WO2014196278A1

WO2014196278A1 - Foamed multilayer polyethylene resin sheet, and glass-panel slip sheet

Info

Publication number: WO2014196278A1
Application number: PCT/JP2014/061010
Authority: WO
Inventors: 森田　和彦; 角田　博俊; 隆一谷口; 兼一後藤
Original assignee: 株式会社ジェイエスピー
Priority date: 2013-06-07
Filing date: 2014-04-18
Publication date: 2014-12-11
Also published as: KR20160014641A; CN105263702B; JP6266901B2; JP2014237770A; CN105263702A; KR102136443B1

Abstract

Provided is a foamed multilayer polyethylene resin sheet which is provided with a foamed layer, and a surface layer stacked upon at least one surface of the foamed layer, said foamed multilayer polyethylene resin sheet being obtained by co-extruding: a foamed-layer-forming first molten substance including a polyethylene resin (A), a polymeric anti-static agent, and a physical blowing agent; and a surface-layer-forming second molten substance including a polyethylene resin (B). The polyethylene resin (A) and the polyethylene resin (B) respectively have an n-heptane extraction amount at 50˚C of not more than 0.5 wt%. In the foamed layer, the polymeric anti-static agent accounts for 3-15 wt% of a total of 100 wt% of the polyethylene resin (A) and the polymeric anti-static agent. The thickness of the surface layer is 2-10 µm.

Description

Polyethylene resin multilayer foam sheet and glass sheet

The present invention relates to a polyethylene-based resin multilayer foamed sheet and its use as an interleaf for glass plates.

Conventionally, polyethylene-based resin foam sheets have been used as materials for cushioning materials and packaging materials. In particular, a polyethylene-based resin foam sheet having antistatic properties has been used as a suitable material as a packaging material because it is difficult to damage dust and is flexible because it is difficult to dust.

In recent years, polyethylene-based resin foam sheets having antistatic properties have been used in the packaging field of electronic devices and their materials, such as being used for slip sheets such as glass plates for liquid crystal panels.

If the liquid crystal panel glass plate is contaminated by the migration of organic substances contained in the foamed sheet, it will lead to failure and deterioration of production yield when an electronic circuit is formed on the glass plate. It is required to reduce the migration of substances and the like.

A typical example of the organic substance that migrates from the foam sheet to the package is a surfactant type antistatic agent that is blended to impart the antistatic performance. Therefore, Japanese Patent Application Laid-Open No. 2005-194433 discloses a polyethylene resin foam sheet in which a polymer type antistatic agent is blended as an antistatic agent. Japanese Patent Application Laid-Open No. 2004-181933 discloses a polyethylene resin multilayer foam sheet in which a polymer type antistatic agent is blended in a surface layer laminated on a foam layer. The foamed sheet using these polymer-type antistatic agents has a greatly reduced amount of migration of organic substances and the like to the package as compared with a foamed sheet using a conventional surfactant.

The polyethylene-based resin foam sheet using the polymer type antistatic agent as described above has a good antistatic property and a low degree of contamination due to migration, so that it can be used as a suitable packaging material for an electronic device or its material. Used as paper.

However, even in the foam sheet using the above-described polymer type antistatic agent, the low molecular weight component contained in the polymer type antistatic agent itself may migrate to the package, and the polyethylene constituting the foam sheet It has been found that low molecular weight components contained in the base resin itself may migrate.

The present invention has been made in view of the above problems, and an object thereof is to provide a polyethylene-based resin multilayer foamed sheet having an antistatic performance and a very small amount of low molecular weight components transferred to a package. It is what.

According to the first aspect of the present invention, a foamed layer forming molten resin obtained by kneading a polyethylene resin (A), a polymer antistatic agent and a physical foaming agent, and a polyethylene resin (B) are kneaded. A multilayer foamed sheet obtained by co-extrusion with a molten resin for forming a surface layer, wherein the surface layer is laminated on at least one side of the foamed layer,
Both the polyethylene resin (A) and the polyethylene resin (B) are polyethylene resins having an n-heptane extraction amount at 50 ° C. of 0.5% by weight or less,
The blending amount of the polymer antistatic agent in the foamed layer is 3 to 15% by weight with respect to 100% by weight in total of the polyethylene resin (A) and the polymer antistatic agent,
A polyethylene-based resin multilayer foamed sheet characterized in that the thickness of the surface layer is 2 to 10 μm is provided.

In a second aspect, the present invention provides the polyethylene-based resin multilayer foam sheet according to the first aspect, characterized in that the surface resistivity of the multilayer foam sheet on the surface layer side is less than 1 × 10 ¹⁴ Ω. To do.
In a third aspect, the present invention provides the polyethylene-based resin multilayer foam sheet according to the first or second aspect, wherein the apparent density of the multilayer foam sheet is 15 to 300 kg / m ³ .
In a fourth aspect, the present invention provides a glass sheet interleaf made of the polyethylene resin multilayer foamed sheet of any of the first to third aspects.

The polyethylene-based resin multilayer foamed sheet of the present invention (hereinafter also simply referred to as a foamed sheet or a multilayer foamed sheet) is laminated on at least one surface of a polyethylene-based resin foamed layer (hereinafter also simply referred to as a foamed layer). And a polyethylene-based resin surface layer (hereinafter also simply referred to as a surface layer). As the polyethylene resin (A) constituting the foam layer and the polyethylene resin (B) constituting the surface layer, a polyethylene resin having a heptane extraction amount at 50 ° C. of 0.5% by weight or less is used. The polymer type antistatic agent is present in the foamed layer in an amount of 3 to 15% by weight based on 100% by weight of the total of the polyethylene resin (A) and the polymer type antistatic agent. The thickness of the surface layer is 2 to 10 μm. With the above configuration, the foamed sheet has an antistatic performance, but has a very small amount of organic substances such as low molecular weight components transferred to the package.

The foamed sheet of the present invention has a multilayer structure in which a surface layer is laminated on at least one surface of a foamed layer, and is formed with a foamed layer comprising a polyethylene resin (A), a polymer antistatic agent, and a physical foaming agent. It is obtained by coextrusion of the first melt for forming and the second melt for forming the surface layer composed of the polyethylene resin (B). In a preferred embodiment, the first melt is heated, kneaded by supplying an additive such as a polyethylene-based resin (A), a polymer-type antistatic agent, and a cell regulator added as necessary to an extruder. It is obtained by melting and further press-fitting and kneading a physical foaming agent, and the second melt is obtained by heating, kneading and melting the polyethylene resin (B). The foam sheet is obtained by introducing the first and second melts into a coextrusion die, merging and laminating, and coextrusion. In addition, the surface layer may be laminated | stacked on the single side | surface, and may be laminated | stacked on both surfaces of the foaming layer.

Each of the polyethylene resin (A) and the polyethylene resin (B) has a heptane extraction amount at 50 ° C. of 0.5% by weight or less. The content of the polymer antistatic agent in the foamed layer is 3 to 15% by weight based on the total of 100% by weight of the polyethylene resin (A) and the polymer antistatic agent, The thickness is 2 to 10 μm. With the combination of these configurations, the foamed sheet of the present invention enables the expression of antistatic performance, while reducing organic substances such as low molecular weight components derived from polyethylene-based resin present on the surface of the foamed sheet. The organic substance such as a low molecular weight component usually inevitably contained in the molecular type antistatic agent is prevented from bleeding out to the surface of the foam sheet, thereby suppressing the organic substance from being transferred to the package. Note that the amount of the polymer antistatic agent relative to the polyethylene resin (A) does not substantially change before and after the coextrusion. Therefore, in the first melt for forming the foam layer, the polymer antistatic agent is When blended in an amount of 3 to 15% by weight based on 100% by weight of the total amount of the polyethylene resin (A) and the polymer antistatic agent, the polymer antistatic agent is added to the polyethylene foam in the formed foamed layer. 3 to 15% by weight is present with respect to 100% by weight of the total of the resin (A) and the polymer antistatic agent.

The polyethylene-based resin (B) used in the surface layer has an ethylene component unit content of 50 mol% or more in the resin. Specific examples thereof include low-density polyethylene (PE-LD), linear Low density polyethylene (PE-LLD), high density polyethylene (PE-HD), ethylene-vinyl acetate copolymer (EVAC), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer ( EEAK) and mixtures thereof. In general, low-density polyethylene, long chain density having a branched structure is a polyethylene resin of less than 910 kg / ^{m 3} or more 930 kg / ^{m 3,} linear low density polyethylene, ethylene and number from 4 to 8 carbon atoms a polyethylene resin density copolymer is a substantially molecular chain is linear is less than 910 kg / ^{m 3} or more 930 kg / ^{m 3} and α- olefin, high density polyethylene has a density of 930 kg / m ^{There are three} or more polyethylene resins, and these polyethylene resins are preferably used. Among these, low density polyethylene is particularly preferable from the viewpoint of buffering properties.

The polyethylene resin (B) and further the polyethylene resin (A) require that the amount of heptane extracted at 50 ° C. is 0.5% by weight or less. Since both the polyethylene resin (A) and the polyethylene resin (B) have a heptane extraction amount of 0.5% by weight or less, they are covered with organic matter such as low molecular weight components contained in the polyethylene resin itself. It becomes a foamed sheet with a small amount of transfer to a product. In addition, since a part of the low molecular weight component derived from the polyethylene resin (A) is transferred to the resin melt of the polyethylene resin (B) constituting the surface layer during coextrusion, the low molecular weight component is packaged. In order to suppress the transition to a product, it is necessary to use not only a polyethylene resin (B) having a small amount of heptane extract but also a polyethylene resin (A) having a small amount of heptane extract. From this viewpoint, the amount of heptane extracted is preferably 0.4% by weight or less, more preferably 0.3% by weight or less, and particularly preferably 0.2% by weight or less.

Examples of the polyethylene resin having a heptane extraction amount of 0.5 wt% or less include those obtained by extracting and removing low molecular weight components from the polyethylene resin with a solvent such as heptane. Moreover, what is manufactured using the slurry method and the solution method among the said polyethylene-type resin is mentioned. Polyethylene resins produced by the slurry method or solution method have low molecular weight components removed in the solvent removal process at the time of production, and extraction and removal treatment with a solvent such as heptane is not necessary. preferable. In addition, even if it is a polyethylene resin having a heptane extraction amount of more than 0.5% by weight, mixing with a polyethylene resin having a heptane extraction amount of 0.5% by weight or less reduces the total to 0.5% by weight or less. As long as it can be used, it can be used as the polyethylene resins (A) and (B).

The amount of heptane extracted from the polyethylene resin is determined as follows.
Crush the polyethylene resin pellets. About 2 g of the pulverized 200 mesh pass sample is weighed. This is put into a flask, 400 ml of normal heptane is added, and the mixture is heated to reflux at 50 ° C. for 48 hours. The resulting solution is filtered and the solvent is removed from the fractionated residue under heating vacuum. The difference between the weight of the obtained residue and the weight of the added polyethylene resin is determined. The amount of n-heptane extracted is weight% based on the amount of polyethylene resin charged with this difference.

Since it is desirable that the polyethylene resin (B) has a surface layer that is thinly and evenly laminated on the surface of the foam layer, the melt mass flow rate (MFR) measured based on the condition D of JIS K7210-1999 is 1 to 30 g / It is preferably 10 minutes. In order to laminate the layers more evenly, the content is more preferably 1.5 to 20 g / 10 minutes, and further preferably 2 to 15 g / 10 minutes.

The surface layer may not contain a polymer antistatic agent. However, in the range that does not hinder the intended purpose of the present invention to suppress the migration of organic substances such as low molecular weight components to the package, that is, the polyethylene resin and polymer antistatic agent used for the surface layer In the range where the amount of n-heptane extracted from the mixture becomes 0.5% by weight, a polymer antistatic agent may be blended in the surface layer. The amount is approximately 1% by weight or less in the surface layer. Thereby, the transfer of the organic substance from the polymer type antistatic agent to the package is suppressed to a low level.

Examples of the polyethylene resin (A) used for the foam layer include the same as the polyethylene resin (B). However, the polyethylene resin (A) and the polyethylene resin (B) may be different resins.

Further, as the polyethylene resin (A), among the above-mentioned polyethylene resins, those having a melt tension at 190 ° C. of 20 mN to 400 mN are preferable. From the viewpoint that it is easy to obtain a foam layer having a low apparent density, the melt tension at 190 ° C. is preferably 20 mN or more, more preferably 30 mN or more, and further preferably 40 mN or more. Further, from the viewpoint of easily obtaining a foamed layer having a low open cell ratio, the melt tension at 190 ° C. is preferably 400 mN or less, more preferably 300 mN or less, and further preferably 250 mN or less.

The melt tension can be measured by, for example, a capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. Specifically, a cylinder with a cylinder diameter of 9.55 mm and a length of 350 mm and an orifice with a nozzle diameter of 2.095 mm and a length of 8.0 mm were used. Place in the cylinder and let stand for 4 minutes, then push the molten resin out of the orifice into a string with a piston speed of 10 mm / min, put this string on a 45 mm diameter tension detection pulley, and take it off in 4 minutes. While increasing the take-up speed at a constant speed so that the speed reaches from 0 m / min to 200 m / min, the maximum value of the tension immediately before the string-like object breaks when the string-like object is taken up by the take-off roller. obtain. Here, the reason why the time until the take-up speed reaches 0 m / min to 200 m / min is set to 4 minutes is to suppress the thermal deterioration of the resin and increase the reproducibility of the obtained value. Using a different sample for the above operation, measuring a total of 10 times, removing the three values in order from the largest value of the maximum value obtained in 10 times, and the three values in order from the smallest value of the maximum value, The value obtained by arithmetically averaging the remaining four local maximum values is the melt tension (cN).

However, when the melt tension is measured by the method described above and the string-like material does not break even when the take-up speed reaches 200 m / min, the melt tension obtained by setting the take-up speed to a constant speed of 200 m / min. The value of (cN) is adopted. Specifically, in the same manner as in the above measurement, the molten resin is extruded into a string from the orifice, and this string is put on a tension detection pulley, and a constant speed increase is made so that the speed reaches 0 m / min to 200 m / min in 4 minutes. Rotate the take-up roller while increasing the take-up speed, and wait until the rotation speed reaches 200 m / min. When the rotational speed reaches 200 m / min, the data acquisition of the melt tension is started, and the data acquisition is finished after 30 seconds. The average value (Tave) of the tension maximum value (Tmax) and the tension minimum value (Tmin) obtained from the tension load curve obtained during this 30 seconds is taken as the melt tension in the method of the present invention.
Here, the Tmax is a value obtained by dividing the total value of detected peak (peak) values in the tension load curve by the detected number, and the Tmin is detected in the tension load curve. It is a value obtained by dividing the total value of the dip (valley) values by the detected number. As a matter of course, when the molten resin is extruded into a string from the orifice in the above measurement, bubbles are prevented from entering the string as much as possible.

The polymer type antistatic agent is blended in the polyethylene resin (A) constituting the foam layer. The blending amount is 3 to 15% by weight with respect to 100% by weight in total of the polyethylene resin (A) and the polymer antistatic agent. If the amount of the polymeric antistatic agent is too large, the low molecular weight component may pass through the surface layer and migrate to the package. The blending amount of the polymer type antistatic agent is preferably as small as possible within the range where the antistatic performance is expressed. In the case where a polymer type antistatic agent is blended in the foamed layer, the same antistatic effect can be obtained even in a smaller blending amount than in the case of blending in the non-foamed layer. The reason for this is that if a polymer type antistatic agent is blended in the foam layer, the polymer type antistatic agent is not only stretched when the foam is widened and taken out, but is also extruded from the die. Even when foaming, the polymer antistatic agent is stretched, and it is considered that the polymer antistatic agent forms a more complicated network structure in the polyethylene resin. From this viewpoint, the upper limit of the amount of the polymeric antistatic agent is preferably 12% by weight, and more preferably 10% by weight. On the other hand, if the amount of the polymeric antistatic agent is too small, there is a possibility that sufficient antistatic performance cannot be obtained. From this viewpoint, the lower limit of the amount of the polymeric antistatic agent is preferably 4% by weight.

Specific examples of the polymer antistatic agent include a hydrophilic polymer having a volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm (hereinafter also simply referred to as a hydrophilic polymer), and a hydrophilic polymer. Examples include block polymers of block and hydrophobic polymer blocks, ionomers, and the like. Examples of the hydrophilic polymer include polyether, cationic polymer, anionic polymer and the like. Examples of the hydrophilic polymer block include the hydrophilic polymer block, and examples of the hydrophobic polymer block include polyolefin and polyamide. Examples of the bond between the hydrophilic polymer block and the hydrophobic polymer block include an ester bond, an amide bond, and an ether bond. Among these, in order to provide an excellent antistatic effect and to suppress the deterioration of physical properties due to the addition of an antistatic agent, a block copolymer having a polyether block and having a polyolefin block as a hydrophobic polymer block. Polymers are preferred. Further, since the amount of the polymer type antistatic agent for obtaining a desired antistatic effect can be reduced, the amount of migration of the organic matter can be reduced, so that the surface resistivity is preferably 1 × 10 ⁷ Ω or less.

The thickness of the surface layer is required to be 2 to 10 μm. When the thickness is smaller than 2 μm, the migration of the low molecular weight component derived from the polymer antistatic agent contained in the foam layer cannot be suppressed by the surface layer. If it is larger than 10 μm, the distance between the foam layer containing the antistatic agent and the surface of the surface layer becomes large, and it becomes difficult to neutralize the charge generated on the surface layer surface. It becomes difficult to do. The thickness of the surface layer can be adjusted by adjusting the discharge amount and the take-up speed.

The thickness of the foamed sheet of the present invention is preferably 10 mm or less, more preferably 8 mm or less from the viewpoint of easy handling when packing an article to be packaged when the foamed sheet is used as a packaging material or an interleaf. 5 mm or less is further preferable, and 2 mm or less is particularly preferable. On the other hand, the thickness is preferably 0.05 mm or more, and more preferably 0.1 mm or more from the viewpoint of obtaining sufficient buffering properties when the multilayer foamed sheet is used particularly for applications requiring buffering properties.

The method for measuring the thickness of the surface layer and the thickness of the foamed sheet is as follows.
First, a foam sheet is cut | disconnected along the width direction (direction orthogonal to an extrusion direction), and a cut surface is divided | segmented into 10 equal parts in the width direction. The central portion in the width direction of each of the 10 portions of the cut surface is defined as the measurement location. Each of the ten portions is photographed with a microscope, and the thickness of the surface layer and the foamed sheet at the measurement location is measured on each photographed image. The arithmetic average value of the ten measured surface layer thickness values obtained is the thickness of the surface layer, and the arithmetic average value of the ten measured foam layer thickness values is the thickness of the foam sheet. Note that either the foam layer or the surface layer can be colored so that the thickness of the surface layer can be easily measured.
The thickness [μm] of the surface layer is determined by the surface layer discharge amount X [kg / hour] and the width W [m] of the foam sheet obtained when the foamed sheet is manufactured. When the length L [m / hour] per unit time of the foamed sheet to be obtained is known, the density ρ [g / cm ³ ] of the polyethylene resin constituting the surface layer is used to Can be obtained.
Surface layer thickness [μm] = [1000 × X / (L × W × ρ)] (1)

The apparent density of the foamed sheet of the present invention is preferably 15 to 300 kg / m ³ . When the apparent density of the foamed sheet is in the above range, the balance between strength and buffering properties is excellent.該見seat Density From this point of view is more preferably 18 kg / ^{m 3} or more, 20 kg / ^{m 3} or more, and on the other hand,該見seat density is more preferably less than 300 kg / ^{m 3,} more preferably 250 kg / ^{m 3} or less, 200 kg / m ³ or less is particularly preferable.

In the present invention, the method for measuring the apparent density of the foam sheet is as follows. First, the thickness of the foam sheet is measured by the method described above. Next, in order to measure the basis weight, a test piece of (full width of foam sheet) × (length in extrusion direction 10 cm) × (thickness of multilayer foam sheet) is cut out from the foam sheet, and the mass [g] of the test piece is measured. To do. The basis weight [g / m ² ] can be obtained by dividing the mass by the area of the test piece [m ² : full width of foam sheet (m) × 0.1 m]. Furthermore, the apparent density [kg / m ³ ] of the foam sheet can be obtained by dividing the calculated basis weight [g / m ² ] by the thickness [mm] of the foam sheet and converting the unit.

In the foam sheet of the present invention, the closed cell ratio is preferably 10% or more, more preferably 20% or more.
The closed cell ratio: S (%) of the polyethylene resin foam sheet is measured using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C described in ASTM D2856-70. The actual volume of the foamed sheet (the sum of the volume of the closed cells and the volume of the resin part): Vx (L) can be obtained by calculation according to the following equation (2).

S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (2)
However, Va, W, and ρ in the above equation (2) are as follows.
Va: Apparent volume of foam sheet used for measurement (cm ³ )
W: Mass of the foam sheet in the test piece (g)
ρ: Density of resin constituting the foam sheet (g / cm ³ )

The foamed sheet of the present invention has antistatic properties. Specifically, in order to be used as a packaging material or a slip sheet of an electronic device or its material, the half-life of the initial voltage on the surface layer side is preferably 60 seconds or less, more preferably 30 seconds or less. . The half-life is a value measured according to A method (half-life measurement method) of JIS L1094-1988. Specifically, a test piece cut out from a foam sheet (length 40 mm × width 40 mm × thickness: thickness of foam sheet to be measured) was left in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% for 36 hours. Adjust the condition. Next, according to method A of JIS L1094 (1988), the turntable rotation speed is 1300 rpm, and after applying for 30 seconds under the condition of (+) 10 kV or (−) 10 kV, the application is stopped and the application is stopped. From the time until the initial charging voltage is attenuated to 1/2, the half-life (second) is obtained. The initial charging voltage is preferably within ± 2.0 kV, more preferably within ± 1.5 kV.

In the foam sheet of the present invention, when a higher antistatic effect is required, the surface resistivity on the surface layer side is preferably less than 1 × 10 ¹⁴ Ω, and 1 × 10 ⁸ to 1 More preferably, it is × 10 ¹³ (Ω). The surface resistivity of the foamed sheet is a value measured according to JIS K6271 (2001). That is, the state of the test piece is adjusted by leaving the test piece cut out from the foamed sheet (length 100 mm × width 100 mm × thickness: thickness of the foamed sheet) in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% for 24 hours. Next, under the condition of an applied voltage of 500 V, voltage application is started on the surface layer side of the test piece, and the surface resistivity after 1 minute is measured.

Next, the preferable example of the manufacturing method of the polyethylene-type resin foam sheet of this invention is demonstrated.
The laminated foam sheet of the present invention is produced by laminating a polyethylene resin surface layer on one or both sides of a polyethylene resin foam layer containing a polymer type antistatic agent by a coextrusion method. Specifically, a coextrusion die is attached to the outlet of the foam layer forming extruder, and a device in which the surface layer forming extruder is connected to the coextrusion die, in the coextrusion die, A foam sheet is produced by joining the first melt for forming the foam layer and the second melt for forming the surface layer and then performing extrusion foaming.

First, the polyethylene-based resin (A), a polymeric antistatic agent, and additives such as an air-conditioning agent blended as necessary are supplied to a foaming layer forming extruder, heated and kneaded, and then physically added. A foaming agent is press-fitted into a first melt.

On the other hand, the polyethylene resin (B) is supplied to a surface layer forming extruder, heated and kneaded to obtain a second melt.

The first melt is cooled to the proper foaming temperature, the second melt is cooled as close as possible to the proper foaming temperature of the foam layer, and both are introduced into the coextrusion die. The first melt and the second melt are merged, the second melt is laminated on at least one side of the first melt, and co-extrusion is performed to take out the first melt while foaming. A foamed sheet is obtained by forming a surface layer on the surface.

In the method of forming a foam sheet by the coextrusion method, a method of coextrusion into a sheet shape using a flat die for coextrusion, a coextrusion using an annular die for coextrusion to form a cylindrical foam, and then For example, there is a method of cutting a tubular foamed body along a columnar widening device while opening the tubular foamed material to obtain a sheet-like foamed sheet. Among these, a method using an annular die for coextrusion is a preferable method because generation of a wavy pattern called a corrugate can be suppressed and the heat shrinkage rate of the foamed sheet can be controlled within a preferable range.

In addition, the said extruder, the coextrusion cyclic | annular die | dye, a cylindrical widening apparatus, the apparatus which opens a cylindrical foam, etc. can use the well-known thing conventionally used in the field | area of extrusion foaming.

Examples of the physical foaming agent that is press-fitted into the extruder include aliphatic hydrocarbons having 2 to 7 carbon atoms, halogenated aliphatic hydrocarbons having 1 to 3 carbon atoms, aliphatic alcohols having 1 to 4 carbon atoms, or Those composed of one or more selected from aliphatic ethers having 2 to 8 carbon atoms, carbon dioxide and the like are preferably used.

The physical foaming agent is preferably 0.1 to 50 parts by weight, more preferably 100 parts by weight in total of the resin constituting the foamed layer such as the polyethylene resin (A) and the polymer antistatic agent. Is 0.5 to 30 parts by weight.

A bubble regulator is usually added to the first melt for forming the foam layer. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic foam regulator include borate metal salts such as zinc borate, magnesium borate, borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like. Examples of the organic bubble regulator include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate.
A combination of citric acid and sodium bicarbonate, a mono-alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble regulator. These bubble regulators can be used in combination of two or more.

It is preferable to add a volatile plasticizer to the second melt for forming the surface layer. When the second melt and the first melt are coextruded by adding a volatile plasticizer, even if the extrusion temperature of the second melt is close to the proper foaming temperature of the foam layer, 2 The melt elongation of the melt can be remarkably improved, and the elongation of the second melt can follow the elongation of the first melt.

The volatile plasticizer volatilizes and disappears from the foam sheet after the foam sheet is manufactured. When the volatile plasticizer is present in the second melt, the melt viscosity of the polyethylene resin can be lowered to form a resin melt suitable for coextrusion, and after extrusion foaming. Is preferred since it volatilizes from the surface layer, does not easily disappear from the surface layer and remains in the foamed sheet, and is very unlikely to cause migration.

Examples of the volatile plasticizer include saturated hydrocarbons having 2 to 7 carbon atoms, halogenated aliphatic hydrocarbons having 1 to 3 carbon atoms, aliphatic alcohols having 1 to 4 carbon atoms, or 2 to 8 carbon atoms. Those composed of one kind or two or more kinds selected from aliphatic ethers are preferably used.
Examples of the saturated hydrocarbon having 2 to 7 carbon atoms exemplified in the volatile plasticizer include ethane, propane, normal butane, isobutane, normal pentane, isopentane, isohexane, cyclohexane and heptane.

Examples of the halogenated aliphatic hydrocarbon having 1 to 3 carbon atoms include methyl chloride, ethyl chloride, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane.

Examples of the aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, sec-butyl alcohol, and tert-butyl alcohol.

Examples of the aliphatic ether having 2 to 8 carbon atoms include methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, methyl isobutyl ether, and methyl amyl ether. Methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl amyl ether, ethyl isoamyl ether, vinyl ether, allyl ether, methyl vinyl ether, methyl allyl ether, ethyl vinyl ether, ethyl allyl ether.

The boiling point of the volatile plasticizer is preferably 80 ° C. or less, more preferably 60 ° C. or less because it easily volatilizes from the surface layer. When the boiling point of the volatile plasticizer is within this range, the volatile plasticizer is volatilized naturally from the surface layer by the heat after co-extrusion and the subsequent gas permeation at room temperature. The lower limit of the boiling point is approximately −50 ° C.

The addition amount of the volatile plasticizer is preferably 0.1 to 100 parts by weight, more preferably 1 to 50 parts by weight with respect to 100 parts by weight of the polyethylene resin (B).

Since the polyethylene-based resin foam sheet of the present invention has antistatic properties, and the amount of organic matter transferred to the package is suppressed to a small level, it can be used for electronic devices such as slip sheets for glass panels for liquid crystal panels and the materials thereof. It can be suitably used as a packaging material.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
The polyethylene resin used in the examples, the bubble regulator, and the evaluation method are described below.

(1) Polyethylene resin (i) “Low density polyethylene: trade name NUC8321” (abbreviation: LDPE1, density: 922 kg / m ³ , MFR: 1.9 g / 10 min, melting point: 111 ° C., heptane extraction amount: 1 .15% by weight)
(Ii) “Low density polyethylene: Trade name 10S54A” manufactured by Tosoh Corporation (abbreviation LDPE2, density 925 kg / m ³ , MFR 1.8 g / 10 min, melting point 111 ° C., heptane extract 0.15% by weight)
(Iii) “High Density Polyethylene: Trade Name Nipolon Hard 2500” manufactured by Tosoh Corporation (density 961 kg / m ³ , MFR 8.0 g / 10 min, melting point 134 ° C., heptane extract 0.2% by weight)
(Iv) The above LDPE1 was immersed in n-heptane at 50 ° C. for 48 hours to extract low molecular weight components (abbreviation LDPE3, density 922 kg / m ³ , MFR 1.7 g / 10 min, melting point 111 ° C., heptane extract amount 0% by weight)

The amount of heptane extracted from the polyethylene resin was determined by the method described above. The heptane extraction amount of the mixed resin in Table 1 is the n-heptane extraction amount of the mixed resin kneaded at 200 ° C. with an extruder.

(2) Polymer type antistatic agent (i) “Polyether-polyolefin block copolymer: Peletron HS (melting point: 134 ° C., surface resistivity: 2.0 × 10 ⁶ Ω) manufactured by Sanyo Chemical Industries, Ltd. (abbreviated as PAA1) )
(Ii) Polymer type antistatic agent VL300
“Polyether-polyolefin block copolymer: trade name: Perestat VL300” manufactured by Sanyo Chemical Industries, Ltd. (melting point 133 ° C., surface resistivity 1.2 × 10 ⁸ Ω) (abbreviation PAA2)

(3) Bubble regulator “Talc: Product name High Filler # 12” manufactured by Matsumura Sangyo Co., Ltd.

[apparatus]
A tandem extruder in which a first extruder having a diameter of 90 mm and a second extruder having a diameter of 120 mm are connected in series is used as an extruder for forming a foam layer, and the diameter is used as an extruder for forming a surface layer. A 50 mm third extruder was used, and an apparatus in which the outlet of the second extruder and the outlet of the third extruder were connected to an annular die for coextrusion was used. The annular die for coextrusion has a structure in which a second melt for forming a surface layer, which will be described later, is merged and laminated on both surfaces of the first melt for forming a foam layer at the middle part of the die, and the diameter of the lip at the die exit is 94 mm. It is. In Example 5, a die exit lip having a diameter of 70 mm was used.

Example 1
The polymer type antistatic agent shown in Table 1 is blended with the polyethylene resin (A) shown in Table 1 in the amount shown in Table 1, and talc (trade name “High Filler # 12” manufactured by Matsumura Sangyo Co., Ltd.) is added thereto. The raw material blended by 1 part by weight was supplied to the raw material inlet of the first extruder, heated and kneaded to obtain a molten resin mixture adjusted to about 200 ° C. Table 1 shows the molten resin mixture as a physical foaming agent. An amount of mixed butane (normal butane / isobutane = 70% by weight / 30% by weight) was injected and then fed to a second extruder connected downstream of the first extruder to obtain the resin temperature shown in Table 2. A first melt for forming a polyethylene resin foam layer was obtained.

At the same time, the polyethylene resin (B) shown in Table 1 is supplied to the raw material charging port of the third extruder, heated and melted to obtain a molten resin mixture adjusted to about 200 ° C., and a volatile plasticizer is added to the molten resin mixture. As shown in Table 2, mixed butane (normal butane / isobutane = 70% by weight / 30% by weight) in the amount shown in Table 2 is injected, and then the resin temperature is adjusted to the resin temperature shown in Table 1 to form a second polyethylene-based resin surface layer forming layer. A melt was obtained.

Each of the first and second melts is introduced into a co-extrusion annular die at a discharge amount shown in Table 1, the second melt is merged and laminated on both sides of the first melt, and is co-extruded from the annular die. A cylindrical multilayer foam having surface layers laminated on the inner and outer surfaces of the foam layer was formed. While the extruded cylindrical laminated foam was widened with a cylindrical widening apparatus having a diameter of 350 mm, the take-up speed was adjusted to obtain the total basis weight shown in Table 3 to obtain a polyethylene-based resin multilayer foamed sheet.

Example 2
A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that those shown in Table 1 were used as the polyethylene-based resin for forming the foam layer and the surface layer.

Example 3
A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that those shown in Table 1 were used as the polyethylene-based resin for forming the foam layer and the surface layer.

Example 4
A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the discharge amount was changed as shown in Table 1 so that the thickness of the surface layer shown in Table 4 was obtained.

Example 5
Using a co-extrusion annular die with a lip diameter of 70 mm, using the raw materials shown in Table 1 as the polyethylene resin (A), press-fitting mixed butane as the foaming agent in the amount shown in Table 1, and adjusting the resin temperature shown in Table 1 The raw material shown in Table 1 is used as the polyethylene resin (B), mixed butane is injected as a volatile plasticizer in the amount shown in Table 1, the resin temperature shown in Table 1 is adjusted, and the foamed layer forming molten resin and surface The molten resin for layer formation is coextruded at the discharge amount shown in Table 1 to form a cylindrical laminated foam, and the basis weight shown in Table 3 along the cylindrical cooling device having a diameter of 212 mm. A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the take-up speed was adjusted so that

Comparative Example 1
A polyethylene-based resin single-layer foamed sheet consisting only of a foamed layer containing a polymer antistatic agent was obtained in the same manner as in Example 1 except that the surface layer was not laminated.
Although the obtained single-layer foamed sheet was excellent in antistatic properties, it did not have a surface layer, so that the amount of the low molecular weight component derived from the polymeric antistatic agent transferred to the package was large.

Comparative Example 2
Example 1 except that the surface layer thickness was set to the thickness shown in Table 4, and the discharge amount and take-up speed of the foamed layer forming molten resin and the surface layer forming molten resin were adjusted to the total basis weight shown in Table 4. Similarly, a polyethylene resin multilayer foamed sheet was obtained.
In the obtained multilayer foamed sheet, the thickness of the surface layer was too thin, so that the amount of the low molecular weight component derived from the polymer antistatic agent transferred to the package was large.

Comparative Example 3
A polyethylene resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the polymer type antistatic agent in the amount shown in Table 2 was blended.
The obtained multilayer foamed sheet was inferior in antistatic property because the blending amount of the antistatic agent was too small.

Comparative Example 4
A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the polymer type antistatic agent was added to the foam layer forming resin in the amount shown in Table 2.
Since the obtained multilayer foamed sheet contained too much antistatic agent, the amount of the low molecular weight component transferred to the package was large.

Comparative Example 5
As the polyethylene resin (A) and the polyethylene resin (B), a polyethylene resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the resin having a large amount of heptane extraction shown in Table 2 was used.
The obtained multilayer foamed sheet had a large transfer amount of the low molecular weight component derived from the polyethylene resin to the package.

Comparative Example 6
As the polyethylene resin (A), a polyethylene resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that the resin having a large amount of heptane extraction shown in Table 2 was used.
The obtained multilayer foamed sheet had a large transfer amount of the low molecular weight component derived from the polyethylene resin to the package.

Comparative Example 7
The foam layer uses a resin with a large amount of heptane extraction shown in Table 2 as the polyethylene resin (A), does not contain a polymer type antistatic agent, and the surface layer shows a polyethylene resin (B) in Table 2. A polyethylene-based resin multilayer foamed sheet was obtained in the same manner as in Example 1 except that a resin and a polymer type antistatic agent of the type and blending amount shown in Table 2 were blended.
The obtained multilayer foamed sheet was excellent in antistatic properties, but had a large amount of low molecular weight components transferred to the package.

Comparative Example 8
Polyethylene resin multilayer as in Example 1, except that the foamed layer was not blended with a polymer antistatic agent and the surface layer was blended with a polymer antistatic agent of the type and blending amount shown in Table 2. A foam sheet was obtained.
Although the obtained multilayer foamed sheet was excellent in antistatic properties, the amount of the low molecular weight component derived from the polymer antistatic agent transferred to the package was large.

Table 1 shows the manufacturing conditions of the examples, and Table 2 shows the manufacturing conditions of the comparative examples. Table 3 shows the physical properties of the foam sheets obtained in the examples, and Table 4 shows the physical properties of the foam sheets obtained in the comparative examples.

Various physical property measurements and evaluations in Tables 3 and 4 were performed as follows.
(1) Apparent density, basis weight, overall thickness, and thickness of the surface layer were measured as described above.

(3) Initial charging voltage and half-life The initial charging voltage was measured by randomly cutting 5 sheets of a 45 mm × 45 mm size (thickness is the thickness of the foamed sheet) from the foamed sheet. After conditioning for 24 hours in a% RH environment, using a static Honest Meter (TIPE S-5109, manufactured by Sisid Electric Co., Ltd.) according to JIS L1094 (1988) A method at 23 ° C. and 50% RH. The turntable rotation speed was 1300 rpm, a voltage of (−) 10 kV was applied to the surface of the test piece for 30 seconds, and the initial voltage when the application was stopped was measured. Subsequently, the time (half-life) until it became 1/2 of the initial charging voltage was measured. These measurements were performed on both sides of each test piece (10 times in total), and each measured value was averaged to obtain an initial charging voltage and a half-life.

(4) Surface resistivity A test piece (length 100 mm × width 100 mm × thickness: thickness of foam sheet) obtained by randomly cutting out three pieces from the foam sheet was used as a sample. In accordance with JIS K6271 (2001), a surface resistance value 1 minute after application at an applied voltage of 500 V was adopted. The measurement was performed on both sides of the test piece (6 times in total), and the surface resistivity was obtained from the average value of the obtained measurement values. As a measuring apparatus, “TR8601” manufactured by Takeda Riken Kogyo Co., Ltd. was used. The surface resistivity of the polymer antistatic agent is a value measured using a test piece obtained by heat-pressing the antistatic agent at 200 ° C. to 0.1 mm.

(5) Migration evaluation In advance, the contact angle of Preclin slide glass manufactured by Matsunami Glass Industry Co., Ltd. was evaluated using a contact angle meter DM500R manufactured by Kyowa Interface Science Co., Ltd. based on the sessile drop method described in JIS-R3257-1999. did. The sample to be evaluated on the slide glass (foamed sheet obtained in Examples / Comparative Examples) was allowed to stand at 60 ° C. for 24 hours while closely contacting with a pressure of 3.8 g / cm ² . Thereafter, the sample was removed from the glass, and the contact angle was again measured in the same manner for the surface on which the sample was in contact. A case where the difference between the contact angles before and after the test was 10 ° or less was evaluated as ○ (good), and a case where the contact angle exceeded 10 ° was evaluated as x (defective).

Claims

A polyethylene-based resin multilayer having a foam layer and a surface layer laminated on at least one side of the foam layer, and obtained by coextrusion of the first melt for forming the foam layer and the second melt for forming the surface layer A foam sheet, wherein the first melt is composed of a polyethylene resin (A), a polymer antistatic agent and a physical foaming agent,
The second melt is composed of a polyethylene resin (B),
Each of the polyethylene resin (A) and the polyethylene resin (B) has an n-heptane extraction amount at 50 ° C. of 0.5% by weight or less,
The polymer antistatic agent is present in the foamed layer in an amount of 3 to 15% by weight based on 100% by weight of the total of the polyethylene resin (A) and the polymer antistatic agent.
The surface layer has a thickness of 2 to 10 μm.
Polyethylene resin multilayer foam sheet.
The polyethylene-based resin multilayer foamed sheet according to claim 1, wherein the surface layer has a surface resistivity of less than 1 × 10 14 Ω.
The polyethylene resin multilayer foamed sheet according to claim 1 or 2, wherein the apparent density of the polyethylene multilayer foamed sheet is 15 to 300 kg / m 3 .
A glass sheet interleaf comprising the polyethylene resin multilayer foamed sheet according to any one of claims 1 to 3.