JP6614697B2 - Multi-layer foam sheet and interleaf paper for glass plate - Google Patents

Description

  The present invention relates to a multilayer foamed sheet, and more particularly to a multilayer foamed sheet that can be suitably used as an interleaf for a plate-like material such as a glass plate for a substrate.

  Conventionally, when glass plates used in a liquid crystal panel are stacked and transported, a slip sheet is interposed between the glass plates for protection. Paper has been used as the slip sheet, but in recent years, a polyethylene resin foam sheet has been used (for example, Patent Document 1).

  The foam sheet used as the interleaving paper has a cushioning property to protect the glass plate as a packaged object, and has a small amount of sag when cantilevered (high strength), and is interposed between the glass plates. It is required to be excellent in handleability when performing. Further, when performing processing and manufacturing operations for glass plates, it is necessary to remove the foamed sheet interposed between the glass plates from the glass plate surface by vacuum suction. At that time, if the amount of sag when the foam sheet is cantilevered is too large (the strength is weak), the part protruding from the glass plate may sag or wrinkle may occur on the foam sheet. Exclusion workability, such as exclusion, is reduced.

JP 2007-262409 A

  On the other hand, in recent years, as the glass plate for liquid crystal panels has been further reduced in thickness, the foam sheet used as a slip sheet has been required to be thinner. Therefore, there is a demand for a thin foam sheet having sufficient cushioning and stiffness as a slip sheet.

  The present invention provides a multilayer foamed sheet that has sufficient cushioning and stiffness, and can be suitably used as an interstitial paper for a glass plate for a substrate, even if it is thinner and lighter than a conventional multilayer foam sheet for slippers. It is for the purpose.

According to the present invention, the following multilayer foam sheet is provided.
[1] A multilayer foam sheet having an apparent density of 30 to 300 kg / m ³ and a thickness of 0.05 to 2 mm, comprising a polyethylene-based resin foam layer and an antistatic layer laminated and adhered to both sides of the foam layer by coextrusion. In
The basis weight per one side of the antistatic layer is 1 to 10 g / m ² ,
The antistatic layer is formed from a mixed resin composition containing a polyethylene resin, a polystyrene resin, a polymer antistatic agent, and a styrene elastomer,
The weight ratio of the polystyrene resin in the mixed resin composition is 15 to 50% by weight,
The weight ratio of the styrenic elastomer in the mixed resin composition is 2 to 20% by weight,
In the mixed resin composition, the polyethylene resin forms a continuous phase, and the polystyrene resin and the polymer antistatic agent individually form dispersed phases dispersed in the continuous phase. Multi-layer foam sheet.
[2] The dispersed phase of the polystyrene-based resin is stretched along the plane direction of the multilayer foamed sheet, and the aspect ratio (length in the long side direction / length in the short side direction) is perpendicular to the multilayer foam sheet. The multilayer foamed sheet according to claim 1, wherein a dispersed phase of 3 or more of the polystyrene-based resin is included.
[3] The multilayer foamed sheet as described in 1 or 2 above, wherein the weight ratio of the polymer antistatic agent in the mixed resin composition is 2 to 30% by weight.
[4] A glass sheet interleaf comprising the multilayer foamed sheet according to any one of 1 to 3 above.

  The multilayer foamed sheet of the present invention has a sandwich structure in which an antistatic layer is laminated and adhered by coextrusion on both sides of a polyethylene-based resin foam layer (hereinafter also simply referred to as a foam layer). Since the foamed layer is formed of a polyethylene-based resin, the multilayer foamed sheet has excellent buffering properties and can be suitably used as a slip sheet for glass plates for precision electronic devices. Further, the antistatic layer is formed of a mixed resin composition containing a polyethylene resin, a polystyrene resin, a polymer antistatic agent, and a styrene elastomer, and the polyethylene resin in the mixed resin composition. Form a continuous phase, and a polystyrene resin and a polymer-type antistatic agent individually form a dispersed phase dispersed in the continuous phase. Therefore, the multilayer foam sheet having the antistatic layer has the same thickness. Compared to conventional foam sheets, it has excellent rigidity and firmness. Therefore, the multilayer foamed sheet is excellent in followability during vacuum suction and the like, and can be suitably used as a slip sheet for glass plates for precision electronic devices even when the thickness is reduced. Moreover, since the antistatic layer exhibits excellent antistatic properties when the polymer type antistatic agent forms a dispersed phase in the mixed resin composition, the multilayer foamed sheet is less likely to accumulate static charge. It is difficult for dust to adhere to it, and from this point, it can be suitably used as a slip sheet for glass plates for precision electronic devices.

FIG. 1 is a transmission electron micrograph (magnification 15400 times) of the longitudinal section of the antistatic layer of the multilayer foamed sheet obtained in Example 1. FIG. 2 is a transmission electron micrograph of the antistatic layer of the multilayer foam sheet obtained in Example 1 (61800 magnifications). FIG. 3 is a transmission electron micrograph (magnification 15400 times) of the longitudinal section of the antistatic layer of the multilayer foamed sheet obtained in Example 2. FIG. 4 is a transmission electron micrograph of the antistatic layer of the multilayer foamed sheet obtained in Example 2 (magnification: 61800 times).

Hereinafter, the multilayer foamed sheet of the present invention will be described in detail.
The multilayer foamed sheet of the present invention comprises a polyethylene-based resin foam layer and an antistatic layer laminated and adhered by coextrusion on both sides of the foam layer, and has a sandwich structure. Further, the antistatic layer of the multilayer foamed sheet is formed from a mixed resin composition having a specific composition as described later, and the mixed resin composition forms a morphology described later, whereby the multilayer of the present invention is formed. The foamed sheet is strong as a whole, has excellent handling properties, and has excellent antistatic properties while maintaining buffering properties.

  The thickness of the multilayer foamed sheet of the present invention is 0.05-2 mm. As described above, in consideration of the recent thinning of the glass plate for substrates, the upper limit is preferably 1.5 mm, more preferably 1.3 mm, and still more preferably 1.0 mm. On the other hand, the lower limit is preferably 0.07 mm, more preferably 0.10 mm, and still more preferably 0.15 mm, in order to ensure higher buffering properties.

The apparent density of the entire multilayer foamed sheet is 30 kg / m ³ or more, preferably 35 kg / m ³ or more, more preferably 40 kg / m ³ or more. Usually, the lower the apparent density, the lower the rigidity. On the other hand, since the multilayer foamed sheet of the present invention has a specific antistatic layer, the entire multilayer foamed sheet is excellent in rigidity even when the apparent density is low. Considering the buffering property, the upper limit of the apparent density is about 300 kg / m ³ , preferably 200 kg / m ³ .

The upper limit of the basis weight of the multilayer foamed sheet is preferably 200 g / m ² , more preferably 100 g / m ² , still more preferably 50 g / m ² , and particularly preferably 30 g, from the viewpoint of handleability. / M ² . On the other hand, the lower limit is preferably about 10 g / m ² , more preferably 20 g / m ² .

  The thickness of the entire multilayer foamed sheet in the present invention is an arithmetic average value of thickness (mm) measured at intervals of 1 cm in the width direction over the entire width of the multilayer foamed sheet.

The apparent density (kg / m ³ ) of the multilayer foamed sheet in the present invention is obtained by dividing the total basis weight (g / m ² ) of the multilayer foamed sheet by the thickness (mm) of the multilayer foamed sheet and converting the unit. This is the value obtained.

  Moreover, since the width | variety of the multilayer foamed sheet | seat of this invention can be used for the packaging of a large sized glass plate, 1000 mm or more is preferable. The upper limit is approximately 5000 mm.

  In addition, the closed cell ratio of the multilayer foamed sheet of the present invention is preferably 15% or more, and more preferably 20% or more, from the viewpoint of the cushioning property of the foamed sheet, the surface protection property of the package, and the appropriate slipping property.

  The closed cell ratio is calculated according to the following formula (1) using the true volume Vx of the multilayer foam sheet (cut sample) measured according to the procedure C of ASTM-D2856-70. . In addition, it is set as the cut sample for a measurement of 25 mm x 25 mm x about 20 mm by cutting out and laminating a plurality of samples of 25 mm x 25 mm x multilayer foam sheet thickness. As a measuring apparatus, an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. can be used.

S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (1)
Vx: the true volume (cm ³ ) of the cut sample measured by the above method, which corresponds to the sum of the volume of the resin constituting the cut sample and the volume of the closed cell portion in the cut sample.
Va: apparent volume (cm ³ ) of the cut sample of the cut sample used for the measurement, the volume of the resin constituting the cut sample, and the total cell volume of the closed cell portion and the open cell portion in the cut sample Is equivalent to the sum of
W: Total weight (g) of cut sample used for measurement.
ρ: Density of resin required by defoaming the multilayer foamed sheet (g / cm ³ )

Next, the resin that forms the foam layer of the multilayer foam sheet of the present invention will be described.
The foam layer is formed of a polyethylene resin. In order to distinguish between the polyethylene resin forming the foam layer and the polyethylene resin in the mixed resin composition forming the antistatic layer described later, the polyethylene resin forming the foam layer is also referred to as polyethylene resin A. The polyethylene resin that forms the mixed resin composition is also referred to as polyethylene resin B.

In the present invention, the polyethylene-based resin means a resin having an ethylene component unit of 50 mol% or more. Specific examples of the polyethylene resin include low density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), and the like. And the like.
As the polyethylene-based resin A, a polyethylene-based resin mainly composed of low-density polyethylene is preferable because the foamability is excellent and the multilayer foamed sheet is more excellent in buffering properties.

  The foamed layer has other synthetic resins and elastomers, bubble regulators, nucleating agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, hard absorbers and the like as long as the objects and effects of the present invention are not impaired. Additives such as a flame retardant, an antibacterial agent, an anti-shrink agent, and an inorganic filler can be added.

Next, the antistatic layer of the multilayer foam sheet of the present invention will be described.
The antistatic layer is formed from a mixed resin composition containing a polyethylene resin B, a polystyrene resin, a polymer antistatic agent, and a styrene elastomer. In the mixed resin composition, the polyethylene resin B Forms a continuous phase, and individually forms a dispersed phase in which a polystyrene-based resin and a polymer-type antistatic agent are dispersed in the continuous phase. Since the polyethylene-based resin B forms a continuous phase in the mixed resin composition, the antistatic layer has excellent adhesion to the foamed layer. In addition, since a polystyrene resin having a higher elastic modulus than that of a polyethylene resin forms a dispersed phase in the mixed resin composition, the multilayer foamed sheet of the present invention is thinner than the conventional foamed sheet. However, it has excellent rigidity and firmness. Furthermore, since the polymer antistatic agent forms a dispersed phase, the antistatic layer exhibits excellent antistatic properties, and the multilayer foam sheet with the antistatic layer laminated and bonded accumulates electrostatic charges. It is difficult to attach dust.

The polyethylene resin B forms a continuous phase in the mixed resin composition constituting the antistatic layer. Since it is easy to form a continuous phase, the melting point thereof is preferably 140 ° C. or lower, more preferably 120 ° C. or lower. The lower limit is approximately 80 ° C.
The melting point of the polyethylene resin is based on the plastic transition temperature measurement method of JIS K7121-1987, and “(2) When measuring the melting temperature after performing a certain heat treatment” is selected as the condition adjustment of the test piece. It is a melting peak temperature measured as follows.

Using the same type of polyethylene resin B constituting the antistatic layer and the polyethylene resin A constituting the foamed layer makes it difficult to destroy the bubbles in the foamed layer at the time of coextrusion, and has excellent adhesion. To preferred. However, different types of resins can be used.

  Since it is easy to form the morphology in the resin layer, the content of the polyethylene resin B in the mixed resin composition constituting the antistatic layer may be 20 to 80% by weight of the entire mixed resin composition. Preferably, 40 to 75% by weight is more preferable, and 50 to 70% by weight is further preferable.

  Examples of the polystyrene resin constituting the mixed resin composition include, for example, polystyrene, rubber-modified polystyrene (impact polystyrene), styrene-α-methylstyrene copolymer, styrene-p-methylstyrene copolymer, styrene- Acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, Examples thereof include styrene-ethyl acrylate copolymer and styrene-acrylonitrile copolymer. Among these, polystyrene or rubber-modified polystyrene is preferable because a good antistatic layer can be easily obtained.

When the mixed resin composition contains a styrene-based elastomer, the film forming property of the antistatic layer is improved, so that a good antistatic layer can be formed. Specifically, by improving the film forming property, an antistatic layer having a basis weight of 1 to 10 g / m ² per side can be laminated on the foamed layer by coextrusion.
Furthermore, the styrenic elastomer can control the morphology of the mixed resin composition. Specifically, the mixed resin composition contains a styrenic elastomer so that the dispersed phase of the polystyrene-based resin and the dispersed phase of the polymer-type antistatic agent are individually dispersed in the continuous phase of the polyethylene-based resin. Can be formed.

  It is possible to achieve both improvement of antistatic layer rigidity and development of antistatic properties by individually dispersing polystyrene resin and polymer antistatic agent in polyethylene resin using the styrene elastomer. Thus, the stiffness of the multilayer foam sheet can be increased while providing antistatic performance. Even when the polystyrene resin is dispersed in the polyethylene resin, a stronger stiffness is obtained by dispersing the resin in a stretched state in the plane direction of the sheet than by dispersing in a granular form.

Examples of the styrenic elastomer used in the present invention include styrene-butadiene copolymers, styrene-diene copolymers such as styrene-isoprene copolymers, partially hydrogenated products and completely hydrogenated products of these copolymers. Can be mentioned. The copolymer is preferably a block copolymer. Examples of the styrene-diene block copolymer include a styrene-butadiene block copolymer and a styrene-ethylene-butylene-styrene block copolymer.
Moreover, it is more preferable that content of the styrene component in a styrene-type elastomer is 20 to 50 weight%, More preferably, it is 30 to 45 weight%.

  The content of the styrene-based elastomer in the mixed resin composition constituting the antistatic layer is preferably 2 to 20% by weight of the entire mixed resin composition. The lower limit of the content is preferably 3% by weight, and the upper limit thereof is preferably 15% by weight, more preferably 10% by weight. If the content is too small, the desired film forming property may not be obtained. On the other hand, if the content is too large, the stiffness of the antistatic layer may be reduced.

  Since it is easy to form the morphology in the mixed resin composition, the content of the polystyrene-based resin in the mixed resin composition is preferably 15 to 50% by weight of the entire mixed resin composition, and is 20 to 45% by weight. % Is more preferable.

The mixed resin composition constituting the antistatic layer contains a polymer antistatic agent, and the polymer antistatic agent is dispersed in a continuous phase of a polyethylene resin. Therefore, the multilayer foamed sheet exhibits antistatic performance, and the surface resistivity can be preferably 1 × 10 ⁷ to 1 × 10 ¹⁴ (Ω), more preferably 1 × 10 ⁷ to 1 × 10 ¹³ Ω. Can be. A multilayer foam sheet having a surface resistivity in such a range is less likely to accumulate static charge and less likely to adhere to dust. Like the polystyrene resin, the polymer antistatic agent is dispersed separately from the polystyrene resin in the polystyrene resin forming the continuous phase, and a sufficient surface resistivity can be obtained with a small amount of the resin. Can be expressed.

  The surface resistivity of the multilayer foamed sheet is a value measured according to JIS K6271 (2001). That is, a test piece (100 mm long × 100 mm wide × thickness: thickness of measurement object) cut out from a multilayer foamed sheet as a measurement object is left for 24 hours in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%. Then, 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.

The polymer antistatic agent is made of a resin having a surface resistivity of less than 1 × 10 ¹² Ω, preferably less than 1 × 10 ¹¹ Ω, more preferably less than 1 × 10 ¹⁰ Ω. Specifically, polyether, polyether ester amide, block copolymer of polyether and polyolefin, ionomer resin, and the like. Among these, a block copolymer of polyether and polyolefin and an ionomer resin are more preferable.

  Examples of the block copolymer include those having a structure in which a polyolefin block and a polyether block are repeatedly and alternately bonded through bonds such as ester bonds, amide bonds, ether bonds, urethane bonds, and imide bonds. .

  The ionomer resin is a metal salt cross-linked product of a copolymer of ethylene and a carboxylic acid such as acrylic acid, methacrylic acid, and maleic acid. Examples of the metal salt include alkali metal salts, alkaline earth metal salts, A typical metal salt, a transition metal salt, etc. are mentioned.

  Specific examples of such a polymer antistatic agent include, for example, “Pelestat 300”, “Pelestat 230”, “Pelestat HC250”, and “Pelestat HC250” manufactured by Sanyo Chemical Industries, Ltd. as block copolymers of polyether and polyolefin. Examples of ionomer resins such as “Peletron PVH”, “Peletron PVL”, and “Peletron HS” that are commercially available under trade names such as “ENTILA SD100” and “ENTILA MK400” manufactured by Mitsui DuPont Polychemical Co., Ltd. may be mentioned.

The content of the polymeric antistatic agent in the antistatic layer depends on the performance of the polymeric antistatic agent itself, but is preferably 2 to 30% by weight of the total mixed resin composition constituting the antistatic layer. More preferably, it is 3 to 20% by weight, still more preferably 4 to 15% by weight, and particularly preferably 5 to 15% by weight.
Moreover, a polymer type antistatic agent can be contained in the foamed layer. When a polymer type antistatic agent is contained in the foamed layer, the polymer type antistatic agent is contained in the foamed layer from the viewpoint of the balance between foamability during extrusion and the antistatic performance of the resulting multilayer foam sheet. The amount is preferably 2 to 15% by weight, more preferably 3 to 8% by weight.

Next, the morphology of the mixed resin composition forming the antistatic layer in the present invention will be described in detail.
In the mixed resin composition, the polyethylene-based resin forms a continuous phase, the polystyrene-based resin forms a dispersed phase, and the polymer antistatic agent also forms a dispersed phase. That is, since the polyethylene-based resin forms a continuous phase and the polystyrene-based resin excellent in rigidity forms a dispersed phase, the multilayer foamed sheet of the present invention is different from the conventional foamed sheet, even if the thickness is thin, It has excellent rigidity and firmness. Therefore, the multilayer foamed sheet is excellent in following ability at the time of vacuum suction, and can be handled in the same manner as the conventional one even when the thickness is thin. In addition to the polystyrene resin, a polymer antistatic agent having excellent permanent antistatic properties also forms a dispersed phase. Therefore, by having the antistatic layer, the multilayer foamed sheet can exhibit antistatic properties.

  As described above, the dispersed phase of the polystyrene resin is preferably stretched along the plane direction of the multilayer foamed sheet. In the vertical cross section of the multilayer foamed sheet, the aspect ratio (long side length / short side direction) It is more preferable that a dispersed phase of polystyrene resin having a length) of 3 or more is included.

  FIG. 1 shows an example in which polystyrene resin and polymer type antistatic agent are individually dispersed. In the figure, 1 is a continuous phase of polyethylene resin, 2 is an island-like dispersed phase of polystyrene resin, and 3 is a dispersed phase of a polymer type antistatic agent. In addition, the morphology of the mixed resin composition of the antistatic layer can be confirmed by observing the cross section with a transmission electron microscope or the like.

The basis weight of the antistatic layer per side of the multilayer foamed sheet of the present invention is 10 g / m ² or less. When the basis weight of the antistatic layer is within this range, the cushioning property of the foamed layer is not impaired, so that the multilayer foamed sheet has sufficient cushioning property. From this viewpoint, the upper limit of the basis weight of the antistatic layer is preferably 5 g / m ² , more preferably 3 g / m ² , and further preferably ² g / m ² . In addition, from the viewpoint of forming a good antistatic layer with no broken portions despite being thin, the lower limit of the basis weight of the antistatic layer is 1 g / m ² . From the viewpoint of handleability, it is preferable to make the basis weights of the antistatic layers on both sides as equal as possible.
As described above, the multilayer foamed sheet of the present invention is such that, even when the basis weight of the antistatic layer is small, the mixed resin composition having a specific composition forms a specific morphology in the antistatic layer. Can exhibit sufficient rigidity.

Next, the manufacturing method of the multilayer foam sheet of this invention is demonstrated.
As a method for producing a multilayer foamed sheet of the present invention, a coextrusion foaming method is adopted in which a molten resin for forming an antistatic layer and a molten resin for forming a foamed layer are joined and laminated in a die and extrusion foamed. The coextrusion foaming method is preferable because the thickness of the antistatic layer can be reduced and a multilayer foamed sheet having high adhesion between the antistatic layer and the foamed layer can be obtained.

  The method for producing a sheet-like multilayer foamed sheet by the coextrusion foaming method includes a method of coextrusion foaming into a sheet using a coextrusion flat die to form a sheet-like multilayer foamed sheet, and a coextrusion annular die There is a method in which a cylindrical laminated foam is obtained by co-extrusion foaming using a sheet, and then the cylindrical foam is cut open to form a sheet-like multilayer foam sheet. Among these, the method using the annular die for coextrusion can easily produce a wide multilayer foam sheet having a width of 1000 mm or more, and the dispersed phase of the polystyrene-based resin in the antistatic layer is used as the plane of the sheet. This is a preferred method because it is easy to stretch in the direction.

A method of co-extrusion using the annular die will be described in detail below.
First, the polyethylene resin A and an additive such as a bubble adjusting agent added as necessary are supplied to an extruder for forming a foamed layer, heated and kneaded, and then a physical foaming agent is injected and further kneaded. To obtain a resin melt for forming a polyethylene-based resin foam layer. At the same time, the polyethylene resin B, the polystyrene resin, the styrene elastomer, and the polymer type antistatic agent are supplied to an antistatic layer forming extruder and heated and kneaded to form an antistatic layer forming resin. Let it be a melt. Next, the foamed layer forming resin melt and the antistatic layer forming resin melt are introduced into a coextrusion annular die, laminated and coextruded to produce a multilayer foamed sheet.

  In addition, since it is excellent in especially foamability, it is preferable that MFR of the polyethylene-type resin A is 0.5-15 g / 10min. In order to laminate the antistatic layer on the foamed layer by coextrusion, the MFR of the polyethylene resin B is preferably the same as or higher than the MFR of the polyethylene resin A.

  In addition, in the antistatic layer, in order to use a polyethylene resin as a continuous phase and a dispersed phase in which a polystyrene resin and a polymer type antistatic agent are dispersed in the continuous phase, as described above, a blend of a styrene elastomer is used. Can control the morphology. Furthermore, it is preferable to employ a method in which a polystyrene resin having a specific melt flow rate (MFR) is used in combination with the addition of a volatile plasticizer.

  The melt flow rate (MFR) of the polyethylene resin B is preferably 5.0 to 15 g / 10 min, more preferably 6.0 to 14 g / 10 min, from the viewpoint of ease of coextrusion. .

From the viewpoint of film forming property of the antistatic layer, the melt flow rate (MFR) of the polystyrene resin is preferably 5.0 to 30 g / 10 min.
In particular, it is preferably 5.0 to 15 g / 10 min, and more preferably 6.0 to 14 g / 10 min because the dispersed phase of the polystyrene resin is easily stretched in the plane direction of the sheet in the antistatic layer. Furthermore, the MFR of the polystyrene resin is within the above range and is preferably about 0.5 to 2 times, more preferably 0.5 to 1.5 times that of the polyethylene resin B. More preferably, it is 0.5 to 1 times.

  When the antistatic layer is coextruded with the foam layer, if the polystyrene resin is very finely dispersed in the melt of the mixed resin composition, the polystyrene resin deforms in the continuous phase of the polyethylene resin during extrusion. And it becomes easy to form a granular dispersed phase while maintaining the dispersion shape of the polystyrene-based resin. On the other hand, when the MFR of the polystyrene resin is within the above range, the dispersion diameter of the polystyrene resin can be increased within the range in which the antistatic layer can be formed into a thin film. As a result, the polystyrene resin becomes a sheet during coextrusion. It becomes easy to be stretched along the plane direction.

  The MFR is a value measured based on the condition H (200 ° C., load 5 kg) of JIS K7210-1999.

  In the resin melt for forming the antistatic layer, a continuous phase of polyethylene resin is formed, a dispersed phase of polystyrene resin is formed, and further a volatilization is performed to form a dispersed phase of the polymer type antistatic agent. It is preferable that a plasticizer is added. As the volatile plasticizer, those that have a function of reducing the melt viscosity of the resin melt and that volatilize from the antistatic layer after formation of the antistatic layer and are not present in the antistatic layer are used. By adding a volatile plasticizer into the resin melt, the co-extrusion temperature of the multilayer foam sheet is such that the extrusion temperature of the antistatic layer forming resin melt approaches that of the foam layer forming resin melt. And the melt elongation of the softened antistatic layer can be remarkably improved. If it does so, it will become difficult to destroy the bubble of a foaming sheet by the heat | fever of an antistatic layer at the time of foaming, and also the elongation of this antistatic layer will follow the elongation at the time of foaming of a foaming sheet easily. In particular, by using a circular die to extrude into a cylindrical shape, and taking up the cylindrical foam while expanding (blowing up), a foamed sheet is produced. Rigidity can be improved by stretching and orienting in the plane direction of the foam sheet.

  The volatile plasticizer is 1 selected from C3-C7 aliphatic hydrocarbons and alicyclic hydrocarbons, C1-C4 aliphatic alcohols, or C2-C8 aliphatic ethers. Species or two or more types are preferably used. When a so-called lubricant having low volatility is used instead of the volatile plasticizer, the lubricant may remain in the antistatic layer and contaminate the surface of the package. On the other hand, the volatile plasticizer is preferable from the viewpoint that the resin of the antistatic layer is efficiently plasticized and the volatile plasticizer itself hardly remains in the obtained antistatic layer.

  The boiling point of the volatile plasticizer is preferably 120 ° C. or lower, more preferably 80 ° C. or lower because it easily volatilizes from the antistatic layer. If the boiling point of the volatile plasticizer is within this range, if the obtained multilayer foamed sheet is allowed to stand after coextrusion, it will volatilize due to heat immediately after coextrusion or further gas permeation at room temperature. The plasticizer is volatilized and removed from the antistatic layer. The lower limit of the boiling point of the volatile plasticizer is approximately -50 ° C.

  The volatile plasticizer is 5 to 50 parts by weight with respect to a total of 100 parts by weight of the polyethylene resin B for forming the antistatic layer, the polystyrene resin, the styrene elastomer, and the polymer antistatic agent. It is preferable to add such that.

  In addition, various additives may be added to the resin forming the melt to the resin melt for forming the antistatic layer as long as the object of the present invention is not impaired. Examples of the various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, antibacterial agents, and the like. In this case, the amount added is appropriately determined according to the purpose and effect of the additive, but is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and more preferably 3 parts by weight with respect to 100 parts by weight of the mixed resin composition. The following are particularly preferred:

  Examples of the physical foaming agent added to the foamed layer forming resin melt include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, and isohexane, and fats such as cyclopentane and cyclohexane. Organic physical foaming agents such as cyclic hydrocarbons, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane, nitrogen, dioxide Examples include inorganic physical foaming agents such as carbon, air, and water. In some cases, a decomposable foaming agent such as azodicarbonamide can be used. The above-mentioned physical foaming agents can be used in combination of two or more. Among these, an organic physical foaming agent is particularly preferable from the viewpoint of compatibility with a polyethylene resin and foaming properties, and among them, those mainly containing normal butane, isobutane, or a mixture thereof are preferable.

  The addition amount of the physical foaming agent is adjusted according to the type of foaming agent and the target apparent density. Moreover, the addition amount of a bubble regulator is adjusted according to the target bubble diameter. For example, in order to obtain a multilayer foamed sheet having an apparent density range using a butane mixture of 30% by weight of isobutane and 70% by weight of normal butane as a foaming agent, the amount of butane mixture added is 100 parts by weight of the base resin. 3 to 30 parts by weight, preferably 4 to 20 parts by weight, more preferably 6 to 18 parts by weight.

As the main additive added to the foamed layer forming resin melt, a bubble regulator is usually added. 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, an 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.
In addition, the addition amount of a bubble regulator is 0.01-3 weight part per 100 weight part of base resin, Preferably it is 0.03-1 weight part.

  As the manufacturing apparatus such as the annular die and the extruder, a known apparatus conventionally used in the field of extrusion foaming can be used.

  Since the multilayer foamed sheet of the present invention has sufficient buffering properties and stiffness, it can be suitably used as an interleaf for glass plates. However, the use of the multilayer foamed sheet is not limited to the slip sheet for glass plates, and the multilayer foamed sheet can be suitably used widely as a packaging material for precision instruments.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples.

  Table 1 shows polyethylene resins and polystyrene resins used in Examples and Comparative Examples, and Table 2 shows polymer antistatic agents and styrene elastomers. In addition, the melt flow rate in Table 1 is a value measured under condition H (200 ° C., load 5 kg) based on JIS K7210-1999.

  As the physical foaming agent and volatile plasticizer, mixed butane composed of 70% by weight normal butane and 30% by weight isobutane was used.

  As the cell regulator, a cell regulator master batch comprising 20% by weight of talc (trade name “High Filler # 12” manufactured by Matsumura Sangyo Co., Ltd.) with respect to 80% by weight of low density polyethylene was used.

  As an extruder for forming a polyethylene resin foam layer, a tandem extruder comprising a first extruder having a diameter of 90 mm and a second extruder having a diameter of 120 mm is used. As an extruder for forming an antistatic layer, the diameter is 50 mm and L / D = 50. A third extruder was used. Further, the respective outlets of the second extruder and the third extruder were connected to the co-extrusion annular die so that the respective molten resins could be laminated in the co-extrusion annular die.

Examples 1-5, Comparative Examples 1-4
The amount of polyethylene resin shown in Table 3 and the master batch that gives the amount of air conditioner shown in Table 3 are supplied to the raw material inlet of the first extruder of the tandem extruder, heated and kneaded, about 200 ° C. It was set as the molten resin mixture adjusted to. Next, mixed butane as a foaming agent in the amount shown in Table 3 is pressed into the molten resin mixture, and then transferred to a second extruder connected to the downstream side of the first extruder. The foamed layer-forming resin melt was adjusted to the indicated extrusion resin temperature, and the foamed layer-forming resin melt was introduced into the coextrusion annular die at the discharge amount shown in Table 3.

  At the same time, a polyethylene resin, a polystyrene resin, a polymer antistatic agent and a styrene elastomer having the composition shown in Table 3 are supplied to a third extruder and heated and kneaded, and the amount of the volatile plasticizer shown in Table 3 is used. The mixed butane was press-fitted, kneaded, adjusted to the extrusion resin temperature shown in Table 3 to obtain a resin melt for forming an antistatic layer, and the resin melt for forming an antistatic layer was coextruded at a discharge amount shown in Table 3. Introduced into an annular die.

The resin melt for forming an antistatic layer introduced into the annular die for coextrusion is introduced to the outside and inside of the resin melt for forming a foam layer that is introduced into the annular die for coextrusion and flows in a resin flow path in the die. The products were joined and laminated, and the laminate of the melt was extruded into the atmosphere from a die having a lip diameter of 135 mm to form a three-layered cylindrical laminated foam composed of antistatic layer / foamed layer / antistatic layer. In Examples 1 to 3 and Comparative Examples 1 and 2, the extruded cylindrical laminated foam was expanded in diameter (blow-up ratio 3.47) and cut in the extrusion direction while being taken up, and wound into a roll. Thus, a multilayer foam sheet having a width of 1400 mm was obtained. Moreover, in Examples 4 and 5 and Comparative Examples 3 and 4, the extruded cylindrical laminated foam was expanded in diameter (blow-up ratio 2.85) and cut in the extrusion direction while being taken up, and rolled. It wound up and obtained the multilayer foam sheet of width 1150mm.
In Comparative Example 2, a polystyrene resin was blended in the antistatic layer, but no styrene elastomer was blended, so the film forming property of the antistatic layer was poor, and the surface of the resulting multilayer foam sheet was It was rough.

  Table 4 shows various physical properties of the multilayer foamed sheets obtained in Examples and Comparative Examples.

About the multilayer foamed sheet obtained in the Example, the morphology of the mixed resin composition in the antistatic layer was observed by the following method. First, a test piece including an antistatic layer was cut out from the multilayer foamed sheet. After the test piece is dyed with ruthenium tetroxide, it is sliced along the extrusion direction of the multilayer foamed sheet to obtain an ultrathin section, and the ultrathin section is accelerated using a Hitachi transmission electron microscope (H-7100). Observation was performed under the condition of a voltage of 100 kV.
Transmission electron micrographs of the vertical cross section of the antistatic layer of the multilayer foam sheet obtained in Example 1 are shown in FIGS. 1 and 2 and the transmission type of the vertical cross section of the antistatic layer of the multilayer foam sheet obtained in Example 2 is shown in FIGS. Electron micrographs are shown in FIGS . 1 to 4, polyethylene-based resin (PE) 1 forms a continuous phase (sea), and polystyrene-based resin (PS) 2 forms a dispersed phase (island) dispersed in the continuous phase of polyethylene-based resin 1. At the same time, the morphology (sea / island / island) forming a dispersed phase (island) dispersed in the continuous phase of the polyethylene-based resin 1 was also confirmed. The styrene elastomer 4 was present mainly at the interface between the polyethylene resin 1 and the polystyrene resin 2. Further, most of the polystyrene-based resin 2 was stretched in the plane direction of the multilayer foamed sheet to form a dispersed phase having an aspect ratio of 3 or more. In addition, the same morphology was confirmed also in the multilayer foam sheet obtained in Examples 3-5.

The thickness of the multilayer foam sheet in Table 4 was measured by the above method (n = 5).
The total basis weight of the multilayer foamed sheet is obtained by cutting out a test piece having a width of 10 cm over the entire width of the sheet from the multilayer foamed sheet unwound from the roll and dividing the weight of the test piece by the total width of the sheet × 10 cm. Obtained (n = 5).
The basis weight of the antistatic layer was determined from the ratio of the ejection amount of the foam layer and the antistatic layer based on the total basis weight.
The apparent density of the multilayer foam sheet was determined by dividing the total basis weight of the multilayer foam sheet by the thickness of the multilayer foam sheet and converting the unit.

The film forming properties in Table 4 were evaluated according to the following criteria.
○: The antistatic layer of the obtained multilayer foamed sheet is not torn ×: The antistatic layer of the obtained multilayer foamed sheet is torn

The amount of sagging in Table 4 was measured as follows.
(Horizontal sag)
Ten measurement test pieces each having a width of 100 mm and a length of 200 mm were cut out from 10 randomly selected portions of the multilayer foam sheet by matching the extrusion direction of the obtained sheet with the length direction of the test piece. The obtained test piece is placed on a horizontal base and fixed in a horizontal direction from the edge of the base with the length of the test piece protruding 100 mm, and the vertical direction from the top of the base to the bottom of the test piece The distance of was measured. This measurement was performed on each test piece, and the arithmetic average value of each measurement value was defined as the amount of horizontal sag.
(60 ° inclination sag)
Ten test specimens each having a width of 200 mm and a length of 200 mm were cut out from 10 randomly selected locations of the multilayer foamed sheet by matching the extrusion direction of the obtained sheet with the length direction of the test piece. Place the obtained test piece on the base surface of the base inclined at 60 ° above the horizontal plane, and fix it with the length direction of the test piece protruding 100 mm in the direction extending straight from the upper end of the base. Then, the distance in the direction perpendicular to the base surface from the free tip of the hanging test piece to the virtual surface obtained by extending the base surface straight was measured. This measurement was performed on each test piece, and an arithmetic average value of each measurement value was defined as a 60 ° inclination sag.

The antistatic performance of the multilayer foam sheet was evaluated as follows.
As described above, the surface resistivity of the multilayer foamed sheet was measured according to JIS K6271 (2001). The surface resistivity on both sides of the measurement sample was measured, and the arithmetic average value thereof was defined as the surface resistivity of the multilayer foam sheet.

1 Polyethylene resin continuous phase 2 Polystyrene resin dispersed phase 3 Polymer antistatic agent dispersed phase

Claims (4)

In a multilayer foamed sheet having an apparent density of 30 to 300 kg / m ³ and a thickness of 0.05 to 2 mm, comprising a polyethylene-based resin foam layer and an antistatic layer laminated and adhered to both sides of the foam layer by coextrusion,
The basis weight per one side of the antistatic layer is 1 to 10 g / m ² ,
The antistatic layer is formed from a mixed resin composition containing a polyethylene resin, a polystyrene resin, a polymer antistatic agent, and a styrene elastomer,
The weight ratio of the polystyrene resin in the mixed resin composition is 15 to 50% by weight,
The weight ratio of the styrenic elastomer in the mixed resin composition is 2 to 20% by weight,
In the mixed resin composition, the polyethylene resin forms a continuous phase, and the polystyrene resin and the polymer type antistatic agent individually form a dispersed phase dispersed in the continuous phase. Multi-layer foam sheet.
The dispersed phase of the polystyrene-based resin is stretched along the plane direction of the multilayer foamed sheet, and the aspect ratio (length in the long side direction / length in the short side direction) is 3 in the vertical cross section of the multilayer foamed sheet. The multilayer foamed sheet according to claim 1, comprising a dispersed phase of the above polystyrene-based resin.
The multilayer foamed sheet according to claim 1 or 2, wherein a weight ratio of the polymer antistatic agent in the mixed resin composition is 2 to 30% by weight.
A slip sheet for a glass plate comprising the multilayer foamed sheet according to claim 1.