WO2011062141A1

WO2011062141A1 - Resin foamed sheet

Info

Publication number: WO2011062141A1
Application number: PCT/JP2010/070294
Authority: WO
Inventors: 正義岩田; 俊信古木
Original assignee: 積水化成品工業株式会社
Priority date: 2009-11-18
Filing date: 2010-11-15
Publication date: 2011-05-26
Also published as: TWI500512B; JP2011105863A; CN102612534B; KR20120116406A; MY159154A; TW201134664A; JP5642957B2; CN102612534A

Abstract

Provided is a resin foamed sheet that is suitable for uses such as the formation of foam-molded products with three-dimensional structures, whereby striped patterns are inhibited from appearing on the surface of the resin foamed sheet by an approach other than adjusting extrusion conditions. The provided resin foamed sheet is formed by extruding (from an extruder) and foaming a polypropylene resin composition consisting primarily of a polypropylene resin. Said polypropylene resin composition is characterized by containing a high-melt-tension polypropylene resin in an amount constituting at least 20% and less than 50% of the contained polymer components, by mass.

Description

Resin foam sheet

The present invention relates to a resin foam sheet formed by extruding and foaming a polypropylene resin composition with an extruder.

Conventionally, a resin foam sheet obtained by foaming a resin composition into a sheet has been widely used in applications where lightness and buffering properties are required.
Especially, the resin foam sheet formed with the polypropylene resin composition which has a polypropylene resin as a main component is widely used since it is comparatively cheap.
Such a foamed resin sheet is usually produced continuously by extruding and foaming a polypropylene resin composition, and not only a foamed resin layer single layer but also a non-foamed resin layer called a film layer on the surface. Are manufactured.
This resin foam sheet is used as a glass sheet buffer sheet in the form of a sheet, and is also used as a raw material for producing a foam molded product having a three-dimensional structure such as a foam tray by a sheet molding method.

By the way, various studies have been made on a method for producing such a foam-molded article. For example, in Patent Document 1 below, a polypropylene resin composition and a high melt tension polypropylene resin (hereinafter referred to as “HMS-PP”). It is described that a resin foam sheet having excellent moldability can be obtained by containing 50% by mass or more.

In addition, when the resin foam sheet is molded into a foam tray or the like, the resin foam sheet is heated and softened, and vacuum molding is performed by adsorbing to a mold in which the tray shape is formed by negative pressure (evacuation). Alternatively, a molding method called pressure air molding in which a resin foam sheet is pressed against a molding die with positive pressure is widely adopted.
In such vacuum forming and pressure forming, the resin foam sheet is not in a uniform condition as a whole because it is performed to form irregularities on the resin foam sheet while gripping the periphery of the resin foam sheet, For example, if the thickness of the resin foam sheet is uneven, thin parts that are easily stretched due to stress are preferentially stretched. Depending on the case, appearance defects may occur in the molded product. There is a risk of forming a tearing point.
In addition, it is a matter calculated | required not only for the resin foam sheet used for a shaping | molding process but when a resin foam sheet is used with a sheet form to make a resin foam sheet into a homogeneous state.

However, it is difficult to make the resin foam sheet uniform on the entire surface, and when forming the resin foam sheet by extrusion foaming, the difference in texture such as surface gloss is continuously applied to the surface of the resin foam sheet in the extrusion direction. Striped patterns may appear.
In many cases where such stripes are seen on the surface of the resin foam sheet, the portions having different surface glossiness slightly differ not only in appearance but also in sheet thickness and density (degree of foaming).

Therefore, usually, when such a stripe is generated in the resin foam sheet, there is a higher possibility of causing a defect in vacuum molding or pressure forming than a resin foam sheet having no stripe on the surface. There is a need to prevent the occurrence of fringes.
However, a method for preventing the stripes has not been established so far, and only symptomatic measures are mainly taken.
For example, based on experience, select extrusion conditions that are less likely to cause stripes and start extrusion foaming of the polypropylene resin composition. If stripes are found in the extruded resin foam sheet, further extrusion conditions A measure is taken to collect the product after searching for a condition where the fringes are not seen by fine-tuning.

As described above, conventionally, no specific means for preventing streaks other than adjustment of extrusion conditions has been established, and in some cases, a resin foam sheet can be produced only in a narrow range of conditions. It has become.

Japanese Laid-Open Patent Publication No. 2003-236916

The present invention has been made in view of the above-described problems, and is intended to suppress fringes by an approach other than adjustment of extrusion conditions, and as a result, can be easily manufactured so that no fringes are seen. The object is to provide a resin foam sheet.

As a result of intensive studies to solve the above problems, the present inventors have found that the composition of the polypropylene resin composition to be used can be set to a predetermined value, and the present invention has been completed. It came to let you.

That is, the present invention relating to a resin foam sheet is a resin foam sheet formed by extruding and foaming a polypropylene resin composition having a polypropylene resin component as a main component with an extruder. Is characterized in that the high melt tension polypropylene resin is contained so that the proportion of the polymer component contained is 20% by mass or more and less than 50% by mass.

In the present invention, since the high melt tension polypropylene resin in the polymer component is set to a predetermined ratio, it is possible to make it difficult for the resulting resin foam sheet to have stripes when extruded and foamed by an extruder.
Therefore, a margin is given to the extrusion conditions, and a high-quality resin foam sheet can be easily obtained.
As a result, a homogeneous foamed resin sheet can be provided. When a three-dimensional structure is imparted by a general sheet forming method such as vacuum forming or pressure forming, there is a risk of causing an appearance defect or the like in the obtained molded product. Low resin foam sheet can be provided.

Sectional drawing which shows the structure of the resin foam sheet which concerns on this embodiment. Schematic which shows the structure of the manufacturing apparatus of the resin foam sheet which concerns on this embodiment. Sectional drawing which shows the structure of a confluence | merging die. Schematic which shows the formation process of a "stripe".

Hereinafter, an embodiment of the present invention will be described while exemplifying a resin foam sheet having a laminated structure in which a surface layer that is a non-foamed resin layer and a foamed resin layer are laminated as a resin foam sheet.
As shown in FIG. 1, the resin foam sheet 1 in this embodiment includes a non-foamed resin layer (surface layers 11 and 12) constituting the respective surfaces of the upper surface side and the lower surface side, and a foamed resin layer formed therebetween. 20 and a three-layer laminated structure.
That is, the resin foam sheet 1 of this embodiment has non-foamed resin layers (surface layers 11 and 12) on both sides of the foamed resin layer 20.

The

surface layers

11 and 12 are both formed in a non-foamed state by a polypropylene resin composition containing a polypropylene resin as a main component.
In the resin foam sheet 1 of the present embodiment, the upper surface layer 11 (hereinafter also referred to as “first surface layer 11”) and the lower surface layer 12 (hereinafter referred to as “second surface layer 12”) in FIG. ")" Is not necessarily required to have the same configuration, and the thickness may be different.
The foamed resin layer 20 is formed by extruding and foaming a polypropylene resin composition mainly composed of a polypropylene resin by a method described later.
The

surface layers

11 and 12 are formed by coextruding a polypropylene resin composition for forming each of the

surface layers

11 and 12 together with the polypropylene resin component for forming the foamed resin layer 20 by a method described later. It is.

Since the polypropylene resin composition used for forming the

surface layers

11 and 12 and the foamed resin layer 20 is usually a composition suitable for each, those having different compositions are used.

In the present embodiment, the polypropylene-based resin composition used for forming the foamed resin layer 20 has a ratio of high melt tension polypropylene resin (HMS-PP) to the polymer component contained in a range from 20% by mass to less than 50% by mass. It is important that

As this HMS-PP, molecules that have been cut or crosslinked by irradiation of active energy rays such as electron beams to form free-end long chain branches in the molecule, or free-end long chains in the molecule by chemical crosslinking are used. What formed the branch and formed high melt tension may be used.
Moreover, what gave high melt tension by introduce | transducing olefin blocks, such as a polyethylene block, into a molecule | numerator, and making the block copolymer of an olefin block and a polypropylene block can be used as HMS-PP.

Examples of polypropylene resins other than HMS-PP include homopolypropylene resins (PP) consisting essentially of propylene components.

Whether the polypropylene resin is HMS-PP or not can be determined not only by the difference in molecular structure as described above but also by its melt tension.
In this specification, the high melt tension polypropylene resin (HMS-PP) is one having a melt mass flow rate (MFR) of 0.5 g / 10 min or more and 10 g / 10 min or less and a melt tension of 5 cN or more and 50 cN or less. Intended.
This MFR was measured at a test temperature of 230 ° C. and a load of 21.18 N (2.16 kgf) in accordance with method A of JIS K7210 (1999). It can be measured as follows.
That is, with respect to “melting tension”, a polypropylene resin as a sample is accommodated in a cylinder with an inner diameter of 15 mm arranged in the vertical direction and heated at a temperature of 230 ° C. for 5 minutes to be melted. And a capillary (die diameter: 2.095 mm, die length: 8 mm, inflow angle :) provided at the lower end of the cylinder so that the extrusion speed is 0.0773 mm / s (constant). The measurement can be performed by extruding the molten resin from 90 degrees (conical).
Specifically, the extruded string-like material can be measured by winding it around a tension detection pulley disposed below the capillary and then winding it using a winding roll. The initial speed at the beginning of the take-up is 4 mm / s, the subsequent acceleration is 12 mm / s ² , and the take-up speed is gradually increased. The maximum tension until this “breaking speed” is observed can be measured as “melt tension”.

In the present specification, even in the case of a block copolymer in which an olefin block is introduced so as to have a certain degree of melt tension, the melt tension value measured by the above measurement does not reach the above value. However, it is not handled as HMS-PP which defines the content in the polypropylene resin composition.
In the following, the terms “block copolymer” and “block PP” mean that the melt tension value of a block copolymer having an olefin block and a polypropylene block does not reach the above value unless otherwise specified. (Not applicable to “HMS-PP”)

Specific examples of the HMS-PP showing the melt tension value include those commercially available from Borealis under the trade names “WB130HMS”, “WB135HMS”, and “WB140HMS”.
A specific example of HMS-PP is commercially available from Basell under the trade name “Pro-fax F814”.
Furthermore, those commercially available from Nippon Polypro as trade names “FB3312”, “FB5100”, “FB7200”, and “FB9100” are also specific examples of HMS-PP.
Among them, the use of the product name “WB135HMS” manufactured by Borealis, in which free end long chain branches are formed in the molecule by chemical crosslinking, improves the foaming degree when the foamed resin layer 20 is formed by extrusion foaming. This is preferable because it can be easily achieved.

It is important that the HMS-PP is contained in the polymer component contained in the polypropylene resin composition in a proportion of 20% by mass or more and less than 50% by mass. This is because, when the ratio is 50% by mass or more, the polypropylene-based resin composition is likely to generate stripes when extruded and foamed to produce a resin foam sheet.

Further, the lower limit of HMS-PP is set to 20% by mass. When the content of HMS-PP is less than this, it becomes difficult to foam the polypropylene resin composition in a good state. This is because the selection range of the extrusion conditions for obtaining good products may be rather narrowed.

From such a viewpoint, the content of HMS-PP in all polymer components is preferably 25% by mass or more and less than 50% by mass, and more preferably 30% by mass or more and 45% by mass or less.

The total amount of all the polypropylene resins including HMS-PP in the total polymer components of the polypropylene resin composition used for forming the foamed resin layer 20 is usually 80% by mass or more. Preferably, it is 90 mass% or more.

In addition to the polypropylene resin, a polymer having a high compatibility with the polypropylene resin is suitable for use as a polymer component. For example, polyethylene resin, ethylene-ethyl acrylate copolymer resin, ethylene-acetic acid Examples thereof include polyolefin resins such as vinyl copolymer resins, polybutene resins, and poly-4-methylpentene-1 resins, and polyolefin-based thermoplastic elastomers (TPO).

In addition, the polypropylene resin composition used for forming the foamed resin layer 20 usually contains a component for foaming in addition to the polymer component as described above.
Examples of the foaming component include a gas component that is in a gaseous state at the extrusion temperature, a nucleating agent that serves as a nucleus when bubbles are formed by the gas component, and a gas that is thermally decomposed at the extrusion temperature. And thermal decomposition type foaming agent.

Examples of the gas component include aliphatic hydrocarbons such as propane, butane, and pentane, nitrogen, carbon dioxide, and water.
These gas components may be used alone or in combination.

Examples of the nucleating agent include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, and sulfuric acid. Examples include inorganic compound particles such as potassium, barium sulfate, and glass beads, and organic compound particles such as polytetrafluoroethylene.
This nucleating agent can be contained in the foamed resin layer forming material by, for example, a masterbatch method, and the nucleating agent is in any proportion within the range of 5% by mass or more and 50% by mass or less. By using the master batch dispersed in the matrix resin, it is possible to increase the effect exhibited with respect to the use amount of the nucleating agent.

Furthermore, examples of the thermal decomposition type foaming agent include azodicarbonamide, sodium hydrogen carbonate, a mixture of sodium hydrogen carbonate and citric acid, and the like.
The effect of the heat decomposable foaming agent is also improved by dispersing it in a matrix resin so as to be in any proportion within the range of 10% by mass or more and 50% by mass or less, and forming a master batch. be able to.

In addition, the polypropylene resin composition used for forming the foamed resin layer 20 can contain various additives in the same manner as the resin composition used for forming a general resin product, for example, an antioxidant. , An anti-aging agent, a processing aid and the like can be appropriately contained.

In addition, the resin foam sheet 1 according to the present embodiment is molded into a foam tray that is widely used as a buffer material for glass plates in the form of a sheet or as a display container for meat, fresh fish, and the like. In many cases, such as cases, it is required to suppress charging due to static electricity.
Therefore, it is preferable to contain a nonionic antistatic agent in the polypropylene resin composition for forming the surface layers 11 and 12.

Examples of the nonionic antistatic agent include alcohol antistatic agents, ether antistatic agents, ester antistatic agents, and ester / ether antistatic agents.
Furthermore, examples of the nonionic antistatic agent include nitrogen-containing antistatic agents such as amine-based antistatic agents and amide-based antistatic agents.
This nonionic antistatic agent is usually added to the polypropylene resin composition at a ratio of 0.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the polymer component contained in the polypropylene resin composition. Contained.

Examples of the alcohol-based antistatic agent include polyalkylene oxides such as polyethylene glycol (or polyethylene oxide) and poly (ethylene oxide) -poly (propylene oxide) block copolymers.
In the alcohol type antistatic agent, the degree of polymerization of the alkylene oxide is usually 1 or more and 300 or less (for example, 5 or more and 200 or less), preferably 10 or more and 150 or less (for example, 10 or more, 100). The following).
More preferably, it is about 15 or more and 50 or less.

Examples of the ether-based antistatic agent include polyoxyethylene alkyl ethers such as polyoxyethylene octyl ether, polyoxyethylene lauryl ether and polyoxyethylene cetyl ether; polyoxyethylene octyl phenyl ether, polyoxyethylene nonylphenyl ether and the like. And polyoxyethylene alkylphenyl ether.

Examples of the ester antistatic agent include many esters such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, (poly) glycerin, pentaerythritol, sorbitan, sorbitol, sucrose, and esters of polyhydric alcohols and fatty acids. Examples thereof include glycerol fatty acid esters such as glycerol monostearate, sorbitan fatty acid esters such as sorbitan monooleate, and sucrose fatty acid esters such as sucrose monostearate.

Examples of the ester / ether antistatic agent include polyoxyethylene glycerin fatty acid esters such as polyoxyethylene glycerin stearate and polyoxyethylene glycerin oleate; polyoxyethylene sorbitan such as polyoxyethylene sorbitan stearate Fatty acid ester; Polyoxyethylene polyhydric alcohol fatty acid ester such as polyoxyethylene sucrose fatty acid ester.
Examples thereof include polyoxyethylene castor oil and polyoxyethylene hydrogenated castor oil.

Examples of the nitrogen-containing antistatic agent include polyoxyethylene alkylamines having an alkyl structure of 6 to 24 carbon atoms in the molecule, such as polyoxyethylene laurylamine; polyoxyethylene stearamide, etc. Polyoxyethylene fatty acid amides having a fatty acid structure of 6 to 24 carbon atoms in the molecule; N-alkanol alkylamines such as N-ethanolalkylamine and N, N-alkanols such as N, N-diethanolalkylamine Alkanol alkylamines such as alkylamines; N-alkanol fatty acid amides such as N-ethanol stearic acid amide; N, N-alkanol fatty acid amides such as N, N-diethanol stearic acid amide;

In addition, as an alkyl and fatty acid which comprise the said nonionic antistatic agent, a C6-C24 thing is normally mentioned.
Examples of fatty acids include saturated fatty acids (for example, saturated fatty acids having 6 to 24 carbon atoms such as capric acid, lauric acid, myristic acid, palmitic acid and stearic acid; unsaturated fatty acids such as oleic acid.

Further, in addition to this nonionic antistatic agent, anionic antistatic agent, cationic antistatic agent, amphoteric antistatic agent and polymer antistatic agent may be used in combination. Examples of the agent include alkyl sulfonates, examples of the cationic low molecular weight antistatic agent include tetraalkylammonium salts, and examples of the amphoteric low molecular weight antistatic agent include alkyl betaine. .

Examples of the polymer antistatic agent include ionomers such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyester amide, and polyether ester amide, quaternary ammonium salts thereof, and polyether-polyolefin block copolymers ( And a copolymer of an olefin block and a hydrophilic block, such as a block copolymer of a polyether block and a polyolefin block). *

The low molecular weight antistatic agent such as the nonionic antistatic agent, the anionic antistatic agent, the cationic antistatic agent, and the amphoteric antistatic agent oozes out on the surface of the resin foam sheet 1, so-called “bleed out”. The phenomenon called "" is produced and the antistatic function is exhibited.
Therefore, the polypropylene resin composition for forming the surface layers 11 and 12 preferably contains, together with the nonionic antistatic agent, a component that promotes bleedout of the nonionic antistatic agent.

As a component that promotes the bleed-out of this nonionic antistatic agent, a resin that is either ethylene-α-olefin copolymer or low-density polyethylene resin and has a crystallinity of 20% to 55% is particularly effective. Is.
These ethylene-α-olefin copolymers and low-density polyethylene resins may be included singly or in combination in the polypropylene resin composition for forming the surface layers 11 and 12. .
It is also possible to use one or more ethylene-α-olefin copolymers and one or more low-density polyethylene resins as a component for promoting bleedout of the nonionic antistatic agent.
In order to promote bleed-out of the nonionic antistatic agent, the total amount of these is preferably 20% by mass or more, and 25% by mass or more in the polymer component of the polypropylene resin composition. More preferably.
The upper limit is usually about 40% by mass, and the total amount of these is preferably 35% by mass or less.

The degree of crystallinity in this ethylene-α-olefin copolymer or low-density polyethylene resin can be measured by JIS K7121: 1987 “Method for measuring transition temperature of plastic”.
Specifically, using a differential scanning calorimeter (DSC) device “DSC6220 type” manufactured by SII Nanotechnology, about 7 mg of a sample is filled in a measurement container, and a nitrogen gas flow rate of 30 ml / min is 10 ° C./min. While the temperature rises (cools) at the rate of temperature rise (cooling), the point where the DSC curve leaves the baseline is the starting point of melting (crystallization), and the point where the DSC curve returns to the baseline again is the end point. The amount of heat and the amount of heat of crystallization are measured, and the degree of crystallinity can be obtained by the following equation.

Crystallinity (%) = (Heat of crystallization (mJ) / Heat of fusion of complete crystal (mJ)) × 100

(However, the complete crystal melting heat (theoretical value) is 285.7 mJ / mg.)

The polymer component of the polypropylene resin composition may be composed only of the HMS-PP and a component for accelerating the bleed-out of the nonionic antistatic agent. Polypropylene resins other than the HMS-PP described as the forming material, and olefin resins and TPO having high affinity with the polypropylene resin can be added as appropriate.

In addition, since this polypropylene-type resin composition comprises the surface of the resin foam sheet 1, it can contain the various additives for exhibiting the function with which this surface is equipped as needed.
For example, it is possible to prevent the deterioration of the resin foam sheet 1 and the foam tray by containing a weathering agent and an anti-aging agent, or to improve slipperiness by containing a slip agent.
Alternatively, it is possible to improve the appearance by coloring by adding a pigment.
In addition, in the resin foam sheet 1 of this embodiment, the 1st surface layer 11 and the 2nd surface layer 12 do not necessarily need to make each thickness common, and the 1st surface layer 11 and the 2nd surface layer 12 are the same. The blending content of the polypropylene resin composition used for forming the two surface layers 12 may be varied.
For example, it is possible to add a pigment only to the side corresponding to the outside of the foaming tray, and to color the side corresponding to the inside of the foaming tray.
Further, the nonionic antistatic agent or the like can be contained only on the side corresponding to the outer side of the foaming tray and not on the side corresponding to the inner side.

The thickness of each layer of the first surface layer 11, the second surface layer 12, and the foamed resin layer 20 in the resin foam sheet 1 is not particularly limited, but the first surface layer 11 and the second surface layer are not limited. The layer 12 usually has any thickness within the range of 50 μm to 150 μm.
The foamed resin layer 20 is usually formed to have any thickness within the range of 0.5 mm to 5.0 mm, and the density (apparent density) is 0.15 g / cm ^{3 to} 0.6 g. / Cm ³ or less.

Such a resin foam sheet 1 can be manufactured by carrying out extrusion foaming of the polypropylene resin composition using an extruder generally used for manufacturing a resin foam sheet.
Below, the manufacturing method of the resin foam sheet 1 is demonstrated in detail, referring FIG. 2, FIG.
FIG. 2 is a schematic configuration diagram according to the apparatus for manufacturing a resin foam sheet, and FIG. 3 is a cross-sectional view showing an internal state of the confluence mold (symbol XH) shown in FIG.
FIG. 4 shows a state in which the polypropylene-based resin composition is extruded and foamed, and shows a state indicated by a broken line A in FIG.

The resin foam sheet manufacturing apparatus shown in FIG. 2 includes two series of extruders: a first extruder 70 that is a tandem extruder and a second extruder 80 that is a single extruder. .
Further, a merge mold XH into which the resin composition melt-kneaded in these extruders is merged, and an annular discharge hole for discharging the resin composition merged in the merge mold XH into a cylindrical shape A circular die CD is provided.

Furthermore, this manufacturing apparatus includes a cooling device CL for air-cooling the resin foam sheet discharged in a cylindrical shape from the circular die CD, and expanding the diameter of the cylindrical resin foam sheet into a cylindrical shape having a predetermined size. And a slitting device that cuts the resin foam sheet after passing through the mandrel MD along the extrusion direction and divides it into two sheets (not shown in FIG. 2: only the state of dividing vertically) And a take-up roller 92 for taking up the slit resin foam sheet 1 after passing the plurality of rollers 91.

The first extruder 70 is for forming the foamed resin layer 20, and the upstream extruder (hereinafter also referred to as “upstream extruder 70 a”) is for forming the foamed resin layer 20. A hopper 71 for introducing the polypropylene resin composition and a gas introduction part 72 for supplying gas components such as hydrocarbons into the cylinder are provided.
Then, on the downstream side of the upstream side extruder 70a, a polypropylene resin composition containing the gas component (hereinafter also referred to as “foamable resin composition”) is melt-kneaded and discharged to the confluence mold XH. Extruder (hereinafter also referred to as “downstream extruder 70b”) is provided.

The second extruder 80 is for forming the first surface layer 11 and the second surface layer 12, and is a polypropylene-based resin composition (hereinafter referred to as a surface layer) for forming the surface layer in a non-foamed state. The "non-foamable resin composition") is introduced from the hopper 81, and the non-foamable resin composition is melted and kneaded inside the cylinder and discharged to the joining mold XH.

As shown in the schematic cross-sectional view of FIG. 3, the confluence mold XH includes a first resin flow path W1 that passes through the center from the right side to the left side of the front view of FIG. 3, and the first resin flow path. A second resin flow path W2 for allowing the resin to flow into the first resin flow path W1 in the middle of W1, and the upstream side of the second resin flow path W2 (right side in front view in FIG. 3) A third resin flow path W3 for allowing the resin to flow into the first resin flow path W1 is formed.
The second resin flow path W2 is formed so that the resin composition can flow into the resin flow path W1 from an annular slit S1 opened in a wall surface forming the resin flow path W1. The resin flow path W3 is connected to a tube P having an open end at the center of the first resin flow path W1, so that the resin composition can flow into the center of the first resin flow path W1. Is formed.

The first resin flow path W1 is connected to the first extruder 70 on the upstream side, and is connected to the circular die CD on the downstream side. The second resin flow path W2 and the third resin flow path W3 is connected to the second extruder 80 via the distribution pipe D so that the non-foamable resin composition can flow from the second extruder 80.
That is, the merge mold XH of the present embodiment is a circle having a triple structure of non-foamable resin composition / foamable resin composition / non-foamable resin composition on the downstream side of the first resin flow path W1. A flow of columnar resin is formed, and these resins are provided so as to be supplied toward the circular die CD.

The circular die CD is fed in triple from the converging mold XH (“non-foamed resin composition” / “foamable resin composition” / “non-foamed resin composition”) from the center toward the outside. The columnar resin composition flow is changed to a cylindrical flow so as to be co-extruded from the annular discharge hole.

In order to produce a resin foam sheet using such an apparatus, first, a polypropylene resin composition used for forming the foamed resin layer 20 is introduced from the hopper 71 of the first extruder 70, and the surface of the second extruder 80 is There is a method in which a polypropylene resin composition for forming the

layers

11 and 12 is charged, melt kneading at a temperature equal to or higher than the melting temperature of the resin is carried out in each extruder, and then co-extruded from the circular die CD.
Each resin composition may be introduced into the hopper after the individual components are brought into a homogeneous mixed state in advance, or may be separately introduced from the hopper and mixed in the extruder.

Among these extruders, in the first extruder 70, it is necessary to melt and knead the components for foaming. Therefore, the gas component is press-fitted from the gas introduction part 72 provided in the upstream extruder 70a. Mixing with molten resin is performed.
Co-extrusion from the circular die CD is performed by adjusting the foamable resin composition melt-kneaded by the upstream extruder 70a in the first extruder 70 to a temperature suitable for extrusion foaming by the downstream extruder 70b. On the other hand, in the second extruder 80, the non-foamable resin composition is adjusted to a temperature suitable for the formation of the first and second surface layers 11 and 12, and sent to the confluence mold XH. This can be implemented by previously forming a laminated structure of molten resin in the confluence mold XH.

Then, the respective resin compositions merged in the merge mold XH are co-extruded from the annular discharge hole of the circular die CD, and the foamed resin layer 20 and the surface layers 11 and 12 are formed by the respective polypropylene resin compositions. A cylindrical foam having a laminated structure with
Thereafter, the foam is stretched in the circumferential direction along the outer peripheral surface of the mandrel MD larger in diameter than the discharge hole of the circular die CD and cooled, and the cooled foam is moved up and down with a cutting tool (not shown). The belt-shaped resin foam sheet 1 is divided into two, and each is wound around a roll 92.

At this time, since the polypropylene resin composition for forming the foamed resin layer 20 contains HMS-PP, it is extruded in a favorable foamed state.
In addition, the cylindrical foam causes an increase in thickness with an increase in the degree of foaming immediately after being discharged, and expands the apparent volume.

The foam does not expand in volume only in the thickness direction, but also expands in the circumferential direction.
Further, the cylindrical foam is moved in the direction of the mandrel MD by the pulling force by the roll 92, and the diameter is gradually increased so as to approach the outer diameter of the mandrel MD along with the movement.

Therefore, as shown in FIG. 4, if the circumferential expansion speed after extrusion is equal to or less than the speed at which the foam FB is expanded, there is little risk of causing a problem. In the vicinity, the slack portion FE is formed in the foam FB because the expansion rate is high.
That is, assuming a circular frustoconical shape with the circle drawn by the discharge hole of the circular die CD as the upper bottom and the circle drawn by the end face MDa of the mandrel MD directed to the circular die CD as the lower bottom, The foam FB between the mandrel MD and the circular die has a portion FT (hereinafter also referred to as “tensile portion FT”) where the pulling force by the roll 92 is applied along the inclination of the side surface of the truncated cone shape. The slack portion FE moves between the circular die CD and the mandrel MD through the inner side than the side surface.
Moreover, in such a case, normally, a plurality of slack portions FE are formed in the foam FB, and in the vicinity of the circular die CD, slack portions FE and tension portions FT are alternately formed in the circumferential direction. Become.

It should be noted that the volume expansion of the foam FB usually converges at a location slightly away from the circular die CD, and a circumferential tension is applied to the slack portion FE as the diameter increases, so that the location close to the mandrel MD In general, no slack is observed.
However, during this time, until the slack portion FE is eliminated, there is a difference in the stretching applied to the slack portion FE and the tension portion FT and how the cooling air strikes (cooling conditions), and the sheet thickness, density, etc. A difference is caused, and a striped pattern is formed on the resin foam sheet after passing through the mandrel MD due to the presence of the slack part FE and the tension part FT.

The polypropylene resin composition in the present embodiment has a mild foaming behavior because the upper limit is set for the content of HMS-PP, and the volume expansion after being extruded from the circular die CD is gentle. It becomes.
Therefore, large slack is hardly generated in the foam FB, the stretching applied to the foam FB is substantially uniformly applied to the whole, and the cooling condition is also substantially uniform, so that the stripes are suppressed.
As described above, when the content of HMS-PP is less than the lower limit, it is difficult to obtain a good foamed state.

In addition, since the speed at which the diameter of the foam FB is increased can be improved by increasing the take-up speed (the length of the resin foam sheet wound around the roll 92 per unit time), this also suppresses the fringes. Although it can be achieved to some extent, the volume expansion occurs instantaneously, so that the effect of suppressing fringes is small as compared with adjusting the content of HMS-PP in the polypropylene resin composition.
In addition, if the take-up speed is increased too much, a large tension is generated in the foam FB. Therefore, it is a simpler method to suppress fringes depending on the content of HMS-PP in the polypropylene resin composition. I can say that.
The take-up speed is usually 2 m / min or more and 10 m / min or less, although it depends on the type and thickness of the resin foam sheet to be produced.

Similarly, the ratio (d2 / d1) between the diameter of the circular die CD (d1: the diameter of the intermediate circle between the inner circle and the outer circle of the discharge port) and the outer shape (d2) of the mandrel MD is increased. By doing so, it is possible to suppress fringes to some extent by increasing the stretching in the circumferential direction, but the effect in such a case is also the effect obtained when adjusting the content of HMS-PP. It is a small one.
This ratio (d2 / d1) is usually 1.9 or more and 3.2 or less, and the slit clearance of the circular die CD is usually selected from the range of 0.3 mm or more and 1.5 mm or less. .

Furthermore, although the volume expansion behavior can be controlled to some extent by adjusting the foaming agent, if the amount of the foaming agent is excessively reduced, naturally the resin foam sheet may not exhibit a good foaming state. .
From this point of view, it can be said that the method of suppressing fringes by the content of HMS-PP is a simple method.
In the case where, for example, butane (n-butane, i-butane, or a mixture thereof) is used as the foaming agent, the ratio relative to 100 parts by mass of the polymer component is usually 1 part by mass or more. The amount is 6 parts by mass or less.

The resin foam sheet produced in this way has a uniform thickness and foamed state.
Further, in the surface layers 11 and 12, an ethylene-α-olefin copolymer having a crystallinity of 20% to 55% or a low density polyethylene resin having a crystallinity of 20% to 55% is a nonionic charge. Since it is contained together with the inhibitor, the nonionic antistatic agent can be quickly bleed out to the surface.
As a result, at room temperature, for example, the surface resistivity is reduced to 1 × 10 ¹³ Ω / □ or less, and the antistatic performance can be exhibited.
Therefore, the resin foam sheet can be used in a short period of time after the production without providing a curing period until the desired antistatic performance is exhibited, or even if it is provided. The inventory period of the sheet can be shortened.

In addition, since such resin foam sheets are homogenized, when they are processed by a sheet molding method, etc., local elongation occurs, resulting in molded products with “bad appearance” and “tearing”. Is less likely to occur.
That is, it is useful for improving the yield of molded products.

If the surface of the resin foam sheet is striped and the thickness of the resin foam sheet is non-uniform, the thick part is first brought into contact with the mold and bleeded out to this part. The antistatic agent is easily moved to a portion not in strong contact with the mold.
Moreover, in the sheet molding method, since the resin foam sheet is in a heated state, the mobility of the antistatic agent is also improved, and if the thickness of the resin foam sheet is uneven, the surface of the molded product There is a possibility of forming a portion where the antistatic agent is concentrated and a portion where the antistatic property has been lost.
That is, it can be said that the resin foam sheet of the present embodiment can be used particularly suitably when the surface layers 11 and 12 are brought into contact with a mold and a molded product is produced by a sheet molding method.

In addition, in this embodiment, although embodiment of this invention is described exemplifying the resin foam sheet of the 3 layer structure which has the surface layer which covers both surfaces of a foamed resin layer, the laminated structure of 4 layers or more is demonstrated. Even in the case of having the foamed resin layer, when the foamed resin layer is formed by extruding and foaming the above-described polypropylene resin composition with an extruder, it is the same as the above example in that the effect of suppressing fringes is exhibited.

The same applies to the case where the surface layer is formed only on one side of the foamed resin layer or the case where the foamed resin layer is a single layer.
Furthermore, even when a plurality of foamed resin layers are coextruded, the effect of suppressing fringes can be exhibited by using the polypropylene resin composition of the present embodiment.

In addition, although it abbreviate | omits description here in detail, about the well-known matter regarding a resin composition, its extrusion foaming technique, or a resin foam sheet, its manufacturing method, etc., the effect of this invention is effective. The present invention can be employed within a range that is not significantly impaired.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
For the production of the resin foam sheet, equipment of the same kind as the apparatus configuration as shown in FIG. 2 was used.
That is, the non-foamable resin composition is supplied from the second extruder 80 through the branch pipe D at two locations upstream and downstream of the resin flow path W1 into which the foamable resin composition flows from the first extruder 70. The first and second extruders were connected to the merging die XH so as to flow in, and the circular die CD was connected to the downstream side of the merging die XH to perform co-extrusion.

First, as a first extruder for melt-mixing the foamed resin layer forming material, a single screw extruder (upstream extruder) having a diameter of 90 mm and a single screw having a diameter of 115 mm connected to the single screw extruder. A tandem type extruder composed of a shaft extruder (downstream extruder) was prepared.

Further, 39% by mass of HMS-PP commercially available from Borealis under the trade name “WB135”, 55% by weight of block PP commercially available from Japan Polypro as trade name “BC6C”, and trade name “Q-100F” from Sun Allomer. As a polymer component containing 6% by mass of commercially available TPO and a total amount of these polymer components of 100 parts by mass, a baking soda-citric acid-based foaming agent (Daiichi Seika) becomes 0.5 parts by mass. A polypropylene resin composition for forming a foamed resin layer containing a master batch manufactured by the company, trade name “Fine Cell Master PO410K”) is supplied to a hopper of a single screw extruder having an upstream diameter of 90 mm. After being heated and melted at a temperature of 200 ° C. to 210 ° C., the gas component is used so that the ratio with respect to 100 parts by mass of the molten resin is 4 parts by mass. That butane (isobutane / n-butane = 35/65 wt%) was injected and kneaded.
This foamable resin composition was supplied to an extruder on the downstream side, the temperature of the foamable resin composition was lowered, and supplied to a confluence mold XH connected to the tip of the extruder at a discharge rate of 120 kg / hour.

On the other hand, a single-screw extruder having a diameter of 65 mm was prepared as a second extruder for melting and mixing the surface layer forming material.
70 mass% of HMS-PP commercially available from Borealis as trade name “WB135”, and ethylene-α-olefin copolymer commercially available as trade name “KS240T” (crystallinity: 26%) from Nippon Polyethylene. A nonionic antistatic agent (trade name “TS-” manufactured by Kao Corporation), which is 2.0 parts by mass when the polymer component contained in a proportion of 30% by mass and the total amount of these polymer components is 100 parts by mass. 2B ") for forming the surface layer was supplied to the hopper of the second extruder and heated and melted at a temperature of 200 ° C.

Then, after the molten (non-foamable) polypropylene-based resin composition is bisected by a distribution pipe having a branch flow path, a tubular body opened at the center of the resin flow path of the confluence mold, From both the slits opened in the outer periphery of the resin flow path, the total amount is 15 kg / hour, each is discharged in an amount of 15 kg / hour, and after being laminated and joined to the inner layer side and the outer layer side of the foamable resin composition, merge Non-foamed on both the inner and outer sides via a foamed resin layer by co-extrusion from a circular die (caliber 140 mm, slit gap 1.0 mm) connected to the die tip in a cylindrical shape with a resin discharge rate of 135 kg / hour A cylindrical foam having a surface layer laminated thereon was formed.
The cylindrical foam produced by extrusion foaming is expanded on a cooling mandrel having a diameter: 414 mm × length: 500 mm, and the outer surface is cooled by blowing air from an air ring. Two strips of foamed resin foam sheets were produced by cutting with a cutter at two points that were symmetrical in the circumferential direction (opened 180 degrees).

The surface resistivity of the obtained resin foam sheet of Example 1 was measured based on JIS K 6911-1995. The pretreatment time was 24 hours.
Specifically, after a flat square test piece having a side of 10 cm is left in an atmosphere of a temperature of 22 ° C. and a humidity of 60% for 24 hours, a test apparatus (manufactured by Advantest Corporation) under an environment of a temperature of 22 ° C. and a humidity of 60% is used. Using a digital ultra-high resistance / microammeter R8340 and a resiliency chamber R12702A), an electrode is crimped to a test piece with a load of about 30 N, a voltage of 500 V is applied, and a resistance value after one minute has elapsed. Measured and calculated by the following formula.
ρs = π (D + d) / (D−d) × Rs
However,
ρs: Surface resistivity (Ω / □)
D: Inner diameter (cm) of the annular electrode on the surface (7 cm for the resiliency chamber R12702A)
d: outer diameter (cm) of inner circle of surface electrode (5 cm for resiliency chamber R12702A)
Rs: Surface resistance (Ω)

As a result, a surface resistivity value of 3.5 × 10 ¹² Ω / □ was observed.
Further, no noticeable stripes were observed on this resin foam sheet.
A foam tray was prepared by a sheet molding method, but the appearance was beautiful and the mechanical strength was excellent.

(Example 2)
In the polypropylene resin composition for forming the surface layer, instead of the ethylene-α-olefin copolymer (KS240T) manufactured by Nippon Polyethylene, the crystallinity of 50 commercially available from Nippon Polyethylene under the trade name “LD400” A resin foam sheet was produced in the same manner as in Example 1 except that% low-density polyethylene (PE) resin was used, and a foam tray was produced.
When the surface resistivity of the resin foam sheet of Example 2 was measured in the same manner as in Example 1, it was found to have a surface resistivity of 5.0 × 10 ¹² Ω / □.
Further, no noticeable stripes were observed, and the foamed tray formed by the resin foamed sheet had a beautiful appearance and excellent mechanical strength.

(Example 3)
In the polypropylene-based resin composition for forming the surface layer, instead of the ethylene-α-olefin copolymer (KS240T) manufactured by Nippon Polyethylene Co., Ltd., a commercial crystallinity of 53% as a trade name “LF441B” from Nippon Polyethylene Co., Ltd. A resin foam sheet was produced in the same manner as in Example 1 except that the low-density polyethylene (PE) resin was used, and a foam tray was produced.
When the surface resistivity of the resin foam sheet of Example 3 was measured in the same manner as in Example 1, it was found that the resin foam sheet had a surface resistivity of 6.5 × 10 ¹² Ω / □.
Further, no noticeable stripes were observed, and the foamed tray formed by the resin foamed sheet had a beautiful appearance and excellent mechanical strength.

Example 4
In the polypropylene resin composition for forming the surface layer, instead of the ethylene-α-olefin copolymer (KS240T) manufactured by Nippon Polyethylene Co., Ltd., commercially available from Sumitomo Chemical Co., Ltd. under the trade name “Eriksen VL-100” A resin foam sheet was produced in the same manner as in Example 1 except that an ultra-low density polyethylene (PE) resin having a crystallinity of 36% was used, and a foam tray was produced.
When the surface resistivity of the resin foam sheet of Example 4 was measured in the same manner as in Example 1, it was found that the resin foam sheet had a surface resistivity of 4.0 × 10 ¹² Ω / □.
Further, no noticeable stripes were observed, and the foamed tray formed by the resin foamed sheet had a beautiful appearance and excellent mechanical strength.

(Example 5)
The proportion of HMS-PP (WB135) in the polypropylene resin composition for forming the foamed resin layer was changed to 25 mass% instead of 39 mass%, and the proportion of block PP (BC6C) was changed to 55 mass% instead. A resin foam sheet was produced in the same manner as in Example 1 except that the content was 69% by mass to produce a foam tray.
The resin foam sheet of Example 5 was measured for surface resistivity in the same manner as in Example 1. As a result, it was found that the resin foam sheet had a surface resistivity of 3.5 × 10 ¹² Ω / □.
Further, no noticeable stripes were observed, and the foamed tray formed by the resin foamed sheet had a beautiful appearance and excellent mechanical strength.

(Example 6)
In the polypropylene resin composition for forming the surface layer, a resin foam sheet was produced in the same manner as in Example 1 except that the polymer component was changed to 100% by mass of HMS-PP (WB135) to produce a foam tray.
When the surface resistivity of the resin foam sheet of this Example 6 was measured in the same manner as in Example 1, it showed a surface resistivity of 4.5 × 10 ¹³ Ω / □.
In addition, no noticeable stripes were observed on the resin foam sheet itself, and the foam tray formed from the resin foam sheet had a beautiful appearance and excellent mechanical strength.

(Example 7)
A resin foam sheet was produced in the same manner as in Example 1 except that the nonionic antistatic agent was not contained in the polypropylene resin composition for forming the surface layer, and a foam tray was produced.
When the surface resistivity of the resin foam sheet of Example 7 was measured in the same manner as in Example 1, it showed a surface resistivity of 6.5 × 10 ¹⁵ Ω / □.
In addition, no noticeable stripes were observed on the resin foam sheet itself, and the foam tray formed from the resin foam sheet had a beautiful appearance and excellent mechanical strength.

(Example 8)
A resin foam sheet was produced in the same manner as in Example 5 except that a nonionic antistatic agent was not included in the polypropylene resin composition for forming the surface layer, and a foam tray was produced.
When the surface resistivity of the resin foam sheet of Example 8 was measured in the same manner as in Example 1, it exhibited a surface resistivity of 6.5 × 10 ¹⁵ Ω / □.
In addition, no noticeable stripes were observed on the resin foam sheet itself, and the foam tray formed from the resin foam sheet had a beautiful appearance and excellent mechanical strength.

(Comparative Example 1)
The ratio of HMS-PP (WB135) in the polypropylene resin composition for forming the foamed resin layer was changed to 18% by mass instead of 39% by mass, and instead the ratio of block PP (BC6C) was changed to 55% by mass. A resin foam sheet was produced in the same manner as in Example 1 except that the content was 76% by mass, and a foam tray was produced.
The resin foam sheet of Comparative Example 1 was measured for surface resistivity in the same manner as in Example 1, and was found to have a surface resistivity of 3.5 × 10 ¹² Ω / □.
However, the foamed resin sheet is not foamed to have a sufficient thickness, and no noticeable stripes were observed, but the foamed tray formed by the resin foamed sheet has mechanical strength in each example. It was inferior to.

(Comparative Example 2)
The proportion of HMS-PP (WB135) in the polypropylene resin composition for forming the foamed resin layer was changed to 50 mass% instead of 39 mass%, and the proportion of block PP (BC6C) was changed to 55 mass% instead. A resin foam sheet was produced in the same manner as in Example 1 except that the content was 44% by mass to produce a foam tray.
When the surface resistivity of the resin foam sheet of Comparative Example 2 was measured in the same manner as in Example 1, it was found to have a surface resistivity of 3.5 × 10 ¹² Ω / □.
However, the resin foam sheet is conspicuous, and the foam tray formed by the resin foam sheet has a perforation defect, making it difficult to obtain a foam tray having a good appearance.

The examination results of the above examples and comparative examples are shown in the following comparative table (Table 1).

Also from this, it can be seen that according to the present invention, a resin foam sheet suitable for a forming material of a foam molded product having a three-dimensional structure can be provided.

1: Resin foam sheet 11: First surface layer (non-foamed resin layer)
12: Second surface layer (non-foamed resin layer)
20: Foamed resin layer

Claims

A resin foam sheet formed by extruding and foaming a polypropylene resin composition mainly composed of a polypropylene resin with an extruder,
The polypropylene-based resin composition contains a high melt tension polypropylene resin so that a proportion of the polymer component contained is 20% by mass or more and less than 50% by mass.
The resin foam sheet according to claim 1, wherein the high melt tension polypropylene resin has a free-end long-chain branch formed by chemical crosslinking.
A nonionic antistatic agent comprising a non-foamed resin layer on the surface and a laminated structure in which the foamed resin layer formed by extrusion foaming of the polypropylene resin composition and the non-foamed resin layer are laminated. The resin foam sheet according to claim 1 or 2, wherein the non-foamed resin layer is formed of a polypropylene-based resin composition containing selenium.
The polypropylene resin composition forming the non-foamed resin layer includes an ethylene-α-olefin copolymer having a crystallinity of 20% to 55% or a low crystallinity of 20% to 55%. The resin foam sheet according to claim 3, further comprising a density polyethylene resin.
5. The resin foam sheet according to claim 3 or 4, wherein the resin foam sheet is used for an application in which the molding process is performed in a heated state and the molding process is performed by bringing the non-foamed resin layer into contact with a mold.