JP6785066B2 - Polyolefin resin foam sheet - Google Patents

Description

The present invention relates to a polyolefin-based resin foam sheet, and more particularly to a polyolefin-based resin foam sheet used for surface protection of a panel with a transparent electrode.

Conventionally, a panel with a transparent electrode in which a transparent electrode pattern is formed on one or both sides of a glass plate or a resin plate by ITO (indium tin oxide) or the like is widely used as a substrate for a flat panel display such as a liquid crystal display or a plasma display. ..
This type of panel with a transparent electrode is not usually stored alone in the manufacturing process of a flat display, but is stored by stacking a plurality of panels in a flat position.
In such a case, if the panels with transparent electrodes are directly laminated, the electrode pattern may be damaged. Therefore, a sheet called "interlaced paper" should be inserted between the panels to protect the surface of the panels with transparent electrodes. Is conventionally performed.

As the sheet used for surface protection of such a panel with a transparent electrode, a resin foam sheet is used because it is soft and has excellent cushioning properties (see Patent Document 1 below).

Japanese Unexamined Patent Publication No. 2005-329999

However, even when the resin foam sheet is used to protect the surface of the panel with the transparent electrode as described above, the transparent electrode may not be kept in a sufficiently healthy state, and the conventional resin foam sheet is the surface of the panel with the transparent electrode. It has the problem that it is not sufficiently suitable for protection.
An object of the present invention is to solve such a problem, and an object of the present invention is to provide a resin foam sheet suitable for surface protection of a panel with a transparent electrode.

As a result of diligent studies to solve the above problems, the present inventor has determined to use a polyolefin-based resin foam sheet having relatively excellent softness among general resin foam sheets in the above-mentioned applications. Found to be advantageous. In addition, the present inventor has found that the transparent electrode may be adversely affected by a trace amount of water, and has completed the present invention.

That is, in order to solve the above problems, the present invention is a polyolefin-based resin foam sheet formed of a polyolefin-based resin composition and used in contact with the electrode-forming surface of a panel with a transparent electrode, and has a relative temperature of 23 ° C. Provided is a polyolefin-based resin foam sheet having an equilibrium water content of 0.15% by mass or less at a humidity of 65% and an arithmetic mean roughness (Ra) of 27 μm or less on the surface abutting the electrode forming surface.

According to the present invention, the electrode-forming surface of the panel with a transparent electrode can be protected by a polyolefin-based resin foam sheet having a low equilibrium water content.
Moreover, since the surface of the polyolefin-based resin foam sheet that comes into contact with the electrode-forming surface is smooth, it has excellent adhesion to a panel with a transparent electrode.
Therefore, according to the present invention, moisture that has entered the interface between the polyolefin-based resin foam sheet and the panel with the transparent electrode from the air, moisture contained in the polyolefin-based resin foam sheet, and the like may adversely affect the transparent electrode. Can be reduced.

The schematic diagram which showed one usage mode of the polyolefin resin foam sheet.

Hereinafter, embodiments of the polyolefin-based resin foam sheet of the present invention will be described.
The polyolefin-based resin foam sheet of the present embodiment is used for surface protection of a panel with a transparent electrode, and is used in contact with the electrode forming surface of the panel with a transparent electrode.
The polyolefin-based resin foam sheet of the present embodiment is an extrusion-foamed sheet formed by extruding and foaming the polyolefin-based resin composition.

As shown in FIG. 1, the polyolefin-based resin foam sheet 1 of the present embodiment is, for example, when a plurality of panels 2 with transparent electrodes in a flat position are laminated in the vertical direction to form a laminated body 10 (up and down). ), It is used by interposing it between the panels 2 with transparent electrodes.

The thicker the polyolefin-based resin foam sheet 1 is, the more reliably it is possible to prevent the panels 2 with transparent electrodes from coming into contact with each other.
The polyolefin-based resin foam sheet 1 exhibits excellent compressive strength when the mass per unit area is large.
The polyolefin-based resin foam sheet 1 has a high foaming ratio and a low apparent density is excellent in cushioning property.

On the other hand, the thinner the polyolefin-based resin foam sheet 1 is, the more compact the laminate 10 can be.
In order to obtain the polyolefin-based resin foam sheet 1 having a thin thickness and excellent cushioning property, the mass of the polyolefin-based resin foam sheet 1 per unit area is preferably small.

From these viewpoints, the polyolefin-based resin foam sheet 1 of the present embodiment preferably has an average thickness of 0.4 mm or more and 3.0 mm or less, and more preferably 0.5 mm or more and 2.5 mm or less. preferable.
Further, the polyolefin-based resin foam sheet 1 preferably has a mass per unit area of 15 g / m ² or more and 110 g / m ² or less, and more preferably 20 g / m ² or more and 100 g / m ² or less.
Preferably the apparent density of the polyolefin-based resin foam sheet 1 is 0.04 g / cm ³ or more 0.1 g / cm ³ or less, more preferably 0.05 g / cm ³ or more 0.1 g / cm ³ or less it is especially preferred 0.05 g / cm ³ or more 0.09 g / cm ³ or less.

The polyolefin-based resin foam sheet 1 of the present embodiment has an equilibrium water content of 0.15% by mass or less at a temperature of 23 ° C. and a relative humidity of 65%, and has an arithmetic mean roughness (Ra) of the surface abutting on the electrode forming surface. ) Is 27 μm or less, which is important for more reliable protection of the transparent electrode.
Since the polyolefin-based resin foam sheet 1 has an equilibrium water content of 0.15% by mass or less, it is possible to prevent the transparent electrode from being adversely affected by the moisture contained in the polyolefin-based resin foam sheet 1. ..
The equilibrium water content of the polyolefin resin foam sheet 1 is preferably 0.14% by mass or less, and more preferably 0.13% by mass or less.
The polyolefin-based resin foam sheet 1 exhibits excellent adhesion to the electrode-forming surface when the arithmetic mean roughness (Ra) is 27 μm or less.
Therefore, the polyolefin-based resin foam sheet 1 has an arithmetic average roughness (Ra) of 27 μm or less, so that moisture in the air can be blocked from coming into contact with the transparent electrode by excellent adhesion.
The arithmetic mean roughness (Ra) of the surface of the polyolefin-based resin foam sheet 1 is preferably 25 μm or less, and more preferably 20 μm or less.
It is important that the polyolefin-based resin foam sheet 1 satisfies the above-mentioned regulations regarding surface roughness on both sides.
The equilibrium water content of the polyolefin resin foam sheet 1 is usually 0.01% by mass or more, and the arithmetic mean roughness (Ra) is usually 0.5 μm or more.

The polyolefin-based resin foam sheet 1 preferably has compression strain characteristics in the thickness direction within a specific range.
Specifically, the thickness of the polyolefin resin foam sheet 1 in the natural state is t ₀ (mm), and the thickness when a compressive load of 140 gf / cm ² is applied in the thickness direction is t ₁ (mm). After applying the compressive load, when the thickness when the compressive load is removed is t ₂ (mm), it is preferable that at least one of the following (1) and the following (2) is satisfied, and both are satisfied. Is more preferable.

20% ≤ [(t _0- t ₁ ) / t ₀ ] x 100% ≤ 60% ... (1)
80% ≤ (t ₂ / t ₀ ) x 100% ... (2)

In the following, the characteristic represented by the above "[(t _0- t ₁ ) / t ₀ ] x 100%" may be referred to as "crush amount".
Further, in the following, the characteristic represented by the above "(t ₂ / t ₀ ) x 100%" may be referred to as "compression restoration rate".

The polyolefin-based resin foam sheet 1 preferably has a bubble shape adjusted to a certain range, and has an average cell diameter of 0.1 mm or more and 2.0 mm or less in both the extrusion direction (MD) and the width direction (TD). Is preferable.

It is preferable that the polyolefin-based resin foam sheet 1 does not generate static electricity when it is removed from the surface of the panel 2 with a transparent electrode.
Therefore, it is preferable that the surface resistivity of the surface of the polyolefin-based resin foam sheet 1 in contact with the electrode-forming surface of the panel 2 with a transparent electrode is 1 × 10 ⁸ Ω or more and 1 × 10 ¹³ Ω or less.
The polyolefin-based resin composition constituting the polyolefin-based resin foamed sheet 1 has a predetermined compounding content in that the above-mentioned preferable properties can be more reliably exhibited with respect to the polyolefin-based resin foamed sheet 1. Is preferable.

Examples of the polyolefin resin to be the base polymer of the polyolefin resin composition include ultra-low density polypropylene resin (VLDPE), low density polypropylene resin (LDPE), linear low density polypropylene resin (LLDPE), and medium density polypropylene resin (LLDPE). MDPE), polyethylene-based resins such as high-density polyethylene resin (HDPE); polypropylene-based resins such as homopolypropylene resin (homoPP), random polypropylene resin (random PP), and block polypropylene resin (blockPP).

The polyolefin-based resin for forming the polyolefin-based resin foamed sheet 1 is preferably a polypropylene-based resin in that it can give a good stiffness (bending) strength to the polyolefin-based resin foamed sheet.
In particular, the main component of the polyolefin-based resin foam sheet is preferably a polypropylene-based resin called a high melt tension polypropylene resin (HMS-PP) or the like.
The HMS-PP is preferably a polypropylene-based block copolymer in which an olefin block has been introduced, or a polymer obtained by partially cross-linking such a polymer with an active energy ray such as radiation or an electron beam, or a chemical cross-link. ..
Further, as the HMS-PP, for example, a polypropylene resin having a melt tension at 230 ° C. as high as 5 cN or more can be adopted.

The melt tension of the polypropylene resin can be measured as follows.
That is, a sample made of a polypropylene resin is housed in a cylinder having an inner diameter of 15 mm arranged vertically in an upright state, and then heated at 230 ° C. for 5 minutes to melt.
After that, a piston is inserted into the cylinder from above, and a capillary (die diameter: 2.095 mm, die length: 8 mm, inflow angle: 90 °) in which the molten sample in the cylinder is provided at the lower end of the cylinder with the piston. (Conical)) is extruded at a constant extrusion speed of 0.0676 mm / s to obtain a string-like body.
Then, after passing this extruded string-like body through a tension detection pulley arranged below the capillary, it is wound up using a take-up roll, the initial speed at the start of winding is set to 3.447 mm / s, and then acceleration is applied. Is 13.1 mm / s ² , the winding speed is gradually increased, and the winding speed when the tension observed by the tension detection pulley drops sharply is defined as the "breaking point speed", and this breaking point speed is observed. Of the tensions observed until this time, the additive average value of the maximum value and the minimum value of the tension immediately before the breaking point velocity is defined as the melt tension.
The melt tension can be measured, for example, by using a testing machine commercially available from Chiast Co., Ltd. under the trade name "Twinbore Capillary Rheometer Rheological 5000T".

It is preferable that the polyolefin-based resin composition contains an olefin-based thermoplastic elastomer such as a polyethylene-based thermoplastic elastomer and a polypropylene-based thermoplastic elastomer together with the polyolefin-based resin.
More specifically, the polyolefin-based resin composition constituting the polyolefin-based resin foam sheet 1 contains the polyolefin-based resin and the olefin-based thermoplastic elastomer, and accounts for the total of the polyolefin-based resin and the olefin-based thermoplastic elastomer. It is preferable that the mass ratio of the polyolefin resin is 75% by mass or more and 95% by mass or less, and the mass ratio of the olefin-based thermoplastic elastomer is 5% by mass or more and 25% by mass or less.

The polyolefin-based resin composition constituting the polyolefin-based resin foam sheet 1 is a component that contributes to foaming such as a foaming agent and a bubble nucleating agent together with the above-mentioned base polymer, and a component that contributes to reduction of surface resistivity such as an antistatic agent. May be contained.

Examples of the foaming agent include hydrocarbons such as isobutane, normal butane, propane, pentane, hexane, cyclobutane and cyclopentane, and inorganic gases such as carbon dioxide and nitrogen.
Among them, as the foaming agent, mixed butane of isobutane and normal butane is preferable.

Examples of the bubble nucleating agent include inorganic particles.
When the inorganic particles are contained in the polyolefin-based resin foamed sheet at a certain ratio or more, it becomes easier to control the foamed state of the polyolefin-based resin foamed sheet.
On the other hand, the smaller the number of inorganic particles, the less likely it is that the transparent electrodes will be damaged by the inorganic particles.
Therefore, the polyolefin-based resin foam sheet of the present embodiment has a content of the inorganic particles of 0.3 mass by mass when the total amount of the polyolefin-based resin and the olefin-based thermoplastic elastomer is 100 parts by mass. The ratio is preferably 3 parts or more and 3 parts by mass or less.
Further, the inorganic particles preferably have a size larger than a certain level, but preferably have a small average particle diameter in that the risk of damaging the transparent electrode can be reduced.
In this respect, the inorganic particles preferably have an average particle diameter of 0.1 μm or more and 15 μm or less.
It should be noted that the inorganic particles are less likely to damage the transparent electrode if they are flat to some extent.
From this, it is preferable that the inorganic particles have a specific surface area of 1 m ² / g or more.
The specific surface area of the inorganic particles is preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and particularly preferably 10 m ² / g or less.

In the present embodiment, the average particle size of the inorganic particles means the median diameter (D50) obtained by the laser diffraction method.
Specifically, the average particle size can be measured using a SALD-2100 particle size distribution measuring device manufactured by Shimadzu Corporation.
The specific surface area means a value obtained by the BET method.
Specifically, the BET specific surface area can be measured using a BELSORP-miniII automatic specific surface area measuring device manufactured by Nippon Bell Co., Ltd.
As a pretreatment, the sample is heated and degassed at 130 ° C. for 3 hours at 1 Pa or less, and nitrogen gas is used as the adsorbed gas.

Examples of the inorganic particles used as the bubble conditioner in the present embodiment include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and potassium carbonate. , Calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, and glass are preferable, and talc particles or calcium carbonate particles are preferable.
That is, the polyolefin-based resin foam sheet of the present embodiment preferably contains at least one of talc particles and calcium carbonate particles.

The antistatic agent is a low molecular weight antistatic agent such as a surfactant that exhibits antistatic properties by bleeding out to the surface of a polyolefin resin foam sheet, or a polymer type antistatic agent composed of a polymer having a polar group. Antistatic agents can be mentioned.
As the antistatic agent of this embodiment, a polymer type antistatic agent is preferable.
It is advantageous for the polyolefin-based resin foam sheet to exhibit excellent antistatic performance when the content of the polymer-type antistatic agent is large.
On the other hand, in the polyolefin-based resin foam sheet, the smaller the amount of the polymer-type antistatic agent, the easier it is for the polyolefin-based resin and the olefin-based thermoplastic elastomer to exhibit the excellent mechanical properties as the sheet physical properties.
Therefore, in the polyolefin-based resin foam sheet of the present embodiment, when the total amount of the polyolefin-based resin and the olefin-based thermoplastic elastomer is 100 parts by mass, the polymer-type antistatic agent is 2 parts by mass or more and 8 parts by mass. It is preferably contained in a proportion of parts or less.

Examples of the polymer-type antistatic agent include ionics such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyesteramide, polyether esteramide, ethylene-methacrylic acid copolymer, and quaternary such as polyethylene glycol methacrylate-based copolymer. Examples thereof include ammonium salts, copolymers of olefin-based blocks and hydrophilic blocks described in JP-A-2001-278985.

Among these, a copolymer of an olefin-based block and a hydrophilic block is preferable, and a polyether-polyolefin block copolymer (a block copolymer of a polyether-based block and a polyolefin-based block) is charged with the polymer type. It is preferable to include it in the polyolefin resin composition as an inhibitor.
The polymer-type antistatic agent may be a mixture of two or more substances, and is a mixture of the block copolymer and polyamide for the purpose of further improving the antistatic performance, or polyamide. The system block may be further copolymerized.

More preferably, the polymer-type antistatic agent contains a copolymer of a polyether block and an olefin block containing 70 mol% or more of propylene as a main component.
The proportion of the polyether-polyolefin block copolymer in the polymer-type antistatic agent is preferably 70% by mass or more, and more preferably 80% by mass or more.
When the polyolefin-based resin composition forming the polyolefin-based resin foam sheet contains a polypropylene-based resin, the melting point Td (° C.) of the polymer-type antistatic agent is the melting point Tp (° C.) of the polypropylene-based resin and the following (3). ) Satisfy the relationship.

30 ° C ≤ (Tp-Td) ≤ 60 ° C ... (3)

A polyolefin-based resin composition containing a polypropylene-based resin satisfying the above relationship and a polymer-type antistatic agent smoothes the surface of the polyolefin-based resin foamed sheet when it is prepared into a polyolefin-based resin foamed sheet by an extrusion foaming method. It has the advantage of being easy to make.

The polyolefin-based resin foam sheet of the present embodiment may contain other components such as the polyolefin-based resin exemplified above, the olefin-based thermoplastic elastomer, and a polymer other than the polymer-type antistatic agent. The polyolefin-based resin foam sheet can further contain other components such as an antioxidant, an antioxidant, an ultraviolet absorber, a flame retardant, an antibacterial agent, and a colorant.
However, regarding these other components, the content in the polyolefin-based resin foam sheet is preferably kept at 5% by mass or less, more preferably 3% by mass or less, and is not substantially contained (for example). , Less than 1% by mass) is particularly preferable.

If a substance having a carbonyl group is contained as another component, the transparent electrode of the panel with the transparent electrode may be corroded. Therefore, it is preferable not to contain such a component.
Regarding whether or not a component having such a carbonyl group is contained, the peak derived from the carbonyl group is clearly visible when the surface of the polyolefin resin foam sheet is analyzed by FT-IR ATR. It can be confirmed by not being seen.
Specifically, the polyolefin-based resin foam sheet has 1700 to 1725 cm ^-1 (C = O expansion and contraction) peculiar to a carbonyl group when FT-IR ATR is performed on the surface of the panel with a transparent electrode in contact with the electrode forming surface. The peak intensity seen in) is preferably 1/2 or less than the peak intensity seen in 1450 to 1460 cm ^-1 (CH variation angle) derived from alkyl, and is preferably 1/3 or less. It is more preferable, and it is particularly preferable that it is 1/5 or less.

The polyolefin-based resin foam sheet of the present embodiment can be produced by extrusion-foaming the above-mentioned polyolefin-based resin composition through a circular die or the like.

In such extrusion foaming, the flat cell conditioner having a large specific surface area as described above is less likely to be exposed on the surface of the polyolefin resin foam sheet with its longitudinal direction in the extrusion direction.
Therefore, since the polyolefin-based resin foam sheet is produced by extrusion foaming, it is possible to suppress the adverse effect of inorganic particles on the panel with a transparent electrode.
Further, in order to make the flat inorganic particles aligned in the plane direction of the polyolefin resin foam sheet in the length direction, not only shearing is applied in the extrusion direction at the time of extrusion, but also stretching of a certain level or more in the circumferential direction is performed. Is preferably added.
That is, when the cylindrical foam sheet extruded from the circular die is cut open to produce the polyolefin-based resin foam sheet, it is preferable to perform an operation of increasing the diameter before cutting the cylindrical foam sheet.
However, excessive expansion of the diameter of the cylindrical foamed sheet may adversely affect the physical properties of the polyolefin-based resin foamed sheet, such as tearing of the bubble film.
Therefore, the degree of expansion of the cylindrical foam sheet is preferably 2.5 times or more and 5.0 times or less with respect to the diameter of the circular die (the diameter of the circle connecting the centers of the slit widths).

At this time, the equilibrium water content of the polyolefin-based resin foam sheet can be adjusted by the content of the polyolefin-based resin composition to be extruded and foamed.
That is, if a large amount of polymer or additive having a hydrophilic functional group is contained, the equilibrium water content of the polyolefin resin foam sheet tends to be high. Therefore, a polymer antistatic agent containing a hydrophilic polymer, a fatty acid metal salt, etc. It is preferable to suppress the content of the compound such as the additive in the polyolefin resin composition to a certain level or less.

At this time, the surface roughness (Ra) of the polyolefin-based resin foamed sheet can be adjusted by adjusting the foamed state of the surface layer portion of the polyolefin-based resin foamed sheet.
The surface roughness (Ra) of the polyolefin-based resin foam sheet usually tends to be higher as the air bubbles on the surface layer become coarser.
Therefore, the surface roughness (Ra) of the polyolefin-based resin foam sheet can be adjusted by adjusting the amount of the foaming agent and the bubble nucleating agent used, the cooling conditions at the time of extrusion foaming, and the like.

The polyolefin-based resin foam sheet of the present embodiment thus obtained is less likely to cause scratches on the panel with a transparent electrode or chemically change the transparent electrode, and is a flat panel display. It is also effective from the viewpoint of improving the yield in production.

The polyolefin-based resin foam sheet of the present embodiment can be used as a bag for wrapping a panel with a transparent electrode, in addition to the mode of being sandwiched between two panels with a transparent electrode as shown in FIG. It can be used.
The above examples are merely limited examples of the present invention, and the present invention should not be construed as being limited to the above examples.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
(Example 1)
Polypropylene resin (HMS-PP, manufactured by Borealis, trade name "WB140", MFR = 2.0 g / 10 min, melting point 160 ° C) 85 parts by mass, polypropylene thermoplastic elastomer (manufactured by Sun Aroma, trade name "Q100F", Blend polymer of random PP and ethylene-propylene copolymer rubber, MFR = 0.6g / 10min) 15 parts by mass, polymer type antistatic agent (polyether-polypropylene block copolymer "Perectron LMP" manufactured by Sanyo Kasei Co., Ltd. , MFR = 40 g / 10 min, melting point 115 ° C.) 4.5 parts by mass, as a bubble nucleating agent, Nitto Powder Co., Ltd. talc master batch (trade name "Tarpet 70P", average particle size (D50) 12 μm, specific surface area 8.5 m ² / g) talc particle-containing product, talc pure content 70% by mass) 1.0 parts by mass (talc pure content 0.7 parts by mass), and green pigment master batch (manufactured by Polypropylene Kogyo Co., Ltd., trade name) as a colorant "G64088") 1.2 parts by mass is supplied to the first extruder (φ90 mm) of a tandem extruder of φ90 mm-φ150 mm, melted in the extruder, and then butane (isobutane / normal butane =) as a foaming agent from the middle of the extruder. 95/5 (molar ratio)) is press-fitted in 5 parts by mass, kneaded, and then cooled to a temperature range (161 ° C.) suitable for foaming with a second extruder (φ150 mm), and the outlet diameter is 96 mm (slit clearance 0.45 mm). ) Was extruded and foamed into the atmosphere from the circular die.
The extruded cylindrical foam sheet is cooled along a cooling mandrel having a diameter of 300 mm and expanded in diameter, and the expanded cylindrical foam sheet is taken over and along the extrusion direction at one point in the circumferential direction. It was cut and opened to obtain a long strip-shaped polypropylene-based resin foam sheet (polyolefin-based resin foam sheet).
The strip-shaped polypropylene-based resin foam sheet was wound by a winder, and 400 m of the sheet was wound into a roll.
The mass per unit area of the polypropylene-based resin foam sheet was 80 g / m ² .
Next, the polypropylene-based resin foam sheet was left in a roll-shaped room at a temperature of 35 ° C. for about 24 hours for aging.
Then, the roll-shaped polypropylene resin foam sheet was rewound into a 3-inch paper tube by a rewinding machine and left in a room at about 20 ° C. for 24 hours to obtain the polypropylene resin foam sheet of Example 1. ..
The polypropylene-based resin foam sheet of Example 1 obtained at this time had a thickness of 1.0 mm.
The physical properties of the polypropylene-based resin foam sheet of Example 1 were measured based on the following method.

<Thickness (average thickness)>
The thickness of the polypropylene-based resin foam sheet was measured using a constant pressure thickness measuring machine (manufactured by Teklock, model "PC-440J").
Specifically, the thickness of the polypropylene-based resin foam sheet is such that a load of 95 g (including its own weight) is applied to a circular surface (area: 7.1 cm ² ) having a diameter of 3 cm using a cylindrical weight. The thickness when applied to the resin foam sheet was measured with a constant pressure thickness measuring machine.
The thickness of the polypropylene-based resin foam sheet was measured at 50 points every 5 cm in the width direction, and was used as the arithmetic mean value of the measured values.
If the width of the polypropylene-based resin foam sheet is narrow and it is not possible to secure 50 measurement points, the arithmetic mean value of all the measured values is used as the average thickness after securing as many measurement points as possible. ..

<Mass per unit area (basis weight)>
The mass per unit area of the polypropylene-based resin foam sheet is parallel to the first line along the direction orthogonal to the extrusion direction and parallel to the first line and separated from the first line by a distance of 20 cm in the extrusion direction. A polypropylene-based resin foam sheet was cut along the two lines with the second line to obtain a measurement sample, and the mass: W (g) and area: S (cm ² ) of the measurement sample were obtained. Based on this, it was calculated by the following formula.
If the polypropylene-based resin foam sheet has a width of 20 cm and is not large enough to cut a sample for measurement, it is cut into a rectangular shape to a possible size to obtain a section, and the mass W (g) of the section is obtained. ) And the area S (cm ² ), the mass per unit area of the polypropylene-based resin foam sheet was calculated by the following formula.

Mass per unit area (g / m ² ) = W / S x 10000

<Surface resistivity>
The surface resistivity of the polypropylene-based resin foam sheet was measured by the method described in JIS K6911-2006 "General Test Method for Thermosetting Plastics".
That is, the surface resistivity of the polypropylene-based resin foam sheet is measured by using a test device (Digital ultra-high resistance / micro ammeter R8340 and resiliency chamber R12702A manufactured by Advantest Co., Ltd.) and a load of about 30 N on the test piece. The electrodes were crimped, and the resistance value after charging at 500 V for 1 minute was measured and calculated by the following formula.
The test piece was usually prepared by cutting out a polypropylene-based resin foam sheet having a width of 100 mm, a length of 100 mm, and a thickness (total thickness of the polypropylene-based resin foam sheet).
The measurement is usually performed after placing the test piece in an atmosphere of a temperature of 20 ± 2 ° C. and a humidity of 65 ± 5% for 24 hours or more, and as a test environment, an atmosphere of a temperature of 20 ± 2 ° C. and a humidity of 65 ± 5%. I went there.
Further, the measurement was usually carried out with the number of test pieces being 5, and the measurement was carried out on both the front and back sides of each test piece so that a total of 10 measured values could be obtained.
The surface resistivity of the polypropylene-based resin foam sheet was, in principle, the arithmetic mean value of all 10 measured values.

ρs = π (D + d) / (D−d) × Rs

ρs: Surface resistivity (Ω / □)
D: Inner diameter (cm) of the annular electrode on the surface (7 cm for the resilience chamber R12702A)
d: Outer diameter (cm) of the inner circle of the surface electrode (5 cm for the resilience chamber R12702A)
Rs: Surface resistance (Ω)

<Surface roughness>
The surface roughness was measured according to JIS B0601: 2001.
Specifically, for the surface roughness, "Double scan high-precision laser measuring instruments LT-9500, LT-9010M" manufactured by Keyence Co., Ltd. are used as the measuring device, and "Non-non" manufactured by Coms Co., Ltd. is used as the data processing software. The measurement was performed using the contact contour shape roughness measurement system MAP-2DS.
Regarding the measurement conditions, the measurement range is 18000 μm, the measurement pitch is 5 μm, the measurement speed is 1000 μm / sec, the evaluation length is 12.5 mm, the reference length is 2.5 mm, the amount of light is set to 40, and the average filter is 2. The noise filter was set to 1.
The test piece was prepared by cutting out a polypropylene-based resin foam sheet having a width of 100 mm, a length of 100 mm, and a thickness of the original fabric.
The number of test pieces was 5, and the surface roughness in the extrusion direction and the width direction of both the front and back surfaces of each test piece was measured.
The arithmetic mean roughness (Ra) was obtained by summing the absolute values of the deviations from the average line to the measurement curve and averaging them with the reference length (n = 20).

<Average cell diameter in the MD direction and average cell diameter in the TD direction>
The average cell diameter in the MD direction and the average cell diameter in the TD direction of the polypropylene-based resin foam sheet were measured by the following test method.
First, a cross section of the polypropylene-based resin foam sheet cut out from the central portion in the width direction along the MD direction (extrusion direction) and a polypropylene-based resin foam sheet cut out along the TD direction (width direction perpendicular to the extrusion direction). The cross section is magnified 18 times (100 times in some cases) with a scanning electron microscope ("S-3000N" manufactured by Hitachi, Ltd. or "S-3400N" manufactured by Hitachi High-Technologies Corporation). I took a picture.
Next, four images were printed on A4 paper, and the average chord length (t) of the bubbles was calculated from the number of bubbles on an arbitrary straight line (length 60 mm) parallel to the cutting direction by the following formula. ..

Average string length t = 60 / (number of bubbles x magnification of photo)

However, for any straight line, the air bubbles should not come into contact only at the contacts as much as possible. If it touches, it is included in the number of bubbles. The measurement was performed at 6 locations in each direction.
The magnification of the photograph was calculated by measuring the scale bar on the photograph to 1/100 mm with "Digimatic Caliper" manufactured by Mitutoyo Co., Ltd. and using the following formula.

Photograph magnification = measured value of the length of the scale bar on the photo (mm) / display value of the scale bar (mm)

Then, the bubble diameter (d) in each direction was calculated by the following formula.

d (mm) = t / 0.616

Furthermore, the arithmetic mean of them was taken as the average bubble diameter.
Then, the average cell diameter of the cut surface cut along the MD direction was defined as Dm, and the average cell diameter of the cut surface cut along the TD direction was defined as Dt.

<Measurement of water content>
The polypropylene-based resin foam sheet was adjusted for about 24 hours in an environment of 23 ° C. and 65% RH before being used for measuring the water content.
That is, the equilibrium water content of the polypropylene-based resin foam sheet was determined by measuring the water content after adjusting the state under the above conditions.
The water content of the polypropylene-based resin foam sheet was measured by the Karl Fischer titration method (moisture vaporization method) of JIS K0068: 2001 (method for measuring the water content of chemical products).
Specifically, about 100 mg of a sample was set in a Karl Fischer water measuring device CA-200 and a water vaporizer VA-236S manufactured by Mitsubishi Chemical Analytech Co., Ltd. for measurement.
Anolyte during measurement, each of the catholyte Corporation API Corporation Ltd. Aquamicron AX, using Aquamicron CXU, measurement temperature to 128 ° C., carrier gas with _{N 2,} the flow rate is 250 ml / min The measurement was performed.
The number of tests for the sample is two, and the amount of water in the blank container measured at the same time (the average value of two tests) is subtracted from each amount of water, and that value is used as the amount of water contained in the sample. (Mass%) was calculated.
The water content of the polypropylene-based resin foam sheet was taken as the arithmetic mean value of the two measured values.

<Melting point>
The melting point of the raw material resin or the like was measured by the method described in JIS K7121: 1987 “Method for measuring transition temperature of plastic”.
However, the measurement method and temperature conditions were as follows.
A differential scanning calorimeter device DSC6220 (manufactured by SI Nanotechnology) is used as the device, and about 6.5 mg of the sample is filled in the bottom of the aluminum measuring container so that there is no gap, and the nitrogen gas flow rate is 30 mL / min. Then, after lowering the temperature from 30 ° C. to -60 ° C, holding for 10 minutes, raising the temperature from -60 ° C to 200 ° C (1st heating), holding for 10 minutes, and then lowering the temperature from 200 ° C to -60 ° C (Cooling). After holding for 10 minutes, a DSC curve was obtained when the temperature was raised (2nd heating) from -60 ° C to 200 ° C.
All temperature raising and lowering were performed at a rate of 10 ° C./min, and alumina was used as a reference material.
The melting point is a value obtained by reading the temperature at the top of the melting peak observed in the 2nd heating process.
When multiple melting peaks were observed, the one on the highest temperature side was taken as the melting point of the resin.

<Measurement of crushing amount and compression restoration rate>
Regarding the amount of crushing, 5 points of 10 cm square sample were cut out from the polypropylene resin foam sheet in the width direction, and the thickness was "t ₀ " under no load using a desktop thickness measuring device ("PC-440J" manufactured by Teclock Co., Ltd.). (Mm) ”is measured. Then, a load of 140 gf / cm ² is applied to measure the thickness“ t ₁ (mm) ”, and the crushing rate is calculated by the following formula.
The measurement was performed with n = 5, and the arithmetic mean value was taken as the crushing rate of the sample.

Crushed amount (%) = [(t _{0 −} t ₁ ) / t ₀ ] × 100%

The compression restoration rate was calculated from the following formula by reading the thickness "t ₂ (mm)" 5 minutes after removing the load from the same sample.

Compression restoration rate (%) = (t ₂ / t ₀ ) x 100%

<ITO corrosion, scratches>
Regarding the corrosiveness and scratch resistance to ITO, two 10 cm × 10 cm sections were cut out from a polypropylene resin foam sheet, and a glass with an ITO film (manufactured by Geomatec Co., Ltd., product number “0002”) was cut between the two sections. With a 1 kg weight placed on it, it can be placed in a high-temperature and high-humidity tank under the conditions of 60 ° C. and 95% RH, and held for 300 hours for evaluation.
Regarding the determination of corrosiveness, a microscope (100 times) was used to check the corrosion status of the ITO film of the glass with the ITO film after holding it for 300 hours as described above, and the state of deposits and damage to ITO was observed. Observe and perform based on the following criteria.

⊚: Corrosion and scratches of 100 μm or less are 3 or less per glass ○: Corrosion and scratches of 100 μm or less are 4 to 20 per glass △: Corrosion and scratches of 100 μm or less are glass 21 or more per glass and no corrosion of 100 μm or more ×: Corrosion or scratches of 100 μm or less are 21 or more per glass and corrosion of 100 μm or more 1 to 10 pieces XX: Corrosion of 100 μm or less 21 or more scratches and scratches per glass, and 11 or more corrosions of 100 μm or more

<Apparent density>
The apparent density of the polypropylene-based resin foam sheet was measured as follows in accordance with the test method described in JIS K 7222-1999.
That is, a 10 cm square test piece was cut from the sample so as not to change the original cell structure of the sample, and the mass and the size of each side were measured with a caliper and calculated by the following formula.

Apparent density (g / cm ³ ) = test piece mass (g) / test piece volume (cm ³ )

(Examples 2 to 6, Comparative Examples 1 to 3)
A polypropylene-based resin foam sheet having the characteristics shown in the table was prepared in the same manner as in Example 1 with the formulation shown in the table, and evaluated in the same manner as in Example 1.
The results are shown in the table.
TD-1:
Polyether-polypropylene block copolymer "Perectron LMP", MFR = 40g / 10min, melting point 115 ° C, manufactured by Sanyo Chemical Industries, Ltd.

TD-2:
Polyether-polypropylene block copolymer "Perestat 300", MFR = 30g / 10min, melting point 135 ° C, manufactured by Sanyo Chemical Industries, Ltd.

TD-3:
Polyether polyester amide-polyolefin copolymer "IPE-107M", MFR = 8 g / 10 min, melting point 156 ° C, manufactured by Ion Phase.

TD-4: Polyether-polypropylene block copolymer "IPE-fSTAT", MFR = 17 g / 10 min, melting point 98 ° C, manufactured by Ion Phase.

(Reference Examples 1 and 2)
A polypropylene-based resin foaming sheet was prepared in the same manner as in Example 1 except that the bubble nucleating agent was replaced with talc and used as a sodium bicarbonate citric acid-based chemical foaming agent (“PO410K” manufactured by Dainichiseika Co., Ltd.). Evaluated in the same way.
The results are shown in the table below together with the results of examples of formulations similar to the reference example.

From the results shown in the above table, it can be seen that according to the present invention, a polyolefin-based resin foam sheet suitable for surface protection of a panel with a transparent electrode can be provided.

1: Polyolefin resin foam sheet 2: Panel with transparent electrode

Claims (5)

A polyolefin-based resin foam sheet formed of a polyolefin-based resin composition containing inorganic particles as a bubble nucleating agent and a polymer-type antistatic agent, and used in contact with the electrode-forming surface of a panel with a transparent electrode. ,
Extruded foam sheet,
The equilibrium moisture content at a temperature of 23 ° C. and a relative humidity of 65% is 0.15% by mass or less, and the arithmetic mean roughness (Ra) of the surface abutting on the electrode forming surface is in either the extrusion direction or the width direction. A polyolefin-based resin foam sheet that is 27 μm or less even when measured . It is formed as an extruded foam sheet having an average thickness of 0.4 mm or more and 3.0 mm or less and an apparent density of 0.04 g / cm ³ or more and 0.1 g / cm ³ or less in the extrusion direction (MD) and width direction. The average cell diameter in (TD) is 0.1 mm or more and 2.0 mm or less, and the surface resistivity of the surface in contact with the electrode forming surface is 1 × 10 ⁸ Ω or more and 1 × 10 ¹³ Ω or less. The polyolefin-based resin foam sheet according to claim 1. The thickness in the natural state is t ₀ (mm).
The thickness when a compressive load of 140 gf / cm ² is applied in the thickness direction is t ₁ (mm).
When the thickness when the compressive load is removed after the compressive load is applied is t2 (mm),
The polyolefin-based resin foam sheet according to claim 1 or 2, which satisfies both the following (1) and the following (2).

20% ≤ [(t _0- t ₁ ) / t ₀ ] x 100% ≤ 60% ... (1)
80% ≤ (t ₂ / t ₀ ) x 100% ... (2)
The polyolefin-based resin composition contains a polyolefin-based resin and an olefin-based thermoplastic elastomer.
The polyolefin-based resin foam sheet according to any one of claims 1 to 3, wherein the weight ratio of the polyolefin-based resin to the total of the polyolefin-based resin and the olefin-based thermoplastic elastomer is 75% by mass or more and 95% by mass or less. .. The polyolefin-based resin contains a polypropylene-based resin, and contains
When the total amount of the polyolefin-based resin and the olefin-based thermoplastic elastomer is 100 parts by mass, the inorganic particles are contained in a proportion of 0.3 parts by mass or more and 3 parts by mass or less, and the polymer-type charging is performed. Contains 2 parts by mass or more and 8 parts by mass or less of the inhibitor.
The polyolefin-based resin foam sheet according to claim 4, wherein the melting point Td (° C.) of the polymer-type antistatic agent and the melting point Tp (° C.) of the polypropylene-based resin satisfy the relationship of the following (3).

30 ° C ≤ (Tp-Td) ≤ 60 ° C ... (3)