CN113308035A

CN113308035A - Method for producing polyethylene resin extruded foam sheet and polyethylene resin extruded foam sheet

Info

Publication number: CN113308035A
Application number: CN202110222603.6A
Authority: CN
Inventors: 藤田干大; 角田博俊; 胜山直哉
Original assignee: JSP Corp
Current assignee: JSP Corp
Priority date: 2020-02-26
Filing date: 2021-02-26
Publication date: 2021-08-27
Also published as: JP7407620B2; KR20210108882A; JP2021134258A

Abstract

The present invention addresses the problem of providing a method for producing a foamed sheet, which can stably produce a foamed sheet exhibiting excellent antistatic properties even when an ionomer resin is used as a polymer-type antistatic agent. The manufacturing method of the present invention is a method comprising: a polyethylene resin foamed extruded sheet is produced by extrusion foaming a foamable resin melt obtained by kneading a polyethylene resin, an ionomer resin antistatic agent and a physical foaming agent, wherein the physical foaming agent contains 1 or 2 or more organic compounds selected from saturated hydrocarbons, dialkyl ethers and hydrofluoroolefins and an alcohol, and the total blending amount of the physical foaming agent, the blending amount A of the organic compounds and the blending amount B of the alcohol are within specific ranges.

Description

Method for producing polyethylene resin extruded foam sheet and polyethylene resin extruded foam sheet

Technical Field

The present invention relates to a method for producing a polyethylene resin extruded foamed sheet, and a polyethylene resin extruded foamed sheet obtained by the production method.

Background

A polyethylene resin extruded foam sheet (hereinafter, also simply referred to as a foam sheet) is lightweight and has excellent cushioning properties, and therefore is widely used in the field of packaging of electronic devices and raw materials thereof. For example, when glass plates are stacked and transported, the foamed sheet is used as an interleaving paper between the glass plates. In such applications, antistatic performance is generally imparted to the foamed sheet in order to prevent dust, dirt, and the like from adhering to the foamed sheet. Examples of the method for imparting antistatic properties to the foamed sheet include the following methods: in the production of a foamed sheet, a polymer antistatic agent is blended with a resin melt for forming a foamed sheet, and extrusion foaming is performed (for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-199893.

Disclosure of Invention

Problems to be solved by the invention

In recent years, in applications such as interleaving paper for glass sheets, in order to prevent contamination of objects to be packaged more thoroughly, there is a demand for a foamed sheet in which transfer of low molecular weight components or the like derived from a polymer type antistatic agent into objects to be packaged is further suppressed.

In order to reduce the amount of transfer of such low molecular weight components and the like, it is preferable to use a high molecular weight antistatic agent having a small content of low molecular weight components. The polymer type antistatic agent containing a small amount of low molecular weight component includes an ionomer resin.

However, when the resin melt blended with the ionomer resin is used for extrusion foaming in the production of a foamed sheet, it is difficult to stably exhibit desired antistatic properties in the foamed sheet when used as a lining paper or the like, and it is difficult to stably produce a foamed sheet having good antistatic properties.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a foamed sheet, which can stably produce a foamed sheet exhibiting excellent antistatic performance even when an ionomer resin is used as a polymer type antistatic agent.

Means for solving the problems

According to the method of the present invention, there are provided a method of producing a foamed sheet and a foamed sheet described below.

[1] A method for producing a polyethylene resin extruded sheet by extruding and foaming a foamable resin melt obtained by kneading a polyethylene resin, an ionomer resin antistatic agent, and a physical foaming agent, the method comprising:

the physical blowing agent comprises: 1 or 2 or more organic compounds selected from saturated hydrocarbons having 3 to 5 carbon atoms, dialkyl ethers having 1 to 3 carbon atoms in an alkyl chain, and hydrofluoroolefins; and an alcohol having a boiling point of 120 ℃ or lower,

the total amount of the physical foaming agent is 1mol or more and 5mol or less per 1kg of the polyethylene resin and the ionomer resin antistatic agent,

the amount A of the organic compound added is 0.2mol or more per 1kg of the total of the polyethylene resin and the ionomer resin antistatic agent,

the amount of the alcohol B to be blended is 0.3mol or more per 1kg of the total of the polyethylene resin and the ionomer resin antistatic agent.

[2] The method for producing a polyethylene resin extruded foam sheet according to item [1], wherein a blending ratio of the ionomer resin antistatic agent is 5% by weight or more and 50% by weight or less with respect to 100% by weight of the total of the polyethylene resin and the ionomer resin antistatic agent.

[3] The method for producing an extruded polyethylene resin foamed sheet according to item [1] or [2], wherein the polyethylene resin has a melting point Tmp of 100 ℃ to 120 ℃,

the difference (Tmp-Tmi) between the melting point Tmp of the polyethylene resin and the melting point Tmi of the ionomer resin antistatic agent is 5 ℃ to 30 ℃.

[4] The method for producing an extruded polyethylene resin foamed sheet according to any one of [1] to [3], wherein the blending amount A of the organic compound and the blending amount B of the alcohol satisfy the following formula (1):

3.5 ≤ B×e^(A＋B)・・・(1)。

[5] the method for producing an extruded polyethylene resin foamed sheet according to any one of [1] to [4], wherein the alcohol is added in a proportion of 75mol% or less based on 100mol% of the total of the amount A of the organic compound and the amount B of the alcohol.

[6] The method for producing an extruded polyethylene resin foamed sheet according to any one of [1] to [5], wherein the alcohol is incorporated in an amount B of 3 to 40mol per 1kg of the ionomer resin antistatic agent.

[7] The method for producing an extruded polyethylene resin foamed sheet according to any one of the above [1] to [6], wherein the alcohol contains ethanol, and a blending ratio of the ethanol in the alcohol is 50% by weight or more.

[8] A polyethylene resin foamed sheet which is a polyethylene resin extruded foamed sheet,

wherein the polyethylene resin extruded foam sheet is composed of a resin composition containing a polyethylene resin and an ionomer resin antistatic agent,

the polyethylene resin extruded foamed sheet had an apparent density of 15kg/m³Above and 200kg/m³In the following, the following description is given,

the polyethylene resin extruded foamed sheet has a volume resistivity of 1X 10¹³Omega cm or less.

[9] The polyethylene resin extruded foam sheet according to item [8], wherein a content ratio of the ionomer resin antistatic agent is 5% by weight or more and 50% by weight or less with respect to 100% by weight of a total of the polyethylene resin and the ionomer resin antistatic agent.

[10] The extruded polyethylene resin foamed sheet according to [8] or [9], wherein the ionomer resin antistatic agent is dispersed in the polyethylene resin in a stripe shape in a vertical cross section along an extrusion direction of the extruded polyethylene resin foamed sheet.

[11]Above-mentioned [8]～[10]The polyethylene resin extruded foam sheet according to any one of the above items, wherein the polyethylene resin extruded foam sheet has a tear strength T in an extrusion direction_MDTear strength T in the transverse direction_TDRatio of (T)_MD/T_TD) Is 1.5 to 2.1 inclusive.

Effects of the invention

The method for producing the foamed sheet of the present invention is a method comprising: an extrusion foamed sheet is produced by extrusion foaming a foamable resin melt using a physical foaming agent containing a specific saturated hydrocarbon, a specific dialkyl ether and a specific alcohol, together with an ionomer resin as an antistatic agent. According to the method of the present invention, even in the case of using an ionomer resin as a polymeric antistatic agent, an extruded foamed sheet exhibiting excellent antistatic properties can be stably obtained.

The extruded foamed sheet of the present invention is formed of a resin composition containing a polyethylene resin and an ionomer resin-based antistatic agent, and has excellent antistatic properties although containing the ionomer resin-based antistatic agent.

Drawings

FIG. 1 is a photograph showing a cross section of an extruded polyethylene resin foamed sheet obtained in example 3 (magnification: 20000 times).

FIG. 2 is a photograph showing a cross section of the polyethylene resin extruded foam sheet obtained in comparative example 1 (magnification: 20000 times).

Detailed Description

The method for producing the polyethylene resin extruded foam sheet and the polyethylene resin extruded foam sheet of the present invention will be described in detail below in this order.

In the present invention, a polyethylene resin extruded foamed sheet is produced by extrusion foaming a foamable resin melt obtained by kneading a polyethylene resin, an ionomer resin antistatic agent, and a physical foaming agent.

Specifically, for example, the foamed sheet can be produced as follows.

First, a polyethylene resin or the like is supplied to an extruder, heated, melted, and kneaded to form a resin melt, and then a physical blowing agent is pressed into the resin melt and kneaded to form a foamable resin melt. The obtained foamable resin melt is passed through an annular die attached to the downstream side of the extruder and extruded under low pressure (usually atmospheric pressure) to form a cylindrical foam. Then, the cylindrical foam is pulled while being widened by a cylindrical widening device, and the cylindrical foam is cut at the same time, thereby obtaining a foamed sheet.

The content of the polyethylene resin in the resin melt is preferably 50% by weight or more, more preferably 60% by weight or more, and still more preferably 70% by weight or more.

Next, the polyethylene resin will be described.

Examples of the polyethylene resin include: low density polyethylene, ultra-low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, or a mixture thereof.

Among these, a polyethylene resin containing low-density polyethylene as a main component is preferably used in view of excellent extrusion foamability and excellent cushioning property of the foamed sheet obtained.

In the present specification, "the low density polyethylene is used as a main component" means that the polyethylene resin contains 50% by weight or more of the low density polyethylene. The content of the low-density polyethylene in the polyethylene resin is preferably 60% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, particularly preferably 90% by weight, and most preferably 100% by weight.

The low density polyethylene means a density of 0.910g/cm³Above and less than 0.930g/cm³The polyethylene resin according to (1).

The Melt Flow Rate (MFR) of the polyethylene resin is preferably 0.5g/10 min to 15g/10 min from the viewpoint of excellent extrusion foamability.

In the present specification, MFR is defined as a value in accordance with JIS K7210-1: 2014 (test temperature: 190 ℃ C., load: 2.16 kg).

The melting point Tmp of the polyethylene resin is preferably 100 ℃ or higher and 120 ℃ or lower. By setting the above range, a foamed sheet having excellent extrusion foamability and excellent cushioning property can be stably produced. For the above reasons, the melting point Tmp of the polyethylene resin is more preferably 100 ℃ to 115 ℃.

In the present specification, the melting point of the polyethylene resin is a value determined by heat flux differential scanning calorimetry in accordance with JIS K7121-1987. In the measurement, a melting peak was measured by heating at 10 ℃/min using a test piece whose state was adjusted according to the conditions of test piece state adjustment (2) according to JIS K7121-1987, 3 (wherein the cooling rate was 10 ℃/min.), and the temperature of the apex of the obtained melting peak was taken as the melting point. However, when 2 or more melting peaks appear, the melting point is defined as the temperature at the top of the melting peak having the largest area.

Next, the ionomer resin-based antistatic agent (hereinafter, also simply referred to as ionomer resin) will be described.

The ionomer resin antistatic agent is a polymer type antistatic agent composed of ionomer resin, has low surface resistivity, and can impart good antistatic performance to a foamed sheet. Since the ionomer resin has a small content of the low-molecular weight component, contamination caused by transfer of the low-molecular weight component into a packaged article can be suppressed.

The ionomer resin is obtained by intermolecular crosslinking of a copolymer of ethylene and an unsaturated carboxylic acid by metal ions. Examples of the unsaturated carboxylic acid include: acrylic acid, methacrylic acid, and the like. Further, as the metal ion, there can be mentioned: lithium, sodium, potassium, calcium, and the like.

Among these ionomer resins, potassium ionomer which is a copolymer of ethylene and an unsaturated carboxylic acid using potassium as a metal ion is also preferable from the viewpoint of imparting good antistatic properties to the foamed sheet.

Of the ionomer resinThe surface resistivity is preferably less than 1X 10¹²Omega. By using a surface resistivity of less than 1X 10¹²Omega ionomer resin, can stably produce a foamed sheet having excellent antistatic properties. For the reasons described above, the surface resistivity is more preferably 1 × 10¹¹Omega is less, more preferably 1X 10¹⁰Omega or less, particularly preferably 1X 10⁹Omega is less than or equal to.

As described later, the surface resistivity of the ionomer resin can be measured by a method in accordance with JIS K6271 (2001).

The Melt Flow Rate (MFR) of the ionomer resin is preferably 10g/10 min or less (190 ℃ C., 2.16kg load), more preferably 7g/10 min or less (190 ℃ C., 2.16kg load), and still more preferably 3g/10 min or less (190 ℃ C., 2.16kg load). On the other hand, the lower limit is about 1g/10 min (temperature 190 ℃ C., load 2.16 kg).

The difference (Tmp-Tmi) between the melting point Tmp of the polyethylene resin and the melting point Tmi of the ionomer resin is preferably 5 ℃ or higher and 30 ℃ or lower. When the difference (Tmp-Tmi) is within this range, a foamed sheet having good cells can be stably obtained by extrusion foaming while the ionomer resin is favorably dispersed in the polyethylene resin. For the reasons described above, the difference (Tmp-Tmi) is more preferably 8 ℃ to 25 ℃, and still more preferably 10 ℃ to 25 ℃.

The ionomer resin preferably has a melting point Tmp of about 80 ℃ or higher and 110 ℃ or lower, more preferably 85 ℃ or higher and 100 ℃ or lower.

The melting point of the ionomer resin in the present specification is measured in the same manner as in the polyethylene resin.

Specific examples of the ionomer resin include: "Entira SD 100" and "Entira MK 400" manufactured by Mitsui DuPont Polymer chemical Co.

The blending ratio of the ionomer resin is preferably 5wt% or more and 50 wt% or less with respect to 100 wt% of the total of the polyethylene resin and the ionomer resin. By setting the above range, a foamed sheet having excellent flexibility and stably exhibiting desired antistatic properties can be formed. The lower limit of the blending ratio is more preferably 6% by weight, and still more preferably 7% by weight in order to exhibit better antistatic property. In order to improve the extrusion foamability, the upper limit of the blending ratio is preferably 40% by weight, more preferably 30% by weight, still more preferably 20% by weight, and particularly preferably 15% by weight.

In the production of the foamed sheet of the present invention by extrusion foaming, other components such as resins or elastomers other than the polyethylene resin and the ionomer resin antistatic agent may be blended in the resin melt within a range not to impair the object and effect of the present invention. In this case, the content of the other component is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and still more preferably 3 parts by weight or less, based on 100 parts by weight of the total of the polyethylene resin and the ionomer resin antistatic agent.

Next, a physical blowing agent used in the method of the present invention will be described. The physical foaming agent is kneaded with the polyethylene resin and the ionomer resin antistatic agent to form a foamable resin melt.

The physical blowing agent comprises: 1 or 2 or more organic compounds selected from saturated hydrocarbons having 3 to 5 carbon atoms, dialkyl ethers having 1 to 3 carbon atoms in an alkyl chain, and hydrofluoroolefins; and an alcohol having a boiling point of 120 ℃ or lower.

Examples of the saturated hydrocarbon having 3 to 5 carbon atoms include: propane, n-butane, isobutane, n-pentane, isopentane. Among these, butane (n-butane and isobutane) is also preferably used in view of its large plasticizing effect on the polyethylene resin and its ability to efficiently reduce the melt viscosity of the resin during extrusion.

When mixed butane is used, the mixing ratio of n-butane to isobutane is not particularly limited, and n-butane is preferably selected from the group consisting of: isobutane = 50: 50-90: 10. more preferably 60: 40-80: 20.

examples of the dialkyl ether having an alkyl chain of 1 to 3 carbon atoms include: dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, and the like. Among these, dimethyl ether is also preferably used in view of its large plasticizing effect on the polyethylene resin, its ability to effectively reduce the melt viscosity of the resin melt, and its ease of producing a good foamed sheet.

Examples of the Hydrofluoroolefin (HFO) include hydrofluoropropane, and specific examples thereof include trans-1, 3,3, 3-tetrafluoropropane (trans HFO-1234ze), cis-1, 3,3, 3-tetrafluoropropane (cis HFO-1234ze), and 2,3,3, 3-tetrafluoropropane (HFO-1234 yf). The hydrofluoroolefins include hydrochlorofluoroolefins obtained by introducing a part of chlorine into 1-chloro-3, 3, 3-trifluoropropane (HFO-1233zd), and the like. These blowing agents may be used alone, or 2 or more of them may be used in combination.

These hydrofluoroolefins are blowing agents having a low ozone depletion potential (ozone destruction coefficient), a very low global warming potential (global warming coefficient), and a low environmental load. Further, since the thermoplastic resin composition has a property of being nonflammable, when a hydrofluoroolefin is used, the amount of a flammable foaming agent such as an aliphatic hydrocarbon remaining in the foamed sheet can be reduced, and a curing step for dissipating the flammable foaming agent can be easily omitted or shortened.

Examples of the aliphatic alcohol having a boiling point of 120 ℃ or lower include: methanol (methane, boiling point 64.7 ℃), ethanol (ethane, boiling point 78.3 ℃), n-propanol (boiling point 97.2 ℃), i-propanol (boiling point 82.4 ℃), butanol (boiling point 117 ℃), sec-butanol (boiling point 100 ℃), etc. Among these, ethanol is preferable because it is easy to handle and is excellent in safety to the environment and human body.

When the alcohol contains ethanol, the proportion of ethanol in the alcohol is preferably 50% by weight or more, more preferably 60% by weight, still more preferably 70% by weight, and particularly preferably 80% by weight or more.

The ionomer resin is a resin in which a pseudo crosslinked structure is formed in the resin by the binding of metal ions and carboxylic acid. Such an ionomer resin has a large temperature dependency of melt viscosity, and when the temperature of the molten resin is high, the melt viscosity is lowered. On the other hand, for example, under a relatively low temperature condition such as an extrusion foaming temperature of a polyethylene resin, the melt viscosity increases. As a result, the ionomer resin is difficult to be well dispersed in the polyethylene resin, and it becomes difficult to stably produce a foamed sheet having good antistatic performance. In particular, in the case of using an ionomer resin having a low MFR, this tendency becomes remarkable.

To solve this problem, physical blowing agents containing alcohols are used in the process of the invention. The alcohol contributes as a blowing agent for foaming the resin, and is also a resin having a large plasticizing effect on the ionomer resin. Therefore, the use of the alcohol can improve the dispersibility of the ionomer resin in the foamable resin melt. This effect is effectively exhibited even when an ionomer resin having a small MFR is used. Therefore, even if the extrusion temperature of the expandable resin melt is lowered to fall within the temperature range suitable for foaming and extrusion foaming is performed, since the ionomer resin is plasticized (the effect of plasticizing the ionomer resin), kneading can be performed while maintaining the melt viscosity of the ionomer resin at a low level, the ionomer resin can be dispersed in the polyethylene resin, and the expandable resin melt can be extrusion foamed in a state in which the ionomer resin is well dispersed in the polyethylene resin.

On the other hand, since the physical blowing agent contains a hydrocarbon, an alkyl ether, or the like having a large plasticizing effect on the polyethylene resin, the melt viscosity of the polyethylene resin can be maintained at a low level. Therefore, the foamable resin melt can be adjusted to a temperature range suitable for foaming to easily perform extrusion foaming. It is considered that the ionomer resin is uniformly dispersed in the polyethylene resin by the action and effect of these components to form a conductive network structure which can exhibit excellent antistatic performance.

Next, the blending amounts and blending ratios of the respective components constituting the physical blowing agent in the method of the present invention will be described.

The total amount of the physical blowing agent is 1mol or more and 5mol or less per 1kg of the total of the polyethylene resin and the ionomer resin antistatic agent.

If the total blending amount is too small, a foamed sheet having a low apparent density that can exhibit a desired cushioning property may not be obtained. If the total amount is too large, the physical blowing agent is easily separated from the foamable resin melt, and a good foamed sheet may not be obtained. For the reasons described above, the lower limit of the total blending amount is preferably 1.5mol, more preferably 2 mol. The upper limit of the total blending amount is preferably 4.5mol, more preferably 4 mol.

The physical blowing agent may contain other physical blowing agents than the organic compound and the alcohol, within a range not to impair the object and the effect of the present invention. In this case, the blending ratio of the other physical blowing agents in the physical blowing agents is preferably 20mol% or less, more preferably 10mol% or less, and further preferably 5mol% or less.

The amount A of the 1 or 2 or more organic compounds selected from the group consisting of the saturated hydrocarbons, dialkyl ethers, and hydrofluoroolefins blended is 0.2mol or more per 1kg of the total amount of the polyethylene resin and the antistatic agent. If the blending amount of the organic compound is too small, it may be difficult to obtain a foamed sheet having a desired apparent density and a good cell structure. Therefore, the blending amount a of the polyethylene resin and the antistatic agent is preferably 0.4mol or more, more preferably 0.6mol or more, further preferably 0.8mol or more, and particularly preferably 1.0mol or more per 1kg of the total amount. When 2 or more of the above organic compounds are used, the total amount of these organic compounds is defined as the blending amount a.

The upper limit of the blending amount A is preferably about 4mol, more preferably 3.5 mol. By setting the above range, a foamed sheet having a desired apparent density and a good cell structure can be easily and stably obtained.

The blending amount B of the alcohol is 0.3mol or more per 1kg of the total of the polyethylene resin and the ionomer resin. If the amount B of the alcohol to be blended is too small, it may be difficult to exhibit desired antistatic properties. Further, since the ionomer resin is difficult to be appropriately dispersed in the resin melt, the foamed sheet is easily torn during production, and it is difficult to stably pull the foamed sheet.

Therefore, the blending amount B is preferably 0.4mol or more, and more preferably 0.5mol or more per 1kg of the total of the polyethylene resin and the ionomer resin.

The upper limit of the blending amount B is preferably about 3mol, more preferably 2.5mol, still more preferably 2.0mol, and particularly preferably 1.8 mol. By setting the above range, the foamed sheet is not easily torn at the time of extrusion foaming, and a foamed sheet having a good cell structure can be easily and stably obtained.

The amount of the alcohol B to be blended is preferably 3 to 40mol per 1kg of the ionomer resin.

By blending the alcohol in an amount within this range, the ionomer resin is appropriately plasticized, and the melt viscosity of the ionomer resin can be easily adjusted to a viscosity range suitable for extrusion foaming. Further, since the ionomer resin is well dispersed in the polyethylene resin and the foamable resin melt can be foamed while maintaining its state, a desired antistatic property can be easily exhibited while forming a good cell structure.

For the reasons mentioned above, the lower limit of the blending amount is preferably 4 mol. On the other hand, the upper limit of the blending amount is preferably 35mol, more preferably 30mol, still more preferably 25mol, and particularly preferably 20 mol.

The physical blowing agent used in the method of the present invention is preferably such that the blending amount A of the organic compound and the blending amount B of the alcohol satisfy the following formula (1):

3.5 ≤ B×e^(A＋B)・・・(1)。

the formula (1) shows the relationship between the blending amount a and the blending amount B that is preferably blended at the minimum in order to stably obtain a good foamed sheet, and is calculated in consideration of the total amount of the physical blowing agent blended during extrusion foaming. When the blending amount a of the organic compound and the blending amount B of the alcohol satisfy formula (1), an extruded foamed sheet exhibiting excellent antistatic properties can be obtained more stably in a wide range of expansion ratio even in the case of using an ionomer resin.

In the formula (1), since (a + B) is the total amount of the physical blowing agent, it is considered that the larger the expansion ratio, the larger the stretching action of the resin during foaming, is, in relation to the expansion ratio of the foamed sheet. Since the stretching action is generated three-dimensionally, it is considered that the dispersion state of the ionomer resin in the polyethylene resin is influenced by an exponential function. The blending amount B of the alcohol affects plasticization of the ionomer resin in the polyethylene resin. Therefore, it is considered that the value on the right side of the formula (1) including these factors becomes a specific value or more within a range of a predetermined blending amount of the physical blowing agent, and becomes an index for stably dispersing the ionomer resin in the polyethylene resin.

The blending ratio of the alcohol (B/(a + B)) is preferably 75mol% or less with respect to 100mol% of the total of the blending amount a of the organic compound and the blending amount B of the alcohol. If the blending ratio is within this range, the extruded foamed sheet is less likely to tear, and the foamed sheet can be pulled more stably. Further, since pulling with excessive force can be suppressed when pulling the foamed sheet, the cells are less likely to become flat, and the mechanical properties of the foamed sheet can be improved. From the above-mentioned viewpoint, the blending ratio of the alcohol (B/(a + B)) is preferably 70mol% or less, more preferably 60mol% or less, and still more preferably 50mol% or less.

From the viewpoint of improving the dispersibility of the ionomer resin in the polyethylene resin, the blending ratio of the alcohol (B/(a + B)) is preferably 5mol% or more, more preferably 10mol% or more, further preferably 15mol% or more, and particularly preferably 20mol% or more.

In the resin melt, various additives may be added within a range not interfering with the object of the present invention. Examples of the various additives include: air bubble regulator, antioxidant, heat stabilizer, weather resisting agent, ultraviolet absorbent, flame retardant, filler, antibacterial agent, etc. The amount of each additive added in this case is appropriately determined depending on the purpose and effect of the additive, and is preferably about 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less, based on 100 parts by weight of the resin melt.

To the resin melt, a bubble control agent is usually added. As the bubble control agent, an organic bubble control agent or an inorganic bubble control agent can be used. Examples of the inorganic bubble control agent include: metal borate salts such as zinc borate, magnesium borate and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate and sodium hydrogen carbonate. Further, examples of the organic bubble control agent include: 2, 2-methylenebis (4, 6-tert-butylphenyl) phosphate sodium, sodium benzoate, calcium benzoate, aluminum benzoate, sodium stearate, and the like. Sodium bicarbonate-citric acid-based chemical foaming agents obtained by combining citric acid with sodium bicarbonate, an alkali salt of citric acid, sodium bicarbonate, or the like can also be used as the bubble controlling agent. These bubble control agents may be used in combination of 2 or more.

Next, the polyethylene resin extruded foam sheet of the present invention will be explained.

The extruded foamed sheet can be obtained by the above-described method for producing a foamed sheet of the present invention. Therefore, the resin composition constituting the extruded foamed sheet is formed by extrusion foaming the foamable resin melt, and includes the polyethylene resin and the ionomer resin antistatic agent.

In the resin composition, the content ratio of the ionomer resin-based antistatic agent is preferably 5% by weight or more and 50% by weight or less with respect to 100% by weight of the total of the polyethylene-based resin and the ionomer resin-based antistatic agent.

When the content is within the above range, the foamed sheet can exhibit desired antistatic properties more stably while having excellent flexibility.

The lower limit of the content ratio is more preferably 5% by weight, and still more preferably 7% by weight. The upper limit of the content is preferably 40% by weight, more preferably 30% by weight, still more preferably 20% by weight, and particularly preferably 10% by weight.

The content of the other components in the resin composition other than the polyethylene resin and the ionomer resin antistatic agent is preferably 10 wt% or less, more preferably 5wt% or less, and still more preferably 3 wt% or less.

For the above reasons, the melting point Tmp of the polyethylene resin is preferably 100 ℃ or more and 120 ℃ or less, and the difference (Tmp-Tmi) between the melting point Tmp of the polyethylene resin and the melting point Tmi of the ionomer resin is preferably 5 ℃ or more and 30 ℃ or less.

The thickness of the foamed sheet is preferably 0.05mm or more and 2mm or less. By setting the above range, when used as an interleaving paper for glass sheets, the loading efficiency when stacking and transporting glass sheets can be improved.

Therefore, the upper limit thereof is preferably 1.5mm, more preferably 1.3mm, and further preferably 1.2 mm. On the other hand, in order to ensure higher cushioning properties, the lower limit thereof is preferably 0.1mm, more preferably 0.2mm, and still more preferably 0.3 mm.

The polyethylene resin foamed sheet preferably has an apparent density of 15kg/m³Above and 200kg/m³The following. The foamed sheet having an apparent density within the above range is excellent in balance among lightweight property, handling property and cushioning property. For the reasons mentioned above, the lower limit of the apparent density is more preferably 20kg/m³More preferably 25kg/m³Particularly preferably 30kg/m³. The upper limit is more preferably 150kg/m³More preferably 120kg/m³Particularly preferably 90kg/m³。

For the same reason, the basis weight (weight per square meter) of the foamed sheet is preferably 10g/m²Above and 200g/m²Below, more preferably 15g/m²Above and 100g/m²The lower, more preferably 20g/m²Above and 80g/m²The following.

As described above, the foamed sheet contains an ionomer resin and has antistatic properties. Specifically, in the foamed sheet, the surface resistivity is preferably 1 × 10¹³Omega or less, more preferably less than 5X 10¹²Ω, more preferably 1 × 10¹²Omega or less, particularly preferably 5X 10¹¹Omega is less than or equal to. If the surface resistivity is within this range, the foamed sheet can exhibit antistatic properties sufficiently stablyThe adhesion of dust and the like can be suppressed. The lower limit of the surface resistivity is preferably about 1 × 10⁶Omega, more preferably 1 × 10⁷Ω。

In the present specification, the surface resistivity is measured as follows.

A plurality of test pieces of a predetermined size (for example, 100mm in length. times.100 mm in width. times.thickness: sheet thickness) were cut out from a foamed sheet, applied at an applied voltage of 500V by a method in accordance with JIS K6271 (2001) using the test pieces, and then the surface resistance value after 1 minute was measured, and the average value of the measured values was taken as the surface resistivity. The surface resistivity of the ionomer resin antistatic agent was measured in the same manner as the surface resistivity of the foamed sheet. Specifically, according to the method of JIS K6271 (2001), a test piece was applied with an applied voltage of 500V, and then the surface resistance value of the test piece after 1 minute was measured, and the average value of the measured values was taken as the surface resistivity.

As the measurement device of the surface resistivity, for example, a model manufactured by japanese laid-open motor (ltd): SM8220, and the like.

The foamed sheet preferably has a volume resistivity of 1X 10¹³Omega cm or less, more preferably less than 5X 10¹²Omega cm, more preferably 1X 10¹²Omega cm or less, particularly preferably 5X 10¹¹Omega cm or less. When the volume resistivity is within this range, the antistatic performance is sufficiently exhibited not only on the surface of the foamed sheet but also on the cross section of the foamed sheet, and the adhesion of dust and the like is further suppressed. The lower limit of the volume resistivity is preferably about 1 × 10⁶Omega cm, more preferably 1X 10⁷Ω·cm。

In the present specification, the volume resistivity is measured as follows.

A plurality of test pieces of a predetermined size (for example, 100mm in length. times.100 mm in width. times.thickness: sheet thickness) were cut out from a foamed sheet, applied with an applied voltage of 500V by a method according to JIS K6271 (2001) using the test pieces, and then the volume resistance value after 1 minute was measured, and the volume resistivity was calculated from the measured value and the sheet thickness.

As described above, the resin composition constituting the foamed sheet of the present invention contains an ionomer resin and a polyethylene resin. In a vertical section along the extrusion direction, more specifically, in a vertical section perpendicular to the transverse direction of the foamed sheet (the direction perpendicular to the extrusion direction and the thickness direction of the extruded foamed sheet), as shown in fig. 1, the ionomer resin is preferably dispersed in the polyethylene-based resin in a stripe shape. That is, in the resin composition constituting the vertical cross section, it is preferable that a continuous phase composed of a polyethylene-based resin and a plurality of dispersed phases composed of an ionomer resin dispersed in a stripe shape in the continuous phase exist. When the polyethylene resin forms a continuous phase, the foamed sheet is excellent in flexibility and cushioning properties. It is also believed that: if the dispersed phase composed of the ionomer resin is stretched into a stripe shape, a network of the polymer type antistatic agent is formed, thereby exhibiting excellent antistatic property.

Preferably, the dispersed phase of the ionomer resin is small and stretched. The size of the dispersed phase is represented by, for example, the central value of a specific dispersion area, and the degree of stretching is represented by, for example, a specific ratio (B/a). Next, the range and meaning of the central value of the dispersion area and the range and meaning of the ratio (B/a) will be described in order.

The central value of the dispersion area based on the number of the dispersed phases in a vertical cross section along the extrusion direction of the foamed sheet is preferably 1 × 10²nm²Above and 1 × 10⁶nm²The following.

The central value is a value located at the center of the total number of the dispersed phases (50% of the total number of the dispersed phases) when the number of the dispersed phases and the cross-sectional area (dispersed area) of each dispersed phase in a vertical cross section along the extrusion direction of the foamed sheet are measured and the measured cross-sectional areas of the dispersed phases are arranged in order of magnitude. By using this central value, the dispersion state of the dispersed phase having a large existence rate in the continuous phase and contributing to the antistatic performance can be appropriately evaluated.

The central value of the dispersion area in the above range means that a large amount of dispersed phase having a small dispersion diameter made of an ionomer resin (polymer type antistatic agent) is dispersed in a continuous phase made of a polyethylene resin. In order to more reliably exhibit good antistatic performance, the lower limit of the median value is preferably 5 × 10²nm²More preferably 1X 10³nm². In addition, in order to more reliably exhibit good antistatic performance by well dispersing the polymer type antistatic agent, the upper limit of the median value is preferably 5 × 10⁵nm²More preferably 1X 10⁵nm²。

In the foamed sheet of the present invention, it is preferable that a ratio (B/a) of a median value B of dispersion diameters in a direction perpendicular to the thickness direction based on the number of dispersed phases in a cross section perpendicular to the extrusion direction of the foamed sheet to a median value a of dispersion diameters in the thickness direction based on the number of dispersed phases is 2 or more. This ratio (B/a) is an index indicating the degree of stretching of the dispersed phase of the ionomer resin in one direction, and a larger (B/a) means that the dispersed phase is present in a state of being stretched into a stripe shape. The foamed sheet having the ratio (B/a) within the above range can easily exhibit excellent antistatic performance. Since the dispersed phase exists in a state of being stretched into a strand, the ionomer resin stretched into a strand forms a conductive network structure in the polyethylene resin, and it is considered that the network structure exhibits excellent antistatic properties.

For the reasons described above, the ratio (B/A) is preferably 3 or more. The upper limit of the ratio (B/a) is preferably about 20, more preferably 15, and still more preferably 10.

The central value of each dispersion Diameter is a value located at the center of the total number of dispersion phases (50% of the total number of dispersion phases) when the number of dispersion phases, each vertical Feret's Diameter and each horizontal Feret Diameter are measured in a vertical cross section along the extrusion direction of the foamed sheet and the measured Feret diameters are arranged in order of size. The vertical ferter diameter corresponds to the length of the dispersed phase in the thickness direction of the foamed sheet, and the horizontal ferter diameter corresponds to the length of the dispersed phase in the direction perpendicular to the thickness direction.

The thickness direction of the dispersed phase is a direction that coincides with the thickness direction of the foamed sheet.

As described above, the foamed sheet of the present invention is produced by an extrusion foaming method, and has an extrusion direction, a thickness direction, and a transverse direction (a direction perpendicular to the extrusion direction and perpendicular to the thickness direction). In the foamed sheet, the tear strength T in the extrusion direction is preferred_MDTear strength T in the transverse direction_TDRatio of (T)_MD/T_TD) Is 1.5 to 2.1 inclusive, more preferably 1.6 to 2.0 inclusive. The range of the ratio is a range of the ratio of the tear strength which is generally exhibited by the polyethylene resin extruded foam sheet containing no ionomer resin. Therefore, the expanded sheet of the present invention satisfying the above ratio has the ionomer resin uniformly dispersed in the polyethylene resin, and does not significantly hinder the physical properties of the expanded sheet due to the ionomer resin. That is, the foamed sheet of the present invention is a foamed sheet obtained by extrusion foaming favorably, has a favorable cell structure, has the same physical properties as a polyethylene resin extruded foamed sheet containing no ionomer resin, has favorable appearance, and can stably exhibit excellent antistatic properties.

In the present specification, the tear strength is measured in accordance with "8.7. tear strength" of JIS K6767 (1999).

The foamed sheet of the present invention is suitably used, for example, as a lining paper for glass plates which is inserted between glass substrates to protect the glass substrates. Examples of the glass substrate include: glass panels for various image display devices such as liquid crystal displays, plasma displays, and electroluminescence displays.

[ example 1]

The present invention will be described in further detail below with reference to examples. The invention is not limited to the examples.

The polyethylene resin, ionomer resin (polymer type antistatic agent), and cell control agent used in examples and comparative examples are described below.

Polyethylene resin

(1) Abbreviated as "8009": "low density polyethylene manufactured by NUC corporation: trade name NUC8009 "(density 917 kg/m)³MFR of 9.0g/10 min, melting point of 106 ℃);

(2) abbreviated as "8321": "low density polyethylene manufactured by NUC corporation: the trade name is NUC8321 "(density 922 kg/m)³MFR of 2.4g/10 min, melting point of 111 ℃);

(3) abbreviated as "F102": "low density polyethylene manufactured by sumitomo chemical corporation: under the trade name Sumikathene F102 "(density 922 kg/m)³MFR was 0.4g/10 min, melting point was 109 ℃ C.

Ionomer resin (Polymer type antistatic agent)

(1) Abbreviated as "MK 400": ethylene-based potassium ionomer resin "Entira MK 400" (density: 970 kg/m) manufactured by Mitsui DuPont Polymer chemical Co., Ltd³MFR of 1.5g/10 min, melting point of 93 ℃ and surface resistivity of 1.0X 10⁷Ω)。

Physical foaming agent

(1) Mixing butane (a mixture of 70 wt% n-butane and 30 wt% isobutane);

(2) dimethyl ether;

(3) mix Ethanol: "mixed alcohol: trade name Mix Ethanol NP "(Ethanol: 85.5wt%, isopropanol 4.9wt%, n-propanol 9.6 wt%).

Air bubble regulator

Large day refining industrial production: PO-217K (citric acid-sodium bicarbonate chemical foaming agent).

Device for measuring the position of a moving object

A device in which a first extruder having a diameter of 90mm and a second extruder having a diameter of 120mm were used, and 2 extruders were connected in series, and the outlet of the second extruder was connected to an annular die. The lip diameter of the outlet of the annular die was 94 mm.

Examples 1 to 7 and comparative examples 1 to 5

Polyethylene resins of the types shown in table 1 and ionomer resins of the types shown in table 1 were blended at the weight ratios shown in table 1, 1.7 parts by weight of the above-mentioned cell regulator was added to 100 parts by weight of the total of the polyethylene resins and ionomer resins, and the mixture was supplied to a raw material inlet of a first extruder, heated, melted and kneaded to form molten resins, and adjusted to about 200 ℃. To this molten resin, mixed butane (organic compound) in an amount a shown in table 1 and ethanol in an amount B shown in table 1 were pressed as physical blowing agents, and further kneaded, and then transferred to a second extruder connected to the downstream side of the first extruder, and the resin temperature was adjusted to about 112 ℃.

The foamable resin melt was extruded and foamed from an annular die into the atmosphere at a discharge rate shown in table 2 to form a cylindrical foam. The extruded tubular foam was widened using a cylindrical widening device (mandrel) having a diameter of 356mm, and cut while being pulled at a blow-up ratio shown in table 2 and a pulling speed shown in table 2 to obtain a polyethylene resin extruded foamed sheet. The physical properties of the foamed sheet thus obtained were measured, and the results are shown in Table 3.

All of the polyethylene resin extruded foamed sheets obtained in examples were observed for a cross-sectional photograph of the surface layer portion of the foamed sheet. Specifically, an ultrathin section is cut out from a portion including the surface layer of the foamed sheet, the ultrathin section is stained, and then a cross-sectional photograph of the ultrathin section is observed with a transmission electron microscope. As a result, it was confirmed that: the ionomer resin-based antistatic agent is dispersed in a polyethylene-based resin in a stripe shape in a vertical cross section along the extrusion direction of the foamed sheet.

[ Table 1]

[ Table 2]

[ Table 3]

Example 2 is the following example: the total amount of the physical blowing agent was the same as in example 1, and the amount of ethanol added B was increased relative to the amount of the organic compound added A. The obtained foamed sheet is excellent in antistatic property, production stability and appearance.

Example 3 is the following example: the blending molar ratio of the blending amount A of the organic compound to the blending amount B of ethanol was the same as that in example 2, and the total blending amount of the physical foaming agent was increased, the blow-up ratio was decreased, the discharge amount was decreased, and the pulling speed was decreased. The resulting foamed sheet was excellent in antistatic properties, good in appearance, and capable of being produced, but the cells were slightly coarser than the foamed sheet of example 1.

The foamed sheet obtained in example 3 was measured for the center value of the dispersion area based on the number of dispersed phases. This measurement was performed on a vertical cross section along the extrusion direction of the foamed sheet by a method described later. As a result, the median was 6.9X 10³. In addition, in a cross section perpendicular to the extrusion direction of the foamed sheet, the ratio (B/a) of the median B of the dispersion diameters in the direction perpendicular to the thickness direction based on the number of the dispersed phases to the median a of the dispersion diameters in the thickness direction based on the number of the dispersed phases was 4.3. The photograph of the section taken (magnification: 20000 times) is shown in FIG. 1.

Example 4 is the following example: the total amount of the physical foaming agent was the same as in example 3, the molar ratio of the amount of ethanol added B was increased, and the blow-up ratio, the discharge amount, and the drawing speed were the same as in example 3. The resulting foamed sheet was excellent in antistatic properties and could be produced, but the cells were coarsened as compared with the foamed sheet of example 1.

Example 5 is the following example: the total amount of the physical foaming agent was increased further than in example 3, the amount of ethanol added B was decreased, the blow-up ratio was the same as in example 1, and the discharge amount and the drawing speed were increased as compared with example 1. The obtained foamed sheet is excellent in antistatic property, production stability and appearance.

Example 6 is the following example: the total amount of the physical foaming agent was the same as in example 5, the amount of ethanol added B was increased, and the blow-up ratio, the discharge amount, and the drawing speed were the same as in example 5. The resulting foamed sheet had a slightly coarse cell structure, but had excellent appearance and antistatic properties.

Example 7 is the following example: the blending amount of the ionomer antistatic agent was reduced as compared with example 3, and the blow-up ratio, the discharge amount, and the drawing speed were the same as those of example 3. The foamed sheet of example 7 has increased surface resistivity and volume resistivity as compared with those of other examples, but exhibits sufficient antistatic performance. In addition, the appearance was excellent.

Example 8 is the following example: the ionomer antistatic agent was increased as compared with example 3, and the blow-up ratio, the discharge amount, and the drawing speed were the same as those of example 3. The foamed sheet of example 8 was excellent in antistatic properties and could be produced, but the cells were slightly coarser than the foamed sheet of example 1.

Example 9 is the following example: the organic compound a in the physical blowing agent was changed to dimethyl ether, the blending amount of the ionomer-based antistatic agent was the same as in example 3, the blending amount of the organic compound a and the alcohol B was the same as in example 1, and the blow-up ratio, the discharge amount, and the pulling rate were the same as in example 3. The obtained foamed sheet is excellent in antistatic property, production stability and appearance.

Comparative example 1 is the following example: the total amount of the physical blowing agents was the same as in example 3, and the amount of ethanol B was 0. The obtained foamed sheet had poor antistatic properties.

In the same manner as in example 3, the ratio (B/a) of the center value of the dispersion area based on the reference number of the dispersed phases in the cross section perpendicular to the extrusion direction of the foamed sheet to the center value B of the dispersion diameter in the direction perpendicular to the thickness direction based on the reference number of the dispersed phases in the cross section perpendicular to the extrusion direction of the foamed sheet to the center value a of the dispersion diameter in the thickness direction based on the reference number of the dispersed phases was measured for the obtained foamed sheet. The former is 2.7X 10⁶The latter is 1.4. The photograph of the section taken (magnification: 20000 times) is shown in FIG. 2.

Comparative example 2 is the following example: the total blending amount of the physical blowing agents was the same as in example 3, and the blending molar ratio of the blending amount B of ethanol was reduced to 0.2 mol/kg. The resulting foamed sheet had low antistatic properties and could not be drawn stably during production.

Comparative example 3 is the following example: the amount of the physical blowing agent was the same as in example 5, and the amount of ethanol B was 0. The obtained foamed sheet has low antistatic performance.

Comparative example 4 is the following example: the amount of the physical blowing agent to be blended was the same as in example 5, and a little ethanol was added thereto, and the amount B to be blended was 0.1 mol/kg. The obtained foamed sheet has low antistatic performance.

Next, various measurement methods in the table and an evaluation method of the obtained foamed sheet will be described.

The thickness, apparent density, basis weight, surface resistivity, volume resistivity, and tear strength of the foamed sheets in table 3 were determined as above.

(method of measuring the center value of the dispersion area based on the number of dispersed phases)

First, the foamed sheet was cut in the thickness direction and the extrusion direction of the foamed sheet in the vicinity of the widthwise central portion and both widthwise end portions of the foamed sheet, and 3 samples having a cross section in the extrusion direction (a cross section perpendicular to the extrusion direction) were cut out.

Next, from the cut-out cross sections of the 3 samples, ultrathin sections were cut out from the surface layer portion including the surface layer of the foamed sheet (the side of the foamed sheet not drawn against the mandrel). Next, the ultrathin section was stained with ruthenium tetroxide so that the polyethylene-based resin and the ionomer resin-based antistatic agent could be distinguished by shade. Next, the stained section was observed at an acceleration voltage of 100kV using a transmission electron microscope (JEM-1400 Plus manufactured by JEOL), and a cross-sectional photograph of the surface layer portion was taken under a magnification of 70000 times (3500 times in comparative example). In the taken cross-sectional photograph, the portion having a higher degree of blackness is a dispersed phase (ionomer resin-based antistatic agent).

The resultant photographs of the cross sections were subjected to pretreatment (processing) for distinguishing the disperse phase and the portions other than the disperse phase by colors, i.e., black and white. Here, the dispersed phase and the phases other than the dispersed phase (continuous phase) are judged based on the depth of the cross-sectional photograph, the presence or absence of a lamellar structure, or the like, and the photograph is color-divided. In general, ionomer resins are distinguished from polyethylene resins by having a smaller amount of amorphous portions than continuous phases in a cross-sectional photograph. In addition, the interface between the dispersed phase and the continuous phase is differentiated as a dispersed phase.

Then, the image of the pretreated sectional photograph was subjected to image processing and measurement under the following conditions using image processing software "NS 2K-pro" manufactured by nanosystems co.

(1) Performing monochrome conversion;

(2) smoothing the filter (processing 1-10 times);

(3) binaryzation is carried out by an NS method (the definition is 41, the sensitivity is 10, noise is removed, and the concentration range is 45-255);

(4) feret diameter, area measurement.

In the measurement under the conditions (1) to (4), the measurement range is randomly selected for the cross-sectional portion of the surface layer portion where the dispersed phase exists, so that the total area of the measurement ranges reaches 100 μm²The number and cross-sectional area (dispersion area) of all dispersed phases included in the measurement range were measured in the above manner. The cross-sectional area of the dispersed phase that intersects the boundary of the measurement range is measured using the dispersed phase as the measurement target. In addition, the cross-sectional area is 1nm²The following dispersed phases were not measured. In the cross-sectional photograph, the black portions other than the dispersed phase, such as the wrinkled portions of the slice produced when the ultrathin slice is produced, or the outermost surface portion of the surface layer portion, are not included in the measurement range. This measurement was performed on the 3 test pieces, and the center value based on the number of cross-sectional areas of the dispersed phases was calculated from the number of all the dispersed phases measured in the 3 test pieces and the cross-sectional area of each dispersed phase. The central value means that the cross-sectional area of the dispersed phase is located in the dispersed phase when the cross-sectional areas of the dispersed phases are arranged in order of sizeThe center of the total (50% of the cumulative number of dispersed phases).

(method of measuring center value A of dispersion diameter in thickness direction based on the number of dispersed phases and center value B of dispersion diameter in direction perpendicular to thickness direction based on the number of dispersed phases)

The vertical Ferrett diameter and the horizontal Ferrett diameter of all dispersed phases were measured by the measurements under the conditions (1) to (4) above. Here, the vertical ferter diameter corresponds to the length of the dispersed phase in the thickness direction of the foamed sheet, and the horizontal ferter diameter corresponds to the length of the dispersed phase in the direction perpendicular to the thickness direction. The dispersed phase crossing the boundary of the measurement range was measured for the vertical and horizontal ferter diameters of the dispersed phase as the measurement target.

This measurement was performed on the 3 test pieces, and the median value based on the number of the respective Ferrett diameters was obtained from the vertical Ferrett diameters or the horizontal Ferrett diameters of all the dispersed phases measured in the 3 test pieces. The obtained central value of the vertical Ferrett diameter is defined as a central value A of the dispersion diameter in the thickness direction based on the number of the dispersed phases, and the obtained central value of the horizontal Ferrett diameter is defined as a central value B of the dispersion diameter in the direction perpendicular to the thickness direction based on the number of the dispersed phases.

The central value is a value located at the center of the total number of dispersed phases (50% of the total number of dispersed phases) when the respective feret diameters of the dispersed phases are arranged in order of size.

Specifically, the surface resistivity of the foamed sheet surface was measured as follows. From the foamed sheet obtained, 3 test pieces (100 mm in length. times.100 mm in width. times.thickness: test piece thickness) were randomly cut out. After the state of the test piece was adjusted, the application of voltage 500V to the test piece was started using "SM 8220" manufactured by japanese laid-open motor (ltd.) as a measuring device, and then the surface resistivity was measured after 1 minute. The surface resistivity of both sides of the test piece was measured (3 times per side), and the arithmetic mean of the obtained measurement values was taken as the surface resistivity of the foamed sheet.

Specifically, the volume resistivity of the foamed sheet was measured as follows. From the foamed sheet obtained, 3 test pieces (100 mm in length. times.100 mm in width. times.thickness: test piece thickness) were randomly cut out. After the state of the test piece was adjusted, the application of voltage 500V to the test piece was started using "SM 8220" manufactured by japanese laid-open motor (ltd.) as a measuring device, and then the volume resistivity was obtained by calculation from the volume resistance after 1 minute and the thickness of the measurement sheet. The volume resistivity of 3 randomly cut test pieces was measured, and the arithmetic mean of the measured values was used as the volume resistivity of the foamed sheet.

The production stability of the foamed sheet was evaluated according to the following criteria.

A: the foamed sheet can be stably produced;

b: although it is possible to manufacture, cutting of the foamed sheet sometimes occurs;

x: the foamed sheet cannot be pulled by the pulling device, or is cut immediately after the foamed sheet is pulled by the pulling device.

The appearance of the foamed sheet was evaluated according to the following criteria.

A: the bubble structure is good, and the appearance is excellent;

b: the bubbles were slightly coarse but the appearance was good;

c: the bubbles become fine and a steep ripple is generated.

The Tear strength (Tear strength) of the foamed sheet was measured in accordance with "8.7. Tear strength" of JIS K6767 (1999). The extrusion direction (MD direction) of the obtained foamed sheet was aligned with the longitudinal direction of the test piece, and 5 test pieces were cut out from the foamed sheet. This was used as a test piece for measuring the tear strength in the extrusion direction.

The transverse direction (TD direction) of the resulting foamed sheet was aligned with the longitudinal direction of the test piece, and 5 test pieces were cut from the foamed sheet. This was used as a test piece for measuring the tear strength in the transverse direction.

The tear strength was measured as follows. The prepared test piece was subjected to a tear test using a universal tester "Tensilon". The tear strength was determined by dividing the maximum load generated until the test piece broke by the thickness of the test piece. Among the measured values measured for 5 test pieces, the tear strength was determined by arithmetically averaging 3 measured values excluding the maximum value and the minimum value. In the tear test, the test was performed such that the longitudinal direction of the test piece was aligned with the tensile direction (the direction in which the test piece was pulled by the test machine).

Reference example 1

A polyethylene resin extruded foam sheet was produced in the same manner as in comparative example 1, except that the ionomer antistatic agent was not blended. When the tear strength of the foamed sheet was measured, T_MDIs 79.0N/cm, T_TD43.8N/cm, T_MD/T_TDIs 1.8.

As a test of transferability, the following haze measurement was performed on the foamed sheets obtained in the examples.

First, 10 precleaned glass slides manufactured by Sonlang glass industries, Inc. were stacked to form a glass laminate as an object to be packaged. Next, the haze (1) in the thickness direction (glass lamination direction) of the glass laminate was measured using "NDH 2000" manufactured by japan electrical decoration industries, ltd. Next, 11 samples (foamed sheets obtained in examples) and 10 sheets of glass were alternately laminated to form a laminate, and the laminate was measured at 3.8g/cm²Under a pressure of 60 ℃ and at a relative humidity of 90% for 24 hours. After that, the sample was removed from the laminate, 10 sheets of glass were stacked to form a glass laminate, and the haze (2) in the thickness direction of the glass laminate was measured in the same manner as in (1). The value (%) of the haze (1) was subtracted from the value (%) of the haze (2) to determine the amount of change in haze (%), and the transferability was evaluated according to the following criteria. The smaller the amount of change in haze, the smaller the shift of the low-molecular-weight component contained in the ionomer resin into glass.

Good: a haze change amount (%) of 1.5 or less;

x: the haze change amount (%) exceeded 1.5.

The foamed sheets obtained in the examples all had a haze change amount (%) of 1.5 or less (good evaluation of transferability), and had little transfer of low-molecular-weight components.

Claims

1. A method for producing a polyethylene resin extruded sheet by extruding and foaming a foamable resin melt obtained by kneading a polyethylene resin, an ionomer resin antistatic agent, and a physical foaming agent, the method comprising:

2. The method for producing the polyethylene resin extruded foam sheet according to claim 1, wherein the ionomer resin antistatic agent is blended in a proportion of 5wt% or more and 50 wt% or less with respect to 100 wt% of the total of the polyethylene resin and the ionomer resin antistatic agent.

3. The method for producing the polyethylene resin extruded foamed sheet according to claim 1 or 2, wherein the polyethylene resin has a melting point Tmp of 100 ℃ or more and 120 ℃ or less,

4. The method for producing an extruded polyethylene resin foamed sheet according to claim 1 or 2, wherein the blending amount a of the organic compound and the blending amount B of the alcohol satisfy the following formula (1):

3.5 ≤ B×e^(A＋B)・・・(1)。

5. the method for producing an extruded polyethylene resin foamed sheet according to claim 1 or 2, wherein the blending ratio of the alcohol is 75mol% or less based on 100mol% of the total of the blending amount A of the organic compound and the blending amount B of the alcohol.

6. The method for producing the polyethylene resin extruded foam sheet according to claim 1 or 2, wherein the blending amount B of the alcohol is 3mol or more and 40mol or less per 1kg of the ionomer resin antistatic agent.

7. The method for producing an extruded polyethylene resin foamed sheet according to claim 1 or 2, wherein the alcohol contains ethanol, and the blending ratio of ethanol in the alcohol is 50% by weight or more.

8. A polyethylene resin foamed sheet which is a polyethylene resin extruded foamed sheet,

9. The polyethylene resin extruded foam sheet according to claim 8, wherein the ionomer resin antistatic agent is contained in an amount of 5wt% or more and 50 wt% or less with respect to 100 wt% of the total of the polyethylene resin and the ionomer resin antistatic agent.

10. The extruded polyethylene resin foamed sheet according to claim 8 or 9, wherein the ionomer resin antistatic agent is dispersed in the polyethylene resin in a stripe shape in a vertical cross section along an extrusion direction of the extruded polyethylene resin foamed sheet.

11. The polyethylene resin extruded foamed sheet according to claim 8 or 9, wherein the polyethylene resin extruded foamed sheet has a tear strength T in an extrusion direction_MDTear strength T in the transverse direction_TDRatio of (T)_MD/T_TD) Is 1.5 to 2.1 inclusive.