KR20170130450A - Method for producing polyethylene-based resin extruded foamed sheet, polyethylene-based resin-extruded foamed sheet and diaper for glass plate using the same - Google Patents

Abstract

A method for producing a polyethylene resin extruded foamed sheet by extruding and expanding a foamable molten resin composition obtained by kneading a low density polyethylene, a physical foaming agent and an antistatic agent, wherein the foamed sheet has a thickness in the range of 0.05 to 0.5 mm, A method of producing a polyethylene-based resin extruded foam sheet characterized by using a high-molecular-weight antistatic agent having a melting point difference in a range of -10 to +10 DEG C with a low-density polyethylene and having a melt flow rate of 10 g / / RTI > As a result, even though the thickness is very thin, it is possible to provide a high-quality, high-strength, and buffering property that prevents or suppresses the occurrence of small holes or through holes even in the continuous production of the medium- A novel polyethylene-based resin extruded foam sheet suitable as a separator for a glass plate can be obtained.

Description

Method for producing polyethylene-based resin extruded foamed sheet, polyethylene-based resin-extruded foamed sheet and diaper for glass plate using the same

The present invention relates to a process for producing a novel polyethylene-based resin extruded foamed sheet, a novel polyethylene-based resin-extruded foamed sheet and a sheet for a glass plate using the same.

A polyethylene-based resin-extruded foam sheet (hereinafter also referred to as a foam sheet) is excellent in antistatic function, flexibility and buffering property to prevent damage and breakage of the article to be wrapped, and therefore can be used as a packaging material for household appliances, Has been widely used. In addition, with the recent development and demand for thin type TVs and the like, it is possible to prevent the surface of the glass substrate from being damaged when the glass substrate for an image display device such as a liquid crystal display, a plasma display or an electroluminescence display is packed or transported A foaming sheet having an antistatic property is used as a separator disposed between the glass plates (Patent Document 1, Patent Document 2)

Up to now, various thicknesses have been developed as glass plates for image display devices such as liquid crystal panels, but in recent years, very thin glass plates having a thickness of about 0.5 mm or less have been produced in terms of weight reduction, energy saving, and production cost . If a thick foamed sheet having a thickness of about 1 mm to 2 mm is used as a separator of such a thin glass plate, not only the stacking efficiency is lowered but also the thickness of the separator becomes excessively thick with respect to the glass plate, The glass plate might be broken.

For this reason, development of a foaming sheet having a thin thickness as a separator corresponding to a thin glass plate is progressing. However, if a foaming sheet having a small thickness is to be produced, a problem that a small hole or a through hole is liable to be generated in the foaming sheet happened.

In order to cope with this problem, the inventors of the present invention first developed a polyethylene resin extruded foamed sheet having an average thickness of 0.5 mm or less by using a specific foam modifier or the like (Patent Document 3, Patent Document 4).

These polyethylene-based resin-extruded foamed sheets have high quality, which prevents or suppresses the occurrence of small holes and through holes even when the average thickness is 0.5 mm or less, and has excellent antistatic performance and buffering properties.

Japanese Patent Application Laid-Open No. 2007-262409 Japanese Patent Application Laid-Open No. 20-20666 Japanese Patent Application Laid-Open No. 2014-43553 International Publication No. 2014/030513

The polyethylene-based resin-extruded foamed sheet can be said to be suitable as a separator of a thin glass plate. In addition, even in continuous production over a long period of 2 to 7 days or more, occurrence of small holes, through holes and the like is prevented / There is a strong demand for the development of a polyethylene resin extruded foam sheet which exhibits high quality and excellent antistatic performance.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a high quality, high strength, and a buffering property which are prevented or suppressed from occurring in small holes or through holes even in continuous production in the medium and long term, The present invention also provides a novel polyethylene-based resin foam sheet and a glass sheet for a glass plate using the novel polyethylene-based resin foam sheet.

The present invention provides a process for producing a novel polyethylene-based resin extruded foam sheet described below, a novel polyethylene-based resin-extruded foam sheet, and a sheet for a glass plate using the same.

A method for producing a polyethylene resin extruded foamed sheet by extruding and expanding a foamable molten resin composition containing low density polyethylene, a physical foaming agent and an antistatic agent, wherein the foamed sheet has a thickness in the range of 0.05 to 0.5 mm, And a high-molecular-weight antistatic agent having a melting point difference from the low-density polyethylene as an inhibitor in the range of -10 to + 10 ° C and a melt flow rate of 10 g / 10 min or more is used. Way.

&Lt; 2 > The method according to < 1 &

Wherein the polymeric antistatic agent has a melting point of 120 占 폚 or less.

&Lt; 3 > The method according to < 1 > or < 2 &

Wherein the ratio of the melt flow rate of the low density polyethylene to the melt flow rate of the high molecular weight antistatic agent (melt flow rate of the low density polyethylene / melt flow rate of the high molecular weight type antistatic agent) is 2 or less. Way.

&Lt; 4 > A method according to any one of < 1 > to < 3 &

Wherein the polymeric antistatic agent is blended in an amount of 3 to 25 parts by mass based on 100 parts by mass of the low-density polyethylene.

<5> A low-density polyethylene resin extruded foamed sheet containing an antistatic agent and a base resin having a low density polyethylene, the extruded foam sheet having a thickness within a range of 0.05 mm to 0.5 mm and an apparent density within a range of 20 to 450 kg / Is a high molecular weight type antistatic agent having a melting point difference from low-density polyethylene of -10 占 폚 to +10 占 폚 and a melt flow rate of 10 g / 10 min or more.

&Lt; 6 > A glass sheet for a glass plate comprising a polyethylene resin extruded foam sheet according to < 5 >.

(Effects of the Invention)

According to the manufacturing method of the present invention, it is possible to provide a high-quality, low-thickness and excellent antistatic performance that prevents or suppresses the occurrence of small holes or through holes in continuous production over a long period of time over several days as well as a short- A polyethylene-based resin foam sheet can be obtained.

In addition, the novel polyethylene-based resin foam sheet according to the present invention is of high quality, which prevents or suppresses the occurrence of small holes or through-holes even though the thickness is extremely small, and exhibits sufficient antistatic performance.

Therefore, the novel polyethylene-based resin foam sheet of the present invention is suitable for use in applications in which an antistatic function or the like is strongly required, particularly in the transporting and packing of thin glass plates for image display devices such as liquid crystal displays, plasma displays, and electroluminescence displays The demand for glass plates for preventing damage is widely expected.

Further, the novel polyethylene-based resin foam sheet of the present invention can be continuously produced over a medium-to-long term, and is a foam sheet which is industrially very high production efficiency.

The method for producing a polyethylene-based resin extruded foam sheet (hereinafter, simply referred to as a foam sheet) of the present invention comprises extruding and expanding a foamable molten resin composition containing low-density polyethylene, a physical foaming agent and an antistatic agent to produce a polyethylene- Wherein the thickness of the foam sheet is in the range of 0.05 to 0.5 mm and the difference in melting point from the low density polyethylene as the antistatic agent has a melting point in the range of -10 to +10 DEG C and the melt flow rate is 10 g / And a polymer type antistatic agent is used.

(Production method of foam sheet)

In the method for producing a foamed sheet of the present invention, an additive such as low density polyethylene, an antistatic agent and an air bubble adjusting agent, which is a material for forming a foam sheet, is added to an extruder and heated and kneaded at about 200 캜 to obtain a molten resin composition . Subsequently, the physical foaming agent is pressed into the molten resin composition and kneaded to obtain a foamable molten resin composition in the extruder. Subsequently, the foamable molten resin composition is cooled to a temperature suitable for foaming.

Here, the proper foaming temperature of the expandable molten resin composition is a temperature at which the foam layer can be easily obtained, and it is preferably in the range of [melting point + 0 deg. C] - [melting point + 15 deg. C] of low density polyethylene, Melting point + 2 占 폚] to melting point + 10 占 폚.

Then, the foamable molten resin composition is introduced into an annular die, extruded from the die end lip portion into the atmosphere to foam the expandable molten resin composition to produce a tubular extruded foam, and the tubular extruded foam is expanded to a mandrel ), And the foam sheet is cut along the extrusion direction while being acquired.

(Material for forming foam sheet)

In the production process of the present invention, a foamable molten resin composition containing low density polyethylene, an antistatic agent, a physical foaming agent, a foam modifier and other additives as described above is formed by extrusion foaming. Hereinafter, the materials used for forming the foam sheet will be described in detail.

(Low density polyethylene)

As the low-density polyethylene, polyethylene having a long-chain branch structure and a density of 900 kg / m 3 or more and less than 930 kg / m 3 can be used. The resin exhibits good foamability, and the obtained foam sheet is excellent in buffering characteristics. From this viewpoint, the density of the low-density polyethylene is preferably 910 kg / m 3 or more and 925 kg / m 3 or less. The melting point of the low-density polyethylene is preferably 100 to 120 ° C, more preferably 105 to 115 ° C. The melting point of the low-density polyethylene can be measured by a method in accordance with JIS K7121-1987. Concretely, heat treatment is performed by heating and melting by raising the temperature from 40 占 폚 to 200 占 폚 at 10 占 폚 / min by using a differential scanning calorimeter, maintaining the temperature at 10 占 폚 for 10 minutes, cooling to 40 占 폚 at 10 占 폚 / The melting peak is obtained by raising the temperature from 40 ° C to 200 ° C at 10 ° C / min. The melting point is the temperature at the peak of the largest melting peak among the obtained melting peaks.

The melt flow rate of the low-density polyethylene is preferably 5 g / 10 min or more, more preferably 10 g / 10 min or more, still more preferably 15 g / 10 min or more. The melt flow rate is a value measured at a temperature of 190 占 폚 under a load of 2.16 kg in accordance with JIS K7210-1: 2014.

When the low-density polyethylene is a mixture of two or more kinds, the melting point and the melt flow rate of the mixture are specified by the melting point and the melt flow rate measured for the melt-kneaded in advance in the extruder.

Examples of commercially available low-density polyethylene that is preferably used in the present invention include "NUC8321" (melt flow rate: 1.9 g / 10 min., Melting point 112 캜) manufactured by NUC Corporation.

The low-density polyethylene may contain other thermoplastic resins, such as polyethylene resins, polypropylene resins and polystyrene resins, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer, and the like, to the extent that the objects and effects of the present invention are not impaired. An elastomer and the like.

The other polyethylene resin is a resin having an ethylene component unit of 50 mol% or more. Specific examples thereof include high density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, Ethyl acrylate copolymer, and mixtures of two or more thereof.

The amount of the resin or elastomer other than low-density polyethylene is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, based on 100 parts by mass of the low-density polyethylene. The resin and the elastomer other than the low-density polyethylene may be kneaded together with the low-density polyethylene to obtain a base resin constituting the expandable molten resin composition.

(Antistatic agent)

In the production method of the present invention, it is necessary to use a high molecular weight antistatic agent as an antistatic agent. The polymer type antistatic agent has a melting point difference from the low-density polyethylene of -10 ° C to + 10 ° C and a melt flow rate of 10 g / 10 min or more.

When such a polymeric antistatic agent is used, it is possible to obtain a polyethylene-based resin extruded foam sheet exhibiting high quality and excellent antistatic function that prevents or suppresses occurrence of small holes and through holes even in continuous production over a long period of time.

The precise reason for this is not clear at this point, but as described later, the polymeric antistatic agent used in the present invention has a low melting point and a high melt flow rate, so that the polymeric antistatic agent having a high melting point It is believed that the precipitation of crystals, which is a cause of generation of small holes or through holes in the substrate, is prevented or suppressed.

(Melting point of low density polyethylene - [melting point of polymeric antistatic agent]) of the melting point of the polymeric antistatic agent used in the present invention and the melting point of the low density polyethylene is in the range of -10 ° C to + 10 ° C, Also, in continuous operation, the melting point difference is preferably -8 ° C to + 8 ° C, more preferably -7 ° C to + 7 ° C, from the viewpoint of obtaining a high-quality one. The melting point of the polymeric antistatic agent is preferably 125 캜 or lower, and more preferably 120 캜 or lower. On the other hand, the lower limit of the melting point is about 100 캜.

The melting point of the polymer-type antistatic agent is determined by the same method as that of the low-density polyethylene.

For the same reason, the polymer type antistatic agent used in the present invention has a melt flow rate of 10 g / 10 min or more, preferably 20 g / 10 min or more, more preferably 30 g / 10 min or more. On the other hand, if the upper limit of the above range is about 100 g / 10 min, the antistatic agent is preferable because it has excellent fluidity and exhibits antistatic performance more effectively. The melt flow rate of the polymeric antistatic agent is a value measured at a temperature of 190 占 폚 under a load of 2.16 kg in accordance with JIS K7210-1: 2014.

The ratio of the melt flow rate of the low density polyethylene B (melt flow rate of the low density polyethylene / melt flow rate of the high molecular weight antistatic agent) to the melt flow rate of the polymer type antistatic agent is preferably 2 or less, more preferably 1 or less , And more preferably 0.8 or less. When the ratio is in the above range, the polymeric antistatic agent is dispersed in the form of a net or a layer so that excellent antistatic performance can be exhibited more effectively. On the other hand, the lower limit of the ratio is preferably about 0.01 or more.

As the polymer type antistatic agent preferably used in the present invention, a block copolymer of polyether and polyolefin is used. Commercially available products include PELECTRON LMP (melting point 114 DEG C, melt flow rate 30 g, manufactured by Sanyo Chemical Industries, Ltd.) / 10 minutes).

The number average molecular weight of the polymeric antistatic agent used in the present invention is preferably 2,000 or more, more preferably 2,000 to 100,000, and still more preferably 5,000 to 80,000. The upper limit of the number average molecular weight of the polymeric antistatic agent is about 500,000. By setting the number average molecular weight of the polymeric antistatic agent within the above range, the antistatic performance is more stably expressed regardless of the environment such as humidity.

The number average molecular weight is determined using high temperature gel permeation chromatography. For example, when the polymeric antistatic agent is polyetheresteramide or polyether as a main component, orthodichlorobenzene is used as a solvent to adjust the concentration of the sample to 3 mg / ml, and polystyrene as a reference material at a column temperature of 135 캜 It is the value measured in the condition. The kind of the solvent and the temperature of the column are appropriately changed according to the type of the high molecular weight antistatic agent.

(Mixing amount of antistatic agent)

The blending amount of the polymeric antistatic agent in the foam is preferably 2 to 30 parts by mass based on 100 parts by mass of the low-density polyethylene constituting the foam in view of obtaining a foam sheet having a sufficient antistatic property and a high quality, Is 3 to 25 parts by mass, more preferably 5 to 20 parts by mass.

(Surface resistivity of foam sheet)

In the method of the present invention, the surface resistivity of the surface of the foam sheet can be adjusted to 1 × 10 ⁷ to 1 × 10 ¹³ Ω by adding the polymeric antistatic agent. If the surface resistivity is within the above range, the foam sheet exhibits sufficient antistatic properties. From the above viewpoint, the surface resistivity is preferably 5 x 10 ¹² ? Or less, and more preferably 1 x 10 ¹² ? Or less.

The surface resistivity in the present invention is measured according to JIS K6271: 2008 after the state of the following test pieces is adjusted. Specifically, the state of the test piece is adjusted by leaving a test piece (100 mm long × 100 mm × thickness: measured object thickness) cut out from a foam sheet as a measurement object for 36 hours under an atmosphere of a temperature of 20 ° C. and a relative humidity of 30%. Subsequently, a voltage is applied to the test piece under the condition of an applied voltage of 500 V under an atmosphere of a temperature of 20 캜 and a relative humidity of 30%. Voltage application is started, and the surface resistivity after 1 minute is measured.

(Physical foaming agent)

In the method of the present invention, a low-density polyethylene is fed to an extruder, heated and kneaded to make a molten resin, and then a physical foaming agent is pressed and kneaded to form a foamable molten resin composition. The physical foaming agent may be an organic or inorganic physical foaming agent. Examples of the organic physical foaming agent include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane and isohexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; There may be mentioned fluorinated hydrocarbons such as chlorinated hydrocarbons, 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane, ethers such as dimethyl ether and methyl ethyl ether, and alcohols such as methanol and ethanol .

Examples of the inorganic physical foaming agent include oxygen, nitrogen, carbon dioxide, air, and water. These physical foaming agents can be used by mixing two or more kinds thereof. Among them, an organic physical foaming agent is preferable from the viewpoint of foaming property, and it is particularly preferable to use, as the main component, n-butane, isobutane, or a mixture thereof.

The amount of the physical foaming agent to be added is adjusted in accordance with the kind and the apparent density of the intended foam sheet. For example, when a foamed sheet having an apparent density of 20 to 450 kg / m 3 is obtained by using a physical foaming agent such as a butane mixture of 30% by weight of isobutane and 70% by weight of n-butane as a physical foaming agent, Is 4 to 35 parts by mass, preferably 5 to 30 parts by mass, and more preferably 6 to 25 parts by mass based on 100 parts by mass of the resin.

(Foam modifier)

In the method of the present invention, the foam modifier may be supplied to the extruder together with the low-density polyethylene. An inorganic powder or a chemical foaming agent may be used as the air bubble adjusting agent. Examples of the inorganic powder include talc, zeolite, silica, calcium carbonate, and the like.

Examples of the chemical foaming agent include azodicarbonamide, hydrazodicarbonamide, azobisisobutyronitrile, sodium hydrogencarbonate (sodium bicarbonate), or a mixture of sodium bicarbonate and citric acid mono alkali metal salts such as citric acid-sodium Based chemical foaming agent, and the like. Of the above-mentioned chemical foaming agents, a bioretention-citric acid-based chemical foaming agent is preferable in order to obtain a foam sheet having a small cell diameter and excellent buffer properties.

Particularly, the use of a neutral-citric acid type chemical foaming agent having an average particle diameter of 3 to 8 탆 is preferable because the occurrence of through-holes passing through the foam sheet can be prevented more effectively. From this viewpoint, it is more preferable that the average particle diameter is 4 to 7 mu m. The maximum particle diameter of the chemical foaming agent is preferably 100 m or less, more preferably 80 m or less. The average particle diameter means a median diameter (d50) measured by laser diffraction scattering particle size distribution measurement. Further, the maximum particle diameter of the chemical foaming agent was observed by a light microscope or the like with a particle group of about 1 to 3 mg randomly sampled from a chemical foaming agent, and the major axis diameter of the particles having the longest major axis diameter Maximum particle diameter shall be used.

The amount of the foam modifier added is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the base resin constituting the foamable molten resin composition. When the amount added is within the above range, the bubble diameter can be easily adjusted to a desired range.

(Other additives)

In the method of the present invention, various additives may be added in addition to the above components within a range not to impair the effects of the present invention. Examples of the additives include antioxidants, heat stabilizers, endurance agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, colorants and the like.

In the production method of the present invention, the reason why the occurrence of small holes or through holes is prevented or suppressed even in continuous continuous production for a long period of time, and a foam sheet capable of sufficiently exhibiting antistatic performance is obtained is not clear at this point, .

Conventionally, in a polyethylene resin extruded foamed sheet containing an antistatic agent of this kind, as the antistatic agent, as shown in a later comparative example, a polymer having a melting point difference of +20 DEG C or more and a melting point of 135 DEG C An antistatic agent is used. When such a conventional polymeric antistatic agent is used, since the temperature in the extruder is maintained at a high temperature of about 200 DEG C or higher as described above, the polymeric antistatic agent is completely melted in the foamable molten resin composition to form an unmelted high molecular weight antistatic agent Crystals are not precipitated.

However, when the foamable molten resin composition is introduced into the annular die as described above, it is cooled to a temperature suitable for foaming, and specifically cooled to about 120 캜 (melting point of the low density polyethylene resin + about 10 캜 or less). Since the conventional polymeric antistatic agent has a temperature of about 135 캜, it is considered that under such a cooling temperature, a part of the polymeric antistatic agent which has been melted in the extruder is crystallized and precipitated.

When the expandable molten resin composition containing the precipitated crystals is extruded in the annular die, the precipitated crystals start to stick to the wall surface in the annular die. In the initial stage (several hours), the retention amount of the residual crystals is small, so the influence on the surface of the foam is small. However, in the case of continuous production for two days, for example, The retention amount or deposition amount of the residual crystals drastically increases, and eventually a small hole or a through hole is formed in the foam sheet due to contact with or falling on the surface of the foam, and a high-quality foam sheet can not be obtained.

On the other hand, in the present invention, since a high-molecular weight antistatic agent having a melting point difference within a range of -10 ° C to + 10 ° C and a melt flow rate of 10 g / 10 min or more is used as an antistatic agent in a low-density polyethylene- In the extruder, as in the conventional polymeric antistatic agent, it is completely melted in the foamable molten resin composition and crystals of the unmelted polymeric antistatic agent are not precipitated.

The foamable molten resin composition is cooled to a temperature suitable for foaming as described above, and specifically cooled to a melting point + 10 占 폚 of, for example, 120 占 폚 of a low-density polyethylene-based resin. Here, since the polymeric antistatic agent used in the present invention has a melting point difference in the range of -10 DEG C to + 10 DEG C with respect to the low-density polyethylene, under such a cooling temperature, completely melted in the annular die as in the extruder It is considered that the crystallization of the polymer type antistatic agent of the present invention is prevented or suppressed.

Therefore, in the present invention, although the thickness is thin, unlike the case of using the conventional polymeric antistatic agent, it is difficult to obtain a polymeric antistatic agent for a long period of time, It is possible to obtain a foam sheet having a high quality which is prevented and suppressed from occurring, and which has excellent strength and buffering property and which sufficiently exhibits antistatic performance.

As described above, the method of producing a foamed sheet of the present invention is excellent in continuous productivity because it is prevented and suppressed in the generation of small holes and through holes, not only for a short period of several hours but also for a medium period of several days. Therefore, in the production of the foamed sheet of the present invention, the foam sheet can be wound in a roll shape having a length of 100 m or more, preferably 300 m or more at the time of manufacturing, though it differs depending on the thickness and width direction.

On the other hand, in the conventional production method, when continuous production is carried out over a medium period of several days, that is, several days, defects of small holes or through holes may occur in the foam sheet. In this case, It is necessary to take up the foam sheet again in the form of a roll after removing the portion, and the production efficiency is remarkably lowered.

From the above viewpoint, in the present invention, the smaller the number of through holes having a diameter of 1 mm or more present in the polyethylene-based resin extruded foam sheet, the more preferable. Concretely, it is preferable that the number of through holes of 1 mm or more occurring in 1 hour after 2 days or 7 days from the start of production is less than 3.

(Thickness of foam sheet)

The thickness (average thickness) of the foam sheet obtained by the production method of the present invention is 0.05 mm or more and 0.5 mm or less. The lower limit of the average thickness is preferably 0.07 mm, more preferably 0.1 mm, and still more preferably 0.15 mm from the viewpoints of buffering property and usability as a separator. On the other hand, the upper limit of the average thickness is preferably 0.4 mm, more preferably 0.35 mm, and still more preferably 0.3 mm.

The average thickness of the foamed sheet can be measured using an off-line thickness measuring instrument TOF-4R manufactured by YAMAHA CHEMICAL INDUSTRIES, LTD. First, the entire thickness of the foam sheet is measured at intervals of 1 cm. Based on the thickness of the foam sheet measured at intervals of 1 cm, the arithmetic mean thickness of the entire width is obtained. The foam sheet to be used for the measurement is conditioned under conditions of a temperature of 23 ± 5 ° C and a relative humidity of 50% for 24 hours or more.

(Apparent density of foam sheet)

The apparent density of the foam sheet obtained by the production method of the present invention is preferably in the range of 20 to 450 kg / m 3. If the apparent density is within the above range, it is preferable that the packaging material such as paperboard is excellent in bufferability. From this viewpoint, the apparent density is more preferably 30 to 300 kg / m 3, and more preferably 50 to 200 kg / m 3.

Further, the apparent density of the foam sheet can be obtained by dividing the weight per unit area of the foam sheet (g / m 2) by the average thickness of the foam sheet, and by unit conversion into [kg / m 3].

The ratio of the diameter of the discharge port of the annular die to the diameter of the mandrel (blow-up ratio: diameter of the mandrel / diameter of the lip of the annular die) is preferably 2.2 to 3.8. Within the above range, there is no waving phenomenon in the circumferential direction due to foaming, which is preferable because the thickness precision is excellent and the bubble is prevented from being excessively flattened in the width direction to obtain a good foam sheet.

(Foam sheet)

The novel polyethylene-based resin extruded foamed sheet according to the present invention is of high quality, which prevents or suppresses the occurrence of small holes and through-holes, and exhibits sufficient antistatic performance even though the thickness is extremely small as described above.

Therefore, the novel polyethylene-based resin extruded foamed sheet of the present invention is suitable for use in fields in which an antistatic function or the like is strongly demanded, and particularly when a thin glass sheet for image display devices such as a liquid crystal display, a plasma display and an electroluminescence display is transported or packed Which is widely used as a glass sheet for preventing the glass sheet from being damaged. Further, it can be continuously produced over a medium to long term, and is a foam sheet which is industrially very high production efficiency.

Example

Hereinafter, the present invention will be described in more detail in the following Examples and Comparative Examples. However, the present invention is not limited to the embodiments.

[Low density polyethylene]

Table 1 shows the low-density polyethylene used in Examples and Comparative Examples.

The antistatic agents used in Examples and Comparative Examples are shown in Table 2.

[Bubble Conditioning Agent]

A foam stabilizer used in Examples and Comparative Examples was a mixture of sodium hydrogen carbonate and citric acid-sodium in a weight ratio of 1: 1, and a chemical foaming agent having an average particle diameter (d50) of 6 mu m and a maximum particle diameter of 30 mu m was used.

[Device]

As the foam sheet manufacturing apparatus, a first extruder (tandem extruder) connected with an extruder having a barrel inner diameter of 115 mm for forming a foam layer and an extruder having a barrel inner diameter of 150 mm on the downstream side thereof was used. In addition, temperature control of the lip part mold of the die was performed for each of the divided parts by dividing the lip part mold into eight parts.

Examples 1 to 3, Comparative Examples 1 to 5

The low density polyethylene resin, the antistatic agent and the cell modifier shown in Table 3 were supplied to the raw material inlet of the extruder in the form shown in Table 3 and heated and kneaded to obtain a resin melt adjusted to 200 캜. Mixed butane of 70% by mass of n-butane and 30% by mass of isobutane as a physical foaming agent were pressed into the resin melt and mixed with 100 parts by mass of the polyethylene-based resin so as to obtain a blending amount shown in Table 3, , And the foamable molten resin composition was introduced into a ring-shaped die for extrusion.

Then, the mixture was extruded through a lip of the die into the air to form a tubular foam having a single-layer structure containing an antistatic agent. The tubular foam was taken in a mandrel at a blow-up ratio shown in Table 3 at a rate shown in Table 3, cut along the extrusion direction, and wound up on a roll having a predetermined length to obtain a single-layer foam sheet containing an antistatic agent .

The blending amounts of the antistatic agent, the foam modifier and the physical foaming agent in Table 3 represent the mass parts of the antistatic agent, the foam modifier and the physical foaming agent with respect to 100 parts by mass of the resin constituting the foam layer.

Table 4 shows the physical properties of the foam sheet obtained in Examples and Comparative Examples.

(Table 4)

As can be seen from Table 4, since the foam sheet obtained in Examples 1 to 3 had a specific high molecular weight type antistatic agent having a melting point difference of + 7 ° C from the low density polyethylene (Daver 1: melting point 114 ° C) The occurrence of through holes on the surface is prevented and suppressed even in the continuous production of organ for 168 hours (7 days) as well as in the continuous production of medium term such as " Therefore, it can be seen that the foam sheet of the present invention is an industrially very valuable foam sheet which has antistatic properties, is stable, and can be mass-produced.

On the other hand, the foam sheet obtained in Comparative Examples 1 to 2 was a high molecular weight type antistatic agent having a high melting point (135 占 폚) having a melting point difference of 28 占 폚 with low density polyethylene (Daad 2, Daad 3) 2 days), the generation of through holes was observed in the continuous production in the medium term, and in the continuous production of the organ for 168 hours (7 days), the generation of the through holes was remarkable and the production efficiency was low have.

The foam sheet obtained in Comparative Example 3 was a high molecular weight antistatic agent having a melting point difference of -15 DEG C from the low density polyethylene (Daughter 4: melting point 92 DEG C). When the blending amount was small, a high quality foam sheet But sufficient antistatic performance is not exhibited. Thus, as in Comparative Example 4, if the mixing amount is increased in order to sufficiently express the antistatic function, it is difficult to stably produce the foamed sheet because the large number of tetraols 4 having a low melt flow rate is large.

The foam sheet obtained in Comparative Example 5 is in contrast to Example 2, and it can be seen that the antistatic agent having a large difference in melting point from the low density polyethylene resin is not suitable for long-term continuous production.

In Table 4, various physical properties were measured as follows.

(Thickness of foam sheet)

The average thickness of the foam sheet was measured using an off-line thickness gauge TOF-4R manufactured by YAMAHA CHEMICAL INDUSTRIES, LTD. First, the thickness of the entire foam sheet was measured at intervals of 1 cm. Based on the thickness of the foam sheet measured at intervals of 1 cm, the arithmetic average thickness of the entire width was obtained. The foam sheet used for the measurement was conditioned for 48 hours under conditions of a temperature of 23 占 폚 and a relative humidity of 50%.

(Basis weight of the foam sheet)

The basis weight of the foam sheet was determined by cutting out a rectangular test piece having a width of 250 mm over the entire width of the foam sheet and dividing the weight (g) of the test piece by the area (sheet width (mm) x 250 mm) (G) of the foam sheet per m &lt; 2 &gt;, and this was regarded as the basis weight (g / m &lt; 2 &gt;) of the foam sheet.

(Apparent density of foam sheet)

The apparent density of the foam sheet was obtained by dividing the basis weight (g / m 2) of the foam sheet obtained by the above method by the average thickness of the foam sheet obtained as described above.

(Occurrence of through holes and the like)

(short-term)

The surface of the foam sheet was observed for one hour after 48 hours from the start of production by using a defect detector at the time of producing the foam sheet, and evaluated according to the following criteria.

good: After 48 hours, the number of through holes of 1 mm or more generated in 1 hour is less than 3

poor: After 48 hours, the number of through holes of 1 mm or more generated in 1 hour was 3 or more and less than 5

bad: After 48 hours, the number of through holes of 1 mm or more generated in one hour was 5 or more

(long time)

The surface of the foam sheet was observed for one hour after the start of production of 168 hours using the defect detector at the time of manufacturing the foam sheet, and evaluated according to the following criteria.

good: After 168 hours, the number of through holes of 1 mm or more generated in 1 hour is less than 3

poor: After 168 hours, the number of through holes of 1 mm or more generated in one hour was 3 or more and less than 5

bad: After 168 hours, the number of through holes of 1 mm or more generated in one hour was 5 or more

-: Unable to evaluate (foam sheet can not be formed)

(Surface resistivity)

The surface resistivity was measured according to JIS K6271: 2008 after adjusting the conditions of the following test pieces. Specifically, five specimens (100 mm long × 100 mm wide × thickness: measured object thickness) randomly cut out from a foam sheet as an object to be measured were allowed to stand for 36 hours in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% Adjustment was made. Subsequently, voltage was applied to both surfaces of each test piece under the condition of a temperature of 23 DEG C and a relative humidity of 50% under an applied voltage of 500V. The surface resistivity was measured after 1 minute from the initiation of voltage application, and their arithmetic mean values (5 pieces of test piece x 2 sides [n = 10]) were determined as the surface resistivity of the laminated foam sheet.

Claims (6)

A method for producing a polyethylene resin extruded foam sheet by extruding and expanding a foamable molten resin composition containing low density polyethylene, a physical foaming agent and an antistatic agent,
Wherein the thickness of the foam sheet is within the range of 0.05 to 0.5 mm and the melting point difference from the low density polyethylene as the antistatic agent is within the range of -10 to +10 占 폚 and the melt flow rate is 10 g / Based resin extruded foamed sheet. The method according to claim 1,
Wherein the polymeric antistatic agent has a melting point of 120 占 폚 or less. 3. The method according to claim 1 or 2,
Wherein the ratio of the melt flow rate of the low density polyethylene to the melt flow rate of the high molecular weight antistatic agent (melt flow rate of the low density polyethylene / melt flow rate of the high molecular weight type antistatic agent) is 2 or less. Way. 4. The method according to any one of claims 1 to 3,
Wherein the polymeric antistatic agent is blended in an amount of 3 to 25 parts by mass based on 100 parts by mass of the low-density polyethylene. A polyethylene resin extruded foamed sheet comprising an antistatic agent and a base resin having a low density polyethylene,
Wherein the antistatic agent has a melting point within a range of from 0.05 mm to 0.5 mm and an apparent density within a range of from 20 to 450 kg / m 3 and the difference in melting point of the antistatic agent from the low density polyethylene is in the range of from -10 ° C to + 10 ° C, And the rate is 10 g / 10 min or more. A sheet for a glass plate comprising the polyethylene-based resin extruded foam sheet according to claim 5.