JP2009242541A - Impact-absorbing tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact-absorbing tape suitable for electronic devices which is of a thin type but has sufficient impact absorption properties and water cut-off properties and whose volatile component does not adversely affect electronic components even in a narrow internal space because of the capability of suppressing its volatile content to an extremely small amount. <P>SOLUTION: The impact-absorbing tape, in which an acrylic adhesive layer is laminated and combined on at least one surface of a substrate layer, is for fixing electronic components in a package and for absorbing impact. The substrate layer is a crosslinked polyolefin-based resin foamed sheet with the degree of cross-linking of 5-60 wt.% and the bubble aspect ratio (the average bubble diameter of MD/the average bubble diameter of CD) of 0.25-1. The acrylic adhesive layer includes an acrylic adhesive containing an acrylic copolymer and 1-50 pts.wt. of a tackifier resin having 13% or less of the content of a component with a weight-average molecular weight of 600 or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a shock absorbing tape, and more particularly to a shock absorbing tape suitably used for an electronic device.

Conventionally, shock absorbing materials have been used in various parts of various electronic devices such as digital cameras, personal computers, and game machines. Specific applications include a wide range of applications such as camera module shock absorption, battery shock absorption, and speaker holding.
For example, Patent Document 1 discloses a camera in which a foam cushion material is disposed between a camera module and a monitor unit. According to Patent Document 1, it is described that such a camera can prevent distortion and breakage of the lens unit.

Patent Document 2 describes that a cushion with an adhesive is used when a camera is arranged in an electronic device. The detailed description of Patent Document 2 discloses a mode in which a cushion member is pasted in a bridge shape on both the camera lens and the electronic device casing. A double-sided tape is used for pasting. In addition, polyurethane foam is disclosed as a material for the cushion member.
Furthermore, Patent Document 3 describes a liquid crystal display device having a rubber cushion material between a housing and a front plate.

Patent Document 4 discloses a liquid crystal panel provided with a cushion material between the liquid crystal panel and the panel guide.
Detailed studies are being conducted on such cushioning materials and shock absorbing materials. For example, Patent Document 5 discloses a shock absorbing tape having a rubber foam and a bubble-containing adhesive layer.

On the other hand, in recent years, with the demand for downsizing / thinning electronic devices, individual electronic components built in the electronic devices are also demanded for downsizing / thinning.
In such an electronic device, the cushioning material used is required to have a high impact absorption capability while being thin. In addition, as the display device becomes thinner and smaller, the internal space also becomes smaller, so there is a concern that the volatile components contained in the shock absorbing material may affect each electronic component. Further, portable electronic devices such as portable game machines and digital cameras may be required to have excellent waterproof properties at the same time as being thinned. However, by improving waterproofness, at the same time, the release of volatile components that volatilize from the shock absorber is hindered, leading to the problem that volatile components accumulate inside the narrow internal space. .

JP 2006-030419 A Japanese Patent Laid-Open No. 2007-215017 JP 2007-047620 A JP 2005-346061 A JP 2006-110773 A

  In view of the above circumstances, the present invention has a sufficient impact absorbability and water-stopping property while being thin, and the amount of volatile components can be suppressed to a very small amount. An object of the present invention is to provide a shock-absorbing tape suitable for an electronic device that does not affect the electronic device.

  In order to achieve the above object, the shock absorbing tape for electronic parts according to the present invention has an acrylic adhesive layer laminated and integrated on at least one side of the base material layer, and absorbs shock while fixing the electronic part in the package. The base material layer has a degree of cross-linking of 5 to 60% by weight, and a bubble aspect ratio (MD average bubble diameter / CD average bubble diameter) of 0.25 to 1. The acrylic pressure-sensitive adhesive layer is an acrylic copolymer and a tackifying resin having a content of a component having a weight average molecular weight of 600 or less of 13% or less. It is characterized by comprising an acrylic pressure-sensitive adhesive containing parts by weight.

When the impact-absorbing tape for electronic parts of the present invention is heated at 90 ° C. for 30 minutes, the concentration of the volatile component calculated by the formula (1) is preferably less than 500 ppm.
Volatile component concentration (ppm)
= Volatile component weight X (μg) / Shock absorbing tape weight before heating (g) Formula (1)
(However, in formula (1), the volatile component weight X represents the weight in terms of hexadecane.)

The acrylic copolymer is copolymerized with a polymerization initiator having a 10-hour half-life temperature of 80 ° C. or lower and a polymerization temperature higher than the 10-hour half-life temperature of the polymerization initiator. Are preferred.
The crosslinked polyolefin resin foam sheet preferably has a thickness of 0.1 to 3 mm, and the acrylic pressure-sensitive adhesive layer preferably has a thickness of 10 to 150 μm.

(Polyolefin foamed resin sheet)
The impact-absorbing tape of the present invention has a crosslinked polyolefin resin foam sheet having a crosslinking degree of 5 to 60% by weight and a bubble aspect ratio (MD average bubble diameter / CD average bubble diameter) of 0.25 to 1. The base material layer which consists of.
By using such a cross-linked polyolefin-based foamed resin sheet as a base material layer, the shock absorbing tape for electronic parts of the present invention has extremely excellent shock absorbing properties even when it is thin, and also has a water-stopping property. It will be excellent.

  That is, if the degree of cross-linking of the crosslinked polyolefin resin foam sheet is small, bubbles in the vicinity of the surface of the foam sheet break up when the foam sheet is stretched, resulting in surface roughness and sufficient adhesion with the adhesive layer. If the foamable polyolefin resin composition is too large, the melt viscosity of the foamable polyolefin resin composition becomes too large, and the foamable polyolefin resin composition follows foaming when heat-foaming the foamable polyolefin resin composition. It becomes difficult to obtain a crosslinked polyolefin resin foamed sheet having a desired expansion ratio, and as a result, the impact absorbability is inferior. Therefore, it is limited to 5 to 60% by weight, and preferably 10 to 40% by weight.

In addition, the degree of crosslinking of the crosslinked polyolefin resin foamed sheet refers to that measured in the following manner. About 100 mg of a test piece is taken from the crosslinked polyolefin resin foam sheet, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, and then filtered through a 200-mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the weight of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the degree of crosslinking (% by weight) is calculated by the following formula.
Crosslinking degree (% by weight) = 100 × (B / A)

Furthermore, the cross-linked polyolefin resin foam sheet has an aspect ratio of bubbles (average bubble diameter of MD / average bubble diameter of CD) of 0.25 to 1, or an aspect ratio of bubbles (average bubble of CD) Diameter / average bubble diameter of VD) is required to be 2 to 18, the aspect ratio of bubbles (average bubble diameter of MD / average bubble diameter of CD) is 0.25 to 1, and the aspect ratio of bubbles (Average bubble diameter of CD / average bubble diameter of VD) is preferably 2-18.
Specifically, when the ratio of the average bubble diameter of MD and the average bubble diameter of CD in the crosslinked polyolefin resin foam sheet, that is, the aspect ratio of the bubbles (average bubble diameter of MD / average bubble diameter of CD) is small. The foaming ratio may decrease and the flexibility may decrease or the thickness, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may vary. Therefore, it is limited to 0.25 to 1, and 0.25 to 0.60 is preferable.

  In addition, when the ratio of the average bubble diameter of CD and the average bubble diameter of VD, that is, the aspect ratio of bubbles (average bubble diameter of CD / average bubble diameter of VD) in the crosslinked polyolefin resin foamed sheet is small, On the other hand, the flexibility of the polyolefin resin foam sheet is reduced. On the other hand, if the ratio is large, the expansion ratio is lowered and the flexibility is lowered, or the thickness, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may vary. Since it exists, 2-18 are preferable and 2.5-15 are more preferable.

  The MD (machine direction) of the cross-linked polyolefin resin foam sheet refers to the extrusion direction, and the CD (crossing direction) of the cross-linked polyolefin resin foam sheet is orthogonal to the MD (machine direction) and cross-linked polyolefin resin foam. The direction along the surface of the sheet 1 is referred to, and the VD (vertical (thickness) direction) of the crosslinked polyolefin resin foamed sheet 1 refers to a direction orthogonal to the surface of the crosslinked polyolefin resin foamed sheet.

Next, the average cell diameter of MD of the cross-linked polyolefin resin foamed sheet is measured in the following manner. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in a plane parallel to VD at a substantially central portion of the CD.
Thereafter, the cross section of the cross-linked polyolefin resin foam sheet is enlarged 60 times using a scanning electron microscope (SEM), and a photograph is taken so that the full length of the VD of the cross-linked polyolefin resin foam sheet is accommodated.

In the obtained photograph, a straight line having a length of 15 cm on the photograph (actual length of 2500 μm before enlargement) corresponding to the central portion of the VD of the crosslinked polyolefin resin foamed sheet is obtained by foaming the crosslinked polyolefin resin foam. Draw to be parallel to the sheet surface.
Next, the number of bubbles located on the straight line is visually counted, and the average bubble diameter of bubbles MD is calculated based on the following formula.
Average bubble diameter of MD (μm) = 2500 (μm) / number of bubbles (pieces)

Moreover, the average cell diameter of VD of a crosslinked polyolefin-type resin foam sheet means what was measured in the following way. That is, photography is performed in the same manner as the procedure for calculating the average cell diameter of MD of the crosslinked polyolefin resin foam sheet.
In the obtained photograph, three straight lines that divide the cut surface of the photographed crosslinked polyolefin resin foam sheet into four parts in MD are foamed in a direction (VD) perpendicular to the surface of the crosslinked polyolefin resin foam sheet. Draw over the entire length of the sheet.
Thereafter, the length of each straight line is measured and the number of bubbles located on each straight line is visually counted, and the average bubble diameter of the bubble VD is calculated for each straight line based on the following formula, and the arithmetic mean of these is calculated. Is the average bubble diameter of the VD of the bubbles.
Average bubble diameter of VD (μm) = length of straight line on photo (μm)
/ (60 x number of bubbles (pieces))

Next, the average cell diameter of CD of the cross-linked polyolefin resin foam sheet is measured in the following manner. That is, the cross-linked polyolefin resin foam sheet is cut over the entire length in the thickness direction on a plane parallel to the CD and parallel to the direction (VD) perpendicular to the surface of the cross-linked polyolefin resin foam sheet.
Thereafter, the cross section of the cross-linked polyolefin resin foam sheet is magnified 60 times using a scanning electron microscope (SEM), and a photograph is taken so that the total length in the thickness direction of the cross-linked polyolefin resin foam sheet is accommodated.
Then, based on the obtained photograph, the average cell diameter of CD is calculated in the same manner as when the average cell diameter of MD of the crosslinked polyolefin resin foamed sheet is measured.

In the above-described procedure for measuring the average bubble diameter, when counting the number of bubbles located on a straight line, the bubble diameter is determined based only on the bubble cross section appearing on the photograph.
That is, even if the bubbles seem to be completely separated from each other by the cell wall on the cut surface of the cross-linked polyolefin resin foam sheet, they communicate with each other at a portion other than the cut surface of the cross-linked polyolefin resin foam sheet. However, in the present invention, the cross-linked polyolefin resin foam sheet is not considered whether or not it is in communication with each other in the portion other than the cut surface, and based only on the cross section of the bubble film shown on the photograph. The bubble form is judged, and one void portion completely surrounded by the bubble film cross section appearing on the photograph is judged as one bubble.

Positioning on a straight line means that the straight line completely penetrates the bubble at any part of the bubble, and the straight line does not completely penetrate the bubble at both ends of the straight line. In the case where the end portion of the bubble is located in the bubble, the bubble was counted as 0.5.
When photographing the cut surface of the cross-linked polyolefin resin foam sheet, coloring the cross-section of the cross-linked polyolefin resin foam sheet facilitates the discrimination of air bubbles and enlarges the 2500 μm scale together to take a photo. This makes it easier to specify the straight line length on the photograph.

The polyolefin resin constituting the crosslinked polyolefin resin foamed sheet preferably contains 40% by weight or more of a polyethylene resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.
Therefore, by using a polyolefin-based resin containing 40% by weight or more of a polyethylene-based resin obtained by using the above metallocene compound, the polyolefin-based resin is given flexibility without increasing the adhesiveness, and is crosslinked. The aspect ratio of the air bubbles of the polyolefin resin foam sheet is within a predetermined range to improve mechanical strength and to have excellent flexibility.

In addition, the polyethylene resin obtained using the metallocene compound has a narrow molecular weight distribution, and in the case of a copolymer, the copolymer component is introduced into each molecular weight component at an approximately equal ratio. Therefore, the foamed sheet can be uniformly crosslinked. And since the foamed sheet is uniformly crosslinked, the foamed sheet can be uniformly stretched, and the thickness of the resulting crosslinked polyolefin resin foamed sheet can be made uniform as a whole.
In the polyolefin resin, the content of the polyethylene resin obtained by using the metallocene compound containing a tetravalent transition metal as a polymerization catalyst is limited to 40% by weight or more, preferably 50% by weight or more, % By weight or more is more preferable, and 100% by weight is particularly preferable. The content of the polyethylene resin obtained using the metallocene compound of 100% by weight means that only the polyethylene resin obtained using the metallocene compound is used as the polyolefin resin.

  As will be described later, the crosslinked polyolefin resin foam sheet is produced by stretching the foam sheet in a predetermined direction while foaming or heating. When the foam sheet is stretched, the foam sheet is expanded in the stretching direction so that the cell walls are close to each other. Therefore, a resin having adhesiveness to the polyolefin resin (for example, ethylene-vinyl acetate copolymer) When coalescing is used, the bubble walls are tightly integrated with each other, and the aspect ratio of the bubbles in the desired range cannot be obtained. On the other hand, the crosslinked polyolefin resin foam sheet of the present invention is required to have flexibility.

As a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as the polymerization catalyst, using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, ethylene and a small amount of an α-olefin are obtained. A linear low density polyethylene obtained by copolymerization is preferred. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene.
The metallocene compound generally refers to a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and a bis (cyclopentadienyl) metal complex is typical.

As the metallocene compound containing a tetravalent transition metal in the present invention, specifically, a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, platinum or the like is added to one or more cyclopentadidienes. Examples thereof include compounds in which an enyl ring or an analog thereof is present as a ligand (ligand).
Examples of such metallocene compounds containing tetravalent transition metals include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, Dimethylsilyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium chloride , Methylphenylsilyltetramethylcyclopentadienyl-t-butylamido hafnium dichloride, indenyl titanium tris (dimethylamide), indenyl titanium tri (Diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

The metallocene compound exhibits an action as a catalyst in the polymerization of various olefins by changing the kind of metal and the structure of the ligand and combining with a specific cocatalyst (co-catalyst).
Specifically, the polymerization is usually performed in a catalyst system in which methylaluminoxane (MAO), a boron-based compound or the like is added to these metallocene compounds as a cocatalyst. In addition, the use ratio of the cocatalyst with respect to the metallocene compound is preferably 10 to 1,000,000 mole times, and more preferably 50 to 5,000 mole times.
The method for polymerizing the polyethylene resin is not particularly limited, and examples thereof include a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, and a gas phase polymerization method. The polymerization temperature is usually from −100 ° C. to 300 ° C., and the polymerization pressure is usually from normal pressure to 100 kg / cm ² .

Since the metallocene compound has uniform properties of active sites and each active site has the same activity, the uniformity of the molecular weight, molecular weight distribution, composition, composition distribution, etc. of the polymer to be synthesized is increased. Therefore, the polyolefin resin polymerized using these metallocene compounds as a polymerization catalyst has a narrow molecular weight distribution, and in the case of a copolymer, the copolymer component is introduced in almost equal proportion to any molecular weight component. Have
Furthermore, examples of polyolefin resins other than polyethylene resins obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst include polyethylene resins and polypropylene resins.

  The polyethylene resin is not particularly limited as long as it is other than a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. For example, linear low density polyethylene, low density Examples thereof include polyethylene, medium density polyethylene, high density polyethylene, ethylene-α-olefin copolymer containing 50% by weight or more of ethylene, ethylene-vinyl acetate copolymer containing 50% by weight or more of ethylene, and the like. Or two or more of them may be used in combination. Examples of the α-olefin constituting the ethylene-α-olefin copolymer include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Can be mentioned.

  Examples of the polypropylene resin include polypropylene and propylene-α-olefin copolymers containing 50% by weight or more of propylene, and these may be used alone or in combination of two or more. Good. Examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Can be mentioned.

In addition, when the 25% compressive strength of the crosslinked polyolefin resin foamed sheet in accordance with JIS K6767 is large, the impact absorbability may be lowered. Therefore, 4.9 × 10 ⁴ Pa or less is preferable. Since the thickness uniformity may be inferior at the stage, 2 × 10 ⁴ to 4 × 10 ⁴ Pa is more preferable.
Furthermore, if the tensile strength at 23 ° C. in at least one direction of MD or CD in the cross-linked polyolefin resin foam sheet is small, the cross-linked polyolefin resin foam sheet may be cut during the bonding operation. × 10 ⁶ Pa or more is preferable, and if it is too large, the handleability may be lowered when the crosslinked polyolefin resin foam sheet is used as the base material of the shock absorbing tape, so 2.2 × 10 ⁶ to 8. 0 × 10 ⁶ Pa is more preferable.
In addition, the tensile strength in 23 degreeC in MD or CD of a crosslinked polyolefin-type resin foam sheet says what was measured based on JISK6767.

Next, a method for producing a crosslinked polyolefin resin foam sheet will be described. The method for producing the crosslinked polyolefin resin foam sheet is not particularly limited. For example,
A polyolefin resin containing 40% by weight or more of a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst and a thermally decomposable foaming agent are supplied to an extruder and melt kneaded. A process for producing a foamable polyolefin resin sheet by extruding the sheet from a sheet,
Crosslinking the foamable polyolefin resin sheet to a crosslinking degree of 5 to 60% by weight;
The obtained foamed resin sheet is melted or softened and stretched in either or both directions of MD or CD to stretch the foam sheet, and the foam aspect ratio (MD average cell diameter / CD A step of producing a crosslinked polyolefin resin foamed sheet having an average cell diameter) of 0.25 to 1 (preferably a cell aspect ratio (CD average cell diameter / VD average cell diameter) of 2 to 18). The method of containing is mentioned.

  And as a method of crosslinking the expandable polyolefin resin sheet, for example, a method of irradiating the expandable polyolefin resin sheet with ionizing radiation such as electron beam, α ray, β ray, γ ray, or the like, expandable polyolefin resin Examples include a method in which an organic peroxide is blended in advance in the composition, and the resulting foamable polyolefin resin sheet is heated to decompose the organic peroxide. These methods may be used in combination.

  The amount of the thermally decomposable foaming agent in the foamable polyolefin resin composition may be appropriately determined according to the expansion ratio of the cross-linked polyolefin resin foam sheet. On the other hand, it may not be possible to obtain a crosslinked polyolefin resin foam sheet having a desired expansion ratio. On the other hand, if it is large, the tensile strength and compression recovery of the resulting crosslinked polyolefin resin foam sheet may be reduced. The amount is preferably 1 to 40 parts by weight, more preferably 1 to 30 parts by weight, based on 100 parts by weight of the polyolefin resin.

  The foamable polyolefin-based resin composition includes, as necessary, an antioxidant, a foaming aid such as zinc oxide, a cell core modifier, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and a filler. Etc. may be added within a range not impairing the physical properties of the crosslinked polyolefin resin foam sheet.

  Examples of the organic peroxide include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis. (T-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α '-Bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t- Butylperoxy) hexyne-3, benzoyl peroxide, cumylperoxyneodecanate, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di ( Benzoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate and the like may be mentioned, and these may be used alone or in combination of two or more.

  When the amount of the organic peroxide added is small, the foamable polyolefin resin sheet may be insufficiently cross-linked. On the other hand, when the amount is large, the organic peroxide decomposition residue in the resulting cross-linked polyolefin resin foam sheet. May remain, so 0.01 to 5 parts by weight is preferable and 0.1 to 3 parts by weight is more preferable with respect to 100 parts by weight of the polyolefin resin.

  Further, the method for foaming the foamable polyolefin resin sheet is not particularly limited, and examples thereof include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, and a method using an oil bath. May be used in combination.

  The stretching of the foamed sheet may be performed after foaming the foamable polyolefin resin sheet to obtain the foamed sheet, or may be performed while foaming the foamable polyolefin resin sheet. In addition, after foaming a foamable polyolefin resin sheet to obtain a foamed sheet, when the foamed sheet is stretched, the foamed sheet is continuously stretched while the foamed sheet is maintained in a molten state without being cooled. Alternatively, after the foam sheet is cooled, the foam sheet may be heated again to be in a molten or softened state and then stretched.

Here, the molten state of the foamed sheet refers to a state in which the temperature of both surfaces of the foamed sheet is heated to the melting point of the polyolefin resin constituting the foamed sheet.
By stretching the foamed sheet, it is possible to produce a crosslinked polyolefin resin foamed sheet in which the foam sheet has an aspect ratio within a predetermined range by stretching and deforming the foamed cells in a predetermined direction.

  Furthermore, in the extending | stretching direction of a foam sheet, it is extended toward MD or CD of a long-shaped expandable polyolefin resin sheet, or toward MD and CD. In addition, when extending | stretching a foamable polyolefin resin sheet toward MD and CD, you may extend | stretch a foam sheet simultaneously toward MD and CD, and may extend | stretch separately for every one direction.

  As a method of stretching the foam sheet into MD, for example, while cooling the long foam sheet after foaming, rather than the speed (supply speed) at which the long foamable polyolefin resin sheet is supplied to the foaming process. The method of extending the foamed sheet to MD by increasing the winding speed (winding speed), and the speed of winding the foamed sheet (winding speed) rather than the speed of supplying the foamed sheet to the stretching process (supplying speed) Examples thereof include a method of stretching the foam sheet into MD by increasing the speed).

  In the former method, the expandable polyolefin resin sheet expands to MD by its own expansion. Therefore, when the foam sheet is stretched to MD, expansion to MD by expansion of the expandable polyolefin resin sheet. In consideration of the amount, it is necessary to adjust the sheet supply speed and the winding speed so that the foamed sheet is stretched to MD more than the expansion amount.

  Further, as a method of extending the foam sheet into the CD, the both ends of the CD of the foam sheet are gripped by a pair of grip members, and the foam sheet is moved by gradually moving the pair of grip members in directions away from each other. A method of stretching to CD is preferred. In addition, since the expandable polyolefin resin sheet expands to CD due to its own foaming, when the expanded sheet is stretched to CD, the expansion to CD due to expansion of the expandable polyolefin resin sheet is taken into consideration. Therefore, it is necessary to adjust so that the foamed sheet is stretched to the CD more than the expansion amount.

  Here, if the draw ratio in MD of the cross-linked polyolefin resin foam sheet is small, the flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may be reduced, while if large, the foam sheet is cut during the stretch. Or the foaming gas escapes from the foaming sheet being foamed, the expansion ratio of the resulting crosslinked polyolefin resin foam sheet is significantly reduced, and the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced. Since it may become non-uniform | heterogenous, 1.1-2.0 times are preferable and 1.2-1.5 times are more preferable.

In addition, the draw ratio in MD of a crosslinked polyolefin-type resin foam sheet is computed in the following way. That is, while obtaining the third root F of the expansion ratio of the crosslinked polyolefin resin foam sheet, the ratio (winding speed / supply speed) V between the winding speed and the supply speed is determined, and the crosslinked polyolefin resin foam is calculated based on the following formula. The draw ratio in the MD of the sheet can be calculated. However, the expansion ratio of the cross-linked polyolefin resin foam sheet is obtained by dividing the specific gravity of the expandable polyolefin resin sheet by the specific gravity of the cross-linked polyolefin resin foam sheet.
Stretch ratio (times) in MD of foam sheet = V / F

  Also, if the draw ratio of the crosslinked polyolefin resin foamed sheet in the CD is small, the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may be reduced. On the other hand, if the stretch ratio is large, the foamed sheet may be cut during stretching. Alternatively, the foaming gas escapes from the foam sheet being foamed, the foaming ratio of the resulting crosslinked polyolefin resin foam sheet is remarkably reduced, and the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced, resulting in poor quality. Since it may become uniform, 1.2 to 4.5 times are preferable, and 1.5 to 3.5 times are more preferable.

In addition, the draw ratio of CD in the crosslinked polyolefin resin foamed sheet is the length of CD of the crosslinked polyolefin resin foamed sheet obtained by heating and foaming the expandable polyolefin resin sheet without stretching the MD and CD. The length of CD of the crosslinked polyolefin-based resin foam sheet stretched to CD is W2, and can be calculated based on the following formula.
Stretch ratio (times) of CD of foam sheet = W2 / W1

(Thickness)
The thickness of the base material layer composed of the crosslinked polyolefin resin foam sheet is not particularly limited, but if it is thin, the flexibility and tensile strength of the crosslinked polyolefin resin foam sheet are reduced, and the resulting impact absorption is obtained. While the impact absorbability, texture, mechanical strength, etc. of the tape are reduced, even if the thickness is increased, the performance of the impact-absorbing tape cannot be expected and the economy is reduced. Therefore, 0.1 to 3 mm is preferable.

(Acrylic adhesive)
The acrylic polymer used for the acrylic pressure-sensitive adhesive is not particularly limited, but a (meth) acrylic acid ester monomer homopolymer, a (meth) acrylic acid ester monomer, and other monomers copolymerizable therewith. And a copolymer is preferable. In addition, (meth) acrylic acid means methacrylic acid or acrylic acid.

The (meth) acrylic acid ester monomer is not particularly limited. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylic Examples include n-butyl acid, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, and (meth) acrylic acid alkyl esters are preferred. Further, (meth) acrylic acid alkyl ester having 4 or more carbon atoms in the alkyl group is more preferable, and (meth) acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group is particularly preferable.
Examples of monomers copolymerizable with (meth) acrylic acid esters include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid and maleic anhydride; 2-hydroxyethyl (meth) acrylate And hydroxyl group-containing monomers such as n-methylolacrylamide; epoxy group-containing monomers such as glycidyl acrylate and allyl glycidyl ether, and acrylic acid and methacrylic acid are preferred.

  The acrylic polymer is preferably a copolymer obtained by polymerizing a monomer containing (meth) acrylic acid and a (meth) acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group. More preferred is a copolymer obtained by polymerizing a monomer containing 50% by weight or more of acrylic acid and (meth) acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group as a total amount. A copolymer obtained by polymerizing an acid and a monomer containing 50 to 100% by weight of a total amount of an alkyl (meth) acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group is particularly preferable.

When the weight average molecular weight of the acrylic polymer is small, the fluidity is good and the initial tack is excellent, but the cohesive force is small, the heat resistance is lowered, and adhesive residue may be generated. Although it has excellent heat resistance, the fluidity is poor and the initial tack may be small, so 300,000 to 800,000 are preferable.
In addition, the weight average molecular weight of an acrylic polymer means what was measured as a polystyrene conversion molecular weight by GPC (Gel Permeation Chromatography: Gel permeation chromatography) method.
Specifically, the weight average molecular weight of the acrylic polymer is determined by filtering a diluted solution obtained by diluting the acrylic polymer with tetrahydrofuran (THF) 50 times with a filter, and based on the obtained filtrate. It can be obtained by measuring the polystyrene equivalent molecular weight of the polymer based on gel permeation chromatography. As said gel permeation chromatograph, what is marketed with the brand name "2690 Separations Model" from Water company etc. can be used, for example.

  The acrylic polymer is produced by polymerizing a monomer in a general manner in the presence of a polymerization initiator, but such a polymerization initiator is not particularly limited, for example, peroxide polymerization. Examples thereof include an initiator and an azo polymerization initiator, and those having a 10-hour half-life temperature of 80 ° C. or less are preferred so that the polymerization initiator and its residue do not remain in the resulting acrylic pressure-sensitive adhesive. In addition, a polymerization initiator may be used independently or may use 2 or more types together.

Furthermore, in producing an acrylic polymer by polymerization, in particular, the polymerization initiator has a 10-hour half-life temperature of 80 ° C. or less so that the polymerization initiator and its residue do not remain in the reaction solution as volatile components. It is preferable to select a certain one and set the polymerization temperature to be higher than the 10-hour half-life temperature of the polymerization initiator, and to perform polymerization for as long as possible. Furthermore, in order to reduce the polymerization initiator remaining in the reaction solution after polymerization and allow the polymerization reaction to proceed rapidly and completely, the polymerization temperature T at the end of the polymerization is adjusted to satisfy the following formula (3), It is preferable to maintain this polymerization temperature T for a long time.
t _1/2 + 5 ≦ T ≦ t _1/2 +25 (3)
(T _1/2 : 10-hour half-life temperature of the polymerization initiator)

  Further, it is preferable that the acrylic polymer has less residual monomer, residual polymerization initiator and other impurities, and the residual monomer, residual polymerization initiator and other impurities are removed as necessary during or after the polymerization. It is preferable to reduce.

  As a method of reducing the residual monomer in the reaction solution at the time of polymerization, for example, a method of replacing the reflux solution of the reaction solution with a new solvent; when the polymerization rate becomes 95% or more, preferably 98% or more, vinyl acetate A method of adding a relatively low boiling point scavenger monomer such as vinyl butyl ether, methyl acrylate and styrene, reacting the remaining monomer with the scavenger monomer, and removing the remaining monomer together with the scavenger monomer; Examples thereof include a method of washing an acrylic pressure-sensitive adhesive using a poor solvent for the pressure-sensitive adhesive, for example, a low boiling point solvent such as methanol, ethanol, n-hexane, and n-heptane.

(Tackifying resin)
The acrylic pressure-sensitive adhesive contains a tackifying resin for the purpose of improving the physical properties of the pressure-sensitive adhesive. Examples of such tackifying resins include rosin ester compounds such as polymerized rosin esters, hydrogenated rosin ester resins, and disproportionated rosin ester resins, rosin resins, polymerized rosin resins, hydrogenated rosin resins, and rosin-modified phenols. Resins, terpene phenol resins, coumarone indene resins, alkylphenol resins, petroleum resins, etc., and low molecular weight components can be removed, so rosin ester compounds, rosin resins, polymerized rosin resins, petroleum resins are preferred, A rosin ester compound is more preferable.
The tackifying resin has a content of volatile components having a weight average molecular weight of 600 or less of 13% by weight or less. By using such a tackifier, volatile components produced by the tackifier can be kept low without impairing the physical properties of the tack, and it is possible to obtain an acrylic pressure-sensitive adhesive with improved tack properties and reduced odor. it can. In addition, the weight average molecular weight of the said tackifier and its content can be measured by GPC, and can be calculated by a polystyrene conversion value and an area ratio.

  Examples of a method for removing a volatile component having a weight average molecular weight of 600 or less from the tackifying resin include a method in which the tackifying resin is heated and melted above the softening point, and a method in which water vapor is blown.

  When the tackifying resin is heated and melted, it is preferably heated in an inert gas such as nitrogen or helium in order to prevent an oxidation reaction with oxygen in the air, and the heating time is a tackifier by heating. In order to avoid decomposition of 1 to 5 hours is preferable.

  When steam is blown, the volatile components can be effectively reduced by blowing the steam after the pressure-reducing pressure of the tackifier resin is reduced to 1 to 50 kPa. As the time for blowing water vapor, if the time is short, the volatile component may not be reduced. On the other hand, if it is long, there is no difference in the effect of reducing the volatile component.

Moreover, it is preferable that the softening point of tackifying resin is 130 degreeC or more. 135-150 degreeC is more preferable. If the softening point is less than 130 ° C., the heat resistance of the entire acrylic pressure-sensitive adhesive cannot be sufficiently obtained, and there is a possibility that the adhesiveness may be lowered due to heat generation of the entire apparatus using the shock absorbing tape. is there. In addition, the softening point of tackifying resin means what was measured based on the ring and ball method of JISK2871.
When the addition amount of the tackifying resin is large, it may cause a volatile component. When the addition amount is small, the effect of adding the tackifying resin may not be manifested. Therefore, the amount is 1 for 100 parts by weight of the acrylic polymer. ~ 50 parts by weight. Preferably it is 1-30 weight part. More preferably, it is 1 to 25 parts by weight.

  Furthermore, you may add additives, such as a crosslinking agent, a plasticizer, an emulsifier, a softening agent, a filler, a pigment, and dye, to an acrylic adhesive. In addition, it is preferable that these additives also remove volatile components as much as possible.

  The crosslinking agent is not particularly limited, and examples thereof include an isocyanate crosslinking agent, an aziridine crosslinking agent, an epoxy crosslinking agent, and a metal chelate crosslinking agent. Further, the acrylic pressure-sensitive adhesive may contain a heat conductive filler such as alumina, boron nitride, aluminum nitride, silicon nitride, silicon carbide, magnesium oxide, silica, magnesia, ceramic powder and the like.

  By adding a thermally conductive filler in the adhesive layer, the thermal conductivity of the shock absorbing tape can be improved. Therefore, the heat of the heater can be smoothly transferred to the storage space to efficiently heat the object to be heated. be able to.

  If the thickness of the pressure-sensitive adhesive layer is thin, the tackiness of the shock-absorbing tape may be lowered. If the space is formed, outgas may be a problem, so 10 to 150 μm is preferable. More preferably, it is 20-100 micrometers, More preferably, it is 30-60 micrometers.

(Tape VOC)
When the shock absorbing tape of the present invention is heated at 90 ° C. for 30 minutes, the concentration of the volatile component calculated by the following formula (1) is less than 500 ppm. Thus, when the volatile component concentration is less than 500 ppm, it can be evaluated that the amount of volatile components generated from the adhesive tape is dramatically small, and adverse effects on electronic components can be prevented. Moreover, it becomes very excellent in adhesiveness with the base material mentioned above. Thus, when the concentration of the volatile component is less than 500 ppm, it can be evaluated that the amount of the volatile component generated from the shock absorbing tape is dramatically small, and adverse effects on the electronic component can be prevented.
Volatile component concentration (ppm)
= Volatile component weight X (μg) / Shock absorbing tape weight before heating (g) Formula (1)
(However, in formula (1), the volatile component weight X represents the weight in terms of hexadecane.)

  The volatile component weight X is measured by concentrating the weight of the volatile component released when the shock absorbing tape is heated at 90 ° C. for 30 minutes using a thermal desorption device and using a GC-MS device. Can do. The volatile component concentration can be calculated by dividing the measured volatile component weight X by the weight of the shock absorbing tape.

Specifically, as a method of measuring the volatile component concentration, specifically, an acrylic pressure-sensitive adhesive constituting the shock absorbing tape is prepared, and about 20 mg of this acrylic pressure-sensitive adhesive is added to a sample tube (inner diameter: about 5 mm, length: about 10 cm) and heating and holding at 90 ° C., helium gas was allowed to flow through the sample tube at a flow rate of 1.5 ml / min for 30 minutes to heat the volatile components. After collecting and concentrating in a trap tube built in the desorption device, the trap tube is heated at 280 ° C. for 10 minutes and supplied to the GC-MS device.
In the GC-MS apparatus, a nonpolar capillary column (trade name “HP-1” manufactured by Agilent Technologies, 0.32 mm × 60 m × 0.25 μm) was used, and the temperature of the capillary column was 40 ° C. for 4 minutes. After the maintenance, the capillary column is heated to 100 ° C. at a heating rate of 5 ° C. per minute, and then the capillary column is heated to 320 ° C. at a heating rate of 10 ° C. per minute, and then at 320 ° C. Hold for 3 minutes. The MS measurement range is 30 to 400 amu, the helium flow rate is 1.5 ml / min, the ionization voltage is 70 eV, the ion source is 230 ° C., the interface is 250 ° C., and the transfer line is 225 ° C. The weight of the volatile component can be calculated by converting the obtained peak area by weight based on an absolute calibration curve created with n-hexadecane.

Then, the weight of the measured volatile component is proportionally converted to the weight of the acrylic pressure-sensitive adhesive constituting the shock absorbing tape to be measured, and the proportionally converted volatile component weight X is calculated by the weight of the shock absorbing tape. The concentration of the volatile component can be calculated by dividing.
The thermal desorption device is commercially available, for example, from Perkin Elmer under the trade name “ATD-400”, and the GC-MS device is commercially available, for example, from JEOL under the trade name “Automass II-15”. ing.

  Such a pressure-sensitive adhesive can reduce low molecular weight components such as residual monomers as much as possible, adjust the weight average molecular weight of the acrylic copolymer to a certain range, or adjust the softening point of the tackifier resin described later. Is achievable.

(Shock absorbing tape manufacturing method)
Examples of the method for producing the shock absorbing tape of the present invention include a method in which an acrylic pressure-sensitive adhesive is applied to at least one surface of a substrate made of a crosslinked polyolefin-based resin foam sheet, and an acrylic pressure-sensitive adhesive layer is laminated and integrated.
Examples of the method of laminating and integrating the pressure-sensitive adhesive layers by coating include, for example, a method of applying an acrylic pressure-sensitive adhesive using at least one surface of a cross-linked polyolefin resin foam sheet using a coating machine such as a coater, Examples thereof include a method of spraying and applying an acrylic pressure-sensitive adhesive using a spray on at least one surface, and a method of applying an acrylic pressure-sensitive adhesive using a brush on at least one surface of a cross-linked polyolefin resin foam sheet.

(Use)
The use of the shock absorbing tape of the present invention is not particularly limited, and can be used for fixing electronic components inside various electronic device packages. Specifically, if the electronic device is a digital camera, a portable game machine, a personal computer, it can be applied to a microphone, speaker, flash, finder, motor, LED display device, speaker, key cushion, battery cushion, and the like.
Above all, because it has very good shock absorption and water-stopping properties and very low volatility, it has closed small portable electronic devices such as digital cameras, portable game machines, mobile phones, and notebook computers. It can be preferably used inside.

  Since the shock absorbing tape according to the present invention is configured as described above, it has a thin shock-absorbing property and water-stopping property while being thin, and the amount of volatile matter can be suppressed to a very small amount, so that it has a narrow internal space. But volatile components do not adversely affect electronic components. Therefore, it exhibits excellent effects for electronic devices.

  Examples of the present invention will be described in detail below, but the present invention is not limited to the following examples.

Example 1
(Preparation of acrylic polymer)
In a reactor equipped with a thermometer, a stirrer, a cooling tube, a dropping funnel, and a nitrogen gas introduction tube, 70 parts by weight of n-butyl acrylate, 27 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, 2-hydroxyethyl methacrylate 0 A monomer mixture consisting of 0.1 part by weight and 0.05 part by weight of dodecanethiol and 80 parts by weight of ethyl acetate were supplied and stirred to dissolve the monomer mixture in ethyl acetate to prepare a monomer mixture solution.

At the reflux point, 4 mmol of lauroyl peroxide (10-hour half-life temperature: 62 ° C.) as a polymerization initiator was added to the monomer mixture solution over a period of 4 to 4 hours to polymerize the monomer.
After 4 hours, 4 mmol of a polymerization initiator was further added over 4 to 6 hours, followed by polymerization for 10 hours. Thereafter, 5 g of vinyl acetate monomer was added to obtain an acrylic polymer.

  To 100 parts by weight of the obtained acrylic polymer (solid), 1.6 parts by weight of an isocyanate-based crosslinking agent (trade name “Coronate L”, active ingredient: 55% by weight, manufactured by Nippon Polyurethane Co., Ltd.) and weight as a tackifier resin An acrylic pressure-sensitive adhesive A was obtained by adding and stirring 25 parts by weight of a rosin ester compound having an average molecular weight of 600 or less and a volatile component of 9.4% by weight.

(Production of expandable polyolefin resin sheet)
Linear low-density polyethylene obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (Exxon Chemical Co., Ltd., trade name “EXACT3027”, density: 0.900 g / cm 3, weight average molecular weight: 2 0.0, melting point: 98 ° C., softening point: 85 ° C.) 100 parts by weight, azodicarbonamide 5 parts by weight, 2,6-di-t-butyl-p-cresol 0.3 part by weight and zinc oxide 1 part by weight The resulting expandable polyolefin resin composition was supplied to an extruder, melted and kneaded at 130 ° C., and extruded into a long expandable polyolefin resin sheet having a width of 200 mm and a thickness of 0.8 mm.

Next, the foamable polyolefin resin sheet is cross-linked by irradiating an electron beam with an acceleration voltage of 800 kV for 5 Mrad on both surfaces of the long foamable polyolefin resin sheet, and then the foamable polyolefin resin sheet is heated with hot air and infrared rays. The mixture was continuously fed into a foaming furnace maintained at 250 ° C. by a heater to be heated and foamed.
Thereafter, after continuously feeding the obtained foamed sheet from the foaming furnace, the foamed sheet is stretched to the CD in a state where the temperature of the both surfaces is maintained at 200 to 250 ° C. The foamed sheet is stretched to MD by winding the foamed sheet at a winding speed higher than the feeding speed (feeding speed) of the foamable polyolefin resin sheet to the foaming furnace, and the foamed cells are expanded into CD and MD. To obtain a crosslinked polyolefin resin foamed sheet A having a width of 1050 mm, a thickness of 0.1 mm, a crosslinking degree of 25% by weight and an expansion ratio of 4.7 times.

(Production of shock absorbing tape)
The acrylic pressure-sensitive adhesive A is applied to both surfaces of the cross-linked polyolefin resin foam sheet A to be a base material layer so that the thickness is 50 μm after drying, and is dried at 105 ° C. for 5 minutes. A shock-absorbing tape A in which a 50 μm-thick pressure-sensitive adhesive layer made of an acrylic pressure-sensitive adhesive A was laminated and integrated was prepared.

(Example 2)
A crosslinked polyolefin resin foam sheet B was prepared in the same manner as in Example 1 except that the thickness of the crosslinked polyolefin resin foam sheet was adjusted to 0.2 mm by adjusting the winding speed. Was made.

(Comparative Example 1)
An impact absorbing tape C was prepared in the same manner as in Example 1 except that instead of the crosslinked polyolefin-based resin foam sheet A, polyurethane foam C (“Polon SR” manufactured by Inoac, thickness 0.2 mm) was used.

(Comparative Example 2)
Acrylic adhesive B using a rosin ester compound (content of volatile component having a weight average molecular weight of 600 or less, 15.6% by weight) that did not remove a volatile component having a weight average molecular weight of 600 or less as a tackifier resin An impact absorbing tape D was produced in the same manner as in Example 1 except that the adhesive layer was formed.

For each of the impact absorbing tapes A to D obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the aspect ratio of the cross-linked polyolefin resin foam sheet (average cell diameter of MD / average cell diameter of CD), 25 % Compressive strength, waterstop, shock absorption, VOC, and cloudiness were examined, and the results are shown in Table 1.
In addition, about the 25% compressive strength, water-stopping property, shock absorption property, VOC, and cloudiness, it evaluated by the following evaluation methods.

(Evaluation methods)
[25% compressive strength]
A 25% compressive strength in accordance with JIS K6767 was determined.

[Waterproof evaluation]
Two acrylic plates of 150 mm × 150 mm × 5 mm were prepared. One acrylic plate was provided with a hole having a diameter of 7 mm. The impact absorbing tapes A to D were cut into donuts having an outer diameter of 60 mm and an inner diameter of 50 mm, respectively, to obtain sample pieces. This donut-shaped sample piece was attached so as to surround the hole of one acrylic plate, and then the other acrylic plate was attached so that the compressibility of the base material was 20%.
Thereafter, a hose was attached to the hole, water was injected at 10 kPa, water was filled in the portion corresponding to the inner diameter of the donut, and water leakage was evaluated in accordance with JISC0920 IPX7 while applying a pressure of 10 KPa.

(Shock absorption)
Two iron plates having a thickness of 2 mm and 100 mm × 100 mm were prepared. An impact pickup device was attached to one iron plate and used as a lower iron plate. At the center of this lower iron plate, the shock absorbing tapes produced in Examples and Comparative Examples cut into 50 mm × 50 mm were mounted, and the other iron plate was attached via this (compression of the base material layer) The rate was 40%).
Next, an iron ball having a weight of 15 g was prepared. The sphere was allowed to fall naturally from a distance of 10 cm perpendicular to the center shell of the iron plate.
The impact acceleration was measured with an impact pickup device, and the average of the absolute values of the positive and negative maximum values was taken as impact conductivity 1.
As a reference evaluation, the impact conductivity 2 when the iron ball was dropped only on the iron plate was measured, and this was taken as 100, and the impact conductivity 1 when the impact absorbing tape was interposed was evaluated.
((Impact conductivity 1 / Impact conductivity 2) x 100)

(Measurement of volatile component concentration)
About the obtained impact-absorbing tape, the volatile component density | concentration calculated by above-mentioned Formula (1) was measured in the above-mentioned way. Measurement was performed at 90 ° C. for the purpose of promoting the volatilization of volatile components.

[Evaluation of cloudy]
About 20 g of shock absorbing tape was put into a glass bottle with an internal volume of 100 ml, covered with a glass plate, heated at 120 ° C. for 24 hours, and the change of the glass plate was visually evaluated. The evaluation criteria are as follows.
○: No change.
Δ: There is a slight amount of cloudiness.
X: There is cloudiness that can be clearly confirmed.

  From Table 1 above, it can be seen that the impact-absorbing tape of the present invention is excellent in water-stopping and impact properties, and can suppress the occurrence of VOCs.

Claims (4)

An acrylic pressure-sensitive adhesive layer is laminated and integrated on at least one side of a base material layer, and is an impact absorbing tape for absorbing an impact while fixing an electronic component in a package,
The base material layer is a crosslinked polyolefin resin foam sheet having a degree of crosslinking of 5 to 60% by weight and a bubble aspect ratio (MD average cell diameter / CD average cell diameter) of 0.25 to 1. ,
The acrylic pressure-sensitive adhesive layer contains 1 to 50 parts by weight of a tackifier resin in which the content of a component having a weight average molecular weight of 600 or less is 13% or less with respect to 100 parts by weight of an acrylic polymer. It is characterized by consisting of
Shock absorbing tape. It has an acrylic pressure-sensitive adhesive layer on at least one side of the base material layer, and when heated at 90 ° C. for 30 minutes, the volatile component concentration calculated by the formula (1) is less than 500 ppm. The shock absorbing tape according to claim 1.
Volatile component concentration (ppm)
= Volatile component weight X (μg) / Shock absorbing tape weight before heating (g) Formula (1)
(However, in formula (1), the volatile component weight X represents the weight in terms of hexadecane.)   The acrylic polymer is copolymerized by selecting a polymerization initiator having a 10-hour half-life temperature of 80 ° C. or lower and a polymerization temperature higher than the 10-hour half-life temperature of the polymerization initiator. The shock absorbing tape according to claim 1, wherein the shock absorbing tape is provided.   The thickness of the said crosslinked polyolefin-type resin foam sheet is 0.1-3 mm, The thickness of the said acrylic adhesive layer is 10-150 micrometers, The thickness in any one of Claims 1-3 characterized by the above-mentioned. Shock absorbing tape.