KR102477346B1 - Polyethylene based resin foamed sheet - Google Patents

Abstract

The present invention provides a thin polyethylene resin foam sheet having excellent antistatic properties by incorporating a polyethylene component having a specific melting point and an antistatic agent component into the polyethylene resin foam sheet.

Description

Polyethylene-based resin foam sheet {POLYETHYLENE BASED RESIN FOAMED SHEET}

The present invention relates to a polyethylene-based resin foam sheet.

BACKGROUND OF THE INVENTION Conventionally, flat panel displays such as liquid crystal displays and plasma displays are manufactured using glass substrates having transparent electrodes formed on the surface thereof.

The said glass substrate is usually stored in the state of the laminated body which laminated|stacked multiple things in a horizontal position instead of being stored independently in the manufacturing process of a flat panel display etc..

In this case, when the glass substrate is directly laminated, there is a risk of damaging the transparent electrode. For this reason, it has conventionally been used as a buffer material by inserting a sheet called "lamination" or the like between glass substrates.

As such a cushioning material sheet, a resin foam sheet is used because it is soft and has excellent buffering properties (see Patent Document 1 below).

Japanese Unexamined Patent Publication No. 2005-329999

As the resin foam sheet used for the above applications, it may be considered to use a polyethylene-based resin foam sheet having relatively excellent softness.

After the glass substrate is covered with this type of resin foam sheet, there is a possibility of generating static electricity when the resin foam sheet is removed.

Foreign matter may adhere to the glass substrate on which static electricity is generated.

In this respect, resin foam sheet is required to have antistatic properties.

In addition, it has been conventionally studied to incorporate a polymer type antistatic agent capable of exhibiting the antistatic property over a long period of time in a resin foam sheet.

However, the conventional polyethylene-based resin foam sheet has a problem in that it is difficult to exhibit sufficient antistatic properties unless a relatively large amount of polymer type antistatic agent is contained.

Further, in general, polymeric antistatic agents are mainly composed of a polymer having a high polar region with low affinity to polyethylene-based resins in their molecular structure, and do not show sufficiently high affinity to polyethylene-based resins as a whole.

For this reason, the polymer type antistatic agent has a problem that it is difficult to exhibit good dispersibility in the polyethylene-based resin foam sheet.

If the polymer type antistatic agent is not sufficiently dispersed and is present in the polyethylene-based resin foam sheet in the form of an agglomerate, it is difficult to sufficiently exhibit the antistatic effect.

In addition, the polyethylene-based resin foam sheet may not exhibit sufficient mechanical strength if aggregates of the polymer type antistatic agent are present.

By the way, when storing a glass substrate in the form of a laminated body, it is generally required to lower the height of the laminated body.

However, the effect of the agglomerates on the sheet strength becomes more remarkable as the thickness of the polyethylene-based resin foam sheet is reduced.

For this reason, when it is desired to obtain a polyethylene-based resin foam sheet having excellent antistatic properties and having a thin thickness, problems such as sheet breakage tend to occur in the sheet manufacturing step.

Here, conventionally, it has been difficult to obtain a polyethylene-based resin foam sheet having excellent antistatic properties and having a thin thickness.

In addition, the requirement to obtain a polyethylene-based resin foam sheet having excellent antistatic properties and having a thin thickness is not limited to the case where it is inserted between glass substrates and used, but is common to all polyethylene-based resin foam sheets. that's what's going on

The present invention has made it a subject to satisfy these demands, and made it a subject to provide a polyethylene-based resin foam sheet having excellent antistatic properties and having a thin thickness.

As a result of intensive studies to solve the above problems, the inventors of the present invention have determined that the melting points of the polyethylene-based resin and the polymer type antistatic agent contained in the polyethylene-based resin foam sheet are in a predetermined relationship during the production of the polyethylene-based resin foam sheet. It was found that the dispersibility of the polymer type antistatic agent in the can be improved.

In addition, the present inventors have found that by improving the dispersibility of the polymer type antistatic agent, it is possible to make a polyethylene-based resin foam sheet having excellent antistatic properties and easy to manufacture, and to complete the present invention. It's early.

That is, in order to solve the above problems, the present invention includes a polyethylene component composed of one or two or more polyethylene-based resins and an antistatic agent component composed of one or more polymer type antistatic agents, and the DSC curve of the polyethylene component and the above The DSC curve of the antistatic agent component shows 1 or 2 or more endothermic peaks, and the peak temperature of the endothermic peak appearing on the highest temperature side in the DSC curve of the polyethylene component is Tm1, and the endothermic peak appearing on the highest temperature side in the DSC curve of the antistatic agent component Provided is a polyethylene-based resin foam sheet that satisfies the following relational expression (1) when the peak temperature of the peak is Tm2.

(Tm1-10)≤Tm2≤(Tm1+17)...(1)

According to the present invention, it is possible to provide a polyethylene-based resin foam sheet having excellent antistatic properties and having a thin thickness.

1 is a schematic view showing one usage mode of a polyethylene-based resin foam sheet.
Fig. 2 is a schematic view showing a method for measuring "amount of sagging" of a polyethylene-based resin foam sheet.

An embodiment of the polyethylene-based resin foam sheet of the present invention is described below.

The polyethylene-based resin foam sheet of the present embodiment is used as a buffer material for glass substrates for flat panel displays.

The polyethylene-based resin foam sheet is used by contacting the surface of the glass substrate.

As shown in Fig. 1, the polyethylene-based resin foam sheet 1 of this embodiment is adjacent to, for example, when a plurality of glass substrates 2 in a horizontal position are laminated in the vertical direction to form the laminate 10. It is used by inserting it between the glass substrates 2.

As for the polyethylene-type resin foam seat|sheet 1, the thick one can prevent contact of glass substrates 2 comrades more reliably.

Further, the polyethylene-based resin foam sheet 1 exhibits excellent compressive strength when the mass per unit area is large, and can prevent contact between the glass substrates 2 more reliably.

On the other hand, when the thickness of the polyethylene-based resin foam sheet 1 is thin, the laminate 1 can be made compact.

The polyethylene-based resin foam sheet 1 tends to be thin in thickness and excellent in cushioning properties when the mass per unit area is small.

From this point of view, it is preferable that the polyethylene-based resin foam sheet 1 of the present embodiment has a thickness of 0.15 mm or more and 0.4 mm or less.

And it is preferable that the mass per unit area of the polyethylene-type resin foam seat|sheet 1 of this embodiment is 15 g/m<2> or more and 30 g/m<2> or less.

In addition, it is preferable that the polyethylene-based resin foam sheet 1 is moderately compressed when subjected to pressure due to the weight of the glass substrate 2 in the laminate, exhibits buffering properties, and secures a certain thickness or more.

In this regard, when the polyethylene-based resin foam sheet 1 is compressed at a pressure of 2 N/cm 2 in the thickness direction, it is preferable to have a thickness of 45% or more and 70% or less before compression.

Further, the polyethylene-based resin foam sheet 1 preferably has a thickness of 0.1 mm or more when compressed with a pressure of 2 N/cm 2 in the thickness direction.

When the polyethylene-based resin foam sheet 1 is removed from the surface of the glass substrate 2, it is preferable not to generate static electricity.

More specifically, the polyethylene-based resin foam sheet 1 preferably has a surface resistivity of 1×10 ⁸ Ω or more and 1×10 ¹² Ω or less.

In addition, about the thickness and surface resistivity concerning the polyethylene-type resin foam seat|sheet 1 of this embodiment, the value calculated|required by the method described in the Example is meant.

The polyethylene-based resin foam sheet 1 of the present embodiment contains a polyethylene component composed of one or more polyethylene-based resins and an antistatic agent component composed of one or more polymer type antistatic agents in order to exhibit the above characteristics. are doing

The polyethylene-based resin foam sheet 1 has a specific DSC curve when differential scanning calorimetry (DSC) is performed on the polyethylene component and the antistatic agent component.

Specifically, in the polyethylene-based resin foam sheet 1 of the present embodiment, the DSC curve of the polyethylene component and the DSC curve of the antistatic agent component show one or two or more endothermic peaks.

In the polyethylene-based resin foam sheet 1 of the present embodiment, the peak temperature of the endothermic peak appearing at the highest temperature in the DSC curve of the polyethylene component is Tm1, and the endothermic peak appearing at the highest temperature in the DSC curve of the antistatic agent component. When the peak temperature of is set to Tm2, the following relational expression (1) is satisfied.

(Tm1-10)≤Tm2≤(Tm1+17)...(1)

As described in a later paragraph, the polyethylene-based resin foam sheet 1 is preferably formed by extrusion foaming of a polyethylene component and an antistatic agent component together with an appropriate foaming agent.

Since the melting point (endothermic peak) of the polyethylene component and the melting point (endothermic peak) of the antistatic agent component of the polyethylene-based resin foam sheet 1 are close to each other as described above, the antistatic agent component relative to the polyethylene component during extrusion foaming. This good dispersibility is shown.

That is, in the present embodiment, it is difficult to form agglomerates of the antistatic agent component on the polyethylene-based resin foam sheet 1.

For this reason, the antistatic effect exhibited with respect to the content of the antistatic agent component of the polyethylene-type resin foam sheet|seat 1 of this embodiment is high.

In addition, the polyethylene-based resin foam sheet 1 of this embodiment is easy to manufacture even if it is a thin sheet.

In order to exert these effects more remarkably, the polyethylene-based resin foam sheet 1 of the present embodiment exhibits two or more endothermic peaks in the DSC curve of the antistatic agent component, and the endothermic peak appears at the highest temperature in the DSC curve. It is preferable that the heat of fusion of is 30 J/g or less.

That is, in the polyethylene-based resin foam sheet 1 of the present embodiment, it is preferable that the antistatic agent component not only approximates the polyethylene component and the melting temperature range, but also melts quickly.

Because the antistatic agent component melts quickly, the polyethylene-based resin foam sheet 1 of the present embodiment exhibits the effect of suppressing the formation of agglomerates more reliably.

In order to exhibit these effects more remarkably, in the polyethylene-based resin foam sheet 1 of the present embodiment, the DSC curve of the antistatic agent component shows two or more endothermic peaks, and the endotherm that appears at the highest temperature in the DSC curve. It is preferable that the difference between the peak temperature of the peak and the peak temperature of the endothermic peak appearing at the lowest temperature in the DSC curve is 95°C or less.

As described above, in the present embodiment, the peak temperature of the endothermic peak appearing at the highest temperature in the DSC curve of the antistatic agent component shows a value close to the peak temperature of the endothermic peak appearing at the highest temperature in the DSC curve of the polyethylene component. .

In the DSC curve of the antistatic agent component, the difference between the peak temperature of the endothermic peak appearing at the lowest temperature and the peak temperature of the endothermic peak appearing at the highest temperature is below a certain level by heating the resin composition forming the polyethylene-based resin foam sheet. , it means that the timing at which the entire antistatic agent component melts and the timing at which the polyethylene component melts are close.

That is, in the antistatic agent component, the difference between the peak temperature of the endothermic peak appearing at the highest temperature and the peak temperature of the endothermic peak appearing at the lowest temperature in the DSC curve is less than or equal to a predetermined value, so that the polyethylene-based resin foam sheet The dispersibility may be even better.

In addition, the antistatic agent component is preferably composed of a plurality of polymeric antistatic agents including a first polymeric antistatic agent and a second polymeric antistatic agent.

By using two or more types of polymer type antistatic agents with different melting points, the endothermic peak appearing at the highest temperature in the DSC curve of the antistatic agent component measured by differential scanning calorimetry (DSC) can be broadened.

That is, when the antistatic agent component contains two or more types of polymer type antistatic agents having different melting points, the melting behavior becomes gentle rather than steep. The antistatic agent component exhibiting a gentle melting behavior becomes more advantageous by dispersion into the polyethylene component.

In addition, one of the first polymer type antistatic agent and the second polymer type antistatic agent (for example, the first polymer type antistatic agent) preferably has a melting point close to that of the polyethylene component, and the other (for example, the second polymer type antistatic agent) 2 polymer type antistatic agent) is preferably higher melting point than one.

In the following, a case where the second polymer type antistatic agent has a higher melting point than the first polymer type antistatic agent is taken as an example, and the polyethylene-based resin foam sheet of the present embodiment is described.

The melting points and heats of fusion of the polyethylene component, the antistatic agent component, the first polymeric antistatic agent, and the second polymeric antistatic agent in the present embodiment refer to values measured by the method described in Examples.

Examples of the polyethylene resin as the main component of the polyethylene resin foam sheet of the present embodiment include ultra low density polyethylene resin (VLDPE), low density polyethylene resin (LDPE), linear low density polyethylene resin (LLDPE), medium density polyethylene resin ( MDPE), and polyethylene-type resins, such as high-density polyethylene resin (HDPE), are mentioned.

It is preferable that the melt flow rate (MFR) of the polyethylene component of this embodiment which consists of one or more types of these polyethylene-type resins is 1.0 g/10min or more and 7.0 g/10min or less.

Also, the melt tension of the polyethylene component is preferably 6 cN or less.

In addition, the lower limit of the melt tension of the polyethylene component is usually 0.5 cN.

The MFR and melt tension values of the polyethylene-based resin foam sheet in the present embodiment mean values measured by the method described in Examples.

On the other hand, as the polymer type antistatic agent, ionomers such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyester amide, polyether ester amide, ethylene-methacrylic acid copolymer, polyethylene glycol methacrylate copolymer, etc. A quaternary ammonium salt, a copolymer of an olefin-based block and a hydrophilic block described in Japanese Unexamined Patent Publication No. 2001-278985, and the like are exemplified.

The polymer type antistatic agent to be contained in the polyethylene-based resin foam sheet is preferably a copolymer of an olefin-based block and a hydrophilic block.

The polyolefin-based resin composition forming the polyethylene-based resin foam sheet preferably contains a polyether-polyolefin block copolymer (a block copolymer of a polyether-based block and a polyolefin-based block) as the polymer type antistatic agent.

Further, as the polymer type antistatic agent, a polyamide may be mixed with the block copolymer for the purpose of further improving the antistatic performance.

Further, the polymer type antistatic agent may be a copolymer having a polyamide-based block as well as a polyether-based block or a polyolefin-based block.

It is more preferable that the above-mentioned polymer type antistatic agent is a copolymer of an olefin-based block and a polyether-based block, and a copolymer having a propylene ratio of 70 mol% or more in the olefin-based block as a main component.

Further, 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.

The polyethylene-based resin foam sheet having a high content of the antistatic agent component is advantageous in exhibiting excellent antistatic performance.

On the other hand, a polyethylene-based resin foam sheet having a small amount of an antistatic agent component is advantageous in preventing formation of agglomerates due to the antistatic agent component.

From this point of view, the content of the antistatic agent component of the polyethylene-based resin foam sheet is preferably 3 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the content of the polyethylene component.

The polyethylene-based resin foam sheet of the present embodiment may contain a cell regulator and various additives in addition to the polyethylene component and antistatic agent component.

Examples of the cell regulator include inorganic particles and organic particles, and examples of the inorganic particles include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, and calcium hydroxide , potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, and glass particles.

Examples of the organic particles include particles such as polytetrafluoroethylene.

Moreover, in this embodiment, what can be used as a chemical foaming agent, such as azodicarbonamide, sodium hydrogencarbonate, or a mixture of sodium hydrogencarbonate and citric acid, can also be used as the said cell conditioner.

The polyethylene-based resin foam sheet of the present embodiment may contain a small amount of polyolefin-based resins other than polyethylene-based resins such as polypropylene-based resins as other components.

The polyethylene-based resin foam sheet of the present embodiment may contain a small amount of resin other than the polyolefin-based resin as other components.

In addition, antiaging agents, antioxidants, ultraviolet absorbers, surfactants, flame retardants, antibacterial agents, coloring agents and the like can be contained in the polyethylene-based resin foam sheet of the present embodiment as other components.

However, the content of the above "other components" in the polyethylene-based resin foam sheet is preferably suppressed to 5% by mass or less, and more preferably 3% by mass or less.

It is particularly preferable to make the other components substantially free (for example, the content in the polyethylene-based resin foam sheet is less than 1% by mass).

The polyethylene-based resin foam sheet of the present embodiment can be produced by a method of extruding and foaming a resin composition containing the above-mentioned polyethylene-based resin, polymer type antistatic agent, cell control agent and foaming agent through a circular die or the like.

Examples of the foaming agent include the chemical foaming agent and the physical foaming agent.

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

In such extrusion foaming, when it is desired to obtain a polyethylene-based resin foam sheet having a thin thickness, the polymeric antistatic agent does not sufficiently diffuse in the extruder and forms agglomerates, the extruded sheet breaks from the agglomerates as the starting point has a risk of causing

In contrast, the polyethylene-based resin foam sheet of the present embodiment is composed of a polyethylene component having a close melting point and an antistatic agent component as main ingredients, and the antistatic agent component exhibits excellent dispersibility in an extruder, so that it is difficult to break.

In addition, the polyethylene-based resin foam sheet of the present embodiment can thereby increase the line speed at the time of production.

For example, when manufacturing the polyethylene-type resin foam seat|seet of this embodiment, with respect to the sheet|seat after extrusion, winding at high speed of 30 m/min - 100 m/min can be performed.

That is, the polyethylene-based resin foam sheet of the present embodiment has an advantage also in terms of production efficiency.

In addition, the polyethylene-based resin foam sheet of the present embodiment is hard to break even when expanding the diameter of the cylindrical foam sheet extruded from the circular die, and is 2.5 times larger than the diameter of the circular die (the diameter of the circle connecting the center of the slit width). It is possible to expand the diameter more than 5.0 times or less.

That is, the polyethylene-based resin foam sheet of the present embodiment has the advantage of being easy to obtain products having a thin thickness while operating the extruder in high discharge operation.

In addition, since the polyethylene-based resin foam sheet of the present embodiment has good dispersibility of the antistatic agent component, excellent antistatic performance can be exhibited even without excessive mixing of the antistatic agent component.

In this way, the polyethylene-based resin foam sheet of the present embodiment not only has excellent antistatic properties and is easy to produce in a thin state, but also has the advantages of being easy to produce in good yield with excellent quality. have

In addition, as shown in FIG. 1, the polyethylene-type resin foam seat|sheet of this embodiment can be used other than the mode so that it may be sandwiched between two glass substrates.

And, the above example is a limited example of the present invention to the last, and the present invention is not limited to the above example at all.

Example

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

(Example 1)

A formulation in which the following materials were blended in the following ratio was prepared.

・Nippon Polyethylene Co., Ltd. low-density polyethylene resin (trade name: "LF580", density: 931 kg / m 3, melting point 115 ° C., MFR = 3.8 g / 10 min, melt tension = 1.7 cN) 100 parts by mass

First polymer type antistatic agent manufactured by Sanyo Chemical Industry Co., Ltd. (polyether-polyolefin block copolymer, trade name "Pelektron LMP", crystallization temperature: 56 ° C., melting point: 115 ° C., heat of fusion: 26 mJ / mg, MFR = 30 g / 10 min ) 3 parts by mass

3 parts by mass of second polymer type antistatic agent (polyether-polyolefin block copolymer, trade name: “Pelestat 300”, crystallization temperature: 99° C., melting point: 135° C., MFR=30 g/10 min) manufactured by Sanyo Chemical Industry Co., Ltd.

・ Cell conditioner masterbatch manufactured by Sankyo Kasei Co., Ltd. (masterbatch containing azodicarbonamide: trade name “Cellmic MB1023”) 0.15 parts by mass

The blend was supplied to the first extruder (cylinder diameter: φ90 mm) of the tandem extruder, and melt-kneaded so that the highest attained temperature in the extruder was 210°C.

In addition, the first polymeric antistatic agent (trade name: "Pelektron LMP", melting point: 106°C) and the second polymeric antistatic agent (trade name: "Pelestat 300", melting point: 135°C) were mixed in a 1:1 ratio as described above. The melting point of the antistatic agent component included was 130°C, and the difference from the melting point (115°C) of the polyethylene component was 15°C.

While melt-kneading the blend in the first extruder, mixed butane (isobutane/normal butane = 50/50 (molar ratio)) as a foaming agent from the middle of the first extruder is mixed at a ratio of 18 parts by mass to 100 parts by mass of the low-density polyethylene resin. It was press-fitted as much as possible, and melt-kneading was performed again.

After melt-kneading in this first extruder, the melt-kneaded product was cooled to a temperature range (111°C) suitable for foaming with a second extruder (cylinder diameter: φ 150 mm) connected to the first extruder, and the outlet diameter was 222 mm ( It was extruded and foamed in the air from a circular die having a slit width of 0.04 mm).

The resin temperature at this time was 116°C.

After cooling by blowing air to the extruded and foamed cylindrical foam sheet, the cylindrical foam sheet was cooled along a cooling mandrel with a diameter of 770 mm and a length of 650 mm, while expanding its diameter.

Next, it cut|disconnected along the extrusion direction at 1 point of the circumferential direction, winding up the cylindrical foam seat|seet after diameter expansion at a take-up speed of 50 m/min.

The cut cylindrical foam sheet was stretched to obtain a long strip-shaped polyethylene resin foam sheet, which was used as the polyethylene resin foam sheet of Example 1.

In addition, physical properties and the like of the polyethylene-based resin foam sheet of Example 1 were measured according to the following methods.

<thickness 1 (natural thickness)>

About the thickness of a polyethylene-type resin foam sheet|seat, it can measure using the static pressure thickness measuring instrument (Teclock Co., Ltd. make, model "SCM-627").

Specifically, the thickness of the polyethylene-based resin foam sheet is determined by applying a load of 95 g (including its own weight) to a circular surface (area: 60.8 cm 2 ) with a radius of 4.4 cm using a cylindrical weight. It can be obtained by measuring the thickness when applied with a constant pressure thickness meter.

The thickness of the polyethylene-based resin foam sheet is usually measured at 50 points every 5 cm in the width direction, and the arithmetic mean value of the measured values is taken.

In addition, when it is not possible to secure 50 measurement points due to the narrow width of the polyethylene-based resin foam sheet, after securing as many measurement points as possible, the arithmetic average value of all measurement values is taken as the thickness.

<Thickness 2 (compressed thickness)>

Cut out a measurement sample of 10 cm × 10 cm × thickness (total thickness of the polyethylene-based resin foam sheet) from the polyethylene-based resin foam sheet, and use a static pressure thickness gauge manufactured by Techrak (product name "PG-14J" terminal diameter: 16 mm) Thus, the thickness of the measurement sample when a weight of 0.41 kg is raised is Tp.

In addition, the measurement is performed by cutting out five of the above-mentioned measurement samples in the sheet width direction of the polyethylene-based resin foam sheet, and taking the average value of the measurement values obtained for each measurement sample as the thickness (Tp) upon compression.

In addition, the natural thickness is assumed to be T0, and the strain (Pr) is calculated based on the following formula.

Pr=(T0−Tp)/T0×100

<Mass per unit area (basis weight)>

A polyethylene-based resin foam sheet is cut and measured along two lines: a first line along a direction orthogonal to the extrusion direction and a second line parallel to the first line and spaced at a distance of 20 cm from the first line in the extrusion direction. get a sample for

The mass per unit area of the polyethylene-based resin foam sheet can be calculated with the following formula based on the mass: W (g) and area: S (cm 2 ) of the sample for measurement.

In addition, when the polyethylene-based resin foam sheet is not large enough to cut out a sample for measurement with a width of 20 cm, it is cut into a rectangular shape as large as possible to obtain a slice, and the mass W (g) and area of the slice are obtained. Based on S (cm 2 ), the mass per unit area of the polyethylene-based resin foam sheet can be obtained by the following formula.

Mass per unit area (g/㎡)＝W/S×10000

<Surface resistivity>

The surface resistivity of the polyethylene-based resin foam sheet can be measured by the method described in JIS K6911-2006 "General Test Methods for Thermosetting Plastics".

That is, the surface resistivity of the polyethylene-based resin foam sheet was measured by compressing an electrode with a load of about 30 N to a test piece using a test device (digital ultra-high resistance/micro ammeter R8340 and resistance chamber R12702A manufactured by Advantest), and at 500 V. The resistance value after charging for 1 minute can be measured and calculated by the following formula.

In addition, a test piece can be produced by cutting out a piece of "width 100 mm x length 100 mm x thickness (total thickness of the polyethylene-based resin foam sheet)" from a normal polyethylene-based resin foam sheet.

In addition, the measurement is normally performed after placing a test piece in an atmosphere of a temperature of 20±2° C. and a humidity of 65±5% for 24 hours or more.

The test environment for measuring the surface resistivity is an atmosphere with a temperature of 20±2° C. and a humidity of 65±5%.

In addition, the measurement is usually performed on both the front and back surfaces of each test piece with the number of test pieces set to 5, so that a total of 10 measured values are obtained.

The surface resistivity of the polyethylene-based resin foam sheet is, in principle, the arithmetic average value of all these 10 measured values.

ρs=π(D+d)/(D-d)×Rs

ρs: specific surface resistivity (Ω/□)

D: Inner diameter (cm) of the ring-shaped electrode on the surface (7 cm in resistance chamber R12702A)

d: outer diameter (cm) of inner circle of surface electrode (5 cm in resistance chamber R12702A)

Rs: surface resistance (Ω)

<Continuous cell rate (smoke rate)>

A plurality of square slices of 25 mm square are cut out of the polyethylene-based resin foam sheet, and the slices are overlapped so as to have a thickness of about 5 cm to prepare a sample. The substantial volume (V) of the sample is measured using a Micromeritics dry type automatic density meter (manufactured by Shimadzu Corporation, model: Acupic II 1340 (V1.0)).

In addition, the samples are laminated so that there is no gap between the slices as much as possible, and the thickness is about 5 cm.

Then, the apparent volume (V0) is calculated from the external shape of the sample.

From the obtained values (V, V0), the open cell rate (%) is calculated by the following formula.

Open cell rate (%) = (V0 - V) / V0 × 100

<Melting point and heat of fusion>

The melting point of polyethylene-based resins and polymeric antistatic agents is usually determined by differential scanning calorimetry (DSC) analysis according to the method described in JIS K7121-2012 "Methods for Measuring Transition Temperature of Plastics", and the temperature at the peak top of the obtained DSC curve. .

In addition, the heat of fusion of the polyethylene-based resin or polymeric antistatic agent can be obtained from the peak area of the DSC curve according to the method described in JIS K 7122-2012 "Methods for Measuring Transition Temperature of Plastics".

Specifically, using a differential scanning calorimeter (for example, "DSC6220" manufactured by S.I.I. Nanotechnology Co., Ltd.), about 6.5 mg of a sample is filled in a measuring container, and the temperature is 10°C under a nitrogen gas flow rate of 30 ml/min. The temperature is raised/cooled between 30°C and 200°C at a heating/cooling rate of /min, and the endothermic peak temperature during the second heating is measured as the melting point.

When the endothermic peaks due to melting do not overlap and are located at two points, the endothermic peak on the high temperature side is taken as the melting point of the resin, and the area of the endothermic peak is taken as the heat of fusion of the resin.

In addition, as a result of the existence of an endothermic peak appearing at the highest temperature during the second temperature increase and one or more endothermic peaks appearing at the lower temperature side at close temperatures, they overlap to form one endothermic peak, and a plurality of endothermic peaks are added to this endothermic peak. In the case where the peak temperature exists, the melting point is set to the highest peak temperature, and the heat of fusion is determined based on the areas of all overlapping peaks.

In addition, regarding the melting point and heat of fusion of a polyethylene component containing a plurality of polyethylene-based resins or an antistatic agent component containing a plurality of polymeric antistatic agents, a sample containing a plurality of polyethylene-based resins in a predetermined ratio or a plurality of polymeric antistatic agents It can be obtained by preparing a sample containing the inhibitor at a predetermined ratio and then obtaining a DSC curve for the sample in the same manner as described above.

<Difference in peak temperature>

According to the measuring method of the said "melting point", differential scanning calorimetry of the antistatic agent component is performed.

Then, the peak temperature (P _H ) of the highest temperature side and the peak temperature (P _L ) of the lowest temperature side appearing on the DSC curve are obtained, and the difference between them (P _H -P _L ) is obtained.

<melt tension>

The melt tension of a polyethylene-type resin can be measured in the following manner.

That is, a sample made of polyethylene-based resin is accommodated in a cylinder having an inner diameter of 15 mm installed in a vertically standing state, and then melted by heating at 190° C. for 5 minutes.

After that, a piston was inserted into the cylinder from the top, and a capillary (die diameter: 2.095 mm, die length: 8 mm, inlet angle: 90° ( conical)) at a constant extrusion speed of 0.0676 mm/s to obtain a string-like body.

Then, after passing the extruded string-like body through a tension detecting pulley disposed below the capillary, it is wound up using a take-up roll.

Winding of the string-shaped body is set at an initial speed of 3.447 mm/s, and then set to an acceleration of 13.1 mm/s ² to increase the winding speed gradually.

In this winding, the winding speed when the tension observed by the tension detecting pulley rapidly decreases is referred to as the "breaking point speed".

Among the tensions observed until this breaking point velocity is observed, the maximum and minimum values of the tension right before the breaking point velocity are measured. The arithmetic average value of this maximum value and minimum value is taken as "melt tension".

In addition, the melt tension can be measured using a tester commercially available under the trade name "Twin Bore Capillary Rheometer Rheologic 5000T" from Chiast, for example.

<MFR>

MFR of a polyethylene-type resin can be measured based on the flow test method of JIS K7210-1999 thermoplastics.

Specifically, MFR (g/10 min) can be measured under test conditions of a temperature of 190°C, a load of 21.18 N, and a preheating time of 5 minutes using a semi-auto melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) as a measuring device.

＜Amount of deflection＞

The amount of deflection can be measured by cutting out three test pieces of 100 mm in width and 200 mm in length so that the extrusion direction is the longitudinal direction from the polyethylene-based resin foam sheet, and then measuring it in the following manner (see Fig. 2).

First, a straight edge R is overlapped on the test piece SP.

In addition, the test piece SP and the straight edge R are overlapped so that their edges may be in a state where they coincide with each other at one end in the longitudinal direction.

This is sandwiched between the acrylic plates A1 and A2 of 2 sheets of width 120mm.

At this time, the edge of one end where the test piece SP and the straightedge R are aligned coincide with the edge of one end in the width direction of the acrylic plates A1 and A2, and the test piece from the other end edge of the acrylic plates A1 and A2. It should protrude 80mm.

Place this on the base (F) again so that the straightedge (R) is in a state of being leveled on the test piece (SP), and the distance in the vertical direction between the tip of the test piece (SP) and the straightedge (R) ( H) is measured.

The same measurement is performed for the remaining two test pieces, and the arithmetic average value of the distance (H) is taken as the amount of deflection.

In addition, this amount of sagging means that the polyethylene-based resin foam sheet has excellent strength, so that the numerical value is low.

<Measurement of bleed out amount>

Quantitative analysis of the bleed-out component in the polyethylene-based resin foam sheet can be measured in the following manner.

That is, 10 samples of 10 cm x 10 cm are cut out from an arbitrary position of the polyethylene-based resin foam sheet.

Five sets of samples were prepared with a commercially available 10 cm x 10 cm glass plate sandwiched between the two cut samples, and maintained in a high-temperature, high-humidity tank manufactured by ISUZU at a temperature of 65 ° C. and a humidity of 90% RH for 100 hours.

Next, the mass of the glass plate after leaving it to stand for 1 hour under conditions of a temperature of 23°C and a humidity of 30% RH and removing the sample is measured using a precision balance (analytical electronic balance GR-202 manufactured by AND Corporation).

Then, the increase in mass relative to the mass of the initial glass plate is determined, and the increased mass is divided by the sample area (200 cm 2 ) to determine the bleed-out amount. In addition, the bleed-out amount is taken as the arithmetic mean value of 5 sets of samples.

(Examples 2 and 3, Comparative Examples 1 to 4)

Polyethylene-based resin foam sheets of Examples 2 and 3 and Comparative Examples 1 to 4 were produced as follows, and evaluated in the same manner as the polyethylene-based resin foam sheet of Example 1.

The results are shown in Table 1.

(Example 2)

A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the type and amount of the polymeric antistatic agent to be contained in the antistatic agent component was changed, and this was used as the polyethylene-based resin foam sheet of Example 2.

Specifically, the first polymeric antistatic agent was replaced with Sanyo Kasei Industrial Co., Ltd. trade name "Pelektron LMP", trade name "Pelektron LMP-FS" (polyether-polyolefin block copolymer, crystallization temperature: 56 ° C, Melting point: 114°C, heat of fusion: 24 J/g), and the blending ratio with respect to 100 parts by mass of the polyethylene component was changed to 3.5 parts by mass instead of 3 parts by mass, the second polymer type antistatic agent (trade name “Pelestat 300”) A polyethylene-based resin foam sheet was produced in the same manner as in Example 1, except that the blending ratio of ) to 100 parts by mass of the polyethylene component was 1 part by mass instead of 3 parts by mass.

(Example 3)

A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the amount of the polymer type antistatic agent to be contained in the antistatic agent component was changed, and this was used as the polyethylene-based resin foam sheet of Example 3.

Specifically, polyethylene-based resin foaming is performed in the same manner as in Example 1 except that the blending ratio of the first polymer type antistatic agent (trade name "Pelektron LMP") to 100 parts by mass of the polyethylene component is 2 parts by mass instead of 3 parts by mass. A sheet was prepared (the blending ratio of the second polymer type antistatic agent (trade name "Pelestat 300") with respect to 100 parts by mass of the polyethylene component was set to 3 parts by mass in the same manner as in Example 1).

(Comparative Example 1)

A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the type and amount of the polymeric antistatic agent to be contained in the antistatic agent component was changed, and this was used as the polyethylene-based resin foam sheet of Comparative Example 1.

Specifically, instead of using two types together as a polymer type antistatic agent, a single type of polymer type antistatic agent (trade name "IPE-U3", melting point: 220 ° C.) manufactured by Ion Pezu Co., Ltd. was used, and 100 mass of polyethylene component A polyethylene-based resin foam sheet was produced in the same manner as in Example 1, except that the blending ratio per part was 10 parts by mass.

(Comparative Example 2)

Polyethylene resin was replaced with low-density polyethylene resin (trade name: "LF580") manufactured by Nippon Polyethylene Co., Ltd., and low-density polyethylene resin manufactured by Dow Chemical Co., Ltd., trade name "DFDJ6775" (density: 921 kg/m 3 , MFR = 0.3 g/10 min, melt tension = 19.6 cN), a polyethylene-based resin foam sheet was prepared in the same manner as in Example 1 except that the polymer type antistatic agent was used alone (only the trade name "Pelektron HS" (melting point: 135 ° C.) manufactured by Sanyo Chemical Industry Co., Ltd.), This was used as the polyethylene-based resin foam sheet of Comparative Example 2 (the ratio of the antistatic agent component to 100 parts by mass of the polyethylene component is 6 parts by mass, the same as in Example 1).

(Comparative Example 3)

A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the type and amount of the polymeric antistatic agent to be contained in the antistatic agent component was changed, and this was used as the polyethylene-based resin foam sheet of Comparative Example 3.

Specifically, instead of using two types of polymeric antistatic agents in combination, a polymeric antistatic agent (trade name "IPE-fSAT", melting point: 89 ° C.) manufactured by Ion Fezu was used alone, and polyethylene component 100 A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the blending ratio with respect to parts by mass was 12 parts by mass.

(Comparative Example 4)

A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1, except that the type of polymeric antistatic agent to be contained in the antistatic agent component was changed, and this was used as the polyethylene-based resin foam sheet of Comparative Example 4.

Specifically, the first polymer type antistatic agent was replaced with Sanyo Kasei Industrial Co., Ltd. trade name "Pelektron LMP", except that the polymer type antistatic agent manufactured by Ion Pez Co., Ltd. (trade name "IPE-U3", melting point: 220 ° C.) was used. A polyethylene-based resin foam sheet was prepared in the same manner as in Example 1.

In addition, the point that the second polymer type antistatic agent is made by Sanyo Chemical Industry Co., Ltd. under the trade name "Pelestat 300" and the ratio of the first and second polymer type antistatic agents to 100 parts by mass of the polyethylene component are both 3 parts by mass. Same as 1.

In addition, the melting point of the antistatic component containing the trade name "IPE-U3" and the trade name "Pelestat 300" in a mass ratio of 1:1 was 178°C.

Also from the results shown in the table above, it can be seen that according to the present invention, a polyethylene-based resin foam sheet excellent in antistatic properties and thin in thickness can be provided.

1: polyethylene-based resin foam sheet
2: glass substrate

Claims (6)

A polyethylene component composed of one or two or more polyethylene-based resins and an antistatic agent component composed of two or more polymer type antistatic agents,
The DSC curve of the polyethylene component shows 1 or 2 or more endothermic peaks,
The DSC curve of the antistatic agent component shows two or more endothermic peaks, the heat of fusion of the endothermic peak appearing at the highest temperature in the DSC curve of the antistatic agent component is 30 J/g or less, and in the DSC curve of the antistatic agent component The difference between the peak temperature of the endothermic peak appearing at the highest temperature and the peak temperature of the endothermic peak appearing at the lowest temperature is 95 ° C or less,
The following relational expression (1 ) Polyethylene-based resin foam sheet that satisfies:
(Tm1-10)≤Tm2≤(Tm1+17)...(1). delete delete According to claim 1,
A polyethylene-based resin foam sheet having a thickness of 0.15 mm or more and 0.4 mm or less, and a mass per unit area of 15 g/m 2 or more and 30 g/m 2 or less. According to claim 1,
When the content of the polyethylene component is 100 parts by mass, the content of the antistatic agent component is 3 parts by mass or more and 15 parts by mass or less, and the surface resistivity is 1 × 10 ⁸ Ω or more and 1 × 10 ¹² Ω or less. A polyethylene-based resin foam sheet. The method of any one of claims 1, 4 and 5,
It is used to protect glass substrates for flat panel displays, and is also used by inserting between two glass substrates,
A polyethylene-based resin foam sheet having a thickness of 45% or more and 70% or less before compression when compressed at a pressure of 2 N/cm in the thickness direction and a thickness of 0.1 mm or more when compressed at a pressure of 2 N/cm in the thickness direction.

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