JP2010013592A - Adhesive sheet for assembling outside mirror - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive sheet for assembling an outside mirror, which is excellent in adhesiveness between a base material layer and an adhesive layer, has satisfactory shock absorptivity and water stoppability though the adhesive sheet is thin and which can keep the adhesiveness, shock absorptivity and water stoppability even at high temperature and even in a temperature-changeable environment. <P>SOLUTION: The adhesive sheet for assembling the outside mirror is formed by laminating an acrylic adhesive layer on both surfaces of the base material layer and integrating them with one another and is interposed between a mirror or a mirror laminate which is housed in a housing part of a mirror holder, and the inner wall surface of the housing part to fix the mirror or the mirror laminate to the mirror holder. The base material layer is a cross-linked polyolefin resin foam sheet having 5-60 wt.% cross-linking degree and air bubbles of 0.25-1 aspect ratio in the sheet facial direction. The acrylic adhesive layer comprises an acrylic adhesive containing 100 parts weight acrylic polymer and 1-30 parts weight adhesiveness imparting resin having ≥130°C softening point. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an adhesive sheet for assembling an outside mirror.

As an outside mirror, that is, a door mirror for mounting outside a vehicle, a fender mirror, a mirror laminate composed of a mirror substrate and a surface heating element provided on the back surface of the mirror substrate, a mixture foam of EPDM and butyl, There has been proposed a mirror in which acrylic foam or urethane foam is fixed to a mirror holder via an adhesive tape using a tape base material (see Patent Document 1).
That is, since such a mirror has a surface heating element on the back surface of the mirror substrate, when the mirror surface of the mirror substrate becomes clouded with water droplets or snow due to condensation, the surface heating element generates heat, thereby It can be evaporated.

  Further, as shown in FIG. 1, the conventional outside mirror includes a mirror laminate 1 including a mirror substrate and a surface heating element fixed to a mirror holder 2a via an adhesive tape 3, and a mirror of the laminate 1 Intrusion of rainwater or the like into the mirror holder 2a is prevented by receiving the periphery of the substrate in a watertight manner by the hook-shaped locking portion 21 provided in the mirror holder 2a (see FIG. 2 of Patent Document 1).

  On the other hand, in recent years, demands for weight reduction of automobile members have been increasing year by year, and for this reason, there is an increasing demand for weight reduction in mirror holders. As one means for responding to such a request, as shown in FIG. 2, the mirror holder 2b is not provided with the hook-like locking portion 21, but is a recess 22 serving as a housing portion having a substantially cross-sectional shape of the mirror laminated body 1. It is conceivable to have a simple cross-sectional shape including only However, when the mirror holder 2b is used and the mirror laminate 1 is fixed to the inner wall surface of the recess 22 using a conventionally known adhesive or adhesive tape 3 or the like, the adhesive or adhesive tape 3 may be affected by an impact such as vibration. Due to peeling or repeated exposure to changes in the outside air temperature, the adhesive force of the adhesive tape 3 becomes insufficient and easily peels off, or the water-stopping property becomes insufficient and moisture accumulates in the recesses 22 of the mirror holder 2b. There is a risk that a defect may be caused, or a fault such as a short circuit may occur in the electric circuit inside the mirror holder 2b.

Japanese Unexamined Patent Publication No. 9-048329

  In view of the above circumstances, the present invention is excellent in adhesion between the base material layer and the pressure-sensitive adhesive layer, is thin and lightweight, has sufficient shock absorption and water-stopping properties, and also under high temperatures and temperature change environments. An object of the present invention is to provide a pressure-sensitive adhesive sheet for assembling an outside mirror that can maintain these physical properties.

  In order to achieve the above object, as a result of intensive studies, the present inventors have used a specific resin foam sheet as a base material layer, and by using an acrylic pressure-sensitive adhesive having a specific composition for the pressure-sensitive adhesive layer, thereby reducing the thickness. Even so, it was found that an adhesive sheet for assembling an outside mirror that has excellent shock absorption and water-stopping properties and that does not impair their physical properties even at high temperatures was obtained, and the present invention was completed.

That is, the pressure-sensitive adhesive sheet for assembling the outside mirror according to the present invention has an acrylic pressure-sensitive adhesive layer laminated and integrated on both surfaces of the base material layer, and a mirror or a mirror laminate that is accommodated in the accommodating portion of the mirror holder; An adhesive sheet for assembling an outside mirror that is interposed between the inner wall surface of the housing portion and fixes a mirror or a mirror laminate to a mirror holder, and the base material layer has a crosslinking degree of 5 to 60% by weight. And a cross-linked polyolefin resin foam sheet having a sheet surface direction aspect ratio of 0.25 to 1, and the acrylic pressure-sensitive adhesive layer has a softening point of 130 ° C. with respect to 100 parts by weight of the acrylic polymer. It consists of the acrylic adhesive which contains 1-30 weight part of tackifying resin which is the above.
The present invention will be described in detail below.

(Polyolefin foamed resin sheet)
The pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention has a degree of cross-linking of 5 to 60% by weight and an air bubble sheet surface aspect ratio (MD average bubble diameter / CD average bubble diameter) of 0.25 to 1. It has a base material layer made of a certain crosslinked polyolefin resin foam sheet.
By using such a cross-linked polyolefin-based foamed resin sheet as a base material layer, the pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention has extremely excellent impact absorbability even when it is thin, and has a water-stopping property. Will also be excellent.

  That is, if the cross-linking degree of the cross-linked polyolefin resin foam sheet is too small, when the foam sheet is stretched, bubbles in the vicinity of the surface of the foam sheet break up, resulting in surface roughness and sufficient adhesion with the pressure-sensitive adhesive layer. When 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 foams when heated and foamed. The cross-linked polyolefin resin foam sheet having a desired expansion ratio cannot be obtained, and as a result, the impact absorbability is inferior. Therefore, the amount is limited to 5 to 60% by weight, and 10 to 40% by weight. preferable.

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)

  Further, the crosslinked polyolefin-based resin foam sheet has a ratio of an average cell diameter of MD and an average cell diameter of CD, that is, an aspect ratio of cells in the sheet surface direction (average cell diameter of MD / average cell diameter of CD). If it is too small, the expansion ratio will decrease and the flexibility may decrease, or the thickness, flexibility and tensile strength of the crosslinked polyolefin resin foam sheet may vary. Since the softness | flexibility of a sheet | seat falls, it is limited to 0.25-1 and 0.25-0.60 is preferable.

Further, the ratio of the average cell diameter of CD and the average cell diameter of VD in the crosslinked polyolefin resin foam sheet, that is, the aspect ratio of the cell thickness direction (average cell diameter of CD / average cell diameter of VD) is 2 to 2. 18 is preferable, and 2.5 to 15 is more preferable.
That is, if the aspect ratio in the sheet thickness direction is too small, the flexibility of the crosslinked polyolefin resin foamed sheet is reduced. On the other hand, if it is too large, the expansion ratio is reduced and the flexibility is reduced, or the crosslinked polyolefin resin foam is reduced. There is a risk of variations in sheet thickness, flexibility and tensile strength.

  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 magnified 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. 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 (number)

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 cross-linked 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 bubbles 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 taking a photograph of the cut surface of the cross-linked polyolefin resin foam sheet, coloring the cut surface 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 by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and is 50% by weight. The above is more preferable, 60% by weight or more is further preferable, and 100% by weight is particularly preferable.
That is, by using a polyolefin resin containing 40% by weight or more of a polyethylene resin obtained using the metallocene compound, the polyolefin resin is given flexibility without increasing the adhesiveness, and is crosslinked. The aspect ratio of the bubbles of the polyolefin resin foam sheet is within a predetermined range, the mechanical strength is improved, and the flexibility is excellent.

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.
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 it may be inferior to thickness uniformity in a step, 2 * 10 < ⁴ > -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 crosslinked polyolefin resin foam sheet is too small, the crosslinked polyolefin resin foam sheet may be cut during the bonding operation. 96 × 10 ⁶ Pa or more is preferable, and if it is too large, the handleability may be reduced when the crosslinked polyolefin-based resin foam sheet is used as the base material layer for the outside mirror assembly pressure-sensitive adhesive sheet. × 10 ⁶ ~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 using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. Supplying a resin and a pyrolytic foaming agent to an extruder, melt-kneading, and extruding the foamable polyolefin resin sheet into a sheet from the extruder; A step of crosslinking to a crosslinking degree of 60% by weight, and 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 bubbles. Sheet surface direction aspect ratio (MD average bubble diameter / CD average bubble diameter) is 0.25 to 1 (preferably more sheet thickness of bubbles) And a method comprising the step of producing 2 to 18) in a crosslinked polyolefin-based resin foam sheet (an average cell diameter of the average cell diameter / VD of CD) direction aspect ratio.

  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 foaming ratio of the crosslinked polyolefin resin foam sheet, but if it is too small, the foaming of the foamable polyolefin resin sheet However, if the amount is too large, the tensile strength and compression recovery of the resulting crosslinked polyolefin resin foam sheet may be reduced. Therefore, 1-40 weight part is preferable with respect to 100 weight part of polyolefin resin, and 1-30 weight part is more preferable.

  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.

  If the amount of the organic peroxide added is too small, crosslinking of the expandable polyolefin resin sheet may be insufficient. On the other hand, if it is excessive, the amount of organic peroxide contained in the resulting crosslinked polyolefin resin foam sheet will be insufficient. Since decomposition residues may remain, 0.01 to 5 parts by weight is preferable with respect to 100 parts by weight of polyolefin resin, and 0.1 to 3 parts by weight is more preferable.

  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 without cooling the foamed sheet while maintaining the molten state at the time of foaming. 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.

  In addition, 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 gripping members, and the foam sheet is moved by gradually moving the pair of gripping members 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 too small, the flexibility and tensile strength of the cross-linked polyolefin resin foam sheet may decrease, while if large, the foam sheet is cut during the stretch. Or the foaming gas escapes from the foaming sheet during foaming, the foaming 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. May become non-uniform, 1.1 to 2.0 times is preferable, and 1.2 to 1.5 times is 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 made 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 obtained outside is obtained. While the impact-absorbing property, texture, mechanical strength, etc. of the pressure-sensitive adhesive sheet for mirror assembly are reduced, the improvement of the performance of the pressure-sensitive adhesive sheet for assembling the outside mirror cannot be expected even if the thickness is increased. 1-3 mm is preferable.

(Acrylic adhesive layer)
The pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention is an acrylic pressure-sensitive adhesive layer containing 1 to 30 parts by weight of a tackifying resin having a softening point of 130 ° C. or higher with respect to 100 parts by weight of the acrylic pressure-sensitive adhesive layer. It is necessary to consist of an agent. That is, when a tackifying resin having a softening point of less than 130 ° C. is blended, the heat resistance of the pressure-sensitive adhesive layer is inferior. For example, when a temperature cycle test is performed, the pressure-sensitive adhesive force is insufficient or the pressure-sensitive adhesive layer is There is a case where it accumulates. If the adhesive force is insufficient or the adhesive layer sags, gaps may be formed between the adherends. As a result, the impact absorption will be significantly inferior when the temperature cycle is applied. Aqueous properties may be significantly reduced. The softening point is preferably 135 to 150 ° C.
In addition, the softening point of tackifying resin means what was measured based on the ring and ball method of JISK2871.

Moreover, if the addition amount of the tackifying resin is too large, the pressure-sensitive adhesive layer becomes hard, and distortion caused by a difference in shrinkage ratio between the mirror holder of the outside mirror and the mirror or mirror laminated body due to temperature change. In some cases, the mirror holder cannot be relaxed or cannot follow the physical distortion of the mirror holder, and a gap may be formed between the inner wall surface of the receiving portion of the mirror holder and the mirror or the mirror laminated body due to long-term use. If a gap is formed in this way, the impact absorbability is remarkably inferior or the water stoppage is remarkably lowered. If the amount is too small, the adhesive strength may be insufficient.
For this reason, tackifying resin is limited to 1-30 weight part with respect to 100 weight part of acrylic polymers, Preferably it is 5-30 weight part, Especially preferably, it is 10-20 weight part.

Examples of the tackifying resin 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, rosin-modified phenol resins, Examples include terpene phenol resins, coumarone indene resins, alkylphenol resins, and petroleum resins. Among these, rosin ester compounds, rosin resins, polymerized rosin resins, and petroleum resins are preferable because low molecular weight components can be removed, and rosin ester compounds are more preferable.
The tackifying resin preferably has a content of volatile components having a weight average molecular weight of 600 or less and 13% by weight or less. By using such a tackifying resin, it is possible to reduce the volatile components generated by the tackifying resin without impairing the physical properties of the tack, and to obtain an acrylic pressure-sensitive adhesive that improves the tack physical properties and suppresses outgas generation as much as possible. be able to. And the adhesiveness with a base material layer can be improved and, as a result, a tape with higher water stopping property can be obtained. In addition, the weight average molecular weight of the said tackifying resin 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 the tackifying resin 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.

  The acrylic polymer used for the acrylic pressure-sensitive adhesive is not particularly limited, but is a homopolymer of a (meth) acrylic acid ester monomer, a (meth) acrylic acid ester monomer, and other copolymerizable with this. A copolymer with a monomer is mentioned, 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. (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 the 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 (1). The polymerization temperature T is preferably maintained for a long time.
t _1/2 + 5 ≦ T ≦ t _1/2 +25 (1)
(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 removing a residual monomer together with a scavenger monomer by adding a relatively low boiling point scavenger monomer such as vinyl butyl ether, methyl acrylate, styrene, etc., and reacting the residual monomer 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.

  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.

  Moreover, it is preferable to add a heat conductive filler to an acrylic adhesive. In other words, the heat conductivity of the adhesive sheet for assembling the outside mirror is improved by the heat conductive filler, and when the mirror and the sheet heating element are laminated, the heat of the sheet heating element is smoothly transferred to the storage space. The visibility of the mirror can be made uniform.

  And if the thickness of the pressure-sensitive adhesive layer is too thin, the pressure-sensitive adhesive sheet for assembling the outside mirror may deteriorate, and if it is too thick, the processability of the tape may be inferior. When a closed space is formed by using the side mirror assembling pressure-sensitive adhesive sheet, outgas may be a problem, so 10 to 150 μm is preferable, 20 to 100 μm is more preferable, and 30 to 60 μm is still more preferable. .

(Tape VOC)
When the pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention is heated at 90 ° C. for 30 minutes, the volatile component concentration calculated by the following formula (2) is preferably less than 500 ppm. That is, 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 problems such as dew condensation in the mirror and peeling of the adhesive sheet due to the volatile components are eliminated. Can be prevented. Moreover, it becomes very excellent in adhesiveness with the base material layer mentioned above.
Volatile component concentration (ppm)
= Volatile component weight X (μg) / Weight of adhesive sheet for assembly of outside mirror before heating (g) Formula (2)
(However, in Formula (2), the volatile component weight X represents the weight in terms of hexadecane.)

  The volatile component weight X is obtained by concentrating the weight of the volatile component released when the outside mirror assembly pressure-sensitive adhesive sheet is heated at 90 ° C. for 30 minutes using a thermal desorption device, and using a GC-MS device. Can be measured. The volatile component concentration can be calculated by dividing the measured volatile component weight X by the weight of the outside mirror assembly pressure-sensitive adhesive sheet.

Specifically, as the method for measuring the volatile component concentration, specifically, an acrylic pressure-sensitive adhesive constituting the outside mirror assembling pressure-sensitive adhesive sheet is prepared, and about 20 mg of this pressure-sensitive adhesive is sample tube. (Inner diameter: about 5 mm, length: about 10 cm) Obtained by flowing helium gas into the sample tube at a flow rate of 1.5 ml / min for 30 minutes while heating and holding at 90 ° C. Volatile components are collected and concentrated in a trap tube built in the thermal desorption apparatus, and then the trap tube is heated at 280 ° C. for 10 minutes and supplied to the GC-MS apparatus.
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 (atomic mass unit), 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 measured weight of the volatile component is proportionally converted to the weight of the acrylic adhesive constituting the pressure-sensitive adhesive sheet for assembling the outside mirror to be measured, and this proportionally converted volatile component weight X is converted to the outside. The volatile component concentration can be calculated by dividing by the weight of the mirror assembly pressure-sensitive adhesive sheet.
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.

Furthermore, when the pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention is heated at 90 ° C. for 30 minutes, the volatile toluene concentration calculated by the following formula (3) is more preferably less than 50 ppm. . Thus, if the volatile toluene concentration is less than 50 ppm, the amount of toluene generated from the outside mirror assembly pressure-sensitive adhesive sheet can be kept low even when the temperature is high, and the generation of odors can be suppressed. Can do.
Volatile toluene concentration (ppm)
= Weight of volatile toluene Y (μg) / Adhesive sheet for assembly of outside mirror before heating (g) .. Formula (3)
(However, in formula (3), the volatile toluene weight Y represents the weight in terms of hexadecane.)
The volatile toluene concentration can be calculated by measuring the volatile toluene weight Y in the same manner as the volatile component weight X and dividing the volatile toluene weight Y by the weight of the double-sided adhesive tape.

  Such acrylic pressure-sensitive adhesives can reduce low molecular weight components such as residual monomers as much as possible, adjust the weight average molecular weight of acrylic polymers to a certain range, or adjust the softening point of the tackifying resin. Achievable.

(Method for manufacturing an adhesive sheet for assembling the outside mirror)
The method for producing the pressure-sensitive adhesive sheet for assembling the outside mirror of the present invention is not particularly limited. For example, the pressure-sensitive adhesive layer is laminated and integrated by applying a pressure-sensitive adhesive to at least one surface of a base material layer made of a crosslinked polyolefin resin foam sheet. The method of making it become is mentioned.
As a method of applying and laminating and integrating the pressure-sensitive adhesive layer, for example, a method of applying a pressure-sensitive adhesive using at least one surface of a crosslinked polyolefin resin foam sheet using a coater or the like, Examples include a method of spraying and applying an adhesive using a spray on at least one surface, and a method of applying an adhesive using a brush on at least one surface of a crosslinked polyolefin resin foam sheet.

  The outside mirror assembling pressure-sensitive adhesive sheet according to the present invention is configured as described above, so that it has a sufficient impact absorption and water-stopping property while being thin, and also under high temperature and temperature change environments. The physical properties of can be kept. Therefore, it is possible to provide an outside mirror that is thin and excellent in durability.

  Further, if the content of the component having a weight average molecular weight of 600 or less is 13% or less as the tackifying resin, the amount of volatile component can be suppressed to a very small amount, so that the volatile component is contained in the heater even in a narrow internal space. It does not adversely affect electronic parts such as control equipment.

  When the volatile component concentration calculated by the above formula (2) is less than 500 ppm when heated at 90 ° C. for 30 minutes, the amount of volatile components generated from the outside mirror assembly pressure-sensitive adhesive sheet is dramatic. Therefore, it is possible to prevent problems such as condensation in the mirror and peeling of the adhesive sheet due to volatile components.

Furthermore, an acrylic pressure-sensitive adhesive having a 10-hour half-life temperature of 80 ° C. or lower is selected as a polymerization initiator, and an acrylic copolymer copolymerized with a polymerization temperature higher than the 10-hour half-life temperature of the polymerization initiator. If a polymer containing a polymer is used, the polymerization initiator and its residue do not remain in the reaction solution as volatile components, and therefore the volatile components can be reduced.
Moreover, if the thickness of the crosslinked polyolefin resin foam sheet is 0.1 to 3 mm and the thickness of the acrylic pressure-sensitive adhesive layer is 10 to 150 μm, sufficient flexibility, tensile strength, impact absorption, texture and mechanical strength are obtained. Etc. are obtained stably and are economically advantageous.

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

Example 1
(Production of acrylic adhesive)
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 polymerization for 4 hours to polymerize.

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 A volatile component having an average molecular weight of 600 or less was removed (content of low-molecular-weight volatile components such as fats and oils was 9.6% by weight), and 19 parts by weight of a rosin ester compound having a softening point of 140 ° C. was added and stirred for acrylic. System adhesive A was obtained.

(Preparation of base material)
Linear low-density polyethylene obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst (trade name “EXACT3027” manufactured by Exxon Chemical Co., Ltd., density: 0.900 g / cm ³ , weight average molecular weight: 2.0, 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 foamable polyolefin resin composition comprising the above was supplied to an extruder, melted and kneaded at 130 ° C., and extruded into a long foamable polyolefin resin sheet having a width of 200 mm and a thickness of 1.0 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. It was continuously fed into a foaming furnace maintained at 250 ° C. by a heater, and heated and foamed.
Then, after continuously feeding the obtained foam sheet from the foaming furnace, the foam sheet is stretched to the CD while maintaining the temperature of both surfaces at 200 to 250 ° C. The foamed sheet is stretched to MD by winding the foamed sheet at a winding speed faster than the feeding speed (feeding speed) of the polyolefin resin sheet to the foaming furnace, and the foamed cells are stretched to CD and MD. A base material A made of a crosslinked polyolefin resin foam sheet having a width of 1050 mm, a thickness of 1.0 mm, a crosslinking degree of 25% by weight and an expansion ratio of 4.7 times was obtained.

(Preparation of outside mirror assembly adhesive sheet)
The acrylic adhesive A is applied to both surfaces of the substrate A so that the thickness is 50 μm after drying, and is dried at 105 ° C. for 5 minutes. The thickness of the acrylic adhesive A on both surfaces of the substrate A An adhesive sheet for assembling an outside mirror, in which 50 μm adhesive layers were laminated and integrated, was prepared.

(Example 2)
Substrate B was obtained in the same manner as in Example 1 except that the thickness of the crosslinked polyolefin resin foamed sheet was adjusted to 0.2 mm by adjusting the winding speed. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the base material A and using the base material B.

(Example 3)
An acrylic pressure-sensitive adhesive B was obtained in the same manner as in Example 1 except that the amount of the rosin ester compound used in Example 1 was 25 parts by weight. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the acrylic adhesive A and using the acrylic adhesive B. FIG.

Example 4
Acrylic pressure-sensitive adhesive as in Example 1 except that a rosin ester compound having a softening point of 140 ° C. that was not removed was used instead of the volatile component having a weight average molecular weight of 600 or less as the tackifying resin. C was obtained. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the acrylic adhesive A and using the acrylic adhesive C. FIG.
(Example 5)
An acrylic pressure-sensitive adhesive D was obtained in the same manner as in Example 4 except that the blending amount of the rosin ester compound having a softening point of 140 ° C. from which volatile components were not removed was 2 parts by weight. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the acrylic adhesive A and using the acrylic adhesive D. FIG.

(Comparative Example 1)
An adhesive sheet for assembling an outside mirror was produced in the same manner as in Example 1 except that polyurethane foam (“Polon SR” manufactured by INOAC, thickness 0.2 mm) was used as the substrate C instead of the substrate A. .

(Comparative Example 2)
An acrylic pressure-sensitive adhesive E was obtained in the same manner as in Example 1 except that the amount of the rosin ester compound used in Example 1 was 32 parts by weight. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the acrylic adhesive A and using the acrylic adhesive E. FIG.

(Comparative Example 3)
Instead of the rosin ester compound used in Example 1, Example 1 except that 19 parts by weight of a tackifying resin having a softening point of 125 ° C. (knitted terpene polymer, “YS Resin PX” manufactured by Yasuhara Chemical Co., Ltd.) was blended. Similarly, an acrylic pressure-sensitive adhesive F was obtained. And the adhesive sheet for an outside mirror assembly was produced like Example 1 except having replaced with the acrylic adhesive A and using the acrylic adhesive F. FIG.

About each of the adhesive sheet for assembling the outside mirror obtained in Examples 1 to 5 and Comparative Examples 1 to 3, the aspect ratio of the crosslinked polyolefin resin foam sheet (average cell diameter of MD / average cell diameter of CD), 25% compressive strength, waterstop, impact conductivity, cold cycle resistance, VOC, and cloudiness were examined, and the results are shown in Table 1.
The sheet surface direction aspect ratio, 25% compressive strength, waterstop, impact conductivity, cold cycle resistance, VOC, and cloudiness were evaluated by the following evaluation methods.

(Evaluation methods)
[Aspect ratio in sheet surface direction]
After calculating the average cell diameter of MD and CD in the crosslinked polyolefin resin foam sheet obtained by the above-described method, it was calculated by the following formula.
Sheet surface direction aspect ratio = average bubble diameter of MD / average bubble diameter of CD

[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 adhesive sheet for assembling the outside mirror obtained in Examples and Comparative Examples was cut into a donut shape having an outer diameter of 60 mm and an inner diameter of 50 mm to obtain a sample piece.
And after bonding two acrylic plates using this donut-shaped sample piece, a hose is attached to the hole so that the compression ratio of the cross-linked polyolefin resin foam sheet constituting the base material layer becomes 20%. In a compressed state, the portion corresponding to the inner diameter of the donut was filled with water so that the pressure was 10 kPa. And the leakage of water was evaluated according to JISC0920 IPX7 while applying a pressure of 10 kPa.

[Cooling and heat cycle resistance]
From the adhesive sheet for assembling the outside mirror, an adhesive sheet frame piece having a rectangular shape of 80 mm × 80 mm on the outside, a rectangular shape of 50 mm × 50 mm cut from the inside, and a width of 25 mm was produced.
Two acrylic resin transparent plates and aluminum plates of 100 × 100 mm × (thickness 5 mm) were prepared. The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet piece was attached to the central portion of one plate, and the other plate was laminated on the pressure-sensitive adhesive sheet piece from the base material layer side. Then, using 12 bolts, two plates were fixed at a thickness that would result in a compression rate of the foamed substrate of 20%, to produce a test piece.
The test piece was subjected to 30 cycles with a cycle of -20 ° C. for 2 hours / 80 ° C. for 2 hours in a cold cycle tester.
After 30 cycles, the test piece was immersed in an aqueous layer containing 40 ° C. water to a depth of 20 cm. The water temperature was kept at 40 ° C. and immersed for 24 hours. Thereafter, the test piece was taken out and visually confirmed whether water had entered the inside of the pressure-sensitive adhesive sheet frame piece.

(Measurement of volatile component concentration)
With respect to the obtained adhesive sheet for assembling the outside mirror, the volatile component concentration calculated by the above equation (2) and the volatile toluene concentration calculated by the equation (3) were measured as described above. Measurement was performed at 90 ° C. for the purpose of promoting the volatilization of volatile components.

[Evaluation of cloudy]
About 20 g of the adhesive sheet for assembling the outside mirror was put in 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.

[Flat surface tensile test: Mirror fixing substitute evaluation]
A mirror of width 50 mm × length 125 mm × thickness 3 mm was prepared. As an alternative to the mirror holder, a resin plate made of width 50 mm × length 125 mm × thickness 3 mm was prepared.
The adhesive sheet for assembling the outside mirror prepared in Examples and Comparative Examples was cut out to a size of 20 mm × 20 mm. And the mirror back surface and the resin board were fixed using the cut-out adhesive sheet, and the test piece was produced.
The produced test piece was left at a temperature of 23 ° C. for 24 hours, and the degree of fixation was evaluated by a plane tensile test strength.

As shown in Table 1 above, it can be seen that the outside mirror assembly pressure-sensitive adhesive sheet of the present invention is excellent in water-stopping and impact resistance and excellent in heat resistance. Also, excellent results have been obtained in the fixation evaluation.
It can also be seen that the generation of VOCs can be reduced by removing volatile components having a weight average molecular weight of 600 or less in the tackifying resin as in Examples 1 to 3 and 5.

It is sectional drawing which represents the structure of the conventional outside mirror typically. It is sectional drawing which represents typically the structure of the outside mirror for thickness reduction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mirror laminated body 2a, 2b Mirror holder 3 Adhesive tape

Claims (6)

An acrylic adhesive layer is laminated and integrated on both sides of the base material layer,
An adhesive sheet for assembling an outside mirror that is interposed between a mirror or a mirror laminated body housed in a housing part of a mirror holder and an inner wall surface of the housing part and fixes the mirror or mirror laminated body to the mirror holder. And
The base material layer is a cross-linked polyolefin resin foam sheet having a cross-linking degree of 5 to 60% by weight and an air bubble sheet surface direction aspect ratio of 0.25 to 1,
The acrylic pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive containing 1 to 30 parts by weight of a tackifying resin having a softening point of 130 ° C. or higher with respect to 100 parts by weight of an acrylic polymer. Adhesive sheet for assembling side mirrors.   The pressure-sensitive adhesive sheet for assembling an outside mirror according to claim 1, wherein the content of the component having a weight average molecular weight of 600 or less is 13% or less. The pressure-sensitive adhesive sheet for assembling the outside mirror according to claim 1 or 2, wherein the volatile component concentration calculated by the formula (1) is less than 500 ppm when heated at 90 ° C for 30 minutes.
Volatile component concentration (ppm)
= Weight of volatile component X (μg) / Adhesive sheet weight for assembly of outside mirror before heating (g) Formula (1)
(However, in formula (1), the volatile component weight X represents the weight in terms of hexadecane.)   The acrylic pressure-sensitive adhesive includes a copolymer obtained by polymerizing a monomer containing (meth) acrylic acid and a (meth) acrylic acid alkyl ester having an alkyl group having 4 to 12 carbon atoms. The pressure-sensitive adhesive sheet for assembling the outside mirror according to any one of claims 3 to 4.   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 pressure-sensitive adhesive sheet for assembling the outside mirror according to any one of claims 1 to 4.   The outside mirror assembly according to any one of claims 1 to 5, wherein the thickness of the crosslinked polyolefin resin foam sheet is 0.1 to 3 mm, and the thickness of the acrylic pressure-sensitive adhesive layer is 10 to 150 µm. Adhesive sheet.

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