JP7288323B2 - packaging sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a packaging sheet, and more particularly to a packaging sheet provided with a polyolefin resin foamed sheet.

Conventionally, polyolefin resin foam sheets have been widely used as packaging sheets and the like because they are flexible and have excellent cushioning properties compared to polystyrene resin foam sheets and polyester resin foam sheets.
Known packaging sheets of this type include a polyolefin resin foam sheet alone and a laminated sheet in which a polyolefin resin foam sheet is laminated with a covering sheet.

Electrical equipment, electronic equipment, electrical equipment members, electronic equipment members, and the like are known as objects to be packaged with this type of packaging sheet.
The packaging sheet is used for the purpose of protecting the packaged object from impact during storage and transportation, and is used to store members such as glass plates, semiconductor substrates, and metal plates that serve as substrates for flat display panels. In some cases, it is also used as interleaving paper to be inserted between members.

Such packaging sheets are sometimes required to have antistatic properties so that static electricity does not adhere to the objects to be packaged.
As a method for exhibiting antistatic properties in polyolefin-based resin foam sheets, polymer-type antistatic agents called high-molecular-weight antistatic agents and surfactants called low-molecular-weight antistatic agents are added to polyolefin-based resin foam sheets. A method of incorporating it into a material for forming a resin foam sheet is known.

Among them, surfactants exhibit antistatic properties by bleeding out onto the surface of the sheet, and therefore tend to adhere to the surface of the object to be protected (see Patent Document 1 below).
On the other hand, polymer-type antistatic agents often contain metal ions, and these metal ions may migrate to such packaged items and adversely affect them.

JP 2010-42556 A

In view of the above, packaging sheets are required to exhibit antistatic properties and to reduce migration of ingredients to packaged objects, but such requirements have not been satisfied.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a packaging sheet that has excellent antistatic properties and that has little migration of components to the packaged object.

As a result of intensive studies to solve the above problems, the present inventors found that a polyolefin-based resin foam sheet in which a donor-acceptor type antistatic agent is kneaded exhibits excellent antistatic properties and a metal The inventors have found that migration of ions and bleeding out are unlikely to occur, and have completed the present invention.

That is, in order to solve the above problems, the present invention is
To provide a packaging sheet provided with a polyolefin resin foam sheet in which a donor-acceptor type antistatic agent is kneaded, and the polyolefin resin foam sheet is exposed on at least one surface.

In a polyolefin resin foam sheet in which a donor-acceptor type antistatic agent is kneaded, the coexistence of a donor such as a boron compound and an acceptor such as a nitrogen compound facilitates the diffusion of holes and electrons. Therefore, good antistatic properties can be exhibited without using the action of metal ions such as sodium ions and lithium ions.
Also, a polyolefin resin foam sheet into which a donor-acceptor type antistatic agent is kneaded exhibits good antistatic properties without containing a compound that causes bleeding out, such as a surfactant.
Therefore, a packaging sheet having such a polyolefin-based resin foam sheet exposed on at least one surface can exhibit excellent antistatic properties while suppressing migration of components to the packaged item.

Schematic diagram showing one mode of use of the packaging sheet. BRIEF DESCRIPTION OF THE DRAWINGS The schematic sectional drawing of the sheet for packaging which concerns on one Embodiment of this invention. The schematic which showed other embodiment of the sheet for packaging.

The packaging sheet of the present invention will be described.
In the following, an embodiment of the present invention will be described by taking as an example a case where the packaging sheet is a single-layer sheet composed only of a polyolefin resin foam sheet, and both front and back sides are composed of a polyolefin resin foam sheet.
Moreover, the case where the polyolefin-based resin foam sheet is an extruded foam is exemplified below.
More specifically, in the following, a packaging sheet provided with a polyolefin resin foamed sheet formed by extruding and foaming a polyolefin resin composition containing a polyolefin resin is used as an electronic component bag or a glass plate interleaving paper. An embodiment of the present invention will be described while exemplifying a case of utilization.

FIG. 1 shows how the packaging sheet of this embodiment is used as a constituent material of a packaging bag 100 for housing a printed circuit board X1.
The packaging bag 100 of the present embodiment is composed of two packaging sheets, a rectangular front sheet 100a and a back sheet 100b having a larger area than the printed circuit board X1.
The packaging bag 100 of the present embodiment is a laminated product in which the front sheet 100a and the back sheet 100b are overlapped with their contours aligned and three-sided sealing is performed.
That is, the packaging bag 100 has a seal portion 101 where three of the four sides of the front sheet 100a and the back sheet 100b are adhered to each other, and the portion along the remaining one side is not adhered. has an opening 102 for inserting and removing the printed circuit board X1.

In the packaging bag 100, the front sheet 100a and the back sheet 100b may be made of a common sheet, or may be made of different sheets.
In the packaging bag 100 of this embodiment, both the front sheet 100a and the back sheet 100b are made of the same polyolefin resin foam sheet 1. As shown in FIG.

FIG. 2 shows a cross-sectional shape of a polyolefin resin foam sheet employed as the front sheet 100a and the back sheet 100b in this embodiment.
As shown in the figure, the polyolefin resin foam sheet 1 of this embodiment constitutes the inner surface of the packaging bag 100 and constitutes the first surface 1a in contact with the printed circuit board X1 and the outer surface of the packaging bag 100. and a second surface 1b.

The polyolefin resin foam sheet 1 of the present embodiment is composed of a polyolefin resin composition containing a polyolefin resin as a base polymer and an antistatic agent.

Examples of the polyolefin-based resin contained in the polyolefin-based resin foamed sheet 1 of the present embodiment include polyethylene-based resin, polypropylene-based resin, ethylene-α-olefin resin, and the like.
The polyolefin-based resin composition constituting the polyolefin-based resin foam sheet does not need to contain only one type of polyolefin-based resin, and may contain two or more types.
A polypropylene-based resin is preferable as the polyolefin-based resin to be contained in the polyolefin-based resin composition.

The polypropylene-based resin may be homopolypropylene (hPP), which is a homopolymer of propylene, or a copolymer containing propylene and a small amount of ethylene, butene-1, or the like.
The polypropylene-based resin is not particularly limited in tacticity, and may be isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), atactic polypropylene (aPP), or the like.
The copolymer may be random polypropylene (rPP) in which propylene and ethylene are randomly copolymerized.
The copolymer is a block polypropylene (bPP) in which a propylene-ethylene copolymer is dispersed to form a domain phase in a homopolypropylene matrix phase by introducing ethylene in the latter stage of the propylene polymerization reaction. may be

The block polypropylene may contain a propylene-ethylene copolymer in a proportion of 40% by mass or more to become rubber-like, and is called an olefinic thermoplastic elastomer (TPO). may be

The polypropylene-based resin may be one in which long chain branches are formed by chemical cross-linking, electron beam cross-linking, or the like, and may be referred to as high melt tension polypropylene (HMS-PP).

As the polypropylene resin contained in the polyolefin resin foam sheet 1, block polypropylene (bPP) and high melt strength polypropylene (HMS-PP) are preferable, and it is preferable to use a blend of both.
The mass ratio of block polypropylene (bPP) to high melt strength polypropylene (HMS-PP) (bPP:HMS-PP) is preferably 2:8 or more, more preferably 3:7 or more, and 4:6. It is particularly preferable that it is above.
The mass ratio (bPP:HMS-PP) is preferably 8:2 or less, more preferably 7:3 or less, and particularly preferably 6:4 or less.

The high melt tension polypropylene preferably exhibits a melt tension of 3 cN or more at 230°C.
The melt tension is more preferably 4 cN or more, particularly preferably 5 cN or more.
The melt tension is preferably 30 cN or less, more preferably 28 cN or less.

The melt tension can be obtained, for example, by the following method.
(Melt tension measurement method)
If the sample is a pellet, it is used as it is, and if it is a sheet such as a polyolefin resin foam sheet, the polyolefin resin foam sheet is put into a pelletizer (for example, Toyo Seiki Seisakusho Co., Ltd. "Hand Truda Model PM -1”), pelletized under the conditions of a cylinder temperature of 220° C. and a standby time of 2.5 minutes from sample filling to the start of extrusion.
Melt tension is measured using a twin-bore capillary rheometer Rheological 5000T (manufactured by Chiasto, Italy).
Specifically, after filling a measurement sample resin in a barrel with a diameter of 15 mm heated to the test temperature, preheating for 5 minutes, from the capillary die (diameter 2.0 mm, length 20 mm, inflow angle flat) of the above measurement device While extruding the string while keeping the piston descending speed (0.1546 mm/s) constant, the string was passed through a tension detecting pulley located 27 cm below the capillary die, and then the take-up roll was passed. , the winding speed is gradually increased to 8.7 mm/s at the initial speed and 12 mm/s at the acceleration, and the average of the maximum and minimum values immediately before the string is cut is taken as the melt tension of the sample. and
If there is only one maximum point in the tension chart, the maximum value is taken as the melt tension.

Polyolefin-based resins that are preferably contained in the polyolefin-based resin composition include low-density polyethylene resins other than the polypropylene-based resins described above.

Examples of the low-density polyethylene resin include linear low-density polyethylene resin (LLDPE) polymerized by a medium-low pressure method and low-density polyethylene resin (LDPE) in which long-chain branches are formed in the molecular structure by a high-pressure method. mentioned.
The low-density polyethylene resin (LDPE) preferably has a resin density of 910 kg/m ³ or more and 930 kg/m ³ or less.
The linear low-density polyethylene resin (LLDPE) preferably has a resin density of 910 kg/m ³ or more and 925 kg/m ³ or less.

The low-density polyethylene resin (LDPE) and the linear low-density polyethylene resin (LLDPE) preferably have a melt mass flow rate (hereinafter also referred to as "MFR") of 1 g/10 min or more and 10 g/10 min or less.
In this specification, unless otherwise specified, the MFR of the polymer type antistatic agent described later is also JIS K 7210: 1999 "Plastics - Melt mass flow rate of thermoplastics (MFR) and Melt Volume Flow Rate (MVR) Test Method B method (test temperature: 190°C, load: 21.18N).

As the donor-acceptor type antistatic agent to be contained in the polyolefin resin composition together with the polyolefin resin, for example, one composed of a combination of an organic boron compound and a basic nitrogen compound can be employed. .
The donor-acceptor type antistatic agent preferably has excellent compatibility with the polyolefin resin, and preferably has a certain length of alkyl chain.

The donor-acceptor type antistatic agent is preferably represented by the following general formula (1).

In the above formula (1), “R ¹ ” and “R ² ” are each independently “R ⁷ CO—OCH ₂ —” or “HOCH ₂ —”, and at least one of “R ⁷ CO—OCH ² —”, and “R ³ ” and “R ⁴ ” are each independently “CH ₃ —”, “C ₂ H ₅ —”, “HOCH ₂ —”, “HOC ₂ H ₄ —” or “HOCH ₂ CH(CH ₃ )—”, “R ⁵ ” is “—C ₂ H ₄ —” or “—C ₃ H ₆ —”, and “R ⁶ ” and Each “R ⁷ ” is independently an alkyl having 11 to 21 carbon atoms.

As the donor-acceptor type antistatic agent, one represented by the following general formula (2) may be used.

In the above formula (1), “R ¹ ” and “R ² ” are each independently “R ⁷ CO—OCH ₂ —” or “HOCH ₂ —”, and at least one of “R ⁷ CO—OCH ² —”, and “R ³ ” and “R ⁴ ” are each independently “CH ₃ —”, “C ₂ H ₅ —”, “HOCH ₂ —”, “HOC ₂ H ₄ —” or “HOCH ₂ CH(CH ₃ )—”, “R ⁵ ” is “—C ₂ H ₄ —” or “—C ₃ H ₆ —”, and “R ⁶ ” and Each “R ⁷ ” is independently an alkyl having 11 to 21 carbon atoms.

In addition, among those represented by the above general formulas (1) and (2), the donor-acceptor type antistatic agent in the present embodiment is represented by the molecular formula "C ₄₂ H ₈₁ O ₈ B". A combination of an organic boron compound represented by _{the molecular formula "C23H48ON2" and a basic nitrogen compound represented by the molecular formula "C42H81O8B " , or a} combination of the organic boron compound represented by the molecular formula " _C42H81O8B " and the molecular formula " _A combination with a basic nitrogen compound represented by " _nC23H47O2N " is preferred _.

The content of the donor-acceptor antistatic agent in the polyolefin resin composition is 0.1 when the total amount of all polyolefin resins contained in the polyolefin resin composition is 100 parts by mass. It is preferably at least 0.2 parts by mass, more preferably at least 0.3 parts by mass.
The content of the donor-acceptor antistatic agent in the polyolefin resin composition is 3.0 when the total amount of all polyolefin resins contained in the polyolefin resin composition is 100 parts by mass. It is preferably no greater than 2.8 parts by mass, and even more preferably no greater than 2.6 parts by mass.

Since the polyolefin resin foam sheet 1 of the present embodiment is produced by an extrusion foaming method, the polyolefin resin composition used in the extrusion foaming method contains components necessary for foaming in addition to the components described above. can be further included.
A foaming agent and a cell control agent can be mentioned as a component for this foaming.

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

When the mixed butane of isobutane/normal butane is used in this way, the isobutane suppresses the sudden escape of the blowing agent during the extrusion process.
On the other hand, since normal butane, which is highly compatible with polyolefin resins, suppresses an increase in open cell ratio, it is possible to obtain a polyolefin resin foamed sheet 1 with little shrinkage and excellent cushioning properties with a low open cell ratio. can.

The amount of the foaming agent used for extrusion foaming depends on the desired degree of foaming, but is usually 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the polyolefin resin.
Usually, the addition ratio of the foaming agent is in such a range because it is difficult to obtain sufficient foaming when the amount of the foaming agent is less than 5 parts by mass, and when it exceeds 25 parts by mass, the cell membrane is broken and a good polyolefin This is because there is a possibility that the resin foam sheet cannot be obtained.

In addition, as the cell adjusting agent for adjusting the cells formed by the foaming agent, inorganic powders such as talc and silica, polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate (sodium bicarbonate), which are also used as decomposition type foaming agents, may be used. ), azodicarboxylic acid amide, and the like.
These may be used alone or may be used in combination. The amount of the foam control agent to be added is preferably 0.5 parts by mass or less per 100 parts by mass of the polyolefin resin.

In addition to the above components, the polyolefin resin foam sheet 1 of the present embodiment may contain additives such as heat stabilizers, ultraviolet absorbers, antioxidants, colorants, etc., if necessary. good.

In addition to the polyolefin resin and the donor-acceptor type antistatic agent, the proportion of components contained in the polyolefin resin foam sheet 1 is preferably 10% by mass or less, and more preferably 5% by mass or less. preferable.
That is, the total ratio of the polyolefin resin and the donor-acceptor antistatic agent in the polyolefin resin composition constituting the polyolefin resin foam sheet 1 is preferably 90% by mass or more, and 95% by mass or more. It is more preferable to have

The density (apparent density) of the polyolefin resin foamed sheet 1 composed of the polyolefin resin composition as described above is not particularly limited as long as it exhibits the generally required cushioning properties. It is usually less than 150 kg/m ³ , preferably 100 kg/m ³ or less, and particularly preferably 70 kg/m ³ or less.
The reason why it is preferable to select such a density is that if the density is equal to or lower than the upper limit, the polyolefin resin foamed sheet 1 can be reliably provided with excellent flexibility and cushioning properties, and the density is equal to or higher than the lower limit. This is because the polyolefin-based resin foamed sheet 1 can exhibit excellent strength by being .
For this reason, the density of the polyolefin resin foamed sheet 1 is preferably 10 kg/m ³ or more, preferably 15 kg/m ³ or more.

The density of the polyolefin-based resin foam sheet 1 is measured by the method described in JIS K7222:1999 "Foamed plastics and rubbers-Determination of apparent density", specifically by the following method.
(Density measurement method)
A sample of 100 cm ³ or more is prepared from a polyolefin resin foam sheet, and after conditioning this sample for 16 hours in a JIS K7100: 1999 symbol 23/50, class 2 environment, the dimensions and mass are measured, Apparent density is calculated by the following formula.

Apparent density (g/cm ³ ) = sample mass (g)/sample volume (cm ³ )

For the dimension measurement of the sample, for example, "DIGIMATIC" CD-15 type manufactured by Mitutoyo Corporation can be used.

The thickness of the polyolefin resin foam sheet is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.3 mm or more.
The thickness of the polyolefin resin foam sheet is preferably 6 mm or less, more preferably 5 mm or less, and even more preferably 4 mm or less.

The thickness of the polyolefin resin foamed sheet 1 can be obtained, for example, as an average value of thicknesses measured at ten or more randomly selected measurement points.

The polyolefin resin foam sheet preferably has a basis weight of 10 g/m ² or more, more preferably 15 g/m ² or more, and even more preferably 25 g/m ² or more.
The basis weight of the polyolefin resin foam sheet is preferably 600 g/m ² or less, more preferably 500 g/m ² or less, and even more preferably 400 g/m ² or less.

The basis weight of the foamed polyolefin resin sheet can be measured by the method described in JIS P8124:2011 “Paper and paperboard—Method for measuring basis weight”.
Specifically, 10 samples of 100 cm ² or more are cut out, the mass and area of each sample are measured, and the mass and area can be obtained by the following equation.

Basis weight (g/m ² ) = 10000 x test piece mass (g)/test piece area (cm ² )

The polyolefin resin foam sheet preferably has a bleed-out amount of 0.3% by mass or less at least on the first surface 1a (the surface in contact with the package), and a bleed-out amount of 0.2% by mass or less. More preferably, the amount of bleeding out is 0.1% by mass or less.

The bleed-out amount of the polyolefin resin foamed sheet can be determined as follows.
A sample is cut into a size of 100 mm×100 mm, and the sample is placed in a thick chuck bag of 120 mm×170 mm.
20 ml of methanol is added thereto, the air is removed as much as possible, the zipper is closed, and the bag is shaken by hand about 100 times.
After shaking, the chuck is opened and the methanol is taken out into a beaker and heated in a constant temperature bath at 105° C. for 24 hours to evaporate to dryness.
After that, it is allowed to cool in a desiccator, and the mass of the evaporated and dried product returned to room temperature is weighed.
In principle, the measurement is performed with n=3.

It is preferable that the amount (total amount) of alkali metal ions and alkaline earth metal ions on at least the first surface 1a (the surface in contact with the object to be packaged) of the polyolefin resin foam sheet is 2 mg/m ² or less.
The amount of alkali metal ions and alkaline earth metal ions on the first surface 1a is more preferably 1 mg/m ² or less, more preferably 0.5 mg/m ² or less.

The amounts of alkali metal ions and alkaline earth metal ions in the polyolefin resin foam sheet can be determined as follows.
A sample is cut into a size of 100 mm×100 mm, and the sample is placed in a thick chuck bag of 120 mm×170 mm.
20 ml of ion-exchanged water is added thereto, the chuck is closed while air is removed as much as possible, the flask is held in a constant temperature bath at 60° C., and after 30 minutes has passed, it is shaken by hand 10 times.
After another 30 minutes, the sample was shaken 10 times by hand in the same manner. Measurement is performed under the measurement conditions.
(Measurement condition)
Observation direction: axial direction
Exposure time: 30 seconds
High frequency output: 1.20 kW
Carrier flow rate: 0.7 mL/min
Plasma flow rate: 10.0 mL/min
Auxiliary flow rate: 0.6mL/min

The polyolefin resin foam sheet preferably exhibits a constant surface resistivity at least on the first surface 1a (the surface in contact with the object to be packaged) even after wiping with ethanol.
Specifically, after wiping with ethanol, the surface resistivity measured under conditions of a temperature of 20° C. and a relative humidity of 60% RH is preferably 1×10 ⁸ Ω or more, more preferably 1×10 ⁹ Ω or more. and more preferably 1×10 ¹⁰ Ω or more.
The surface resistivity is preferably 1×10 ¹² Ω or less, more preferably 1×10 ¹¹ Ω or less.

The surface resistivity can be measured by the method described in JIS K6911:1995 "General Test Methods for Thermosetting Plastics".
That is, using a test device (ADVANTEST Co., Ltd. digital ultra-high resistance/micro current meter, model name "R3840" and resistivity chamber, model name "R12702A"), a sample taken from a polyolefin resin foam sheet , the electrode is crimped with a load of about 30 N, and the resistance value after charging at 500 V for 1 minute is measured and calculated by the following equation.
A sample has a width of 100 mm, a length of 100 mm, and a thickness (thickness of the polyolefin resin foam sheet as it is).
The measurement is carried out after conditioning for 24 hours or more in an environment with a temperature of 20±2° C. and a relative humidity of 65±5% RH, and the test environment is a temperature of 20±2° C. and a relative humidity of 65±5% RH.
The number of samples (n number) is 5, and in principle both the front and back surfaces are measured.
The surface of the sample is wiped with ethanol after conditioning.
Wiping with ethanol is performed as follows.
After conditioning, the entire surface of the 100 mm square sample to be measured is wiped several times with a paper wiper (for example, product name "Kimwipe") impregnated with a small amount of ethanol.
Surface resistivity is performed after 1 hour in the test environment after this wipe.

The surface resistivity of each sample is determined by the following formula, the measured values of all the samples are calculated and averaged, and the average value is taken as the surface resistivity of the polyolefin resin foam sheet.

ρs=(π(D+d)/(D−d))×Rs

ρs: Surface resistivity (MΩ)
D: Inner diameter of surface annular electrode (cm)
d: Outer diameter of the inner circle of the surface electrode (cm)
Rs: Surface resistance (MΩ)

The polyolefin-based resin foam sheet 1 in this embodiment may contain a small amount of a polymeric antistatic agent or a small amount of a surfactant within the range that exhibits the surface properties as described above.

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 copolymers, and quaternary antistatic agents such as polyethylene glycol methacrylate copolymers. Examples include ammonium salts, copolymers of olefinic blocks and hydrophilic blocks described in JP-A-2001-278985, and the like.
The content of the polymeric antistatic agent in the polyolefin resin foam sheet is preferably 1% by mass or less, more preferably 0.5% by mass or less, and 0.1% by mass or less. is particularly preferred.
It is particularly preferable that the polyolefin resin foam sheet of the present embodiment does not contain a polymeric antistatic agent.

Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.
The surfactant content in the polyolefin resin foam sheet is preferably 1% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.1% by mass or less. .
It is particularly preferable that the polyolefin resin foam sheet of the present embodiment does not contain a surfactant.

The polyolefin resin foam sheet 1 of the present embodiment can be used without distinguishing between the front and back surfaces, so that not only the first surface 1a but also the second surface 1b have the surface properties as described above. preferable.
However, since the second surface 1b does not come into contact with the printed circuit board X1, which is the object to be packaged, the packaging sheet (front sheet 100a, back sheet 100b) of the present embodiment is a polyolefin resin foam sheet 1 Either fiber sheet (paper, cloth, etc.), film (resin film, metal film, composite film, etc.), or resin foam sheet that does not contain a donor-acceptor type antistatic agent is laminated on one side of the It may have a multilayer structure.
That is, the packaging sheet in the present embodiment may be provided with a polyolefin resin foam sheet in which a donor-acceptor antistatic agent is kneaded so as to be exposed on at least one surface.

In the above description, the packaging bag 100 is exemplified as a mode of use of the packaging sheet, but the packaging sheet in this embodiment can also be used in other applications.
Another embodiment of the packaging sheet according to the present embodiment will be described with reference to FIG. 3 as an example.

The packaging sheet shown in FIG. 3 is a single-layer sheet composed only of the polyolefin-based resin foam sheet 1, and when a plurality of glass plates 2 are vertically laminated to form a laminate 10, adjacent glass plates It is used as interleaving paper by inserting it between 2.

The glass plate 2 in this embodiment is a glass plate for flat display panels such as plasma display panels and liquid crystal display panels.
The packaging sheet that constitutes the packaging bag 100 is used so that only one surface (first surface 1a) of both surfaces is in contact with the printed circuit board X1, which is the object to be packaged. In the packaging sheet shown, both the first surface 1a and the second surface 1b of the foamed polyolefin resin sheet 1 are contact surfaces that contact the glass plate 2, which is the object to be packaged.
Therefore, it is preferable that the packaging sheet used in this type of embodiment has a polyolefin resin foam sheet in which the donor-acceptor type antistatic agent is kneaded so that both surfaces thereof are exposed.

When polyolefin resin foam sheets are required to be exposed on both surfaces, the packaging sheet does not need to be composed of a single polyolefin resin foam sheet 1, and two polyolefin resin foam sheets 1 are directly connected to each other. Alternatively, it may be a laminated sheet laminated with another sheet interposed therebetween.
That is, in the packaging sheet, the first surface layer provided on one side and the second surface layer provided on the other side are each made of a polyolefin-based material in which a donor-acceptor type antistatic agent is kneaded. It may have a two-layer structure composed of a resin foam sheet, and three or more layers provided with one or two or more intermediate layers between the first surface layer and the second surface layer. and wherein each of the first surface layer and the second surface layer is composed of a polyolefin resin foam sheet in which a donor-acceptor type antistatic agent is kneaded. may

When the packaging sheet comprises a plurality of polyolefin resin foam sheets as described above, one polyolefin resin foam sheet has the same thickness and the content of the donor-acceptor type antistatic agent as the other polyolefin resin foam sheets. may be the same or different.

As described above, the polyolefin resin foam sheet 1 as described above is manufactured by an extrusion foaming method in the present embodiment.
Specifically, the polyolefin resin foam sheet 1 is produced by an extrusion step of continuously extruding and foaming the polyolefin resin composition into a sheet form from a circular die or the like mounted at the tip of an extruder to produce an extruded foam sheet. can go and manufacture.
In the extrusion process, since the donor-acceptor antistatic agent exhibits affinity for the polyolefin resin, the donor-acceptor antistatic agent is kneaded into the polyolefin resin foam sheet in a good dispersion state. state.

In the extrusion step in the present embodiment, the cylindrical foam continuously extruded from the circular die is cooled by blowing cooling air from the inside and outside immediately after extrusion, and the foam after air cooling is cooled. Secondary cooling is performed with additional cooling on the mandrel.
In the extrusion step, the tubular foam is taken up while being cut in the extrusion direction by a cutter provided downstream of the cooling mandrel.

In the extrusion process of the present embodiment, secondary cooling is performed using a cooling mandrel having an outer diameter larger than the diameter of the circular die.
Therefore, the secondary cooling is performed by bringing the outer peripheral surface of the cooling mandrel into sliding contact with the inner peripheral surface of the primarily cooled tubular foam.
In the secondary cooling, the primary cooled cylindrical foam is cooled and at the same time expanded in diameter by the cooling mandrel.
The foam cut by the cutter in the direction of extrusion as described above is expanded into a belt shape and then wound up to form the raw fabric roll.

In the present embodiment, in order to make the polyolefin resin foam sheet 1 exhibit excellent cushioning properties, the above-mentioned high melt tension polypropylene (HMS-PP) and block polypropylene (bPP) are used as polyolefin resins to be contained in the polyolefin resin composition. ), and preferably both of them, and the crystallinity is preferably lower than that of the polyolefin resin composition homopolypropylene (hPP).

The heat of crystal fusion of an ideal polypropylene crystal is 209 J/g, and the crystallinity of homopolypropylene (hPP) is usually 50% to 70%.
For the reasons described above, the polyolefin resin composition preferably has a crystallinity of 40% or less, more preferably 30% or less.
That is, the heat of crystallization of the polyolefin resin composition is preferably 83 J/g or less, more preferably 62 J/g or less.

The heat of crystallization of the polyolefin resin composition can be measured by the method described in JIS K7122:2012 "Method for measuring transition heat of plastics".
Specifically, it can be obtained as follows.
(Method for obtaining heat of crystallization)
Using a differential scanning calorimeter (for example, model name "DSC6220" manufactured by SII Nanotechnology Co., Ltd.), fill the bottom of an aluminum measurement container with about 6 mg of the sample so that there is no gap, and run a nitrogen gas flow rate of 20 mL / min. Then, the temperature was lowered from 30 ° C. to -40 ° C., held for 10 minutes, heated from -40 ° C. to 220 ° C. (1st Heating), held for 10 minutes, then cooled from 220 ° C. to -40 ° C. (Cooling), and held for 10 minutes. After holding for a minute, the temperature is raised from -40°C to 220°C (2nd heating) to obtain a DSC curve.
All temperature rises and falls are performed at a rate of 10° C./min, and alumina is used as a reference substance.
The amount of heat of crystallization is determined from the area of the crystallization peak observed during the cooling process.
The amount of heat of crystallization is determined using the analysis software attached to the device. can be calculated from the area of

In the present embodiment, in order to make the polyolefin resin foam sheet 1 exhibit excellent cushioning properties, the polyolefin resin foam sheet is quickly cooled to a crystallization temperature or lower by cooling with the cooling air or the cooling mandrel, and the inside is may be made to suppress the formation of polypropylene crystals.
The fact that the crystallization of the polyolefin resin foam sheet 1 is suppressed means that the heat of fusion in the "1st Heating" in the operation for obtaining the heat of crystallization is lower than the heat of fusion required in the "2nd Heating". can be confirmed by
The ratio (Qm1/Qm2) of the heat of fusion (Qm1) in the "1st heating" to the heat of fusion (Qm2) in the "2nd heating" of the polyolefin resin foam sheet 1 is preferably 0.9 or less.
More preferably, the ratio (Qm1/Qm2) is 0.8 or less.

The heat of fusion of the polyolefin resin foam sheet can be obtained using the analysis software attached to the apparatus in the same way as the heat of crystallization. It can be calculated from the area surrounded by the straight line connecting the points returning to the baseline and the DSC curve.

In the present embodiment, the case where the polyolefin resin foam sheet is produced by extrusion foaming is exemplified in that it is easy to prepare the polyolefin resin foam sheet into a suitable state as a packaging sheet as described above. The polyolefin resin foam sheet provided in the packaging sheet of the present invention may be produced by other manufacturing methods.

In this embodiment, a printed circuit board or a glass plate is mentioned as the object to be packaged with the packaging sheet. Examples of the object to be packaged include silicon wafers, hard disks, microprocessors, light-emitting diodes, and sapphire wafers. , disk substrates, IC chips, magneto-optical disks (MO), DVDs, BDs, various memories, liquid crystal filters, magnetoresistive heads for hard disks, CCDs, reticles, and other electric and electronic equipment members.
In addition, the article to be packaged may be an electrical or electronic device such as a personal computer, monitor, video recorder, smart phone, tablet, etc. in which these are incorporated.
That is, the use of the packaging sheet of the present invention is not particularly limited.
In addition, the packaging sheet of the present invention is not limited to the above examples in any way other than the intended use.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these.
(Example 1)
As an extruder, a tandem extruder in which the first-stage (upstream) extruder is a single-screw extruder with a diameter of 90 mm and the second-stage (downstream) extruder is a single-screw extruder with a diameter of 115 mm is used. A polypropylene resin foam sheet was produced.
A donor-acceptor type antistatic agent (organic A mixture of a boron compound and a basic nitrogen compound) is added at a rate of 0.5 parts by mass, and a cell control agent (talc-based cell control agent) is added at a rate of 0.2 parts by mass. prepared.
After supplying this blend to the hopper of an extruder with a diameter of 90 mm in the first stage and heating and melting at 200 ° C., butane (isobutane / Normal butane=35/65) was injected from the middle of the first stage extruder and melt-kneaded in the extruder.
The kneaded material obtained by melt-kneading was supplied to the second-stage extruder through a connecting pipe, and the temperature of the kneaded material was lowered to 170°C while continuing to knead the kneaded material inside the extruder. .
The temperature-lowered kneaded material was introduced into the atmosphere through an annular slit of a circular die with a bore diameter of 140 mm and a slit gap of 0.95 mm, which was connected to the tip of the extruder so that the extrusion rate was 98.5 kg/hour. The kneaded material was extruded into a shape to foam the kneaded material to form a cylindrical foam.
While expanding the diameter of the foam with a cooled mandrel (mandrel diameter: φ414 mm, length: 500 mm) and taking it out, air is blown to the outer surface of the foam using an air ring to cool the foam, A cutter was used to cut open the cooled foam to produce a polyolefin resin foam sheet.

( Reference example 2)
Using low density polyethylene (LDPE) instead of mixed polypropylene resin, changing the amount of donor-acceptor type antistatic agent from 0.5 parts by mass to 0.3 parts by mass, and extruding conditions A polyolefin-based resin foam sheet was produced in the same manner as in Example 1, except for the changes.

( Reference example 3)
A polyolefin resin foam sheet was produced in the same manner as in Reference Example 2, except that the amount of the donor-acceptor antistatic agent was changed from 0.3 parts by mass to 2.0 parts by mass.

(Comparative example 1)
Example 1 except that a polymeric antistatic agent was used instead of the donor-acceptor antistatic agent, and the amount of the polymeric antistatic agent added to 100 parts by weight of the mixed polypropylene resin was 8 parts by weight. A polyolefin resin foam sheet was produced in the same manner as in the above.

(Comparative example 2)
Except that a surfactant (stearic acid monoglyceride) was used instead of the donor-acceptor antistatic agent, and that the amount of the surfactant was 1.5 parts by mass with respect to 100 parts by mass of low-density polyethylene (LDPE). A polyolefin resin foam sheet was produced in the same manner as in Example 2.

(Comparative Example 3)
Comparative example except that the surfactant was changed from stearic acid monoglyceride to alkyldiethanolamide, and the amount of surfactant per 100 parts by mass of low-density polyethylene (LDPE) was changed from 1.5 parts by mass to 3.4 parts by mass. A polyolefin resin foam sheet was produced in the same manner as in 2.

The physical properties of the obtained polyolefin resin foamed sheet are shown in the table.
(Physical property evaluation items)
Thickness: thickness of polyolefin resin foam sheet Basis weight: thickness of polyolefin resin foam sheet Surface resistivity measured under conditions Bleed-out amount: Bleed-out amount on the surface of the polyolefin resin foam sheet Metal ion amount: Total amount of alkali metal ions and alkaline earth metal ions on the surface of the polyolefin resin foam sheet

From the above results, it can be concluded that providing a packaging sheet with a polyolefin-based resin foam sheet in which a donor-acceptor type antistatic agent is kneaded works effectively to reduce the transfer of components to the package. I understand.
That is, from the above, it can be seen that the packaging sheet of the present invention has little transfer of components to the packaged article and is excellent in antistatic properties.

Claims (2)

Polypropylene-based resin foam containing high melt tension polypropylene (HMS-PP) having a melt tension of 3 cN or more and 30 cN or less at 230° C. and block polypropylene (bPP), and in which a donor-acceptor type antistatic agent is kneaded. equipped with a seat
The content of the antistatic agent contained in the polypropylene resin foam sheet is 0.1 part or more and 3 parts or less with respect to 100 parts by mass of the polypropylene resin contained in the polypropylene resin foam sheet. ,
In the polypropylene resin foam sheet, the mass ratio of the block polypropylene (bPP) to the high melt strength polypropylene (HMS-PP) (bPP:HMS-PP) is 4:6 or more and 6:4 or less,
A packaging sheet provided with the foamed polypropylene resin sheet exposed on at least one surface. The polypropylene resin foam sheet is composed of a polypropylene resin composition containing a polypropylene resin containing the high melt strength polypropylene (HMS-PP) and the block polypropylene (bPP), and the antistatic agent. ,
The crystallinity of the polypropylene-based resin composition is 40% or less,
The packaging sheet according to claim 1.

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