JP2012030509A - Method of manufacturing water-absorbent foam molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve moldability of a resin foamed sheet having water-absorbing holes bored thereon.SOLUTION: In this method of manufacturing a water-absorbent foam molding, a water intake hole forming step of boring the plurality of water intake holes leading to an open cell layer from at least one face side of the resin foam sheet including the open cell layer is executed, and then, thermoforming is performed by secondary foaming of the resin foam sheet. The secondary foaming of the resin foam sheet is performed followed by the water intake hole forming step.

Description

  The present invention relates to a method for producing a water-absorbent foam molded article, and more specifically, a water absorption hole forming step of drilling a plurality of water absorption holes from at least one surface side of a resin foam sheet having an open cell layer to the open cell layer. It is related with the manufacturing method of the water absorptive foaming molded article which carries out thermoforming by carrying out secondary foaming of this resin foam sheet.

Conventionally, resin foam sheets made of polyolefin resin or polystyrene resin, and resin foam sheets with a resin film laminated on the surface (hereinafter also referred to as “film laminated foam sheets”) are foam molded products such as food trays. It is adopted as a raw material for manufacturing.
In the production of this type of foam-molded product, a raw roll obtained by winding a strip-shaped resin foam sheet produced by foam extrusion into a roll, or a strip-shaped film stack in which a resin film is laminated on the resin foam sheet. An original fabric roll obtained by winding a foamed sheet into a roll is used.
This type of foamed molded product is supplied with raw materials such as a film-laminated foam sheet sequentially from the raw roll to a sheet-forming machine by the length required for one thermoforming, and film-laminated foaming with the sheet-forming machine. After one or more product shapes are formed on the sheet, continuous production is performed such that the foamed product is taken out from the film-laminated foam sheet by cutting along the outer edge of the product shape with a Thomson blade mold or the like. .

  Since the foamed molded article is required to have excellent strength, cushioning properties, or moldability during thermoforming, open cells are generally formed when forming a resin foam sheet as a raw material. In recent years, the open cell layer has been used for water absorption. For example, a film-laminated foam in which a resin film is laminated on the surface of a resin foam sheet having an open cell layer The sheet is provided with a plurality of holes that penetrate the resin film from the resin film side to reach the open cell layer, and the open cell layer absorbs water adhering to the resin film through the holes. It is used as a hole (see Patent Document 1 below).

This film-laminated foam sheet or a mere resin foam sheet that is not laminated with a resin film is rolled up when the resin foam sheet is extruded and wound up as a raw roll or when a roll of a predetermined length is cut from the raw roll. In carrying out the process, a step of forming water absorption holes in the movement path of the resin foam sheet (water absorption hole forming step) is performed.
This water-absorbing hole forming step is usually carried out by arranging a perforating roller having a sharp cutting edge of a plurality of needle-like blades protruding on the surface in the movement path, for example, accompanying the movement of the film-laminated foam sheet. The water-absorbing holes are formed by a continuous method in which the perforating roller is rotated on the film-laminated foam sheet so that the plurality of blades enter the film-laminated foam sheet one after another.
Such a film-laminated foam sheet is molded into a lid of a container with a lid by the continuous molding method as described above.
In the case of producing a water-absorbing foam molded product by thermoforming a resin foam sheet having water absorption holes including such a film-laminated foam sheet, it is required to exhibit good moldability.
However, until now, sufficient study has not been made on the moldability of the resin foam sheet in which the water absorption holes are formed, and no countermeasure has been established.
For this reason, conventionally, it has been difficult to sufficiently improve the moldability of the resin foam sheet during the production of the water-absorbent foam-molded product.

Utility Model Registration No. 3127439

  The present invention has been made in view of the above-described problems, and an object thereof is to improve the moldability of a resin foam sheet having water absorption holes.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors rapidly disperse the foaming agent remaining in the resin foam sheet after the water-absorbing holes are formed, thereby rapidly reducing the moldability. As a result, the present invention has been completed.

  That is, the present invention relating to a method for producing a water-absorbing foam molded article for solving the above-described problem is that a plurality of water-absorbing holes extending from at least one side of a resin foam sheet having an open cell layer to the open cell layer are formed. A method for producing a water-absorbent foam-molded article in which the foamed resin sheet is secondarily foamed and thermoformed after the water-absorbing hole forming step is performed, wherein secondary foaming of the resin foamed sheet is performed in the water-absorbing hole forming step. It is characterized by continuous implementation.

Conventionally, when the resin foam sheet is wound up as a raw roll or when the raw roll is cut to produce a cut roll, water absorption holes are formed. In the present invention, the resin foam sheet is subjected to secondary foaming. Prior to the step of forming, the water absorption holes are formed, and the secondary foaming is continuously performed.
Therefore, since the thermoforming is performed in a state where the foaming agent remains sufficiently, the moldability of the resin foam sheet can be improved as compared with the conventional case.

The front view and side view which show one part (disk with a blade) of the drilling jig | tool for forming a water absorption hole in a resin foam sheet. The front view which shows the perforation jig | tool (perforation roller) for forming a water absorption hole in a resin foam sheet. Schematic which showed a mode that the water absorption hole was formed in a film lamination foam sheet. The front view and sectional drawing of the water absorption hole drilled in Example 1. FIG.

Below, the manufacturing method of the water absorptive foam-molded article which concerns on this embodiment is demonstrated.
In addition, embodiment of this invention is described, showing the example which uses the film lamination foam sheet as a resin foam sheet, and manufactures the cover body for food packaging containers as a water absorbing foam molded product here.

First, a film laminated foam sheet used as a material for forming the lid will be described.
In the method for producing a water-absorbing foam molded article of the present embodiment, a film-laminated foam sheet in which a resin film is laminated on a general resin foam sheet having an open cell layer can be used.
The resin foam sheet constituting this film laminated foam sheet is a polyolefin resin foam sheet obtained by foam extrusion of a resin composition mainly composed of polyethylene resin or polypropylene resin, a styrene homopolymer, or copolymerized with styrene. And a polystyrene-based resin foam sheet obtained by foam-extruding a resin composition mainly composed of a polystyrene-based resin such as a copolymer of a monomer and styrene that can be prepared.

In addition, the resin foam sheet used as a material for forming the film-laminated foam sheet in the present embodiment can adopt the same structure as that of a conventional open-cell foam sheet for the internal structure. For example, the resin composition Examples thereof include those obtained by melt-kneading with a single extruder and foam extrusion from a circular die connected to the extruder.
In the resin foam sheet obtained by such a method, a surface skin layer having a high closed cell ratio and a fine cell diameter is usually formed on the surface, and the inside of the surface skin layer is more than the surface skin layer. Also, an open cell layer having a large number of open cells (high open cell ratio) having a large bubble size and having a bubble film between adjacent bubbles and being in communication is provided.
That is, it has a three-layer configuration of “surface skin layer / open cell layer / surface skin layer”, and the open cell layer can be used as a layer for water absorption (water retention).

  In addition, the resin composition is melt-kneaded with an extruder and a resin composition different from the resin composition is melt-kneaded in a condition that makes it easy to form closed cells using another extruder, and these melt-kneaded materials are A resin foam sheet having a three-layer structure of “surface skin layer / open cell layer / closed cell layer” obtained by coextrusion from a circular die after merging can also be employed.

The former foamed sheet has a simpler manufacturing process, and the film laminated foamed sheet can be manufactured easily. On the other hand, the latter foamed sheet has the thickness and strength of the film laminated foamed sheet. It is easy to make adjustments.
Moreover, it can be said that the latter foam sheet | seat is excellent also in the point which can aim at the moldability improvement of a film lamination foam sheet using the secondary foam property of a closed cell layer.

In order to form a film-laminated foam sheet using a resin foam sheet having a closed cell layer together with the open cell layer, a resin film may be laminated on the closed cell layer side to form water absorption holes on this side. Usually, a resin film is laminated on the surface skin layer side to form water absorption holes on the surface skin layer side.
This is because the closed cell layer produced as described above is usually thicker than the surface skin layer, so that the water absorption holes are provided on the surface skin layer side in consideration of the path length to the open cell layer. This is because it tends to be advantageous in terms of water absorption, and if the water absorption holes are formed so as to penetrate the closed cell layer, the secondary foamability may be impaired.
Also in such a point, it is preferable that the film-laminated foam sheet has a structure of “resin film / surface skin layer / open cell layer / closed cell layer” in order from the resin film side.

  In the resin foam sheet having the closed cell layer and the open cell layer, as a resin composition for constituting the open cell layer side, for example, a styrene homopolymer called general-purpose polystyrene resin (GPPS) and the like, styrene And a mixture of a hydrogenated product of a copolymer of conjugated diene and a polyolefin resin and a foaming component.

As a hydrogenated product of a copolymer of styrene and conjugated diene, a hydrogenated product of a block of styrene and conjugated diene or a random copolymer is preferable.
In particular, those having a durometer type A hardness (HDA) value of 30 to 90 described in JIS K 7215 are preferred.
Examples of the conjugated diene include conjugated dienes having 4 to 10 carbon atoms such as butadiene, isoprene, and 2-ethylbutadiene. Preferred hydrogenated styrene-conjugated diene copolymers include styrene-isoprene block copolymers. A hydrogenated product of a coalescence, a hydrogenated product of a styrene-butadiene block copolymer, and a hydrogenated product of a styrene-butadiene random copolymer.
The fully saturated structure of these copolymers includes, for example, styrene-ethylene-butylene copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene copolymer, styrene-ethylene-propylene-styrene block. Such as a copolymer.
These copolymers may be used alone or in combination of two or more.

  The polyolefin resin is a component that facilitates the formation of open cells by generating bubbles in the bubble film during foaming. As the polyolefin resin, a high-density polyethylene resin, a polypropylene resin, or the like is adopted. Is possible.

  The ratio of the polystyrene resin, the hydrogenated copolymer of styrene and conjugated diene, and the polyolefin resin is usually 50 to 94% by weight of polystyrene resin and styrene when the total amount is 100% by weight. The hydrogenated copolymer of conjugated diene is selected from the range of 5 to 49% by mass and the polyolefin resin is selected from the range of 1 to 10% by mass.

In addition, the foaming components include an air conditioner such as inorganic fillers such as talc, mica and montmorillonite, and organic fine particles such as fluororesin, hydrocarbons such as propane, isobutane, normal butane and pentane, nitrogen, dioxide It can be used in combination with a blowing agent such as an inert gas such as carbon.
In addition, a decomposable foaming agent such as azodicarbonamide, which can be used as a bubble regulator, can be used alone or in combination with the foaming agent.
As the foaming agent, considering the foamability at the time of producing the resin foam sheet (at the time of primary foaming) and at the time of secondary foaming, mixed butane in which isobutane and normal butane are mixed at a ratio of 50:50 to 80:20 is preferable.

On the other hand, as a resin composition which comprises a closed cell layer, what mix | blended the above foaming components with GPPS is mentioned.
In addition, with respect to the resin foam sheet, the closed cell layer has 1 to 5 mass immediately after the production of the resin foam sheet so that good moldability can be exhibited in the subsequent secondary foaming process and the thermoforming process. It is preferable to contain a foaming agent in an amount of%.

In order to form a film-laminated foam sheet using a resin foam sheet having a closed cell layer together with the open cell layer, a resin film may be laminated on the closed cell layer side to form water absorption holes on this side. Normally, a resin film is laminated on the surface skin layer side, and water absorption holes are formed on the surface skin layer side.
This is because the closed cell layer produced as described above is usually thicker than the surface skin layer, so that the water absorption holes are provided on the surface skin layer side in consideration of the path length to the open cell layer. This is because it tends to be advantageous in terms of water absorption, and if the water absorption holes are formed so as to penetrate the closed cell layer, the secondary foamability may be impaired.
Also in such a point, it is preferable that the film-laminated foam sheet has a structure of “resin film / surface skin layer / open cell layer / closed cell layer” in order from the resin film side.

In addition, as the resin foam sheet for constituting the film-laminated foam sheet in the present embodiment, a sheet having an overall thickness before secondary foaming of 1.5 mm to 3.5 mm can be generally adopted. Of these, the open cell layer may occupy a thickness of 0.5 mm to 1.5 mm.
The closed cell layer is usually 1 mm to 3 mm thick.
The open cell rate of the open cell layer that can be measured based on ASTM D2856-87 is usually 60% to 90%, and the open cell rate of the closed cell layer is usually 0% to 30%. %.

Although it does not specifically limit as a resin film laminated | stacked on such a resin foam sheet, Usually, the thickness shall be 10 micrometers-100 micrometers.
Moreover, although the material of the resin film is not particularly limited, it is preferable to use the same type of resin as the resin foam sheet from the viewpoint of recycling and the like.
For example, the resin foam sheet is widely used in food packaging containers and the like, and a polystyrene-based resin foam sheet can be preferably used in terms of low cost and excellent strength. It is preferable to employ a polystyrene resin film.
It can be said that the combination of the polystyrene resin film and the polystyrene resin foam sheet is also preferable in that these can be directly heat laminated.
However, if necessary, the properties required for water-absorbent foam molded products that also produce polystyrene-laminated foam sheets and dry laminated polypropylene resin films, and film-laminated foam sheets laminated with polyethylene terephthalate films via adhesives. It can be adopted as appropriate.

As will be described later, in this embodiment, when the film-laminated foam sheet is subjected to secondary foaming, mechanical tension is applied to the film-laminated foam sheet to generate tension in the resin film, thereby opening the water absorption holes. Although the operation is performed to enlarge the portion, expect a more remarkable effect in enlarging the opening of the water absorption hole by adopting a resin film that can cause heat shrinkage in secondary foaming Can do.
Therefore, it is preferable to employ a uniaxially stretched or biaxially stretched film as the resin film.

Moreover, in this embodiment, since the said film | membrane laminated foam sheet is used as a raw material of the cover body for food packaging containers, as the said resin film, what gave the anti-fogging process is preferable.
For this anti-fogging treatment, a method of improving the wettability of the resin film with water by dispersing a surfactant or the like on the resin film itself, or an anti-fogging treatment agent containing a surfactant on the surface of the resin film. Conventionally adopted methods such as a method of forming an antifogging film by coating can be employed.

Among these, a polystyrene resin film that has been subjected to an antifogging treatment with an antifogging treatment agent comprising a mixed composition of 80 to 99% by mass of a nonionic surfactant composition and 20 to 1% by mass of polyvinyl alcohol is preferable. The polystyrene resin film preferably has a contact angle of 1 to 15 degrees between the surface subjected to the antifogging treatment and water.
The antifogging treatment agent includes a nonionic surfactant having an HLB (Hydrophile-Lipophile Balance) of 12 to 18 and a surface tension of a 0.1% by weight aqueous solution at 25 ° C. of 30 to 39 mN / m. (Component A) and a nonionic surfactant (Component B) having a surface tension of 40 to 60 mN / m at 25 ° C. in a 0.1 mass% aqueous solution, the Component A and Component B are 30 : It is preferable to make it contain in the ratio used as 70-95: 5 (A component: B component).

“HLB value” is a Japanese translation called “Hydrophilic Lipophilic Balance”, etc., and the degree of affinity of surfactant for water and oil (organic compounds insoluble in water) Is a value representing
The specific index is as follows.
Surfactants are hardly dispersed in water when their HLB values are about 1 to 3, and are used as antifoaming agents and the like.
When the HLB value is about 3 to 6, a part is dispersed in water and used as an emulsifier for a w / o emulsion.
When the HLB value is about 6 to 8, it is dispersed in water by mixing well to form an emulsion, which is used as an emulsifier and wetting agent for w / o emulsion.
When the HLB value is about 8 to 10, it is stably dispersed in water to form an emulsion, which is used as a wetting agent or an emulsifier for an o / w emulsion.
When the HLB value is about 10 to 13, it is translucently dissolved in water and used as an emulsifier for o / w type emulsion.
When the HLB value is about 13 to 16, it is transparently dissolved in water and used as an emulsifier and a cleaning agent for an o / w emulsion.
When the HLB value is about 16 to 19, it is transparently dissolved in water and used as a solubilizer.

  Even if condensed water adheres to the inside of the lid by using a resin film that has been subjected to an antifogging treatment with such an antifogging treatment agent, it can be easily spread and prevented from dripping and the condensed water. Opportunities for contact with the water absorption holes are expanded, and good water absorption is exhibited.

  In addition, in this embodiment, since the lid | cover for food packaging containers is illustrated, the example which employ | adopts a film laminated foam sheet as a suitable aspect as a resin foam sheet is described, but the said resin film is this It is not essential in the invention, and it is also possible to form a water-absorbing foam molded article with a simple resin foam sheet not provided with a resin film or the like.

In the method for producing a water-absorbent foam molded body according to the present embodiment, a water-absorbing hole forming step in which a plurality of water-absorbing holes reaching the open cell layer are formed in the resin foam sheet, and the resin foam sheet having the water-absorbing holes formed therein. A secondary foaming step for secondary foaming and a thermoforming step for thermoforming the resin foam sheet after the secondary foaming step are performed.
In the following, a lid for a food packaging container is formed by a film-laminated foam sheet obtained by laminating a polystyrene-based resin foam sheet having an open-cell layer together with an open-cell layer and an expanded polystyrene resin film subjected to an antifogging treatment. Each process in the case will be described.

(Water absorption hole forming process)
In order to form the lid, first, a water absorption hole forming step is performed in which a plurality of water absorption holes are formed in the film-laminated foam sheet through the resin film from the resin film side to reach the open cell layer.
The water absorption hole forming step can be performed by using a drilling jig provided with a plurality of blades for forming the water absorption holes.

This drilling jig will be described with reference to the drawings.
FIG. 1 is a front view and a side view of a bladed disk 1 having a plurality of blades 1x on the outer periphery, and FIG. 2 shows this bladed disk 1 and a disk having a smaller diameter than the bladed disk 1. It is a figure which shows the perforation roller (drilling jig | tool) formed by arranging the spacers 2 alternately and penetrating the rotating shaft 3 at the center.
In the outer peripheral portion of the disc 1 with blade, irregularities that are angular in the radial direction are continuously formed in the circumferential direction, and this convex portion is used as a blade 1x for forming a water absorption hole.

Although this convex part (blade 1x) is in a state of being sharpened radially outward so that the shape in a side view is a triangle, as shown in FIG. Is constant from the root to the tip.
That is, the plurality of blades 1x provided on the outer periphery of the bladed disk 1 are triangular blades having a constant blade thickness, and the length of the ridge line 1a at the tip is made to coincide with the length of the valley 1b.
The circular disc 1 with a blade is provided with a circular center hole 10 through which the rotating shaft 3 is inserted at the center thereof, and a part of the inner peripheral edge defining the center hole 10 is rectangular. A keyway 11 for fixing to the rotary shaft 3 is formed in a cutout shape.
The blade thickness of the tip portion of the blade 1x is preferably 0.5 mm to 2 mm, particularly preferably 0.75 mm to 1.5 mm, although it depends on the size of the water absorption holes to be formed.

Although not shown in the drawing, the spacer 2 is also formed with a center hole and a key groove having a size corresponding to the thickness (diameter) of the rotary shaft 3 as in the case of the bladed disk 1. Yes.
On the other hand, the rotary shaft 3 is provided with a key groove along its length so that a rectangular key hole can be formed together with the key groove of the bladed disk 1 and the spacer 2.
The perforated roller has blades 1 and spacers 2 alternately set on a rotating shaft 3 and a key 4 is inserted into the key hole and fixed. The rotating shaft 3 rotates around the shaft. By doing so, the bladed disc 1 can be rotated around the rotation axis 3.

In the water absorption hole forming step according to the present embodiment, for example, if the water absorption hole is formed in a band-shaped film laminated foam sheet, the rotation shaft 3 is orthogonal to the length direction of the film laminated foam sheet. In addition, a roller having a substantially same size as the perforation roller and a flat outer peripheral surface is arranged in parallel with the perforation roller, and between the outer peripheral surface of the roller and the blade edge of the perforation roller. It can be carried out by providing a slight gap and passing the film-laminated foam sheet between the rollers.
That is, the gap is set to about the thickness of the closed cell layer, and the resin film side is a perforated roller side, and the film laminated foam sheet is passed through these rollers to pass through the resin film continuously. The water absorption holes reaching the bubble layer can be continuously formed in the band-shaped film laminated foam sheet, and the water absorption hole forming step can be carried out efficiently.

  Further, regardless of such a method, the perforation roller is arranged on a flat stage so that a slight gap is formed between the blade edge and a gap between the stage and the perforation roller. Similarly, the method of moving the film-laminated foam sheet can efficiently form the water absorption holes.

At this time, since the blade 1x has the blade thickness (0.5 to 2.0 mm) as described above, water absorption holes advantageous for water absorption can be formed.
This will be described with reference to FIG.
FIG. 3A shows, in order from the top, a film-laminated foam sheet 20 having a laminated structure of a resin film 21, a surface skin layer 22, an open cell layer 23, and a closed cell layer 24 in the longitudinal direction (extrusion of the resin foam sheet). (MD) direction) In the schematic side view and main part expansion schematic perspective view which showed a mode that the hole 1x was penetrate | invaded into the said resin film 21 and the water absorption hole 30 was pierced by rotating the said perforating roller. FIG. 3B is a plan view of the formed water absorption holes 30 as viewed from the upper surface side of the film-laminated foam sheet 20.

First, the tip of the blade 1x (ridge line 1b) is in contact with the surface of the film-laminated foam sheet 20 by the rotation of the bladed disk 1 and is obliquely directed to the resin film 21 (rotating direction of the perforating roller. FIG. The resin film 21 is cracked by applying a force in the direction (FIG. 3 (a) left).
Thereafter, as the rotation of the bladed disk 1 proceeds, the resin film 21 is completely torn and tears in the direction (the width (TD) direction of the resin foam sheet) along the ridge line 1a at the tip of the blade 1x. By having a certain blade thickness, the resin film 21 is torn in the direction (MD direction) perpendicular to the ridge line 1a direction by both edges e1 and e2 of the blade 1x that has entered, and the shape is like the letter “H” of the capital letter of the alphabet Thus, the resin film 21 is torn and the water absorption holes 30 are formed.

The formation of such intersecting tears in the resin film 21 is an important factor for expanding the water absorption holes 30 in the subsequent secondary foaming step.
For example, if only a tear along the MD direction is formed, applying tension in the TD direction to the resin film 21 widens the width of the tear and greatly expands the opening, but tension was applied in the MD direction. In some cases, the effect of widening the opening may not be exhibited.
On the other hand, in this embodiment, since a tear is formed in the TD direction and the MD direction, even when tension is applied in any direction, any one of the tears widens to enlarge the opening of the water absorption hole. Can be made.

In addition, in the present embodiment, the blade edge is not sharp and the water absorption hole is formed by the blade 1x having a certain blade thickness, so that the blade edge of the resin film 21 is cut so as to tear a part of the resin film 21. The piece 21a which penetrated and cut | disconnected the resin film 21 can be made into the state penetrated into the bottom part of the water absorption hole.
Therefore, even if the resin film 21 bent inward by the intrusion of the blade 1x is restored to a straight state, the opening is secured at least by the amount of the fragment 21a.

The formation of the intersecting rips and the effect of cutting part of the resin film 21 are not necessarily exhibited only by the perforating roller, and are provided on the outer periphery of the bladed disc 1. A film-laminated foam using a perforated plate with a triangular plate blade (triangular blade) standing upright on one side of the plate-like substrate at a predetermined interval as a perforating jig instead of the perforating roller Even if the water absorption holes are sequentially formed in the sheet with the perforated plate, the sheet is also exhibited.
It is important that the water absorption holes formed in this way are formed so as to penetrate the resin film and reach the open cell layer, and preferably through the entire thickness of the open cell layer.

Conventionally, a sharp blade such as a polygonal pyramid or a cone is used as a blade for drilling such holes, but a deeper water absorption hole can be reliably opened by using a sharp blade. On the other hand, if the water absorption hole is drilled with a sharp blade, the resin film may simply be formed into a tear, and the resin film will return to the state before drilling after the blade is removed. Have
In this embodiment, as will be described later, since the operation of expanding the opening of the water absorption hole is performed in the secondary foaming process, the water absorption hole forming process is performed using a conventional sharp blade. Although it is possible to make the water-absorbent foam molded article excellent in water absorption, it is possible to prevent the resin film from being restored to the state before drilling after the blade is removed. It is preferable to use a blade having a certain thickness up to the leading edge, such as the triangular blade of the bladed disk 1.

In addition, even when using a blade with a certain area secured at the forefront, the effect of cutting a part of the resin film 21 can be expected as in the case of using the bladed disk 1. Restoration of the resin film is suppressed by using a blade having a truncated cone shape with a diameter of 0.5 mm to 2 mm, or a polygonal truncated cone shape having a tip area (equivalent to a circle) comparable to this, and more absorbency An excellent water-absorbing foam molded article can be produced.
In addition, such an effect is exhibited more notably by using the stretched film which is easy to tear as the resin film.

The area (size) of the opening of the water absorption hole thus formed is preferably in the range of 0.5 mm ² / piece to ² mm ² / piece.
When the opening is less than 0.5 mm ² / piece, there is a possibility that the tension to be applied to the resin film when the opening is enlarged in the secondary foaming process becomes too large. In some cases, the opening is too narrow. There is a risk that the absorbability of steam and water may be insufficient.
On the other hand, even if the size of the opening exceeds 2 mm ² / piece, it is difficult to improve the absorbability of steam and water. There is a risk of lowering the strength.

  Note that the number of water-absorbing holes to be formed in the film-laminated foam sheet in this water-absorbing hole forming step may be appropriately selected according to the use, but the water-absorbing holes in the lid for a general food packaging container The number is preferably such that the water absorption holes are formed so that the opening area is 1 to 30% of the surface area of the inner surface of the lid.

(Secondary foaming process)
After performing the water absorption hole forming process as described above, the secondary foaming process is continuously performed.
Specifically, a step of introducing a film-laminated foam sheet having water-absorbing holes into a heating apparatus provided with heaters on the top and bottom and holding it for a predetermined time between the heaters to perform secondary foaming is performed.
In the secondary foaming step, for producing a lid having good water absorption, for example, if it is a belt-like film-laminated foam sheet, its both ends in the width direction are clamped and introduced into a heating device, and It is preferable to stretch the opening of the water absorption holes by pulling the film-laminated foam sheet in the direction of separating the clamps (TD direction) to apply tension to the resin film.
Further, if necessary, the opening of the water absorption hole may be expanded by applying tension in the longitudinal (MD) direction of the film-laminated foam sheet.
At this time, although it depends on the thickness, size, material, etc. of the film-laminated foam sheet, the width of the film-laminated foam sheet in the heating device is usually compared with the width (length) before being introduced into the secondary foaming step. The expansion ratio of width (length) ([width after secondary foaming (length) −width before secondary foaming (length)] / width before secondary foaming (length) × 100%) is 0 It is preferable to carry out the pulling in the width direction so as to be 5% or more, preferably 1.0% or more.
As a result, since the size of the opening of the water absorption hole is enlarged as compared with that before the secondary foaming, improvement in water absorption can be expected.
In addition, since there exists a possibility of causing a detachment | clamp etc. if it pulls too much, it is preferable that the expansion | extension rate to the width direction of the film laminated foam sheet in a heating apparatus shall be 5.0% or less.

About other conditions in this secondary foaming process, for example, heating temperature and time, it can determine suitably by the thickness, size, material, etc. of a film lamination foam sheet.
Furthermore, about the heating temperature and time in a secondary foaming process, it can determine suitably also from the residual amount of the foaming agent in a film lamination foam sheet.

  In the conventional method for producing a water-absorbent foam-molded article, when a strip-like film-laminated foam sheet is used as the raw material, the water-absorbing foam is produced in the process of producing the film-laminated foam sheet and winding it as a raw roll. In the present embodiment, the secondary foaming step is performed continuously to the water absorption hole forming step for the film-laminated foam sheet.

  For example, in the case of adopting a polystyrene-based resin foam sheet as a resin foam sheet constituting a film-laminated foam sheet, foamability at the time of extrusion using a mixed butane of normal butane and isobutane as a foaming agent While making the primary foamability good, it is possible to give good secondary foamability over a long period of time by allowing butane to remain for a certain period of time in the resulting polystyrene resin foam sheet. If the water absorption holes were previously drilled, gas exchange with the outside was actively performed. For example, even if a closed cell layer was formed on the back side of the open cell layer, foam remaining in the closed cell layer This is because the agent is easily dissipated through the open cell layer and the water absorption holes.

That is, in order to improve the thermoformability of the water-absorbing foam molded product, it is necessary to carry out the secondary foaming step in succession to the water absorption hole forming step.
As a specific method, the perforated roller is disposed from the raw roll to the heating device, that is, in front of the heating device, and a strip-shaped resin foam sheet is sequentially supplied to the heating device. A method in which the perforating roller is rotated according to the movement of the resin foam sheet, and the blade of the perforation roller is allowed to enter the resin foam sheet so that the water absorption hole forming step and the secondary foaming are continuously performed. Is mentioned.
In this case, after the water absorption holes are drilled, the time until introduction into the secondary foaming process varies depending on the distance between the heating device and the perforating roller, the line speed (thermoforming shot time), and the like. However, if a time exceeding 1 hour is usually required, it cannot be said that the water absorption hole forming step and the secondary foaming step are continuously performed.
Therefore, after the water absorption holes are formed, secondary foaming is preferably performed within 1 hour, and secondary foaming is preferably performed within 30 minutes.

(Thermoforming process)
The thermoforming step carried out following the secondary foaming step can be carried out using a so-called sheet molding machine, and a desired shape can be obtained by a forming method such as vacuum forming, pressure forming, vacuum / pressure forming, press forming or the like. A method of forming a film-laminated foam sheet can be employed.
When forming a lid for a food packaging container as a water-absorbing foam-molded product according to the present embodiment, thermoforming is performed so that the water-absorbing holes come inside the lid that is likely to cause condensation due to moisture generated from food. It is preferable to do.

In addition, as a method for taking out the water-absorbing foam molded product from the film-laminated foam sheet formed into a product shape by this thermoforming, a conventionally known method can be adopted, for example, a Thomson die-cutting method, Nichrome A cutting method can be adopted.
The water-absorbing foam molded article thus obtained has excellent water absorption because it has water-absorbing holes that are larger than the water-absorbing holes initially formed in the film-laminated foam sheet. To do.
Further, in the present embodiment, since the secondary foaming step is performed continuously to the water absorption hole forming step, the dissipation of the foaming agent in the resin foam sheet is suppressed, and the secondary foaming step is good. The secondary foamability is exhibited, and good moldability is exhibited even in thermoforming.
As described above, the method for producing a water-absorbent foam molded article in the present embodiment exhibits good moldability in the production of a water-absorbent foam molded article such as a lid.

  In the present embodiment, since a lid for a food packaging container is illustrated, a resin foam sheet in which a resin film subjected to an antifogging treatment is laminated is illustrated. The foam sheet is not limited to a film-laminated foam sheet, but a water absorption hole forming process and a secondary foaming process are continuously performed on a resin film or other non-laminated resin foam sheet. This is also within the scope of the present invention.

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

<Water absorption evaluation>
A substantially rectangular container made of a polystyrene foam sheet having a length of 205 mm, a width of 108 mm, and a height of 45 mm was prepared as a container body for covering a lid serving as a sample.
260 g of freshly cooked cooked rice was put into the container body, and a lid whose mass was measured in advance: M ₀ (g) was immediately covered.
After standing for 30 minutes, the state of adhesion of water droplets inside the lid was visually confirmed, and the mass of the lid together with the adhering water: M ₁ (g) was measured.
Next, after wiping off the adhering moisture, the mass of the lid: M ₂ (g) was measured.

(A) Amount of water adhering to the lid (g) = M ₁ −M ₀
(B) Water absorption amount of the lid (g) = M ₂ −M ₀

<Example 1>
For the formation of the open cell layer (and surface skin layer), 78.9% by mass of polystyrene resin (manufactured by Dainippon Ink and Chemicals, trade name “XC-515”, melt mass flow rate: 1.3 g / 10 min), Hydrogenated product of copolymer of styrene and conjugated diene (product name “SS9000” manufactured by Asahi Kasei Co., Ltd.) 15.8 mass%, high-density polyethylene resin (product name “HJ565W” manufactured by Nippon Polyethylene Co., Ltd.), density: 0.00. 968 g / cm ³ , melt mass flow rate: 5.0 g / 10 min) For 100 parts by mass of the mixed resin composition containing 5.3% by mass, the trade name “Erestmaster S-520” (Kao Corporation) is used as a surfactant. 10 parts by mass of a polystyrene resin masterbatch containing 20% by mass of an alkylsulfonic acid surfactant, and a mixed raw material in which 0.6 parts by mass of talc is mixed as a bubble regulator. A first extruder having an inner diameter of 115 mm, a second extruder having an inner diameter of 150mm was fed to the hopper of the first extruder of the tandem extruder connected.
The maximum cylinder temperature of the extruder is 220 ° C., and butane (isobutane / normal butane = 70/30) as a blowing agent is press-fitted and kneaded so that the ratio with respect to 100 parts by mass of the mixed resin composition is 3.5 parts by mass. Then, the foamable molten mixture was cooled in the second extruder, the resin temperature was adjusted to 161 ° C., and the mixture was poured into the confluence mold at an extrusion rate of 150 kg / h.

On the other hand, for the formation of an open cell layer, 0.7 parts by mass of talc as a cell regulator for 100 parts by mass of polystyrene resin (“HRM-12” manufactured by Toyo Styrene Co., Ltd., melt mass flow rate: 5.5 g / 10 min) Is supplied to a hopper of a single-screw extruder having an inner diameter of 115 mm, the cylinder temperature of the extruder is set to 230 ° C., and butane (isobutane / normal butane = 70/30) as a blowing agent is 100 mass of the polystyrene resin. The mixture was press-fitted and kneaded so that the ratio to the part was 4.0 parts by mass, and then cooled, and the resin temperature of the molten mixture was adjusted to 154 ° C. and flowed into the confluence mold at an extrusion rate of 100 kg / h.
The resin merged in the merge mold is poured into an annular mold having a diameter of 175 mm, extruded into a cylindrical shape from a slit having a thickness of 0.45 mm, taken along a cooling mandrel having a diameter of 670 mm, and attached to the rear part of the mandrel. The cylindrical foam was cut by two cutters to obtain two upper and lower resin foam sheets.
At this time, air was blown into and out of the foam immediately after coming out of the slit to cool the foam surface.

The open cell ratio in the total portion of the surface skin layer and the open cell layer was 72%, the thickness was 1.9 mm, and the density was 0.063 g / cm ³ .
Further, the open cell ratio in the closed cell layer was 9.9%, the thickness was 0.9 mm, and the density was 0.089 g / cm ³ .

A biaxially stretched polystyrene resin film (trade name “OPS film GM grade (MBC type)”, thickness 25 μm) manufactured by Asahi Kasei Co., Ltd. on this polystyrene resin foam sheet at a hot roll temperature of 175 ° C. and a take-up speed of 10 m / min. Heat laminated.
This film laminated foam sheet has a shape as shown in FIG. 1 and has an outer diameter (diameter to the blade edge) of 127 mm, a blade count of 50, a blade angle (vertex angle in a side view) of 60 degrees, and a constant blade thickness ( 1.0 mm) blades were used to set the penetration depth from the resin film surface to 1.5 mm, and water absorption holes were formed at intervals of 8 mm in length and 16 mm in width (water absorption hole forming step).
However, since the film-laminated foam sheet was elastically deformed in the thickness direction, the penetration depth of the blade edge was not necessarily 1.5 mm.

Immediately after forming the water absorption holes, the film-laminated foam sheet is subjected to secondary foaming while applying tension in the TD direction so that the width after secondary foaming is about 2% wider than that before secondary foaming. (Secondary foaming step).
Subsequently, thermoforming was performed to produce a substantially rectangular lid for a food packaging container having a length of 205 mm, a width of 108 mm, and a height of 2.4 mm (thermoforming step).
The opening area of the water absorption holes after molding was 1.44 mm ² , which was larger than before the secondary foaming.
Moreover, the ratio of the opening part of the water absorption hole which occupies for the inner surface area of a cover body was 1.2%.
Furthermore, the result of the previous water absorption evaluation is
(A) The amount of water adhering to the lid is 1.08 g,
(B) Lid water absorption is 0.67g
It became.

<Example 2>
Water absorption hole forming step as in Example 1 except that a 90-degree blade was used instead of a blade angle of 60 degrees, and that the setting value of the penetration depth of the blade edge was changed to 1.6 mm instead of 1.5 mm The lid was prepared. (The secondary foaming process and thermoforming process are the same as in Example 1)
The opening area of the water absorption hole after molding was 1.58 mm ² , which was larger than that before the secondary foaming.
Moreover, the ratio of the opening part of the water absorption hole which occupies for the inner surface area of a cover body was 1.8%.
Furthermore, the result of the previous water absorption evaluation is
(A) The amount of moisture adhering to the lid is 1.14 g,
(B) Lid water absorption is 0.91g
It became.

<Example 3>
A water absorbing hole forming step was performed in the same manner as in Example 1 except that a sharp needle-like blade having a root diameter of 1.2 mm was used, and a lid body was produced.
Although the opening area of the water absorption holes after molding was larger than that before the secondary foaming, the ratio of the opening portions of the water absorption holes in the inner surface area of the lid was slightly inferior to that of Example 2 above. 4%.
Furthermore, the result of the previous water absorption evaluation is
(A) The amount of moisture adhering to the lid is 3.55 g,
(B) Lid water absorption is 0.34g
It became.

The water absorption holes after the water absorption hole drilling step of Example 1 and the water absorption holes after secondary foaming as seen from the front and the state of the cross section are shown in FIG.
Thus, it can be seen that the water absorption holes after the secondary foaming are larger than those after the water absorption hole drilling process, although the resin film is restored to a straight state.
4 also shows that a part of the resin film is cut and invaded into the bottom of the water absorption hole.

In all the examples described above, lack of foaming was not observed, and a good product (lid) could be obtained.
Moreover, it has confirmed that the cover was equipped with the water absorption to the inside as mentioned above.
In Examples 1 and 2, the value of the water absorption amount (B) of the lid showed a value more than half of the amount of attached water (A), and it was confirmed that a large amount of water was absorbed inside the lid. .
On the other hand, in Example 3, the lid water absorption amount (B) was about 10% of the attached water amount (A) although the ratio of the opening was larger than that in Example 1.
In Example 3, although the opening area on the surface of the resin film was secured to some extent, the water absorption holes were used in comparison with Examples 1 and 2 using a blade with a constant blade thickness because a needle-like blade was used. This is thought to be due to the rapid reduction in diameter in the depth direction.
From this, it can be seen that using a blade having a certain thickness at the tip portion or a blade having a truncated cone shape having a certain tip area is more effective in improving water absorption.

1: Disc with blade 1x: Blade 20: Film laminated foam sheet 21: Resin film 23: Open cell layer 30: Water absorption hole

Claims (4)

After performing the water absorption hole forming step of forming a plurality of water absorption holes reaching the open cell layer from at least one surface side of the resin foam sheet having the open cell layer, the resin foam sheet is secondarily expanded and thermoformed. A method for producing a water-absorbing foam molded article,
A method for producing a water-absorbent foam-molded article, wherein secondary foaming of the resin foam sheet is carried out continuously with the water-absorbing hole forming step.   When a perforating roller having a plurality of blades for forming the water absorption holes is provided in front of the heating device for secondary foaming, and a strip-shaped resin foam sheet is sequentially supplied to the heating device. Both the perforating roller is rotated according to the movement of the resin foam sheet, the blade of the perforation roller is allowed to enter the resin foam sheet, and the water absorption hole forming step and the secondary foaming are continuously performed. The method for producing a water-absorbent foam-molded article according to claim 1 to be carried out.   The method for producing a water-absorbent foam-molded article according to claim 2, wherein the blade is a triangular blade having a blade thickness of 0.5 mm to 2.0 mm at the tip.   The resin foam sheet is a film laminated foam sheet in which a resin film is laminated on one side, and an antifogging treatment is applied to the surface of the resin film in order to produce a lid for a food packaging container as the water absorbent foam molded product. The method for producing a water-absorbent foam-molded product according to any one of claims 1 to 3, wherein the thermoforming is performed using a film-laminated foam sheet that is applied so that the resin film side is on the inside.