JP7095311B2 - Polyolefin resin foam - Google Patents

Description

The present invention relates to a polyolefin-based resin foam.

Polyolefin-based resin foams are widely used in fields such as automobile interior materials, building materials as heat insulating materials, and adhesive tapes as cushioning materials. Among them, the double-sided adhesive tape is widely used in a scene such as fixing a component constituting an electronic device, and in many cases, a foam is used. This double-sided adhesive tape is used for fixing to the protective panel and body of the image display unit that constitutes small electronic devices such as mobile electronic terminals, cameras, and personal computers, and for fixing exterior parts and rigid parts such as batteries to small electronic devices. Is used for. The foam used for the double-sided adhesive tape is thin and has excellent followability to the adherend and impact resistance. For example, a double-sided adhesive tape having adhesive layers on both sides of a flexible foam base material. Is known (see, for example, Patent Document 1).

On the other hand, as mobile electronic terminals and the like are becoming thinner and more sophisticated, they are thin and expensive, for example, made of rigid bodies such as protective panels, image display modules, touch panels, and thin batteries that make up an image display unit. Many parts are being used. Therefore, it is preferable that the main body (body) of the electronic device can be easily separated and the main body of the electronic device, the removed parts, and the like can be reused when a malfunction occurs in the portable electronic terminal or the like. Therefore, Patent Document 2 discloses that the easily disassembled layers are laminated so that the fixed portion can be easily disassembled. However, in this case, since the easily disassembled layer is laminated on the foam base material again, the number of steps increases, which may be economically disadvantageous.

Japanese Unexamined Patent Publication No. 2010-260880 Japanese Unexamined Patent Publication No. 2016-79361

In view of the background of the prior art, the present invention is intended to provide a polyolefin-based resin foam suitable for a double-sided adhesive tape that can be easily disassembled when a malfunction occurs in a mobile terminal or the like.

The gist of the present invention is as follows in order to solve such a problem.
(1) A sheet-like polyolefin resin foam having a laminated structure, the layer constituting the outermost layer on the side of the A side, which is one main surface, is the a layer, and the side of the B surface, which is the one main surface. When the layer constituting the outermost layer of is b layer, the interlayer strength required by the following measurement method for any one surface (A surface) is 10 N / cm or more, and the following measurement for the other surface (B surface). The interlayer strength required by the method is less than 10 N / cm, the apparent density of the a layer is 200 to 500 kg / m ³ , the apparent density of the b layer is 25 to 150 kg / m ³ , and the interlayer fracture thickness is A polyolefin-based resin foam having a thickness of 80% or less of the b-layer.
<Measurement of interlayer strength>
Squeeze 100 μm of the polyolefin resin foam from the surface of the surface to be measured with a slicing machine in the thickness direction (however, when the thickness of the a layer or b layer is less than 100 μm, the a layer or b layer is concerned. The thickness of the stripped material shall be the thickness of the layer).
The sample collected from the A surface side is referred to as sample A, and the sample collected from the B surface side is referred to as sample B. Subsequently, one adhesive layer having an adhesive strength that does not peel off from the sample surface in the measurement by the high-speed peeling tester described later with a thickness of 50 μm is bonded to both sides of these samples one by one, and then aged at 40 ° C. for 48 hours. By doing so, a double-sided adhesive tape for measuring the interlayer strength is produced.
Next, one of the pressure-sensitive adhesive layers constituting the double-sided adhesive tape for measuring the interlayer strength is lined with a polyester film having a thickness of 25 μm, and the sample base material is cut into a size of 1 cm in the width direction and 15 cm in the flow direction. The adhesive tape thus obtained and a polyester film having a thickness of 50 μm, a width of 3 cm, and a length of 20 cm were pressure-bonded at 23 ° C. and 50% RH by reciprocating a 2 kg roller once, and at 60 ° C. for 48 hours. After allowing to stand, it is allowed to stand at 23 ° C. for 24 hours.
At 23 ° C. and 50% RH, the side bonded to the 50 μm-thick polyester film is fixed to the mounting jig of the high-speed peeling tester, and the 25 μm-thick polyester film is placed in the 90-degree direction at a tensile speed of 15 m / min. The maximum strength when pulled and the sample substrate is torn is measured. The maximum strength obtained from the sample A is defined as the interlayer strength of the A surface, and the maximum strength obtained from the sample B is defined as the interlayer strength of the B surface.
(2) The polyolefin-based resin according to (1), wherein the relationship between the interlayer strength Da (N / cm) on the A surface and the interlayer strength Db (N / cm) on the B surface satisfies the following equation 1. Foam.

Da-Db> 5 (N / cm) (Equation 1)
( 3 ) The thickness of the b layer constituting the outermost layer on the B surface side is 100 to 500 μm, or 1/3 or less of the total thickness of the foam, according to (1) or (2) . The polyolefin-based resin foam according to the above.
( 4 ) The main components of the resin constituting the a layer constituting the outermost layer on the A surface side are ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer and ethylene propylene rubber (EPR, EPDM, etc.). The polyolefin-based resin foam according to any one of (1) to ( 3 ), which is at least one resin selected from the group consisting of.
( 5 ) The main component of the resin constituting the b layer constituting the outermost layer on the B surface side is at least one resin selected from the group consisting of polyethylene-based resin and polypropylene-based resin ((5). The polyolefin-based resin foam according to any one of 1) to ( 4 ).
( 6 ) A step of preparing two or more kinds of polyolefin-based resin compositions having different compositions, a step of co-extruding the two or more kinds of polyolefin-based resin compositions to obtain a polyolefin-based resin sheet, and a step of subjecting the resin sheet to a cross-linking treatment. The method for producing a polyolefin-based resin foam according to any one of (1) to ( 5 ) above, which comprises a step.
( 7 ) An adhesive tape using the polyolefin-based resin foam according to any one of (1) to ( 5 ) above.

According to the present invention, it is possible to provide a polyolefin-based resin foam suitable for a double-sided adhesive tape having excellent dismantability. Further, it is preferable to provide a polyolefin-based resin foam having excellent cushioning properties, appearance or heat resistance.

The present invention has been diligently studied on the above-mentioned problems, and is intended to provide a polyolefin-based resin foam suitable for a double-sided adhesive tape having excellent cushioning properties and excellent disintegration properties. Hereinafter, the present invention will be described in detail with reference to examples.

Examples of the polyolefin-based resin used in the present invention include polyethylene-based resins such as low-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene (the definition of density here is as follows. Ultra-low density: less than 0.910 g / cm ³ , low density: 0.910 g / cm ³ or more and 0.940 g / cm ³ or less, high density: greater than 0.940 g / cm ³ and 0.965 g / cm ³ or less), Further, a copolymer containing polyethylene as a main component, a polypropylene resin typified by a homopolypropylene, an ethylene-propylene random copolymer, an ethylene-propylene block copolymer, etc., and EPR (ethylene / propylene rubber) and EPDM (ethylene / propylene rubber) Examples thereof include polyethylene propylene rubber (also referred to as EPM) such as polyethylene / propylene / diene rubber), and a mixture thereof may be used. A vinyl-based polymer containing an aromatic ring, such as a polymer containing polystyrene or styrene units, does not fall under the polyolefin-based resin referred to in the present invention. Examples of the ethylene-based copolymer include ethylene and an α-olefin having four or more carbon atoms (for example, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, etc.). Examples thereof include ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers and the like obtained by polymerizing 1-heptene, 1-octene and the like. The polyolefin-based resin is more preferably low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, an ethylene-α-olefin copolymer, or an ethylene-vinyl acetate copolymer. More preferably, it is low density polyethylene, linear low density polyethylene, or ultra low density polyethylene. These polyolefin-based resins may be either one kind or a mixture of two or more kinds. Most preferably, it is a mixture of low density polyethylene and linear low density polyethylene.

In a polyethylene-based resin preferably used for a polyolefin-based resin foam, the melt flow rate (MFR) thereof is measured based on JIS K7210 (1999) under normal conditions of a temperature of 190 ° C. and a load of 2.16 kgf. , 1.0 to 30 g / 10 minutes are preferable. If the MFR is less than 1.0 g / 10 minutes, the surface of the sheet becomes rough when the sheet is formed in the step of producing the polyolefin-based resin foam, and the obtained foam causes a problem in appearance. In some cases. If the MFR exceeds 30 g / 10 minutes, the heat resistance of the polyolefin resin foam may be insufficient. The melt flow rate (MFR) of the polyethylene resin is more preferably 2.0 to 15 g / 10 minutes.

The melt flow rate (MFR) of a polypropylene resin preferably used for a polyolefin resin foam is measured under normal conditions of a temperature of 230 ° C. and a load of 2.16 kgf in accordance with JIS K7210 (1999). Those in the range of 0.5 to 15 g / 10 minutes are preferable. If the MFR is less than 0.5 g / 10 minutes, the surface of the sheet becomes rough when the sheet is formed in the step of producing the polyolefin resin foam, and the obtained foam causes a problem in appearance. In some cases. If the MFR exceeds 15 g / 10 minutes, the heat resistance of the polyolefin resin foam may be insufficient. The melt flow rate (MFR) of the polypropylene-based resin is more preferably 1.0 to 10 g / 10 minutes.

Further, as long as the characteristics of the polyolefin-based resin foam of the present invention are not significantly impaired, a thermoplastic resin other than the polyolefin-based resin may be contained. The thermoplastic resins other than the polyolefin resin referred to here are, in the case of halogen-free resins, polystyrene, acrylic resins such as polymethylmethacrylate and styrene-acrylic acid copolymers, and styrene-butadiene copolymers. , Polyvinyl acetate, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methyl cellulose, hydroxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose and other cellulose derivatives, saturated alkyl polyester resin, polyethylene terephthalate, poly Examples thereof include aromatic polyester resins such as butylene terephthalate and polyaritate, polyamide resins, polyacetal resins, polycarbonate resins, polyester sulfone resins, polyphenylene sulfide resins, polyether ketone resins, vinyl polymerizable monomers and copolymers having nitrogen-containing vinyl monomers. .. Further, elastomers such as isoprene rubber, styrene butadiene rubber, butyl rubber, and dimethyl silicone rubber are also included. Examples of the resin containing halogen include polyvinyl chloride, polyvinylidene chloride, polyvinylidene trichloride, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin and the like. As the thermoplastic resin other than these polyolefin resins, one type may be used, or a plurality of types may be used. The type and amount can be selected according to the desired physical properties.

It is important that the polyolefin-based resin foam of the present invention contains a polyolefin-based resin as a main component. Here, the main component means the component having the largest mass in the polyolefin-based resin foam. More preferably, the polyolefin-based resin is 50% by mass or more and 100% by mass or less in 100% by mass of all the components of the polyolefin-based resin foam. The amount of the thermoplastic resin other than the above-mentioned polyolefin resin, other additives, and the like is preferably 0% by mass or more and 50% by mass or less with respect to 100% by mass of all the components of the polyolefin resin foam.

Further, the polyolefin-based resin foam of the present invention can have a laminated structure of two or more layers. It may have three or more layers. Further, since the present invention can be suitably used for adhesive tapes, it is preferably in the form of a sheet.

The polyolefin-based resin foam of the present invention will be described by taking the case of a sheet shape as an example. The sheet shape has two main surfaces, but when one surface is the A surface and the other surface is the B surface, the layers constituting the outermost layer on the A surface side are the a layer and the outermost layer on the B surface side. It is possible to adopt a laminated structure in which the layers constituting the above are b layers. Here, another layer may exist between the a layer and the b layer. However, the polyolefin-based resin foam of the present invention is characterized in that the interlayer strength differs depending on the surface, and it is defined that the one with higher interlayer strength is the A surface and the one with lower interlayer strength is the B surface.

The main component of the resin constituting the outermost layer a is, for example, at least selected from ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and ethylene propylene rubber (EPR, EPDM, etc.). One type of resin is preferably used. On the other hand, the main components of the resin constituting another outermost layer, layer b, are polyethylene-based resins typified by low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, homopolyethylene, and ethylene. -At least one resin selected from the group consisting of polypropylene-based resins typified by a polyethylene random copolymer, an ethylene-propylene block copolymer and the like is preferably used.

In selecting the resin, it is important that the difference in strength at high temperatures when the foam is formed is within a range that is unlikely to occur in the a layer and the b layer. Therefore, an elastomer-based polyolefin resin is selected for the layer a having a relatively low foaming ratio, and a general polyolefin resin is selected for the layer b on the high foaming ratio side. By selecting the resin in this way, it is advantageous in that appearance problems such as wrinkles are less likely to occur in the process of producing the foam. Here, the main component means that the resin constituting the layer occupies 50% by mass or more when 100% by mass is taken.

In selecting the resin for the a layer and the b layer, the flexural modulus of the resin is one index. The flexural modulus of the resin in layer a is preferably 150 MPa or less, more preferably 100 MPa or less. On the other hand, the flexural modulus of the resin in the b layer is preferably 200 MPa or more, more preferably 250 MPa. If the flexural modulus of the resin in the a layer is larger than 150 MPa, it is difficult to follow the foaming of the b layer and there is a possibility of appearance problems such as wrinkles. There is no elasticity when taped, which may affect workability.

When the polyolefin-based resin foam of the present invention is in the form of a sheet, the thickness thereof is not particularly limited. When the thickness is thick, a rectangular parallelepiped shape is typically assumed, but in this case, the A surface and the B surface are surfaces including the longest side and the second longest side.

It is preferable that the thickness of the layer a constituting the outermost layer on the A side of the polyolefin resin foam of the present invention is in the range of 100 to 500 μm, or 1/3 or less of the total thickness of the foam. This is because if it is not within this range, when it is used as an adhesive tape, it is too hard to follow the shape.

The polyolefin-based resin foam of the present invention needs to have an interlayer strength of the A surface of 10 N / cm or more and an interlayer strength of the B surface of less than 10 N / cm. When the interlayer strength of the A surface is less than 10 N / cm, the adhesion to the pressure-sensitive adhesive is enhanced, and the selective destruction of the b layer constituting the B surface is less likely to proceed. The interlayer strength of the A surface is preferably 25 N / cm or more, and more preferably 50 N / cm or more. The upper limit is not particularly limited, but is preferably 100 N / cm or less.

On the other hand, if the interlayer strength of the B surface is 10 N / cm or more, the strength of the foam becomes high and disassembly becomes difficult. The interlayer strength of the B surface is preferably less than 7 N / cm, and more preferably less than 5 N / cm. The lower limit is not particularly limited, but is preferably 0.1 N / cm or more.

The method for measuring the interlayer strength is as follows. That is, first, 100 μm of the polyolefin-based resin foam is squeezed from the surface of the surface to be measured by the slicing machine in the thickness direction (however, the a layer when the thickness of the a layer or the b layer is less than 100 μm). Alternatively, the stripping thickness of layer b shall be the thickness of that layer). Among the samples thus obtained, the sample collected from the A surface side is referred to as sample A, and the sample collected from the B surface side is referred to as sample B. Subsequently, a strong adhesive adhesive layer having a thickness of 50 μm was attached to both sides of each of these samples one by one, and then aged at 40 ° C. for 48 hours to prepare a double-sided adhesive tape for measuring the interlayer strength. do. The strong adhesiveness refers to a level of adhesive strength at which the adhesive layer does not peel off from the sample surface even in the high-speed peeling test described later. Needless to say, in selecting the pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer that does not cause destruction or creep of the pressure-sensitive adhesive layer in the high-speed peeling test should be selected.

Next, one of the pressure-sensitive adhesive layers constituting the double-sided adhesive tape for measuring the interlayer strength is lined with a polyester film having a thickness of 25 μm, and the sample base material is cut into a size of 1 cm in the width direction and 15 cm in the flow direction. The adhesive tape thus obtained and a polyester film having a thickness of 50 μm, a width of 3 cm, and a length of 20 cm were pressure-bonded at 23 ° C. and 50% RH by reciprocating a 2 kg roller once, and at 60 ° C. for 48 hours. After allowing to stand, it is allowed to stand at 23 ° C. for 24 hours.

At 23 ° C. and 50% RH, the side bonded to the 50 μm-thick polyester film is fixed to the mounting jig of the high-speed peeling tester, and the 25 μm-thick polyester film is placed in the 90-degree direction at a tensile speed of 15 m / min. The maximum strength when pulled and the sample substrate is torn is measured. The maximum strength obtained from the sample A is defined as the interlayer strength of the A surface and is defined as Da (N / cm), and the maximum strength obtained from the sample B is defined as the interlayer strength Db (N / cm) of the B surface.

In the polyolefin resin foam of the present invention, the relationship between the interlayer strength Da (N / cm) of the foam A surface and the interlayer strength Db (N / cm) of the foam B surface is the difference between Da and Db. Is preferably greater than 5 (see Equation 1).

Da-Db> 5 (N / cm) (Equation 1)
If this difference is smaller than 5 (N / cm), the adhesive layer may not be able to be smoothly released from the A surface, and the adhesive layer may be cut or separated. This difference is preferably 10 (N / cm), more preferably 20 (N / cm).

Further, in the present invention, the interlayer fracture thickness means the thickness from the B surface side of the place where the fracture occurred when the above interlayer strength measurement was carried out using the foam as it is without being strained by a slicing machine. The polyolefin-based resin foam of the present invention needs to have an interlayer fracture thickness of 80% or less of the thickness of the b layer. If the interlayer fracture thickness exceeds 80%, the tape is used as an adhesive tape, and when the tape is subsequently disassembled, the residual amount of the b layer is large and the dismantability deteriorates.

The gel fraction of the polyolefin-based resin foam of the present invention is not particularly limited, but 10 to 60% is preferably used. The gel fraction referred to here is a kind of method for expressing the degree of cross-linking, and is calculated by immersing in a heated solvent for a certain period of time and dividing the mass of the remaining insoluble matter by the mass before dissolution. More preferably, the gel fraction is 15-40%. If the gel fraction is less than 10%, the surface tends to be rough when foaming, and if it is more than 60%, it may be difficult to process when foaming and the yield may be poor, which is not preferable.

The polyolefin-based resin foam of the present invention can be preferably obtained by using a foaming agent, and the thermally decomposable foaming agent that can be used is higher than the melting temperature of the resin composition containing the polyolefin-based resin that is the raw material of the foam. It is not particularly limited as long as it has a high decomposition temperature. Preferably, azodicarboxylic amide is mentioned, and further, hydrazosicarboxylic amide, azodicarboxylic acid barium salt, dinitrosopentaethylenetetramine, nitrosoguanidine, p, p'which have a decomposition temperature equal to or higher than that of azodicarboxylic amide. -Oxybisbenzenesulfonyl semicarbazide, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, barium azodicarbaxylate, azobisisobutyronitrile, toluenesulfonylhydrazide and the like can be used. These pyrolyzable foaming agents may be used alone or in combination of two or more. The blending amount of the heat-decomposable foaming agent is 100 parts by mass of the total amount of resin components (hereinafter, 100 parts by mass of the total amount of resin components is the total amount of 100 parts of all resins such as polyolefin resins and other thermoplastic resins. It means a part by mass. In this case, the resin in the pellet obtained by master batching (pelletizing with the resin) the additive or the like is also included in the resin component), which is generally about 2 to 40 parts by mass. It is set according to the desired foaming ratio.

The apparent density of the polyolefin-based resin foam of the present invention is not particularly limited, but is preferably 15 to 500 kg / m ³ . More preferably, it is 20 to 200 kg / m ³ . Most preferably, it is 20 to 50 kg / m ³ . If it is less than 15 kg / m ³ , the base material itself is easily broken when it is made into an adhesive tape, and if it is more than 500 kg / m ³ , it is difficult to maintain the cushioning property intended by the present invention.

The thickness of the a layer and the b layer is not particularly limited, but is preferably 100 μm or more. In particular, the b layer is preferably 100 to 500 μm. If it is less than 100 μm, the desired characteristics may not be obtained, and if it is more than 500 μm, the foam does not break cleanly and it becomes difficult to reuse the mobile terminal or the like. On the other hand, this is not the case when the total thickness of the polyolefin resin foam is less than 500 μm, and the thickness of the b layer in this case is preferably 1/3 or less of the total thickness of the foam.

It is more preferable that the apparent densities of the a layer forming the outermost layer on the A side and the b layer forming the outermost layer on the B side of the polyolefin resin foam of the present invention are different. The range of the apparent density of the layer a is preferably 200 to 500 kg / m ³ , and more preferably 250 to 400 kg / m ³ . On the other hand, the apparent density of the b layer is preferably 25 to 150 kg / m ³ , and more preferably 50 to 125 kg / m ³ . If the apparent density of layer a is lower than 200 kg / m ³ , the desired interlayer strength may not be obtained, and if it exceeds 500 kg / m ³ , the affinity with the pressure-sensitive adhesive may be lowered. Further, if the apparent density of the b layer is lower than 25 kg / m ³ , the closed cell ratio may decrease, and if it exceeds 150 kg / m ³ , a sufficient cushioning feeling may not be obtained. The difference in the apparent density between the a layer and the b layer is also required to be within the range in which the difference in the tensile strength at high temperature when the foam is formed is unlikely to occur in the a layer and the b layer, as in the case of selecting the resin. It is adjusted according to the resin selected in the a layer and the b layer. By doing so, it is advantageous in that appearance problems such as wrinkles are less likely to occur in the production of the foam.

The apparent density can be controlled by the amount of the above-mentioned pyrolysis foaming agent added. It is important to arbitrarily select the amount to be added depending on the type of pyrolysis foaming agent, the amount of gas, the polyolefin resin used, other thermoplastic resins, and the like.

When producing the polyolefin-based resin foam of the present invention, a polyfunctional monomer is used as a cross-linking aid in a resin composition containing the polyolefin-based resin which is the raw material of the foam, as long as the characteristics of the foam are not impaired. Can be contained. Examples of the polyfunctional monomer include divinylbenzene, diallylbenzene, divinylnaphthalene, divinylbiphenyl, divinylcarbazole, divinylpyridine and their nuclear substitution compounds and related homologues, ethylene glycol di (meth) acrylate, butylene glycol di (meth). Acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol. (Meta) acrylic acid compounds such as di (meth) acrylate, vinyl esters of aliphatic and aromatic divalent carboxylic acids such as divinyl phthalate, diallyl phthalate, diallyl malate, bisacryloyloxyethyl terephthalate, allyl esters, acryloyloxy. Divinyl ethers of aliphatic and aromatic dihydric alcohols such as alkyl esters, methacryloyloxyalkyl esters, diethylene glycol divinyl ethers, triethylene glycol divinyl ethers, tetraethylene glycol divinyl ethers, polyethylene glycol divinyl ethers, hydroquinone divinyl ethers, and bisphenol A diallyl ethers. It is possible to use monomers such as maleimide-based compounds such as allyl ether, N-phenylmaleimide, N, N'-m-phenylene bismaleimide, and compounds having two triple bonds such as dipropagil phthalate and dipropagil maleate. .. In addition, trimethylol propanetri (meth) acrylate and 1,6-hexanediol di (meth) acrylate, trimethylol propanetri (meth) acrylate and 1,6-hexanediol di (meth) acrylate and 1,9-nonanediol. Di (meth) acrylate, trimethylolpropane tri (meth) acrylate and divinylbenzene, trimethylolpropanetri (meth) acrylate and triallyl cyanurate, 1,6-hexanediol di (meth) acrylate, triallyl cyanurate and 1 , 6-Hexanediol di (meth) acrylate, triallyl isocyanurate and 1,6-hexanediol di (meth) acrylate can also be used. For example, divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, trimellitic acid triallyl ester, triallyl isocyanurate, ethyl vinylbenzene and the like can be used. .. The above-mentioned cross-linking aid may be used alone or in combination of two or more. The blending amount of the cross-linking aid is 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of the total amount of the resin components, and is set according to a desired gel fraction. Will be done.

Further, a cross-linking aid and an organic peroxide can be used in combination. As the organic peroxide, for example, methyl ethyl ketone peroxide, t-butyl peroxide, dicumyl peroxide and the like are used. The blending amount of the organic peroxide is 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the total amount of the resin components, depending on the desired gel fraction. Set.

In addition, various additives such as foaming agent decomposition accelerators, bubble nucleating agents, antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, and inorganic fillers, as long as the characteristics of the present invention are not impaired. Can be included in the polyolefin-based resin composition which is the raw material of the polyolefin-based resin foam of the present invention.

The polyolefin-based resin foam of the present invention preferably has a closed cell structure. The closed-cell structure referred to here means that the resin film between the bubbles has no holes and the air layer is not exchanged between the adjacent bubbles. On the other hand, in the open cell structure, the resin film has holes, and the air layer moves back and forth. By having a closed cell structure, there is no feeling of bottoming out and it has a firm cushioning property. Further, the closed cell ratio is preferably at least 90% by volume or more of the total volume of bubbles.

In the present invention, a polyolefin-based resin composition obtained by blending the above components is molded into a predetermined shape, and then crosslinked and foamed to produce a polyolefin-based resin foam.

Specifically, for example, the following manufacturing method can be mentioned. A predetermined amount of the polyolefin-based resin composition is uniformly melted at a temperature lower than the decomposition temperature of the pyrolysis foaming agent by using a kneading device such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader mixer, or a mixing roll. Knead and mold this into a sheet.

It is important to perform coextrusion when molding into this sheet shape. In this case, the polyolefin-based resin compositions having different compositions are laminated in a sheet shape using a plurality of kneading devices. The method is not particularly specified, but is preferably selected from a single-screw extruder and a twin-screw extruder, such as a feed block method and a multi-manifold method.
Other methods include not only extruders, Banbury mixers, kneader mixers, and mixing rolls, but also laminating methods in which a sheet containing layer a and a sheet containing layer b are separately molded and then heated and welded with a frame or hot air. There is an extrusion laminating method in which a sheet containing one of the layers is flown on a line and welded while being extruded by a single-screw or twin-screw extruder. It is preferable to select coextrusion because it is economically advantageous because the affinity is lower than that of coextrusion.

Next, the obtained sheet is irradiated with an ionizing radiation at a predetermined dose to crosslink the olefin resin, and the crosslinked sheet is heated to a temperature equal to or higher than the decomposition temperature of the pyrolytic foaming agent to be foamed. Instead of cross-linking by ionizing radiation irradiation, cross-linking with peroxide or silane cross-linking may be performed. As the ionizing radiation, electron beam, X-ray, β ray, γ ray and the like are used. The irradiation dose is generally about 1 to 300 kGy, and the dose is set according to the desired gel fraction.

By irradiating the sheets with ionizing radiation after laminating, a crosslinked structure straddling the layers can be formed, so that a polyolefin-based resin foam having excellent affinity and uniform crosslinkability can be obtained. Therefore, there is an advantage that the dissociation between layers is less likely to occur.

The foamable sheet on which the resin is crosslinked is, for example, by hot air, infrared rays, metal bath, oil bath, salt bath, etc., at a temperature equal to or higher than the decomposition temperature of the pyrolytic foaming agent and higher than the melting point of the resin, for example, 190 to 290 ° C. The resin is foamed by the decomposition gas of the foaming agent, thereby obtaining a polyolefin-based resin foam.

In addition, an adhesive tape can be obtained by using the polyolefin-based resin foam obtained by the method described so far. The pressure-sensitive adhesive to be laminated when the polyolefin-based resin foam of the present invention is used to form an adhesive tape contains, for example, a binder resin such as a natural rubber-based, synthetic rubber-based, acrylic-based, silicone-based, urethane-based, or vinyl ether-based binder resin. You can use what you want. The form of the pressure-sensitive adhesive includes a solvent-based pressure-sensitive adhesive, an emulsion-type pressure-sensitive adhesive, a water-based pressure-sensitive adhesive such as a water-soluble pressure-sensitive adhesive, a hot-melt type pressure-sensitive adhesive, a UV-curable pressure-sensitive adhesive, and a solvent-free type such as an EB-curable pressure-sensitive adhesive. Adhesives and the like can be mentioned.

The method for processing the polyolefin-based resin foam of the present invention into an adhesive tape is not particularly specified, but for example, a method of directly applying the polyolefin resin foam to the foam using a coater or the like, or applying an adhesive to the release paper side for transfer. There are publicly known and public methods such as a method and a method of attaching a base material-less adhesive tape, and any of them may be used.

The polyolefin-based resin foam obtained in the present invention is suitably used as a double-sided adhesive tape used for mobile terminals and the like. When the double-sided adhesive tape using the polyolefin-based resin foam obtained in the present invention is used for a mobile terminal or the like, it can be easily disassembled when a defect occurs, the defective part or the like is removed, and the other parts are re-used. It is economically advantageous because it can be used.

In addition to the double-sided adhesive tape, it can also be suitably used for cushioning materials, packaging / packing materials, and the like.

Physical characteristics were evaluated by the following methods.

(Thickness measurement method)
According to ISO 1923 (1981) "Measurement of foamed plastic and rubber-wire dimensions". Specifically, the thickness of the foam was measured using a dial gauge having a measurement area of about 10 cm ² .

(Resin density measurement method)
Measurements were performed in accordance with JIS K6922 (2010) "Plastic-Polyethylene (PE) molding and extrusion materials".

(Method for measuring resin flexural modulus)
Measurements were performed in accordance with JIS K6922 (2010) "Plastic-Polyethylene (PE) molding and extrusion materials".

(Measurement method of melt flow rate)
JIS K7210 (1999) "Plastic-Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics" is applied. Based on Annex B (Reference) "Standards and Designations of Thermoplastic Plastic Materials and Their Test Conditions" of the above standards, polypropylene-based resin has a temperature of 230 ° C, load 2.16 kgf (21.7 N), and polyethylene-based resin has a temperature of 190 ° C. The procedure was carried out under the condition of a load of 2.16 kgf (21.7 N). Melt indexer model F-B01 manufactured by Toyo Seiki Seisakusho Co., Ltd. is used, a manual cutting method is adopted, and it is defined by the mass of the resin that comes out from the die in 10 minutes.

(Measuring method of gel fraction)
The gel fraction is a value calculated by the following method. First, the polyolefin resin foam was cut into strips in the longitudinal direction at 0.5 mm intervals with a single blade, and then cut at 0.5 mm intervals in the width direction using a scissors, weighed precisely at about 50 mg, and weighed at 130 ° C. After soaking in 200 ml of tetraline for 3 hours, it is naturally filtered with a 200 mesh stainless wire mesh, washed with acetone, exposed to dry air for 15 seconds, and then the insoluble matter on the wire mesh is removed in a hot air oven at 120 ° C. for 1 hour. dry. Then, it was cooled in a desiccator containing silica gel for 10 minutes, the mass of this insoluble matter was precisely weighed, and the gel fraction was calculated as a percentage according to the following formula.
Gel fraction (%) = {mass of insoluble matter (mg) / mass of weighed polyolefin resin foam (mg)} x 100
Then, the average value of 3 points excluding the upper and lower limit values from the value obtained by the measurement of 5 samples was taken as the gel fraction.

(Measuring method of apparent density)
It was measured based on JIS K6767 (1999) "Foam Plastic-Polyethylene-Test Method".
For example, the sample size is punched to a sample size of 15 cm ³ or more (for example, 10 cm square), and the thickness and mass are measured. The volume was calculated from the area of the sample (100 cm ² in the case of 10 cm square) and its thickness, and the apparent density was calculated by the following formula.
Apparent density (kg / m ³ ) = sample weight (kg) / {sample thickness (m) x sample area (m ² )}
Then, the average value of three points obtained by measuring the five samples minus the upper and lower limit values was taken as the apparent density.

(Measuring method of 25% compression hardness)
The method for measuring the 25% compression hardness is based on JIS K6767 (1999) "Foam Plastic-Polyethylene-Test Method". Specifically, the foams were laminated so that the total thickness was 25 mm or more, and the drag force when this was compressed by 25% and 50% of the total thickness was measured. As a measuring device, a Tensilon universal tester UCT-500 manufactured by Orientec Co., Ltd. was used.

(Measurement method of interlayer strength)
The method for measuring the interlayer strength is as follows. As a preparation in the previous step, 100 μm of the polyolefin resin foam is squeezed from the surface of the surface to be measured with a slicing machine in the thickness direction (however, when the thickness of the a layer or the b layer is less than 100 μm). The thickness of the a-layer or the b-layer is taken as the thickness of the layer).

Among the samples thus obtained, the sample collected from the A surface side is referred to as sample A, and the sample collected from the B surface side is referred to as sample B. Subsequently, a strong adhesive adhesive layer having a thickness of 50 μm was attached to both sides of each of these samples one by one, and then aged at 40 ° C. for 48 hours to prepare a double-sided adhesive tape for measuring the interlayer strength. do.

Next, one of the pressure-sensitive adhesive layers constituting the double-sided adhesive tape for measuring the interlayer strength is lined with a polyester film having a thickness of 25 μm, and the sample base material is cut into a size of 1 cm in the width direction and 15 cm in the flow direction. The adhesive tape thus obtained and a polyester film having a thickness of 50 μm, a width of 3 cm, and a length of 20 cm were pressure-bonded at 23 ° C. and 50% RH by reciprocating a 2 kg roller once, and at 60 ° C. for 48 hours. After allowing to stand, it is allowed to stand at 23 ° C. for 24 hours.

At 23 ° C. and 50% RH, the side bonded to the 50 μm-thick polyester film is fixed to the mounting jig of the high-speed peeling tester, and the 25 μm-thick polyester film is placed in the 90-degree direction at a tensile speed of 15 m / min. The maximum strength when pulled and the sample substrate is torn is measured. The maximum strength obtained from the sample A is defined as the interlayer strength of the A surface and is defined as Da (N / cm), and the maximum strength obtained from the sample B is defined as the interlayer strength Db (N / cm) of the B surface. (Interlayer fracture thickness)
When the above interlayer strength measurement was carried out using the foam as it was without scraping with a slicing machine, the thickness from the B surface side of the place where the fracture occurred was randomly measured at 5 points in the peeling direction, and the highest and lowest were measured. The value of the three-point average without the value was taken as the interlayer fracture thickness.

(Removability)
The state of the foam when the A-side and B-sides of the obtained foam are laminated with strong adhesive layers of the same strength and then lined with a polyester film of 25 μm and the film on the A-side is peeled off by hand. Judgment was made by. The number of repetitions is five.
⊚: Material destruction occurred cleanly on the B side.
〇: Material destruction occurs on the B side, but the peeled surface is not stable.
X: Interface peeling occurs without destroying the material, peeling occurs at the interface of layer a or layer b, or the peeled surface is not stable.

(Appearance)
Judgment was made based on the degree of appearance defects such as wrinkles on the surface of the foam.

◎: A product with a beautiful appearance without wrinkles.

○: Wrinkles are inconspicuous but occur.

Δ: Wrinkles are clearly visible but not uneven.

×: Wrinkled and uneven.

(Cushioning)
The obtained foam was evaluated by the feel of touch.

◎: Those that feel cushioning.

◯: Hard but cushioning.

×: Those that do not feel cushioning.

(Heat-resistant)
It was evaluated by the dimensional change when it was heated at 100 ° C. and measured after 3 hours.

⊚: Dimensional change less than 5% ○: Dimensional change less than 10% △: Dimensional change less than 15% ×: Dimensional change more than that (Comprehensive evaluation)
The result of comprehensive judgment from the above result is shown.

In terms of peelability, ◎ is 15 points, 〇 is 10 points, △ is 5 points, and × is 0 points. For other characteristics, ◎ is 5 points, 〇 is 3 points, △ is 1 point, and × is 0 points, and the total of these is calculated. The value that came out was used as an index for comprehensive evaluation. ○ The above was accepted.

⊚: 20 points or more ○: 14 points or more and less than 20 points ×: less than 14 points.

(Ingredients used)
<Polyethylene resin (PE)>
PE1: Petrosen 170 manufactured by Tosoh Co., Ltd.
MFR 1.0g / 10 minutes, flexural modulus 240MPa
PE2: Novatec LL UJ960 manufactured by Japan Polyethylene Corporation
MFR 5.0g / 10 minutes, flexural modulus 440MPa
<Polypropylene resin (PP)>
PP1: Novatec PP BC6C manufactured by Japan Polypropylene Corporation
MFR 2.5g / 10 minutes, flexural modulus 1650MPa
PP2: Novatec PP EG8B manufactured by Japan Polypropylene Corporation
MFR 0.8g / 10 minutes, flexural modulus 950MPa
<Ethylene-vinyl acetate copolymer (EVA)>
EVA1: Novatec EVA LV430 manufactured by Japan Polyethylene Corporation
MFR 1.0g / 10 minutes, flexural modulus 50MPa
EVA2: Tosoh Ultrasen 520F
MFR 2.0g / 10 minutes, flexural modulus 100MPa
<Effervescent agent>
・ Uniform AZ manufactured by Otsuka Chemical Co., Ltd.
<Crosslinking aid>
・ DVB810 manufactured by Nippon Steel Chemical Co., Ltd.
<Heat stabilizer>
-Irganox 1010 manufactured by BASF Japan.

(Examples 1 , 2, 4, 5, 7, 8, Reference Examples 1 to 4, Comparative Examples 1 to 3)
For each of the a layer and the b layer, as shown in Table 1 or Table 2, each main raw material and each auxiliary raw material, a foaming agent, and a cross-linking aid are added to prepare a raw material, and Iruga is further added to the raw material as a heat stabilizer. Add 3 parts by mass of Knox 1010 (the ratio when the total mass of the main raw material and the auxiliary raw material is 100 parts by mass), mix with a Henshell mixer, put into a 60φ extruder, and the temperature inside the cylinder is 150 ° C. After melting and kneading in a state where the temperature was controlled so as to be so, the sheet formed by coextrusion molding to a predetermined foam thickness was once wound up. In the table, mass% indicates the ratio to the total mass of the main raw material and the auxiliary raw material, and the mass part indicates the ratio when the total mass of the main raw material and the auxiliary raw material is 100 parts by mass.

Next, the polyolefin resin foam sheet was crosslinked using an electron beam irradiator and then foamed on a salt salt bath (salt bath temperature 230 ° C.) to obtain a foam having the characteristics shown in the table. rice field. The physical characteristics and evaluation results of each are also described in the table.

(Comparative Examples 4 and 5)
As shown in Table 2, for each of the layers a and b, raw materials are prepared by adding each main raw material, each auxiliary raw material, a foaming agent, and a cross-linking aid, and Irganox as a heat stabilizer is further added to the raw material. Add 3 parts by mass of 1010 (the ratio when the total mass of the main raw material and the auxiliary raw material is 100 parts by mass), mix with a Henshell mixer, and then separately put into a 60φ extruder, and the temperature inside the cylinder is 150. After melting and kneading at a temperature controlled to ℃, sheet molding was performed by extrusion molding so as to have a predetermined foam thickness, and each was wound once. In the table, mass% indicates the ratio to the total mass of the main raw material and the auxiliary raw material, and the mass part indicates the ratio when the total mass of the main raw material and the auxiliary raw material is 100 parts by mass.

Next, each of the polyolefin-based resin foam sheets to be the a layer and the b layer was crosslinked using an electron beam irradiator, and then foamed on a salt salt bath (salt bath temperature 230 ° C.). Then, the opposite side of the surface to be the A surface of the a layer and the opposite side of the surface to be the B surface of the b layer were melted and pasted with hot air at 320 ° C. to obtain a foam having the characteristics described in the table. The physical characteristics and evaluation results of each are also described in the table.

Claims (7)

A sheet-like polyolefin resin foam having a laminated structure, the layer constituting the outermost layer on the A-side side, which is one main surface, is the a layer, and the outermost layer on the B-side side, which is the other main surface. When the layer constituting the above is layer b, the interlayer strength required by the following measurement method for any one surface (A surface) is 10 N / cm or more, and the layer strength is determined by the following measurement method for the other surface (B surface). The interlayer strength is less than 10 N / cm, the apparent density of the a layer is 200 to 500 kg / m ³ , the apparent density of the b layer is 25 to 150 kg / m ³ , and the interlayer fracture thickness is the b layer thickness. A polyolefin-based resin foam, characterized in that it is 80% or less of the above.
<Measurement of interlayer strength>
Squeeze 100 μm of the polyolefin resin foam from the surface of the surface to be measured with a slicing machine in the thickness direction (however, when the thickness of the a layer or b layer is less than 100 μm, the a layer or b layer is concerned. The thickness of the stripped material shall be the thickness of the layer).
The sample collected from the A surface side is referred to as sample A, and the sample collected from the B surface side is referred to as sample B. Subsequently, one adhesive layer having an adhesive strength that does not peel off from the sample surface in the measurement by the high-speed peeling tester described later with a thickness of 50 μm is bonded to both sides of these samples one by one, and then aged at 40 ° C. for 48 hours. By doing so, a double-sided adhesive tape for measuring the interlayer strength is produced.
Next, one of the pressure-sensitive adhesive layers constituting the double-sided adhesive tape for measuring the interlayer strength is lined with a polyester film having a thickness of 25 μm, and the sample base material is cut into a size of 1 cm in the width direction and 15 cm in the flow direction. The adhesive tape thus obtained and a polyester film having a thickness of 50 μm, a width of 3 cm, and a length of 20 cm were pressure-bonded at 23 ° C. and 50% RH by reciprocating a 2 kg roller once, and at 60 ° C. for 48 hours. After allowing to stand, it is allowed to stand at 23 ° C. for 24 hours.
At 23 ° C. and 50% RH, the side bonded to the 50 μm-thick polyester film is fixed to the mounting jig of the high-speed peeling tester, and the 25 μm-thick polyester film is placed in the 90-degree direction at a tensile speed of 15 m / min. The maximum strength when pulled and the sample substrate is torn is measured. The maximum strength obtained from the sample A is defined as the interlayer strength of the A surface, and the maximum strength obtained from the sample B is defined as the interlayer strength of the B surface.
The polyolefin-based resin foam according to claim 1, wherein the relationship between the interlayer strength Da (N / cm) on the A surface and the interlayer strength Db (N / cm) on the B surface satisfies the following equation 1.
Da-Db> 5 (N / cm) (Equation 1) The polyolefin-based resin foam according to claim 1 or 2, wherein the thickness of the b layer constituting the outermost layer on the B surface side is 100 to 500 μm, or 1/3 or less of the total thickness of the foam. body. A group in which the main component of the resin constituting the a layer constituting the outermost layer on the A surface side is an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer and ethylene propylene rubber (EPR, EPDM, etc.). The polyolefin-based resin foam according to any one of claims 1 to 3 , wherein the resin is at least one selected. From claim 1, the main component of the resin constituting the b layer constituting the outermost layer on the B surface side is at least one resin selected from the group consisting of polyethylene-based resin and polypropylene-based resin. 4. The polyolefin-based resin foam according to any one of 4. It includes a step of preparing two or more kinds of polyolefin resin compositions having different compositions, a step of coextruding the two or more kinds of polyolefin resin compositions to obtain a polyolefin resin sheet, and a step of subjecting the resin sheet to a cross-linking treatment. The method for producing a polyolefin-based resin foam according to any one of claims 1 to 5 . An adhesive tape using the polyolefin-based resin foam according to any one of claims 1 to 5 .