JP2005074771A - Polyolefinic resin foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefinic resin foamed sheet having an antistatic function capable of obtaining an antistatic effect without being largely affected by a humidity condition in air and having flexibility and cushioning properties. <P>SOLUTION: In this polyolefinic resin foamed sheet 1 constituted by providing a polyolefinic resin layer 3 at least on one side of a polyolefinic resin foamed layer 2 with an apparent density of 0.015-0.3 g/cm<SP>3</SP>, the polyolefinic resin layer 3 contains a polymeric antistatic agent and is formed so that a basis weight becomes 0.1-20 g/m<SP>2</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polyolefin resin foam sheet in which a polyolefin resin layer containing an antistatic agent is laminated on at least one surface of a foam layer. More specifically, the present invention relates to a polyolefin-based resin foam sheet having a multilayer structure excellent in antistatic performance, flexibility and buffering property.

  Conventionally, foams made of polyolefin resins have been used as materials for cushioning materials and packaging materials. In particular, polyolefin resin foams that contain conductive additives and antistatic agents in the resin are less susceptible to dust and have flexibility and buffering properties, making it difficult to damage packages, precision equipment, home appliances, etc. It has been suitably used as a packaging cushioning material. For example, carbon black is used as the conductive additive (see, for example, Patent Document 1).

  Also known is a multilayer foam sheet in which a conductive or antistatic polyolefin resin layer made of a polyolefin resin is laminated on a foam layer made of a polyolefin resin. The polyolefin-based resin layer is mainly composed of a thermoplastic resin and is blended with a conductive additive or an antistatic agent. As the antistatic agent, a so-called surfactant is used, and examples thereof include glycerin fatty acid ester, polyoxyethylene alkylamine, and alkyldiethanolamide (see, for example, Patent Document 2).

JP 2001-347589 A (page 3, paragraph number 0018) Japanese Patent Laid-Open No. 9-169072 (pages 3 to 4, paragraph number 0016)

  As described in Patent Document 1, in the case of a foamed sheet made of a resin added with carbon black, a large amount of inorganic carbon black is added, so that the foamability deteriorates and the physical properties and appearance are good. There is a problem that it becomes difficult to obtain the color and the color of the foam sheet is limited to black.

  In addition, in the case of a foam sheet made of a resin to which an antistatic agent made of a surfactant such as glycerin fatty acid ester is added, the problem of causing surface contamination of the packaged body by bleeding out of the added surfactant or humidity There is a problem that the antistatic function does not sufficiently develop in a low environment.

  In addition, the multilayer foamed sheet described in Patent Document 2, in which an antistatic function is provided by laminating a polyolefin-based resin layer containing an antistatic agent made of a surfactant such as glycerin fatty acid ester on the foamed sheet, There are problems that cause surface contamination, and that the antistatic function does not sufficiently develop in a low humidity environment.

  In order to solve the above-described problem that the antistatic function does not appear in the low humidity environment, the present inventors tried to obtain a foamed sheet by adding a so-called polymer type antistatic agent to the polyolefin resin. However, the antistatic function is not sufficiently exhibited with a small amount of the polymer type antistatic agent. On the other hand, when the addition amount is increased, a good polyolefin resin foam sheet having a small apparent density cannot be obtained.

  Next, the present inventors have studied a multilayer foamed sheet in which a resin sheet containing a polymer type antistatic agent is laminated on the foamed sheet to provide an antistatic function. According to the study, in order to develop an appropriate antistatic function, in the case of an antistatic agent comprising a conventionally used surfactant, addition of less than 1% by weight is sufficient, whereas a polymer is In the case of the type antistatic agent, it was found that it was necessary to add much more than 1% by weight. A multilayer foam sheet that solves the problem that the antistatic function does not appear in a low-humidity environment by laminating and bonding a resin sheet formed by adding an appropriate amount of a polymeric antistatic agent to a separately formed foam sheet Succeeded in getting.

  However, in a molten resin mixture obtained by adding an appropriate amount of a polymeric antistatic agent, it is difficult to form a thin resin sheet due to deterioration of thin film formation due to insufficient elongation, and the molten resin mixture In order to improve the elongation of the resin and form a thin resin sheet, an appropriate antistatic function is exhibited even if a resin having high fluidity at the time of melting is selected and an appropriate amount of a polymeric antistatic agent is added to the resin. Nothing was obtained. Eventually, only a thick material could be obtained in order to achieve a sufficient antistatic effect, and it was extremely difficult to reduce the thickness to less than 50 μm.

  The multilayer foamed sheet formed by laminating the thick resin sheet is insufficient in lightness, flexibility and buffering property, and in order to express the effect of the polymer type antistatic agent, In addition, since the polymer antistatic agent is expensive, an increase in the thickness of the resin sheet leads to an increase in the amount of the polymer antistatic agent used. Had to be extremely expensive.

  The present invention has been made in view of the above problems, and provides a polyolefin-based resin foam sheet having an antistatic effect that is not greatly influenced by humidity conditions in the air and having flexibility and buffering properties. For the purpose.

That is, the present invention relates to (1) a foamed sheet having a polyolefin resin layer on at least one surface of a polyolefin resin foam layer having an apparent density of 0.015 to 0.3 g / cm ³ , wherein the polyolefin resin layer is a polymer type antistatic agent. The polyolefin resin foam sheet, wherein the basis weight is 0.1 to 20 g / m ² , (2) the number average molecular weight of the polymer antistatic agent is 2000 or more, The polyolefin resin foam sheet according to 1), characterized in that the polymer type antistatic agent is added in a proportion of 5 to 50 parts by weight with respect to 100 parts by weight of the base resin of the polyolefin resin layer. The polyolefin resin foam sheet according to (1) or (2) above, (4) the average cell membrane thickness in the polyolefin resin foam layer is 20 μm or less, (1), (2) Or the polyolefin resin according to (3) Foam sheets, the gist.

  Since the foamed sheet of the present invention is formed by laminating a polyolefin resin layer containing a polymeric antistatic agent on at least one surface of a polyolefin resin foam layer, the surface does not depend on humidity conditions. It has a good antistatic performance. In addition, the antistatic effect is not lost even if the surface of the foam sheet is washed.

In addition, since the basis weight of the polyolefin-based resin layer containing the polymer type antistatic agent is 0.1 to 20 g / m ^2, it is lightweight, flexible and buffering without affecting the properties of the foam layer. In particular, the smaller the apparent density of the foamed layer, the greater the significance.

  When the polyolefin resin layer and the polyolefin resin foam layer are made of a polyethylene resin, a flexible foam sheet having a low surface hardness and particularly excellent surface protection of the packaged body can be obtained.

  Moreover, when the average cell membrane thickness of the polyolefin resin foam layer is 20 μm or less, the foam sheet is more excellent in flexibility.

  In addition, since the foam sheet of the present invention exhibits a sufficient antistatic effect immediately after production, an ignition accident caused by static electricity occurs when the foam sheet is produced using a combustible physical foaming agent such as butane. Etc. can be prevented, and the foamed sheet can be produced safely.

  Further, the foamed sheet of the present invention does not completely exclude the conventional antistatic agent comprising a surfactant from the scope of rights, but it is not necessary to use an antistatic agent comprising the surfactant. Sufficient antistatic performance can be exhibited, and in this case, the contact surface of the package body or the like is not contaminated.

  Examples of the use of the foam sheet of the present invention include buffer packaging materials such as electronic parts, resin plate surface protection materials such as acrylic resin plates, and the like.

  FIG. 1 is a cross-sectional view of an essential part showing an example of a polyolefin resin foam sheet (hereinafter referred to as a foam sheet) of the present invention. As shown in FIG. 1, the foamed sheet 1 has a polyolefin resin layer 3 containing a polymer type antistatic agent laminated on at least one surface of a polyolefin resin foam layer 2, which is greatly affected by humidity conditions in the air. It has a good antistatic effect without being influenced.

Further, the basis weight B3 [g / m ² ] of the polyolefin resin layer 3 is 0.1 to ²⁰ g / m ² , and the polyolefin resin foam layer 2 has an apparent density of 0.015 to 0.3 g / cm ³ and has flexibility and buffering properties. A foam sheet provided. Note that the foam sheet 1 of the embodiment shown in FIG. 1 is one in which a polyolefin resin layer 3 is laminated on both front and back surfaces. The polyolefin resin layer 3 is preferably a resin layer having the same composition and basis weight on both the front and back surfaces.

  As the layer structure of the foam sheet 1 of the present invention, a polyolefin resin layer 3 containing a polymer type antistatic agent is preferably laminated as a surface layer on one side of the polyolefin resin foam layer 2. As shown in FIG. 1, as the surface layer on both the front and back surfaces of the polyolefin resin foam layer 2, one obtained by laminating a polyolefin resin layer 3 containing a polymer type antistatic agent is particularly preferable.

In addition to the above embodiment, the foamed sheet 1 of the present invention has the polyolefin resin layer 3 laminated on at least one surface of the polyolefin resin foam layer 2, and further on the surface side of the polyolefin resin layer 3. It may be a laminate (not shown in particular) of polymer layers that can achieve the intended effect. Furthermore, in the present invention, the polyolefin resin foam layer 2 and the polyolefin resin layer 3 can be laminated (not particularly shown) with a polymer layer made of a polyolefin resin or the like interposed therebetween. However, from the viewpoint of flexibility of the foamed sheet 1, it is preferable to laminate the polyolefin resin foam layer 2 and the polyolefin resin layer 3 without providing the polymer layer. In the case of providing the polymer layer in the foamed sheet 1 of the present invention, the basis weight of the polymer layer is 0.1 to 20 g / m ² similarly to the polyolefin resin layer 3, and further 0.5 to 10 g / m ² , particularly preferably in the range of 1 to 5 g / m ^2, further, the expression foam layer total basis weight of the resin layer 3 laminated with the polymer layer 2, 50 g / m on one side of the emitting foam layer 2 It is preferable for achieving the intended purpose to be less than ² , particularly 20 g / m ² or less.

As described above, in the foamed sheet 1 of the present invention, the basis weight B of the polyolefin resin layer 3, 0.1 to 20 g / m ^2, is preferably 0.5 to 10 g / m ^2, more preferably 1 to 5 g / m ² . When the basis weight B3 of the polyolefin resin layer 3 is less than 0.1 g / m ² , sufficient antistatic properties cannot be imparted to the foamed sheet 1. On the other hand, if the basis weight B3 of the polyolefin-based resin layer 3 is too large, there is a risk that the light weight and flexibility may be insufficient depending on the use of the foam sheet 1, and the raw material cost during the production of the foam sheet 1 is also high. turn into.

  In the polyolefin resin layer 3, a continuous layer of a polymer type antistatic agent must be formed in the polyolefin resin in order to develop an antistatic function. Therefore, the antistatic agent has a concentration of a certain amount or more. It must be added, and the amount of addition of the polymer type antistatic agent is inevitably increased as the basis weight of the resin layer 3 is large, leading to an increase in cost. In addition, unexpectedly within the basis weight range specified in the present invention, the smaller the basis weight, the smaller the surface specific resistance at the same concentration in the resin layer 3 of the polymer type antistatic agent is. It has been recognized as a result of our study.

  Further, the thickness T3 of the polyolefin resin layer 3 is preferably uniform, but there may be uneven thickness as long as the objects and effects of the present invention are achieved. In the present invention, the basis weight of the polyolefin-based resin layer 3 and the polymer layer provided as necessary can be determined by one of the following two methods.

As a first method for measuring the basis weight, when the foamed sheet 1 is manufactured, the extruded amount of the polyolefin-based resin layer 3 or the polymer layer X [kg / hour] in the extrusion foaming condition and the obtained foamed sheet When the width W [m] of the obtained foam sheet 1 and the length L [m / hour] per unit time are known, the basis weight of the polyolefin-based resin layer 3 or the polymer layer is expressed by the following formula (1): The quantity [g / m ² ] can be determined.
(Equation 1)
Basis weight [g / m ² ] = [1000X / (L × W)] (1)

As a second method for measuring the basis weight, the thickness T3 of the polyolefin resin layer 3 is measured at 10 points in the width direction at equal intervals from the cross section in the direction perpendicular to the extrusion direction of the foam sheet 1, that is, the vertical cross section in the width direction. The arithmetic average value of the obtained values is the average thickness of the polyolefin-based resin layer 3, and the average thickness is multiplied by the density of the base resin constituting the polyolefin-based resin layer 3, and the unit is converted into a polyolefin-based resin. The basis weight [g / m ² ] of the layer 3 can be determined.

  Further, the basis weight of the polymer layer is also measured in the same manner as the basis weight measurement of the polyolefin-based resin layer 3, and the average thickness of the polymer layer is measured, and the polymer layer is configured with the average thickness of the obtained polymer layer. It can be obtained by multiplying the density of the base resin that is present and converting the unit. The layers can also be colored so that the thickness of the polyolefin resin layer 3 or the thickness of the polymer layer can be easily measured.

  The thickness T1 [mm] of the foamed sheet 1 of the present invention is preferably 0.3 to 10 mm from the viewpoint that the foamed sheet 1 is excellent in buffering properties and flexibility. The thickness T1 of the foamed sheet 1 is preferably 8 mm or less, more preferably 5 mm or less, particularly from the viewpoint of flexibility. In addition, the foamed sheet of the present invention may have a thickness increased by bonding a plurality of foamed sheets. In this case, the upper limit of the thickness can be arbitrarily increased by increasing the number of stacked layers. On the other hand, from the viewpoint that the foamed sheet 1 has sufficient buffering properties, the thickness T1 of the foamed sheet 1 is preferably 0.5 mm or more, and more preferably 0.8 mm or more. The thickness T1 of the foamed sheet 1 is the total thickness of the foamed sheet 1 (total thickness), which is the sum of the thickness of the polyolefin resin foam layer 2 and the thickness of the polyolefin resin layer 3, and the thickness of the polymer layer provided as necessary. ).

  In the present invention, the thickness T1 [mm] of the foamed sheet 1 is obtained by the following measuring method. First, in the widthwise vertical cross section of the foam sheet 1, the thickness t [mm] of the foam sheet 1 was measured at 10 points in the width direction at equal intervals, and the arithmetic average of the thickness t [mm] of the foam sheet 1 at each measured point The value is the thickness T1 [mm] of the foam sheet 1.

In the present invention the polyolefin-based resin foam layer 2 apparent density P [g / cm ^3] is a 0.015~0.3g / cm ^3. If the apparent density P of the polyolefin resin foam layer 2 is less than 0.015 g / cm ³ , the foam sheet 1 may have insufficient strength such as tension and tear. Apparent density P of the polyolefin-based resin foam layer 2 from the point of view is preferably from 0.016 g / cm ³ or more, 0.018 g / cm ³ or more is more preferable.

On the other hand, if the apparent density P of the polyolefin resin foam layer 2 exceeds 0.3 g / cm ³ , the cushioning property, light weight and flexibility of the foam sheet 1 may be lowered. Apparent density of the polyolefin-based resin foam layer 2 from the point of view is preferably from 0.1 g / cm ³ or less, more preferably 0.06 g / cm ³ or less, 0.045 g / cm ³ or less is particularly preferred.

In the present invention, the apparent density P of the polyolefin resin foam layer 2 can be measured by the following operation, for example, in the case of a laminate of a foam layer and a resin layer not provided with a polymer layer. First, the thickness T1 of the foamed sheet 1 and the thickness T3 of the polyolefin resin layer 3 are measured in advance by the method described above. Next, the basis weight B1 of the foamed sheet 1 and the basis weight B3 of the polyolefin resin layer 3 are measured. The basis weight B1 (g / m ² ) of the foam sheet 1 is 25 mm long x 25 mm wide (thickness remains the thickness T1 of the foam sheet 1), and the weight (g) of this test piece is cut out. After measurement, it is obtained by multiplying its weight by 1600. The basis weight B3 of the polyolefin-based resin layer 3 can be determined by one of the two measurement methods described above.

Next, the basis weight B2 (g / m ² ) of the polyolefin resin foam layer 2 is determined by subtracting the basis weight B3 of the polyolefin resin layer 3 from the basis weight B1 of the foam sheet 1. Further, the thickness T2 of the polyolefin resin foam layer 2 is obtained by subtracting the thickness T3 of the polyolefin resin layer 3 obtained by the above measurement method from the thickness T1 of the foam sheet 1. The apparent density P of the polyolefin resin foam layer 2 is a unit obtained by dividing the basis weight B2 (g / m2) of the polyolefin resin foam layer 2 by the thickness T2 (mm) of the polyolefin resin foam layer 2. Converted to the apparent density P (g / cm ³ ) of the foam layer 2. In the case where a polymer layer is provided, the basis weight B2 of the polyolefin resin foam layer 2 by subtracting the basis weight B3 of the polyolefin resin layer 3 and the basis weight of the polymer layer from the basis weight B1 of the foam sheet 1 ( g / m ² ), and the thickness T2 of the polyolefin resin foam layer 2 is obtained by subtracting the thickness T3 of the polyolefin resin layer 3 and the thickness of the polymer layer obtained by the above measurement method from the thickness T1 of the foam sheet 1. Thereafter, the apparent density P of the foamed layer 2 can be determined by the same operation.

  Examples of the polyolefin resin used in the polyolefin resin foam layer 2 and the polyolefin resin layer 3 constituting the foam sheet 1 of the present invention include a polyethylene resin, a polypropylene resin, and a mixture of two or more thereof. Examples of the polyethylene resin include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and a copolymer of ethylene and a comonomer such as an ethylene-vinyl acetate copolymer with an ethylene component exceeding 50 mol%. Furthermore, a mixture of two or more of these may be mentioned. In addition, as polypropylene resins, propylene homopolymers, propylene-ethylene copolymers, propylene-butene copolymers, propylene copolymers such as propylene-ethylene-butene copolymers, and mixtures of two or more thereof Is mentioned. Among the polyolefin resins, a polyethylene resin is preferably used from the viewpoint of flexibility such as low surface hardness and excellent surface protection performance of the package.

  In the present invention, the polyolefin resin used for the polyolefin resin foam layer 2 and the polyolefin resin layer 3 is a styrene resin such as polystyrene, ethylene propylene rubber, etc., as long as the object and effect of the present invention are not impaired. Polymers other than polyolefin resins such as rubber and elastomers such as styrene-butadiene-styrene block copolymers can be added. In that case, it is preferable that the polyolefin resin is contained in an amount of 50% by weight or more, more preferably 75% by weight or more, and particularly preferably 85% by weight or more.

  The polymer type antistatic agent used in the foamed sheet 1 of the present invention is preferably blended in an amount of 5 to 50 parts by weight, more preferably the base resin, with respect to 100 parts by weight of the base resin of the polyolefin resin layer 3. It is desirable that it is blended at a ratio of 10 to 25 parts by weight with respect to 100 parts by weight in terms of antistatic performance and formability of the polyolefin resin layer.

  The polymer layer provided as necessary includes the above-mentioned polyolefin resins, polyamide resins such as nylon, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, conductivity, antibacterial properties, gas barrier properties, and fragrances. Functional polymers having or added functions such as properties, light reflectivity, electromagnetic wave shielding properties and adhesiveness.

As the antistatic performance of the foamed sheet 1 of the present invention, it is preferable that the surface resistivity after ultrasonic cleaning of the foamed sheet 1 with ethanol is 1.0 × 10 ¹³ (Ω) or less, 8.0 × 10 ¹² (Ω ) Or less, more preferably 5.0 × 10 ¹² (Ω) or less. Further, from the viewpoint of preventing excessive quality, the surface resistivity of the foam sheet 1 is preferably 1.0 × 10 ⁸ (Ω) or more.

If the surface resistivity of the foam sheet 1 exceeds 1.0 × 10 ¹³ (Ω), there is a risk that the antistatic performance will be insufficient, and static charge will accumulate on the surface of the foam sheet 1 and dust will adhere to it. It's easy to do. Further, when the surface resistivity of the foamed sheet 1 is less than 1.0 × 10 ⁸ (Ω), the quality becomes excessive as antistatic performance, leading to high cost. From the viewpoint of preventing the adhesion of dust, the surface resistivity of the foam sheet 1 is preferably 5.0 × 10 ¹² (Ω) or less, and more preferably 1.0 × 10 ¹² (Ω) or less.

  The polyolefin resin layer 3 containing the polymer antistatic agent does not lose its antistatic effect even after ultrasonic cleaning with ethanol. When an antistatic agent comprising a surfactant such as a partial ester of glycerin and a fatty acid is added to the polyolefin resin layer 3, the antistatic agent bleeds out to the surface of the molded product under normal conditions, Even if moisture is taken in and exhibits an antistatic effect, the antistatic agent is washed away from the resin surface after ultrasonic cleaning with ethanol, and the antistatic effect is lost. Therefore, the measurement of the surface resistivity after ultrasonic cleaning with ethanol is effective as a means for determining whether or not the antistatic agent contained in the polyolefin-based resin layer 3 is of a polymer type.

  Since the foamed sheet 1 of the present invention comprises the polyolefin resin layer 3 containing a polymer type antistatic agent, it exhibits an appropriate antistatic effect before and after ultrasonic cleaning using ethanol, and is also antistatic even immediately after cleaning and drying. The effect is exhibited, and the effect hardly depends on the humidity condition.

  The surface resistivity of the foamed sheet 1 after washing with ethanol is measured according to JIS K6911 (1995) after the condition adjustment of the test piece. Specifically, a test piece cut into a size of 100 mm x 100 mm (thickness is the thickness of the foam sheet) from the foam sheet as the measurement object is submerged in ethanol at 23 ° C and subjected to ultrasonic cleaning. After a period of time, the test piece was left to dry for 36 hours in an atmosphere at a temperature of 30 ° C and a relative humidity of 30% to complete the condition adjustment of the test piece, and voltage application was started under the condition of an applied voltage of 500V. The surface resistivity after 1 minute is obtained.

The polymer type antistatic agent contained in the polyolefin-based resin layer 3 is an antistatic agent having a number average molecular weight of 2000 or more, preferably 2000 to 100,000, more preferably 5000 to 60000, and particularly preferably 8000 to 40000, A distinction is made from antistatic agents consisting of surfactants. The upper limit of the number average molecular weight of the polymer type antistatic agent is approximately 1000000. The polymer antistatic agent is preferably a resin having a surface resistivity of less than 1 × 10 ¹⁰ Ω. By setting the number average molecular weight of the polymer type antistatic agent within the above range, the antistatic performance is more stably expressed without being influenced by the environment, and the antistatic agent migrates to the packaged body surface. There is no pollution.

In addition, the said number average molecular weight is calculated | required using high temperature gel permeation chromatography. For example, when the polymer type antistatic agent is a hydrophilic resin mainly composed of polyetheresteramide or polyether, the sample concentration is 3 mg / ml using orthodichlorobenzene as a solvent, and the column temperature is 135 ° C. using polystyrene as a reference substance. It is a value measured under the conditions. In addition, the kind of said solvent and column temperature are suitably changed according to the kind of polymeric antistatic agent.
The polymer antistatic agent has a melt viscosity of 90 Pa · s or more, more preferably 100 to 1200 Pa · s, particularly 150 to 500 Pa · s, measured at a temperature of 190 ° C. and a shear rate of 100 sec ^−1. Is preferred. When the melt viscosity is within the above range, the viscosity balance between the antistatic agent and the polyolefin resin used in the polyolefin resin layer is improved, so that the addition of a relatively small amount of antistatic agent provides sufficient antistatic properties. An effect can be obtained.
The melt viscosity under the conditions of the temperature of 190 ° C. and the shear temperature of 100 sec ⁻¹ is determined as follows. As a melt viscosity measuring device, Leobis 2100 manufactured by Thiast Co., Ltd. is used, and the melt of the antistatic agent is extruded and discharged from the tip nozzle attached to the device under conditions of a resin temperature of 190 ° C. and a shear rate of 100 sec ^−1. Measured by. In this case, the hole diameter D of the nozzle is 1.0 mm, and the ratio L / D of the nozzle length L to the nozzle hole diameter D is 10.

  Further, the melting point of the polymer type antistatic agent is preferably 70 to 270 ° C., more preferably 80 to 230 ° C., and particularly preferably 80 to 200 ° C. Desirable from the viewpoint of sex.

  The melting point of the polymer antistatic agent can be measured by a method based on the following JIS K7121 (1987). That is, pretreatment is performed under the condition (2) for condition adjustment of the specimen in JIS K7121 (1987) (however, the cooling rate is 10 ° C./min), and the melting peak is obtained by raising the temperature at 10 ° C./min. The temperature at the top of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the melting point is the temperature at the top of the melting peak having the largest area. However, when there are a plurality of melting peaks having the largest area, the melting point is the temperature at the apex of the melting peak on the highest temperature side among the melting peaks.

  As the polymer type antistatic agent used in the present invention, an ionomer resin containing an alkali metal selected from the group consisting of potassium, rubidium and cesium as metal ions, a polyether ester amide, and a hydrophilic mainly composed of a polyether. Is preferred. In addition, the polymer type antistatic agent improves the compatibility of the polyolefin resin layer 3 with the base resin and gives an excellent antistatic effect, and also has the effect of suppressing the deterioration of physical properties due to the addition of the antistatic agent. In order to obtain this, it is more preferable to use a block copolymer of the same type of polyolefin resin as the base resin of the polyolefin resin layer 3.

Particularly preferred polymer antistatic agents include ionomers in which part or all of the ethylene-unsaturated carboxylic acid copolymer is neutralized with an alkali metal selected from the group consisting of potassium, rubidium and cesium, and The composition described in -278985 gazette is mentioned.
The composition described in JP-A-2001-278985 comprises a polyolefin (a) block and a hydrophilic polymer (b) block having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm, which are repeatedly bonded alternately. This is a block polymer (A) having a number average molecular weight (Mn) of 2000 to 60000 having the above structure. The block (a) and the block (b) have a structure in which they are alternately and repeatedly bonded via at least one bond selected from an ester bond, an amide bond, an ether bond, a urethane bond, and an imide bond. is there.

  The block of the polyolefin (a) of the block polymer (A) used as the polymer type antistatic agent includes a carbonyl group (preferably a carboxyl group. In addition, as a preferable embodiment of all the carbonyl groups exemplified below, A polyolefin having a hydroxyl group at both ends of the polymer (a2) and a polyolefin having a hydroxyl group at both ends of the polymer (a3) can be used. Further, polyolefin (a4) having a carbonyl group at one end of the polymer, polyolefin (a5) having a hydroxyl group at one end of the polymer, and polyolefin (a6) having an amino group at one end of the polymer can be used. Of these, polyolefins (a1) and (a4) having a carbonyl group are preferable because of easy modification.

  Polyether (b1), polyether-containing hydrophilic polymer (b2), cationic polymer (b3) and anionic polymer (b4) are used as the block of the hydrophilic polymer (b) constituting the block polymer (A). it can. As (b1), polyether diol (b1-1), polyether diamine (b1-2), and modified products thereof (b1-3) can be used. (b2), as polyether segment forming component polyether amide (b2-1) having a segment of polyether diol (b1-1), polyether amide imide (b2) having a segment of (b1-1) (b2) -2), polyether ester (b2-3) having the same segment (b1-1), polyether amide (b2-4) having the same segment (b1-2) and (b1-1) or ( Polyether urethane (b2-5) having the segment b1-2) can be used. As (b3), a cationic polymer having 2 to 80, preferably 3 to 60, cationic groups (c2) separated by a nonionic molecular chain (c1) in the molecule can be used. As (b4), dicarboxylic acid (e1) having a sulfonyl group and diol (b0) or polyether (b1) as essential structural units, and 2 to 80, preferably 3 to 60 in the molecule An anionic polymer having a sulfonyl group can be used.

  Specific examples of the block polymer (A) include the following block polymers (A1) to (A4).

[Block polymer (A1)]
The block polymer (A1) has a structure in which the block (a1) and the block (b1) are alternately and repeatedly bonded, and includes a polymer having a repeating unit represented by the general formula (1). In the general formula (1), n is an integer of 2 to 50, ^one of R ¹ and R ² is a hydrogen atom and the other is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, y is an integer of 15 to 800, E ¹ is a residue obtained by removing a hydroxyl group from diol (b0), A ¹ is an alkylene group having 2 to 4 carbon atoms, m and m ′ represent an integer of 1 to 300, and X and X ′ are represented by the general formula (2) to A group selected from the group represented by (8) and a group selected from the corresponding groups represented by (2 ′) to (8 ′), that is, when X is a group represented by the general formula (2), X ′ Is a group represented by the general formula (2 ′), and the same relationship applies to the general formulas (3) to (8) and (3 ′) to (8 ′).

In general formulas (2) to (8) and (2 ′) to (8 ′), R ³ and R ³ ′ are trivalent hydrocarbon groups having 2 to 3 carbon atoms, and R ⁴ is a carbon group having 1 to 11 carbon atoms. A divalent hydrocarbon group, R ⁵ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ⁶ is a hydrocarbon group having 2 to 22 carbon atoms, E ² represents an organic diisocyanate residue, and r is 1 to 10 , U and v are 0 or 1. Q, Q ′, T and T ′ are groups represented by the following formula.

However, R ⁵ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ⁷ is a hydrogen atom or a methyl group, t is 0 when R ⁷ is a methyl group, and 1 when a hydrogen atom. The polyether segment {(OA ¹ ) mOE ¹ -O- (A ¹ O) m ′} in {} in the repeating unit represented by the general formula (1) is formed by the polyether portion of the polyether (b1). And E ¹ , A ¹ , m and m ′ in the formula are the same as described above. E ¹ in the general formula (1) is preferably a residue obtained by removing a hydroxyl group from an aliphatic dihydric alcohol, a dihydric phenol, or a tertiary amino group-containing diol.

In the general formula (1), the block polymer (A1) in which X is a group represented by the general formula (2) and X ′ is a group represented by the general formula (2 ′) is a polyolefin (a1 ) And polyether diol (b1-1) can be directly reacted. R ³ and R ³ ′ in the general formulas (2) and (2 ′) are represented by [Chemical Formula 3]. (R ⁴ is a hydrogen atom or a methyl group, t is 1 when R ⁴ is a hydrogen atom, and 0 when R ⁴ is a methyl group.) For example, for carbonyl modification of polyolefin, maleic acid or When fumaric acid is used, R ³ is —CH ₂ —CH <and R ³ ′ is> CH—CH ₂ —.

  The amount of the polyether (b1) constituting the block polymer (A1) is usually 20 to 90% by weight, preferably 25 to 90% by weight, particularly preferably, based on the total weight of (a1) and (b1). 30 to 70% by weight. Mn of (A1) is usually 2000 to 60000, preferably 5000 to 40000, particularly preferably 8000 to 30000.

  In the structure of the block polymer (A1), the average number of repeating units (Nn) of the repeating unit of the polyolefin (a) block and the hydrophilic polymer (b) block is usually 2 to 50, preferably 2.3 to 30. More preferably, it is 2.7 to 20, particularly preferably 3 to 10.

[Block polymer (A2)]
The block polymer (A2) comprises a polyolefin (a) block and a hydrophilic polymer (b) block bonded in the (a)-(b) type or (a)-(b)-(a) type. Block polymer. (A2) can be obtained by reacting (b2) with a polyolefin (a4) having a carbonyl group represented by any one of the general formulas (9) to (11) at one end of the polymer.

In the formula, R ⁸ is a polyolefin residue, Q ′ is a group represented by the formula —CH (R ¹⁰ ) —CH═C (R ¹⁰ ) —CH ₂ —, and R ⁹ is a trivalent carbon atom having 2 to 3 carbon atoms. A hydrogen group, R ¹⁰ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ¹¹ is a hydrogen atom or a methyl group. (b2) is preferably the one represented by the general formula (19). In the formula (19), E ³ is a polyether group-containing hydrophilic polymer residue, R ¹² and R ¹³ are hydrogen atoms, the formula —CO—NH—E ² —NHCOO—R ¹⁴ —NH ₂ , the formula —CO—NH -E ² -NCO, a group represented by the formula -G or -CH ₂ CH (OH) CH ₂ -OE ⁴ -OG, p is 0 or 1, A ² is an alkylene group having 2 to 4 carbon atoms, or a formula- A group represented by (R ¹⁵ —CO) r—, wherein R ¹⁵ is a divalent hydrocarbon group having 1 to 11 carbon atoms (hereinafter, including both a saturated hydrocarbon group and an unsaturated hydrocarbon group), and r is An integer of 1 to 10, R ¹⁴ is a divalent hydrocarbon group having 2 to 12 carbon atoms, E ² is a residue of an organic diisocyanate, G is a glycidyl group, E ⁴ is glycidyl from diglycidyl ether (GOE ⁴ -OG) Represents a residue excluding an oxy group. R ¹² and R ¹³ are preferably a hydrogen atom and / or a group represented by the formula —CO—NH—E ² —NCO. In general formula (19), E ³ is preferably a group represented by general formula (20). In general formula (20), E ⁵ is a residue of polyether (b1), D is an oxygen atom and / or imino group, Z is a polymer segment selected from the group consisting of polyesteramide, polyamideimide, polyester, polyamide and polyurethane And a segment represented by any one of the general formulas (21) to (27) is preferable. u is 0 or 1, and w is usually 2 to 50, preferably 3 to 30. Z is preferably a polyesteramide segment represented by the general formula (21). In the general formulas (21) to (27), E ⁶ is a residue obtained by removing a carboxyl group from a dicarboxylic acid having 4 to 20 carbon atoms, and E ⁷ is a three carboxyl group from a trivalent or tetravalent aromatic carboxylic acid. E ⁸ is a residue formed from a polyamide-forming component selected from the group consisting of monoamides of dicarboxylic acids having 4 to 12 carbon atoms and diamines having 2 to 12 carbon atoms and aminocarboxylic acids having 6 to 12 carbon atoms. residue obtained by removing an amino group and a carboxyl group, E ⁹ is polyester selected from the group consisting of esters and oxycarboxylic acids having 6 to 12 carbon atoms and diols described above with a dicarboxylic acid having 4 to 12 carbon atoms (b0) residue excluding hydroxyl group and a carboxyl group of the terminal from the formation component, s, s ', s'' is 0 or 1 to 50 integer, (s + s') at least 1, a ³ is C2-4 alkylene group or a group of the formula -R ¹⁶ -CO- in, R ¹⁶ is a divalent hydrocarbon group having 1 to 11 carbon atoms, q is 0 or 1 to 10 Integer, E ¹⁰ is the formula ^{-CO-DE 11 -D-CO-} NH-E 2 -NH- a group represented, E ² is the residue of an organic diisocyanate, D is an oxygen atom and / or an imino group, E ¹¹ is It is the residue of a chain extender. As (A2), one or both of the ends of (b2) were replaced with groups represented by the following general formulas (12) to (14) {when the end of (b2) is a hydroxyl group or an epoxy group} Having a structure (bonded via an ester bond); having a structure represented by the general formulas (15) to (17) {when the terminal of (b2) is an amino group or an isocyanate group} (amide bond) And a group represented by the general formula (18) (when the terminal of (b2) is an amino group) is substituted (bonded via an imide bond).

The polyolefin residue R ⁸ has the formula R ¹⁷ — {CH (R ¹⁸ ) —CH (R ¹⁹ )} y— (wherein R ¹⁷ is a hydrogen atom or a group represented by H ₂ C═CH—, R ¹⁸ And one of R ¹⁹ is a hydrogen atom, the other is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and y is an integer of 15 to 800).

  The amount of (b2) constituting the block polymer (A2) is usually 20 to 80% by weight, preferably 30 to 70% by weight, based on the weight of (A2). Mn of (A2) is usually 2000 to 60000, preferably 5000 to 40000. In the structure of the block polymer (A2), the average repeating number (Nn) of the repeating units of the polyolefin (a) block and the hydrophilic polymer (b) block is usually 0.4 to 2.1, preferably 0. 0.5 to 2.0, more preferably 0.6 to 1.9, and particularly preferably 0.7 to 1.8.

[Block polymer (A3)]
The block polymer (A3) contains 2 to 80, preferably 3 to 60 cationic groups (c2) separated by a nonionic molecular chain (c1) in the molecule as the hydrophilic polymer (b). And has a structure in which (a) and (b3) are repeatedly bonded alternately. Mn in (A3) is usually 2000 to 60000, preferably 5000 to 40000, particularly preferably 8000 to 30000. The content of the cationic group (c2) in (A3) is 2 to 500, preferably 10 to 300, particularly preferably 15 to 250, per molecule of (A3). The Mn of (A3) per cationic group (c2) is usually 120 to 30000, preferably 200 to 6000, particularly preferably 300 to 4000.

  In the structure of the block polymer (A3), the average repeating number (Nn) of repeating units of the polyolefin (a) block and the hydrophilic polymer (b) block is usually 2 to 50, preferably 2.3 to 30. More preferably, it is 2.7 to 20, particularly preferably 3 to 10.

[Block polymer (A4)]
The block polymer (A4) has, as (b), dicarboxylic acid (e1) having a sulfonyl group and diol (b0) or polyether (b1) as essential structural units, and 2 to 80 in the molecule, preferably Has a block of an anionic polymer (b4) having 3 to 60 sulfonyl groups, and has a structure in which (a) and (b4) are bonded alternately and repeatedly. Mn of (A4) is usually 2000 to 60000, preferably 5000 to 40000, particularly preferably 8000 to 30000. The content of the sulfonyl group in (A4) is 2 to 500, preferably 10 to 300, particularly preferably 15 to 250, per molecule of (A4). The Mn of (A4) per sulfonyl group is usually 120 to 30000, preferably 200 to 6000, particularly preferably 300 to 4000.

  In the structure of the block polymer (A4), the average repeating number (Nn) of repeating units of the polyolefin (a) block and the hydrophilic polymer (b) block is usually 2 to 50, preferably 2.3 to 30. More preferably, it is 2.7 to 20, particularly preferably 3 to 10.

The polymer antistatic agents can be used alone or in combination.
The polymer antistatic agent as described above is commercially available, for example, under the trade names “SD100” manufactured by Mitsui DuPont Polychemical Co., Ltd. and “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.

In the foam sheet 1 of the present invention, the open cell ratio of the polyolefin-based resin foam layer 2 is preferably 60% or less, more preferably 40%, in order to provide particularly excellent buffering properties. Below, most preferably 30% or less. Open cell ratio of polyolefin resin foam layer: S (%) conforms to the procedure C described in ASTM D2856-70 (1976 recertification), air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. The actual volume of the test piece measured using (the sum of the volume of the closed cell and the volume of the resin part): Vx (cm ³ ), which is a value calculated by the following formula.
S (%) = (Va-Vx) x 100 / (Va-M / ρ)
However, Va, M, and ρ in the above formula are as follows.
Va: Apparent volume (cm ³ ) obtained from the outer dimensions of the test piece used for measurement
M: Weight of test specimen (g)
ρ: Density of resin constituting the test piece (g / cm ³ )

The density ρ (g / cm ³ ) of the resin constituting the test piece is determined by cooling the test piece used for measuring the weight M (g) of the test piece after defoaming the bubbles with a hot press. It can be determined by dividing by the sample volume (cm ³ ) obtained. In addition, since the test piece must be stored in a non-compressed state in the sample cup attached to the air comparison hydrometer, multiple foam sheet pieces with a length of 25 mm, a width of 40 mm, and a thickness of the foam sheet are prepared. Then, a minimum number of sheets are stacked and used as a test piece so that the apparent volume is approximately 25 cm ³ . However, if the foam sheet is too thick to be stored in the sample cup, use a test piece having a thickness of 25 mm by slicing, a length of 25 mm, a width of 40 mm, and a thickness of 25 mm.

  Further, in the foamed sheet 1 of the present invention, the average cell membrane thickness of the polyolefin resin foam layer 2 is 20 μm or less, more preferably 15 μm or less, so that particularly excellent buffering properties, flexibility and appearance are exhibited. Is preferable. The lower limit of the average bubble film thickness is approximately 2 μm.

The average bubble film thickness th (μm) can be obtained by the following formula.
th (μm) = (0.46 / ρp) ρf ・ D
Where D is the average cell diameter (μm) of the polyolefin resin foam layer, ρp is the density of the base resin of the polyolefin resin foam layer (g / cm ³ ), and ρf is the apparent density of the polyolefin resin foam layer (g / cm ³ ). g / cm ³ ). The average cell diameter D of the polyolefin resin foam layer is a value calculated by the following formula based on ASTM D3576-77.
Arithmetic mean value (μm) /0.616 of average bubble chord length in D = 3 directions (thickness direction, width direction and extrusion direction)
The average cell membrane thickness can be adjusted by the apparent density of the polyolefin resin foam layer and the average cell diameter of the polyolefin resin foam layer. The apparent density change of the polyolefin resin foam layer can be adjusted by the amount of foaming agent added, and the average cell diameter of the polyolefin resin foam layer is the pressure inside the die during extrusion foaming when the foaming agent addition amount is constant. And the amount of the bubble regulator added. Specifically, the average cell diameter of the polyolefin-based resin foam layer may be decreased as the pressure in the die is increased and / or the amount of the air conditioner is increased under the condition that the amount of the foaming agent added is constant. it can.

  Incidentally, the foam sheet 1 of the present invention does not completely exclude from the scope of rights what the conventional antistatic agent comprising a surfactant is contained in the polyolefin resin foam layer 2 and / or the polyolefin resin layer 3. In addition, since it is possible to exhibit sufficient antistatic performance without using an antistatic agent comprising the surfactant, and in such a case, the contact surface of the packaged body and the like will not be contaminated. It is preferable that the resin layer is substantially free of an antistatic agent composed of a surfactant, and further not contained at all. In addition, the antistatic agent is substantially not included as long as the contamination of the contact surface of the packaged body can be adjusted within an allowable range according to the application. It means that it doesn't matter.

  FIG. 2 is an explanatory view showing an example of a method for producing the foamed sheet of the present invention. Hereinafter, a method for producing the foamed sheet 1 of the present invention will be described. As shown in FIG. 2, a polyolefin resin layer forming resin melt 7 obtained by kneading the polyolefin resin 4, the polymer antistatic agent 5 and the hydrocarbon compound 6 in the first extruder 11, and A polyolefin resin 8, a foam regulator and a physical foaming agent 9 are kneaded in a second extruder 12 and laminated with a polyolefin resin foam layer forming resin melt 10 in a merging die. By coextrusion foaming, a foamed sheet 1 having a polyolefin resin layer on at least one surface of the polyolefin resin foam layer is obtained.

In addition, in the base resin of the polyolefin resin foam layer 2, the melt flow rate (MFR) is 0.05 to 10 g / 10 minutes, further 0.1 to 8.0 g / 10 minutes, the melt tension (MT) is 3 to 30 cN, Further, a polyethylene resin of 3.5 to 25 cN is preferable for obtaining a polyolefin resin foam layer 2 having a desired apparent density. Further, the base resin preferably has a polyethylene resin having a density of 0.900 to 0.935 g / cm ³ as a main component.

The melt tension (MT) of the polyolefin resin 8 used in the polyolefin resin foam layer forming resin melt 10 can be measured by, for example, a melt tension tester type II manufactured by Toyo Seiki Seisakusho. Specifically, using a melt tension tester equipped with a nozzle having a nozzle diameter of 2.095 mm and a length of 8 mm, the resin was extruded from the nozzle at a resin temperature of 190 ° C. and a piston speed of 10 mm / min. After this string is hung on a 45 mm diameter tension detection pulley, the stringing speed is gradually increased at a rate of about 5 rpm / sec (strike acceleration of the string: 1.3 x 10 ^-2 m / sec ² ). While letting go, pick up with a picking roller with a diameter of 50mm.

  The specific method for obtaining the melt tension of the polyolefin resin is to measure the melt tension of the string-like material detected with a detector connected to the tension detecting pulley by scooping at a scooping speed of 500 (rpm) over time. Measurements are shown on a chart with MT (mN) on the vertical axis and time (seconds) on the horizontal axis, and a graph with amplitude can be obtained. Next, the median value (X) of the amplitude of the stable portion is taken. This value (X) is taken as the melt tension. However, when the string-like material hung on the pulley for tension detection is cut up to a stringing speed of 500 (rpm), the stringing speed R (rpm) when the string-like object is cut is obtained. Next, the median value (X) of the amplitude is adopted as the melt tension from the graph obtained in the same manner as described above at a constant scraping speed of R × 0.7 (rpm). In the measurement, a specific amplitude that occurs infrequently is ignored.

  Production of the foam sheet 1 by coextrusion foaming method, in the embodiment shown in FIGS. 1 and 2, a polyolefin resin layer containing a polymer type antistatic agent is laminated as a surface layer on both the front and back sides of the polyolefin resin foam layer. A polyolefin resin layer containing a polymer-type antistatic agent is laminated only on one side of the polyolefin resin foam layer by the same method. can do.

  The hydrocarbon-based compound 6 is added to the polyolefin-based resin layer forming resin melt 7 of the first extruder 11. The hydrocarbon compound 6 is added to the polyolefin-based resin 4 in a polymer type. It is preferable to add the antistatic agent 5 after sufficiently dispersing it. As a result, when the polyolefin resin 4 and the polymer antistatic agent 5 are kneaded, the viscosity is kept high to some extent, and the polymer antistatic agent 5 is reliably dispersed to the polyolefin resin layer. A conductive network structure can be reliably formed. In addition, when coextruding with the polyolefin resin foam layer, a hydrocarbon compound is added to plasticize the resin melt for forming the polyolefin resin layer, so that the resin temperature of the melt is expanded. It is possible to adjust the cooling down to a temperature that does not impede, and to impart extensibility to follow the foamed layer. Such means is particularly effective when the polyolefin resin foam layer 2 has a high expansion ratio, and can produce a foam sheet 1 having a good antistatic effect and low open cell ratio. .

  In the foam sheet manufacturing method described above, the hydrocarbon compound 6 in the polyolefin resin layer is almost volatilized by the heat during extrusion at the time of extrusion. Depending on the hydrocarbon compound, a part of the hydrocarbon compound may remain in the foam sheet, but it volatilizes with time and hardly remains in the polyolefin resin layer 3.

  The resin melt 7 for forming the polyolefin resin layer and the resin melt 10 for forming the polyolefin resin foam layer are adjusted to an appropriate temperature in each of the extruders 11 and 12, and then laminated in the junction die 13. By co-extrusion from the die 13, a foamed sheet in which the polyolefin resin foam layer 2 is laminated on the polyolefin resin foam layer 2 is formed. As the die 13 at the tip of the extruder, a flat die, an annular die or the like can be used.

  The appropriate temperature of the melt 10 in the extruder 12 is a temperature at which the polyolefin resin foam layer-forming resin melt 10 exhibits optimum viscoelasticity for forming a foam layer. The appropriate temperature of the melt 7 in the extruder 11 is a temperature at which the resin melt 7 for forming a polyolefin-based resin layer exhibits good extensibility to form a resin layer and does not hinder the formation of a foam layer. That is. Specifically, the appropriate temperatures of the melts 7 and 10 are not less than [crystallization temperature + 5 ° C.] and not more than [crystallization temperature + 30 ° C.] of the olefin resin of each layer, and The appropriate temperature relationship is that the temperature of the resin melt 7 for forming the resin layer is not less than [the temperature of the resin melt 10 for forming the foam layer −30 ° C.] or more and the temperature of [the temperature of the resin melt 10 for forming the foam layer + 30 ° C.] or less. It is preferable from the viewpoint of suppressing a decrease in the open cell ratio of the foam layer and shrinkage of the obtained foam sheet, and more preferably, the temperature of the resin melt 7 for resin layer formation is [the temperature of the resin melt 10 for foam layer formation]. -15 ° C.] or more and [Temperature of foamed layer forming resin melt 10 + 15 ° C.] or less. In this specification, the crystallization temperature is a cooling rate of 10 ° C. for a sample that has been melted by heating from room temperature to 200 ° C. at a heating rate of 10 ° C./min in accordance with a method in accordance with JIS K7122 (1987). The peak temperature of the crystallization heat peak of the DSC curve obtained when the temperature is lowered to 40 ° C. at / min is defined as the crystallization temperature (° C.).

  The method for obtaining the foamed sheet 1 of the present invention by the coextrusion foaming method will be described in more detail. (1) Using a flat die, a method of coextrusion into a sheet from the beginning to form a foamed sheet, (2) Using an annular die There is a method of producing a cylindrical foam by co-extrusion and then cutting the cylindrical foam into a foam sheet.

  Among the methods described above, the method using the annular die (2) as the die 13 at the end of the extruder can suppress the occurrence of a corrugated pattern called a corrugate, and a wide foam sheet having a width of 1000 mm or more. There is an advantage that it can be manufactured easily.

  When coextrusion foaming using the annular die of (2) above, first, polyolefin resin 4 and polymer type antistatic agent 5 etc. are supplied to the first extruder 11, heated and kneaded, and then hydrocarbons A compound 6 is added and further kneaded to obtain a resin melt 7 for forming a polyolefin resin layer. At the same time, the polyolefin resin 8 and the air conditioner are supplied to the second extruder 12, heated and kneaded, and then the physical foaming agent 9 is press-fitted and further kneaded to form a resin melt for forming the polyolefin resin foam layer. 10

  Next, the foam layer forming resin melt 10 and the resin layer forming resin melt 7 are adjusted to appropriate temperatures, respectively, and then introduced into one annular joining die 13, and the die 13 is formed into a cylindrical shape. Coextrusion as a laminated foam. Next, after the inner surface of the cylindrical laminated foam is cooled by passing it over the side surface of the cylindrical cooling device, the foamed sheet 1 can be formed by cutting the cylindrical laminated foam. .

  In the coextrusion method, the polyolefin resin layer and the foamed layer can be laminated in the slit corresponding to the molten resin outlet of the joining die or immediately after the outside of the slit. Moreover, the said joining die, an extruder, a cylindrical cooling device, the apparatus which opens a cylindrical laminated foam, etc. can use the well-known thing conventionally used in the field of extrusion foaming.

  In the above production method, the dispersion state of the polymer antistatic agent in the resin is important for the polyolefin resin layer containing the polymer antistatic agent to exhibit sufficient antistatic performance. That is, by mixing the base resin of the polyolefin-based resin layer and the polymer antistatic agent, the dispersion state of the polymer antistatic agent in the obtained resin layer becomes a network-like or layered continuous layer, whereby the polymer The mold antistatic agent forms a conductive network in the resin. On the other hand, if the kneading of the polymer antistatic agent is insufficient, the polymer antistatic agent will not be uniformly dispersed in the polyolefin-based resin, but will be present in a discrete manner, and sufficient in the resin layer. A conductive network cannot be formed.

Polyolefin resin layer 3 containing polymer antistatic agent 5 has a surface resistivity of preferably 1.0 × 10 ⁸ (Ω) to 1.0 × 10 ¹³ (Ω) by forming a conductive network structure inside. Formed. The polymer antistatic agent 5 does not exhibit antistatic performance if it is simply added to the polyolefin resin 4, and the polymer antistatic agent 5 has a conductive network structure in the polyolefin resin layer 3. It needs to be formed. The conductive network structure is a structure in which a polymer layer antistatic agent 5 is disposed in a state where a continuous layer is formed when dispersed in a resin constituting the polyolefin resin layer 3.

  The conductive network structure is easily formed by applying an appropriate orientation when the polyolefin resin layer forming resin melt 7 is extruded to form the polyolefin resin layer 3.

  In the resin melt 7 for forming a polyolefin resin layer, in order to disperse the polymer antistatic agent 5 so that a conductive network is formed, the melt flow rate (MFR) of the polymer antistatic agent 5 and the polyolefin resin are used. The balance with the melt flow rate (MFR) of the base resin of the resin layer 3 is important. Specifically, the balance can be achieved by selecting the melt flow rate value of the base resin of the polyolefin resin layer to be lower than the melt flow rate value of the polymer antistatic agent.

  In this specification, the melt flow rate (MFR) adopts a value measured at a test temperature of 190 ° C. and a load of 21.18 N in accordance with JIS K7210 (1999) A method, regardless of the type of resin. .

In the foamed sheet 1 of the present invention, the polyolefin resin layer having a basis weight of 0.1 to 20 g / m ² is a hydrocarbon compound having a boiling point of −100 to 120 ° C. in preparing the polyolefin resin layer forming resin melt 7. It can be formed by containing 6.

  The hydrocarbon compound 6 contained in the resin melt 7 for forming a polyolefin resin layer has a function of reducing the melt viscosity in a state dissolved in the resin melt 7 for forming a polyolefin resin layer, and a polyolefin. After the resin-based resin layer 3 is formed, it is selected as a material that volatilizes from the polyolefin-based resin layer 3 and can be removed from the polyolefin-based resin layer 3.

By using the polyolefin resin layer forming resin melt 7 to which the hydrocarbon compound 6 is added, when the foamed sheet 1 of the present invention is produced by coextrusion, the melt elongation of the polyolefin resin layer 3 is remarkably increased. The elongation of the polyolefin-based resin layer 3 can be made to follow the elongation of the polyolefin-based resin foam layer 3, so that cracking due to insufficient elongation of the polyolefin-based resin layer 3 can be prevented. Note that the occurrence of cracks hinders the development of the antistatic function.
Therefore, by using the polyolefin resin layer forming resin melt 7 adjusted as described above, the polyolefin resin layer 3 is adjusted by adjusting the discharge amount and take-off speed of the resin layer forming resin melt 7. Can be formed to the desired basis weight.

The polyolefin resin layer forming resin melt 7 has a small discharge rate and has a polyolefin resin layer with a basis weight of 0.1 to 20 g / m ² by a normal coextrusion method not using a hydrocarbon compound. Even if a foamed sheet is to be formed, if the temperature of the melt 7 is adjusted to a temperature that does not hinder the formation of the foamed layer, the fluidity of the polyolefin-based resin layer forming resin melt 7 becomes poor. Further, as described above, the balance adjustment between the polyolefin resin constituting the resin layer and the melt flow rate of the polymer antistatic agent for forming the network structure of the polymer antistatic agent in the polyolefin resin layer. Becomes difficult.
On the other hand, the resin melt 10 for forming a polyolefin-based resin foam layer has improved fluidity due to a plasticizing effect due to containing a foaming agent.
Therefore, when the melt 7 and the melt 10 are co-extruded, the melt 10 must be adjusted to an appropriate temperature showing melt viscoelasticity suitable for foaming in order to form a foam layer. The melt 10 with improved properties must be cooled. Further, the temperature of the melt 7 is adjusted to substantially the same temperature as the appropriate temperature in accordance with the appropriate temperature of the melt 10 so as not to inhibit the foaming property of the melt 10. As a result, although the foamability of the melt 10 is ensured, the fluidity of the melt 7 is poor, and due to the volume expansion due to foaming of the melt 10 and the lack of elongation of the melt 7, the polyolefin resin layer 3 In this case, cracks are generated and the antistatic function is not exhibited.
In addition, in order to prevent cracks in the polyolefin resin layer 3, even if cracks are prevented by selecting a polyolefin resin having a high melt flow rate as the main component of the resin layer, It is difficult to adjust the balance between the molecular type antistatic agent and the melt flow rate, and a foam sheet having an appropriate antistatic function cannot be obtained.

The foamed sheet of the present invention is one in which a polyolefin resin layer having a basis weight of 0.1 to 20 g / m ² is formed. The reason why the upper limit of the basis weight is 20 g / m ² is as follows, in addition to ensuring the intended purpose, that is, lightness and flexibility. When an attempt is made to form a polyolefin resin layer having a large basis weight by increasing the discharge amount of the polyolefin resin layer forming resin melt 7 by the coextrusion method, the hydrocarbon in the polyolefin resin layer forming resin melt Since the compound 6 acts as a foaming agent, if the basis weight is too large, a good polyolefin resin layer cannot be formed, and the resulting foamed sheet has a poor appearance.

As described above, in order to form the foamed sheet of the present invention having a resin layer having a basis weight of 0.1 to 20 g / m ² , the temperature of the resin melt 7 for resin layer formation and the resin melt 10 for foam layer formation is as follows. It is necessary to adjust the temperature to an appropriate temperature as described above, and it is an effective means to add the hydrocarbon-based compound 6 to the melt for improving the fluidity of the resin melt for resin layer formation at that time, In particular, this is a very effective means for obtaining a foam sheet having a small apparent density.

  Moreover, the adjustment of the thickness of the foam sheet 1 described above is adjusted to the above-described range by adjusting the discharge amount and take-up speed of the molten resin in coextrusion foaming.

  The hydrocarbon compound 6 is one selected from an aliphatic hydrocarbon having 2 to 7 carbon atoms, an aliphatic alcohol having 1 to 4 carbon atoms, or an aliphatic ether having 2 to 8 carbon atoms, or 2 More than one species can be used, and in particular, an aliphatic hydrocarbon having 3 to 6 carbon atoms is preferably used. The hydrocarbon compound 6 is preferable from the viewpoint that the resin of the polyolefin resin layer 3 is efficiently plasticized, and the hydrocarbon compound itself hardly remains in the obtained polyolefin resin layer 3.

  Examples of the aliphatic hydrocarbon having 2 to 7 carbon atoms include ethane, propane, normal butane, isobutane, normal pentane, isopentane, isohexane, cyclohexane, heptane and the like.

  Examples of the aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, normal butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol.

  Examples of the aliphatic ether having 2 to 8 carbon atoms include methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl amyl ether, Examples include methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl amyl ether, ethyl isoamyl ether, vinyl ether, allyl ether, methyl vinyl ether, methyl allyl ether, ethyl vinyl ether, and ethyl allyl ether.

  The hydrocarbon compound 6 has a boiling point of −100 to 120 ° C. at which the above functions and effects can be exerted, and preferably has a boiling point of 80 ° C. or less from the viewpoint of being easily volatilized from the polyolefin resin layer. The hydrocarbon-based compound 6 is co-extruded and then allowed to stand, so that it volatilizes spontaneously from the polyolefin-based resin layer of the foam sheet due to heat immediately after co-extrusion and subsequent gas permeation of the hydrocarbon-based compound, It can be removed from the polyolefin resin layer.

  The addition amount of the hydrocarbon compound 6 is 5 to 50 parts by weight with respect to 100 parts by weight of the kneaded product of the polyolefin resin 4 and the polymer antistatic agent 5. When the addition amount of the hydrocarbon compound 6 is less than 5 parts by weight, the polyolefin resin obtained by adding the polymer type antistatic agent constituting the polyolefin resin layer generates heat due to kneading, and the heat causes the polyolefin resin layer. The resin temperature of the foam layer forming resin melt laminated with the forming resin melt and the converging die rises. There is a possibility that a small foam layer cannot be obtained. Moreover, there exists a possibility that film forming property itself may worsen by the melt elongation lack of a polyolefin resin layer.

  Further, the amount of the hydrocarbon compound 6 added to 100 parts by weight of the kneaded product of the polyolefin resin 4 and the polymer antistatic agent 5 is such that the polyolefin resin layer 3 follows the polyolefin resin foam layer 2. 7 parts by weight or more is preferable, and 10 parts by weight or more is more preferable from the viewpoint of excellent and easy thin lamination of the polyolefin-based resin layer 3 uniformly.

On the other hand, if the addition amount of the hydrocarbon compound 6 exceeds 50 parts by weight, the physical properties of the polyolefin resin layer 3 itself deteriorates and the kneadability of the hydrocarbon compound with the resin of the polyolefin resin layer 3 becomes insufficient. There is a possibility that the hydrocarbon-based compound is ejected from the die lip, and as a result, a hole is formed in the polyolefin-based resin layer 3 of the foamed sheet 1, the surface becomes uneven, and the appearance is deteriorated. From the above viewpoint, the addition amount of the hydrocarbon compound 6 is preferably 45 parts by weight or less, and more preferably 40 parts by weight or less.
By making the addition amount of the hydrocarbon-based compound 6 within the above range, it is possible to ensure the effect of lowering the melt viscosity and improving the extensibility of the polyolefin-based resin layer forming resin melt at the time of coextrusion.

  As described above, the polyolefin resin foam layer 3 is formed by extrusion foaming the polyolefin resin foam layer forming resin melt 10. Examples of the physical foaming agent 9 added to the polyolefin resin foam layer forming resin melt 10 include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane, and cyclohexane, and chloride. Organic physical foaming agents such as chlorohydrocarbons such as ethyl, fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, water, oxygen, nitrogen, carbon dioxide, air, etc. An inorganic physical foaming agent is mentioned. The above physical foaming agents can be used in combination of two or more. Among these, an organic physical foaming agent is preferable from the viewpoint of compatibility with a polyethylene resin and foaming efficiency, and normal butane, isobutane, or a mixture thereof is particularly preferable.

  A bubble regulator is usually added to the resin melt 10 for forming a polyolefin resin foam layer. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic foam regulator include borate metal salts such as zinc borate, magnesium borate, borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like. Examples of the organic foam regulator include sodium 2,2-methylenebis (4,6-tert-butylphenyl) phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. A combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can also be used as the bubble regulator. These bubble regulators can be used as a mixture of two or more.

  The amount of the foaming agent added to the polyolefin resin foam layer forming resin melt 10 is adjusted according to the type of foaming agent and the desired apparent density. Moreover, the addition amount of a bubble regulator is adjusted according to the target bubble diameter. That is, when a butane mixture of 30% by weight of isobutane and 70% by weight of normal butane is used as the blowing agent, the amount of the butane mixture added is 3 to 35 parts by weight, preferably 4 to 33 parts by weight per 100 parts by weight of the polyolefin resin. Parts, more preferably 10 to 30 parts by weight. The addition amount of the cell regulator is 0.01 to 10 parts by weight, preferably 0.03 to 8 parts by weight, per 100 parts by weight of the polyolefin resin.

  Various additives may be added to the resin described above in the resin melt 7 for forming a polyolefin resin layer and the resin melt 10 for forming a polyolefin resin foam layer. Examples of the various additives include crystal nucleating agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, and shrinkage inhibitors. In this case, the amount added is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 3% by weight or less. The lower limit is approximately 0.01% by weight.

  Examples of the present invention will be described below.

Example 1
Low-density polyethylene [a] (density 920g / L, MFR = 0.3g / 10min, trade name “DFDJ6775” manufactured by Nihon Unicar Co., Ltd.) is blended with an air-conditioning agent masterbatch and charged into the raw material of an extruder with an inner diameter of 115mm The mixture was supplied to the mouth, heated and kneaded to obtain a molten resin mixture adjusted to about 200 ° C. Using a molten butane mixed foaming agent of 70% by weight normal butane and 30% by weight isobutane (simply referred to as “butane” in Table 1) as a physical foaming agent, 100 parts by weight of low density polyethylene [a] is used. On the other hand, it was press-fitted so as to be 20 parts by weight, and then the resin temperature was adjusted to 110 ° C. to obtain a resin melt for forming a polyolefin-based resin foam layer.

  On the other hand, for 100 parts by weight of low-density polyethylene [b] (density 924 g / L, MFR = 1.5 g / 10 min, trade name “JE330N” manufactured by Nippon Polyolefin Co., Ltd.), a polyether-polypropylene block as a polymer type antistatic agent 18 parts by weight of copolymer (number average molecular weight 14000, MFR = 25 g / 10 min, melting point 136 ° C., density 990 g / L, trade name “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.) Blended, supplied to the raw material inlet of an extruder with an inner diameter of 65 mm, heated and melted to obtain a molten resin mixture adjusted to about 200 ° C. A mixture of 70% by weight of normal butane and 30% by weight of isobutane as a hydrocarbon compound (simply referred to as “butane” in the table) as a hydrocarbon-based compound is mixed with low-density polyethylene [b] and a polymeric antistatic agent. Press-fitted so as to be 20 parts by weight with respect to 100 parts by weight of the molten resin mixture, and then adjusted the resin temperature to 110 ° C. to obtain a resin melt for forming a polyolefin-based resin layer containing a polymer type antistatic agent. .

The obtained resin melt for forming a polyolefin-based resin layer and the resin melt for forming a polyolefin-based resin foam layer are supplied into a confluence die, and are laminated and joined so that the resin melt for forming a resin layer becomes a surface layer. Co-extruded from an annular slit with a diameter of 95 mm at a die pressure of 70 kg / cm ² and contains a polyolefin resin layer / polyolefin resin foam layer / polymer antistatic agent containing a polymer antistatic agent from the outside A cylindrical laminated foam having a three-layer structure was formed in the order of the polyolefin resin layers to be formed. After the extruded cylindrical laminated foam was taken along the side surface of the cylindrical cooling device, the cylindrical laminated foam was cut open to obtain a foam sheet having a width of 1100 mm.
The discharge amount of the melt for forming the polyolefin resin foam layer at the time of coextrusion foaming is 95 kg / hr, and the amount of addition of the cell regulator master batch is 0.3 parts by weight with respect to 100 parts by weight of the low density polyethylene [a]. Was adjusted to 7.8 μm.
Furthermore, the take-up speed during the production of the foam sheet is 71.6 m / min. For forming the polyolefin resin layer so that the basis weight of the polyolefin resin layer is 3.7 g / m ^{2 on} both sides of the polyolefin resin foam layer. The discharge rate of the melt was adjusted to 35 kg / hr.
The obtained foamed sheet was excellent in flexibility and buffering properties.

Example 2
28 parts by weight of butane as a blowing agent is blended with 100 parts by weight of the resin melt for forming a foam layer, and 28 parts by weight of butane is blended as a hydrocarbon compound with respect to 100 parts by weight of the resin melt for forming a polyolefin-based resin layer. A foam sheet having a width of 1100 mm was produced using the same raw materials and production method as in Example 1 except that the amount of the adjustment agent master batch was adjusted to 0.14 parts by weight with respect to 100 parts by weight of the low density polyethylene [a]. The temperature of the foamed layer forming resin melt was adjusted to 111 ° C., and the temperature of the polyolefin resin layer forming resin melt was adjusted to 111 ° C.
The discharge amount of the melt for forming the polyolefin resin foam layer at the time of coextrusion foaming is 78 kg / hr, and the addition amount of the foam regulator masterbatch is 0.14 parts by weight with respect to 100 parts by weight of the low density polyethylene [a]. Was adjusted to 4.9 μm.
Furthermore, the take-up speed during foam sheet production is 95.3 m / min, and for polyolefin resin layer formation so that the basis weight of the polyolefin resin layer is 0.95 g / m ^{2 on} both sides of the polyolefin resin foam layer, respectively. The discharge rate of the melt was adjusted to 12 kg / hr.
The obtained foamed sheet was excellent in flexibility and buffering properties.

Example 3
28 parts by weight of butane as a blowing agent is blended with 100 parts by weight of the resin melt for forming a foam layer, and 28 parts by weight of butane is blended as a hydrocarbon compound with respect to 100 parts by weight of the resin melt for forming a polyolefin-based resin layer. Except for adjusting the addition amount of the adjusting agent master batch to 0.2 parts by weight with respect to 100 parts by weight of the low density polyethylene [a] and co-extrusion from the annular die at a die pressure of 65 kg / cm ² , the same as in Example 1. A foam sheet with a width of 1100 mm was manufactured using the raw materials and the manufacturing method. The temperature of the foamed layer forming resin melt was adjusted to 111 ° C., and the temperature of the polyolefin resin layer forming resin melt was adjusted to 111 ° C.
The discharge amount of the melt for forming the polyolefin resin foam layer at the time of coextrusion foaming is 78 kg / hr, and the addition amount of the foam regulator masterbatch is 0.2 parts by weight with respect to 100 parts by weight of the low density polyethylene [a]. Was adjusted to 4.8 μm.
Furthermore, the take-up speed during the production of the foam sheet is 68.6 m / min. For forming the polyolefin resin layer so that the basis weight of the polyolefin resin layer is 1.8 g / m ^{2 on} both sides of the polyolefin resin foam layer. The discharge rate of the melt was adjusted to 16 kg / hr.
The obtained foamed sheet was excellent in flexibility and buffering properties.

Comparative Example 1
Antistatic agent consisting of a surfactant (trade name “PEX94AS-026” manufactured by Tokyo Ink Co., Ltd .: 10 polyoxyethylene alkylamine nonadecanoic acid ester having a molecular weight of less than 1000) per 100 parts by weight of low density polyethylene [a] Low-density polyethylene base masterbatch containing 1% by weight.The melt viscosity of polyoxyethylene alkylamine nonadecanoic acid ester cannot be measured because it is liquid at a measurement temperature of 190 ° C.) 0.2 parts by weight of the batch was added, and 28 parts by weight of butane was added as a blowing agent after heating and melting. After that, the resin temperature was adjusted to 112 ° C., and extrusion foaming was performed from a circular slit part with a diameter of 95 mm of the circular die at a die pressure of 65 kg / cm ^{2 to} obtain a 1100 mm wide sheet consisting only of a foam layer to which an antistatic agent was added. Obtained. The discharge amount of the polyolefin resin foam layer forming melt at this time was 150 kg / hr, and the average cell membrane thickness was adjusted to 5.5 μm by adding the cell regulator master batch as described above.
The obtained foamed sheet was excellent in flexibility and buffering properties, but the surface resistivity after the ethanol cleaning was extremely lowered in the surface resistivity.

Comparative Example 2
17 parts by weight of the polymer type antistatic agent (trade name “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.) used in Example 1 for 100 parts by weight of low density polyethylene [a], 0.2 part by weight was added, and 28 parts by weight of butane was added as a foaming agent after heating and melting. Annular slit portion from the discharge 150 kg / hr of thereafter adjusting the resin temperature to 110 ° C. of the annular die diameter 95 mm, by performing the extrusion foaming at the die pressure 65 kg / cm ^2, only the foamed layer added an antistatic agent A foam sheet with a width of 1100 mm was obtained.
The obtained foamed sheet was excellent in flexibility, but the bubbles in the foamed layer were broken, so that the surface of the foamed sheet became uneven and the appearance was poor, and the open cell ratio was high enough. It was not possible to obtain a foam sheet having a sufficient buffer property. Further, since the bubbles break, it is difficult to adjust the average bubble film thickness.

Comparative Example 3
Add 0.2 parts by weight of a foam regulator masterbatch to 100 parts by weight of low density polyethylene [a], mix 28 parts by weight of butane as a foaming agent after heating and melting, and then adjust the resin temperature to 110 ° C. Extrusion foaming was performed from an annular slit portion of a circular die having a diameter of 95 mm at a discharge of 150 kg / hr and a die pressure of 65 kg / cm ² to obtain a polyethylene resin foam sheet having an apparent density of 23 g / L, a thickness of 1 mm, and a width of 1100 mm. Next, from T-die to low-density polyethylene [c] (density 917 g / L, crystallization temperature 93.5 ° C., MFR = 4.6 g / 10 min, trade name “NUC8008” manufactured by Nippon Unicar Co., Ltd.) 18 parts by weight of type antistatic agent (trade name “Pelestat 300” manufactured by Sanyo Chemical Industries Co., Ltd.) is blended so that the discharge is 60 kg / hr, the resin temperature is 230 ° C., and the line speed is 15.2 m / min. Extrusion was performed into a sheet shape, and the polyethylene resin foam sheet was heat-laminated. However, although the obtained resin layer laminated foam sheet was excellent in buffering properties, the resin layer basis weight was too large, so that it did not have sufficient flexibility.

  The composition of the foam control agent master batch used in Examples 1 to 3 and Comparative Examples 1 to 3 is 80% by weight of low density polyethylene, 4.5% by weight of sodium bicarbonate, and 15.5% by weight of sodium citrate. .

  For the foam sheets of Examples 1 to 3 and Comparative Examples 1 to 3, the type of resin in the polyolefin resin foam layer, MFR, MT, the type of physical foaming agent, the blending amount, the type of resin in the polyolefin resin layer, MFR, Table 1 shows the melt viscosity, number average molecular weight and blending amount, type of hydrocarbon compound, blending amount of the polymer type antistatic agent. Items that are not necessary in the table are indicated by “—”, and low density polyethylene is abbreviated as LDPE.

  Also, the temperature of the resin melt for forming the foam layer, the temperature of the resin melt for forming the resin layer, the apparent density of the foam layer, the total thickness of the foam sheet, the basis weight of the resin layer (the polyolefin on each of the front and back layers laminated on both sides of the foam layer) System resin layer basis weight), average cell membrane thickness, surface resistivity and open cell rate were measured. The results are shown in Table 2. Items that are not required in the table are marked with “-”. The method for measuring the surface resistivity is shown below.

[Surface resistivity before ethanol cleaning]
The surface resistivity was basically measured according to JIS K6911 (1995). Specifically, Takeda Riken after adjusting the test piece (length 100mm, width 100mm, thickness: thickness of the foamed sheet) cut out from the foamed sheet for 24 hours in an atmosphere of 23 ° C and 50% humidity Using a “TR8601 HIGH MEGOHM METER” manufactured by Kogyo Co., Ltd., the surface resistivity was determined one minute after the voltage application was started under the condition of an applied voltage of 500V.

[Surface specific resistivity after ethanol cleaning]
The surface resistivity after cleaning was determined by submerging a test piece cut out from a foamed sheet in ethanol at 23 ° C. and ultrasonically cleaning it for 24 hours, and then subjecting the test piece to an atmosphere of 30 ° C. and a relative humidity of 30%. Measurement was performed in accordance with JIS K6911 (1995) except that the specimen was dried by being left for a period of time and the specimen immediately after the drying operation was used as a conditioned specimen. For the condition adjustment of the test piece in the method for measuring the surface resistivity after cleaning, “BRANSONIC 220” manufactured by Branson was used as an ultrasonic cleaning device. A specific state adjustment method is shown below.

  First, put 500 ml of ethanol in a beaker for 500 ml, maintain the temperature of ethanol at 23 ° C., and then put a test piece (length 100 mm, width 100 mm, thickness is the thickness of the foam sheet) in the beaker with a wire mesh. The work of submerging the specimen in ethanol at 23 ° C. was completed by submerging. After that, the beaker in which the test piece is submerged is covered with a foil, and the beaker is placed in the concave storage portion of the ultrasonic cleaning device containing 1.7 liters of water at 23 ° C. The cleaning device was turned on and cleaning was started. After 8 hours had passed since the start of washing and further 16 hours after the start of washing, an operation of adding ethanol at 23 ° C. was performed so that the ethanol in the beaker became 500 ml. This additional operation of ethanol is an operation of replenishing ethanol because it is volatilized by ultrasonic cleaning and is reduced from the amount originally present in the beaker. After 24 hours from the start of cleaning, the ultrasonic cleaning device was stopped, the test piece was taken out of the beaker, and this test piece was immediately left to dry for 36 hours in an atmosphere with a relative humidity of 30% and a temperature of 30 ° C. To complete the condition adjustment of the test piece.

It can be said that the foam sheet having a surface resistivity of 1 × 10 ¹³ Ω or less after washing has an appropriate permanent antistatic effect. The measurement of the surface resistivity after the ethanol cleaning was performed by cutting out a test piece from the foamed sheet and adjusting the state after the ultrasonic cleaning with the ethanol, similarly to the measurement of the surface resistivity before the cleaning. Further, for each of the test pieces, a surface specific resistivity one minute after the voltage application was started under the condition of an applied voltage of 500 V using “TR8601 HIGH MEGOHM METER” manufactured by Takeda Riken Kogyo Co., Ltd. was obtained.

It is sectional drawing which shows an example of this invention foam sheet. It is explanatory drawing which shows an example of the manufacturing method of this invention foam sheet.

Explanation of symbols

1 Foam sheet
2 Polyolefin resin foam layer
3 Polyolefin resin layer
4 Polyolefin resin
5 Polymer type antistatic agent
6 Hydrocarbon compounds
7 Resin melt for forming polyolefin resin layer
8 Polyolefin resin
9 Physical blowing agent
10 Resin melt for forming polyolefin resin foam layer
11 First extruder
12 Second extruder

Claims (4)

In a foamed sheet having a polyolefin resin layer on at least one surface of a polyolefin resin foam layer having an apparent density of 0.015 to 0.3 g / cm ^3, the polyolefin resin layer contains a polymer-type antistatic agent and has a basis weight of 0.1 to A polyolefin-based resin foam sheet characterized by being 20 g / m ² . 2. The polyolefin resin foam sheet according to claim 1, wherein the polymer type antistatic agent has a number average molecular weight of 2000 or more. 3. The polyolefin resin foam according to claim 1, wherein the polymer type antistatic agent is added in a ratio of 5 to 50 parts by weight with respect to 100 parts by weight of the base resin of the polyolefin resin layer. Sheet. 4. The polyolefin resin foam sheet according to claim 1, wherein an average cell membrane thickness in the polyolefin resin foam layer is 20 μm or less.

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