KR20120116406A - Resin foamed sheet - Google Patents

Abstract

It is an object to suppress the occurrence of streaks on the surface of the resin foam sheet by approaches other than the adjustment of the extrusion conditions, and to provide a resin foam sheet suitable as a material for forming a molded foam article having a three-dimensional structure. A polypropylene resin composition comprising polypropylene resin as a main component is a resin foam sheet formed by extrusion foaming with an extruder, wherein the polypropylene resin composition has a ratio of 20% by mass or more and less than 50% by mass to the polymer component contained therein. A resin foam sheet comprising a high melt tension polypropylene resin is provided as the means.

Description

Resin foam sheet {RESIN FOAMED SHEET}

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

Conventionally, the resin foam sheet which foamed the resin composition into the sheet form is widely used for the use which requires light weight and buffer property.

Especially, the resin foam sheet formed with the polypropylene resin composition which has polypropylene resin as a main component is widely used by the point which is comparatively cheap.

Such a resin foam sheet is normally manufactured continuously by extrusion foaming a polypropylene resin composition, and what has a non-foamed resin layer called a film layer etc. on the surface as well as a foamed resin layer single layer itself is manufactured.

This resin foam sheet is used as a raw material at the time of producing foam molded articles which have a three-dimensional structure, such as a foam tray, by the sheet molding method, besides being used for the buffer sheet of a glass plate, etc. in a sheet form.

However, various examinations are made about the manufacturing method of such a foamed molded article. For example, Patent Document 1 below discloses a high melt tension polypropylene resin (hereinafter also referred to as "HMS-PP") in a polypropylene resin composition. It is described that it becomes a resin foam sheet excellent in moldability by containing 50 mass% or more.

When the resin foam sheet is molded into a foam tray or the like, the resin foam sheet is subjected to vacuum molding or adsorption to a molding die in which a tray shape is formed by negative pressure (air removal) while heating and softening the resin foam sheet. BACKGROUND OF THE INVENTION A molding method called pressure molding, which is brought into close contact with a molding die, has been widely adopted.

In such vacuum forming and pressure forming, since the irregularities are formed in the resin foam sheet while holding the periphery of the resin foam sheet, the resin foam sheet is not in a homogeneous condition as a whole. If thickness irregularity or the like occurs, thinner portions which tend to increase due to stress are preferentially increased, and in some cases, appearance defects may occur in the molded article, or heat insulation may be formed in the molded article.

In addition, making a resin foam sheet homogeneous is a matter requested | required not only in the resin foam sheet provided for shaping | molding but also when a resin foam sheet is used in sheet form.

However, it is difficult to make the entire surface of the resin foam sheet homogeneous, and when the resin foam sheet is formed by extrusion foaming, streaks appear on the surface of the resin foam sheet continuously in the extrusion direction due to the difference in the texture such as surface gloss. There is a case.

In many cases where such streaks are seen on the surface of the resin foam sheet, the parts having different surface gloss slightly vary not only the appearance but also the thickness and density (foaming degree) of the sheet.

Therefore, when such streaks usually occur in the resin foam sheet, the occurrence of such streaks is required to be more likely to cause problems in vacuum forming or pressure forming than the resin foam sheet in which streaks are not recognized on the surface.

However, a method for preventing the streaks has not been established to date, and mainly symptomatic treatments are only being implemented.

For example, based on experience, extrusion conditions in which streaks are less likely to be selected are selected to start extrusion foaming of the polypropylene resin composition, and if streaks are seen in the extruded resin foam sheet, extrusion conditions are further reduced. Measures are taken to take the product after adjusting to find the conditions where the streaks are not visible.

As described above, since a specific means for preventing streaks is not conventionally established other than adjustment of extrusion conditions, in some cases, a resin foam sheet can be produced only within a narrow range of conditions.

Japanese Patent Publication No. 2003-236961

The present invention has been devised in view of the above problems, and aims to provide a resin foam sheet which is easy to manufacture so that streaks are suppressed by an approach other than adjustment of extrusion conditions, and furthermore, streaks are not visible. It is aimed at.

As a result of earnestly examining in order to solve the said subject, the present inventor discovered that the composition of the polypropylene resin composition used is predetermined, and found that the suppression of a striation can be aimed at and completed this invention.

That is, the present invention for the resin foam sheet is a resin foam sheet formed by extrusion foaming of a polypropylene resin composition having a polypropylene resin component as a main component, and a proportion of the polymer component contained in the polypropylene resin composition. It is characterized by containing a high melt tension polypropylene resin so as to be 20 mass% or more and less than 50 mass%.

In the present invention, since the high melt tension polypropylene resin of the polymer component is determined at a predetermined ratio, streaks can be less likely to occur in the resin foam sheet obtained by extrusion foaming with an extruder.

Therefore, the extrusion conditions can be afforded and a high quality resin foam sheet can be obtained easily.

As a result, since a homogeneous resin foam sheet can be provided, a resin foam sheet having a low risk of producing a poor appearance or the like in a molded article obtained when giving a three-dimensional structure in accordance with a general sheet molding method such as vacuum molding or pressure molding is provided. Can be.

1 is a cross-sectional view showing the structure of the resin foam sheet according to the present embodiment.
2 is a schematic view showing the configuration of an apparatus for producing a resin foam sheet according to the present embodiment.
3 is a cross-sectional view showing the structure of the joining die.
4 is a schematic diagram showing a process of forming a "stripe pattern".

EMBODIMENT OF THE INVENTION Below, embodiment of this invention is demonstrated, illustrating a resin foam sheet which has a laminated structure by which the surface layer which is a non-foamed resin layer, and foamed resin layer were laminated | stacked as a resin foam sheet.

As shown in FIG. 1, in this embodiment, the resin foam sheet 1 has the non-foamed resin layer (surface layers 11 and 12) which comprise each surface of the upper surface side and the lower surface side, and the foaming number formed between them. It has a three-layer laminated structure of the ground layer 20.

That is, the resin foam sheet 1 of this embodiment has the non-foaming resin layer (surface layers 11 and 12) on both sides with this foamed resin layer 20 interposed.

These surface layers 11 and 12 are formed so that it may become a non-foaming state by the polypropylene resin composition which has polypropylene resin as a main component.

In the resin foam sheet 1 of this embodiment, when looking at FIG. 1 from the front, the upper surface layer 11 (henceforth "the 1st surface layer 11") and the lower surface layer 12 (henceforth " 2 surface layer 12 ") does not necessarily need to match the structure, and may change each thickness.

In addition, the foamed resin layer 20 is formed by extrusion foaming of a polypropylene resin composition containing polypropylene resin as a main component described below.

The surface layers 11 and 12 are co-extruded together with the polypropylene resin component for forming the foamed resin layer 20 in a manner to be described later by the polypropylene resin composition for forming each.

Since the polypropylene resin composition used for formation of the said surface layer 11, 12 and the said foamed resin layer 20 is made into the composition suitable for each, different compositions are used.

In this embodiment, the ratio of the high melt tension polypropylene resin (HMS-PP) in the polypropylene resin composition used for forming the foamed resin layer 20 in the polymer component contained is 20% by mass or more and 50% by mass. It is important to be less than%.

In this HMS-PP, a molecule is cleaved or crosslinked by irradiation with an active energy ray such as an electron beam to form free terminal long chain branch in the molecule, or free terminal long chain branch is formed in the molecule by chemical crosslinking to impart high melt tension. Can be used.

In addition, an olefin block such as a polyethylene block can be introduced into the molecule so that a high melt tension is imparted by block copolymerization of the olefin block with the polypropylene block can also be used as the HMS-PP.

As polypropylene resins other than this HMS-PP, the homopolypropylene resin (PP) which consists essentially of a propylene component is mentioned.

And whether polypropylene resin is HMS-PP or not can be judged not only with the difference in molecular structure mentioned above but with the melt tension normally.

In this specification, the high melt tension polypropylene resin (HMS-PP) is intended to have 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.

The MFR is measured at a test temperature of 230 ° C. and a load of 21.18 N (2.16 kgf) in accordance with the method A of JIS K7210 (1999), and the “melting tension” can be specifically measured as follows.

That is, about "melt tension", the polypropylene resin used as a sample is accommodated in the cylinder of the inner diameter 15mm arrange | positioned in the vertical direction, and it heats and melts at the temperature of 230 degreeC for 5 minutes, and inserts a piston from the top of a cylinder, Molten resin is removed from the capillary (die diameter: 2.095mm, die length: 8mm, inflow angle: 90 ° (conical)) installed at the lower end of the cylinder with the piston at an extrusion speed of 0.0773 mm / s (constant). It can measure by extruding to a string form.

Specifically, the extruded string can be wound around the tension detection pulley disposed below the capillary and passed through, and then can be measured by winding up using a winding roll. The initial velocity at the beginning of winding is 4 mm / s. Then, the subsequent acceleration is 12 mm / s ² , the winding speed is gradually increased, and the winding speed when the tension observed by the tension detection pulley suddenly decreases is defined as the "break speed". The maximum tension until "is observed can be measured as" melt tension ".

And in this specification, even if it is a block copolymer in which an olefin block was introduce | transduced so that it may have some melt tension, it is content in a polypropylene resin composition in this embodiment that the value of melt tension by the said measurement does not reach the said value. It shall not be dealt with by HMS-PP.

Hereinafter, unless the term "block copolymer" or "block PP" is used, the value of the melt tension in the block copolymer having an olefin block and a polypropylene block does not reach the above value ("HMS-PP"). It does not correspond to) and intends to use it.

As a specific example of HMS-PP which shows the value of the said melt tension, what is marketed by Borealis company under the brand names "WB130HMS", "WB135HMS", and "WB140HMS" is mentioned, for example.

In addition, specific examples of HMS-PP include those sold under the trade name "Pro-fax F814" by Basell.

Furthermore, Nippon Polypro Co., Ltd., which is marketed under the trade names "FB3312", "FB5100", "FB7200" and "FB9100", is also mentioned as a specific example of HMS-PP.

Among them, adopting the brand name "WB135HMS" manufactured by Borealis, which formed free terminal long-chain branches in the molecule by chemical crosslinking, can easily improve the degree of foaming when forming the foamed resin layer 20 by extrusion foaming. It is preferable to.

The reason why 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 is 50% by mass of the HMS-PP in the whole polymer component. This is because streaks are likely to occur when the polypropylene resin composition is extruded and foamed to produce a resin foam sheet.

In addition, the lower limit of HMS-PP of 20 mass% makes it difficult to foam the polypropylene-based resin composition in a good state when the content of HMS-PP is less than this, so that the choice of extrusion conditions for obtaining a good product becomes narrower. Because there is a fear.

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

And as a ratio of the total amount of all the polypropylene resins containing this HMS-PP to all the polymer components of the polypropylene resin composition used for formation of the foamed resin layer 20, it is 80 mass% or more normally, Preferably it is It is 90 mass% or more.

As the polymer component other than the polypropylene resin, a polymer having high compatibility with the polypropylene resin is preferable. For example, a polyethylene resin, an ethylene-ethyl acrylate copolymer resin, an ethylene-vinyl acetate copolymer Polyolefin resins such as resins, polybutene resins, poly-4-methylpentene-1 resins, and polyolefin thermoplastic elastomers (TPO).

In addition, the polypropylene-based resin composition used to form the foamed resin layer 20 will contain components for foaming in addition to the polymer components as described above.

As the component for foaming, for example, a gas component that becomes a gas at an extrusion temperature, a nucleating agent that becomes a nucleus when bubbles are formed by the gas component, or a pyrolysis type in which gas is generated by thermal decomposition at an extrusion temperature. A blowing agent etc. are mentioned.

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 independently and may be used together in multiple numbers.

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, potassium sulfate, and sulfuric acid. Inorganic compound particles such as barium and glass beads, organic compound particles such as polytetrafluoroethylene, and the like.

This nucleating agent can be contained in the formation material of a foamed resin layer by the master batch system, for example, The master batch disperse | distributed to the matrix resin so that it may become any ratio within the range of 5 mass% or more and 50 mass% or less. By using, the effect exerted on the usage amount of the nucleating agent can be increased.

Moreover, as a thermal decomposition type blowing agent, azodicarbonamide, sodium hydrogencarbonate, the mixture of sodium hydrogencarbonate and citric acid, etc. are mentioned, for example.

Also about this heat decomposition type blowing agent, the effect can be improved by disperse | distributing to a matrix resin so that it may become any ratio within the range of 10 mass% or more and 50 mass% or less, and arrange | positioning master.

In addition, the polypropylene resin composition used for forming the foamed resin layer 20 may contain various additives in the same manner as the resin composition used for forming a general resin product. For example, an antioxidant, an antioxidant, and a processing Adjuvants etc. can be contained suitably.

And the resin foam sheet 1 which concerns on this embodiment is electrostatic in many cases, such as when it is used as a cushioning material of a glass plate in the form of a sheet, or when it is shape | molded by the foam tray which is widely used for display containers, such as meat and fish. It is required to suppress the charging by

Therefore, it is preferable to contain a nonionic antistatic agent in the polypropylene resin composition for forming the surface layers 11 and 12.

As this nonionic antistatic agent, an alcohol type antistatic agent, an ether type antistatic agent, ester type antistatic agent, ester ether ether antistatic agent, etc. are mentioned, for example.

Moreover, as said nonionic antistatic agent, nitrogen containing antistatic agent, such as an amine antistatic agent and an amide antistatic agent, is mentioned, for example.

This nonionic antistatic agent is contained in a polypropylene resin composition in the ratio normally 0.5 mass part or more and 5.0 mass parts or less with respect to 100 mass parts of polymer components contained in a polypropylene resin composition.

As said alcohol type antistatic agent, polyalkylene oxide, such as polyethyleneglycol (or polyethylene oxide) and a poly (ethylene oxide) poly (propylene oxide) block copolymer, etc. are mentioned, for example.

In the alcohol type antistatic agent, the polymerization degree 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 and 100 or less).

More preferably, they are about 15 or more and 50 or less.

As said ether type antistatic agent, For example, Polyoxyethylene alkyl ether, such as polyoxyethylene octyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether; Polyoxyethylene alkyl phenyl ether, such as polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether, etc. are mentioned.

As said ester antistatic agent, For example, polyhydric alcohols, such as ester of polyhydric alcohols, such as ethylene glycol, propylene glycol, trimethylol propane, glycerin, (poly) glycerol, pentaerythritol, sorbitan, sorbitol, sucrose, and a fatty acid Fatty acid ester, For example, glycerol fatty acid ester, such as glycerol monostearic acid ester, sorbitan fatty acid ester, such as sorbitan monooleic acid ester, and sucrose fatty acid ester, such as sucrose monostearic acid ester, etc. are mentioned.

As said ester-ether type antistatic agent, For example, polyoxyethylene glycerin fatty acid ester, such as polyoxyethylene glycerin stearic acid ester and polyoxyethylene glycerin oleic acid ester; Polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan stearic acid ester; Polyoxyethylene polyhydric alcohol fatty acid ester, such as polyoxyethylene sucrose fatty acid ester, is mentioned.

Moreover, polyoxyethylene castor oil, polyoxyethylene hardened castor oil, etc. are mentioned, for example.

As said nitrogen-containing antistatic agent, For example, Polyoxyethylene alkylamine which has a C6-C24 alkyl structure, such as polyoxyethylene laurylamine, in a molecule | numerator; Polyoxyethylene fatty acid amide which has a C6 or more fatty acid structure, such as polyoxyethylene stearic acid amide, in a molecule | numerator; Alkanol alkylamines such as N-alkanol alkylamines such as N-ethanol alkylamine and N, N-alkanol alkylamines such as N, N-diethanol alkylamine; And alkanol fatty acid amides such as N-alkanol fatty acid amides such as N-ethanol stearic acid amide and N, N-alkanol fatty acid amides such as N, N-diethanol stearic acid amide.

Examples of the alkyl or fatty acid constituting the nonionic antistatic agent include those having about 6 to 24 carbon atoms.

As for a fatty acid, saturated fatty acids, such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, etc., saturated fatty acids having 6 to 24 carbon atoms; Unsaturated fatty acids, such as oleic acid, are mentioned.

Moreover, not only this nonionic antistatic agent but also anionic antistatic agent, cationic antistatic agent, amphoteric antistatic agent, and polymeric antistatic agent may be used together, Alkyl sulfonate etc. are mentioned as said anionic low molecular antistatic agent. Examples of the cationic low molecular antistatic agent include tetraalkyl ammonium salts, and the amphoteric low molecular antistatic agent includes alkyl betaine.

Further, as the polymer type antistatic agent, ionomers such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyesteramide, polyetheresteramide, quaternary ammonium salts and polyether-polyolefin block copolymers ( And copolymers of olefinic blocks and hydrophilic blocks such as polyether block and polyolefin block).

Low molecular antistatic agents such as nonionic antistatic agents, anionic antistatic agents, cationic antistatic agents and amphoteric antistatic agents exude to the surface of the resin foam sheet 1 and are called "bleed out". It causes a phenomenon and exerts antistatic function.

Therefore, it is preferable that the polypropylene resin composition for forming the surface layers 11 and 12 contains a component which promotes the bleed out of the nonionic antistatic agent together with the nonionic antistatic agent.

As a component which promotes the bleed-out of this nonionic antistatic agent, resin which has 20% or more and 55% or less of crystallinity is especially effective as either a ethylene-alpha-olefin copolymer or a low density polyethylene resin.

This ethylene-alpha-olefin copolymer and low density polyethylene resin may be contained individually by 1 type in the polypropylene resin composition for forming the surface layers 11 and 12, and may contain multiple types.

Moreover, it is also possible to mix 1 or more types of ethylene-alpha-olefin copolymer, and 1 or more types of low density polyethylene resin, and to use as a component which accelerates the bleed out of a nonionic antistatic agent.

In order to promote the bleed out of the nonionic antistatic agent, the total amount thereof is preferably 20% by mass or more, more preferably 25% by mass or more in the polymer component of the polypropylene resin composition.

In addition, an upper limit is about 40 mass% normally, and, as for the total amount of these, 35 mass% or less is preferable.

In this ethylene-α-olefin copolymer or low density polyethylene resin, crystallinity can be measured by JIS K7121: 1987 "Transition temperature measuring method of plastic."

Specifically, about 7 mg of sample was filled into a measuring vessel using a differential scanning calorimeter (DSC) device manufactured by SII Nanotechnology Co., Ltd., and the temperature rising (cooling) rate was 10 ° C / min under a nitrogen gas flow rate of 30 ml / min. The melting point and crystallization calorie were measured by measuring the amount of heat of fusion and the amount of crystallization with the point where the DSC curve was separated from the base line as the start point of melting (crystallization) while the temperature was raised (cooled). Can be obtained by

Crystallinity (%) = (Crystalization of Crystallization (mJ) / Heat of Fusion (mJ) of Complete Crystal) ×

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

The polymer component of the polypropylene resin composition may be composed only of a component for promoting bleeding out of the HMS-PP and the nonionic antistatic agent, and HMS-PP described therein as a material for forming the foamed resin layer 20. Other polypropylene resins, olefin resins having high affinity with the polypropylene resins, and TPO can be further appropriately added.

And since this polypropylene resin composition comprises the surface of the resin foam sheet 1, it can contain various additives for exhibiting the function provided in this surface as needed.

For example, a weathering agent and an anti-aging agent are contained, and the resin foam sheet 1 and foam tray can be prevented from deterioration, or a slip agent can be included to improve the slipperiness.

Or a pigment can be contained and the improvement of aesthetics by coloring can be aimed at.

And in the resin foam sheet 1 of this embodiment, the 1st surface layer 11 and the 2nd surface layer (as the 1st surface layer 11 and the 2nd surface layer 12 do not necessarily need to make common each thickness, The compounding content of the polypropylene resin composition used for formation with 12) may differ.

For example, coloring may be performed by containing a pigment only on the side corresponding to the outer side of a foam tray, and the side corresponding to the inner side of a foam tray may be natural color (or white).

Moreover, it is also possible to contain the said nonionic antistatic agent only in the side corresponding to the outer side of a foam tray, and to not contain it in the side corresponding to an inner side.

In such a resin foam sheet 1, the thickness of each layer of the 1st surface layer 11, the 2nd surface layer 12, and the foamed resin layer 20 is not specifically limited, The 1st surface layer 11 or the 2nd The surface layer 12 is usually any thickness within the range of 50 µm or more and 150 µm or less.

In addition, the foamed resin layer 20 is usually formed so as to have any thickness within a range of 0.5 mm or more and 5.0 mm or less, and the density (appearance density) is 0.15 g / cm ³ or more and 0.6 g / cm ³ or less.

Such a resin foam sheet 1 can be manufactured by performing extrusion foaming of the said polypropylene resin composition using the extruder generally used for manufacture of a resin foam sheet.

Hereinafter, the manufacturing method of the resin foam sheet 1 is demonstrated in detail with reference to FIG. 2, FIG.

It is a schematic block diagram of the manufacturing apparatus of the resin foam sheet, and FIG. 3 is sectional drawing which shows the internal state of the joining metal mold | die (symbol XH) shown in FIG.

4 shows the state in which the polypropylene resin composition is extruded and foamed, and shows the state of the part shown by the broken line A of FIG.

The manufacturing apparatus of the resin foam sheet shown in the said FIG. 2 is equipped with the 2nd extruder of the 1st extruder 70 which is a tandem extruder, and the 2nd extruder 80 which is a single extruder.

In addition, a circular die (CD) having an annular discharge hole for discharging, in a cylindrical shape, a joining die (XH) into which the resin composition melt-kneaded in these extruders joins and the resin composition joined by the joining die (XH). Is provided.

Moreover, this manufacturing apparatus has the cooling apparatus CL which air-cools the resin foam sheet discharged in cylindrical shape from the circular die CD, and the said cylindrical resin foam sheet to enlarge the diameter of the cylindrical shape of predetermined size. A slit device (not shown in FIG. 2 shows only a state of splitting up and down) and a slit for cutting the mandrel MD for cutting and the resin foam sheet after the mandrel MD passes and dividing the resin foam sheet into two sheets. The winding roller 92 for winding up the obtained resin foam sheet 1 after passing through the some roller 91 is provided.

The first extruder 70 is for forming the foamed resin layer 20, and the poly for forming the foamed resin layer 20 is formed in the upstream extruder (hereinafter, also referred to as the "upstream extruder 70a"). The hopper 71 for inject | pouring a propylene resin composition and the gas introduction part 72 for supplying gas components, such as a hydrocarbon, are provided.

On the downstream side of the upstream extruder 70a, an extruder (hereinafter, referred to as “extruder for discharging and kneading a polypropylene resin composition (hereinafter also referred to as a“ foamable resin composition ”) containing the gas component to the joining die XH) Downstream extruder 70b ").

In addition, the second extruder 80 is for forming the first surface layer 11 and the second surface layer 12, and a polypropylene resin composition for forming the surface layer in a non-foamed state (hereinafter referred to as “non-foaming property”). Resin composition " ") from the hopper 81, melt kneading the non-foamable resin composition inside the cylinder, and discharging the non-foamable resin composition into the joining die XH.

As shown in the schematic cross-sectional view in FIG. 3, the joining die XH includes a first resin flow path W1 that penetrates a central portion from the right side to the left side when viewed from the front, and the first resin flow path W1. ), The second resin flow path W2 for introducing the resin into the first resin flow path W1 and the second resin flow path W2 on the upstream side (right side when FIG. 3 is viewed from the front). The third resin flow path W3 for introducing the resin 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 the annular slit S1 opened in the wall surface forming the resin flow path W1, and the third resin flow path (W3) is connected to the pipe body (P) which has the opening end arrange | positioned in the center part of the said 1st resin flow path W1, and is formed so that a resin composition may flow in the center part of the 1st resin flow path W1.

The first resin flow path W1 is connected to the first extruder 70 on the upstream side thereof, and the downstream side is connected to the circular die CD, and the second resin flow path W2 and the third resin flow path. W3 is connected to the 2nd extruder 80 via the distribution pipe D so that a non-foamable resin composition can flow in from the 2nd extruder 80. As shown in FIG.

That is, the joining mold XH of this embodiment forms the flow of the cylindrical resin which becomes the triple structure of a non-foamable resin composition / foamable resin composition / non-foamable resin composition downstream of the 1st resin flow path W1, These resins are provided so that they can be supplied toward the circular die CD.

And the circular die CD is the flow of the columnar resin composition which flows in from the joining metal mold XH (triple-free non-foaming resin composition / foamable resin composition / non-foaming resin composition) from the center toward the outside. It is formed to be coextruded from the annular discharge hole by changing the flow into a cylindrical flow.

In order to produce a resin foam sheet by such an apparatus, the polypropylene resin composition used for formation of the foamed resin layer 20 is first thrown in from the hopper 71 of the 1st extruder 70, and the 2nd extruder 80 A polypropylene-based resin composition for forming the surface layers 11 and 12, and melt-kneading is performed in each extruder above the melting temperature of the resin, and then co-extruded from the circular die (CD). .

Each resin composition may be put into a hopper after putting individual components into a homogeneous mixed state beforehand, or may be separately put from a hopper and mixed in an extruder.

In these extruders, since it is necessary to melt-knead the components for foaming in the 1st extruder 70, the gas component is indented from the gas introduction part 72 provided in the upstream extruder 70a, and mixing with molten resin is carried out. Conduct.

The co-extrusion from the circular die (CD) is performed by mixing the foamable resin composition melt-kneaded with the upstream extruder 70a of the first extruder 70 to a temperature suitable for extrusion foaming with the downstream extruder 70b. (XH), while in the second extruder 80, the non-foamable resin composition is adjusted to a temperature suitable for formation of the first and second surface layers 11 and 12, and sent to the joining mold XH to be laminated by molten resin. This can be carried out by forming the structure in the joining die XH in advance.

Then, the respective resin compositions joined in the joining die XH are coextruded from the annular discharge holes of the circular die CD, and the foamed resin layer 20 and the surface layer 11 are each made of a polypropylene resin composition. , 12) to form a cylindrical foam having a laminated structure.

Thereafter, the foam is stretched in the circumferential direction along the outer circumferential surface of the mandrel MD having a larger diameter than the discharge hole of the circular die CD, and cooled, and the cooled foam is divided up and down by a cutting tool (not shown). It is set as the strip | belt-shaped resin foam sheet 1, and is wound up to the roll 92, respectively.

At this time, since HMS-PP is contained in the polypropylene resin composition for forming the foamed resin layer 20, it will be extruded in a favorable foamed state.

In addition, the cylindrical foam causes an increase in thickness due to an increase in the degree of foaming immediately after discharge, thereby expanding an apparent volume.

In addition, the foam not only expands in the thickness direction but also causes expansion in the circumferential direction.

In addition, the cylindrical foam is moved in the direction of the mandrel MD by the winding force of the roll 92, and is enlarged so as to gradually approach the outer diameter of the mandrel MD in accordance with the movement.

Therefore, as shown in FIG. 4, if the expansion speed in the circumferential direction is lower than the speed at which the foam FB is expanded after being extruded, there is a low possibility of causing a problem, but in general, the expansion speed is near the circular die CD. Since is high, the loosening portion FE is formed in the foam FB.

That is, assume the shape of a truncated cone that lays the circle drawn by the discharge hole of the circular die CD as the upper bottom, and the circle drawn by the cross section MDa of the mandrel MD toward the circular die CD as the lower bottom. In the lower surface, the foam FB between the circular die CD and the mandrel MD has a position FT (hereinafter referred to as "tension portion FT") in which the winding force by the roll 92 acts. The circular die (CD) is moved between the mandrel (MD) from the circular die (CD) in the form along the slope of the side of the truncated conical shape, but the loosening portion (FE) from the circular die (CD) through the mandrel (MD) To move between.

In this case, moreover, the foam FB is usually provided with a plurality of loosening portions FE, and the vicinity of the circular die CD is a state in which the loosening portions FE and the tensioning portions FT are alternately formed in the circumferential direction. Becomes

Since the volume expansion of the foam FB is usually converged at a position slightly away from the circular die CD, the circumferential tension is applied to the loosening portion FE as the diameter of the mandrel MD is increased. Relaxation is not usually observed at a point near).

However, during this time, while the loosening part FE is eliminated, there is a difference between the stretching part applied to the loosening part FE and the tensioning part FT and the side where the cooling wind touches (cooling condition). Is generated, and streaks are formed in the resin foam sheet after passing through the mandrel MD to cause the presence of the relaxed portion FE and the tension portion FT.

In the present embodiment, since the upper limit is determined in the content of HMS-PP in the polypropylene resin composition, the foaming behavior is smooth and the volume expansion after being extruded from the circular die (CD) becomes smooth.

Therefore, large relaxation is unlikely to occur in the foam FB, and the streaks are suppressed because the stretching applied to the foam FB acts substantially uniformly throughout and the cooling conditions are also substantially uniform.

And when content of HMS-PP becomes less than a lower limit, it becomes as mentioned above about what becomes difficult for it to become a favorable foaming state.

In addition, since the speed at which the foam FB is expanded can be improved by increasing the winding speed (the length of the resin foam sheet wound up to the roll 92 per unit time), this also helps to suppress streaks to some extent. Although the said volume expansion occurs instantaneously, compared with adjusting content of HMS-PP in a polypropylene resin composition, the inhibitory effect of a striation is small.

In addition, when the winding speed is too high, a large tension is generated in the foam (FB). Therefore, it can be said that it is a convenient method to suppress the streaks by the content of HMS-PP in the polypropylene resin composition.

And although this winding speed changes with the kind, thickness, etc. of the resin foam sheet to produce, they are 2 m / min or more and 10 m / min or less normally.

Similarly, by increasing the ratio (d2 / d1) of the diameter (d1: diameter of the intermediate circle between the inner circle of the discharge port and the outer circle) of the circular die CD and the outer shape d2 of the mandrel MD, Although it is possible to some extent suppress the stripe by increasing the stretching in the direction, the effect in this case is also smaller than the effect obtained in the case of adjusting the content of HMS-PP.

Usually, this ratio (d2 / d1) is 1.9 or more and 3.2 or less, and about the slit clearance of the circular die CD, it is normally selected in 0.3 mm or more and 1.5 mm or less.

In addition, although the behavior of volume expansion can be controlled to some extent by adjusting a foaming agent, when the content of a foaming agent is excessively reduced, there exists a possibility that a resin foam sheet may not show a favorable foaming state naturally.

From this point of view, the method of suppressing streaks by the content of HMS-PP can be said to be a simple method.

In addition, when a blowing agent uses butane (n-butane, i-butane, or mixed liquid thereof), for example, the ratio with respect to 100 mass parts of polymer components is 1 mass part or more and 6 mass parts or less normally.

The resin foam sheet produced in this way becomes homogeneous in thickness and foaming state.

In the surface layers 11 and 12, since the ethylene-α-olefin copolymer having a crystallinity of 20% or more and 55% or less or a low density polyethylene resin having a crystallinity of 20% or more and 55% or less is contained together with the nonionic antistatic agent, The nonionic antistatic agent can quickly bleed out to the surface.

Accordingly, at room temperature, for example, the surface resistivity may be lowered to 1 × 10 ¹³ Ω / □ or less to thereby exhibit antistatic performance.

Therefore, since it does not provide a curing period until the desired antistatic performance is exhibited, or even if it provides, it ends in a short period of time, so that a resin foam sheet can be used for a short period of time, and thus the stock period of the resin foam sheet Can be shortened.

Moreover, since the physical properties of such a resin foam sheet are homogenized, when forming by the sheet forming method or the like, local elongation occurs, and there is a low possibility that "appearance defect" or "crack" occurs in the molded article.

That is, it is useful for improving the yield of molded articles.

In addition, when streaks are formed on the surface of the resin foam sheet and the thickness of the resin foam sheet is uneven, the thick portion comes into contact with the molding die for the first time, and the antistatic agent bleeding out of this portion strongly resists the molding mold. It is easier to move to parts that are not in contact.

In addition, in the sheet forming method, since the resin foam sheet is in a heated state, the mobility of the antistatic agent is also increased, and if the thickness of the resin foam sheet is uneven, the area where the antistatic agent is concentrated on the surface of the molded article and the antistatic property are lost. There is a risk of forming a discarding point.

That is, when the molded article is produced according to the sheet molding method by bringing the surface layers 11 and 12 into contact with the mold, it can be said that the resin foam sheet of the present embodiment can be particularly preferably used.

In this embodiment, although embodiment of this invention was demonstrated, illustrating the three-layered resin foam sheet which has the surface layer which covers both surfaces of foaming resin layer, Even if it has a laminated structure of four or more layers, When the same polypropylene resin composition is formed by extrusion foaming with an extruder, the effect of suppressing streaks is exhibited as in the above example.

The same applies to the case where the surface layer is formed only on one side of the foamed resin layer or the foamed resin layer single layer.

Furthermore, also in the case of coextruding a some foamed resin layer, the suppression effect of a streak can be exhibited by using the polypropylene resin composition of this embodiment.

Although a detailed description thereof is omitted here, any known matters in the technical matters related to the resin composition, the extrusion foaming technique, the resin foam sheet, the production method, and the like are included in the present invention within a range in which the effects of the present invention are not significantly impaired. It can be adopted.

(Example)

Next, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

(Example 1)

The equipment of the same kind as the apparatus structure as shown in FIG. 2 was used for preparation of the resin foam sheet.

That is, the non-foamable resin composition is separated from the second extruder 80 through the branch pipe D in two places on the upstream side and the downstream side of the resin flow path W1 into which the expandable resin composition flows from the first extruder 70. The 1st, 2nd extruder was connected to the joining metal mold | die XH so that it might flow in, and the circular die CD was connected to the downstream side of the said joining die XH, and coextrusion was performed.

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

39 mass% of HMS-PP sold by Borealis under the trade name "WB135", and 55 mass% of block PP sold by Nihon Polyprosa under the trade name "BC6C" under the trade name "Q-100F" by Sunalomer. Polymer components containing 6% by weight of TPO to be added, and a heavy sodium citrate-based foaming agent (a master batch manufactured by Daiichi Purification Co., Ltd.), which becomes 0.5 parts by mass when the total amount of these polymer components is 100 parts by mass. The polypropylene resin composition for foaming resin layer formation containing "fine cell master PO410K") was supplied to the hopper of a single screw extruder having an upstream diameter of 90 mm, and heated and melted at a temperature of 200 to 210 ° C in the extruder. Thereafter, butane (isobutane / normal butane = 35/65 mass%) as a gas component was pressed and kneaded so that the ratio with respect to 100 parts by mass of the molten resin was 4 parts by mass.

This foamable resin composition was supplied to the downstream extruder, the temperature of the foamable resin composition was lowered, and it was supplied to the joining metal mold | die (XH) connected to the extruder tip by the discharge amount of 120 kg / hour.

On the other hand, the single screw extruder whose diameter is 65 mm was prepared as a 2nd extruder for melt-mixing the formation material of a surface layer.

And 70 mass% of HMS-PP marketed by Borealis under the brand name "WB135", and 30 mass% of the ethylene-alpha-olefin copolymer sold by Nihon Polyethylene company under the brand name "KS240T" (crystallinity: 26%). The polypropylene resin composition for surface layer formation containing the polymer component to contain and the nonionic antistatic agent (The Kao Corporation make, brand name "TS-2B") which becomes 2.0 mass parts when the total amount of these polymer components is 100 mass parts. The hopper of the second extruder was fed and heated and melted to a temperature of 200 ° C.

Subsequently, the molten (non-foamable) polypropylene-based resin composition is divided into two in a distribution pipe having a branch flow path, and thereafter, the pipe body is opened in the center of the resin flow path of the joining die and the outer circumference of the resin flow path. 135 kg from the circular die (diameter 140 mm, slit gap 1.0 mm) connected to the joining die front end after discharging each sum in an amount of 15 kg / hour in both slits and laminating and joining the inner and outer layers of the foamable resin composition. By co-extrusion in a cylindrical shape with the amount of resin discharged per hour, a cylindrical foam in which a non-foamed surface layer was laminated on both sides thereof was formed through the foamed resin layer.

The cylindrical foam produced by the extruded foam is expanded along a cooling mandrel for diameter: 414 mm x length: 500 mm, and the outer surface is cooled by blowing air from the air ring to become symmetrical in the circumferential direction of the mandrel. Two strip | belt-shaped resin foam sheets were cut | disconnected by the cutter at two points (opened 180 degree | times).

About the obtained resin foam sheet of Example 1, surface resistivity was measured based on JISKK6969-1995. The pretreatment time was measured for 24 hours.

Specifically, after leaving a test piece having a flat square shape of 10 cm on one side for 24 hours in an atmosphere of temperature 22 ° C. and humidity 60%, a test device (advan test company manufactured) under an environment of temperature 22 ° C. and humidity 60%. Using a digital ultra-high resistance / micro-ammeter R8340 and resistance chamber R12702A), crimping the electrode at a load of about 30N and applying a voltage of 500V to the test piece, measuring the resistance value after 1 minute, and calculating it by the following equation. It was.

ρs = π (D + d) / (D-d) × Rs

only,

ρs: Surface resistivity (Ω / □)

D: Inner diameter (cm) of the surface annular electrode (7 cm in resistive chamber R12702A)

d: Outer diameter (cm) of the inner circle of the surface electrode (5 cm in the resistance chamber R12702A)

Rs: Surface resistance (Ω)

As a result, a surface resistivity value of 3.5 × 10 ¹² Ω / □ was observed.

In addition, no noticeable streaks were observed in this resin foam sheet.

The foam tray was produced according to the 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, low-density polyethylene (PE) having a crystallinity of 50% sold under the trade name "LD400" by Nippon Polyethylene, in place of Nippon Polyethylene's ethylene-α-olefin copolymer (KS240T). ) A resin foam sheet was produced in the same manner as in Example 1 except that a resin was used, and a foam tray was produced.

When the resin foam sheet of this Example 2 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 5.0x10 <^{12> (} ohm) / (square).

In addition, no noticeable streaks were observed, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Example 3)

In the polypropylene resin composition for forming the surface layer, low-density polyethylene (PE) having a crystallinity of 53% sold under the trade name "LF441B" by Nippon Polyethylene Co., Ltd. instead of Nippon Polyethylene Co., Ltd. ethylene-α-olefin copolymer (KS240T) ) A resin foam sheet was produced in the same manner as in Example 1 except that a resin was used, and a foam tray was produced.

When the resin foam sheet of this Example 3 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 6.5x10 <^{12> (} ohm) / (square).

In addition, no noticeable streaks were observed, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Example 4)

In the polypropylene resin composition for forming the surface layer, the crystallinity degree of 36% sold by Sumitomo Chemical Co., Ltd. under the brand name "Erixen VL-100" in place of Nippon Polyethylene Co., Ltd. ethylene-alpha-olefin copolymer (KS240T) Except having used the ultra low density polyethylene (PE) resin, it carried out similarly to Example 1, and produced the resin foam sheet, and produced the foam tray.

When the resin foam sheet of this Example 4 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 4.0x10 <^{12> (} ohm) / (square).

In addition, no noticeable streaks were observed, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Example 5)

In the polypropylene resin composition for forming the foamed resin layer, the proportion of HMS-PP (WB135) is set to 25 mass% instead of 39 mass%, and the proportion of block PP (BC6C) is 69 mass instead of 55 mass% instead. Except having made%, it carried out similarly to Example 1, and produced the resin foam sheet, and produced the foam tray.

When the resin foam sheet of Example 5 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 3.5x10 <^{12> (} ohm) / square.

In addition, no noticeable streaks were observed, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in 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 100 mass% of HMS-PP (WB135) to prepare a foam tray.

When the resin foam sheet of this Example 6 measured the surface resistivity similarly to Example 1, it showed the surface resistivity of 4.5 * 10 <^{13> (} ohm) / (square).

In addition, no noticeable streaks were observed in the resin foam sheet itself, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Example 7)

A resin foam sheet was produced and a foam tray was produced in the same manner as in Example 1, except that the nonionic antistatic agent was not included in the polypropylene resin composition for forming the surface layer.

When the resin foam sheet of this Example 7 measured the surface resistivity similarly to Example 1, it showed the surface resistivity of 6.5x10 <^{15> (} ohm) / square.

In addition, no noticeable streaks were observed in the resin foam sheet itself, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Example 8)

A resin foam sheet was produced and a foam tray was produced in the same manner as in Example 5 except that the nonionic antistatic agent was not included in the polypropylene resin composition for forming the surface layer.

When the resin foam sheet of this Example 8 measured the surface resistivity similarly to Example 1, it showed the surface resistivity of 6.5x10 <^{15> (} ohm) / square.

In addition, no noticeable streaks were observed in the resin foam sheet itself, and the foam tray formed by the resin foam sheet was beautiful in appearance and excellent in mechanical strength.

(Comparative Example 1)

In the polypropylene resin composition for forming the foamed resin layer, the ratio of HMS-PP (WB135) is set to 18 mass% instead of 39 mass%, and instead, the proportion of block PP (BC6C) is 76 instead of 55 mass%. Except having made mass%, it carried out similarly to Example 1, and produced the resin foam sheet, and produced the foam tray.

When the resin foam sheet of this comparative example 1 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 3.5x10 <^{12> (} ohm) / (square).

However, the resin foam sheet was not foamed to a sufficient thickness and no noticeable streaks were observed, but the foam tray formed by the resin foam sheet had a lower mechanical strength than in the case of the respective examples.

(Comparative Example 2)

In the polypropylene resin composition for forming the foamed resin layer, the ratio of HMS-PP (WB135) is set to 50 mass% instead of 39 mass%, and instead, the ratio of block PP (BC6C) is 44 instead of 55 mass%. Except having made mass%, it carried out similarly to Example 1, and produced the resin foam sheet, and produced the foam tray.

When the resin foam sheet of this comparative example 2 measured the surface resistivity similarly to Example 1, it turned out that it has a surface resistivity of 3.5x10 <^{12> (} ohm) / (square).

However, the resin foam sheet was streaked, and the foam tray formed by the said resin foam sheet was found to be defective in which a hole was punched, and it was difficult to obtain a foam tray of good appearance.

The examination result of the above Example and a comparative example is shown to the following comparison table (Table 1).

Also in this respect, according to this invention, it turns out that the resin foam sheet suitable for the formation material of the foamed molded article which has a three-dimensional structure by suppressing a stripe can be provided.

One… Resin foam sheet, 11... First surface layer (non-foamed resin layer), 12... Second surface layer (non-foamed resin layer), 20... Foamed resin layer

Claims (5)

A polypropylene resin composition comprising polypropylene resin as a main component is a resin foam sheet formed by extrusion foaming with an extruder,
The said polypropylene resin composition contains the high melt tension polypropylene resin so that the ratio to the polymer component contained may be 20 mass% or more and less than 50 mass%. The method of claim 1,
A resin foam sheet in which the high melt tension polypropylene resin has a free terminal long chain branch formed by chemical crosslinking. The method according to claim 1 or 2,
The polypropylene type which has a non-foamed resin layer on the surface, has a laminated structure by which the expanded resin layer formed by the extrusion foaming of the said polypropylene resin composition, and the said non-foamed resin layer was laminated | stacked, and contains a nonionic antistatic agent. The resin foam sheet in which the said non-foaming resin layer is formed of the resin composition. The method of claim 3, wherein
In the polypropylene resin composition forming the non-foamed resin layer, the foamed resin further contains an ethylene-α-olefin copolymer having a crystallinity of 20% or more and 55% or less or a low density polyethylene resin having a crystallinity of 20% or more and 55% or less. Sheet. The method according to claim 3 or 4,
The resin foam sheet used for the use by which shaping | molding process is performed in a heated state, and the said shaping | molding process is performed by making the said non-foaming resin layer contact a shaping | molding die.

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