JP2013086471A - Cushion material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cushion material which can prevent the appearance of deposit more than before in a cushion material which is used suitably as a cushion material or the like for a substrate for a flat panel display or a display module for a flat panel display.SOLUTION: This is a cushion material where resin foam is used. In this cushion material, at least its surface is made of a polyolefin resin composition which contains at least one kind, between a polyethylene resin and a polypropylene resin, a polymeric antistatic agent, and an acid-modified polyolefin resin.

Description

  The present invention relates to a cushion material made of a resin foam, and more particularly, to a cushion material suitable for use in contact with a flat panel display substrate, the base plate for the substrate, a touch panel, and the like.

  Conventionally, base plates such as glass plates and acrylic plates used for flat panel displays such as flat-screen televisions are stored in a state where a sheet-like resin foam having excellent cushioning properties is interposed so as not to be damaged by impact. ing.

On the other hand, in a display module in which a component such as a semiconductor element is mounted on a flat panel display substrate in which a circuit is formed on the base plate, the sheet-like resin foam is subjected to a molding process, etc. Storage until the time of use is made by using a cushion material in which a mounting portion of the semiconductor element is recessed.
In other words, with a cushioning material with a flat surface, the protruding part of the semiconductor element or the like is strongly contacted when it is brought into contact with the display module. Therefore, the display module has a shape opposite to the shape on the back side. The cushion material is formed in a three-dimensional shape to be stored in a uniform contact state on the entire surface, or the cushion material is formed using a cushion material having a slightly larger recess than a semiconductor element or the like. The cushion material is stored so as not to contact the semiconductor element.

Conventionally, this type of cushioning material has been made of polyethylene resin foam or polypropylene resin foam, but using these foams simply generates static electricity between the substrate and foreign matter on the substrate. Therefore, an antistatic agent has been added to the polyethylene resin foam or polypropylene resin foam.
For example, Patent Document 1 below describes that a polyethylene resin foam sheet containing a polymer antistatic agent is used for packaging a glass for a thin TV.

JP 2009-62442 A

  Although the polymer type antistatic agent used in this Patent Document 1 has a low migration property compared to the low molecular type antistatic agent, the results of investigation and investigation by the present inventor show that it is a polyethylene resin or a polypropylene resin. In the case of using a polymer type antistatic agent for antistatic to a foam made of polyolefin resin, the substrate that has been considered to be sufficiently clean up to now by contact with a cushion material made of the foam. It was found that deposits were actually generated on the surface.

  That is, according to the knowledge obtained by the present inventors, at least a flat panel display substrate is formed by a polyolefin resin composition containing at least one of a polyethylene resin and a polypropylene resin and a polymer type antistatic agent. The conventional cushion material in which the surface which contacts is formed has the problem that the adhesion | attachment with respect to a board | substrate is not fully suppressed.

  The present invention aims to solve the above problems, and in a cushion material suitably used as a cushion material for a flat panel display substrate, a cushion material for a display module of a flat panel display, etc. An object of the present invention is to provide a cushioning material that can prevent the occurrence of deposits.

  The present invention relating to a cushioning material for solving the above-mentioned problem is a cushioning material using a resin foam, wherein at least one of a polyethylene resin and a polypropylene resin, a polymer antistatic agent, It is characterized in that at least the surface is formed of a polyolefin resin composition containing an acid-modified polyolefin resin.

  In addition, it is preferable that the cushion material of the present invention is used by bringing the surface into contact with any of a flat panel display substrate, the substrate base plate, and a touch panel.

  Further, the cushion material of the present invention is in the form of a flat surface, and at least three layers of a non-foamed layer constituting both surfaces and a foamed layer made of the resin foam provided inside the non-foamed layer. Preferably, the non-foamed layer has a laminated structure and is formed of the polyolefin resin composition.

  In the cushion material of the present invention, a three-dimensional shape is formed by molding a laminated foam sheet, and the laminated foam sheet is provided on both surfaces of a non-foamed layer constituting both surfaces and the non-foamed layer. It is preferable to have a laminated structure of at least three layers with a foamed layer made of the resin foam obtained, and the non-foamed layer is formed of the polyolefin resin composition.

In the cushion material of the present invention, it is preferable that at least one of maleic anhydride-modified polypropylene resin or maleic anhydride-modified polyethylene resin is contained in the polyolefin-based resin composition as the acid-modified polyolefin resin. As the polymer-type antistatic agent, it is preferable that a block copolymer having a polyether block and a polyolefin block in the molecule is contained in the polyolefin resin composition.
Furthermore, it is preferable that the acid value of the acid-modified polyolefin resin based on JIS K 0070 is 20 or more.

  In the present invention, since the polyolefin resin composition forming the surface contains an acid-modified polyolefin resin, a polyethylene resin or a polypropylene resin as a main component of the polyolefin resin composition and a polymer antistatic agent Compatibility can be improved, and the occurrence of deposits caused by the polymer antistatic agent can be suppressed.

  Since the cushion material of the present invention is preferably used for applications that require more cleanliness, the cushion material is brought into contact with any one of the flat panel display substrate, the substrate base plate, and the touch panel. The effect can be made more remarkable by being used.

  In addition, as described above, the cushion material of the present invention is a sheet having a flat surface, and at least 3 of a non-foamed layer constituting both surfaces and a foamed layer made of a resin foam provided inside the non-foamed layer. Preferably, the non-foamed layer is formed of the polyolefin-based resin composition, and according to this preferred structure, the surface strength is excellent and the common used widely in the extrusion foaming method. The further effect that it can manufacture easily by the method of extrusion may be exhibited.

  Moreover, the cushion material of this invention can be made into the cushion material suitable for the display module which has a complicated shape by shape | molding a laminated foam sheet as mentioned above, and forming a three-dimensional shape.

Furthermore, by adopting at least one of maleic anhydride-modified polypropylene resin or maleic anhydride-modified polyethylene resin, which is mentioned as a preferable acid-modified polyolefin resin, a polyethylene resin or polypropylene resin and a polymer type antistatic agent are used. There is an effect that the compatibility with can be further improved.
Similarly, by adopting a block copolymer having a polyether block and a polyolefin block in the molecule, which is listed as a preferred polymer type antistatic agent as described above, a polyethylene resin or polypropylene resin and a polymer type antistatic agent are used. There is an effect that the compatibility with the agent can be further improved.
In addition, if the acid value of the acid-modified polyolefin resin according to JIS K 0070 is 20 or more, the compatibility between the polyethylene resin or polypropylene resin and the polymer antistatic agent can be further improved.

  An embodiment of the cushion material of the present invention will be described with reference to a flat panel display substrate and a case where it is used for storage of a display module in which a semiconductor element or the like is mounted on the substrate.

As the substrate cushion material, for example, a relatively thick plate-like sheet having a thickness of 2 mm or more and 5 mm or less is used, and in this embodiment, a non-foamed layer in which a sheet-like resin foam is sandwiched between resin films. A laminated foam sheet having a three-layer structure of / foam layer / non-foam layer is used as a substrate cushion material.
On the other hand, as the cushion material for the display module, in the present embodiment, the laminated foam sheet is molded and provided with a three-dimensional shape in which concave portions are formed at the mounting positions of semiconductor elements and the like in the display module. Use.
First, this laminated foam sheet (plate-shaped cushion material) is demonstrated.

  Since the cushion material according to the present embodiment causes the non-foamed layer to contact the substrate, at least the non-foamed layer is made of at least one of polyethylene resin and polypropylene resin (A), a polymer type charging It is important to form with a polyolefin resin composition containing the inhibitor (B) and the acid-modified polyolefin resin (C).

  The polyethylene resin (A1) or the polypropylene resin (A2) serves as a base resin of the polyolefin resin composition, and specifically, the following can be employed.

(A1) Polyethylene resin Examples of the polyethylene (PE) resin include high-density polyethylene resin, medium-density polyethylene resin, linear low-density polyethylene resin, and low-density polyethylene resin (having long-chain branching).

(A2) Polypropylene resin Examples of the polypropylene (PP) resin include a homopolypropylene resin composed only of a propylene component, and a random copolymer and a block copolymer containing an olefin component such as ethylene in addition to the propylene component.
In addition, when employ | adopting a copolymer, it is desirable to use what contained olefins other than propylene 0.5-30 weight% in the copolymer in the ratio of 1-10 weight% especially preferably. .
Examples of the olefin component in this case include ethylene or an α-olefin having 4 to 10 carbon atoms.
In particular, a high melt tension polypropylene resin (HMS-PP) is preferable, and for example, those described in Japanese Patent No. 2521388 can be suitably used.

(A3) Other polyolefin resins In addition to these, as the base resin of the polyolefin-based resin composition of the present embodiment, polyethylene resins (A1) such as polybutene resins and poly-4-methylpentene-1 resins, and polypropylene A small amount of a polyolefin resin excellent in compatibility with the resin (A2) can be contained.
The ratio of the other polyolefin resin to the total amount of the polyethylene resin (A1) and the polypropylene resin (A2) is 10% by mass or less, preferably 5% by mass or less, and particularly preferably 1% by mass or less. The base resin of the polyolefin-based resin composition is composed of only one or more kinds of polyethylene resins and / or only one or more kinds of polypropylene resins, and substantially contains other polyolefin resins. Most preferably, it is not contained.

(B) Polymeric antistatic agent Examples of the polymeric antistatic agent include ionomers (ionomer resins) such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyesteramide, polyetheresteramide, and ethylene-methacrylic acid copolymer. And quaternary ammonium salts such as polyethylene glycol methacrylate copolymers, and copolymers of olefin blocks and hydrophilic blocks described in JP-A No. 2001-278985.

  Examples of the ionomer resin that can be used as the polymer antistatic agent include commercially available potassium ionomer resins from Mitsui DuPont Polychemical Co., Ltd. under the trade name “ENTILA MK400” and the trade name “ENTILA SD100”. .

  Among these, from the viewpoint of compatibility with the polyethylene resin (A1) and polypropylene resin (A2) as described above, a copolymer of an olefin block and a hydrophilic block is preferable, and a polyether-polyolefin block copolymer is preferable. A blend (a block copolymer of a polyether block and a polyolefin block) can be suitably employed as the polymer-type antistatic agent.

(C) Acid-modified polyolefin resin Examples of the acid-modified polyolefin resin in the present embodiment include those obtained by acid-modifying the molecular ends of polyethylene resins and polypropylene resins, and acid-modified groups and acid-terminated polyethylene resins and polypropylene resins. Examples include a graft of a polymer or oligomer having a modifying group, a block copolymer of a polyethylene block or a polypropylene block and an acid-modified block.
Among these, from the viewpoint of compatibility with the polyethylene resin (A1) and the polypropylene resin (A2), those having an acid-modified group only at the molecular terminal are preferable, and a terminal acid-modified polyethylene resin having a molecular weight (Mw) of about 15,000 to 50,000. Alternatively, it is preferable to employ a terminal acid-modified polypropylene resin.

Examples of the acid for modifying the molecular terminal include maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid, and acid anhydrides thereof.
Among these, maleic anhydride is preferable, and the acid-modified polyolefin resin (C) is a maleic anhydride-modified polypropylene resin having a molecular weight (Mw) of about 15,000 to 50,000, and a maleic anhydride-modified polyethylene. It is preferable to employ a resin.

The acid-modified polyolefin resin such as maleic anhydride-modified polypropylene resin or maleic anhydride-modified polyethylene resin preferably has an acid value of 20 or more determined based on JIS K 0070 (neutralization titration method).
The acid value is preferably 20 or more because the effect of the compatibility between the polyethylene resin (A1) or the polypropylene resin (A2) and the polymer antistatic agent (B) is particularly remarkable. It is.
In addition, the upper limit of an acid value is 60 normally, and it is preferable that it is 55 or less.

The contents of the base resin (A1 to A3) and the polymer antistatic agent (B) in the polyolefin resin composition in the present embodiment are not particularly limited, but the surface resistivity of the cushion material Is preferably in the range of 1 × 10 ⁸ Ω / □ or more and 1 × 10 ¹³ Ω / □ or less. Therefore, among those capable of imparting such a surface resistivity to the non-foamed layer, a higher polymer is used. It is preferable to select a blending ratio that can reduce the content of the mold antistatic agent.
The surface resistivity of the cushion material is more preferably in the range of 1 × 10 ⁹ Ω / □ to 1 × 10 ¹² Ω / □, and more preferably 1 × 10 ⁹ Ω / □ to 1 × 10 ¹¹ Ω / □. □ Most preferably within the following range.

The content of the polymer-type antistatic agent capable of imparting such a surface resistivity value to the surface of the non-foamed layer (the surface of the cushion material) is usually 2% by mass or more in the entire polyolefin resin composition. 30% by mass or less.
The reason why the lower limit of the polymer type antistatic agent is set to 2% by mass is that if the content is lower than this, the cushioning material may not exhibit a sufficient antistatic effect. Yes, the upper limit is set to 30% by weight. Even if a polymer type antistatic agent is included exceeding this, not only is it difficult to obtain an antistatic effect corresponding to the content, but the polymer type This is because there is a possibility that the adhesion of the antistatic agent to the substrate cannot be sufficiently suppressed.
In addition, since the polymer antistatic agent is generally more expensive than polyethylene resin or polypropylene resin, if it is excessively contained, the material cost of the cushion material may be increased.

  Therefore, from the viewpoint of the effect of suppressing deposits on the substrate, the polymer-type antistatic agent has a proportion in the range of 3% by mass or more and 20% by mass or less of the entire polyolefin-based resin composition. It is preferable to contain, and it is especially preferable that it is contained in the ratio which becomes the ratio for the whole polyolefin resin composition in the range of 5 mass% or more and 10 mass% or less.

  On the other hand, the acid anhydride-modified polyolefin resin is usually a polyolefin-based resin in order to more reliably exert a function as a compatibilizer between a polyethylene resin or a polypropylene resin and a polymer type antistatic agent. It can be made to contain so that the ratio to the whole resin composition may be 2-15 mass%, and it is preferable to contain so that it may become 2-10 mass% especially.

  Although not described in detail here, the polyolefin-based resin composition can contain a general compounding agent, for example, various stabilizers such as weathering agents and deterioration inhibitors, processing aids such as lubricants, A slip agent, an antifogging agent, a pigment, a filler and the like can be appropriately added as additives.

In addition, in order to enhance the antistatic effect, an anionic surfactant such as alkylbenzene sulfonate, for example, sodium dodecylbenzenesulfonate, and other low molecular weight antistatic agents such as other surfactants or alkali metal salts are used in combination. May be.
However, these additions may increase the amount of deposits on the substrate. Therefore, the amount used is preferably contained so that the proportion of the polyolefin resin composition is less than 0.5% by mass. It is preferable not to contain a low molecular type antistatic agent.

In addition, the non-foamed layer on the one surface side and the non-foamed layer on the other surface side may be formed of a polyolefin resin composition having the same composition, or may be formed of polyolefin resin compositions having different compositions.
Further, the non-foamed layer on the one surface side and the non-foamed layer on the other surface side may have the same thickness or different thicknesses.
In general, in the case of a plate-like laminated foamed sheet having a thickness of 2 mm or more and 5 mm or less as described above, the thickness of each non-foamed layer can be usually 20 μm or more and 90 μm or less, preferably 40 μm. The thickness is not less than 90 μm.

The foam layer formed between these non-foam layers is a layer made of a resin foam for imparting appropriate cushioning properties to the cushion material.
The foamed layer can be formed of the same polyolefin-based resin composition as exemplified in the non-foamed layer.
If the antistatic performance is not required even for the foamed layer, the non-foamed layer need not contain a polymer antistatic agent or an acid-modified polyolefin resin.
However, in consideration of the case where the surface of the cushion material is damaged and the foamed layer is exposed, it is desirable that the foamed layer contains a polymer type antistatic agent or an acid-modified polyolefin resin.

The polyethylene resin for forming the foamed layer has a melt mass flow rate (hereinafter also referred to as “MFR”) of 2 g / 10 min to 6 g / 10 min and a resin density of 925 kg / m ³ to 935 kg / A low density polyethylene resin of m ³ or less is preferred.
The low density polyethylene resin of MFR as described above is preferable, if the MFR is less than 2 g / 10 min, a problem occurs in the kneadability with the polymer type antistatic agent in the extruder and the antistatic performance is lowered. This is because it may be difficult to form a good foamed layer due to foam breakage during extrusion foaming.
Also, it is preferable that the MFR is 6 g / 10 min or less. If the MFR exceeds 6 g / 10 min, the melt tension becomes too low to make it difficult to obtain a low-density foam layer, or the foam layer is formed by extrusion foaming. This is because a meander-like deposit is likely to be generated at the tip of the die.
That is, it is preferable to have the MFR as described above. By adopting a polyethylene resin exhibiting such an MFR, the cushion material according to this embodiment can be easily manufactured by extrusion foaming. In addition, the cushioning property can be improved.

  The melt mass flow rate is a method described in JIS K 7210: 1999 “Plastic-thermoplastic plastic melt mass flow rate (MFR) and melt volume flow rate (MVR) test method” B method (provided that the test temperature is 190 ° C. , Load 21.18 N).

The polyethylene-based resin preferably has the density as described above. When the resin density is less than 925 kg / m ³ , the foaming agent diffuses quickly after extrusion, and the rigidity of the resin itself is small. This is because shrinkage may not be suppressed, and if the resin density exceeds 935 kg / m ³ , the rigidity of the resin itself may be too high and the cushioning property may be impaired.
That is, as for the point that it is preferable to have the density as described above, the cushion material according to the present embodiment is formed by extrusion foaming by adopting a polyethylene resin exhibiting such density as in the case of the MFR. This is because it can be easily manufactured and has excellent cushioning properties.

  In the case where the foamed layer is formed of a polypropylene resin, the polypropylene resin is preferably a high melt tension polypropylene resin (HMS-PP). In particular, the melt tension after passing through an extruder is 4 cN. It is preferable to employ a high melt tension polypropylene resin that is 10 cN or less and has a breaking point speed of 12 m / min or more and 26 m / min or less after passing through an extruder.

  In addition, about "the melt tension after passing through an extruder and the breaking point speed", for example, "Toyo Seiki Seisakusho Co., Ltd." "Lab plast mill (model: 4M150 (main body) to model: 2D15W (two-screw extruder, Attaching a die having a diameter of 15 mm, L / D: 17) and a circular opening of 3 mm in diameter)) is used to set the temperature of all zones of the twin screw extruder to 220 ° C. After fixing the number of revolutions to 60 rpm and extruding a strand-shaped measurement sample (HMS-PP), and subsequently cooling the strand-shaped sample through a 1 m water tank containing 20 ° C. water, the length Can be obtained by measuring the melt tension and the breaking speed of the sample cut with a cutter so as to form a 4 mm rod-shaped pellet.

Further, “melt tension and breaking speed” can be measured using a twin-bore capillary rheometer, and specifically can be measured as follows.
First, a high melt tension polypropylene resin (HMS-PP) serving as a sample is accommodated in a cylinder having an inner diameter of 15 mm arranged in a vertical direction, heated at 230 ° C. for 5 minutes, and then melted. And a capillary (die diameter: 2.095 mm, die length: 8 mm, inflow angle :) provided at the lower end of the cylinder so that the extrusion speed is 0.0773 mm / s (constant). The molten resin is extruded in a string shape from 90 degrees (conical), and the string is passed through a tension detection pulley disposed below the capillary, and then wound using a winding roll.
At this time, the initial speed at the beginning of winding is 4 mm / s, the subsequent acceleration is 12 mm / s ² , the winding speed is gradually increased, and the winding speed when the tension observed by the tension detection pulley is drastically reduced The “breaking point speed” is measured, and the maximum tension until the “breaking point speed” is observed is measured as “melting tension”.

  The high melt tension polypropylene resin having such characteristics is preferable as the foam layer forming material, and by using such a high melt tension polypropylene resin, the moldability superior to the cushion material according to the present embodiment is obtained. For example, by forming a foam layer with the above high melt tension polypropylene resin, a three-dimensional shape can be formed by performing a molding process to improve the plate-like cushion material according to the present embodiment for the display module. This is because excellent formability can be exhibited during the application.

  Examples of the high melt tension polypropylene resin exhibiting such characteristics include those sold under the trade names “WB135” and “WB140” by Borealis, and commercially available under the trade name “Pro-fax F814” from Basell. And the like.

In forming the foam layer, it is possible to employ a method of extrusion foaming by adding a material for forming bubbles to the polyethylene resin or polypropylene resin as described above.
That is, the polyolefin resin composition for forming the foamed layer can further contain a foaming agent, a bubble regulator, and the like. Examples of the foaming agent include a volatile foaming agent, an inorganic gas foaming agent, and a decomposition type. A foaming agent etc. can be used individually or in combination of 2 or more, respectively.

Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane and hexane, and cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane. As the agent, an inert gas such as carbon dioxide, nitrogen or air is used.
Examples of the decomposable foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate, and the like.

  In addition, the bubble regulator is not particularly limited as long as it is generally used as a bubble regulator. For example, talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, Examples include magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, inorganic compounds such as glass beads, and organic compounds such as polytetrafluoroethylene. .

  The foamed layer formed of such a material preferably has a foaming ratio of 2 times or more and an open cell ratio of 70% or less in that the cushioning material can exhibit good cushioning properties. It is preferable.

Next, a manufacturing method for manufacturing such a plate-shaped cushion material will be described.
In this embodiment, a cushioning material can be produced by carrying out extrusion foaming using an extruder that is carried out in the production of a general sheet-like resin foam (foamed sheet).
For example, a first extruder for extruding a polyolefin resin composition for forming a non-foamed layer on one side, a second extruder for extruding a polyolefin resin composition for forming a foamed layer, and the other side Three extruders with a third extruder for extruding the polyolefin resin composition for forming the non-foamed layer on the side are prepared, and the melt extruded from these is joined to form a non-foamed layer / foamed layer / A method of forming a laminated state of non-foamed layers and co-extruding from a flat die or a circular die can be employed.

In the case of using a circular die, a cylindrical resin foam extruded from a circular die is plated with a pinch roller using two extruders, the first extruder and the second extruder. The cushioning material according to the present embodiment can be produced by adopting a method of crushing into a shape.
That is, extrusion foaming is performed from a circular die so that a non-foamed layer is formed on the outer side of the cylindrical resin foam, and a foamed layer is formed on the inner side. It is possible to produce a plate-like cushion material having a non-foamed layer / foamed layer / non-foamed layer laminated structure by allowing the foamed layers to be thermally fused with each other.

  In place of such a method, a polyolefin resin composition containing at least one of polyethylene resin and polypropylene resin, a polymer antistatic agent, and an acid-modified polyolefin resin is melt-kneaded with an extruder. Then, it is extruded into a film using a flat die on one side of a separately prepared foamed sheet, laminated and cooled, and after the cooling, the molten resin is similarly extruded on the other side to form a non-foamed layer / foam. A plate-shaped cushioning material having a layer / non-foamed layered structure can also be produced.

Further, a plate-shaped cushion having a non-foamed layer / foamed layer / non-foamed layer laminated structure in which a resin film is produced from the polyolefin-based resin composition and the resin film is thermally laminated on both sides of a separately produced foamed sheet. Materials can also be made.
Furthermore, it is also possible to form a non-foamed layer with a resin other than the polyolefin resin by using a dry film in which one surface side is formed of the polyolefin resin composition and the other surface side is formed of another resin.
For example, a dry laminate film obtained by laminating a resin film formed of the polyolefin resin composition and a resin film formed of a polystyrene resin with an adhesive is laminated on both surfaces of a polystyrene resin foam sheet to form a non-foamed layer / foam A plate-shaped cushioning material having a layer / non-foamed layered structure can also be produced.
However, if different materials are included, there is a risk of problems in the recyclability of the used cushioning material. Therefore, when the non-foamed layer is formed of a polyolefin resin composition, the foamed layer is also polyolefin. It is preferable to form with a resin-based resin composition.

  The cushion material according to the present embodiment thus obtained can prevent the occurrence of deposits due to static electricity when it is interposed between plasma display panel substrates in the form of interleaving paper. Component transfer from the material to the substrate surface can be suppressed, and deposits can be suppressed as compared to conventional cushion materials.

  Further, the cushion material for the display module according to the present embodiment produces a laminated foam sheet having a non-foamed layer / foamed layer / non-foamed layer laminated structure in the same manner as the cushion material for the substrate. The laminated foam sheet can be produced by forming a three-dimensional shape by subjecting it to a molding process such as a cutting process, a punching process, or a press molding.

For example, in a display module of a plasma display panel, a light emitting cell is formed between two glass substrates, a front glass substrate and a back glass substrate, and the back glass substrate also serves as a heat radiator. A printed circuit board on which a semiconductor element or other chip component is mounted is mounted via a metal chassis, and the display module is mounted in such a manner that the back side is directly abutted on a plate-shaped cushion material. If placed, the weight of the display module is concentrated on some components mounted on the printed circuit board, which may cause the components to fail.
Therefore, by forming a three-dimensional shape on one surface side by press molding so that the printed circuit board or the like does not directly contact the cushion material, a cushion material suitable for storage and transportation of the display module can be obtained.

  In addition, when this cushion material and the display module are stored as a set and stacked in a plurality of stages, the lower surface of the cushion material that supports the uppermost display module from below is placed on the second display module from the top. Although it will contact | abut on a front glass substrate, the deposit | attachment to a glass substrate will be suppressed also in this case.

In the present embodiment, the case where a laminated foam sheet having a non-foamed layer / foamed layer / non-foamed layer laminated structure is used as a cushion material is exemplified. For example, only a foamed layer single-layer resin foam is used. The cushion material made of is also within the scope of the present invention.
For example, a resin foam sheet obtained by extruding and foaming a polyolefin resin composition containing at least one of a polyethylene resin and a polypropylene resin, a polymer-type antistatic agent, and an acid-modified polyolefin resin is used as the cushion material of the present invention. It can be.
Even in such a case, as long as the surface in contact with the substrate is formed of the polyolefin resin composition as described above, the laminated foam sheet having a non-foamed layer / foamed layer / non-foamed layer laminated structure is cushioned. As in the case of the material, the antistatic performance of the polymer antistatic agent can be exhibited, and the occurrence of deposits on the substrate surface can be suppressed by the polymer antistatic agent property.

In addition to such cases, the present invention can be implemented by adding various modifications to the specific examples shown in the present embodiment, and is not limited to the above examples.
For example, in the present embodiment, the cushion material of the present invention has been described mainly by using the flat panel display substrate as an example, but the cushion material of the present invention is used for a flat panel display. It is also suitable for protection of touch panels made by combining a base plate (glass plate, acrylic plate, etc.) or flat panel display and a transparent sheet-like touch sensor before forming a substrate. The cushion material used in contact with the body is also within the range intended as the cushion material of the present invention.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

(Production of foam sheet)
The composition shown in Table 1 below is extruded and foamed to form a foam sheet having a foaming ratio of 3 times and a thickness of 2.3 mm. In Example 6, the foam sheet thus formed is used as a cushion material, and in other cases, A non-foamed layer was formed with the formulation shown in Table 1 on both surfaces of the obtained foamed sheet, and a cushion material composed of a laminated foamed sheet having a three-layer structure of non-foamed layer / foamed layer / non-foamed layer was produced.
In Example 7, a foam sheet having a foaming ratio of 19 times and a thickness of 0.5 mm was formed, and this foam sheet was used as a cushion material.

(Evaluation)
Each cushion material was evaluated as follows.

(Cloudy phenomenon evaluation)
The evaluation of the contamination due to the component transfer to the partner material to be contacted is carried out by placing a cushioning material on the glass plate, leaving the weight on it, and observing the degree of dirt on the glass plate with the naked eye. went.
Specifically, the cushion material is cut into a size of 5 cm × 5 cm, placed on a glass plate, and further loaded with a 4 kg weight (load of about 15.7 kPa), temperature 65 ° C., relative humidity After being left in a 90% tank for 24 hours, it was naturally cooled for 1 hour at a temperature of 25 ° C. and a relative humidity of 60%.
Then, the cushion material was removed, and the occurrence of cloudiness (dirty condition) on the surface of the glass plate was evaluated with the naked eye, and the results were evaluated in five stages as shown below.

(Criteria)
1. I can not confirm the transition at all.
2. If you look closely, you can see the transition.
3. The transition can be confirmed slightly.
4). The transition can be clearly seen at a glance.
5. Migrate can be confirmed on the entire surface.

(Contact angle evaluation)
Drop Master300 type contact angle meter with water contact angle of 22 ° C and humidity of 60% to the sample (glass plate with transferred cushion material component) prepared in the same way as the sample used for cloudy phenomenon evaluation The contact angle was measured by the droplet method using Kyowa Interface Science Co., Ltd.
The distilled water was distilled water that was allowed to stand for 24 hours in an environment of a temperature of 22 ° C. and a humidity of 60%. The dropping amount was 1.0 μL, and the contact angle after 3 seconds had been measured after dropping. The contact angle was calculated by the θ / 2 method.
The contact angle generally decreases as the surface of the substrate becomes cleaner, and it can be determined that a contact angle of 10 degrees or less is in a clean state with almost no deposits. it can.

(Surface specific resistivity)
For the cushion materials of Examples and Comparative Examples, the surface resistivity was measured by the method described in JIS K 6911: 1995 “Thermosetting Plastics—General Test Method”.
Specifically, after a flat square test piece having a side of 10 cm is left in an atmosphere of a temperature of 22 ° C. and a humidity of 60% for 24 hours, a test apparatus (manufactured by Advantest Corporation) under an environment of a temperature of 22 ° C. and a humidity of 60% is used. Using a digital ultra-high resistance / microammeter R8340 and a resiliency chamber R12702A), an electrode is crimped to a test piece with a load of about 30 N, a voltage of 500 V is applied, and a resistance value after one minute has elapsed. Measured and calculated by the following formula.
ρs = π (D + d) / (D−d) × Rs
However,
ρs: Surface resistivity (Ω / □)
D: Inner diameter (cm) of the annular electrode on the surface (7 cm for the resiliency chamber R12702A)
d: outer diameter (cm) of inner circle of surface electrode (5 cm for resiliency chamber R12702A)
Rs: Surface resistance (Ω)

The measurement was performed on three sheets, and an arithmetic average was obtained to obtain each surface specific resistivity.

These evaluation results are shown in Table 2 below.

  From the above, it can be seen that according to the present invention, it is possible to prevent the occurrence of deposits on a flat panel display substrate or the like more than a conventional cushion material.

Claims (7)

A cushion material using a resin foam,
A cushioning material characterized in that at least a surface is formed by a polyolefin resin composition containing at least one of a polyethylene resin and a polypropylene resin, a polymer antistatic agent, and an acid-modified polyolefin resin.   The cushioning material according to claim 1, wherein the surface is in contact with any one of a flat panel display substrate, the substrate base plate, and a touch panel.   The non-foamed layer has a laminated structure of at least three layers of a non-foamed layer that forms a flat surface and has both surfaces and a foamed layer made of a resin foam provided inside the non-foamed layer. The cushion material of Claim 1 or 2 currently formed by the said polyolefin resin composition.   The laminated foam sheet is molded to form a three-dimensional shape, and the laminated foam sheet is composed of a non-foamed layer constituting both surfaces, and a foamed layer formed of a resin foam provided inside the non-foamed layer The cushion material according to claim 1, wherein the non-foamed layer is formed of the polyolefin resin composition.   The cushion according to any one of claims 1 to 4, wherein at least one of maleic anhydride-modified polypropylene resin or maleic anhydride-modified polyethylene resin is contained in the polyolefin resin composition as the acid-modified polyolefin resin. Wood.   6. The polyolefin resin composition according to any one of claims 1 to 5, wherein the polyolefin-based resin composition contains a block copolymer having a polyether block and a polyolefin block in the molecule as the polymer-type antistatic agent. Cushion material.   The cushion material according to any one of claims 1 to 6, wherein an acid value of the acid-modified polyolefin resin based on JIS K 0070 is 20 or more.