JP6845271B2 - Shock absorbing film - Google Patents

Description

The present invention relates to a shock absorbing film having a non-foamed resin film layer that absorbs shock and a film layer of one or more layers of polyolefin or polyester laminated thereto.

In electronic devices such as so-called smartphones, double-sided tape is used to fix the edge of the liquid crystal screen. In this double-sided tape, a tape capable of absorbing the impact so as not to be peeled off by the impact received on the liquid crystal screen is used (see, for example, Patent Document 1).

As a sheet used for such a tape having shock absorption, a foam such as polyurethane foam is often used.

Japanese Unexamined Patent Publication No. 2009-242541

Here, with the recent miniaturization of electronic devices, the width of the edge portion tends to be narrowed. However, since the foam has air bubbles, there have been problems such as low sheet strength and insufficient airtightness.

On the other hand, when the unfoamed resin is used, it is difficult to obtain the same shock absorption as the foam.

An object of the present invention is to provide a film which is not foamed but has shock absorption equal to or higher than that of a foam.

The present inventor has obtained the following findings as a result of repeated diligent studies in order to solve the above-mentioned problems. That is, it is a finding that by having an unfoamed resin layer made of a resin having hardness and loss tangent within a specific range, shock absorption equal to or higher than that of a foam can be obtained even though it is unfoamed.

The present invention is based on the findings of the present inventor, and the means for solving the above-mentioned problems are as follows.

<1> A non-foamed resin film layer that absorbs impact and a layer or more of a polyolefin or polyester film layer laminated on the non-foamed resin film layer, and the unfoamed resin film layer has a shore A hardness of 40 or less. A shock absorbing film characterized in that it is made of a resin having a loss tangent by JIS K7244-4 of 0.1 or more in a temperature environment of -20 to 80 ° C., and the measured value of shock absorption according to the following is 52 or less. Is.
Measurement of shock absorption: A device that measures the amplitude in three directions of X (vertical), Y (horizontal), and Z (height). A sample is placed on the detector of the recorder, and 30 cm is placed on the placed sample. The frequency when a 7 g iron ball is dropped from the height of is measured, and among the measured frequencies in the three directions, the Z-axis data is used as the measured value of shock absorption.

<2> The shock absorbing film according to <1>, wherein a film layer made of the same material of the polyolefin or polyester is laminated on both sides of the unfoamed resin film layer.

<3> The shock absorbing film according to <1> or <2>, wherein the thickness of the unfoamed resin film layer is 3/4 or more of the total thickness.

The phrase "the loss tangent is 0.1 or more in a temperature environment of -20 to 80 ° C." means that the loss tangent is maintained at 0.1 or more in the range of -20 to 80 ° C.

The shock absorbing film of the present invention has a non-foamed resin film layer that absorbs shock and a polyolefin or polyester film layer laminated on the non-foamed resin film layer, and has a shore A hardness of 40 or less and loss direct contact with the non-foamed resin film layer. By using a resin of 0.1 or more in a temperature environment within a predetermined range, it is possible to obtain shock absorption equal to or higher than that of a foam while being unfoamed.

FIG. 1 is a cross-sectional view showing one form of a layer structure of the shock absorbing film of the present invention. FIG. 2 is a graph showing loss tangent data at −80 to 80 ° C. when the material of the unfoamed resin film layer is changed. FIG. 3 is a graph showing loss tangent data at 0 to 80 ° C. when the material of the unfoamed resin film layer is changed.

The shock-absorbing film of the present invention includes an unfoamed resin film layer that absorbs shock (hereinafter referred to as "shock-absorbing layer") and a polyolefin or polyester film layer laminated thereto (hereinafter referred to as "surface layer"). And have.

FIG. 1 is a diagram showing an example of a layer structure of the shock absorbing film of the present invention, and the shock absorbing film 10 shown in this figure is laminated on the central shock absorbing layer 11 and both surfaces thereof. It is composed of surface layers 12 and 13.

As the unfoamed resin of the shock absorbing layer 11, a resin having a shore A hardness of 40 or less and a loss tangent of 0.1 or more in a temperature environment in the range of -20 to 80 ° C. is used. Here, the shore A hardness is a standard for measuring the hardness of general rubber, and can be measured according to JIS K6253 using a durometer (spring type rubber hardness meter). The loss tangent is an index of the viscous element and the elastic element of the object based on the relationship between the waveform peak value of the stress and strain phase (sine wave) and the phase difference (strain delay) on the time axis. It can be measured according to -4.

When the shore A hardness exceeds 40, the repulsion is large, and it is difficult to obtain the same level of shock absorption as the foam. Further, it is preferable that the lower the Shore A hardness is, the more remarkable the impact absorption is exhibited, but if the value is too low, it may be difficult to laminate the surface layer. Therefore, a desired impact is desired for film production. As long as absorbability can be obtained, the condition of 40 or less may be satisfied.

The loss tangent was measured in the above temperature range because of the temperature that can be expected when the shock absorbing film of the present invention is used in a normal living environment, and the loss tangent is less than 0.1 in the above temperature range. If it becomes, it is difficult to flexibly deform when a force is applied, and it is difficult to obtain the same level of shock absorption as a foam.

The specific unfoamed resin used for the shock absorbing layer 11 is not particularly limited as long as it satisfies the above-mentioned hardness and loss tangent, but for example, styrene elastomer is preferable because it has a low shore A hardness.

The styrene elastomer is not particularly limited as long as it satisfies the above-mentioned hardness and loss tangent. For example, styrene ethylene butylene styrene block copolymer (SEBS), styrene butadiene rubber (SBR), and styrene ethylene propylene styrene block are all used. One or a combination of two or more commonly known resins such as elastomer (SEPS), styrene butadiene (SB), and styrene block copolymer (SBC) can be used. However, among these, SEPS is particularly preferable because it has a low shore A hardness and exhibits high shock absorption.

The ratio of the thickness of the shock absorbing layer 11 to the entire shock absorbing film 10 is not particularly limited as long as the desired shock absorbing property of the present invention can be obtained, but it is preferably 3/4 or more of the total thickness. .. Since the shock absorbing layer 11 is an essential portion of the film that exhibits shock absorbing properties, if it is thin, the desired shock absorbing properties may not be obtained. However, for example, when the thickness of the shock absorbing layer 11 and the surface layers 12 and 13 are the same, high shock absorbing property may be obtained. Therefore, the thickness is not necessarily required as long as the desired shock absorbing property is obtained. You may.

As the surface layers 12 and 13, polyolefin or polyester, which is known as a material harder than the unfoamed resin used for the shock absorbing layer 11, is preferably used from the viewpoint of maintaining and improving the shock absorbing effect of the shock absorbing layer 11. Be done.

The polyolefin is not particularly limited. For example, in addition to polyethylene, polypropylene, polybutylene and the like, an ethylene-α / olefin copolymer polymerized using a metallocene catalyst, polypropylene, an ethylene-vinyl acetate copolymer, an ionomer resin, and ethylene. Examples thereof include an ethyl acrylate copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-propylene copolymer, and a methylpentene polymer. In addition, polyolefin resins having heat-sealing properties such as acid-modified polyolefin resins obtained by modifying polyolefin resins such as polyethylene and polypropylene with acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, and other unsaturated carboxylic acids are also mentioned. Be done. Furthermore, polyolefin resins other than polyethylene can also be used. It should be noted that these may be used alone or in combination of two or more.

However, polyethylene is preferable in consideration of the ability to exert the function of the shock absorbing layer 11 more strongly and the versatility.

The polyethylene may be low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), or linear (linear) low-density polyethylene, but LDPE may be used from the viewpoint of versatility. Is preferable.

Further, as the polyester, polyethylene terephthalate (PET) is preferably mentioned from the viewpoint of versatility, but polyethylene terephthalate (PEN), polybutylene terephthalate (PBT) and the like are not particularly limited, and these may be used alone or 2 More than seeds may be used in combination.

It should be noted that the surface layer may be one layer or more, but in order to be used for the double-sided tape at the edge of the electronic device, as shown in FIG. 1, one or more layers are laminated on both sides of the shock absorbing layer. Is preferable.

At this time, when three or more surface layers are laminated, the surface layers and the shock absorbing layers are alternately laminated, for example, surface layer / shock absorbing layer / surface layer / shock absorbing layer / surface layer. Alternatively, a plurality of surface layers may be laminated with the shock absorbing layer interposed therebetween, such as a surface layer / surface layer / shock absorbing layer / surface layer / surface layer. However, in order to efficiently exhibit shock absorption, it is preferable to stack them alternately as in the former case. By laminating three or more surface layers in this way, the ratio of the thickness of the shock absorbing layer to the total thickness of the shock absorbing film is high as compared with the case where the surface layer is two or less layers. It may be easier to obtain shock absorption.

Further, when the surface layer is laminated on both sides of the shock absorbing layer, the material and the thickness may be different between the two, but it is preferable that the surface layer is the same in consideration of ease of manufacture and no unevenness in performance. ..

In addition to the above-mentioned resins, the shock-absorbing layer and the surface layer are usually added to the above-mentioned resins such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and fillers. The material to be obtained may be added within a range that does not affect the physical properties. Further, each material of the shock absorbing layer and the surface layer may be a commercially available product or may be prepared according to a conventional method.

The shock absorbing film of the present invention can be suitably used as a double-sided tape for fixing the edge of a small portable electronic device such as a tablet or a smartphone by applying an adhesive.

The pressure-sensitive adhesive to be applied in this case is not particularly limited, but for example, the acrylic pressure-sensitive adhesives described in [0059] to [0072] of JP2009-242541A can be preferably used.

In the shock absorbing film of the present invention, if a surface layer can be laminated on the shock absorbing layer, a generally known method may be appropriately selected. For example, the surface layer is extruded and laminated on the shock absorbing layer. The method etc. can be mentioned.

Further, by utilizing the shock absorption property, it can be used, for example, for medical applications such as a wound protective film and a transdermal drug film, and for acoustic applications such as an acoustic vibration material, a sound absorbing material, and a vibration damping material.

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

Verification 1. Relationship between hardness and shock absorption First, in order to search for a suitable unfoamed resin for the shock absorption layer, the present inventors examined the relationship with shock absorption by focusing on the hardness.

That is, when each unfoamed resin having different physical properties is used as the shock absorbing layer, the shore A hardness and the shock absorbing property are measured as follows, and the foam (PE foam) made of LDPE is used as the shock absorbing layer. Compared. The results are shown in Table 1. The specific gravity and physical property data of each resin were measured according to a conventional method defined by JIS or the like (the same applies to the verification described later unless otherwise specified). As the PE foam, a commercially available foam sheet having a thickness of 0.1 mm and a foaming ratio of 1.1 to 1.2 was used.

Measurement of Shore A hardness: Measurement was performed according to JIS K6253 using a durometer (spring type rubber hardness tester).

Measurement of shock absorption: The frequency was measured using a three-way shock / vibration recorder "SOROCABA-1" manufactured by Cosmic ME. Specifically, the recorder is a device that measures the amplitude in three directions of X (vertical), Y (horizontal), and Z (height). A sample is placed on the detector of the recorder, and the sample is placed on the sample. The frequency when a 7 g iron ball was dropped from a height of 30 cm was measured. Then, among the measured frequencies in the three directions, the Z-axis data that can most affect the shock absorption against dropping was adopted as the shock absorption data. The lower this value, the lower the frequency and the higher the shock absorption. The example in which this value shows a minus indicates that there was more downward runout than the upper part of the sample. In addition, "no detection" means that there was no vibration.

The thickness was confirmed by measuring as follows. That is, it was measured according to JIS Z1072 using a film thickness measuring instrument "dial gauge 0.001 mm" manufactured by Ozaki Seisakusho Co., Ltd.

From the results in Table 1, when an unfoamed resin having a Shore A hardness of 40 or less is used as the shock absorbing layer, better shock absorption can be easily obtained than when a foam is used, and the shock absorbing film can replace the foam. It was found that it can be used as a non-foamed resin. It was also found that the lower the Shore A hardness, the better the shock absorption.

On the other hand, as a material for the shock absorbing layer, styrene elastomer, especially SEPS, was found to be preferable because it has a low shore A hardness and easily exhibits high shock absorbing properties.

However, it was also found that there are cases where the shock absorption is not sufficient even for SEPS with a shore A hardness of 40 or less, and it is necessary to study further indexes in order to obtain excellent shock absorption.

Verification 2. Relationship between loss tangent and shock absorption Based on Verification 1, the present inventors focused on loss tangent as an index to ensure that the desired shock absorption is exhibited when the shore A hardness is 40 or less. Then, the relationship with shock absorption was verified.

That is, each unfoamed resin having different physical properties is used as the shock absorbing layer, the shore A hardness and shock absorbing property are measured in the same manner as in Verification 1, and the dynamic viscoelasticity manufactured by TA Instruments Japan Co., Ltd. is measured. The loss tangent was measured according to JIS K7244-4 in an environment of 25 ° C. using the elasticity measuring device "Q800". The results are shown in Table 2.

From the results in Table 2, it was found that excellent shock absorption can be obtained for the first time when the shore A hardness is 40 or less and the loss tangent in a 25 ° C environment is 0.1 or more as the shock absorbing layer. It was.

Subsequently, the fluctuations of the above-mentioned loss tangent at -80 to 80 ° C. were measured for the five types of styrene resins in Table 2, SEPS (shore A hardnesses of 36, 12, and 5, respectively), SBR, and SEBS. The overall result is shown in FIG. 2, and the detailed result at 0 to 60 ° C. is shown in FIG.

As shown in FIGS. 2 and 3, all three types of SEPS in Table 2 maintain a loss tangent of 0.1 or more at a temperature that can be assumed in a living environment of -20 to 80 ° C. It was found that excellent shock absorption can be obtained even if there is a temperature change in the environment.

Verification 3. Surface layer In products, a surface layer is required to protect the shock absorbing layer, but in order to verify what kind of material can be applied as the surface layer, excellent impact in the above verifications 1 and 2 is performed. As shown in FIG. 1, for SEPS exhibiting absorbency, surface layers 12 and 13 were laminated on both sides by extrusion lamination to prepare a shock absorbing film 10 having a three-layer structure.

At this time, the resins used for the surface layers 12 and 13 were changed, and the thickness, shore A hardness, loss tangent in an environment of 25 ° C., and shock absorption were measured in the same manner as in the method described in Verification 1 or 2. The results are shown in Table 3.

In Table 3, the following samples were used for PET, LDPE, and HDPE.

PET: Biaxially stretched film with a thickness of 0.038 mm,
LDPE: density Shore D hardness is based on 49, JIS K7112 based on JIS K7215 is 0.924 g / cm ³ of the sample,
HDPE: A sample having a Shore D hardness of 66 based on JIS K7215 and a density of 0.963 g / cm ^{3 based on JIS K7112.}

From the results in Table 3, if an unfoamed resin having a shore A hardness of 40 or less and a loss tangent at 25 ° C. of maintaining 0.1 or more at a predetermined temperature is used in the shock absorbing layer, polyester is used as the surface layer. It was found that good shock absorption can be obtained by using either or polyolefin. However, in a comparison between the two, it was also found that the use of polyolefin was preferable because it was possible to obtain slightly better shock absorption.

Verification 4. Relationship between the thickness of the shock absorbing layer and the surface layer, etc. Does the shock absorbing property change by changing the thickness of the shock absorbing layer in the entire film, and how much shock absorbing property is obtained only by the surface layer? In order to verify whether it is shown or not, in the combination of the shock absorbing layer by SEPS and the surface layer by LDPE (LDPE / SEPS / LDPE) used in the above verification 3, the thickness of the shock absorbing layer and the surface layer is changed to have the shock absorbing property. Was measured.

Also, regarding whether the shock absorption is affected when the number of layers is increased, the shock absorbing layer and the surface layer (SEPS / LDPE) are further laminated one by one in the three-layer structure composed of LDPE / SEPS / LDPE. , The one with a five-layer structure was verified as an example. The results of each are shown in Table 4.

From the results in Table 4, when the thickness of the shock absorbing layer is 3/4 or more of the total thickness (total thickness), it has excellent shock absorbing properties, and the higher the ratio of this thickness to the whole, the higher the ratio. , It was found that the shock absorption was improved. In addition, even in the above-mentioned verification 3, this is supported by the fact that the thickness of the shock absorbing layer is 3/4 or more of the total thickness and the desired shock absorbing property is obtained.

Further, in the example in which the number of layers is increased, even if the thickness of the shock absorbing layer is less than 3/4 of the total thickness, the thickness of the shock absorbing layer is 3/4 or more of the total thickness in the three-layer structure. It was found that the same excellent shock absorption as the above can be obtained.

On the other hand, in the case without the shock absorbing layer, the desired shock absorbing property could not be obtained. From these facts, in the shock absorbing film of the present invention, it can be seen that the shock absorbing layer exhibits the shock absorbing property which is the original function of the film, and the higher the ratio of this portion, the more the shock absorbing layer is concerned. It was judged that the shock absorption would be improved because the proportion of the part that could exert the function would increase.

Further, even when the thickness of the three layers of the shock absorbing layer and the surface layers on both sides is the same, excellent shock absorbing property was exhibited. Therefore, it was speculated that if the thickness of each layer is balanced, the function of the shock absorbing layer is efficiently transmitted to the surface layer, and a synergistic effect is exerted such that the shock absorbing property is improved. This means that in the above-mentioned example of increasing the number of layers, even if the ratio of the thickness of the shock absorbing layer to the total thickness is slightly low, the thickness of the shock absorbing layer is 3 of the total thickness of the three layers. It is considered that this is supported by the fact that the same level of shock absorption as when the value is set to 4/4 or more is obtained.

Although the embodiments and examples of the present invention have been described in detail above, the shock absorbing film of the present invention is not limited to the above-described embodiments, and may include any technical idea assumed within the scope. ..

INDUSTRIAL APPLICABILITY The present invention can be used for double-sided tape for fixing the edge of an electronic device, medical applications such as a wound protective film and a percutaneous absorbent film, and acoustic applications such as an acoustic vibration material, a sound absorbing material, and a vibration damping material. ..

10 Shock absorption film 11 Shock absorption layer 12, 13 Surface layer

Claims (5)

It has a non-foamed resin film layer that absorbs impact and one or more layers of polyolefin or polyester film layer laminated on the unfoamed resin film layer.
The unfoamed resin film layer is made of a resin having a shore A hardness of 40 or less and a loss tangent by JIS K7244-4 of 0.1 or more in a temperature environment of -20 to 80 ° C.
Moreover, in the shock absorbing film in which the measured value of the shock absorbing property according to the following is 52 mV / m / s ² or less, the thickness of the unfoamed resin film layer is 3/4 or more of the total thickness. Shock absorbing film.
Measurement of shock absorption: A device that measures the amplitude in three directions of X (vertical), Y (horizontal), and Z (height). A sample is placed on the detector of the recorder, and 30 cm is placed on the placed sample. The frequency when a 7 g iron ball is dropped from the height of is measured, and among the measured frequencies in the three directions, the Z-axis data is used as the measured value of shock absorption. The shock absorbing film according to claim 1, wherein a film layer made of the same material of the polyolefin or polyester is laminated on both sides of the unfoamed resin film layer. It has a non-foamed resin film layer that absorbs impact and one or more layers of polyolefin or polyester film layer laminated on the unfoamed resin film layer.
The unfoamed resin film layer is made of a resin having a shore A hardness of 40 or less and a loss tangent by JIS K7244-4 of 0.1 or more in a temperature environment of -20 to 80 ° C.
In addition, in a shock absorbing film in which the measured value of shock absorption according to the following is 52 mV / m / s ^{2 or less.}
A shock absorbing film characterized in that a film layer made of the same material of the polyolefin or polyester is laminated on both sides of the unfoamed resin film layer, and the thickness of each layer is the same.
Measurement of shock absorption: A device that measures the amplitude in three directions of X (vertical), Y (horizontal), and Z (height). A sample is placed on the detector of the recorder, and 30 cm is placed on the placed sample. The frequency when a 7 g iron ball is dropped from the height of is measured, and among the measured frequencies in the three directions, the Z-axis data is used as the measured value of shock absorption. It has a non-foamed resin film layer that absorbs impact and one or more layers of polyolefin or polyester film layer laminated on the unfoamed resin film layer.
The unfoamed resin film layer is made of a resin having a shore A hardness of 40 or less and a loss tangent by JIS K7244-4 of 0.1 or more in a temperature environment of -20 to 80 ° C.
In addition, in a shock absorbing film in which the measured value of shock absorption according to the following is 52 mV / m / s ^{2 or less.}
A film layer made of the same material of the polyolefin or polyester is laminated on both sides of the unfoamed resin film layer, and each layer is laminated.
The unfoamed resin film layer and the film layer made of the same material of the polyolefin or polyester were further laminated in this order on either one of the polyolefin or polyester film layers laminated on the unfoamed resin film layer. A characteristic shock absorbing film.
Measurement of shock absorption: A device that measures the amplitude in three directions of X (vertical), Y (horizontal), and Z (height). A sample is placed on the detector of the recorder, and 30 cm is placed on the placed sample. The frequency when a 7 g iron ball is dropped from the height of is measured, and among the measured frequencies in the three directions, the Z-axis data is used as the measured value of shock absorption. The shock absorbing film according to any one of claims 1 to 4, wherein the polyolefin or polyester film layer is made of low density polyethylene (LDPE).