JP7837872B2 - interleaf paper - Google Patents

Description

(Cross-reference of related applications)
This application claims priority under Japanese Patent Application No. 2020-162454, which is incorporated into the description of this application by reference.

This invention relates to a resin foam sheet.

Resin foam sheets possess excellent lightweight properties and cushioning due to their foamed layer. Therefore, resin foam sheets are used in a variety of applications. Known types of resin foam sheets include those with a single-layer structure consisting only of a foamed layer, and those with a non-foamed layer in addition to the foamed layer.

Examples of raw material resins for the foamed resin sheet include polyethylene resin, polypropylene resin, polystyrene resin, and polyester resin.

Resin foam sheets with a single-layer structure consisting only of a foamed layer are generally manufactured by the extrusion foaming method. This type of resin foam sheet is produced by melting and kneading the raw resin with a foaming agent in an extruder, and then extruding the resulting molten mixture into a sheet through a circular die or flat die to create foam. Resin foam sheets with a multilayer structure, consisting of a foamed layer and a non-foamed layer, are produced by methods such as laminating a resin film that will form the non-foamed layer onto a resin foam sheet that has been first produced, or by co-extruding the foamed and non-foamed layers.

Resin foam sheets are used as raw material sheets when manufacturing containers and other items by thermoforming, and are also used as cushioning materials in their flat sheet form. For example, Patent Document 1 below describes the use of a multilayer resin foam sheet with a non-foamed layer as interposing paper between adjacent glass plates when stacking multiple glass plates.

Japanese Patent Application Publication No. 2019-64048

In order to provide excellent cushioning properties to a foamed resin sheet, it is considered effective to form at least the surface layer of the foamed resin sheet with a relatively soft resin such as polyethylene resin. However, some polyethylene resins are commercially available with additives such as antioxidants and lubricants mixed in. If the surface of a foamed resin sheet is formed with such polyethylene resin, the additives will also be present on the surface of the foamed resin sheet, and these additives may adhere to the mating material that comes into contact with the surface. Although the amount of additive adhesion is small, this adhesion can become a problem if the mating material is an item that requires high cleanliness, such as electronic equipment components.

To address these problems, one option is to use commercially available polyethylene resin in an additive-free state as the raw material for foamed resin sheets. However, if additive-free and additive-containing polyethylene resins are used in the same manufacturing facility, there is a risk of additive contamination in the stockyard or production line, potentially contaminating the additive-free polyethylene resin. On the other hand, establishing a dedicated line for additive-free polyethylene resin in the foamed resin sheet manufacturing facility to prevent this is not desirable from the standpoint of production line operational efficiency.

If the resin foam sheet itself could be given a function to prevent the transfer of additives to the mating material, even if additives are present, the above-mentioned problems could be resolved. However, a method for imparting such a function to a resin foam sheet has not yet been established. Therefore, the present invention aims to provide a resin foam sheet that is less likely to cause deposits to form on the mating material.

The present invention, which solves the above problems,
A resin foam sheet having at least one foam layer,
The foamed resin sheet is composed of a resin composition in which at least one surface contains polyethylene resin.
The present invention provides a resin foam sheet in which the polyethylene resin contained in the resin composition has a density of 928 kg/ ^m³ or more and 933 kg/ ^m³ or less, and the degree of crystallinity of the polyethylene resin is 44% or more and 58% or less.

The present invention, which solves the above problems,
It comprises at least one foam layer,
A resin foam sheet having a multilayer structure in which the foam layer and other layers are laminated,
The foamed resin sheet is composed of a resin composition in which at least one surface contains polyethylene resin.
The present invention provides a resin foam sheet in which the polyethylene resin contained in the resin composition has a density of 928 kg/ ^m³ or more and 933 kg/ ^m³ or less, and the degree of crystallinity of the polyethylene resin is 44% or more and 58% or less.

Figure 1 is a schematic diagram showing one way in which a resin foam sheet is used. Figure 2 is a schematic cross-sectional view showing the structure of a resin foam sheet according to one embodiment. Figure 3 is a schematic cross-sectional view showing a resin foam sheet according to another embodiment. Figure 4 is a schematic cross-sectional view showing a resin foam sheet according to another embodiment. Figure 5 is a schematic diagram showing a method for evaluating the transferability of additives from a resin foam sheet to a mating material.

An embodiment of the present invention will be described below with reference to the figures.
The resin foam sheet in this embodiment is not particularly limited in its use and can be used for various applications. Regarding the migration of additives, the migration of fatty acid compounds tends to be a problem. In this embodiment, the migration of fatty acid compounds and other substances to the mating material is suppressed by using a specific polyethylene resin in the resin foam sheet.

In the following, the resin foam sheet of this embodiment will be described in detail, using the case where it is used as a laminate for glass plates as an example. As shown in Figure 1, the resin foam sheet 1 of this embodiment is used as a laminate for glass plates. The resin foam sheet 1 of this embodiment is used as a laminate by being interposed between adjacent glass plates 2 when stacking multiple glass plates 2 in the vertical direction to form a laminate 100. The laminate in this embodiment is made of a resin foam sheet 1 manufactured by an extrusion foaming method. As shown in Figure 2, the laminate in this embodiment is made of a resin foam sheet 1 having a single-layer structure, with the foam layer 10 exposed on both sides. As described above, in the resin foam sheet 1 of this embodiment, both sides of the foam layer 10 are contact surfaces that come into contact with the mating material (glass plate 2).

In this embodiment, the glass plate 2 can be, for example, a glass plate used as a substrate or cover glass in a display panel such as a liquid crystal display or an organic EL display.

This type of glass plate generally has a high demand for cleanliness. Therefore, if fatty acid compounds, which are commonly mixed as additives in many commercially available resins, adhere to this type of glass plate, it can easily become a problem. Accordingly, the resin foam sheet 1 of this embodiment, which can suppress the migration of fatty acid compounds, is particularly effective when used as a lamination for glass plates.

The foamed resin sheet 1 (foamed layer 10) of this embodiment is composed of a resin composition containing polyethylene resin. The resin composition in this embodiment contains the polyethylene resin and additives. The resin composition in this embodiment does not need to contain the polyethylene resin or the additives individually; it may contain multiple polyethylene resins or multiple additives.

The resin composition may include, for example, a high-density polyethylene resin (PE-HD) produced by a catalytic method (medium-low pressure polymerization method) having almost no branching in its molecular structure and a high density of 942 kg/ ^m³ or more as the polyethylene resin. The resin composition may also include, for example, a linear low-density polyethylene resin (PE-LLD) produced by introducing a comonomer to have a density of 910 kg/ ^m³ or more and 925 kg/ ^m³ or less as the polyethylene resin. The resin composition may also include, for example, a medium-density polyethylene resin (PE-MD) produced to have a density between that of the linear low-density polyethylene resin (PE-LLD) and the high-density polyethylene resin (PE-HD) as the polyethylene resin.

The resin composition may contain extremely low-density polyethylene resin (PE-VLD) as the polyethylene resin. The polyethylene resin may be, for example, a low-density polyethylene resin (PE-LD) produced by a high-pressure polymerization method and having long-chain branching in its molecular structure.

As stated above, the polyethylene resin contained in the resin composition of this embodiment does not need to be just one of these polyethylene resins. The resin composition of this embodiment may contain multiple polyethylene resins from among these. That is, the resin composition may contain a first polyethylene resin and a second polyethylene resin as the polyethylene resin.

The first polyethylene resin and the second polyethylene resin may, for example, be high-density polyethylene resin (PE-HD) and low-density polyethylene resin (PE-LD), or both may be low-density polyethylene resin (PE-LD).

In order to obtain a resin foam sheet that is less likely to cause adhesion to the mating material, the density of the polyethylene resin is preferably within a predetermined range. In the resin composition of this embodiment, the polyethylene resin preferably has a density (density at 23°C) of 928 kg/ ^m³ or more, and more preferably 930 kg/ ^m³ or more. In the resin composition, the polyethylene resin preferably has a density of 933 kg/ ^m³ or less, and more preferably 932 kg/ ^m³ or less.

To bring the density of the polyethylene resin contained in the resin composition within the above range, one type of polyethylene resin with a density within the above range can be included in the resin composition alone. Alternatively, multiple polyethylene resins with densities within the above range can be prepared and included in the resin composition. Furthermore, multiple polyethylene resins, including one with a density outside the above range, can be combined and adjusted so that the density of the polyethylene resin in the resin composition falls within the above range. That is, if the resin composition contains multiple polyethylene resins, the proportion of the multiple polyethylene resins can be adjusted so that the density of the mixed polyethylene resins falls within the above numerical range. Therefore, the polyethylene resin with the above preferred density may consist of, for example, one type of low-density polyethylene resin (PE-LD) with a density of 928 kg/ ^m³ or more and 932 kg/ ^m³ or less, or it may consist of a first polyethylene resin with a density of less than 928 kg/ ^m³ and a second polyethylene resin with a density exceeding 933 kg/ ^m³ .

The density of the polyethylene resin can be determined, for example, if the resin composition contains multiple polyethylene resins, by preparing a mixture by blending the multiple polyethylene resins in the mass ratio required for inclusion in the resin composition, preparing a sample from the molten mixture obtained by melting and kneading the mixture, and measuring the density of the sample. If the resin composition contains only one polyethylene resin, the density can be measured using a sample prepared from that polyethylene resin.

The density of the polyethylene resin can be measured, for example, by the method described in JIS K 7112, and can be determined by Method D (density gradient tube).

To obtain a resin foam sheet that is less likely to cause adhesion to the mating material, the degree of crystallinity of the polyethylene resin is preferably within a predetermined range. The degree of crystallinity of the polyethylene resin is preferably 44% or more, and more preferably 45% or more. The degree of crystallinity of the polyethylene resin is even more preferably greater than 45%. The degree of crystallinity of the polyethylene resin is preferably 58% or less, and more preferably 51% or less. The degree of crystallinity of the polyethylene resin is even more preferably 47% or less.

To ensure the degree of crystallinity of the polyethylene resin contained in the resin composition is within the above-mentioned range, one type of polyethylene resin with a degree of crystallinity within that range can be included in the resin composition. Alternatively, multiple polyethylene resins with a degree of crystallinity within that range can be included in the resin composition. Furthermore, multiple polyethylene resins, including one with a degree of crystallinity outside the above-mentioned range, can be combined and adjusted so that the degree of crystallinity of the polyethylene resin in the resin composition falls within the above-mentioned range. In other words, if the resin composition contains multiple polyethylene resins, the proportion of the multiple polyethylene resins can be adjusted so that the degree of crystallinity in the mixed state falls within the above-mentioned numerical range.

The degree of crystallinity of the polyethylene resin can be determined, for example, if the resin composition contains multiple polyethylene resins, by preparing a mixture by blending the multiple polyethylene resins in the mass ratio required for inclusion in the resin composition, preparing a sample from the molten kneaded product obtained by melting and kneading the mixture, and measuring the degree of crystallinity of the sample. If the resin composition contains only one polyethylene resin, the degree of crystallinity can be measured using a sample prepared from that polyethylene resin.

The degree of crystallinity of the polyethylene resin can be measured by the method described in JIS K7122:1987 and JIS K7122:2012, "Method for Measuring the Heat of Transfer of Plastics".
In other words, the degree of crystallinity of the polyethylene resin can be measured by differential scanning calorimetry (DSC).
The sampling method and temperature conditions can be as follows:
After filling the bottom of the aluminum measuring container with 5.5 ± 0.5 mg of the sample, ensuring there are no gaps, the aluminum lid is placed over it.
Next, differential scanning calorimetry will be performed using a Hitachi High-Tech Science Corporation "DSC7000X, AS-3" differential scanning calorimetry meter.
Under a nitrogen gas flow rate of 20 mL/min, the sample is heated and cooled in the following steps to obtain a DSC curve.
(Step 1) Cool the temperature from 30°C to -40°C and hold for 10 minutes.
(Step 2) Increase the temperature from -40°C to 220°C (first heating), and hold for 10 minutes.
(Step 3) Cool down from 220°C to -40°C and hold for 10 minutes.
(Step 4) Increase the temperature from -40°C to 220°C (second heating).
All heating and cooling operations will be performed at a rate of 10°C/min.
Alumina will be used as the reference material.
The heat of crystallization (J/g) is determined from the area of the crystallization peak observed during the cooling process (step 3).
The degree of crystallization is determined by dividing this heat of crystallization by the theoretical heat of fusion of polyethylene, which is 285.7 J/g.
The heat of crystallization is calculated using the analysis software attached to the device, from the area enclosed by the straight line connecting the point where the DSC curve deviates from the high-temperature baseline and the point where the DSC curve returns to the low-temperature baseline, and the DSC curve itself.
The degree of crystallinity can be calculated using the following formula.
Crystallinity (%) = (crystallization heat (J/g)/285.7 (J/g)) x 100 (%)

In order to obtain a resin foam sheet that is less likely to cause adhesion to the mating material, it is particularly preferable that the polyethylene resin has a density of 930 kg/ ^m³ or more and 932 kg/ ^m³ or less, and a degree of crystallinity of 45% or more and 51% or less. If the resin composition contains multiple polyethylene resins, the density of the mixed polyethylene resins should be 930 kg/ ^m³ or more and 932 kg/ ^m³ or less, and the degree of crystallinity of the mixed polyethylene resins should be 45% or more and 51% or less. The resin composition can be easily adjusted to achieve the above-mentioned preferred conditions by containing multiple polyethylene resins, including a first polyethylene resin and a second polyethylene resin.

Preferably, at least one of the first polyethylene resin and the second polyethylene resin is a low-density polyethylene resin (PE-LD) polymerized by a high-pressure polymerization method. The resin composition is advantageous for capturing fatty acid compounds because the low-density polyethylene resin (PE-LD) has long-chain branching. Low-density polyethylene resin (PE-LD) is considered advantageous for forming a morphology in the resin composition that includes amorphous regions with free volume together with crystalline regions.

Long-chain branching in polyethylene can be confirmed, for example, by ^13C -NMR. For example, if the presence of alkyl groups with a length of hexyl group or longer can be confirmed by ^13C -NMR, it can be determined that long-chain branching exists in the polyethylene. Low-density polyethylene resin (PE-LD) preferably has alkyl groups with a length of heptyl group or longer, and more preferably has alkyl groups with a length of octyl group or longer.

When the resin composition contains multiple polyethylenes, including the first polyethylene resin and the second polyethylene resin, it is preferable that both are low-density polyethylene resins (PE-LD). In a resin composition containing two or more low-density polyethylene resins (PE-LD), the crystallization peak in the DSC curve of the resin composition becomes broader. That is, by including two or more low-density polyethylene resins (PE-LD), the overall crystallization behavior of the polyethylene resin during the cooling process of the molten resin composition can be slowed down. Therefore, a resin foam sheet containing two or more low-density polyethylene resins (PE-LD) is considered advantageous in that it can suppress changes in the formed morphology due to cooling conditions.

The polyethylene resin described above preferably has a somewhat bulky molecular structure, for example, it is preferable that the melt mass flow rate is moderately low. The melt mass flow rate (MFR) of the polyethylene resin is preferably 6 g/10 min or less. The melt mass flow rate (MFR) of the polyethylene resin is more preferably 5 g/10 min or less, and even more preferably 4 g/10 min or less. In order to reduce the equipment load when manufacturing the resin foam sheet 1 by the extrusion foaming method, the melt mass flow rate (MFR) of the polyethylene resin is preferably 0.1 g/10 min or more. The melt mass flow rate (MFR) of the polyethylene resin is more preferably 0.2 g/10 min or more, and even more preferably 0.3 g/10 min or more.

The melt mass flow rate (MFR) can be measured according to JIS K7210:1999 "Plastics - Test methods for melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastic plastics". The melt mass flow rate (MFR) can be measured by "b) Method for measuring the time it takes for a piston to travel a predetermined distance" as described in Method B of the same standard. Specifically, the melt mass flow rate (MFR) can be measured using, for example, the "Semi-Automatic Melt Indexer 2A" manufactured by Toyo Seiki Seisakusho Co., Ltd.
The measurement conditions can be as follows:
Sample: 3-8 g
Preheating: 270 seconds Load hold: 30 seconds Test temperature: 190°C
Test load: 21.18 N
Piston travel distance (interval): 25 mm
The sample should be tested three times, and the average of these tests can be used as the meltmass flow rate (g/10min).

The polyethylene resin content in the resin composition is preferably 80% by mass or more, more preferably 83% by mass or more, even more preferably 85% by mass or more, particularly preferably 88% by mass or more, and especially preferably 90% by mass or more. If the resin composition contains multiple polyethylene resins, the polyethylene resin content refers to the total amount.

Examples of additives included in the resin composition together with the polyethylene resin include high-molecular-weight antistatic agents, low-molecular-weight antistatic agents (surfactants), lubricants, weather-resistant stabilizers, light stabilizers, antioxidants, antibacterial agents, deodorants, pigments, and inorganic fillers.

In this embodiment, the additive is, for example, included in the resin composition in a total content of 1% by mass or more and 20% by mass or less. The total content of the additive in the resin composition is preferably 17% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

The resin foam sheet 1 of this embodiment, composed of the resin composition described above, is used as a laminate for the glass plate 2, as described above. Since the laminate is used in a manner in which it is in surface contact with the glass plate 2 and then peeled off from the surface of the glass plate 2, it is preferable that it is provided with antistatic properties. For this reason, it is preferable that the resin composition constituting the contact surface of the resin foam sheet 1 contains a polymer-type antistatic agent or a surfactant as an additive. The resin composition of this embodiment may also contain a fatty acid compound. The fatty acid compound may be included in the resin composition as an additive or as an unavoidable impurity (foreign matter).

Examples of the polymer-type antistatic agent include polyethylene oxide, polypropylene oxide, polyethylene glycol, polyester amide, polyether ester amide, ionomers such as ethylene-methacrylic acid copolymer, quaternary ammonium salts such as polyethylene glycol methacrylate copolymer, and copolymers of olefin-based blocks and hydrophilic blocks.

As the polymeric antistatic agent, a copolymer of an olefin-based block and a hydrophilic block is preferred. The olefin-based block may be composed of a polyolefin in which one or more alkenes having 2 to 8 carbon atoms are used as constituent units. The hydrophilic block may be composed of a polyoxyalkylene in which alkylene oxides having 2 to 8 carbon atoms, such as ethylene oxide, propylene oxide, and butylene oxide, are used as constituent units.

In this embodiment, the polymer-type antistatic agent is, for example, included in the resin composition in a total content of 0.5% by mass or more and 10% by mass or less. The total content of the polymer-type antistatic agent is preferably 1% by mass or more, and more preferably 2% by mass or more. The total content of the polymer-type antistatic agent is preferably 8% by mass or less, and more preferably 6% by mass or less.

Examples of the aforementioned surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

Examples of the nonionic surfactants include ester-type surfactants in which polyhydric alcohols such as glycerin and sugars are ester-bonded to fatty acids; ether-type surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene alkylphenyl ethers; ester-ether-type surfactants in which alkylene oxides are added to fatty acids or polyhydric alcohol fatty acid esters; and amide-type surfactants such as fatty acid alkanolamides in which hydrophobic and hydrophilic groups are linked via amide bonds.

Examples of the anionic surfactants include sulfonate-type surfactants such as alkyl sulfonates, dialkyl sulfosuccinates, alphaolefin sulfonates, linear alkylbenzene sulfonates, naphthalene sulfonate-formaldehyde condensates, alkyl naphthalene sulfonates, and N-methyl-N-acyl taurate salts; carboxylate-type surfactants such as aliphatic monocarboxylates, polyoxyethylene alkyl ether carboxylates, N-acyl sarcosinate, and N-acyl glutamate; sulfate-type surfactants such as alkyl sulfates, polyoxyethylene alkyl ether sulfates, and oil sulfates; and phosphate-type surfactants such as alkyl phosphates, polyoxyethylene alkyl ether phosphates, and polyoxyethylene alkylphenyl ether phosphates. Examples of metals constituting the salts include alkali metals such as sodium, potassium, and lithium, and alkaline earth metals such as calcium and magnesium.

Examples of the cationic surfactants include quaternary ammonium salt type surfactants such as alkylammonium salts and alkylbenzylammonium salts; and amine salt type surfactants such as N-methylbishydroxyethylamine fatty acid ester hydrochloride.

Examples of the aforementioned amphoteric surfactants include betaine-type surfactants such as alkyl betaines; amino acid-type surfactants such as alkylamino fatty acid salts; and amine oxide-type surfactants such as alkylamine oxides.

In this embodiment, the surfactant is, for example, present in a total content of 0.5% by mass or more and 10% by mass or less in the resin composition. The total content of the surfactant is preferably 1% by mass or more, and more preferably 2% by mass or more. The total content of the surfactant is preferably 8% by mass or less, and more preferably 6% by mass or less.

The resin composition of this embodiment preferably contains an anionic surfactant or a nonionic surfactant among the surfactants. The resin composition of this embodiment is particularly preferably composed of an anionic surfactant. Specifically, it is preferable that 50% or more by mass of the surfactant contained in the resin composition is an anionic surfactant, more preferably 75% or more by mass is an anionic surfactant, and even more preferably 90% or more by mass is an anionic surfactant. The surfactant contained in the resin composition may consist substantially of anionic surfactants.

The fatty acid compound in this embodiment may be included in the resin composition as a lubricant or as an antistatic agent. Examples of the fatty acid compound include fatty acids, fatty acid metal salts, fatty acid amides, and fatty acid esters.

Specific examples of fatty acids include saturated fatty acids such as lauric acid, palmitic acid, stearic acid, and behenic acid; unsaturated fatty acids such as oleic acid, erucic acid, linoleic acid, and linolenic acid; and in addition to these monocarboxylic acids, dicarboxylic acids such as dimer acids. Metals that constitute fatty acid metal salts include calcium, magnesium, aluminum, and zinc.

Fatty acid amides are acid amides derived from fatty acids. Examples of such fatty acid amides include those derived from aliphatic amines.

Specific examples of fatty acid amides include stearic acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, methylenebisstearate amide, ethylenebisstearate amide, ethylenebisoleic acid amide, and ethylenebishydroxystearate amide.

Specific examples of fatty acid esters include butyl stearate, monoglyceride stearate, monoglyceride oleate, monoglyceride behenic acid, monoglyceride linoleate, monoglyceride ricinoleate, triglyceride hydroxystearate, sorbitan fatty acid esters, polyoxyethylene (5) glycerin monostearate, polyoxyethylene (20) glycerin monostearate, polyoxyethylene (5) monooleate, pentaerythritol tetrastearate, pentaerythritol polyadipate stearate, stearyl stearate, 1,2-oxystearic acid, and hydrogenated castor oil.

The total content of fatty acid compounds in the resin composition constituting the foamed resin sheet of this embodiment is preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 100 ppm or less, and particularly preferably 10 ppm or less. The total content of fatty acid compounds may be 7 ppm or less, or 5 ppm or less. The total content of fatty acid compounds in the resin composition constituting the foamed resin sheet of this embodiment may be 1 ppm or more, or 3 ppm or more. If necessary, the total content of fatty acid compounds may be 5 ppm or more, or 10 ppm or more, or 100 ppm or more.

The fatty acid compound content of a resin foam sheet can be measured using known methods. For example, the following methods can be used.

The aforementioned fatty acid metal salts can be measured, for example, as follows: A resin foam sheet is immersed in boiling methanol for extraction, and the precipitate is filtered off after cooling. The precipitate is suspended in dilute hydrochloric acid and solvent-extracted using ether. Free fatty acids are extracted into the ether phase, and metals into the aqueous phase. The fatty acids can then be identified and quantified using the method described later, while the metals can be identified and quantified using an ICP (inductively coupled plasma) emission spectrometer or the like.

The quantitative determination of the fatty acids, fatty acid amides, and fatty acid esters can be performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) (for example, "ACCELA" manufactured by Termo SCIENTIFIC).

Furthermore, the calibration curve used for the quantitative determination of fatty acid compounds is prepared using five standard solutions (5 ppm, 2 ppm, 1 ppm, 0.5 ppm, 0.2 ppm) of different concentrations, which are prepared by diluting a 1000 ppm reference solution (methanol solution) of the fatty acid compound to be quantified (fatty acid, fatty acid amide, fatty acid ester) with methanol.
Furthermore, samples to be measured by LC-MS/MS are prepared as follows.
Cut the resin foam sheet into pieces approximately 2 mm square and collect approximately 0.15 g of the extracted sample.
The extracted sample is weighed accurately, and the extracted sample is placed in a PTFE (polytetrafluoroethylene) pressure vessel together with 10 ml of methanol, and the pressure vessel is sealed.
- Heat the sealed pressure container in a 120°C oven for 2 hours, then remove it from the oven and allow it to cool naturally at room temperature.
- Open the pressure-resistant container that has been cooled to room temperature and filter the extract inside the container using filter paper (No. 5A).
The filtrate obtained by the above filtration is used as the sample for measurement by LC-MS/MS.
Based on the measurement results, the amount of fatty acid compounds in the filtrate is calculated using the calibration curve obtained earlier.
- Determine the fatty acid compound content (ppm) in the resin foam sheet from the amount of fatty acid compounds contained in the filtrate.

The foamed resin sheet 1 of this embodiment can be produced by melting and kneading the above-mentioned resin composition together with a foaming agent in an extruder, and then extruding the molten mixture obtained by the melting and kneading into a sheet shape from a die attached to the leading end of the extrusion direction of the extruder to cause foaming. The width and thickness of the foamed resin sheet 1 are not particularly limited, but the thickness is preferably 0.2 mm or more. The thickness of the foamed resin sheet 1 is more preferably 0.5 mm or more. The thickness of the foamed resin sheet 1 is preferably 2.0 mm or less, and more preferably 1.5 mm or less.

Resin foam sheets produced by the extrusion foaming method are usually hot and flexible immediately after extrusion. Resin foam sheets produced by the extrusion foaming method are usually rapidly cooled immediately after being extruded from the extruder to prevent unintended deformation. If the resin foam sheet 1 of this embodiment is produced in such a way, the polyethylene resin will solidify without sufficient crystallization. It is preferable for the contained polyethylene resin to be sufficiently crystallized in the resin foam sheet 1 in order to reduce the risk of adhesion to the mating material. The proportion of polyethylene resin crystals contained in the resin foam sheet 1 can be confirmed by performing a DSC measurement as described above using the resin foam sheet 1 as a sample. In the following, the mass ratio of polyethylene resin crystals contained in the resin foam sheet 1 will be referred to as the "apparent crystallinity."

The apparent crystallinity of the resin foam sheet 1 can be determined specifically as follows.
In other words, apparent crystallinity can be measured using a sample taken from a foamed resin sheet. The sample can be taken from a randomly selected location on the foamed resin sheet.
The sampling method and temperature conditions can be as follows:
After filling the bottom of the aluminum measuring container with 5.5 ± 0.5 mg of the sample, ensuring there are no gaps, the aluminum lid is placed over it.
Next, differential scanning calorimetry will be performed using a Hitachi High-Tech Science Corporation "DSC7000X, AS-3" differential scanning calorimetry meter.
Under a nitrogen gas flow rate of 20 mL/min, the sample is heated and cooled in the following steps to obtain a DSC curve.
(Step 1) Cool the temperature from 30°C to -40°C and hold for 10 minutes.
(Step 2) Increase the temperature from -40°C to 220°C (first heating), and hold for 10 minutes.
The heating and cooling processes will be performed at a rate of 10°C/min.
Alumina will be used as the reference material.
The heat of fusion (J/g) is determined from the area of the melting peak observed during the cooling process (step 2).
The apparent degree of crystallinity is obtained by dividing this heat of fusion by the theoretical heat of fusion of perfect polyethylene crystals, which is 285.7 J/g.
The heat of fusion is calculated using the analysis software attached to the device, from the area enclosed by the straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve itself.
The apparent degree of crystallinity can be calculated using the following formula.
Apparent crystallinity (%) = (Heat of fusion (J/g) / 285.7 (J/g)) × 100 (%)

In this embodiment, the apparent crystallinity of the foamed resin sheet 1 is preferably similar to the crystallinity of the polyethylene resin contained in the foamed resin sheet 1. The apparent crystallinity of the foamed resin sheet 1 is preferably 44% or higher, and more preferably 45% or higher. It is even more preferable that the apparent crystallinity of the foamed resin sheet 1 exceeds 45%. The apparent crystallinity of the foamed resin sheet 1 is preferably 58% or lower, and more preferably 51% or lower. It is even more preferable that the apparent crystallinity of the foamed resin sheet 1 is 47% or lower.

The apparent crystallinity (C1 (%)) of the resin foam sheet 1 is usually lower than the crystallinity (C2 (%)) of the polyethylene resin. That is, the ratio (C1/C2) of the apparent crystallinity (C1) of the resin foam sheet 1 to the crystallinity (C2) of the polyethylene resin is usually 1.0 or less. Preferably, this ratio (C1/C2) is 0.8 or higher. It may also be 0.9 or higher.

To make the apparent crystallinity of the foamed resin sheet 1 close to that of polyethylene resin, it is necessary to prevent a rapid temperature drop in the foamed resin sheet 1 extruded from the extruder. Methods to prevent a rapid temperature drop in the foamed resin sheet 1 include slowing down the movement speed of the extruded foamed resin sheet 1 and blowing warm air onto the sheet 1 during its movement. Furthermore, to make the apparent crystallinity of the foamed resin sheet 1 close to that of polyethylene resin, the resin composition that forms the foamed resin sheet 1 may contain a crystallization nucleating agent or a crystallization accelerator.

The thickness of the resin foam sheet 1 can be determined by measuring the thickness at multiple randomly selected locations (for example, 20 locations) using a thickness gauge (for example, Teclock's "Dial Thickness Gauge SM-112") and calculating the arithmetic mean.

In this embodiment, the foamed layer 10 preferably has an apparent density of 10 kg/ ^m³ or more. More preferably, the apparent density is 15 kg/ ^m³ or more. The apparent density of the foamed layer 10 preferably is 200 kg/ ^m³ or less. More preferably, the apparent density is 150 kg/ ^m³ or less, and even more preferably 100 kg/ ^m³ or less.

The apparent density of the foamed layer 10 can be determined as follows.
[Method for measuring apparent density]
The apparent density of the foam layer 10 can be measured by the method described in JIS K7222:2005 "Foamed plastics and rubber - Method for determining apparent density". Specifically, a test specimen with an apparent volume of 100 ^cm³ or more is prepared, and its mass is measured. When cutting the test specimen from the resin foam sheet, care should be taken to avoid altering the original cell structure as much as possible. If a test specimen of 100 ^cm³ or more cannot be prepared, a test specimen with the largest possible volume should be prepared. The apparent density is then calculated using the following formula.
Apparent density (kg/ ^m³ ) = Mass of test specimen (g) / Volume of test specimen ( ^mm³ ) × ^10⁶
In principle, the test specimens are taken 72 hours or more after the resin foam sheet is prepared, and then conditioned by leaving them in an atmosphere of 23±2°C and 50±10% relative humidity for 16 hours or more before measuring their mass and volume under the same conditions.

As shown in Figure 2, the resin foam sheet 1 of this embodiment is an extruded foam sheet having a single-layer structure consisting only of a foam layer 10. Therefore, the surface of the foam layer 10 comes into contact with the mating material that the resin foam sheet 1 comes into contact with. In order to ensure that the amount of fatty acid compounds retained in the surface layer of the resin foam sheet 1 is above a certain level, it is preferable that the surface layer of the foam layer 10 has a larger amount of resin than the central part in the thickness direction. Specifically, when the resin foam sheet 1 is divided into three parts in the thickness direction, and the foam layer 10 is divided into a sheet in the central part of the thickness direction and two sheets including the surface layer, it is preferable that the apparent density of the sheet including the surface layer is 1.1 times or more, and more preferably 1.2 times or more, than the apparent density of the sheet in the central part. The apparent density of the sheet including the surface layer may be 1.3 times or more, or 1.5 times or more, than the apparent density of the sheet in the central part. Furthermore, it is preferable that the apparent density of the sheet including the surface layer is 3 times or less the apparent density of the sheet in the central part.

In the above, the resin foam sheet 1 is exemplified as having a single-layer structure consisting only of a foam layer 10, but the resin foam sheet 1 in this embodiment may also have a multilayer structure. The multilayer resin foam sheet 1 may be an extruded foam sheet having a non-foamed layer 20 on one side of the foam layer 10, as shown in Figure 3. The multilayer resin foam sheet 1 may also be an extruded foam sheet having non-foamed layers 20 on both sides of the foam layer 10, as shown in Figure 4. The resin foam sheet 1 in this embodiment does not necessarily have to be an extruded foam sheet.

In the multilayer resin foam sheet 1, the non-foamed layer 20 can typically have a thickness of 5 μm to 500 μm.

When the foamed resin sheet 1 has a non-foamed layer 20, the surface of the non-foamed layer 20 becomes the contact surface that comes into contact with the mating material. Therefore, the non-foamed layer 20 can be formed from the same resin composition as described above for the foamed layer 10 in Figure 2. In this embodiment, since the fact that the surface of the foamed resin sheet 1 that comes into contact with the mating material is composed of the aforementioned resin composition is effective in suppressing the migration of fatty acid compounds, in the foamed resin sheet 1 having non-foamed layers 20 on both sides of the foamed layer 10 as shown in Figure 4, the material used to form the foamed layer 10 is not particularly limited. On the other hand, in the foamed resin sheet 1 shown in Figure 3, the non-foamed layer 20 is provided only on one side of the foamed layer 10, and the other side of the foamed layer 10 becomes the contact surface that comes into contact with the mating material. Therefore, it is preferable to form both the foamed layer 10 and the non-foamed layer 20 from the aforementioned resin compositions.

Furthermore, in the resin foam sheet 1 shown in Figure 4, the same resin composition may be used for the non-foamed layer 20 on one side and the resin composition may be used for the non-foamed layer 20 on the other side, or different resin compositions may be used. Also, in the resin foam sheet 1 shown in Figure 3, the same resin composition may be used for the resin composition constituting the foamed layer 10 and the resin composition constituting the non-foamed layer 20, or different resin compositions may be used.

The foamed resin sheet 1 of this embodiment comprises at least one foamed layer and has a single-layer structure consisting only of the foamed layer, or a multilayer structure in which the foamed layer and other layers are laminated, and at least one surface is composed of a resin composition containing polyethylene resin, and the polyethylene resin contained in the resin composition has a density of 928 kg/ ^m³ to 933 kg/ ^m³ and a crystallinity of 44% to 58%, so that even if fatty acid compounds are unintentionally included in the resin composition, the migration of the fatty acid compounds to the mating material in contact with the foamed resin sheet 1 can be suppressed.

Although the resin foam sheet 1 of this embodiment is preferably used as a laminated sheet due to its functions as described above, the use of the resin foam sheet 1 is not limited to laminated sheets and can be used for various purposes. In other words, the resin foam sheet of the present invention is not limited in any way to the above examples.

The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

First, we prepared four types of polyethylene resin, represented by the abbreviations "PE1" through "PE4".
PE1: Low-density polyethylene resin manufactured by high-pressure polymerization, density: 931 kg/ ^m³ , MFR = 1.1 g/10 min
PE2: Low-density polyethylene resin manufactured by high-pressure polymerization, density: 934 kg/ ^m³ , MFR = 3.0 g/10 min
PE3: Low-density polyethylene resin manufactured by high-pressure polymerization, density: 921 kg/ ^m³ , MFR = 0.4 g/10 min
PE4: Low-density polyethylene resin manufactured by high-pressure polymerization, density: 926 kg/ ^m³ , MFR = 3.5 g/10 min
Furthermore, one type of polymer-type antistatic agent, referred to by the abbreviation "AS1," was prepared.
AS1: A polymeric antistatic agent comprising a polyolefin block composed of polyolefins and a hydrophilic block composed of polyoxyalkylene.
Furthermore, we prepared one type of surfactant, which is abbreviated as "SA1".
SA1: Sodium alkylsulfonate. And, as a fatty acid compound, one type was prepared, represented by the abbreviation "FA1".
FA1: Stearic acid amide. In addition, one type of foam regulator, abbreviated as "NA1", was prepared.
NA1: Azodicarbonamide-containing masterbatch

(Example 1)
(Production of resin foam sheets)
(Manufacturing example a)
A mixture was prepared by blending polyethylene resin "PE1", polymer antistatic agent "AS1", surfactant "SA1", and foam regulator "NA1" in the proportions shown in Table 1.
A circular die with an outlet diameter of 100 mm (slit width of 0.2 mm) was attached to the tip of a tandem extruder, which consisted of two extruders connected in the order of first extruder and second extruder in the direction of extrusion.
The aforementioned mixture was supplied to the first extruder of a tandem extruder, and while melt-kneading was carried out in the first extruder, a mixture of butane (isobutane/n-butane = 50/50 (molar ratio)) was injected under pressure from the middle of the first extruder as a blowing agent, and further melt-kneading was performed.
The amount of mixed butane injected was adjusted so that it was 18 parts by mass relative to 100 parts by mass of polyethylene resin.
After melting and kneading in the first extruder, the molten mixture was cooled to a temperature range suitable for foaming (111°C) in a second extruder connected to the first extruder. Then, this molten mixture was extruded in a cylindrical shape into the atmosphere through the circular die to induce foaming.
The resin temperature at that time was 116°C.
The extruded tubular foam was cooled by blowing air onto it, and then cooled by placing it on a cooling mandrel with a diameter of 380 mm and a length of 500 mm. The tubular foam was cut along the extrusion direction with a cutter provided on the rear side of the cooling mandrel, and the resulting strip-shaped foam sheet was wound up at a speed of 20 m/min to obtain a long strip-shaped foam sheet. In this way, the resin foam sheet (single layer of foam) of production example (a) of Example 1 was obtained.
(Manufacturing example b)
A resin foam sheet was prepared in the same manner as in manufacturing example (a), except that the fatty acid compound "FA1" was included in the proportions shown in Table 1 below.

(Examples 2-4)
A single-layer foamed resin foam sheet was prepared in the same manner as in Example 1, except that the materials used were changed to those shown in Table 1 below.

(Example 5)
A three-layer resin foam sheet was prepared using the same resin composition as in Example 1, with non-foamed layers on both sides of the foamed layer.
Specifically, the resin foam sheet was manufactured as follows.
One of the two extruders connected to a combined die was supplied with raw material for forming the foamed layer, and the other extruder was supplied with raw material for forming the non-foamed layer. These two raw materials were co-extruded from a single die to produce a three-layer resin foam sheet consisting of a non-foamed layer, a foamed layer, and another non-foamed layer.
In Example 1, the amount of mixed butane used was 18 parts by mass, but in forming the foamed layer in Example 5, the amount of mixed butane used was changed to 6 parts by mass.
In the production example b of Example 5, the fatty acid compound (FA1) was added only to the non-foaming layer.

(Comparative Examples 1-4)
A single-layer foamed resin foam sheet was prepared in the same manner as in Example 1, except that the materials used were changed to those shown in Table 2 below.

(Preparation of glass for migration amount evaluation)
A glass for evaluating the amount of transfer was prepared by transferring a fatty acid compound and a surfactant from the resin foam sheet obtained by the above manufacturing method to glass using the procedure shown below.
Two 60 mm x 80 mm test sheets were cut from randomly selected locations on the resin foam sheets obtained by the manufacturing methods of the examples and comparative examples.
A glass plate measuring 50 mm x 75 mm was prepared, and this glass plate was sandwiched between two test sheets cut from a resin foam sheet to form a laminate as shown in Figure 5.
The laminate L was manufactured such that both the upper and lower surfaces of the glass plate G were completely covered with the test sheet S.
This laminate L was placed in a high-temperature, high-humidity chamber manufactured by ISUZU Corporation and held for 240 hours under conditions of 50°C and 90% RH, allowing the stearic acid amide and surfactant contained in the test sheet to transfer to the glass plate.
Furthermore, to prevent the test sheet from shifting inside the high-temperature, high-humidity chamber, a 2 kg iron weight W, measuring 50 mm wide x 100 mm long x 50 mm high, was placed on the laminated body L.
The weight W was placed on the laminate L such that its length was aligned with the longitudinal direction of the glass plate G, so that the load was applied to the entire surface of the glass plate G.
Then, the glass plate G after 240 hours was used as the glass for evaluating the amount of migration.

(Measurement method)
The amount of fat oxides and surfactants transferred was measured using the transfer amount evaluation glass obtained by the method described above.
Measurements were performed using the LC/MS/MS method described below.

(LC/MS/MS method)
The amount of fatty acid compound (stearic acid amide) and surfactant (sodium alkyl sulfonate) transferred to the transfer amount evaluation glass was measured by extracting the stearic acid amide and sodium alkyl sulfonate attached to the transfer amount evaluation glass with methanol solvent. A liquid chromatography-linear ion trap mass spectrometer (LC/MSn) was used for the measurement.
For measuring the amounts of stearic acid amide and sodium alkylsulfonate, the following LC/MSn instruments were used: the "UHPLC ACCELA" and the "Linear Ion Trap LC/MSn LXQ" manufactured by Thermo Fisher Scientific.
Furthermore, the amount of stearic acid amide was measured by the method shown below.

(Evaluation of the amount of fatty acid compound (stearic acid amide) transferred)
(Measurement method)
A glass sample for evaluating the amount of fluid transferred was placed in a 120 mm x 170 mm resealable bag (made by ASKUL), and then 5 mL of methanol was poured in before the bag was closed.
The resealable bag containing the glass for evaluating the amount of migration and methanol was shaken about 50 times, and the methanol inside the bag was collected.
The collected methanol was measured using the LC/MSn method described above.
Using a pre-prepared calibration curve, the concentration of stearamide in methanol (μg/mL) was determined from the peak area values on the chromatogram.
The calibration curve is created as follows:
After preparing an intermediate standard solution (methanol solution) of stearic acid amide at approximately 1000 ppm, calibration curve standards at 5 ppm, 2 ppm, 1 ppm, 0.5 ppm, and 0.2 ppm were prepared by further stepwise dilution with methanol.
Standard solutions for calibration curve creation at each concentration were measured under the following conditions, and the peak area values on the chromatogram for the monitor ion (m/z) n = 284.3 → n2 = 102.0 were obtained.
Each concentration and area value were plotted, and an approximate curve (quadratic curve) was obtained using the least squares method, which was used as the calibration curve for quantification.
The LC measurement conditions are as follows:
• Measurement device: UHPLC ACCELA (manufactured by Thermo Fisher Scientific)
• Column: Thermo Fisher Scientific Hypersil GOLD C18 1.9 μm (inner diameter 2.1 mm, length 100 mm)
Column temperature: 40°C
Mobile phase conditions: (A: 10 mM ammonium acetate / B: acetonitrile = 25 / 75)
・Amount: 0.3mL/min
Pump temperature: Room temperature (25°C)
・Injection volume: 2μL
Measurement time: 8 min
The MS measurement conditions are as follows:
• Measurement device: Linear Ion Trap LC/MSn LXQ (manufactured by Thermo Fisher Scientific)
Ionization method (ESI/positive):
Sheath Gas: 35 arb
• Auxiliary gas (AUX Gas): 10 arb
Sweep Gas: 0 arb
• Spray Voltage: 5.0kV
Capillary temperature: 350°C
Capillary voltage: 20V
Tube lens voltage: 100V
Monitoring Mass (m/z): Oleamide (n=282.2 → n2=265.1), Stearamide (n=284.3 → n2=102.0)

The concentration of stearic acid amide in methanol (μg/mL) obtained from the above measurement and the amount of methanol (5 mL) were combined to calculate the mass of stearic acid amide (μg) adhering to the glass used for migration evaluation.
Then, the amount of stearic acid amide deposited per unit area (fatty acid compound transfer amount (mg/ ^m² )) was calculated from the area of the glass used for migration evaluation (50 mm × 75 mm × 2 (both sides)).

(Evaluation of the amount of anionic surfactant (sodium alkyl sulfonate) transferred)
(Measurement method)
A glass sample for evaluating the amount of fluid transferred was placed in a 120 mm x 170 mm resealable bag (made by ASKUL), and then 5 mL of methanol was poured in before the bag was closed.
The resealable bag containing the glass for evaluating the amount of migration and methanol was shaken about 50 times, and the methanol inside the bag was collected.
The collected methanol was measured using the LC/MSn method described above.
Using a pre-prepared calibration curve, the sodium alkyl sulfonate (μg/mL) in methanol was determined from the peak area values on the chromatogram.
The calibration curve is created as follows:
After preparing an intermediate standard solution (methanol solution) of sodium alkyl sulfonate at approximately 1000 ppm, calibration curve standard solutions at 5 ppm, 2 ppm, 1 ppm, 0.5 ppm, and 0.2 ppm were prepared by further diluting with methanol.
Standard solutions for calibration curve creation at each concentration were measured under the following conditions, and the peak area values on the chromatogram for monitor ion (m/z) n = 291.3 were obtained.
Each concentration and area value were plotted, and an approximate curve (quadratic curve) was obtained using the least squares method, which was used as the calibration curve for quantification.
The LC measurement conditions are as follows:
• Measurement device: UHPLC ACCELA (manufactured by Thermo Fisher Scientific)
• Column: Thermo Fisher Scientific Hypersil GOLD C18 1.9 μm (inner diameter 2.1 mm, length 100 mm)
Column temperature: 40°C
Mobile phase conditions: (A: 10 mM ammonium acetate / B: acetonitrile = 25 / 75)
・Flow rate: 0.3mL/min
Pump temperature: Room temperature (25°C)
・Injection volume: 5μL
Measurement time: 3 min
The MS measurement conditions are as follows:
• Measurement device: Linear Ion Trap LC/MSn LXQ (manufactured by Thermo Fisher Scientific)
Ionization method (ESI/positive):
Sheath Gas: 30 arb
• Auxiliary gas (AUX Gas): 10 arb
Sweep Gas: 0 arb
• Spray Voltage: 5.0kV
Capillary temperature: 260°C
Capillary voltage: -20V
Tube lens voltage: -100V
• Monitoring Mass (m/z): Sodium alkylsulfonate (n = 291.3)

The concentration of sodium alkylsulfonate in methanol (μg/mL) obtained from the above measurement and the amount of methanol (5 mL) were combined to calculate the mass (μg) of sodium alkylsulfonate adhering to the glass used for migration evaluation.
Then, the amount of sodium alkyl sulfonate deposited per unit area (anionic surfactant transfer amount (mg/ ^m² )) was calculated from the area of the glass used for migration evaluation (50 mm × 75 mm × 2 (both sides)).

The degree of crystallinity of the polyethylene resin used in each example and comparative example was measured using a Hitachi High-Tech Science "DSC7000X, AS-3" differential scanning calorimeter.
Furthermore, the degree of crystallinity was measured using a resin foam sheet as a sample.
The specific measurement method was as described above.
These evaluation results are shown together in Tables 1 and 2.

As can be seen from the above results, the present invention provides a resin foam sheet that is less likely to cause deposits to form on the mating material.

1: Resin foam sheet, 2: Glass plate, 10: Foamed layer, 20: Non-foamed layer

Claims (7)

Laminating paper for glass plates,
It consists of an extruded foam sheet having at least one foam layer,
The extruded foam sheet has at least one surface composed of a resin composition containing polyethylene resin,
The resin composition constituting the surface of the extruded foam sheet contains one or more types of polyethylene resins,
The resin composition contains one type of polyethylene resin, and the density of that polyethylene resin is 928 kg/m³ ^or more and 933 kg/m³ or ^less , or the resin composition contains multiple types of polyethylene resins, and the density of the mixture of the multiple polyethylene resins is 928 kg/ ^m³ or more and 933 kg/ ^m³ or less.
Furthermore, the laminated paper is characterized in that the degree of crystallinity of the extruded foam sheet, which is determined by dividing the heat of fusion of the extruded foam sheet (J/g) by the theoretical heat of fusion of polyethylene perfect crystals, which is 285.7 J/g, is 44% or more and 58% or less. The laminated paper according to claim 1, wherein the extruded foamed sheet has a single-layer structure consisting only of the foamed layer. The laminated paper according to claim 1, wherein the extruded foamed sheet has a multilayer structure in which the foamed layer and other layers are laminated. The laminated paper according to claim 2 or 3 , wherein the resin composition contains an anionic surfactant. The laminated paper according to claim 2 or 3, wherein the density is 930 kg/ ^m³ or more and 932 kg/ ^m³ or less, and the degree of crystallinity is 45% or more and 51% or less. The laminated paper according to claim 2 or 3, wherein the degree of crystallinity is greater than 45% and less than or equal to 47%. The laminated paper according to claim 2 or 3, having a thickness of 0.2 mm or more and 2.0 mm or less.