JP2018021170A - Foam sheet, electrical and electronic equipment and touch panel-mounted apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam sheet excellent in impact absorptivity and also excellent in resistance to repeated impact.SOLUTION: Provided is a foam sheet in which an average cell diameter is 10 to 200 μm, resiliency when a thickness is compressed by 50% is 6.0 N/cmor lower, a loss tangent (tanδ) as a ratio between a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad/s in dynamic viscoelastic measurement has a peak top in the range of -60 to 20°C, and a thickness recovery defined by a following formula is 90% or more: the thickness recovery (%)=(a thickness after 0.5 s after a release of a compressed state)/(an initial thickness)×100. The initial thickness: the thickness of the foam sheet before an application of load. The thickness after 0.5 s after a release of a compressed state: the thickness of the foam sheet 0.5 s after the release of a compression after maintaining a state where a load of 100 g/cmis applied to the foam sheet for 120 s.SELECTED DRAWING: None

Description

  The present invention relates to a foam sheet, an electric / electronic device, and a touch panel-mounted device. More specifically, the present invention relates to a foam sheet, an electric / electronic device using the foam sheet, and a touch panel mounting device using the foam sheet.

Conventionally, an image display member fixed to an image display device such as a liquid crystal display, an electroluminescence display, a plasma display, a display member attached to a so-called “mobile phone”, “smart phone”, “portable information terminal”, camera, A foam material is used when an optical member such as a lens is fixed to a predetermined part (for example, a housing). Examples of such a foam material include a low-foam, fine-cell urethane foam having a closed cell structure and a product obtained by compression molding a highly foamed urethane, and a polyethylene foam having a closed cell and an expansion ratio of about 30 times. It was used. Specifically, for example, a gasket (see Patent Document 1) made of a polyurethane foam having a density of 0.3 to 0.5 g / cm ³ , and an electric / electronic product made of a foamed structure having an average cell diameter of 1 to 500 μm. A sealing material for equipment (see Patent Document 2) or the like is used.

JP 2001-100216 A JP 2002-309198 A

  Such a foamed material is required to have a characteristic (impact absorbability) that absorbs an impact when it is applied. For example, when an electric or electronic device with a display member such as a “smartphone” is dropped on the ground, a foam sheet with excellent shock absorption is used to absorb the impact of the collision and prevent the display member from being damaged. Has been. However, the conventional foam sheet having excellent impact absorbability tends to have better impact absorbability as it is more flexible, but on the other hand, it tends to take time to return to the original thickness after the impact is released. For this reason, the conventional foamed sheet with excellent shock absorption cannot receive the second and subsequent shocks because it receives an impact before it completely returns to its original thickness when repeated impacts are applied. It was often inferior in resistance. For this reason, there is a need for a foam sheet that is excellent in impact absorption and excellent in resistance to repeated impacts.

  Furthermore, in recent years, with the spread of touch panel-equipped devices such as smartphones and portable terminals, there are increasing opportunities for users to touch and push the screen using a jig (stylus) such as a finger or a touch pen. In addition, these touch panel-equipped devices are becoming increasingly thinner, and members (for example, a display panel represented by an LCD panel and a touch panel that knows a touched place) are also becoming thinner. . Therefore, when the user presses the screen, the display panel and the touch panel are very easy to bend (bend). When the bending occurs, the display panel may interfere with other internal members (for example, a circuit board, a battery, etc.) due to the bending, and display unevenness (a ripple-like bleeding pattern) may occur on the display panel. As a cause of the occurrence of display unevenness, it is considered that the display panel is pressed against other members in the interior, stress is applied to the display panel, and the alignment of liquid crystal molecules is disturbed.

  In response to the problem of display unevenness (ripple blurring pattern) that may occur due to stress applied to the display panel, even if a gap is provided around the display panel and the display panel is deformed, the stress is applied to the display panel. It has been proposed to make it difficult to apply, to change the design of the display panel and touch panel to make it thicker and less flexible, and to increase the rigidity of the housing of the device equipped with the touch panel to make it difficult to deform. . However, there is an adverse effect that the touch panel-equipped device becomes thicker and heavier. For this reason, touch-panel-equipped devices are required to solve the problem of display unevenness (ripple blurring pattern) that may occur due to stress applied to the display panel, while responding to the thinning that is progressing remarkably. ing.

Accordingly, an object of the present invention is to provide a foamed sheet that is excellent in impact absorption and excellent in resistance to repeated impacts.
Another object of the present invention is that it has excellent shock absorption and resistance to repeated impacts, and when used in a touch panel-mounted device, it causes display unevenness in the display unit due to a user's touch operation. The object is to provide a foam sheet that can be highly suppressed.
Another object of the present invention is to provide a foam sheet that is excellent in the above characteristics even when the thickness is very small.
Another object of the present invention is to provide a foamed sheet that can prevent misalignment without laminating an adhesive layer when laminating other members in addition to the above characteristics.

As a result of intensive studies to achieve the above object, the present inventors have found that the average cell diameter is within a specific range, the repulsive force when compressing the thickness by 50% is 6.0 N / cm ² or less, and According to the foam sheet having a thickness recovery rate of 90% or more after 0.5 seconds after releasing a compressed state with a specific load applied, it has excellent shock absorption and excellent resistance to repeated impacts. I found it. The present invention has been completed based on these findings.

That is, in the present invention, the average cell diameter is 10 to 200 μm, the repulsion force when the thickness is compressed by 50% is 6.0 N / cm ² or less, and the thickness recovery rate defined by the following formula is 90% or more. A foam sheet is provided.
Thickness recovery rate (%) = (thickness 0.5 seconds after releasing the compressed state) / (initial thickness) × 100
Initial thickness: Thickness of foam sheet before applying load Thickness 0.5 seconds after releasing compression: Maintaining 120 seconds with 100 g / cm ² applied to foam sheet, releasing compression The thickness of the foam sheet 0.5 seconds after release

The foamed sheet preferably has a thickness of 30 to 1000 μm and a density of 0.2 to 0.7 g / cm ³ .

  The foamed sheet has a peak top in a range where a loss tangent (tan δ), which is a ratio of a storage elastic modulus and a loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement, is −60 ° C. or higher and 20 ° C. or lower. It is preferable to have.

  In the shock absorption test using a pendulum type impact tester, the foamed sheet was allowed to collide with the impactor five times continuously at intervals of 1 second on the support plate of the structure composed of the support plate and the foamed sheet. The rate of increase of the impact force at the time of the fifth collision with respect to the impact force at the time of the first collision is preferably 5% or less.

  The foamed sheet preferably contains a crosslinking agent and a silicone compound.

  The foamed sheet preferably has a solvent insoluble content with respect to methyl ethyl ketone of 80% by weight or more.

  The foamed sheet preferably has a maximum loss tangent (tan δ) within a range of −60 ° C. to 20 ° C. of 0.2 or more.

The foam sheet preferably has a thickness recovery rate of 50% or more at a high temperature defined below.
Thickness recovery rate at high temperature: The foamed sheet was compressed in the thickness direction so as to have a thickness of 50% of the initial thickness in an 80 ° C atmosphere, and after 22 hours, it was left in a 23 ° C atmosphere for 2 hours. Then, the compressed state is released, and the ratio of the thickness to the initial thickness after 24 hours from the release of the compressed state

  The foam sheet is preferably a foam sheet using an acrylic polymer as a resin material.

The foamed sheet preferably has a shear adhesive force (23 ° C., tensile speed 50 mm / min) of at least one surface to a SUS304BA plate of 0.5 N / 100 mm ² or more.

  The foam sheet is preferably a mechanical foam of an emulsion resin composition.

  The foam sheet may have an adhesive layer on one side or both sides.

  The foam sheet is preferably used as an impact absorbing sheet for electric and electronic equipment.

  The foam sheet is preferably used for a touch panel-mounted device.

  The present invention also provides an electrical / electronic device having the foam sheet.

  The electrical / electronic device preferably includes a display member, and the foam sheet is sandwiched between a housing of the electrical / electronic device and the display member.

  Moreover, this invention provides the touchscreen mounting apparatus which has the said foam sheet.

  The touch panel-mounted device preferably includes the foam sheet, the display panel, and the touch panel, and the foam sheet is disposed in a space on the back side of the display panel.

  The foamed sheet of the present invention is excellent in impact absorption and excellent in resistance to repeated impacts. The foam sheet of the present invention is excellent in shock absorption and resistance to repeated impacts when used in a touch panel-mounted device, and is highly resistant to display unevenness in the display unit due to a user's touch operation. Can be suppressed. In addition, the foamed sheet of the present invention is excellent in shock absorption and resistance to repeated impacts even when the thickness is very small. Accordingly, the occurrence of display unevenness in the display unit can be highly suppressed.

  Moreover, when the foamed sheet of the present invention is laminated with other members, it is possible to have a configuration that can prevent misalignment without having an adhesive layer.

It is a schematic block diagram of a pendulum type impact tester (impact test device). It is a figure which shows schematic structure of the holding member of a pendulum type impact tester (impact test apparatus).

The foamed sheet of the present invention has an average cell diameter of 10 to 200 μm, a repulsive force when the thickness is compressed by 50% is 6.0 N / cm ² or less, and a thickness recovery rate defined by the following formula is 90%. That's it. In the present specification, the thickness recovery rate defined above may be simply referred to as “thickness recovery rate after 0.5 seconds”.
Thickness recovery rate (%) = (thickness 0.5 seconds after releasing the compressed state) / (initial thickness) × 100
Initial thickness: Thickness of foam sheet before applying load Thickness 0.5 seconds after releasing compression: Maintaining 120 seconds with 100 g / cm ² applied to foam sheet, releasing compression The thickness of the foam sheet 0.5 seconds after release

  The average cell diameter of the foamed sheet of the present invention is 10 to 200 μm as described above. The lower limit is preferably 15 μm, more preferably 20 μm, and the upper limit is preferably 180 μm, more preferably 150 μm, and even more preferably 100 μm. When the average cell diameter is 10 μm or more, more excellent impact absorbability is exhibited. Further, when the average cell diameter is 200 μm or less, the compression recovery property is excellent, and since it can return to the original thickness in a short time after receiving an impact, it is excellent in resistance to repeated impacts. The maximum cell diameter of the foamed sheet is, for example, 40 to 400 μm, and the lower limit thereof is preferably 60 μm, more preferably 80 μm, and the upper limit is preferably 300 μm, more preferably 220 μm. The minimum cell diameter of the foamed sheet is, for example, 5 to 70 μm, and the lower limit is preferably 8 μm, more preferably 10 μm, and the upper limit is preferably 60 μm, more preferably 50 μm.

Repulsive force upon compression of 50% the thickness of the foamed sheet of the present invention is 6.0 N / cm ² or less as described above, preferably 4.0 N / cm ² or less, more preferably 2.9 N / cm ² or less, more preferably ^2.5 N / cm ² or less. When the repulsive force is 6.0 N / cm ² or less, the foamed sheet of the present invention is more excellent in impact absorption. Although the minimum of the said repulsive force is not specifically limited, 0.1 N / cm < ² > is preferable. In addition, the repulsion force at the time of 50% compression can be measured according to the compression hardness measurement method described in JIS K 6767.

  As described above, the thickness recovery rate after 0.5 seconds of the foamed sheet of the present invention is 90% or more, preferably 90.5% or more, and more preferably 91% or more. The foamed sheet of the present invention is excellent in resistance to repeated impact since the thickness recovery rate is 90% or more, and can return to the original thickness in a short time after receiving an impact. Moreover, it is also excellent in dustproofness and sealing performance. The thickness recovery rate after 0.5 seconds is a recovery rate measured by applying a load to the foamed sheet with a certain area and compressing it. It is different from the dent recovery rate.

  Although the thickness of the foam sheet of this invention is not specifically limited, It is preferable that it is 30-1000 micrometers. The lower limit is preferably 40 μm, more preferably 50 μm, and the upper limit is preferably 700 μm, more preferably 500 μm, and even more preferably 300 μm. When the thickness of the foamed sheet is 30 μm or more, bubbles can be contained uniformly, and more excellent impact absorbability can be exhibited. Further, if the thickness of the foamed sheet is 1000 μm or less, it is possible to easily follow a minute clearance. When the thickness of the foamed sheet is within the above range, the shock absorbing property is excellent even though the thickness is small.

The density of the foamed sheet of the present invention is not particularly limited, but is preferably 0.2 to 0.7 g / cm ³ . The lower limit is preferably 0.21 g / cm ³ , more preferably 0.22 g / cm ³ , and the upper limit is preferably 0.50 g / cm ³ , more preferably 0.40 g / cm ³ , still more preferably 0.00. 35 g / cm ³ . When the density is 0.2 g / cm ³ or more, it is easy to maintain the strength of the foamed sheet. When the density is 0.7 g / cm ³ or less, higher impact absorbability is exhibited. Further, when the density is in the range of 0.2 to 0.7 g / cm ³ , even higher shock absorption is exhibited. In the present specification, the density of the foam sheet (foam) means “apparent density”.

  In the present invention, from the viewpoint of impact absorption, the ratio of the average cell diameter (μm) to the thickness of the foamed sheet (μm) (the former / the latter) is preferably in the range of 0.1 to 0.8. The lower limit of the ratio of the average cell diameter (μm) to the thickness of the foamed sheet (μm) is preferably 0.15, more preferably 0.2, and the upper limit is preferably 0.75, more preferably 0.00. 6.

  The peak top of the loss tangent (tan δ), which is the ratio of the storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement of the foamed sheet of the present invention, is not particularly limited, but is −60 ° C. It is preferable that it exists in the range below 20 degreeC. The lower limit of the temperature range where the peak tangent of the loss tangent exists is preferably −50 ° C., more preferably −40 ° C., still more preferably −30 ° C., and the upper limit is preferably 10 ° C., more preferably 0 ° C. It is. In the case of a material having two or more peak tops of loss tangents, it is desirable that at least one of them falls within the above range. When the peak temperature is within the above range, the temperature dependency of the foamed sheet is low, and excellent compression recovery is exhibited even in a high temperature environment, and high flexibility is exhibited and excellent shock absorption is exhibited. .

  The peak top strength (maximum value) of loss tangent (tan δ) in the range of −60 ° C. or higher and 20 ° C. or lower is preferably higher from the viewpoint of shock absorption, for example, 0.2 or higher, preferably 0.3 or higher. . The upper limit value of the peak top intensity (maximum value) is, for example, 2.0.

  In the foam sheet of the present invention, the ratio of the peak top strength of the loss tangent (tan δ) to the density (the former / the latter) is preferably in the range of 1 to 5. The lower limit of the ratio of the peak top intensity of the loss tangent (tan δ) to the density is preferably 1.5, more preferably 2, and the upper limit is preferably 4.5, more preferably 4. When the ratio of the peak top strength of the loss tangent (tan δ) to the density is within the above range, more excellent impact absorbability is exhibited.

The initial elastic modulus of the foamed sheet of the present invention is desirably 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. Hereinafter, it is more preferably 1 N / mm ² or less. The lower limit value of the initial elastic modulus is, for example, 0.1 N / mm ² .

  As long as the foamed sheet of the present invention has the above-mentioned characteristics, its composition, cell structure and the like are not particularly limited. The cell structure may be any of an open cell structure, a closed cell structure, and a semi-continuous semi-closed cell structure. From the viewpoint of impact absorption, an open cell structure and a semi-open semi-closed cell structure are preferable.

The foamed sheet of the present invention has excellent impact absorbability. In addition, it has high shock absorption even for very weak shocks, and exhibits excellent shock absorption regardless of the magnitude of the shock. For example, in an impact absorption test using a pendulum type impact tester, the impact absorption rate (%) defined by the following formula is divided by the thickness (μm) of the foamed sheet to determine the impact absorption rate R per unit thickness.
Impact absorption rate (%) = {(F ₀ −F ₁ ) / F ₀ } × 100
(In the above formula, F ₀ is the impact force when the impactor collides only with the support plate, and F ₁ causes the impactor to collide with the support plate of the structure composed of the support plate and the foam sheet. Is the impact force when

  A schematic configuration of a pendulum type impact tester (impact test apparatus) will be described with reference to FIGS. As shown in FIGS. 1 and 2, the impact test apparatus 1 (pendulum tester 1) includes a holding member 3 as a holding means for holding the test piece 2 (foamed sheet 2) with an arbitrary holding force, and the test piece 2 An impact load member 4 for applying an impact stress to the test piece, a pressure sensor 5 as an impact force detection means for detecting an impact force of the impact load member 4 against the test piece 2 and the like. The holding member 3 that holds the test piece 2 with an arbitrary holding force includes a fixing jig 11 and a holding jig 12 that is slidable so as to sandwich and hold the test piece 2 facing the fixing jig 11. It is configured. Further, the pressing jig 12 is provided with a pressing pressure adjusting means 16. Further, the impact load member 4 for applying an impact force to the test piece 2 held by the holding member 3 is supported so that one end 22 is pivotally supported with respect to the column 20 and an impactor 24 is provided on the other end side. It is composed of a rod 23 (shaft 23) and an arm 21 that lifts and holds the impactor 24 at a predetermined angle. Here, since a steel ball is used as the impactor 24, it is possible to lift the impactor 24 integrally by a predetermined angle by providing an electromagnet 25 at one end of the arm. Furthermore, the pressure sensor 5 that detects the impact force acting on the test piece 2 by the impact load member 4 is provided on the opposite side of the surface of the fixing jig 11 that contacts the test piece.

  The impactor 24 is a steel ball (iron ball). The angle at which the impactor 24 is lifted by the arm 21 (the swing angle a in FIG. 1) is 40 °. The weight of the steel ball (iron ball) is 66 g.

  As shown in FIG. 2, the test piece 2 (foamed sheet 2) is a highly elastic plate material such as a resin plate (acrylic plate, polycarbonate plate, etc.) or a metal plate between the fixing jig 11 and the holding jig 12. It is clamped via the support plate 28 configured.

The impact absorption rate is determined by impact force F ₀ measured by causing the impactor 24 to collide with the support plate 28 after the fixing jig 11 and the support plate 28 are closely fixed using the impact test apparatus described above. The impact force F ₁ measured by causing the impactor 24 to collide with the support plate 28 after inserting the test piece 2 between the fixing jig 11 and the support plate 28 and fixing the test piece 2 tightly is calculated. The The impact test apparatus is the same apparatus as that of Example 1 of JP-A-2006-47277.

F ₁ when the weight of the impactor is 66 g and the swing angle is 40 °, that is, in the impact absorption test using the pendulum impact tester, the impact is applied to the support plate of the structure composed of the support plate and the foam sheet. The impact force when the child collides is preferably 1000 N or less, more preferably 900 N or less, still more preferably 800 N or less, and particularly preferably 750 N or less. When the impact force is 1000 N or less, the impact absorbing ability of the foam sheet is more excellent. The lower limit of the impact force is 0N or more, and may be 100N or more, 300N or more, or 500N or more. In addition, the said impact force is an impact force of the initial stage foam sheet which has not received the big impact.

  The number of impacts when the impactor collides with the support plate of the structure consisting of the support plate and the foamed sheet in a shock absorption test using a pendulum type impact tester at intervals of 1 second, 5 times. The x-axis and impact force (N) as y-axis are plotted at 5 points, and the slope of the linear approximation line obtained from the 5 points by the least square method is not particularly limited, but is preferably 10 or less, more preferably 5 Hereinafter, it is more preferably 1 or less, particularly preferably 0.5 or less. When the inclination is 10 or less, the resistance to repeated impacts is more excellent. The lower limit of the inclination is, for example, −5.

  In the shock absorption test using a pendulum type impact tester, when the impactor is collided five times continuously at intervals of 1 second on the support plate of the structure composed of the support plate and the foamed sheet, the first time Rate of increase of impact force at the time of the fifth collision (%) with respect to the impact force at the time of the collision [(impact force at the fifth collision−impact force at the first collision) / impact force at the first collision × 100] Is preferably 5% or less, more preferably 3.5% or less, and still more preferably 2% or less. When the increase rate is 5% or less, the resistance to repeated impacts is more excellent. The lower limit of the increase rate is, for example, -10%.

The foamed sheet of the present invention preferably has a thickness recovery rate at a high temperature defined below of 50% or more, more preferably 70%, still more preferably 80%, and particularly preferably 90% or more. . In the present specification, the thickness recovery rate at a high temperature defined below may be simply referred to as a “thickness recovery rate at a high temperature”.
Thickness recovery rate at high temperature: The foamed sheet was compressed in the thickness direction so as to have a thickness of 50% of the initial thickness in an 80 ° C atmosphere, and after 22 hours, it was left in a 23 ° C atmosphere for 2 hours. Then, the compressed state is released, and the ratio of the thickness to the initial thickness after 24 hours from the release of the compressed state

  When the thickness recovery rate of the foamed sheet of the present invention at a high temperature is 50% or more, in addition to a normal temperature environment, an impact is generated even in a high temperature environment (for example, a temperature environment of 40 to 120 ° C.). The recovery speed of the thickness after the addition is fast, and the resistance to repeated impacts in a high temperature environment is excellent.

The foam sheet of this invention can be comprised with the resin composition containing a resin material (polymer). In addition, the loss which is a ratio of the storage elastic modulus and the loss elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement of the resin composition in an unfoamed state [resin composition when not foamed (solid matter)] The peak top of tangent (tan δ) is preferably in the range of −60 ° C. or higher and 20 ° C. or lower. The lower limit of the temperature range where the peak tangent of the loss tangent exists is preferably −50 ° C., more preferably −40 ° C., still more preferably −30 ° C., and the upper limit is preferably 10 ° C., more preferably 0 ° C. It is. In the case of a material having two or more peak tops of loss tangents, it is desirable that at least one of them falls within the above range. Peak top strength of loss tangent (tan δ) within a range of −60 ° C. or higher and 20 ° C. or lower of the resin composition (solid matter) (this value is within a range of −60 ° C. or higher and 20 ° C. or lower in the foamed sheet) The peak tangent strength of loss tangent (tan δ) is equivalent to the value obtained by dividing the peak top strength by the density (g / cm ³ ) of the foam sheet. For example, the peak top strength of the loss tangent (tan δ) within the range of −60 ° C. or more and 20 ° C. or less of the resin composition (solid material) is preferably 0.9 (g / cm ³ ) ⁻¹ or more. The upper limit is about 3, for example.

Further, the initial elastic modulus (23 ° C., tensile speed 300 mm / min) of the unfoamed resin composition (solid material) is desirably lower, 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 solvent-insoluble content (gel fraction) of the foamed sheet of the present invention with respect to methyl ethyl ketone is not particularly limited, but is preferably 80% by weight or more, and more preferably 90% by weight or more. In addition, the solvent insoluble content with respect to the said methyl ethyl ketone is 100 weight% or less normally.

The solvent insoluble content (gel fraction) with respect to methyl ethyl ketone is determined as follows. About 0.2 g of a sample is obtained from the foamed sheet, this sample is precisely weighed, and the weight obtained by the precise weighing is defined as “weight before storage (g)”. Next, this sample is put into 50 g of methyl ethyl ketone (MEK) and stored at room temperature for 5 days. Thereafter, the sample is taken out from methyl ethyl ketone, and the taken sample is dried at 130 ° C. for 1 hour. After drying, leave the sample at room temperature for 30 minutes, and then weigh the sample precisely. The weight obtained by this precise weighing is defined as “weight after storage (g)”. And the solvent insoluble content with respect to methyl ethyl ketone is calculated from the following formula.
Solvent insoluble content (% by weight) with respect to methyl ethyl ketone = (weight after storage) / (weight before storage) × 100

  It does not specifically limit as a resin material (polymer) which comprises the foam sheet of this invention, The well-known thru | or well-known resin material which comprises a foam can be used. Examples of the resin material include acrylic polymer, rubber, urethane polymer, and ethylene-vinyl acetate copolymer. Among these, an acrylic polymer is preferable from the viewpoints that permanent set is small, heat resistance (resistance to deformation strain) is excellent, compressive load can be easily reduced, and shock absorption is excellent. The resin material (polymer) constituting the foamed sheet may be one kind alone, or two or more kinds.

  In addition, the peak top of the loss tangent (tan δ), which is the ratio of the storage elastic modulus and the loss elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement of the foamed sheet, is in the range of −60 ° C. or higher and 20 ° C. or lower. In order to do this, the Tg of the resin material (polymer) can be used as an index or a guide. For example, as the resin material (polymer), Tg is −60 ° C. or higher and 20 ° C. or lower (the lower limit is preferably −50 ° C., more preferably −30 ° C., and the upper limit is preferably 10 ° C., more preferably 0 ° C.). It can be selected from resin materials (polymers) within the range.

  The acrylic polymer is preferably an acrylic polymer formed by using 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. Using such an acrylic polymer, the ratio of the storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement is obtained by adjusting the amount ratio of the former monomer and the latter monomer. A foamed sheet having a loss tangent (tan δ) peak top of −60 ° C. or higher and 20 ° C. or lower can be obtained relatively easily.

  In the present invention, “glass transition temperature (Tg) when forming a homopolymer” (sometimes simply referred to as “Tg of homopolymer”) means “glass transition temperature (Tg of homopolymer of the monomer)”. ) ”, Specifically,“ Polymer Handbook ”(3rd edition, John Wiley & Sons, Inc, 1987). In addition, Tg of the homopolymer of the monomer which is not described in the said literature says the value (refer Unexamined-Japanese-Patent No. 2007-51271) obtained by the following measuring methods, for example. That is, in a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser, 100 parts by weight of monomer, 0.2 part by weight of 2,2′-azobisisobutyronitrile, and ethyl acetate 200 as a polymerization solvent. A part by weight is charged and stirred for 1 hour while introducing nitrogen gas. After removing oxygen in the polymerization system in this way, the temperature is raised to 63 ° C. and the reaction is carried out for 10 hours. Next, the mixture is cooled to room temperature to obtain a homopolymer solution having a solid concentration of 33% by weight. Next, 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. Then, 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 of 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 peak top temperature of tan δ is defined as Tg of the homopolymer. The Tg of the resin material (polymer) can also be measured by this method.

  In the monomer having a homopolymer Tg of −10 ° C. or higher, the Tg is, for example, −10 ° C. to 250 ° C., preferably 10 to 230 ° C., and more preferably 50 to 200 ° C.

  Examples of monomers having a Tg of −10 ° C. or higher as homopolymers described above include (meth) acrylonitrile; amide group-containing monomers such as (meth) acrylamide and N-hydroxyethyl (meth) acrylamide; (meth) acrylic acid; methacrylic acid (Meth) acrylic acid alkyl ester having a homopolymer such as methyl or ethyl methacrylate having a Tg of −10 ° C. or higher; (meth) acrylic acid isobornyl; heterocyclic ring-containing vinyl monomer such as N-vinyl-2-pyrrolidone; Examples thereof include hydroxyl group-containing monomers such as ethyl methacrylate. These can be used individually by 1 type or in combination of 2 or more types. Among these, (meth) acrylonitrile (particularly acrylonitrile) is particularly preferable. When (meth) acrylonitrile (especially acrylonitrile) is used as a monomer having a Tg of −10 ° C. or higher for the homopolymer, the peak top strength of the loss tangent (tan δ) of the foam sheet is increased because of the strong intermolecular interaction. be able to.

  In a monomer having a Tg of a homopolymer of less than −10 ° C., 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 monomer having a Tg of the homopolymer of less than −10 ° C. include, for example, (meth) acrylic acid alkyl esters having a Tg of less than −10 ° C. of a homopolymer such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Is mentioned. These can be used individually by 1 type or in combination of 2 or more types. Among these, acrylic acid C _2-8 alkyl ester is particularly preferable.

  The content of the monomer having a Tg of the homopolymer of −10 ° C. or higher with respect to all monomer components (total monomer component) forming the acrylic polymer is, for example, 2 to 30% by weight, and the lower limit is preferably 3%. %, More preferably 4% by weight, and the upper limit is preferably 25% by weight, more preferably 20% by weight. In addition, 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), urethane rubber (AU), and silicone rubber. Among these, nitrile rubber (NBR), methyl methacrylate-butadiene rubber (MBR), and silicone rubber are preferable.

  Examples of the urethane polymer include polycarbonate polyurethane, polyester polyurethane, and polyether polyurethane.

  As the ethylene-vinyl acetate copolymer, a known or well-known ethylene-vinyl acetate copolymer can be used.

In addition to the resin material (polymer), the foamed sheet of the present invention may contain a surfactant, a crosslinking agent, a thickener, a rust inhibitor, a silicone compound, and other additives as necessary. Above all, the repulsive force when compressing the thickness by 50% is 6.0 N / cm ² or less, and the viewpoint that the foam recovery sheet having the thickness recovery rate after 0.5 seconds of 90% or more can be easily obtained. Therefore, it is preferable to contain a crosslinking agent and a silicone compound.

  For example, an optional surfactant may be included for reducing the bubble diameter and stabilizing the foamed foam. The surfactant is not particularly limited, and any of an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, and the like may be used. From the viewpoint of the stability of the foam, an anionic surfactant is preferable, and a fatty acid ammonium surfactant such as ammonium stearate is more preferable. Surfactant may be used individually by 1 type and may be used in combination of 2 or more type. Different surfactants may be used in combination, for example, an anionic surfactant and a nonionic surfactant, or an anionic surfactant and an amphoteric surfactant may be used in combination.

  When the surfactant is included, the addition amount of the surfactant [solid content (nonvolatile content)] exceeds, for example, 0 part by weight with respect to 100 parts by weight of the resin material (polymer) [solid content (nonvolatile content)]. The lower limit is preferably 0.5 parts by weight, and the upper limit is preferably 8 parts by weight.

The foamed sheet of the present invention can easily form a foamed sheet having a repulsive force of 6.0 N / cm ² or less when the thickness is compressed by 50% and a thickness recovery rate of 0.5% or more after 90 seconds. In order to obtain and to improve the strength, heat resistance, and moisture resistance of the foamed sheet, an arbitrary crosslinking 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-based, oxazoline-based, isocyanate-based, carbodiimide-based, melamine-based, silicone-based (for example, silane coupling agent), metal oxide-based, and the like. As said crosslinking agent, only 1 type may be used and 2 or more types may be used. Among these, it is preferable to include at least an oxazoline-based crosslinking agent.

  When the crosslinking agent is included, the addition amount of the crosslinking agent [solid content (nonvolatile content)] exceeds 10 parts by weight with respect to 100 parts by weight of the resin material (polymer) [solid content (nonvolatile content)], for example. The lower limit is preferably 0.01 parts by weight, and the upper limit is preferably 9 parts by weight.

  Furthermore, in order to improve the stability of the foamed foam and the film forming property, an optional thickener may be included. It does not restrict | limit especially as a thickener, An acrylic acid type, a urethane type, a polyvinyl alcohol type etc. are mentioned. Of these, polyacrylic acid thickeners and urethane thickeners are preferred.

  When the thickener is included, the addition amount of the thickener [solid content (nonvolatile content)] exceeds, for example, 0 part by weight with respect to 100 parts by weight of the resin material (polymer) [solid content (nonvolatile content)]. The lower limit is preferably 0.1 parts by weight, and the upper limit is preferably 5 parts by weight.

  Moreover, arbitrary rust preventives may be included for the corrosion prevention of the metal member adjacent to a foam sheet. As the rust inhibitor, an azole ring-containing compound is preferable. When an azole ring-containing compound is used, it is possible to achieve both high levels of corrosion prevention for metals and adhesion to adherends.

  The azole ring-containing compound may be a compound having a 5-membered ring containing one or more nitrogen atoms in the ring, such as a diazole (imidazole, pyrazole) ring, triazole ring, tetrazole ring, oxazole ring, isoxazole. And compounds having a ring, a thiazole ring, or an isothiazole ring. These rings may be condensed with an aromatic ring such as a benzene ring to form a condensed ring. Examples of the compound having such a condensed ring include a compound having a benzimidazole ring, a benzopyrazole ring, a benzotriazole ring, a benzoxazole ring, a benzoisoxazole ring, a benzothiazole ring, or a benzoisothiazole ring.

The azole ring and the condensed ring (benzotriazole ring, benzothiazole ring, etc.) each may have a substituent. Examples of the substituent include an alkyl group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms) such as a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group; a methoxy group, an ethoxy group, and isopropyloxy An alkoxy group having 1 to 12 carbon atoms (preferably 1 to 3 carbon atoms) such as a butoxy group; an aryl group having 6 to 10 carbon atoms such as a phenyl group, a tolyl group or a naphthyl group; an amino group; a methylamino group; (Mono or di) C _1-10 alkylamino group such as dimethylamino group; amino-C _1-6 alkyl group such as aminomethyl group, 2-aminoethyl group; N, N-diethylaminomethyl group, N, N— Mono or di (C _1-10 alkyl) amino-C _1-6 alkyl group such as bis (2-ethylhexyl) aminomethyl group; mercapto group; carbon number 1 such as methoxycarbonyl group, ethoxycarbonyl group Carboxyl group; carboxy-C _1-6 alkyl group such as carboxymethyl group; carboxy-C _1-6 alkylthio group such as 2-carboxyethylthio group; N, N-bis (hydroxymethyl) N, N-bis (hydroxy-C _1-4 alkyl) amino-C _1-4 alkyl group such as aminomethyl group; sulfo group and the like. The azole ring-containing compound may form a salt such as a sodium salt or a potassium salt.

  From the viewpoint of rust prevention action on metals, a compound in which an azole ring forms a condensed ring with an aromatic ring such as a benzene ring is preferable. Among them, a benzotriazole compound (a compound having a benzotriazole ring), a benzothiazole compound ( A compound having a benzothiaazole ring) is particularly preferred.

  Examples of the benzotriazole compounds include 1,2,3-benzotriazole, methylbenzotriazole, carboxybenzotriazole, carboxymethylbenzotriazole, and 1- [N, N-bis (2-ethylhexyl) aminomethyl] benzotriazole. 1- [N, N-bis (2-ethylhexyl) aminomethyl] methylbenzotriazole, 2,2 ′-[[(methyl-1H-benzotriazol-1-yl) methyl] imino] bisethanol, or these A sodium salt etc. are mentioned.

  Examples of the benzothiazole-based compound include 2-mercaptobenzothiazole, 3- (2- (benzothiazolyl) thio) propionic acid, or a sodium salt thereof.

  An azole ring containing compound may be used individually by 1 type, and may be used in combination of 2 or more type.

  When a rust preventive agent is included, the addition amount of the rust preventive agent (for example, the above azole ring-containing compound) [solid content (nonvolatile content)] [solid content (nonvolatile content)] is within a range that does not impair the original properties of the foam. For example, 0.2 to 5 parts by weight is preferable with respect to 100 parts by weight of the resin material (polymer) [solid content (nonvolatile content)]. The lower limit is more preferably 0.3 parts by weight, still more preferably 0.4 parts by weight, and the upper limit is more preferably 3 parts by weight, still more preferably 2 parts by weight.

  Also, in order to improve the recoverability and recovery speed of the thickness of the foamed sheet after being compressed (particularly to increase the thickness recovery rate after 0.5 seconds above 90%), a silicone compound should be added. Is preferred. For the same purpose, a silicone-modified polymer (for example, a silicone-modified acrylic polymer, a silicone-modified urethane polymer, etc.) may be used as at least a part of the resin material (polymer). These may use 1 type and may use 2 or more types.

  As the silicone compound, a silicone compound having a siloxane bond of 2000 or less is preferable. Examples of the silicone compound include silicone oil, modified silicone oil, and silicone resin.

  Examples of the silicone oil (straight silicone oil) include dimethyl silicone oil and methylphenyl silicone oil.

  Examples of the modified silicone oil include polyether-modified silicone oil (polyether-modified dimethyl silicone oil, etc.), alkyl-modified silicone oil (alkyl-modified dimethyl silicone oil, etc.), aralkyl-modified silicone oil (aralkyl-modified dimethyl silicone oil, etc.), and higher fatty acids. Examples include ester-modified silicone oil (higher fatty acid ester-modified dimethyl silicone oil and the like), fluoroalkyl-modified silicone oil (fluoroalkyl-modified dimethyl silicone oil and the like), and the like.

  Of these, polyether-modified silicone is preferred. Commercially available products of polyether-modified silicone oil include, for example, “PEG11 methyl ether dimethicone”, “PEG / PPG-20 / 22 butyl ether dimethicone”, “PEG-9 methyl ether dimethicone”, “PEG-32 methyl ether dimethicone”, “ Linear type such as “PEG-9 dimethicone”, “PEG-3 dimethicone”, “PEG-10 dimethicone”; branched such as “PEG-9 polydimethylsiloxyethyl dimethicone”, “lauryl PEG-9 polydimethylsiloxyethyl dimethicone” Type (above, manufactured by Shin-Etsu Chemical Co., Ltd.) and the like.

  The silicone resin includes a straight silicone resin and a modified silicone resin. Examples of the straight silicone resin include methyl silicone resin and methylphenyl silicone resin. Examples of the modified silicone resin include alkyd-modified silicone resin, epoxy-modified silicone resin, acrylic-modified silicone resin, and polyester-modified silicone resin.

  The total content of the silicone compound and the silicone chain part present in the silicone-modified polymer in the foamed sheet of the present invention is non-volatile with respect to 100 parts by weight of the resin material (polymer) in the foamed sheet of the present invention. For example, 0.01 to 5 parts by weight in terms of minutes (in terms of solids). The lower limit of the total content is preferably 0.05 parts by weight, more preferably 0.1 parts by weight, and the upper limit is preferably 4 parts by weight, more preferably 3 parts by weight. When the total content of the silicone component and the silicone chain portion in the foamed sheet of the present invention is within the above range, it is easy to improve the recoverability and recovery speed after compression without impairing the properties as the foamed sheet.

  Further, the total content of the silicone compound and the silicone chain part present in the silicone-modified polymer in the foamed sheet of the present invention is, for example, 0.01 to 5 weight in terms of nonvolatile content (solid content). %. The lower limit of the total content is preferably 0.05% by weight, more preferably 0.1% by weight, and the upper limit is preferably 4% by weight, more preferably 3% by weight. When the total content of the silicone component and the silicone chain part in the foamed sheet of the present invention is within the above range, it is easier to improve the recovery and recovery speed after compression without impairing the properties as the foamed sheet.

  In addition, any appropriate other component may be included within a range not impairing the impact absorbability. 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, gelling agents, curing agents, plasticizers, fillers, reinforcing agents, foaming agents, flame retardants, and light stability. Agents, ultraviolet absorbers, colorants (pigments, dyes, etc.), pH adjusters, solvents (organic solvents), thermal polymerization initiators, photopolymerization initiators, and the like.

  Examples of the filler include silica, clay (mica, talc, smectite, etc.), alumina, titania, zinc oxide, tin oxide, zeolite, graphite, carbon nanotube, inorganic fiber (carbon fiber, glass fiber, etc.), and organic fiber. , Metal powder (silver, copper, etc.). In addition, piezoelectric particles (such as titanium oxide), conductive particles, thermally conductive particles (such as boron nitride), and organic fillers (such as silicone powder) can be added as fillers.

  The foamed sheet of the present invention can be produced by subjecting a resin composition containing a constituent resin material (polymer) to foam molding. As the foaming method (bubble forming method), methods usually used for foam molding, such as physical methods and chemical methods, can be employed. That is, the foam sheet of the present invention may be a foam (physical foam) formed by foaming by a physical method, or a foam (chemical foam) formed by foaming by a chemical method. It may be. In general, a physical method is a method in which gas components such as air and nitrogen are dispersed in a polymer solution and bubbles are formed by mechanical mixing (mechanical foam). 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.

  As 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. . That is, the foam sheet of the present invention is preferably a foam of the emulsion resin composition. As an emulsion, you may blend and use 2 or more types of emulsion. Moreover, the said resin composition may be preserve | saved as a resin composition which does not contain a crosslinking agent, and a crosslinking agent may be mixed just before attaching | subjecting foam molding.

  A higher solid content concentration of the emulsion is preferable 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.

  In this invention, the method of producing a foam through the process (process A) of foaming mechanically by foaming an emulsion resin composition is preferable. That is, the foam sheet of the present invention is preferably a mechanical foam of an emulsion resin composition. 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 with respect 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. Although it does not specifically limit as said base material, For example, the peeled plastic film (peeled polyethylene terephthalate film etc.), the plastic film (polyethylene terephthalate film etc.), a heat conductive layer (after-mentioned heat conductive layer) etc. are mentioned. It is done. When coating is performed using the heat conductive layer as a base material, the adhesion between the foamed sheet and the heat conductive layer can be improved, and the efficiency of the drying process during the preparation of the foamed sheet can also be improved.

  In the 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 200 ° C. or lower. Preferably it is.

  By providing the preliminary drying step B1 and the main drying step B2, it is possible to prevent coalescence of bubbles and bursting of bubbles due to a rapid temperature rise. In particular, in a foam sheet having a small thickness, bubbles are united and ruptured due to a rapid rise in temperature, and therefore, the provision of the preliminary drying step B1 is significant. The temperature in the preliminary drying step B1 is preferably 50 ° C. or higher and 100 ° C. or lower. The time of preliminary drying process B1 is 0.5 minute-30 minutes, for example, Preferably it is 1 minute-15 minutes. Moreover, the temperature in this drying process B2 becomes like this. Preferably they are 130 degreeC or more and 180 degrees C or less, More preferably, they are 130 degreeC or more and 160 degrees C or less. The time of this drying process B2 is 0.5 minute-30 minutes, for example, Preferably it is 1 minute-15 minutes.

  A foam sheet having an average cell diameter in the range of 10 to 200 μm can be obtained by adjusting the type and amount of the surfactant, and by adjusting the stirring speed and stirring time during mechanical stirring.

A foam sheet having a density of 0.2 to 0.7 g / cm ³ can be obtained by adjusting the amount of gas (gas) component taken into the emulsion resin composition during mechanical stirring.

  The foamed sheet of the present invention may have an adhesive layer (adhesive layer) on one side or both sides of the foamed sheet. 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 | stack the release liner which protects an adhesive layer until the time of use on the surface. In addition, when the foam sheet which comprises the foam sheet of this invention has a fine tack property, a member etc. can be fixed even if it does not provide an adhesive layer.

In the foamed sheet of the present invention, the foamed sheet has a shear adhesive force (measurement conditions: 23 ° C., tensile speed 50 mm / min) of at least one surface of the foamed sheet of 0.5 N / 100 mm ² or more to the SUS304BA plate. And other members (for example, a heat conductive layer) are used in a laminated manner, the above-mentioned other members will not be peeled off without providing an adhesive layer on the foamed sheet, and the effect of preventing displacement can be obtained. . Moreover, since it is not necessary to provide an adhesive layer, the thickness of the laminated body of a foam sheet and another member can be made small, and it can contribute to further thickness reduction of the electrical and electronic equipment etc. which are the object of attachment. Furthermore, the manufacturing efficiency of the laminate can be improved and the cost can be reduced. In addition, as an example of the layer structure of the laminated body of the foam sheet of this invention and other members (for example, heat conductive layer etc.), for example, other member / foam sheet, other member / adhesive layer / foam sheet, foam sheet / Other members / foamed sheets, foamed sheets / adhesive layers / other members / adhesive layers / foamed sheets and the like can be mentioned.

When the foamed sheet of the present invention has tackiness, the shear adhesive force of the foamed sheet of the present invention to the SUS304BA plate is, for example, the type of monomer constituting the resin material (polymer) constituting the foamed sheet of the present invention and its composition It can be adjusted by selecting the ratio. For example, as a monomer constituting the resin material (polymer such as acrylic polymer) constituting the foamed sheet of the present invention, the homopolymer Tg is less than −10 ° C. (for example, −70 ° C. or more and less than −10 ° C., preferably −70). For example, 70 to -12 ° C., more preferably −65 ° C. to −15 ° C.) with respect to all monomer components (total amount of monomer components) constituting the resin material (polymer such as acrylic polymer). ~ 98 wt% (lower limit is preferably 75 wt%, upper limit is preferably 97 wt%), and by appropriately selecting the type and amount of other monomers, the shear adhesive strength of the foamed sheet to the SUS304BA plate is reduced to 0 .5 N / 100 mm ² or more.

The lower limit of the shear adhesive strength of the foamed sheet of the present invention to the SUS304BA plate is preferably 0.5 N / 100 mm ² , more preferably 0.7 N / 100 mm ² . The upper limit of the shear adhesive force is not particularly limited, but is, for example, 100 N / 100 mm ² .

  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 resistance to repeated impacts while being excellent in impact absorption. For this reason, for example, in electrical and electronic equipment, various members or parts (for example, optical members and the like) are used when attaching (attaching) to a predetermined part (for example, a casing or the like), particularly members for electrical and electronic equipment. It is useful as a shock absorbing sheet. Since the foamed sheet of the present invention is used, the electrical / electronic device of the present invention is not easily damaged by an impact at the time of dropping, and is not easily damaged when repeatedly subjected to an impact. Further, since the foamed sheet of the present invention is excellent in shock absorption and resistance to repeated impacts even when the thickness is very thin, the electric and electronic device of the present invention can be reduced in size and thickness. It is difficult to break due to impact when dropped, and is also difficult to break when repeatedly impacted. “Electrical and electronic equipment” refers to equipment corresponding to at least one of electrical equipment and electronic equipment.

  As an optical member that can be attached (attached) using the foam sheet of the present invention, for example, an image display member attached to an image display device such as a liquid crystal display, an electroluminescence display, a plasma display (particularly, a small image display). Members), 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), etc. Can be mentioned.

  The electrical and electronic equipment of the present invention uses the foamed sheet of the present invention. Such an electric / electronic device is, for example, an electric / electronic device provided with a display member, wherein the foam sheet is sandwiched between a casing of the electric / electronic device and the display member. Includes electrical and electronic equipment. Examples of the electric and electronic devices include mobile communication devices such as so-called “mobile phones”, “smartphones”, and “portable information terminals”.

  In addition, when the foam sheet of the present invention is used in a touch panel mounted device, even if the display panel or the touch panel bends and deforms due to the user's touch operation, the force generated by the deformation is effectively reduced. Can disperse and absorb. Therefore, the foamed sheet of the present invention can highly suppress the occurrence of display unevenness (ripple-like blurring pattern) in the display unit that may be caused by stress applied to the display panel. For this reason, the foam sheet of this invention can be preferably used for a touch panel mounting apparatus.

  The touch panel mounted device means a device having a display panel and mounted with a touch panel. The touch panel-equipped device is not particularly limited. For example, mobile phones; smart phones; personal digital assistants (PDAs); tablet computers; desktop computers, notebook computers, tablet computers, and other personal computers (computers); Various displays (monitors) such as displays and electroluminescence displays (organic EL displays); portable game machines; digital audio players; electronic book readers (devices for viewing electronic books, terminals dedicated to electronic books); wearable computers (wearable devices) ; Digital signage (electronic signboards); Automatic teller machines (ATMs); Automatic ticket machines and vending machines used for sales of tickets, various cash vouchers, beverages, food, tobacco, magazines, newspapers, etc. ; A television receiver (TV); such as an electronic blackboard (interactive whiteboard), and the like.

  The foam sheet of the present invention is used in the touch panel-mounted device of the present invention. As such a touch panel mounting device, for example, a device having the foam sheet, a display panel, and a touch panel, in which the foam sheet is disposed in a space on the back side of the display panel can be mentioned. Since the foamed sheet of the present invention is used for the touch panel-mounted device of the present invention, the touch panel mounted device is not easily damaged by an impact when dropped, and is not easily damaged when repeatedly subjected to an impact. In addition, the foamed sheet of the present invention is excellent in shock absorption and resistance to repeated impacts even when the thickness is very thin. Therefore, the touch-panel-equipped device of the present invention is small and thin. It is difficult to break due to impact when dropped, and is also difficult to break when repeatedly impacted. Furthermore, in the touch panel mounted device of the present invention, the occurrence of display unevenness in the display unit due to the user's touch operation is highly suppressed.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “%” representing the content means% by weight. In addition, all the compounding parts (parts by weight) are values in terms of solid content (non-volatile content).

Example 1
100 parts by weight of acrylic emulsion solution (solid content 57%, butyl acrylate-methyl methacrylate-acrylonitrile-acrylic acid copolymer (weight ratio 91: 4: 3: 2)), fatty acid ammonium surfactant (ammonium stearate) Aqueous dispersion, solid content 33%) (surfactant A) 1.5 parts by weight, carboxybetaine type amphoteric surfactant ("Amogen CB-H", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (surfactant B) 1.0 part by weight, 0.35 part by weight of an oxazoline-based crosslinking agent (Epocross WS-500, manufactured by Nippon Shokubai Co., Ltd., solid content 39%), polyacrylic acid thickener (ethyl acrylate- Acrylic acid copolymer (acrylic acid 20%), solid content 28.7% 0.78 parts by weight, lubricant (modified silicone oil, “X-22-163C”, Shin-Etsu Chemical) Co., Ltd.)) 1.0 parts by weight of the disperser ( "Robo mix", was caused blowing and stir-mixed in a PRIMIX Co., Ltd.). This foamed composition was applied onto a release-treated PET (polyethylene terephthalate) film (thickness: 38 μm, trade name “MRF # 38”, manufactured by Mitsubishi Plastics, Inc.), at 80 ° C. for 5 minutes, and at 140 ° C. It was dried for 5 minutes to obtain a foam (foamed sheet) having an open cell structure having a thickness of 150 μm, a density of 0.31 g / cm ³ , a maximum cell diameter of 110 μm, a minimum cell diameter of 20 μm, and an average cell diameter of 45 μm.

Comparative Example 1
100 parts by weight of acrylic emulsion solution (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, (Solid content 33%) (surfactant A) 1.5 parts by weight, carboxybetaine type amphoteric surfactant ("Amogen CB-H", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (surfactant B) 1.0 Parts by weight, 0.35 parts by weight of an oxazoline-based cross-linking agent (“Epocross WS-500”, manufactured by Nippon Shokubai Co., Ltd., solid content 39%), polyacrylic acid-based thickener (ethyl acrylate-acrylic acid copolymer) 0.78 parts by weight (acrylic acid 20%), solid content 28.7%) was stirred and mixed with a disper (“Robomix”, manufactured by Primics Co., Ltd.) to foam. This foamed composition was applied onto a release-treated PET (polyethylene terephthalate) film (thickness: 38 μm, trade name “MRF # 38”, manufactured by Mitsubishi Plastics, Inc.), at 80 ° C. for 5 minutes, and at 140 ° C. It was dried for 5 minutes to obtain a foam (foamed sheet) having an open cell structure having a thickness of 150 μm, a density of 0.32 g / cm ³ , a maximum cell diameter of 110 μm, a minimum cell diameter of 20 μm, and an average cell diameter of 45 μm.

Comparative Example 2
100 parts by weight of acrylic emulsion solution (solid content 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, (Solid content 33%) (surfactant A) 1.5 parts by weight, carboxybetaine type amphoteric surfactant ("Amogen CB-H", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (surfactant B) 1.0 Disperse 0.3 parts by weight of oxazoline-based crosslinking agent (Epocross WS-500, manufactured by Nippon Shokubai Co., Ltd., solid content 39%), 25 parts by weight of filler (silica particles, average particle size: 5 μm) ("Robomix", manufactured by Primics Co., Ltd.) was stirred and mixed to foam. This foamed composition was applied onto a release-treated PET (polyethylene terephthalate) film (thickness: 38 μm, trade name “MRF # 38”, manufactured by Mitsubishi Plastics, Inc.), at 80 ° C. for 5 minutes, and at 140 ° C. It was dried for 5 minutes to obtain a foam (foamed sheet) having an open cell structure having a thickness of 150 μm, a density of 0.31 g / cm ³ , a maximum cell diameter of 110 μm, a minimum cell diameter of 20 μm, and an average cell diameter of 45 μm.

<Evaluation>
The following evaluation was performed about the foam (foamed sheet) obtained by the Example and the comparative example. The results are shown in Table 1. Table 1 shows the number of parts (parts by weight) [converted to solid content (nonvolatile content)] of each component in each example and comparative example.

(Average cell diameter)
An average cell diameter (μm) 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 Co., Ltd.) and analyzing the image. . The analyzed number of bubbles is about 10-20. Moreover, the minimum cell diameter (micrometer) and the maximum cell diameter (micrometer) of the foam sheet were calculated | required by the method similar to an average cell diameter.

(density)
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 (φ) 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.

(Dynamic viscoelasticity)
A temperature dispersibility test was performed at an angular frequency of 1 rad / s in a film tension measurement mode of a viscoelasticity measuring apparatus (“ARES2KFRTN1-FCO”, manufactured by TA Instruments Japan). The peak top temperature (° C.) and strength (maximum value) of loss tangent (tan δ), which is the ratio of storage elastic modulus E ′ and loss elastic modulus E ″ at that time, were measured.
In the column of “tan δ temperature” in Table 1, the peak top temperature (° C.) of the loss tangent (tan δ) of the foam is described, and in the “tan δ maximum value” column, the strength (maximum value) of the peak top In the column of “tan δ maximum value / density”, the value obtained by dividing the strength (maximum value) of the above peak top by the density of the foam [peak of tan δ of the material constituting the foam itself (excluding bubbles) It corresponds to the top strength (maximum value)].

(Thickness recovery rate)
The foam was cut into a width: 25 mm and a length: 40 mm to obtain a sheet-like test piece. 1 kg (100 g per 1 cm ² ) of the test piece was measured in the thickness direction under an atmosphere of 23 ° C. using an electromagnetic force type micro testing machine (micro servo) (trade name “MMT-250”, manufactured by Shimadzu Corporation). ) And the compressed state was maintained for 120 seconds. In a 23 ° C atmosphere, the compressed state is released, and the foam thickness recovery behavior (thickness change, thickness recovery) is shot with a high-speed camera (high-speed camera). The thickness of the foam after 5 seconds was determined. And the recovery rate was calculated | required from the following formula. The evaluation results are shown in the column of “Thickness recovery rate” in Table 1.
Thickness recovery rate (%) = (thickness 0.5 seconds after releasing the compressed state) / (initial thickness) × 100

(Repulsive force at 50% compression (Repulsive load at 50% compression, 50% compression load))
It measured according to the compression hardness measuring method described in JIS K 6767.
The foam was cut into a width of 30 mm and a length of 30 mm to obtain a sheet-like test piece. Next, when the test piece was compressed at a compression rate of 10 mm / min in the thickness direction until the compression rate became 50%, the stress (N) was converted per unit area (1 cm ² ) and the repulsive force ( N / cm ² ). The evaluation results are shown in the column of “50% compression load” in Table 1.

(Shock absorption test)
An impact absorption test was performed using the above-described pendulum type impact tester (impact test apparatus) (see FIGS. 1 and 2). For the foamed sheets (sample size: 20 mm × 20 mm) obtained in the examples and comparative examples, an impact test was performed by colliding a continuous iron ball 5 times at intervals of 1 second under a condition in which a 66 g iron ball was tilted by 40 °. The impact force (N) at each collision was measured. The evaluation results are shown in the column of “Shock absorption test” in Table 1.
Further, the impact force (N) at the time of each collision is plotted at five points with the number of impacts as the x-axis and the impact force (N) as the y-axis, and a linear approximation straight line obtained by the least square method is obtained from the five points. The inclination was obtained. The evaluation results are shown in the column of “Slope of repeated impact force” in Table 1.

As shown in Table 1, in the foamed sheets of the examples, the average cell diameter is 10 to 200 μm, the repulsive force when the thickness is compressed by 50% is 6.0 N / cm ² or less, and the thickness after 0.5 seconds. The recovery rate was 90% or more, indicating high shock absorption, and at the time of the fifth collision, the same level of shock absorption as in the first collision was exhibited. On the other hand, in the foamed sheets of Comparative Examples 1 and 2, the thickness recovery rate after 0.5 seconds is not 90% or more, and the shock absorption is larger at the time of the fifth collision than at the time of the first collision. It was falling.

Reference example 1
Block copolymer of polybutylene terephthalate as a hard segment and polyether as a soft segment (trade name “Perprene P-90BD”, manufactured by Toyobo Co., Ltd., 230 ° C. melt flow rate: 3.0 g / 10 min, melting point : 204 ° C.): 100 parts by weight, acrylic lubricant (trade name “Metablene L-1000”, manufactured by Mitsubishi Rayon Co., Ltd.): 5 parts by weight, hard clay that has been surface-treated with a silane coupling agent (trade name) “ST-301”, manufactured by Shiraishi Calcium Co., Ltd .: 1 part by weight, carbon black (trade name “Asahi # 35”, manufactured by Asahi Carbon Co., Ltd.): 5 parts by weight and an epoxy modifier (epoxy-modified acrylic) Polymer, weight average molecular weight (Mw): 50000, epoxy equivalent: 1200 g / eq, viscosity: 2850 mPa · s): 2 The parts by weight were kneaded at a temperature of 220 ° C. with a twin-screw kneader, extruded into a strand, cooled with water, cut into a pellet, and molded. The pellets were put into a single screw extruder, and carbon dioxide gas was injected at a pressure of 17 (13 after injection) MPa in an atmosphere of 240 ° C. After sufficiently saturating the carbon dioxide gas, it was cooled to a temperature suitable for foaming and extruded from a die to obtain a sheet-like polyester elastomer foam having a thickness of 2.0 mm. The obtained foam was sliced and adjusted to a thickness of 0.2 mm.

(Thickness recovery rate at high temperature)
The foam obtained in Example 1 and Reference Example 1 was cut into a width of 30 mm and a length of 30 mm to obtain a sheet-like test piece. The thickness of this test piece was accurately measured and designated as thickness a. Next, using a jig, the test piece is made of two compression plates (aluminum plates) with a spacer (the thickness of the spacer) from the both sides of the test piece in the thickness direction so that the thickness is 50% of the initial thickness. c) (ie 50% compression state), and this compression state was maintained and stored for 22 hours under conditions of 50% humidity and 80 ° C. After 22 hours, it was stored in an atmosphere at 23 ° C. for 2 hours, after which the test piece was uncompressed and left for 24 hours. After standing, the thickness of the test piece was measured accurately and set as thickness b.
From the thickness a, the thickness b, and the thickness c, the thickness recovery rate (%) at a high temperature was calculated from the following formula.
Thickness recovery rate at high temperature (%) = (1− (thickness a−thickness b) / (thickness a−thickness c)) × 100
The thickness a and the thickness b were measured in an environment where the temperature was 23 ± 2 ° C. and the relative humidity was 50 ± 5%. The thickness recovery rate at high temperature of the foam obtained in Example 1 was 96%, and the thickness recovery rate at high temperature of the foam obtained in Reference Example 1 was 60%.

1 Pendulum type impact tester (impact tester)
2 Test piece (foamed sheet)
DESCRIPTION OF SYMBOLS 3 Holding member 4 Impact load member 5 Pressure sensor 11 Fixing jig 12 Holding jig 16 Pressure adjusting means 20 Support | pillar 21 Arm 22 End of support rod (shaft) 23 Support rod (shaft)
24 Impactor 25 Electromagnet 28 Support plate a Swing angle

Claims (17)

Storage modulus and loss at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement when the average cell diameter is 10 to 200 μm, the repulsive force when compressing the thickness by 50% is 6.0 N / cm ² or less Loss tangent (tan δ), which is a ratio of elastic modulus, has a peak top in a range of −60 ° C. or more and 20 ° C. or less, and a thickness recovery rate defined by the following formula is 90% or more. Sheet.
Thickness recovery rate (%) = (thickness 0.5 seconds after releasing the compressed state) / (initial thickness) × 100
Initial thickness: Thickness of foam sheet before applying load Thickness 0.5 seconds after releasing compression: Maintaining 120 seconds with 100 g / cm ² applied to foam sheet, releasing compression The thickness of the foam sheet 0.5 seconds after release The foam sheet according to claim 1, wherein the foam sheet has a thickness of 30 to 1000 µm and a density of 0.2 to 0.7 g / cm ³ .   In the shock absorption test using a pendulum type impact tester, when the impactor is collided five times continuously at intervals of 1 second on the support plate of the structure composed of the support plate and the foamed sheet, the first time The foam sheet according to claim 1 or 2, wherein an increase rate of impact force at the time of the fifth collision with respect to impact force at the time of collision is 5% or less.   The foam sheet according to any one of claims 1 to 3, comprising a crosslinking agent and a silicone compound.   The foamed sheet according to any one of claims 1 to 4, wherein a solvent-insoluble content with respect to methyl ethyl ketone is 80% by weight or more.   The foamed sheet according to any one of claims 1 to 5, wherein a maximum value of loss tangent (tan δ) within a range of -60 ° C to 20 ° C is 0.2 or more. The foam sheet according to any one of claims 1 to 6, wherein a thickness recovery rate at a high temperature defined below is 50% or more.
Thickness recovery rate at high temperature: The foamed sheet was compressed in the thickness direction so as to have a thickness of 50% of the initial thickness in an 80 ° C atmosphere, and after 22 hours, it was left in a 23 ° C atmosphere for 2 hours. Then, the compressed state is released, and the ratio of the thickness to the initial thickness after 24 hours from the release of the compressed state   The foam sheet according to any one of claims 1 to 7, wherein an acrylic polymer is used as the resin material. The foamed sheet according to any one of claims 1 to 8, wherein the shear adhesive force (23 ° C, tensile speed 50 mm / min) to the SUS304BA plate on at least one surface is 0.5 N / 100 mm ² or more.   The foam sheet according to any one of claims 1 to 9, which is a mechanical foam of an emulsion resin composition.   The foam sheet according to any one of claims 1 to 10, which has an adhesive layer on one side or both sides.   The foam sheet according to any one of claims 1 to 11, which is used as an impact absorbing sheet for electrical and electronic equipment.   The foam sheet of any one of Claims 1-12 used for a touch panel mounting apparatus.   An electrical and electronic device having the foam sheet according to claim 1.   The electric and electronic device according to claim 14, further comprising a display member, wherein the foam sheet is sandwiched between a housing of the electric and electronic device and the display member.   A touch-panel-equipped device having the foam sheet according to claim 13.   The touch panel mounting apparatus according to claim 16, comprising the foam sheet, a display panel, and a touch panel, wherein the foam sheet is disposed in a space on the back side of the display panel.

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