JP7271407B2 - Polyolefin resin multi-layer foamed sheet and interleaving paper for glass plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyolefin resin multilayer foam sheet and an interleaf sheet for glass plates comprising the multilayer foam sheet.

Polyolefin resin multi-layer foamed sheets have been widely used as packaging materials for home electric appliances, glassware, pottery, etc., because they are excellent in flexibility and shock-absorbing properties and can prevent damages, scratches, etc. of packaged items. In recent years, along with the development and expansion of demand for flat-panel televisions, multi-layered polyolefin resin foam sheets are used for packaging glass sheets used in the manufacture of display panels such as liquid crystal displays, plasma displays, and electroluminescence displays. Widely used as paper.

The interleaving paper for glass plates is a sheet material used by being interposed between glass plates. Specifically, it is used to prevent scratching or breakage of glass sheets when multiple glass sheets are stacked and handled, such as when multiple glass sheets are stored or transported together. .

As the definition of the display panel becomes higher, higher quality is required for the glass plate for the display. Usually, when a glass plate is used, the surface of the glass plate is washed with water or the like to keep the surface of the glass plate in an extremely clean state. Therefore, it is required that the interleaving paper for glass plates does not interfere with the cleaning property of the glass plates and the like, and that the cleaning property of the glass plates and the like is improved so that the glass plates can be cleaned more effectively.

With respect to interleaf paper for glass plates that improves the washability of glass plates, for example, Patent Document 1 proposes a polyolefin-based resin laminated foam in which a surface layer contains a hydrophilic compound such as polyethylene glycol. When this laminated foam is used as interleaving paper for glass plates, it is possible to improve the washability of the packaged object. Dirt on the surface of the item to be packaged can be easily removed.

JP 2010-42556 A

BACKGROUND ART In recent years, objects to be packaged such as glass sheets are sometimes placed in a hot and humid atmosphere during storage, transportation, or the like. In such a hot and humid atmosphere, when the laminated foam described in Patent Document 1 is used, there are cases where the washability of objects to be packaged such as glass plates becomes somewhat insufficient.

The present invention provides a multilayer foam sheet capable of imparting excellent washability to a packaged object such as a glass sheet even under high temperature and high humidity, and a glass sheet using such a multilayer foam sheet. The purpose is to provide an interleave.

In order to solve the above problems, the present inventors have studied in detail the components of the dirt attached to the packaged item after washing, and found that when a conventional laminated foam sheet is used in a hot and humid atmosphere, organic matter In addition to components derived from metal compounds such as calcium compounds, the present inventors have found that the packaged items may be contaminated by components derived from metal compounds such as calcium compounds, and have completed the present invention.

That is, according to the present invention, the following polyolefin-based resin multilayer foam sheet is provided.
[1] It has a polyolefin-based resin foam layer and a polyolefin-based resin surface layer laminated and adhered to at least one side of the foam layer, and the surface layer comprises a polyolefin-based resin and a polyether-polyolefin block copolymer. In a multilayer foam sheet containing a polymeric antistatic agent containing as a main component and a polyalkylene glycol,
The amount of the polyalkylene glycol compounded is 1.0 parts by mass or more with respect to 100 parts by mass of the polyolefin resin constituting the surface layer,
The main component of the polyalkylene glycol is polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800,
the polyalkylene glycol is liquid at 25°C;
A polyolefin resin multilayer foam sheet characterized by having a water content of 1500 to 4000 ppm measured after the multilayer foam sheet is left to stand in an atmosphere of 50°C and 80% RH for 24 hours.
[2] The polyolefin-based resin multilayer foam sheet according to [1], wherein the blending ratio of polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800 in the polyalkylene glycol is 70% by mass or more.
[3] The multi-layered polyolefin resin foam sheet according to 1 or 2 above, wherein the water content of the polyolefin resin multi-layer foamed sheet is 2000 to 3500 ppm.
[4] The polyolefin system according to any one of 1 to 3 above, wherein the ratio of the amount of the polyalkylene glycol to the amount of the high-molecular antistatic agent is 0.10 to 0.60. Resin multilayer foam sheet.
[5] The melting point difference between the melting point of the polymer type antistatic agent and the melting point of the polyolefin resin constituting the surface layer is within the range of -10 ° C. to +10 ° C. 5. The polyolefin resin multilayer foam sheet according to any one of 4.
[6] Any one of the above 1 to 5, wherein the blending amount of the polymer type antistatic agent is 8 to 30 parts by mass with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. The polyolefin resin multilayer foam sheet according to 1.
[7] The polyolefin resin constituting the surface layer is low density polyethylene, and the polyolefin resin constituting the foam layer is low density polyethylene. Polyolefin resin multilayer foam sheet.
[8] The polyolefin resin multilayer foam sheet according to any one of [1] to [7] above, wherein the foam layer contains a cell control agent, and the cell control agent is talc.
[9] Interleaf paper for glass plates comprising the polyolefin resin multilayer foam sheet according to any one of 1 to 8 above.

The polyolefin-based resin multilayer foam sheet of the present invention contains, as a main component, polyethylene glycol having a specific number-average molecular weight together with a high-molecular antistatic agent in the surface layer, and contains a specific amount or more of polyalkylene glycol that is liquid at 25°C. By setting the moisture content of the multilayer foam sheet within a specific range, it is possible to provide excellent antistatic performance and to impart excellent washability to glass plates and the like even under high temperature and high humidity. It is.

The polyolefin resin multilayer foamed sheet of the present invention will be described in detail below.
The polyolefin resin multilayer foam sheet (hereinafter also simply referred to as a multilayer foam sheet) of the present invention is laminated and adhered to a polyolefin resin foam layer (hereinafter also simply referred to as a foam layer) and at least one side of the foam layer. and a polyolefin-based resin surface layer (hereinafter also simply referred to as a surface layer).

The surface layer is laminated and adhered to at least one side of the front and back surfaces of the foam layer, and is located on the outermost surface side of the multilayer foam sheet. However, an intermediate layer may be formed between the foam layer and the surface layer. The intermediate layer may be, for example, a layer made of a resin having adhesiveness to both the foam layer and the surface layer.

Next, materials constituting the foam layer and the surface layer of the multilayer foam sheet will be described in this order.

The foam layer of the multilayer foam sheet of the present invention uses a polyolefin resin as a base resin. In the present invention, the polyolefin resin is a resin in which the proportion of component units derived from olefin monomers is 50 mol % or more. Examples of the polyolefin-based resins include polyethylene-based resins, polypropylene-based resins, polybutene-based resins, and the like. Among polyolefin-based resins, polyethylene-based resins are particularly preferable because they are excellent in flexibility and cushioning properties and have strength required for cushioning materials.

Examples of the polyethylene-based resin include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-1-butene copolymer, Ethylene-butene-1 copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-1-pentene copolymer, ethylene-1-octene copolymer, mixtures of two or more thereof, and the like. mentioned.

Among the polyethylene-based resins, low-density polyethylene is more preferable from the viewpoint of flexibility, cushioning properties, and the like. Low-density polyethylene refers to a polyethylene-based resin having a density of 890 kg/m ³ or more and 935 kg/m ³ or less, preferably a polyethylene-based resin having a density of 900 kg/m ³ or more and 930 kg/m ³ or less.

Examples of polypropylene-based resins include propylene homopolymers and copolymers of propylene and other olefins. Other olefins copolymerizable with propylene include, for example, ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1 -heptene, 3-methyl-1-hexene, and other α-olefins having 4 to 10 carbon atoms.

The polyolefin resin preferably has a melting point of 100 to 170°C. In particular, when the polyolefin resin is low-density polyethylene, the melting point of the low-density polyethylene is preferably 100 to 120°C, more preferably 105 to 115°C.

The melting point of the polyolefin resin can be measured by a method conforming to JIS K7121-1987. Specifically, using a differential scanning calorimeter, the temperature is increased from 40° C. to 200° C. at 10° C./min to heat and melt, the temperature is maintained for 10 minutes, and then the temperature is increased to 40° C. at 10° C./min. After the heat treatment of cooling at , the melting peak is obtained by heating again from 40° C. to 200° C. at a heating rate of 10° C./min. Then, the temperature at the top of the melting peak having the largest area among the obtained melting peaks is taken as the melting point.

For the polyolefin resin constituting the foam layer, other resins such as styrene resins, elastomers such as ethylene propylene rubbers and styrene-butadiene-styrene block copolymers, etc. may be used as long as the effects of the present invention are not impaired. You may add. In this case, the amount of the other resin or elastomer to be added is preferably 25 parts by mass or less, more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin forming the foam layer.

Additives may be added to the polyolefin-based resin forming the foam layer as long as the effects of the present invention are not impaired. Examples of additives include functional additives such as cell control agents, nucleating agents, antioxidants, heat stabilizers, weathering agents, UV absorbers, flame retardants, antibacterial agents, and shrinkage inhibitors, inorganic fillers, and the like. can be mentioned.

The foam layer preferably contains talc as a cell regulator. By using talc as the cell control agent, the moisture content of the sheet due to the cell control agent can be further reduced, and the washability of the glass plate or the like under high temperature and high humidity can be further improved.

The surface layer of the multilayer foam sheet of the present invention contains a polyolefin resin, a polymeric antistatic agent containing a polyether-polyolefin block copolymer as a main component, and polyalkylene glycol.

The surface layer is formed of a resin composition having a polyolefin resin as a base resin. Examples of the polyolefin-based resin and other resins, additives, and the like to be blended therein include the same as those described above for the foam layer. The content of the polyolefin resin in the surface layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

In the multi-layer foam sheet of the present invention, the polyolefin resin forming the foam layer and the polyolefin resin forming the surface layer may be the same resin, or different resins may be used for the foam layer and the surface layer. . When the foam layer and the surface layer are made of the same kind of resin, the multilayer foam sheet has excellent adhesiveness between the foam layer and the surface layer. Therefore, from the viewpoint of adhesiveness, it is preferable to use low-density polyethylene for the surface layer as well.

The surface layer of the multilayer foam sheet of the present invention contains polyalkylene glycol. The polyalkylene glycol migrates from the surface layer to the object to be packaged, such as a glass plate, and can be easily removed together with dirt adhering to the surface of the object when the object to be packaged is washed with water or the like. .

A feature of the present invention is that when a conventional laminated foam sheet is used in an atmosphere of high temperature and high humidity, the items to be packaged are contaminated with components derived from metal compounds such as calcium compounds in addition to components derived from organic substances. It is found that there is a case where the moisture content of the laminated foam sheet is within a specific range, thereby successfully suppressing the contamination due to the component derived from the metal compound.

BACKGROUND ART In recent years, objects to be packaged such as glass sheets are sometimes placed in a hot and humid atmosphere during storage, transportation, or the like. In such a high-temperature and high-humidity atmosphere, when a conventional laminated foam is used, there are cases in which the washability of a packaged object such as a glass plate becomes somewhat insufficient. Therefore, when the components of the dirt on the glass plate were examined in detail, calcium compounds were detected in addition to components derived from organic substances caused by dust and dirt in the air and high-molecular-type antistatic agents. Calcium compounds are inferior in washability with water or the like compared to organic substances caused by dust, dirt, polymeric antistatic agents, and the like.
The present inventors considered that the calcium compound was contained in the moisture in the air and adhered to the glass plate via the multilayer foam sheet. Therefore, the inventors have completed the present invention based on the idea that contamination of the glass sheet by components derived from metal compounds such as calcium compounds can be reduced by controlling the hygroscopicity of the multilayer foam sheet and keeping the moisture content low. rice field.

The multilayer foamed sheet of the present invention has a moisture content (mass ppm) of 1,500 to 4,000 ppm measured after standing in an atmosphere of 50° C. and 80% RH for 24 hours. If the water content is within the above range, even if the laminated foam sheet is stored in contact with a packaged object such as a glass plate under hot and humid conditions, the calcium compound or the like may be added to the laminated foam sheet. The adhesion of the metal compound is suppressed, and contamination of the packaged object by the metal compound can be suppressed.
If the water content is too high, it may not be possible to suppress contamination caused by metal compounds such as calcium compounds in the air. On the other hand, if the moisture content is too low, the polyalkylene glycol will be difficult to migrate to the packaged material, and there is a risk that the packaged material will not be sufficiently imparted with detergency. From this point of view, the upper limit of the water content is preferably 3700 ppm, more preferably 3500 ppm, and still more preferably 3300 ppm. The lower limit of the water content is preferably 2000 ppm, more preferably 2500 ppm.

The moisture content (mass ppm) of the multilayer foam sheet is measured by the following method. First, a test piece cut from the laminated foam sheet to a size of 500 mm wide x 400 mm long x sheet thickness was stored in an atmosphere with a temperature of 50 ° C. and a humidity of 80% RH for 24 hours, and then in an air-blocked closed space. The test piece is dried at 180° C. to remove vapors other than water, and the water is selectively adsorbed by the adsorbent, and the water content (mass ppm) is determined from the change in mass by the following formula (1). RH indicates relative humidity.
Moisture content=[M ₂ −M ₃ /M ₁ ]×10 ⁶ (1)
M ₁ : Mass of test piece before drying (g)
M ₂ : Mass (g) of adsorbent after water adsorption
M ₃ : Mass (g) of adsorbent before moisture adsorption

In the present invention, the polyalkylene glycol is required to contain polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800 as a main component. By using polyethylene glycol (PEG1) having a number average molecular weight within the above range as the main component of the polyalkylene glycol, the water content of the multilayer foam sheet can be controlled within the above specific range. If the number-average molecular weight is too small, the hygroscopicity of polyethylene glycol becomes too high and the moisture content of the multilayer foam sheet increases under high temperature and high humidity. It may not be possible to prevent contamination of packaged items such as glass plates. On the other hand, if the number-average molecular weight is too large, the migration of polyethylene glycol to the object to be packaged becomes low, and the polyalkylene glycol that has migrated to the object to be packaged becomes difficult to wash away with water or the like. There is a risk that contamination of the packaged items cannot be suppressed. From this point of view, the lower limit of the number average molecular weight is preferably 450, more preferably 500. On the other hand, the upper limit of the number average molecular weight is preferably 750, more preferably 700.

In the present specification, "the main component of the polyalkylene glycol is polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800" means polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800 in the entire polyalkylene glycol. means that the blending ratio of is 50% by mass or more, and the blending ratio is preferably 70% by mass or more, more preferably 80% by mass or more, because the washability of the packaged object under high temperature and humidity is further enhanced, 90% by mass or more is more preferable, and 100% by mass is particularly preferable. That is, it is particularly preferred that the polyalkylene glycol consists only of polyethylene glycol (PEG1) having a number average molecular weight of 400-800. As PEG1, a plurality of polyethylene glycols having a number average molecular weight within the range of 400 to 800 may be used together.

The number average molecular weight of the polyalkylene glycol can be obtained by a well-known method calculated from the hydroxyl value. Moreover, when the molecular weight is too high and it is difficult to calculate the number average molecular weight from the hydroxyl value, it is determined by a method using high temperature gel permeation chromatography.

The polyalkylene glycol may contain polyalkylene glycol other than polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800. Examples of other polyalkylene glycols include polyethylene glycol having a number average molecular weight of less than 400, polyethylene glycol having a number average molecular weight of more than 800, polypropylene glycol, polybutylene glycol, polyoxyethylene polyoxypropylene glycol, and the like. and alkylene glycols having 2 to 6 carbon atoms. Moreover, these can be used together.

The polyalkylene glycol of the present invention should be liquid at 25°C. Since the polyalkylene glycol, which is liquid at 25°C, bleeds out easily from the surface layer, it can impart excellent detergency to the packaged items. Further, the temperature of water used for washing packaged objects such as glass plates is usually about 25°C. Therefore, if the polyalkylene glycol is liquid at 25°C, it can be easily washed away with water, and the water washability is improved. Contaminants caused by molecular antistatic agents and the like can be removed more easily.

From the same point of view, the solidification point of the polyalkylene glycol used in the present invention is preferably 0 to 25°C.

As used herein, the freezing point can be determined by the method described in JIS K 0065 (1992).

Preferably, the polyalkylene glycol is substantially free of polyalkylene glycols that are solid at 25°C. Since the polyalkylene glycol does not contain a polyalkylene glycol that is solid at 25° C., the washability with water is better.
In the present specification, "substantially free of polyalkylene glycol that is solid at 25°C" means that the mass ratio of polyalkylene glycol that is solid at 25°C in the total polyalkylene glycol is 3% by mass or less. , preferably 2% by mass or less, more preferably 1% by mass or less, and more preferably 0% by mass. That is, it is more preferable that the polyalkylene glycol consists only of polyalkylene glycol that is liquid at 25°C.

In the surface layer, the blending amount (Wp) of the polyalkylene glycol is required to be 1.0 parts by mass or more with respect to 100 parts by mass of the polyolefin resin forming the surface layer. If the blending amount is too small, there is a possibility that the effect of polyalkylene glycol for improving detergency may not be exhibited. From this point of view, the blending amount (Wp) of the polyalkylene glycol is preferably 1.5 parts by mass or more and 2.0 parts by mass or more with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. is more preferable, and 2.5 parts by mass or more is even more preferable.
The upper limit of the compounding amount (Wp) is preferably 5.0 parts by mass or less with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. When the amount is 5.0 parts by mass or less, the moisture content of the multilayer foam sheet can be kept lower. In addition, the polyalkylene glycol prevents the multilayer foam sheet from excessively bleeding out on the surface of the multilayer foam sheet and making the multilayer foam sheet sticky, and the peel strength of the multilayer foam sheet to a glass plate or the like is low, resulting in a multilayer foam sheet with excellent workability.

Next, the polymeric antistatic agent contained in the surface layer of the present invention will be explained.
The surface layer in the present invention contains a polymeric antistatic agent containing a polyether-polyolefin block copolymer as a main component. Specific polyether-polyolefin copolymers include, for example, "Pelestat (trademark) VL300", "Pelestat HC250", "Pelektron (trademark) HS", "Pelektron PVH", " Those commercially available under trade names such as "Plectron LMP" can be mentioned.

In the present specification, "mainly composed of a polyether-polyolefin block copolymer" means that the proportion of the polyether-polyolefin block copolymer in all polymer-type antistatic agents contained in the surface layer is It is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass.

The melting point difference between the melting point of the polymeric antistatic agent mainly composed of a polyether-polyolefin block copolymer and the melting point of the polyolefin resin constituting the surface layer is -10°C. It is preferably in the range of ~+10°C.
The fact that the melting point difference is in the range of -10°C to +10°C means that the melting point of the polymeric antistatic agent is close to the melting point of the polyolefin resin that is the base resin of the surface layer. By using a polymeric antistatic agent that satisfies the melting point difference, the peel strength of the multi-layer foam sheet against the object to be packaged such as a glass plate is reduced even under high temperature and high humidity, and workability is improved. Become.
The reason for this is not clear, but is considered as follows. When the melting point difference is within the above range, the compatibility between the polymer antistatic agent and the polyolefin resin is further improved, and accordingly the polymer antistatic agent is dispersed in the polyalkylene glycol and the polyolefin resin. It is thought that it becomes easier. As a result, the polymer-type antistatic agent can retain the polyalkylene glycol appropriately, suppressing excessive bleeding out of the polyalkylene glycol to the surface layer, and peeling the multi-layer foam sheet from the package. It is considered that the increase in strength is suppressed.

In the present invention, the melting point difference between the melting point of the polymeric antistatic agent and the melting point of the polyolefin resin constituting the surface layer is the value obtained by subtracting the melting point of the polyolefin resin from the melting point of the polymeric antistatic agent. say.

The melting point difference is preferably -8°C to +8°C, more preferably -7°C to +7°C, and even more preferably -5°C to +5°C.
Also, the melting point of the polymeric antistatic agent is preferably 125° C. or lower, more preferably 120° C. or lower. On the other hand, the lower limit of the melting point is approximately 100°C.

The melting point of the polymeric antistatic agent can be measured by a method conforming to JIS K7121-1987. Specifically, using a differential scanning calorimeter, the temperature is increased from 40° C. to 200° C. at 10° C./min to heat and melt, the temperature is maintained for 10 minutes, and then the temperature is increased to 40° C. at 10° C./min. After the heat treatment of cooling at , the melting peak is obtained by heating again from 40° C. to 200° C. at a heating rate of 10° C./min. Then, the temperature at the top of the melting peak having the largest area among the obtained melting peaks is taken as the melting point.

The blending amount (Wa) of the polymeric antistatic agent is preferably 8 to 30 parts by mass with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. When the amount of the antistatic agent is within the above range, the multi-layer foamed sheet will have excellent antistatic performance and excellent washability for objects to be packaged such as glass plates. From this point of view, the amount of the polymeric antistatic agent is preferably 9 to 18 parts by mass, more preferably 10 to 15 parts by mass, with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. is more preferred.

In the present invention, the ratio (Wp/Wa) of the blending amount (Wp) of the polyalkylene glycol to the blending amount (Wa) of the polymeric antistatic agent is preferably 0.10 to 0.60. When the blending ratio is within the above range, the antistatic performance of the multi-layer foam sheet and excellent detergency for packaged items under high temperature and high humidity are obtained. In addition, excessive bleeding out of polyalkylene glycol is further suppressed. From this point of view, the ratio (Wp/Wa) is more preferably 0.15 to 0.55, more preferably 0.20 to 0.45.

Next, physical properties of the foamed sheet of the present invention will be described. The average thickness of the multilayer foam sheet of the present invention is generally 0.05 to 10 mm. When the average thickness of the multilayer foam sheet is within the above range, sufficient cushioning properties can be ensured without being bulky when used as interleaving paper for glass plates. From the above viewpoint, the average thickness of the multilayer foam sheet is preferably 0.07 mm or more and 1.0 mm or less, more preferably 0.1 mm or more and 0.5 mm or less, and still more preferably 0.12 mm or more and 0.3 mm or less.

The average thickness of the multilayer foam sheet in the present invention is specified as the arithmetic mean value of the total thickness (mm) of the multilayer foam sheet measured at intervals of 1 cm in the width direction across the entire width of the multilayer foam sheet. The width direction is a direction perpendicular to the extrusion direction of the multilayer foam sheet and a direction perpendicular to the thickness direction, for example, when the multilayer foam sheet is produced by a production method using an extruder.

The apparent density of the multilayer foam sheet of the present invention is preferably 20-450 kg/m ³ . When the apparent density of the multilayer foam sheet is within the above range, the multilayer foam sheet will have excellent flexibility and mechanical strength such as shape retention and compressive strength. The upper limit of the apparent density is preferably 300 kg/m ³ , more preferably 200 kg/m ³ , since the multilayer foam sheet has excellent flexibility. In addition, the lower limit of the apparent density is preferably 30 kg/m ³ , more preferably 40 kg/m ³ , still more preferably 50 kg/m ³ , and particularly preferably 50 kg/m 3 , since the multilayer foam sheet has excellent mechanical strength and stiffness. is 100 kg/ ^m3 .

The apparent density of the multilayer foam sheet is measured by cutting a test piece from the multilayer foam sheet and dividing the mass (kg) of the test piece by the volume (m ³ ) obtained from the external dimensions of the test piece. .

The basis weight of the surface layer in the present invention is preferably 0.5 g/m ² or more, more preferably 0.7 g/m ² or more, and even more preferably 1.0 g/m ^{2 or} more per side. . When the basis weight of the surface layer satisfies the above range, the desired washability of the packaged object is sufficiently enhanced. The upper limit of the basis weight of the surface layer is not particularly limited from the viewpoint of the washability of the packaged item, but from the viewpoint of cushioning properties and light weight, the upper limit is preferably 100 g/m ² , and 50 g/m 2 . m ² is more preferred, 10 g/m ² is even more preferred, and 5 g/m ² is particularly preferred.

The basis weight [g/m ² ] of the surface layer in the present invention is the discharge amount X [kg/ h], the width W [m] of the resulting multilayer foam sheet, and the take-up length L [m/h] of the multilayer foam sheet per unit time, it can be obtained by the following formula (2). When the surface layers are laminated on both sides of the foam layer, the basis weight of each surface layer is obtained from the discharge amount of each surface layer.

Basis weight (g/m ² ) = 1000 x X/(L x W) (2)

In the multilayer foam sheet of the present invention, it is preferred that polyalkylene glycol and antistatic agent are not substantially added to the foam layer in order to maintain a high closed cell ratio.
Here, "substantially not added" means that the total amount is 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin constituting the foam layer, preferably 2 parts by mass. part or less, more preferably 1 part by mass or less, and particularly preferably 0 part by mass.

The closed cell ratio of the multilayer foam sheet as a whole is preferably 30% or more, more preferably 50% or more, and still more preferably 80% or more, since excellent mechanical strength and excellent cushioning properties can be obtained.

The closed cell content of the multilayer foam sheet of the present invention is measured using a comparative air hydrometer 930 model manufactured by Toshiba Beckman Co., Ltd. (from the multilayer foam sheet to 25 mm × 25 mm × 20 mm) according to procedure C of ASTM-D2856-70. The cut sample is placed in a sample cup and measured.In addition, if the multilayer foam sheet is too thin to cut out a cut sample of the above size, multiple samples of 25 mm × 25 mm × thickness of the multilayer foam sheet Cut out a sheet and stack the samples so that the total thickness of the sample approaches 20 mm to obtain a cut sample for measurement. Calculate the void ratio S (%).
S(%)=(Vx−W/ρ)×100/(Va−W/ρ) (3)
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 total volume of closed cells in the cut sample.
Va: Apparent volume (cm ³ ) of the cut sample calculated from the outer dimensions of the cut sample used for measurement.
W: Total weight of cut sample used for measurement (g).
ρ: Density of the resin composition obtained by defoaming the multilayer foam sheet (g/cm ³ )

The surface resistivity of the surface layer side of the multilayer foam sheet of the present invention is preferably 1×10 ⁸ to 1×10 ¹⁴ (Ω).
When the surface resistivity is within the above range, the multi-layer foamed sheet has excellent antistatic properties, and adhesion of dust and dirt can be further suppressed. From this point of view, the surface resistivity is more preferably 1×10 ¹³ Ω or less, and even more preferably 1×10 ¹² Ω or less.

The surface resistivity in this specification is measured according to JIS K6271 (2001) after the test piece is conditioned as described below. That is, a test piece (length 100 mm x width 100 mm x thickness: thickness of the test piece) cut out from the multi-layered foam sheet to be measured was left in an atmosphere of 20°C and 30% relative humidity for 36 hours. After adjusting the condition, voltage application is started under the condition of an applied voltage of 500 kV in accordance with JIS K6271 (2001), and the surface resistivity is obtained after one minute has elapsed.

Next, the method for producing the multilayer foam sheet of the present invention will be described.
The multilayer foam sheet of the present invention can be produced, for example, by a coextrusion method using an annular die. First, a polyolefin resin for forming a foam layer and additives such as a cell control agent added as necessary are supplied to an extruder for forming a foam layer, and the mixture of the polyolefin resin and additives is heated and kneaded. Then, a physical foaming agent is further injected, and the mixture and the physical foaming agent are kneaded to obtain a resin melt for forming a foamed layer. On the other hand, a surface layer-forming polyolefin resin, a polymeric antistatic agent, and polyalkylene glycol are supplied to a surface layer-forming extruder and heated and kneaded to obtain a surface layer-forming resin melt. Thereafter, the melted resin for forming the foamed layer and the melted resin for forming the surface layer are introduced into an annular die for co-extrusion and laminated, followed by co-extrusion foaming to form a cylindrical lamination in which the surface layer is laminated on the foamed layer. A multilayer foam sheet can be obtained by forming a foam and cutting open the cylindrical laminated foam while enlarging its diameter and taking it off.

Polyalkylene glycol is added to obtain a resin melt for forming a surface layer in the method for producing a multilayer foam sheet. At this time, the method of adding the polyalkylene glycol is not particularly limited. For example, the polyalkylene glycol may be supplied to the surface layer forming extruder together with the polyolefin resin, or may be supplied to the surface layer forming extruder using a submersible pump or the like. A masterbatch obtained by kneading polyalkylene glycol with a polyolefin resin for forming the surface layer in advance may be supplied to the extruder for forming the surface layer.

As the cell control agent used when forming the foamed layer, it is possible to use an organic type or an inorganic type without particular limitation. Examples of inorganic cell control agents include metal borate salts such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and calcium bicarbonate. In addition, examples of the organic foam control agent include 2,2-methylenebis(4,6-tert-butylphenyl)sodium phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. can. In addition, 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 cell control agent. Furthermore, each of these exemplified cell control agents may be used in combination of two or more.

As the cell adjusting agent, among those described above, talc is preferably used because it facilitates adjustment of the cell diameter of the foam layer and can reduce the moisture content of the multilayer foam sheet. The cell control agent is preferably added in a range of approximately 0.1 parts by mass or more and 3 parts by mass or less, more preferably 0.2 parts by mass, with respect to 100 parts by mass of the polyolefin resin constituting the foam layer. It is more than 2 mass parts or less.

The physical foaming agent is not particularly limited as long as it can be applied to the production of the foam layer of the multilayer foam sheet. As the physical foaming agent, an inorganic physical foaming agent or an organic physical foaming agent can be used. Examples of inorganic physical foaming agents include oxygen, nitrogen, carbon dioxide, and air. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane, methyl chloride, ethyl chloride, 1,1,1,2-tetra Halogenated hydrocarbons such as fluoroethane, 1,1-difluoroethane, 1,3,3,3-tetrafluoropropene and 1-chloro-3,3,3-trifluoropropene, ethers such as dimethyl ether and methyl ethyl ether and alcohols such as methanol and ethanol. Furthermore, two or more kinds of the physical foaming agents may be mixed and used.

Among these physical foaming agents, normal butane, isobutane, or these physical foaming agents are preferred from the viewpoint that the coextrusion method can be stably carried out and a good foamed layer can be stably obtained. Preference is given to using mixtures.

Next, applications of the multilayer foam sheet of the present invention will be described.
The multilayer foam sheet of the present invention can be suitably used as interleaving paper for glass plates. The interleaving paper for glass plates is used by being interposed between the glass plates, and can prevent the risk of breakage due to contact between the glass plates. A glass plate for a liquid crystal display is exemplified as a glass plate for which such an interleaving paper for a glass plate is used. When using the glass plates for a liquid crystal display, after removing the glass plate interleaving paper interposed between the glass plates, the individual glass plates are usually washed with water or the like, and the washed glass plates are used. is used. At this time, it is difficult to wash off the organic substances with water or the like if dust, dirt, organic substances originating from polymeric antistatic agents, or metallic compounds such as calcium compounds adhere to the surface of the glass plate. In this respect, when the interleaving paper for glass plates is made of the multilayer foam sheet of the present invention, the polyalkylene glycol satisfactorily migrates from the multilayer foam sheet to the surfaces of the glass plates, and the individual glass plates are washed with water or the like. Organic matter adhering to the surface of the glass plate is easily washed away.

In addition, the glass plate interleaving paper may be placed in a hot and humid atmosphere while being interposed between the glass plates. In this regard, when the interleaving paper for glass plates is made of the multi-layer foam sheet of the present invention, the moisture content of the multi-layer foam sheet is kept low. Metal compounds such as calcium compounds contained in moisture in the air are less likely to adhere to the surface of the foamed sheet. Therefore, it is effectively suppressed that metal compounds or the like adhere to the glass plate through the multi-layer foamed sheet and contaminate the glass plate.

Furthermore, as described above, the multilayer foam sheet of the present invention suppresses excessive bleeding out of the polyalkylene glycol, so that the peel strength against the packaged object such as a glass plate can be kept small even in a hot and humid atmosphere. can be done. Therefore, for example, when a flat glass plate is lifted and taken out, the multilayer foam sheet does not follow the glass plate and is lifted together with the glass plate, thereby ensuring good workability. From this point of view as well, the multilayer foam sheet of the present invention can be suitably used as interleaving paper for glass plates.

In the multilayer foam sheet of the present invention, the surface layer may be laminated only on one side of the foam layer, or the surface layer may be laminated on both sides. However, when the multilayer foam sheet is used as interleaving paper for glass plates, it is preferable that surface layers are laminated on both sides of the foam layer. By providing a surface layer on both sides of the foam layer, the glass plate interleaving paper reduces the contamination of both of the two glass plates that come into contact with the glass plate interleaving paper when interposed between the glass plates. and improve washability.

The present invention will be described in detail below based on examples. However, the present invention is not limited by the examples.
As the polyolefin-based resin, low-density polyethylene "LDPE1" manufactured by NUC Co., Ltd. shown in Table 1 was used.

Polyether-polyolefin copolymers "ASP1" and "ASP2" shown in Table 2 were used as the polymer-type antistatic agents.

As polyethylene glycol, "PEG300", "PEG600", "PEG1000" and "PEG10000" shown in Table 3 were used.

A mixed butane containing 70% by mass of normal butane and 30% by mass of isobutane was used as a physical blowing agent.

(1) As a talc-based cell control agent masterbatch, a cell control agent masterbatch obtained by blending 20% by mass of talc (manufactured by Matsumura Sangyo Co., Ltd., trade name High Filler #12) with 80% by mass of low-density polyethylene. was used.
(2) A citric acid masterbatch (manufactured by Eiwa Kasei Co., Ltd., trade name: Polystyrene EE27C) and a sodium bicarbonate masterbatch (manufactured by Eiwa Kasei Co., Ltd., trade name: Polystyrene EE35C4) obtained by blending 20% by mass of sodium bicarbonate with 80% by mass of low-density polyethylene.

As an extruder for forming a foam layer, a tandem extruder consisting of a first extruder with an inner diameter of 90 mm and a second extruder with an inner diameter of 120 mm was used. A triple extruder was used. Further, the outlets of the second extruder and the third extruder were connected to a co-extrusion annular die so that the respective resin melts could be stacked in the co-extrusion annular die.

Examples 1-4, Comparative Examples 1-6
A resin composition obtained by blending a low-density polyethylene resin "LDPE1" and 1.5 parts by mass of a cell control agent masterbatch with respect to 100 parts by mass of the low-density polyethylene resin is supplied to the first extruder and melted. , and kneaded to obtain a resin melt adjusted to about 200°C. Next, 10 parts by mass of the mixed butane is injected with respect to 100 parts by mass of the resin composition, kneaded, and then transferred to a second extruder connected downstream of the first extruder, The extruded resin temperature was adjusted to 115° C. to obtain a resin melt for forming a foam layer, which was introduced into the annular co-extrusion die.
In Examples 1 to 4 and Comparative Examples 1, 2, and 4 to 6, a talc-based cell control agent masterbatch was used, and in Comparative Example 3, the sodium bicarbonate citrate-based cell control agent masterbatch was used. 1.8 parts by mass (0.6 parts by mass of citric acid masterbatch/1.2 parts by mass of sodium bicarbonate masterbatch) were mixed with 100 parts by weight of low-density polyethylene.

On the other hand, the type and amount of low-density polyethylene resin shown in Table 4, the type and amount of polymeric antistatic agent shown in Table 4, and the type and amount of polyethylene glycol shown in Table 4 are supplied to the third extruder. The temperature of the extruded resin was adjusted to 115.degree. PEG300 and PEG600 were supplied via a submersible pump connected to the third extruder, and PEG1000 and PEG10000 were added to the third extruder together with the low-density polyethylene resin.

The resin melt for forming the surface layer introduced into the annular co-extrusion die is merged and laminated on the outside and the inside of the resin melt for forming the foamed layer introduced into the annular die for co-extrusion, and the amount of discharge from the annular die is reduced. Extruded into the air at 130 kg/hr, expanded to a blow-up ratio of 2.8, taken at a take-up speed of 67 m/min, and further cut open along the extrusion direction to form a surface layer/foamed layer/surface layer. A multilayer foam sheet (width 1400 mm) having a layer structure was produced.
The front and back surface layers had the same amount of discharge and the same basis weight.

The obtained multilayer foam sheet was measured for basis weight per side of the surface layer, average thickness, apparent density of the entire multilayer foam sheet, surface resistivity, water content, calcium compound adhesion amount, organic matter adhesion amount, and peel strength, Glass plate washability was evaluated. Table 5 shows the results.

The polyolefin-based resin multilayer foam sheets of Examples 1 to 4 are mainly composed of polyethylene glycol having a specific number-average molecular weight, contain polyalkylene glycol that is liquid at 25°C, and have a moisture content within a specific range. is controlled to Therefore, it had excellent antistatic performance, and even under high temperature and high humidity, both the amount of adhered organic matter and the amount of adhered calcium compound were reduced, and the washability for the glass plate was excellent.

Comparative Example 1 is an example using polyethylene glycol having a number average molecular weight of 300 as the polyalkylene glycol. Since the number average molecular weight of polyethylene glycol is too small, the moisture content of the multi-layer foamed sheet increases, resulting in a large amount of calcium compound adhering.

Comparative Example 2 is an example using polyethylene glycol having a number average molecular weight of 11,000 as the polyalkylene glycol. Since the number average molecular weight of polyethylene glycol was too large, the washability with water was lowered and the amount of adhered organic substances increased.

Comparative Example 3 is an example using a sodium bicarbonate citrate-based cell control agent. Citric acid and sodium bicarbonate reacted in the extruder to generate water, which increased the moisture content of the multilayer foam sheet and increased the amount of calcium compound adhered.

Comparative Example 4 is an example in which the blending amount of polyethylene glycol was 5.2 parts by weight, and a polyether-polyolefin copolymer having a melting point of 135° C. was used as the polymeric antistatic agent. Since the water content of the multilayer foam sheet was too high, the amount of calcium compound adhered increased. Moreover, the peel strength against the glass plate increased, and the workability slightly decreased.

Comparative Example 5 is an example using polyethylene glycol having a number average molecular weight of 1000 as the polyalkylene glycol. Since the number average molecular weight of polyethylene glycol was too large, the washability with water was lowered and the amount of adhered organic substances increased.

Comparative Example 6 is an example in which the blending amount of polyethylene glycol was 0.5 parts by weight. Since the blending amount of polyethylene glycol was too small, the effect of improving the washability with water could not be obtained, and the amount of adhered organic substances increased.

In Table 5, each item was measured and evaluated as follows.
(Basis weight per side of surface layer)
It was determined using the formula (2) by the method described above.

(Average thickness of multilayer foam sheet)
The thickness (mm) of the sheet is measured at intervals of 1 cm along the width direction over the entire width of the multilayer foam sheet using an offline thickness measuring device (manufactured by Yamabun Denki Co., Ltd.: TOF-4R), and the arithmetic average is obtained. Thickness was calculated. The measurement was performed at three randomly selected locations on the multilayer foam sheet, and the arithmetic mean value of the calculated average thickness values at the three locations was taken as the average thickness (mm) of the multilayer foam sheet.

(Apparent density of multilayer foam sheet)
Five test pieces were prepared by randomly selecting five points in the direction of extrusion of the multilayer foam sheet and cutting each point into a sheet width×width of 100 mm over the entire width of the sheet. Then, the mass (kg) of each test piece is measured and the volume (m ³ ) is obtained from the external dimensions, and the mass (kg) is divided by the volume (m ³ ) to obtain the apparent density (kg/m ³ ) was obtained, and the arithmetic mean value of the obtained values was taken as the apparent density (kg/m ³ ).

(Surface resistivity of multilayer foam sheet)
The surface resistivity of the multilayer foam sheet was measured according to JIS K 6271 (2008). Specifically, a test piece of 100 mm long×100 mm wide was casually cut out from the multilayer foam sheet, and the test piece was conditioned by leaving it in an atmosphere of 20° C. and 30% relative humidity for 36 hours. Then, a voltage of 500 V was applied to both surfaces of each test piece. One minute after the start of voltage application, the surface resistivity of the test piece was measured, and the arithmetic mean value (5 test pieces x both sides [n=10]) was taken as the surface resistivity of the multilayer foam sheet.

(Water content of multilayer foam sheet)
The moisture content (mass ppm) of the multilayer foam sheet was measured as follows. First, a test piece with a size of 500 mm in width and 400 mm in length was cut out from a multilayer foam sheet and stored under conditions of a temperature of 50°C and a humidity of 80% RH for 24 hours. Dry at 180 ° C. to remove vapors other than water, selectively adsorb water to a molecular sieving adsorbent (manufactured by Nacalai Tesque Co., Ltd., molecular sieve 3A °), and from the change in mass, the formula ( 1) to determine the water content (mass ppm). In this specification, RH indicates relative humidity.

(Glass plate washability)
The washability of the glass plate was evaluated according to the following criteria based on the measurement results of the calcium compound adhesion amount and the organic matter adhesion amount described below.
○: Calcium compound adhesion amount is 0.35 μg/100 cm ² or less and organic matter adhesion amount is 0.10 mg/100 cm ² or less ×: Calcium compound adhesion amount is more than 0.35 μg/100 cm ² and/or organic matter adhesion amount is 0 greater than .10 mg/100 ^cm2

(Amount of calcium compound adhered)
As an indicator of the amount of calcium compound adhered, the amount of adhered calcium compound was measured. The calcium compound adhesion amount was measured by ion chromatography.
First, six multilayer foam sheets and six glass plates were alternately stacked and stored under a load condition of 3.8 g/cm ² at 50° C. and 80% RH for 24 hours. After washing with water (water temperature: about 25°C), the washed glass plate was completely immersed in deionized water and subjected to ultrasonic treatment for 15 minutes to ionize and extract the calcium component adhering to the glass. , ion chromatography (manufactured by Thermo Fisher Scientific: INTEGRION) was used to measure the amount of calcium compound adhered per 100 cm ² of the glass surface (μg/100 cm ² ). A 10 mM methanesulfonic acid solution was used as an eluent.

(Amount of adhered organic matter)
The amount of adhered organic matter was measured by liquid chromatography-mass spectrometry (LC/MS).
First, six multilayer foam sheets and six glass plates were alternately stacked and held under a load condition of 3.8 g/cm ² at 50° C. and 80% RH for 24 hours, and then the glass plates were removed. Washed with detergent-containing water (water temperature about 25°C). After that, the cleaned glass plate surface was wiped with quartz wool impregnated with a solvent in which methanol and chloroform were mixed at a volume ratio of 1:1. Next, the quartz wool after wiping off the glass plate was completely immersed in a mixed solvent of methanol and chloroform at a volume ratio of 1:1, and subjected to ultrasonic treatment for 15 minutes to remove the organic matter adhering to the glass plate. The components were extracted and separated by liquid chromatography manufactured by Shimadzu Corporation, and the amount of organic substances attached per 100 cm ² of the glass surface (mg/100 cm ² ) was measured using a mass spectrometer manufactured by Thermo Fisher Scientific. In the measurement, Cadenza CD-C18 (φ2 mm×150 mm) manufactured by Imtakt was used as a column, and a mixed solution of 0.1% aqueous ammonium acetate solution and acetonitrile was used as a mobile phase. The temperature of the column during the measurement was 40° C., and the flow rate was 0.2 mL/min.
As an indicator of adhered organic matter, the total adhered amount of trimethylimidazole, trifluoromethanesulfonic acid, long-chain fatty acid, alkylbenzene sulfonic acid and polyethylene glycol derived from the polymer antistatic agent was measured. Quantity.

(Glass plate peel strength)
The peel strength (glass plate peel strength) (N) between the multilayer foam sheet and the glass plate was measured as follows. First, 5 test pieces with a size of 60 mm wide × 90 mm long were cut out from the multilayer foam sheet, and the 5 cut test pieces and 5 glass plates were alternately stacked, and the temperature was 50 ° C. and the humidity was 80% RH. It was crimped for 7 days under a load of 25 g/cm ² . After that, the load when the test piece pressed against the glass plate was peeled off at a speed of 100 mm/min was measured and defined as the peel strength (N) (atmospheric conditions for measurement: temperature 25° C., humidity 50% RH).

Claims (9)

It has a polyolefin resin foam layer and a polyolefin resin surface layer laminated and adhered to at least one side of the foam layer, and the surface layer is mainly composed of polyolefin resin and polyether-polyolefin block copolymer. In a multilayer foam sheet containing a polymeric antistatic agent and a polyalkylene glycol,
The amount of the polyalkylene glycol compounded is 1.0 parts by mass or more with respect to 100 parts by mass of the polyolefin resin constituting the surface layer,
The main component of the polyalkylene glycol is polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800,
the polyalkylene glycol is liquid at 25°C;
A polyolefin resin multilayer foam sheet characterized by having a water content of 1500 to 4000 ppm measured after the multilayer foam sheet is left to stand in an atmosphere of 50°C and 80% RH for 24 hours.
2. The polyolefin resin multilayer foam sheet according to claim 1, wherein the blending ratio of polyethylene glycol (PEG1) having a number average molecular weight of 400 to 800 in the polyalkylene glycol is 70% by mass or more.
3. The polyolefin resin multilayer foam sheet according to claim 1, wherein the moisture content of the polyolefin resin multilayer foam sheet is 2000 to 3500 ppm.
4. The polyolefin system according to any one of claims 1 to 3, wherein the ratio of the blending amount of the polyalkylene glycol to the blending amount of the polymeric antistatic agent is 0.10 to 0.60. Resin multilayer foam sheet.
Claims 1 to 4, characterized in that the melting point difference between the melting point of the polymer type antistatic agent and the melting point of the polyolefin resin constituting the surface layer is within the range of -10°C to +10°C. The polyolefin resin multilayer foam sheet according to any one of the items.
6. The method according to any one of claims 1 to 5, wherein the amount of the polymer type antistatic agent is 8 to 30 parts by mass with respect to 100 parts by mass of the polyolefin resin constituting the surface layer. The polyolefin-based resin multilayer foam sheet described above.
7. The polyolefin according to any one of claims 1 to 6, wherein the polyolefin resin constituting the surface layer is low density polyethylene, and the polyolefin resin constituting the foam layer is low density polyethylene. A multi-layer foamed sheet made of resin.
8. The polyolefin resin multilayer foam sheet according to any one of claims 1 to 7, wherein the foam layer contains a cell control agent, and the cell control agent is talc.
A slip-sheet for glass plates comprising the polyolefin resin multilayer foam sheet according to any one of claims 1 to 8.