KR101500468B1 - Foamed sheet - Google Patents

Abstract

The present invention provides a foam sheet exhibiting excellent impact absorbability even when the thickness is very small.
The foam sheet of the present invention has a thickness of 30 to 500 占 퐉, a density of 0.2 g / cm3 to 0.4 g / cm3, a loss of a ratio of a storage elastic modulus to a loss elastic modulus at an angular frequency of 1 rad / And a foam having a tangent (tan delta) in the range of -30 DEG C to 30 DEG C inclusive. The average cell diameter of the foam is, for example, 10 m to 150 m. It is preferable that the maximum value of the loss tangent (tan?) Of the foam in the range of -30 占 폚 to 30 占 폚 is 0.2 or more.

Description

Foam sheet {FOAMED SHEET}

The present invention relates to a foam sheet excellent in impact absorbability even when the thickness is small, and an electric / electronic device using the foam sheet.

Description of the Related Art Conventionally, image display members fixed to image display devices such as liquid crystal displays, electroluminescence displays and plasma displays, display members mounted on so-called "mobile phones", "smart phones" and "portable information terminals" BACKGROUND ART A foaming material is used to fix an optical member such as a lens to a predetermined site (e.g., a case). As such a foaming material, a microcellular urethane foam or a low foaming foam having a low foaming property and a closed cell structure is extrusion-molded, and a polyethylene foam having an independent foam and a foaming magnification of about 30 is used. Specifically, for example, a gasket made of a polyurethane foam having a density of 0.3 g / cm 3 to 0.5 g / cm 3 (see Patent Document 1) or a foam structure having an average cell diameter of 1 탆 to 500 탆 A sealing material (see Patent Document 2) and the like are used.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-100216 Patent Document 2: JP-A-2002-309198

However, in recent years, as a product to which an optical member (an image display device, a camera, a lens, or the like) is mounted becomes thinner and thinner, the clearance of the portion where the foam member is used tends to be remarkably reduced. As the clearance is reduced, it is necessary to reduce the thickness of the foam member. However, in the conventional foam member, if the thickness is reduced, sufficient shock absorbability is not exhibited. For this reason, there is a demand for a foam sheet that absorbs shocks when colliding with an electric or electronic device having a display member such as a " smart phone "

In addition, as electronic devices such as a personal computer (PC), a tablet PC, a personal digital assistant (PDA), and a mobile phone become more sophisticated, a shock absorbing sheet used for preventing breakage of a display member, , And a heat conductive layer) are laminated and assembled. It is desired to further thin a member such as an impact-absorbing sheet used in the above-mentioned electronic apparatus in accordance with the further thinning of the above-described electronic apparatus, so that the thickness of the pressure-sensitive adhesive layer at the time of laminating the above- Is desired.

In addition, in recent years, with the spread of devices equipped with touch panels such as smart phones and portable terminals, opportunities for users to touch or press the screen using a jig (a stylus) such as a finger or a touch pen are increasing. In addition, these touch panel-mounted devices are progressively thinned, and members making up these devices (for example, a display panel typified by an LCD panel or a touch panel touching the touch panel) are becoming thinner. Therefore, when the user presses the screen, the display panel or the touch panel becomes very flexible. When warping occurs, the display panel interferes with other members (for example, a circuit board, a battery, and the like) in accordance with the warping, and display unevenness (wavy form of a ripple) may occur on the display panel. As a cause of occurrence of display unevenness, it is considered that the orientation of the liquid crystal molecules is disturbed by stressing the display panel by the display panel being pressed by other members inside.

A gap is provided in the periphery of the display panel in order to solve the problem of display unevenness (a blurred form of a ripple) which may be caused by stress in the display panel, and even if the display panel is deformed, It has been proposed that the design of the display panel or the touch panel is changed so as to make it harder to be bent by increasing the thickness and the rigidity of the case of the touch panel mounted device is increased to make it difficult to be deformed. However, there is a problem that a device with a touch panel becomes thick and becomes heavy. For this reason, in touch panel-mounted devices, it is required to solve the problem of display unevenness (blurred form of a ripple type) in which stress is caused in such a situation on the display panel in correspondence with the remarkably progressive thinning .

Accordingly, an object of the present invention is to provide a foam sheet exhibiting excellent impact absorbability even when the thickness is very small.

Another object of the present invention is to provide a foam sheet which, in addition to the above properties, is capable of preventing positional deviation even when other members are laminated without having a pressure-sensitive adhesive layer.

It is another object of the present invention to provide an electric / electronic device which is less susceptible to breakage due to an impact at the time of dropping, even if the device is downsized and thinned.

It is still another object of the present invention to provide a display device capable of highly suppressing the occurrence of display unevenness in a display portion according to a user's touch operation when used in a touch panel- Sheet.

Another object of the present invention is to provide a touch panel mounted device which is less likely to be damaged by an impact upon dropping, and in which occurrence of display irregularities in a display portion due to a user's touch operation is highly suppressed.

The inventors of the present invention have made intensive investigations to achieve the above object, and as a result, they have found that the loss tangent (tan?), Which is the ratio of the storage elastic modulus to the loss elastic modulus at an oscillating speed of 1 rad / s in the dynamic viscoelasticity measurement, ° C or less, a foamed sheet having a peak top in the range of 30 to 500 ° C is remarkably superior in impact absorbability even when the thickness is in the range of 30 to 500 占 퐉. Therefore, in an electric / electronic appliance using such a foamed sheet, Even if the touch panel mounted device is thin, it is difficult to damage the display device due to impact or the like, and even if the impact is low, the impact absorption rate is high. Therefore, It is possible to highly suppress the occurrence of display unevenness in the display section according to the touch operation, It was.

That is, the present invention relates to a method for measuring dynamic viscoelasticity, which has a thickness of 30 탆 to 500 탆, a density of 0.2 g / cm 3 to 0.4 g / cm 3, a loss tangent of a ratio of a storage elastic modulus to a loss elastic modulus at an oscillating speed of 1 rad / (tan?) of from -30 占 폚 to 30 占 폚 and having a peak top in the range of -30 占 폚 to 30 占 폚.

In the foam sheet, it is preferable that the average cell diameter of the foam is 10 mu m to 150 mu m. It is also preferable that the maximum value of the loss tangent (tan?) Of the foam in the range of -30 占 폚 to 30 占 폚 is 0.2 or more.

It is also preferable that the initial modulus of elasticity of the foam in a tensile test at a tensile rate of 300 mm / min under an environment of 23 캜 is 5 N / mm 2 or less.

In the impact absorbability test using the pendulum type impact tester, the value (R) obtained by dividing the impact absorption rate (%) defined by the following formula by the thickness (占 퐉) of the foam sheet was 28 g, °, it is preferably at least 0.15.

Impact absorption rate (%) = {(F ₀ -F ₁ ) / F ₀ } × 100

Wherein, F ₀ is the impact force of collision when sikyeoteul cut impact only the supporting plate, the impact force F ₁ is the time of the collision sikyeoteul cut impact on the support plate of the structure formed of a support plate and a foam sheet.

The shear adhesive strength (23 DEG C, tensile speed 50 mm / min) of at least one surface of the foam to the SUS304BA plate is preferably 0.5 N / 100 mm < 2 >

The foam may be formed of at least one resin material selected from the group consisting of an acryl-based polymer, a rubber, a urethane-based polymer, and an ethylene-vinyl acetate copolymer.

The foam may be formed through a step (A) of mechanically foaming the emulsion resin composition. The foam may be formed by further adding a step (B) of coating a mechanically foamed emulsion resin composition onto a base material and drying the base material. The step (B) comprises a preliminary drying step (B1) of drying the bubble-containing emulsion resin composition coated on the substrate at a temperature of not lower than 50 ° C and lower than 125 ° C, (B2).

The foam sheet may have a pressure-sensitive adhesive layer on one side or both sides of the foam.

The foam sheet may be used as an impact-absorbing sheet for electric or electronic devices. The foam sheet may be a foam sheet used in a touch panel-mounted device.

The present invention also provides an electric / electronic device in which the foam sheet is used. The electric / electronic apparatus includes an electric / electronic apparatus having a display member, wherein the foam sheet has a structure sandwiched between a case of the electric or electronic apparatus and the display member.

The present invention also provides a touch panel mounted device using the foam sheet. In this touch panel mounted device, the foam sheet may have the foam sheet, the display panel, and the touch panel, and the foam sheet may be disposed in the space on the back side of the display panel.

The foam sheet of the present invention has a low density and has a loss tangent (tan delta), which is a ratio of a storage elastic modulus and a loss elastic modulus at an oscillating frequency of 1 rad / s, in a dynamic viscoelasticity measurement of -30 ° C to 30 ° C. It is excellent in impact absorbability even if the thickness is thin. Further, when the shear adhesive force of at least one surface of the foamed body with respect to the SUS304BA plate is 0.5 N / 100 mm2 or more, positional shift can be prevented even when other members (e.g., thermoelectric layers, etc.) . Therefore, even if the electric / electronic apparatus using the foam sheet of the present invention falls on the ground, it is possible to prevent breakage of display due to impact.

Further, since the foam sheet of the present invention has a low compression load, even when the display panel or the touch panel is bent or deformed by a user's touch operation when used in a touch panel-mounted device, It can be dispersed and absorbed effectively. Therefore, the foam sheet of the present invention can highly suppress the occurrence of uneven display (blurred form of a ripple form) in a display portion where a stress is generated in such a display panel. Therefore, the foam sheet of the present invention can be suitably used for a touch panel mounted device.

1 is a schematic configuration diagram of a pendulum impact tester (impact test apparatus).
2 is a view showing a schematic configuration of a holding member of a pendulum impact tester (impact testing apparatus).
3 is a schematic top view of the stress relaxation tester.
4 is a schematic cross-sectional view of the stress relaxation tester.
5 is a pressure image of a pressure acting on a pressure-sensitive paper in the confirmation test of occurrence of display unevenness in Example 1. Fig.
6 is a pressure image of a pressure acting on a decompression paper in the confirmation test of occurrence of display unevenness in the second embodiment.
7 is a pressure image of a pressure acting on a pressure-sensitive paper in the confirmation test of occurrence of display unevenness in the third embodiment.
8 is a pressure image of a pressure acting on a pressure-sensitive paper in the confirmation test of occurrence of display unevenness in Example 4. Fig.
9 is a pressure image of a pressure acting on a pressure-sensitive paper in the confirmation test of occurrence of display unevenness in the fifth embodiment.
10 is a pressure image of a pressure acting on a decompression paper in the confirmation test of occurrence of display unevenness in Comparative Example 1. Fig.
11 is a pressure image of a pressure acting on a pressure-sensitive paper in the confirmation test of occurrence of display unevenness in Comparative Example 3. Fig.

The foam sheet of the present invention has a thickness of 30 to 500 占 퐉, a density of 0.2 g / cm3 to 0.4 g / cm3, a dynamic viscoelasticity loss of 1 loss / And a foam having a tangent (tan delta) in the range of -30 DEG C to 30 DEG C inclusive. Therefore, it has a desired shock absorbing property. In the present specification, the density of the foam means " apparent density ".

The thickness of the foam sheet of the present invention is 30 mu m to 500 mu m. The lower limit thereof is preferably 40 占 퐉, more preferably 50 占 퐉, and the upper limit is preferably 400 占 퐉, more preferably 300 占 퐉, still more preferably 200 占 퐉. In the present invention, since the thickness of the foam sheet is 30 占 퐉 or more, bubbles can be uniformly contained, and excellent shock absorbing properties can be exhibited. Further, since the thickness of the foam sheet is 500 mu m or less, it is possible to easily follow a minute clearance. The foam sheet of the present invention is excellent in shock absorption property despite its thickness being as thin as 30 탆 to 500 탆.

The density of the foam constituting the foam sheet of the present invention is 0.2 g / cm 3 to 0.4 g / cm 3. The lower limit thereof is preferably 0.21 g / cm3, more preferably 0.22 g / cm3, and the upper limit is preferably 0.39 g / cm3, more preferably 0.38 g / cm3, still more preferably 0.35 g / cm3 . The strength of the foam can be maintained by the density of 0.2 g / cm 3 or more, and it is 0.4 g / cm 3 or less, thereby exhibiting a high shock absorbing property. Further, when the density of the foam is in the range of 0.2 g / cm 3 to 0.4 g / cm 3, a further higher shock absorbing property is exhibited.

The average cell diameter of the foam is, for example, 10 m to 150 m. The lower limit thereof is preferably 15 占 퐉, more preferably 20 占 퐉, and the upper limit is preferably 140 占 퐉, more preferably 130 占 퐉, still more preferably 100 占 퐉. When the average cell diameter is 10 占 퐉 or more, a better shock absorbing property is exhibited. Further, when the average cell diameter is 100 占 퐉 or less, the compression recovery property is also excellent. The maximum cell diameter of the foam is, for example, 40 to 400 占 퐉, the lower limit thereof is preferably 60 占 퐉, more preferably 80 占 퐉, the upper limit is preferably 300 占 퐉, more preferably 220 Mu m. The minimum cell diameter of the foam is, for example, 5 mu m to 70 mu m, and the lower limit thereof is preferably 8 mu m, more preferably 10 mu m, and the upper limit is preferably 60 mu m, more preferably 50 mu m Mu m.

In the present invention, the ratio (former / latter) of the average cell diameter (占 퐉) to the thickness (占 퐉) of the foam sheet is preferably in the range of 0.2 to 0.9 from the viewpoint of impact absorbability. The lower limit of the ratio of the average cell diameter (占 퐉) to the thickness (占 퐉) of the foam sheet is preferably 0.25, more preferably 0.3, and the upper limit is preferably 0.85, more preferably 0.8.

In the dynamic viscoelasticity measurement of the foam, the peak top of the loss tangent (tan delta), which is the ratio of the storage elastic modulus to the loss elastic modulus at an oscillating speed of 1 rad / s, is in the range of -30 캜 to 30 캜. The lower limit of the temperature range in which the peak of the loss tangent is present is preferably -25 캜, more preferably -20 캜, still more preferably -10 캜, and the upper limit is preferably 20 캜, more preferably Lt; / RTI > In the case of a material having two or more peak tow of loss tangent, it is preferable that at least one of these materials falls within the above range. When the peak temperature is -30 DEG C or higher, excellent compression recoverability is exhibited. Further, when the peak temperature is 30 占 폚 or less, high flexibility is exhibited and excellent shock absorbing property is exhibited.

The peak top strength (maximum value) of the loss tangent (tan?) In the range of -30 占 폚 to 30 占 폚 is preferably higher, for example, 0.2 or more, and more preferably 0.3 or more from the viewpoint of impact absorbability. The upper limit value of the peak top strength (maximum value) is, for example, 2.0.

Thus, the peak temperature and the peak strength of the loss tangent tan? Contribute significantly to the impact absorbability of the foam. When the peak top of the loss tangent (tan delta), which is the ratio of the storage elastic modulus at a vibration of 1 rad / s to the loss elastic modulus, is in the range of -30 DEG C to 30 DEG C in the dynamic viscoelasticity measurement of the foam, The reason for the increase is presumably due to the fact that there is a peak of the loss tangent tan? That is, since the range of the loss tangent (tan?) Of -30 占 폚 to 30 占 폚 is converted into the frequency range corresponding to the drop impact of the structure from the temperature time conversion rule in the viscoelasticity measurement, It is presumed that the foam sheet having the peak tangent of loss tangent (tan?) In the range of 30 占 폚 or less has higher shock absorbability. The storage elastic modulus is a repulsive force against the impact energy applied to the foam sheet, and if the storage elastic modulus is high, the shock is repelled as it is. On the other hand, the loss elastic modulus is a physical property that changes the impact energy applied to the foam sheet to heat. The higher the loss elastic modulus is, the more shock energy is absorbed to change the impact energy into heat. From this, it is presumed that the shock absorption rate is higher for a foam sheet having a large loss tangent (tan delta), which is a ratio of the storage elastic modulus to the loss elastic modulus, and which has a large impact force and a small repulsive force.

The initial elastic modulus of the foam is preferably low in view of shock absorption. The initial elastic modulus (value calculated from the slope at 10% strain in a tensile test at a tensile rate of 300 mm / min under a 23 캜 environment) is preferably 5 N / mm 2 or less, more preferably 3 N / mm2, more preferably not more than 1 N / mm2. The lower limit value of the initial modulus of elasticity is, for example, 0.1 N / mm < 2 >.

With respect to the foam constituting the foam sheet of the present invention, the composition and the cell structure are not particularly limited as long as they have the above properties. The bubble structure may be any of an open cell structure, a closed cell structure, and a semi-continuous cell structure. From the standpoint of shock absorption, an open cell structure or a semi-continuous, semi-open cell structure is preferable.

The foam sheet of the present invention has excellent impact absorbability while being thin. In addition, it has a high shock absorbing property against a very weak impact, and exhibits excellent shock absorbing property irrespective of the magnitude of impact. For example, in the impact absorbability test using a pendulum impact tester, the impact absorption rate (R) per unit thickness is obtained by dividing the shock absorption rate (%) defined by the following formula by the thickness (mu m) of the foam sheet.

Impact absorption rate (%) = {(F ₀ -F ₁ ) / F ₀ } × 100

Wherein, F ₀ is the impact force of collision when sikyeoteul cut impact only the supporting plate, the impact force F ₁ is the time of the collision sikyeoteul cut impact on the support plate of the structure formed of a support plate and a foam sheet.

The weight of the impactor is 28 g, the swing-up angle is 30 ° (hereinafter sometimes referred to as "low impact condition (a)"), R1 is the impactor weight, 28 g is the swing- (Hereinafter, sometimes referred to as " low impact condition (b) ") in the case where R is R2, the weight of the impactor is 96 g, and the swing- In the foamed sheet of the present invention, R1 is, for example, at least 0.15, R2 is at least 0.15, and R3 is at least 0.10, for example. The upper limit value of R (R1, R2, R3) is, for example, about 0.5.

The impact absorption rate varies depending on the thickness of the foamed sheet, but is usually from 5% to 80%, preferably 7%, and preferably 60%. The impact absorption rate (%) in the case of the high impact condition is preferably 14% or more, and more preferably 15% or more. The impact absorption rate (%) in the case of the low impact condition (a) is preferably 18% or more, and more preferably 25% or more.

Further, in the present invention, as described above, it has an excellent shock absorbing property irrespective of the magnitude of the impact. For example, in the foam sheet of the present invention, the sum (R1 + R3) of R1 and R3 is usually 0.25 or more (e.g., 0.25 to 1.0), preferably 0.28 or more (e.g., 0.28 to 1.0) The ratio of R1 to R3 (R1 / R3) is usually in the range of 0.5 to 3.0, preferably 0.8 to 2.8. In the foam sheet of the present invention, the difference (R1-R3) between R1 and R3 is usually within ± 0.25, preferably within ± 0.21. The sum of R1 and R2 (R1 + R2) is usually 0.40 or more (e.g., 0.40 to 1.0), preferably 0.45 or more (e.g., 0.45 to 1.0) / R2) is usually in the range of 0.5 to 2.5, preferably 0.8 to 2.0.

A schematic configuration of a pendulum impact tester (impact tester) will be described with reference to Figs. 1 and 2. Fig. 1 and 2, the impact test apparatus 1 (pendulum tester 1) is provided with a holding member 3 (holding member) 3 as holding means for holding the test piece 2 (foam sheet 2) An impact load member 4 for applying an impact stress to the test piece 2 and a pressure sensor 5 as impact force detection means for detecting an impact force on the test piece 2 by the impact load member 4 Consists of. The holding member 3 for holding the test piece 2 with an arbitrary holding force is provided with a fixing jig 11 and a slide jig jig 11 for holding the test piece 2 with the test piece 2 facing the fixing jig 11 (12). The pressing jig 12 is provided with a pressing pressure adjusting means 16. The impact load member 4 that applies the impact force to the test piece 2 held by the holding member 3 is configured such that one end 22 is pivotally supported pivotally with respect to the pillar 20, A support rod 23 (shaft 23) having a shaft 24 and an arm 21 for lifting and holding the impactor 24 at a predetermined angle. Since the steel ball is used as the impactor 24, the electromagnet 25 is provided at one end of the arm so that the impactor 24 can be lifted integrally by a predetermined angle. The pressure sensor 5 for detecting the impact force acting on the test piece 2 by the impact load member 4 is provided on the opposite surface side of the surface of the fixing jig 11 which is in contact with the test piece.

The impactor 24 is a steel ball. The angle (swing-up angle a in Fig. 1) at which the impactor 24 is lifted by the arm 21 is about 30 to 47 degrees (in the embodiment, 30 degrees, 40 degrees, 47 Deg.]. The weight of the steel ball (steel ball) is about 20 g to 100 g. (2) the weight of the steel ball (steel ball) of 28 g, the swing-up angle of 40 degrees, (3) the weight of the steel ball (steel ball) Weight 96 g, and swing-up angle 47 [deg.].

2, the test piece 2 (foam sheet 2) is provided between the fixing jig 11 and the press jig 12 such as a resin plate (acrylic plate, polycarbonate plate, etc.) And is sandwiched by a support plate 28 composed of a highly elastic plate material.

The impact absorbing property is determined by the impact force F ₀ measured by colliding the impact jig 24 against the support plate 28 after the fixture jig 11 and the support plate 28 are tightly fixed to each other, The impact force F ₁ measured by inserting the test piece 2 between the jig 11 and the support plate 28 and making the impact member 24 collide against the support plate 28 after the impact member 24 is brought into tight contact with the support plate 28 is calculated, do. The impact test apparatus is the same apparatus as the first embodiment of Japanese Patent Application Laid-Open No. 2006-47277.

When the thickness of the foam sheet is large enough, the impact absorbability can be adjusted by selecting the average cell diameter, density and the like. However, when the foam sheet has a very small thickness (for example, thickness of 30 탆 to 500 탆) The impact can not be sufficiently absorbed. When the thickness of the foam sheet is very thin, the foam in the foam is directly crushed by the impact, and the shock buffer function by the foam is lost. In the present invention, as described above, in the dynamic viscoelasticity measurement of the foam, the peak top of the loss tangent (tan?), Which is the ratio of the storage modulus and the loss modulus at an oscillation frequency of 1 rad / s, The constituent material of the foam exhibits a function of buffering the impact even after the bubble is crushed.

The foam may be composed of a resin composition containing a resin material (polymer). Further, in the dynamic viscoelasticity measurement of the resin composition in the unfoamed state (the resin composition (solid matter) in the case of not foaming), the peak top of the loss tangent (tan delta), which is the ratio of the storage elastic modulus to the loss elastic modulus at an angular frequency of 1 rad / Is preferably in the range of -30 占 폚 to 30 占 폚. The lower limit of the temperature range in which the peak of the loss tangent is present is preferably -25 캜, more preferably -20 캜, still more preferably -10 캜, and the upper limit is preferably 20 캜, more preferably Lt; / RTI > In the case of a material having two or more peak tow of loss tangent, it is preferable that at least one of these materials falls within the above range. The peak top strength of the loss tangent (tan?) Of the resin composition (solid matter) in the range of -30 占 폚 to 30 占 폚 (the value is a loss in the range of -30 占 폚 to 30 占 폚 (Corresponding to a value obtained by dividing the peak top strength of tangent (tan delta) by the density (g / cm < 3 >) of the foamed material) is preferably high in view of impact absorbability. For example, the peak top strength of loss tangent (tan?) Of the resin composition (solid matter) in the range of -30 占 폚 to 30 占 폚 is preferably 0.9 (g / cm3) ^-1 or more, 3.

The initial elastic modulus (23 DEG C, tensile speed 300 mm / min) of the resin composition (solid matter) in an unfoamed state is preferably low, preferably 50 N / mm2 or less, more preferably 30 N / Mm2 or less. 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 may be used. Examples of the resin material include an acrylic polymer, a rubber, a urethane polymer, and an ethylene-vinyl acetate copolymer. Of these, acrylic polymer, rubber, and urethane polymer are preferable from the standpoint of impact absorbability. The resin material (polymer) constituting the foam may be one kind alone, or two or more kinds.

In order to set the peak top of the loss tangent (tan?), Which is the ratio of the storage elastic modulus and the loss elastic modulus at an angular frequency of 1 rad / s, to the range of -30 占 폚 to 30 占 폚 in the dynamic viscoelasticity measurement of the foam, (Polymer) can be used as an indicator or reference. For example, the resin material (polymer) preferably has a Tg of -50 DEG C to less than 50 DEG C (the lower limit is preferably -40 DEG C, more preferably -30 DEG C, and the upper limit is preferably 40 DEG C, Lt; RTI ID = 0.0 > 30 C). ≪ / RTI >

The acrylic polymer is preferably an acrylic polymer formed from a monomer having a Tg of -10 DEG C or higher and a monomer having a Tg of the homopolymer of lower than -10 DEG C as essential monomer components. By adjusting the ratio of the former monomer to the latter monomer by using such an acrylic polymer, the peak top of the loss tangent (tan delta), 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, A foam having a temperature of 30 DEG C or more and 30 DEG C or less can be relatively easily obtained.

The term "glass transition temperature (Tg) when a homopolymer is formed" (simply referred to as "Tg of a homopolymer") in the present invention refers to "glass transition temperature (Tg ). Specifically, the numerical values are given in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc, 1987). The Tg of a homopolymer of a monomer not described in the above literature refers to a value obtained according to the following measuring method (see Japanese Patent Laid-Open No. 2007-51271). That is, 100 parts by weight of a monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile and 200 parts by weight of ethyl acetate as a polymerization solvent were fed into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube and a reflux condenser, And stirring is carried out for 1 hour while introducing nitrogen gas. After the oxygen in the polymerization system was removed in this manner, the temperature was raised to 63 캜 and the reaction was carried out for 10 hours. Subsequently, the solution is cooled to room temperature to obtain a homopolymer solution having a solid concentration of 33% by weight. Subsequently, this homopolymer solution is applied on a separator in a pourable manner and dried to produce a test sample (homopolymer of sheet form) having a thickness of about 2 mm. The test samples were punched into a disk having a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to shear strain at a frequency of 1 Hz using a viscoelasticity tester (ARES, Rheometrics) The viscoelasticity is measured by a shearing mode at a temperature raising rate of ~150 ° C and 5 ° C / min, and the peak temperature of tan δ is defined as the Tg of the homopolymer. The Tg of the resin material (polymer) can also be measured according to this method.

In the case of a monomer having a Tg of the homopolymer of -10 占 폚 or higher, the Tg is, for example, -10 占 폚 to 250 占 폚, preferably 10 占 폚 to 230 占 폚, and more preferably 50 占 폚 to 200 占 폚.

As the monomer having a Tg of -10 캜 or more of the homopolymer, for example, (meth) acrylonitrile; Amide group-containing monomers such as (meth) acrylamide and N-hydroxyethyl (meth) acrylamide; (Meth) acrylic acid; (Meth) acrylic acid alkyl ester having a Tg of -10 占 폚 or more of a homopolymer such as methyl methacrylate or ethyl methacrylate; Isobornyl (meth) acrylate; Vinyl monomers containing heterocyclic rings such as N-vinyl-2-pyrrolidone; And hydroxyl group-containing monomers such as 2-hydroxyethyl methacrylate. These may be used alone or in combination of two or more. Among them, (meth) acrylonitrile (particularly, acrylonitrile) is particularly preferable. When (meth) acrylonitrile (particularly acrylonitrile) is used as a monomer having a Tg of -10 ° C or higher of the homopolymer, it is possible to suppress the peak top strength of the loss tangent (tan?) Of the foam to a large value can do.

For a monomer having a Tg of the homopolymer of lower than -10 占 폚, the Tg is, for example, from -70 占 폚 to less than -10 占 폚, preferably from -70 占 폚 to -12 占 폚, more preferably from -65 占 폚 to -15 占 폚 to be.

Examples of the monomer having a Tg of the homopolymer of less than -10 占 폚 include (meth) acrylic acid alkyl ester having a Tg of less than -10 占 폚 of a homopolymer such as ethyl acrylate, butyl acrylate or 2-ethylhexyl acrylate. These may be used alone or in combination of two or more. Of these, C _2-8 alkyl acrylate esters are particularly preferred.

The content of the monomer having a Tg of the homopolymer of -10 ° C or higher relative to the total monomer component (total amount of the monomer components) forming the acrylic polymer is, for example, 2% by weight to 30% 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 캜 with respect to the total monomer component (total amount of the monomer components) forming the acrylic polymer is, for example, 70% by weight to 98% by weight, 75% by weight, more preferably 80% by weight, and the upper limit is preferably 97% by weight, more preferably 96% by weight.

As the rubber, any of natural rubber and synthetic rubber may be used. As the rubber, for example, a rubber such as nitrile rubber (NBR), methyl methacrylate-butadiene rubber (MBR), styrene-butadiene rubber (SBR), acrylic rubber (ACM, ANM), urethane rubber . Of these, nitrile rubber (NBR), methyl methacrylate-butadiene rubber (MBR), and silicone rubber are preferred.

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

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

The foam constituting the foam sheet may contain, in addition to the resin material (polymer), a surfactant, a crosslinking agent, a thickening agent, a rust inhibitor and other additives, if necessary.

For example, for the purpose of miniaturizing the bubble diameter and stabilizing the foamed bubble, any surfactant may be contained. The surfactant is not particularly limited and any of anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants and the like may be used. From the viewpoints of miniaturization of the cell diameter and stability of foamed cells, , An anionic surfactant is preferable, and a fatty acid ammonium surfactant such as ammonium stearate is more preferable. The surfactants may be used alone or in combination of two or more. In addition, a heterogeneous surfactant may be used in combination. For example, an anionic surfactant, a nonionic surfactant, an anionic surfactant, and an amphoteric surfactant may be used in combination.

The addition amount of the surfactant (solid content (nonvolatile content)) is, for example, 0 to 10 parts by weight based on 100 parts by weight of the resin material (polymer (solid content (nonvolatile component)), the lower limit is preferably 0.5 part by weight, Is preferably 8 parts by weight.

In order to improve the strength, heat resistance and moisture resistance of the foam, any cross-linking agent may be included. The crosslinking agent is not particularly limited, and any of the usability and water solubility may be used. Examples of the cross-linking agent include epoxy-based, oxazoline-based, isocyanate-based, carbodiimide-based, melamine-based and metal oxide based ones. Among them, an oxazoline crosslinking agent is preferable.

The addition amount of the crosslinking agent (solid content (nonvolatile content)) is, for example, 0 to 10 parts by weight based on 100 parts by weight of the resin material (polymer (solid content (nonvolatile content)), the lower limit is preferably 0.01 part by weight, Preferably 9 parts by weight.

In order to improve the stability of the foamed foam and the film formability, any thickener may be contained. The thickening agent is not particularly limited, and examples thereof include acrylic acid type, urethane type, polyvinyl alcohol type and the like. Of these, a polyacrylic acid-based thickener and a urethane-based thickener are preferred.

The addition amount of the thickener (solid content (nonvolatile content)) is, for example, 0 to 10 parts by weight, preferably 0.1 part by weight, and preferably 0.1 part by weight, based on 100 parts by weight of the resin material (polymer) Preferably 5 parts by weight.

In order to prevent corrosion of the metal member adjacent to the foam sheet, an optional rust inhibitor may be contained. As the rust preventive, azole ring-containing compounds are preferred. When the azole ring-containing compound is used, both the corrosion inhibition against metal and the adhesion to the adherend can be achieved at a high level.

The azole ring-containing compound may be a compound having a five-membered ring containing one or more nitrogen atoms in the ring, and examples thereof include a diazole (imidazole, pyrazole) ring, a triazole ring, a tetrazole ring, An isoxazole ring, a thiazole ring, or a compound having an isothiazole ring. These rings may be condensed with an aromatic ring such as a benzene ring to form a condensed ring. As the compound having such a condensed ring, for example, a compound having a benzoimidazole ring, a benzopyrazole ring, a benzotriazole ring, a benzoxazole ring, a benzoisoxazole ring, a benzothiazole ring, or a benzoisothiazole ring .

The azole ring, the condensed ring (benzotriazole ring, benzothiazole ring, etc.) may each 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; An alkoxy group having 1 to 12 carbon atoms (preferably 1 to 3 carbon atoms) such as a methoxy group, an ethoxy group, an isopropyloxy group and a butoxy group; An aryl group having 6 to 10 carbon atoms such as a phenyl group, a tolyl group and a naphthyl group; An amino group; A (mono or di) C _1-10 alkylamino group such as methylamino group, dimethylamino group and the like; An amino-C _1-6 alkyl group such as an aminomethyl group and a 2-aminoethyl group; Mono- or di (C _1-10 alkyl) amino-C _1-6 alkyl group such as N, N-diethylaminomethyl group and N, N-bis (2-ethylhexyl) aminomethyl group; A mercapto group; An alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; A carboxyl group; A carboxy-C _1-6 alkyl group such as a carboxymethyl group; A carboxy-C _1-6 alkylthio group such as a 2-carboxyethylthio group; N, N-bis (hydroxy-C _1-4 alkyl) amino-C _1-4 alkyl group such as N, N-bis (hydroxymethyl) 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 standpoint of rust-inhibiting action against metals, compounds in which an azole ring forms a condensation ring with an aromatic ring such as a benzene ring are preferable. Among them, a benzotriazole compound (a compound having a benzotriazole ring), a benzothiazole Compounds (compounds having a benzothiazole ring) are particularly preferred.

Examples of the benzotriazole compound include 1,2,3-benzotriazole, methylbenzotriazole, carboxybenzotriazole, carboxymethylbenzotriazole, 1- [N, N-bis (2-ethylhexyl) amino Methyl] benzotriazole, 1- [N, N-bis (2-ethylhexyl) aminomethyl] methylbenzotriazole, 2,2 '- [[ Imino] bisethanol, or a sodium salt thereof.

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

The azole ring-containing compounds may be used singly or in combination of two or more kinds.

The addition amount (solid content (nonvolatile content)) of the rust inhibitor (for example, the azole ring-containing compound) (solid component (nonvolatile component)) is not particularly limited as long as it does not impair the adhesion to the adherend or the inherent properties of the foam. For example, 0.2 parts by weight to 5 parts by weight relative to 100 parts by weight of the polymer (solid content (nonvolatile component)). The lower limit thereof is more preferably 0.3 part by weight, still more preferably 0.4 part by weight, and the upper limit thereof is more preferably 3 parts by weight, still more preferably 2 parts by weight.

In addition, any appropriate other components may be included within a range that does not impair the impact absorbability. These other components may contain only one kind or two or more kinds. Examples of the other components include a polymer component other than the above, a softener, an antioxidant, an antioxidant, a gelling agent, a curing agent, a plasticizer, a filler, a reinforcing agent, a foaming agent, a flame retardant, a light stabilizer, an ultraviolet absorber, a pH adjusting agent, a solvent (organic solvent), a thermal polymerization initiator, and a photopolymerization initiator.

Examples of the filler include inorganic fillers such as silica, clay (mica, talc, smectite, etc.), alumina, titania, zinc oxide, tin oxide, zeolite, graphite, carbon nanotubes, Metal powder (silver, copper, etc.) and the like. As the filler, it is also possible to add piezoelectric particles (titanium oxide, etc.), conductive particles, thermally conductive particles (boron nitride, etc.), organic fillers (silicon powder, etc.) and the like.

The foam sheet of the present invention can be produced by subjecting a resin composition comprising a resin material (polymer) constituting a foam to foam molding. As the foaming method (bubble formation method), a method commonly used for foam molding such as a physical method and a chemical method can be adopted. Generally, a physical method is to disperse a gas component such as air or nitrogen into a polymer solution to form bubbles by mechanical mixing. The chemical method is a method of obtaining a foam by forming a cell by gas generated by thermal decomposition of a foaming agent added to a polymer base. From the standpoint of environmental problems, physical methods are preferable. The bubbles formed in accordance with the physical method are often open-cell bubbles.

As the resin composition containing the resin material (polymer) to be subjected to foam molding, a resin solution in which a resin material is dissolved in a solvent may be used, but from the viewpoint of the foaming property, it is preferable to use an emulsion containing a resin material. As the emulsion, two or more kinds of emulsions may be blended and used.

The solid content concentration of the emulsion is preferably higher in view of the film formability. The solid content concentration of the emulsion is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more.

In the present invention, a method of producing a foam through a step (step (A)) of mechanically foaming and bubbling the emulsion resin composition is preferred. The bubbling apparatus is not particularly limited, and examples thereof include a high-speed shearing type, a vibration type, and a pressurized gas discharging type. Among these, from the viewpoint of miniaturization of the bubble diameter and production of large capacity, a high-speed shearing method is preferable.

Bubbles at the time of vaporization by mechanical stirring are those in which gas (gas) is blown 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. Above all, from the viewpoint of economy, air is preferable.

The foamed sheet of the present invention can be obtained by carrying out a process (step (B)) of coating a base-emulsion resin composition on a substrate and drying it by the above method. Examples of the base material include, but are not limited to, a plastic film (a peeled polyethylene terephthalate film and the like), a plastic film (a polyethylene terephthalate film and the like), a heat conduction layer (a heat conduction layer to be described later) . When the thermally conductive layer is coated as a base material, the adhesion between the foam layer and the thermally conductive layer can be improved, and the efficiency of the drying process at the time of manufacturing the foam layer can be improved.

As the coating method and the drying method in the step (B), a general method can be employed. The step (B) includes a preliminary drying step (B1) of drying the bubble-containing emulsion resin composition coated on the substrate at a temperature of 50 캜 or more and less than 125 캜, and a main drying step B2).

By provision of the preliminary drying step (B1) and the main drying step (B2), it is possible to prevent the coalescence of bubbles and rupture of bubbles due to a rapid temperature rise. Especially, in the foam sheet having a small thickness, the bubbles coalesce due to the rapid rise of the temperature, and the bubbles rupture. Therefore, it is significant to provide the preliminary drying step (B1). The temperature in the preliminary drying step (B1) is preferably 50 DEG C or more and 100 DEG C or less. The time of the preliminary drying step (B1) is, for example, 0.5 to 30 minutes, preferably 1 to 15 minutes. The temperature in this drying step (B2) is preferably 130 占 폚 or more and 180 占 폚 or less, and more preferably 130 占 폚 or more and 160 占 폚 or less. The time of this drying step (B2) is, for example, 0.5 to 30 minutes, preferably 1 to 15 minutes.

The average cell diameter, the maximum cell diameter and the minimum cell diameter of the foam can be adjusted by adjusting the kind and amount of the surfactant and by adjusting the stirring speed or stirring time at the time of mechanical stirring so as to obtain an average cell of 10 m to 150 m Diameter foam sheet can be obtained.

The density of the foam can be obtained by adjusting the amount of the gas (gas) component blown into the emulsion resin composition at the time of mechanical stirring to obtain a foam sheet having a density of 0.2 g / cm 3 to 0.4 g / cm 3.

The foam sheet of the present invention may have a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer) on one side or both sides of the foam. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited and may be, for example, an acrylic pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, or a silicone pressure-sensitive adhesive. When a pressure-sensitive adhesive layer is provided, a release liner for protecting the pressure-sensitive adhesive layer before use may be laminated on the surface thereof. When the foam constituting the foam sheet of the present invention has a non-sticky property, the member or the like can be fixed without providing a pressure-sensitive adhesive layer.

In the foam sheet of the present invention, the shear adhesive force (measurement conditions: 23 ° C, tensile speed 50 mm / min) of at least one surface of the foam constituting the foam sheet to the SUS304BA plate is 0.5 N / 100 mm 2 or more, When a foam sheet and another member (for example, a thermally conductive layer or the like) are laminated and used, the other member is not peeled off without providing a point-adhesive layer on the foam sheet, and the positional shift can be prevented . Further, since it is unnecessary to provide a point-adhesive layer, the thickness of the laminated body of the foam sheet and other members can be reduced, contributing to the further thinning of the electrical / electronic devices to be attached. Further, the production efficiency of the laminate can be improved, and the cost can be reduced. Examples of the layer structure of the laminate of the foam sheet of the present invention and other members (for example, a thermally conductive layer and the like) include, for example, other members / foams, other members / adhesive layer / foams, foams / other members / foams, / Pressure-sensitive adhesive layer / other member / pressure-sensitive adhesive layer / foam.

The shear adhesive strength of the foam to the SUS304BA plate can be adjusted, for example, by selecting the type of monomer constituting the resin material (polymer) constituting the foam and the composition ratio thereof. For example, as the monomer constituting the resin material (polymer such as acrylic polymer) constituting the foam, the homopolymer may have a Tg of less than -10 캜 (for example, from -70 캜 to less than -10 캜, (Total amount of monomer components) constituting the resin material (polymer such as acrylic polymer) constituting the above-described foam is set to, for example, 70 The sheath for the SUS304BA plate of the foam is selected by appropriately selecting the kind and amount of the other monomer by using the weight% to 98 wt% (lower limit, preferably 75 wt%, upper limit, preferably 97 wt% The adhesive force can be 0.5 N / 100 mm 2 or more.

The lower limit of the shear adhesive force of the foam 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 strength of the foam to the SUS304BA plate is not particularly limited, but is, for example, 100 N / 100 mm < 2 >.

The foam sheet of the present invention may be rolled into a rolled product (roll-shaped product) and distributed on the market.

The foam sheet of the present invention is excellent in impact absorbability even if it is small in thickness. Therefore, for example, in an electric / electronic device, a member for an electric / electronic device used when attaching (mounting) various members or parts (for example, optical members and the like) , And is particularly useful as an impact-absorbing sheet.

As the optical member that can be attached (attached) using the foam sheet of the present invention, for example, an image display member (particularly, a small image display member) mounted on an image display device such as a liquid crystal display, an electroluminescence display, A display device such as a touch panel mounted on a mobile communication device such as a so-called "mobile phone", a "smart phone" or a "portable information terminal", a camera or a lens (particularly, a small camera or a lens) have.

In the electric and electronic device of the present invention, the foam sheet of the present invention is used. Such electric and electronic apparatuses include, for example, electric and electronic apparatuses each having a display member, wherein the foam sheet has a structure sandwiched between the case of the electric or electronic apparatus and the display member . Examples of the electric / electronic device include mobile communication devices such as so-called "mobile phone", "smart phone", and "portable information terminal".

Further, since the foam sheet of the present invention has a very low density of 0.2 g / cm 3 to 0.4 g / cm 3 and has a low compression load, when used in a touch panel-mounted device, Even if the panel is warped and deformed, the force generated by the deformation can be effectively dispersed and absorbed. Therefore, the foam sheet of the present invention can highly suppress the occurrence of uneven display (blurred form of a ripple form) in the display portion which may be caused by stress applied to the display panel. Therefore, the foam sheet of the present invention can be suitably used for a touch panel mounted device.

The touch panel mounted device refers to a device having a display panel and equipped with a touch panel. The touch panel mounted device is not particularly limited, and examples thereof include mobile phones; Smartphone; A portable information terminal (PDA); Tablet computer; Various types of personal computers (personal computers) such as a desktop type, a notebook type, and a tablet type; Various displays (monitors) such as a plasma display, a liquid crystal display, and an electroluminescence display (organic EL display); Portable game machine; Digital audio player; An electronic book reader (electronic book reading device, electronic book dedicated terminal); Wearable computer (wearable device); Digital signage; Automatic teller machine (ATM); Automatic vending machines and vending machines used for selling tickets, various kinds of gold, drinks, food, tobacco, magazines and newspapers; TV receiver (TV); And an electronic blackboard (interactive whiteboard).

In the touch panel mounted device of the present invention, the above-described foam sheet of the present invention is used. Examples of such a touch panel mounted device include the foam sheet, the display panel, and the touch panel, and the foam sheet is disposed in the space on the back side of the display panel.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples at all. Unless otherwise stated, "% " representing the content means weight%. In addition, the number of parts (parts by weight) is a value in terms of solid content (nonvolatile matter).

Example 1

100 parts by weight of a synthetic rubber emulsion (Lactaster 1570, solid content 42.4%, NBR), 100 parts by weight of a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%) (Surfactant (A) And 0.74 parts by weight of a urethane-based thickener ("Hydran Assister T10", manufactured by DIC Corporation, solids content 25.1%) were stirred and mixed with a disperser ("Robomix" Primimix). This foamed composition was applied onto a PET film (thickness: 38 탆, trade name: MRF # 38, manufactured by Mitsubishi Chemical Company) subjected to the peeling treatment and dried at 70 캜 for 4.5 minutes and at 140 캜 for 4.5 minutes, , A density of 0.26 g / cm < 3 >, and an average cell diameter of 55 mu m.

Example 2

, 3.4 parts by weight of a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33%), 100 parts by weight of a synthetic rubber emulsion (Lactaster DM886, manufactured by DIC, solid content 48.6%, MBR) (Manufactured by DIC Corporation, solids content 25.1%) were mixed with stirring with a disperser ("Robomix", manufactured by Primix Co., Ltd.) to form a pellet. This foamed composition was applied onto a PET film (thickness: 38 탆, trade name: MRF # 38, manufactured by Mitsubishi Chemical Company) subjected to the peeling treatment and dried at 70 캜 for 4.5 minutes and at 140 캜 for 4.5 minutes, , A density of 0.28 g / cm 3, and an average cell diameter of 88 탆 (foam sheet).

Example 3

100 parts by weight of an acrylic emulsion solution (solid content: 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33% And 1.3 parts by weight of a polyacrylic acid-based thickener (20% by weight of acrylic acid-acrylic acid copolymer (acrylic acid 20% by weight) and a solid content of 28.7%) were stirred and mixed with a disperser ("Robomix" Primimix). This foamed composition was applied onto a PET film (thickness: 38 μm, trade name: "MRF # 38" manufactured by Mitsubishi Chemical Corporation) subjected to the peeling treatment and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes, , A density of 0.38 g / cm 3, and an average cell diameter of 68 탆 (foam sheet).

Example 4

100 parts by weight of an acrylic emulsion solution (solid content: 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33% , 1.5 parts by weight of a surfactant (surfactant (A)), 1 part by weight of a carboxybetaine type amphoteric surfactant (Amogen CB-H, manufactured by Daiichi Kyoei Co., Ltd.) (Surfactant (B) 0.35 part by weight of "Epochros WS-500" manufactured by Nippon Shokubai Co., Ltd., solid content 39%), 0.78 part by weight of a polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (acrylic acid 20 wt%), solid content 28.7% And 0.5 part by weight of a triazole-based rust inhibitor (" SEETEC BT-NA ", manufactured by Cipro Kasei Corporation) were stirred and mixed with a disperser ("Robomix" The foamed composition was applied on a peeled PET (polyethylene terephthalate) film (thickness: 38 μm, trade name "MRF # 38" manufactured by Mitsubishi) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes (Foamed sheet) having an open cell structure having a thickness of 130 占 퐉, a density of 0.33 g / cm3, a maximum cell diameter of 110 占 퐉, a minimum cell diameter of 20 占 퐉, and an average cell diameter of 45 占 퐉.

Example 5

100 parts by weight of an acrylic emulsion solution (solid content: 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33% , 2 parts by weight of an oxazoline crosslinking agent (Epocross WS-500 manufactured by Nippon Shokubai Co., Ltd., solid content 39%), 2 parts by weight of a polyacrylic acid thickener (ethyl acrylate-acrylic acid copolymer (20% by weight of acrylic acid) , 0.78 parts by weight of a silane coupling agent (28.7% by weight), and 0.5 parts by weight of a benzotriazole-based rust preventive agent (SEETEC BT-NA, manufactured by Cipro Kase Corporation) were stirred and mixed with a disperser ("Robomix" The foamed composition was applied on a peeled PET (polyethylene terephthalate) film (thickness: 38 μm, trade name "MRF # 38" manufactured by Mitsubishi) and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes (Foamed sheet) having an open cell structure having a thickness of 130 탆, a density of 0.24 g / cm 3, a maximum cell diameter of 69.5 탆, a minimum cell diameter of 15 탆 and an average cell diameter of 34 탆.

Comparative Example 1

100 parts by weight of an acrylic emulsion solution (solid content: 55%, ethyl acrylate-butyl acrylate-acrylonitrile copolymer (weight ratio 45: 48: 7)), a fatty acid ammonium surfactant (aqueous dispersion of ammonium stearate, solid content 33% And 0.78 parts by weight of a polyacrylic acid-based thickener (20% by weight of acrylic acid-acrylic acid copolymer (acrylic acid 20% by weight) and a solid content of 28.7%) were stirred and mixed with a disperser ("Robomix" Primimix). This foamed composition was applied onto a PET film (thickness: 38 μm, trade name: "MRF # 38" manufactured by Mitsubishi Chemical Corporation) subjected to the peeling treatment and dried at 70 ° C. for 4.5 minutes and at 140 ° C. for 4.5 minutes, , A density of 0.62 g / cm 3, and an average cell diameter of 58 탆 (foam sheet).

<Evaluation>

The foams (foamed sheets) obtained in Examples and Comparative Examples were subjected to the following evaluations. The results are shown in Tables 1 and 2. In Table 1, the number of parts (parts by weight) (in terms of solid content (nonvolatile content)) of each component in each of the examples and comparative examples is shown. &Quot; Em &quot; represents an acrylic emulsion solution.

(Average cell diameter)

An average cell diameter (占 퐉) was obtained by taking an enlarged image of the cross-section of the foam by a low-vacuum scanning electron microscope ("S-3400N-type scanning electron microscope", Hitachi High-Tech Science Systems) and analyzing the image. The number of analyzed bubbles is about 10 ~ 20. Further, the minimum cell diameter (占 퐉) and the maximum cell diameter (占 퐉) of the foam sheet were determined in the same manner as the average cell diameter.

(density)

A foam (foamed sheet) is punched out with a punching blade of 100 mm x 100 mm, and the dimensions of the punched sample are measured. Further, the thickness is measured with a 1/100 dial gauge having a measuring 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 dish scale of 0.01 g or more on the minimum scale. The density (g / cm 3) of the foam was calculated from these values.

(Dynamic viscoelasticity)

A temperature dispersion test was carried out at an angular velocity of 1 rad / s in a film tensile measurement mode of a viscoelasticity measuring apparatus ("ARES2KFRTN1-FCO" manufactured by TA Instruments Japan). (Peak) of the loss tangent (tan?), Which is the ratio of the storage elastic modulus (E ') to the loss elastic modulus (E' '), was measured.

The temperature (° C) of the loss tangent (tan delta) of the foam is described in the column of "tan delta" in Table 2 and the strength (maximum value) of the peak is described in the column of " (Peak value of tan? Of the material itself (excluding bubbles) (maximum value of tan? Of the material constituting the foam (excluding bubbles) (maximum value Value). &Lt; / RTI &gt;

(Initial modulus)

(N / mm &lt; 2 &gt;) calculated from the slope at 10% strain in a tensile test at a tensile rate of 300 mm / min under an environment of 23 deg.

(Shock absorption test)

Impact absorbency test was performed using the pendulum type impact tester (impact test apparatus) (see Figs. 1 and 2). The foam sheet (sample size: 20 mm x 20 mm) obtained in the examples and the comparative example was subjected to a low impact condition (a) in which a 28 g iron ball was inclined by 30 DEG and a low impact condition b) and a high impact condition in which 96 g of iron balls were inclined by 47 DEG, and the impact absorption rate (%) under each condition was determined.

Next, the impact absorption rate (%) was divided by the thickness (占 퐉) of the foam sheet to obtain the impact absorption rate (R) per unit thickness.

(Shear adhesive force)

The foam sheet was cut into 25 mm x 25 mm, and SUS304BA plates were respectively attached to both surfaces of the foamed product to prepare a measurement sample. A 5 kg roller was reciprocated and pressed on the measurement sample placed horizontally. After compression, the sample was allowed to stand at room temperature (23 DEG C) for 30 minutes, and then the sample was fixed to Tensilon so that the sample to be measured was vertical, and the shear adhesive force in the center thereof was measured by pulling at a tensile speed of 50 mm / min. The measured sample was measured as n = 2, and the average value was defined as a shear adhesive force (N / 100 mm &lt; 2 &gt;).

(Confirmation test of occurrence of display unevenness)

The commercial smartphone was disassembled. In this smartphone, there was a space between the lower part of the display panel and the case, and the height of this space was 0.2 mm. This space was used as a cavity for foam insertion.

Next, a sample to be evaluated was inserted into the void for inserting the foam, and the disassembled smartphone was again assembled. In Comparative Example 2, nothing was inserted in the void for inserting the foam.

I activated the smartphone and pressed the center of the screen with my thumb. The force at this time was approximately 12 N. Then, it was confirmed whether or not display unevenness occurred, and evaluated according to the following criteria.

A: Display unevenness does not occur.

B: Display spots occur, but the user can visually confirm without problems and can operate the smartphone without problems.

C: Display unevenness adversely affects the visibility, and the user is discomforted with the operation of the smartphone.

(Stress relaxation test)

Using a stress relaxation tester shown below, a sample to be evaluated was inserted into the void for inserting foam, and the stress relaxation property was evaluated.

The stress relaxation tester is shown in Fig. 3 and Fig. Fig. 3 is a schematic top view of the stress relaxation tester, and Fig. 4 is a schematic cross-sectional view of the stress relaxation tester (sectional view taken along the line A-A 'in Fig. 3). Reference numeral 6 denotes a stress relaxation tester. Reference numeral 61 denotes a pressing member (indenter), 62 denotes a window lens, 63 denotes a liquid crystal display (LCD), 64 denotes a pressure sensitive paper, Base plate), 661 and 662 are adhesive tapes, and 67 is a case. The area 68 enclosed by the dotted line represents the void for inserting the foam. The stress relaxation tester 6 has a pressure sensitive paper 64 on the back surface side of the liquid crystal display 63 and a window lens 62 on the surface side of the liquid crystal display 63. In the stress relaxation tester 6, the case 67 is disposed on the substrate 65 with the adhesive tape 662 interposed therebetween. The window lens 62 is fixed on the case with the adhesive tape 661 interposed therebetween A window lens 62, an adhesive tape 661, an adhesive tape 662, a case 67 and a substrate 68. The liquid crystal display 63 and the pressure sensitive paper 64 ) Are disposed on the surface of the substrate. In addition, a void 68 for inserting foam is provided in the inner space below the pressure-sensitive paper 64.

Further, the window lens in this stress relaxation tester can be regarded as a touch panel.

The pressing member 61 has a tip shape of a sphere having a diameter of 13 mm. As the adhesive tape 661, a double-faced adhesive tape (thickness 300 mu m, trade name &quot; double-faced adhesive tape HJ-90130B &quot;, manufactured by Nitto Denka Kogyo K.K.) was used. As the adhesive tape 662, a double-sided adhesive tape (thickness: 40 mu m, trade name &quot; Double-sided adhesive tape No. 5603 &quot;, manufactured by Nitto Denka Kogyo K.K.) was used. The thickness of the touch panel 62 is 0.8 mm. The thickness of the liquid crystal display 63 is 1.7 mm. The thickness of the substrate 65 is 5 mm. As the pressure sensitive paper 64, a stress measuring film (trade name: "Presskel" (two sheets, unlabeled (4 LW), manufactured by Fuji Photo Film Co., Ltd .; Respectively.

In the stress relaxation tester 6, the case 67 can be replaced, and the height of the cavity 68 for foam insertion can be adjusted by adjusting the height of the case 67.

A sample to be evaluated and a PET film (thickness: 38 mu m, trade name &quot; MRF # 38 &quot;, manufactured by Mitsubishi Jusi Co., Ltd.) were placed in the voids for inserting foam of the stress relaxation tester at a total thickness Was inserted in the vicinity of 200 탆 and a stress relaxation tester was used to evaluate the stress relaxation property by applying a load of 12 N to the center of the touch panel using a pressing member and confirming discoloration of the pressure sensitive paper.

In Comparative Example 3, five PET films (thickness: 38 mu m, trade name &quot; MRF # 38 &quot;, manufactured by Mitsubishi Chemical Corporation) were laminated on the pores for inserting foam.

The evaluation results of the stress relaxation test are shown in Fig. 5 to Fig. 5 to 11 are pressure images obtained by digitalizing the discoloration of pressure-sensitive paper of Examples 1 to 5 and Comparative Examples 1 and 3, respectively, and visualizing the pressure acting on the pressure-sensitive paper.

As shown in Table 2, in the foam sheet of the examples, the R was 0.15 or more in the low-impact conditions (a) and (b) and 0.10 or more in the high-impact conditions, And showed excellent shock absorption regardless of the magnitude of the impact. On the contrary, in the foam sheet of the comparative example, all the criteria were not satisfied at the same time. In addition, the foam sheet of the examples exhibited a high shear adhesive force to the SUS304BA plate. Therefore, when the foamed sheet is laminated with another member, the positional deviation can be prevented without peeling off the other member without providing a pressure-sensitive adhesive layer on the foamed sheet.

Further, as shown in Figs. 5 to 11, the foam sheet of the example has a smaller pressure acting on the pressure-sensitive paper and is excellent in the stress relaxation property as compared with the comparative example. Therefore, when the foam sheet of the embodiment is used in a touch panel-mounted device, it is possible to highly suppress the occurrence of display unevenness in the display portion according to the touch operation of the user.

Impulse tester (Impact tester)
2 Specimen (foam sheet)
3 retaining member
4 shock load member
5 Pressure sensor
11 Fixing Jig
12 pressing jig
16 Pressure regulating means
20 Supports
21 arm
22 One end of the support shaft (shaft)
23 Support Rod (Shaft)
24 Strikers
25 electromagnets
28 Support plate
a Swing-up angle
6 Stress relaxation tester
61 pressing member
62 window lens
63 liquid crystal display
64 Compressed area
65 substrate
661 adhesive tape
662 Adhesive tape
67 cases
68 Pore for foam insertion

Claims (17)

A loss tangent (tan delta), which is a ratio of a storage elastic modulus to a loss elastic modulus at an oscillating speed of 1 rad / s, in a dynamic viscoelasticity measurement is -30 Lt; 0 &gt; C to 30 &lt; 0 &gt; C, and which is formed by using an emulsion resin composition. The foam sheet according to claim 1, wherein the foam has an average cell diameter of 10 mu m to 150 mu m. The foam sheet according to claim 1 or 2, wherein the maximum value of the loss tangent (tan?) Of the foam in the range of -30 占 폚 to 30 占 폚 is 0.2 or more. The foam sheet according to any one of claims 1 to 5, wherein the initial modulus of elasticity of the foam in the tensile test at a tensile rate of 300 mm / min at 23 캜 is 5 N / mm 2 or less. The impact absorbing structure according to any one of claims 1 to 3, wherein a value (R) obtained by dividing an impact absorption rate (%) defined by the following formula by the thickness (占 퐉) A weight of 28 g, and a swing-up angle of at least 0.15 when the swing-up angle is 30 °:
Impact absorption rate (%) = {(F ₀ -F ₁ ) / F ₀ } × 100
F ₀ is the impact force when the impactor collides against the support plate, and F ₁ is the impact force when the impactor collides against the support plate of the structure composed of the support plate and the foam sheet. The foam sheet according to claim 1 or 2, wherein a shear adhesive force (23 DEG C, tensile speed 50 mm / min) of at least one surface of the foam to an SUS304BA plate is 0.5 N / 100 mm2 or more. The foam sheet according to claim 1 or 2, wherein the foam is formed of at least one resin material selected from the group consisting of an acryl-based polymer, a rubber, a urethane-based polymer, and an ethylene-vinyl acetate copolymer. The foam sheet according to claim 1 or 2, wherein the foam is formed through a step (A) of mechanically foaming the emulsion resin composition. The foam sheet according to claim 8, wherein the foam is formed by further adding a step (B) of coating a mechanically foamed emulsion resin composition onto a substrate and drying the foam. The method according to claim 9, wherein the step (B) comprises a preliminary drying step (B1) of drying the bubble-containing emulsion resin composition coated on the substrate at a temperature of from 50 캜 to less than 125 캜, (B2) which is further dried. The foam sheet according to claim 1 or 2, wherein the foam sheet has a pressure-sensitive adhesive layer on one side or both sides of the foam. The foam sheet according to claim 1 or 2, used as an impact-absorbing sheet for electric or electronic equipment. The foam sheet according to claim 1 or 2, wherein the foam sheet is used in a touch panel-mounted device. An electric or electronic device using the foam sheet according to claim 1 or 2. The electric or electronic device according to claim 14, wherein the foam sheet has a structure sandwiched between a case of the electric or electronic device and the display member. A touch panel mounted device using the foam sheet according to claim 1 or 2. The touch panel mounted device according to claim 16, wherein the foam sheet has 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.

Images