抑制率[%]を算出することができる。
そして、歪みゲージ6からの信号は、歪み検出部7に入力される。この歪み検出部7において、歪みゲージ6からの信号は、歪みεに変換されてPC8に出力される。PC8は、歪み検出部7から入力された歪みεの時間データを順次記憶し、歪みの時間変化、歪み量の最大値、歪み抑制率等を算出して液晶ディスプレイ等に表示する。従って、衝撃試験装置1は、厚さが30~200μmの薄い発泡シートから形成された試験片2に衝撃力を負荷した際の、歪み検出部材5に発生する歪みの時間変化、歪み量の最大値、歪み抑制率等を検出して、出力することができる。
次に、図21に示すスマートフォン101に試験片2と同じ材質で同じ厚さの発泡シート107を装着した状態で、OLEディスプレイ106に歪みゲージ6を貼り付けて落下試験(以下、「実機試験」という。)を行う落下試験装置31の概略構成について図5に基づいて説明する。
ここで、衝撃試験装置1による、試験片2を歪み検出部材5と支持部材9との間に装着していない状態で、ハンマ24を支持部材9に衝突させて測定した検出部材5の第1板部材5Aの歪み特性(以下、「基準歪み特性」という。)の一例を図6に基づいて説明する。また、落下試験装置31による、スマートフォン101に発泡シート107を装着していない状態で水平落下させて測定したOLEディスプレイ106の歪み特性(以下、「実機基準歪み特性」という。)の一例を図6に基づいて説明する。
次に、本発明の発泡シートについて説明する。本発明の発泡シートは、厚さが30~200μmであり、密度が0.2~0.7g/cm3、平均セル径が10~100μm、歪み抑制率が20%以上の発泡体で構成されている。そのため、所望の衝撃吸収性を発揮することができる。
アクリルエマルション(固形分量55%、アクリル酸エチル-アクリル酸ブチル-アクリロニトリル共重合体(重量比45:48:7))100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、ポリアクリル酸系増粘剤(アクリル酸エチル-アクリル酸共重合体(アクリル酸20wt%)、固形分量28.7%)2.5重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ130μm、密度0.38g/cm3、平均セル径68μmの発泡体(発泡シート)を得た。
アクリルエマルション(固形分量55%、アクリル酸エチル-アクリル酸ブチル-アクリロニトリル共重合体(重量比45:48:7))100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、オキサゾリン系架橋剤(「エポクロスWS-700」日本触媒社製、固形分量24.9%)4重量部、ポリアクリル酸系増粘剤(アクリル酸エチル-アクリル酸共重合体(アクリル酸20wt%)、固形分量28.7%)1.5重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ150μm、密度0.33g/cm3、平均セル径87μmの発泡体(発泡シート)を得た。
アクリルエマルション(固形分量55%、アクリル酸エチル-アクリル酸ブチル-アクリロニトリル共重合体(重量比45:48:7))100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、エポキシ系架橋剤(ソルビトールポリグリシジルエーテル)4重量部、ポリアクリル酸系増粘剤(アクリル酸エチル-アクリル酸共重合体(アクリル酸20wt%)、固形分量28.7%)重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ150μm、密度0.35g/cm3、平均セル径61μmの発泡体(発泡シート)を得た。
合成ゴムエマルション(「ラックスター1570」DIC社製、固形分量42.4%、NBR)100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、ウレタン系増粘剤(「ハイドランアシスターT10」DIC社製、固形分量25.1%)1.3重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ150μm、密度0.26g/cm3、平均セル径55μmの発泡体(発泡シート)を得た。
アクリルエマルション(固形分量60%、アクリル酸ブチル-メチルメタクリレート-アクリロニトリル共重合体(アクリロニトリル5重量%))100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、ポリアクリル酸系増粘剤(アクリル酸エチル-アクリル酸共重合体(アクリル酸20wt%)、固形分量28.7%)1.5重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ140μm、密度0.38g/cm3、平均セル径75μmの発泡体(発泡シート)を得た。
アクリルエマルション(固形分量60%、アクリル酸ブチル-メチルメタクリレート-アクリロニトリル共重合体(アクリロニトリル5重量%))100重量部、脂肪酸アンモニウム系界面活性剤(ステアリン酸アンモニウムの水分散液、固形分量33%)5重量部、ポリアクリル酸系増粘剤(アクリル酸エチル-アクリル酸共重合体(アクリル酸20wt%)、固形分量28.7%)1重量部をディスパー(「ロボミックス」プライミクス社製)で撹拌混合して起泡化した。この発泡体を、剥離処理をしたPETフィルム(厚さ:38μm、商品名「MRF♯38」三菱樹脂社製)上に塗布し、70℃で4.5分、140℃で4.5分乾燥させ、厚さ150μm、密度0.45g/cm3、平均セル径69μmの発泡体(発泡シート)を得た。
実施例及び比較例で得られた発泡体(発泡シート)について、以下の評価を行った。結果を図7乃至図20に示す。
低真空走査電子顕微鏡(「S-3400N型走査電子顕微鏡」日立ハイテクサイエンスシステムズ社製)により、発泡体断面の拡大画像を取り込み、画像解析することにより平均セル径(μm)を求めた。なお解析した気泡数は10~20個程度である。
100mm×100mmの打抜き刃型にて発泡体(発泡シート)を打抜き、打抜いた試料の寸法を測定する。また、測定端子の直径(φ)20mmである1/100ダイヤルゲージにて厚さを測定する。これらの値から発泡体の体積を算出した。
次に、発泡体の重量を最小目盛り0.01g以上の上皿天秤にて測定する。これらの値より発泡体の密度(g/cm3)を算出した。
前記の衝撃試験装置1を用いて、各発泡体(発泡シート)を歪み検出部材5と支持部材9との間に挟んで衝撃試験を行った。ハンマ24の重量は96グラム、シャフト23の支柱20に対する振り上げ角度θは47度となるように設定して、歪み検出部材5の歪み特性を測定した。また、前記の落下試験装置31を用いて、各発泡体(発泡シート)をスマートフォン101に装着して、落下試験(実機試験)を行った。落下高さは1.5mに設定して、OLEディスプレイ106の実機歪み特性とOLEディスプレイ106の落下割れの有・無を測定した。
粘弾性測定装置(「RSA-G2」TA Instruments社製)により、測定温度は-60℃~25℃、昇温間隔は5℃/sec、周波数は0.1~10Hzの測定条件で、各発泡体(発泡シート)の周波数温度分散試験を行った。そして、測定結果を用いて基準温度25℃でマスターカーブを作成した。また、その際の貯蔵弾性率G’と損失弾性率G”の比率である損失正接(tanδ)を測定した。図9、図11、図13、図15、図17、図19に各実施例1~4、各比較例1、2のマスターカーブと損失正接(tanδ)を示す。
次に、図20に示すように、「tanδ(1kHz)」を横軸にとり、「歪み抑制率(%)」を縦軸にとった歪み抑制率と損失正接(tanδ)との相関を表す相関図61を作成した。そして、図7に示す評価結果テーブル45から、各実施例1~4及び各比較例1、2の「tanδ(1kHz)」と「歪み抑制率(%)」の各データを読み出し、相関図61上に、各実施例1~4を「○」印で、各比較例1、2を「×」印でプロットした。その結果、図20に示すように、各実施例1~4及び各比較例1、2の「tanδ(1kHz)」と「歪み抑制率(%)」の各データ間には、相関関係があると考えられる。
2 試験片(発泡シート)
3 保持部材
4 衝撃負荷部材
5 歪み検出部材
5A 第1板部材
5B 第2板部材
6 歪みゲージ
7 歪み検出部
8 パーソナルコンピュータ(PC)
9 支持部材
10 テーブル
11 固定治具
12 押さえ治具
12A 開口部
16 押さえ圧力調整手段
24 ハンマ
25 電磁石
27 凹部
31 落下試験装置
101 スマートフォン
102 画像表示部材
106 OLEディスプレイ
107 発泡シート
108 筐体
Claims (15)
- 厚さが30~200μmであり、密度が0.2~0.7g/cm3、平均セル径が10~100μmの発泡体で構成された発泡シートであって、
前記発泡シートを支持部材と歪み検出部材との間に挟んだ状態で保持可能に構成され、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の歪みを歪みゲージによって測定する衝撃試験装置を用いた場合に、下記式で表される歪み抑制率が20%以上であることを特徴とする発泡シート。
歪み抑制率(%)={(ε0-ε1)/ε0}×100
(上式において、ε0は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着していない状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みであり、ε1は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着した状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みである。) - 前記衝撃試験装置は、
前記発泡シートを前記支持部材と前記歪み検出部材との間に挟んだ状態で保持すると共に、前記発泡シートを任意の厚さ方向の圧縮率で保持する保持手段と、
前記保持手段に保持された前記支持部材に衝撃力を負荷する衝撃負荷手段と、
前記衝撃負荷手段によって前記支持部材を介して前記発泡シートに負荷された衝撃力によって前記歪み検出部材に発生する歪みを前記歪みゲージによって検出する歪み検出手段と、
前記歪み検出手段によって検出された歪みに基づいて、前記歪み抑制率を算出して出力する出力手段と、
を備えたことを特徴とする請求項1に記載の発泡シート。 - 前記保持手段は、
テーブルに対して垂直に固定されて、前記歪み検出部材の一面側が密着されると共に、該歪み検出部材の前記衝撃力を受ける部分が荷重方向に変形可能となるように中央部分に凹部が形成された固定治具と、
中央部に開口部が形成されて前記固定治具に向かう方向へスライド可能に設けられて、前記歪み検出部の他面側に固定された前記発泡シートの全面を覆うように該発泡シートに密着された前記支持部材の前記発泡シートに密着される面と反対側の面に当接して、該支持部材を前記発泡シート側へ押圧した状態で前記テーブルに固定される押さえ治具と、
前記押さえ治具が前記支持部材を押圧する押さえ圧力を調整して前記発泡シートの厚さ方向の圧縮率を任意に設定する圧力調整手段と、
を有し、
前記衝撃負荷手段は、前記押さえ治具の開口部内に入って前記発泡シートを覆う前記支持部材に衝撃力を負荷し、
前記歪み検出手段は、前記歪みゲージによって前記歪み検出部材の前記凹部内側への変形によって発生する歪みを検出することを特徴とする請求項2に記載の発泡シート。 - 前記衝撃負荷手段は、一端が回動可能に軸支された振り子式のハンマと、
前記ハンマを所定角度に持ち上げて保持するハンマ保持手段と、を有し、
前記ハンマ保持手段に保持されたハンマを振り下ろすことによって前記衝撃力を負荷することを特徴とする請求項2又は請求項3に記載の発泡シート。 - 前記歪み検出部材は、2枚の板部材が密着されて構成され、
前記歪みゲージは、前記2枚の板部材のうち、前記発泡シートが密着される第1板部材の該発泡シートが密着される面に対して反対側の面に貼り付けられて、前記2枚の板部材の間に積層されていることを特徴とする請求項1乃至請求項4のいずれかに記載の発泡シート。 - 動的粘弾性測定による貯蔵弾性率に対する損失弾性率の比率である損失正接(tanδ)が、500Hzから50000Hzまでの範囲内に最大値を有し、
500Hzから3000Hzにおける前記損失正接(tanδ)が、0.2以上であることを特徴とする請求項1乃至請求項5のいずれかに記載の発泡シート。 - 電気・電子機器用衝撃吸収シートとして用いられることを特徴とする請求項1乃至請求項6のいずれかに記載の発泡シート。
- 厚さが30~200μmであり、密度が0.2~0.7g/cm3、平均セル径が10~100μmの発泡体で構成された発泡シートであって、
前記発泡シートを支持部材と歪み検出部材との間に挟んだ状態で保持可能に構成され、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の歪みを歪みゲージによって測定する衝撃試験装置を用いた場合に、下記式で表される歪み抑制率が20%以上である発泡シートが用いられていることを特徴とする電気・電子機器。
歪み抑制率(%)={(ε0-ε1)/ε0}×100
(上式において、ε0は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着していない状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みであり、ε1は前記発泡シートを前記支持部材と前記歪み検出部材との間に装着した状態で、前記支持部材に衝撃力を負荷した際の前記歪み検出部材の最大歪みである。) - 前記衝撃試験装置は、
前記発泡シートを前記支持部材と前記歪み検出部材との間に挟んだ状態で保持すると共に、前記発泡シートを任意の厚さ方向の圧縮率で保持する保持手段と、
前記保持手段に保持された前記支持部材に衝撃力を負荷する衝撃負荷手段と、
前記衝撃負荷手段によって前記支持部材を介して前記発泡シートに負荷された衝撃力によって前記歪み検出部材に発生する歪みを前記歪みゲージによって検出する歪み検出手段と、
前記歪み検出手段によって検出された歪みに基づいて、前記歪み抑制率を算出して出力する出力手段と、
を備えたことを特徴とする請求項8に記載の電気・電子機器。 - 前記保持手段は、
テーブルに対して垂直に固定されて、前記歪み検出部材の一面側が密着されると共に、該歪み検出部材の前記衝撃力を受ける部分が荷重方向に変形可能となるように中央部分に凹部が形成された固定治具と、
中央部に開口部が形成されて前記固定治具に向かう方向へスライド可能に設けられて、前記歪み検出部の他面側に固定された前記発泡シートの全面を覆うように該発泡シートに密着された前記支持部材の前記発泡シートに密着される面と反対側の面に当接して、該支持部材を前記発泡シート側へ押圧した状態で前記テーブルに固定される押さえ治具と、
前記押さえ治具が前記支持部材を押圧する押さえ圧力を調整して前記発泡シートの厚さ方向の圧縮率を任意に設定する圧力調整手段と、
を有し、
前記衝撃負荷手段は、前記押さえ治具の開口部内に入って前記発泡シートを覆う前記支持部材に衝撃力を負荷し、
前記歪み検出手段は、前記歪みゲージによって前記歪み検出部材の前記凹部内側への変形によって発生する歪みを検出することを特徴とする請求項9に記載の電気・電子機器。 - 前記衝撃負荷手段は、一端が回動可能に軸支された振り子式のハンマと、
前記ハンマを所定角度に持ち上げて保持するハンマ保持手段と、を有し、
前記ハンマ保持手段に保持されたハンマを振り下ろすことによって前記衝撃力を負荷することを特徴とする請求項9又は請求項10に記載の電気・電子機器。 - 前記歪み検出部材は、2枚の板部材が密着されて構成され、
前記歪みゲージは、前記2枚の板部材のうち、前記発泡シートが密着される第1板部材の該発泡シートが密着される面に対して反対側の面に貼り付けられて、前記2枚の板部材の間に積層されていることを特徴とする請求項8乃至請求項11のいずれかに記載の電気・電子機器。 - 前記発泡シートは、動的粘弾性測定による貯蔵弾性率に対する損失弾性率の比率である損失正接(tanδ)が、500Hzから50000Hzまでの範囲内に最大値を有し、
500Hzから3000Hzにおける前記損失正接(tanδ)が、0.2以上であることを特徴とする請求項8乃至請求項12のいずれかに記載の電気・電子機器。 - 前記発泡シートが電気・電子機器用衝撃吸収シートとして用いられることを特徴とする請求項8乃至請求項13のいずれかに記載の電気・電子機器。
- 筐体と画像表示部材を備え、
前記発泡シートが前記筐体と前記画像表示部材との間に挟持された構造を有することを特徴とする請求項14に記載の電気・電子機器。
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