JPH10249948A - Foam molding and its molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam molding of a low cost having excellent moldability, cushionability, flexibility and recylability without necessity of changing a container to suit for type of fruit, and a method for molding it. SOLUTION: This molding method comprises the steps of heating to secondarily foam rubber modified thermoplastic polymer foam resin sheet 1 having 5 to 15wt.% of rubber-like polymer particles in thermoplastic resin polymer, 0.1 to 0.03g/cm<3> of a density and 70% or more of a closed cell rate, sandwiching it via a molding time mold molding gap X1 of 0.7 to 2.2 times as large as a free foam thickness X0 between a pair of male and female molds 2 and 3, vacuum sucking it simultaneously or alternately by the molds 2, 3 to be shaped, then compressing it to forming time mold molding gap X2 of 0.15 to 0.8 times as large as the gap X1 by the molds 2, 3, and molding a foam molding 6 of a density of 0.05 to 0.012g/cm<3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed molded article having excellent moldability, cushioning property, flexibility and recyclability, and a molding method thereof, which is particularly suitable as a packaging container for fruits.

[0002]

2. Description of the Related Art Conventionally, fruit packaging containers include crosslinked foamed polyethylene (PE) and crosslinked foamed polypropylene (P).
P), expanded polystyrene (PS), expanded polypropylene (PP), etc., thermoformed containers, pulp molds, vinyl chloride (PVC), unexpanded polystyrene (P
A container formed by thermoforming a sheet of S), unexpanded polypropylene (PP), unexpanded polyethylene terephthalate (PET), or the like is used.

[0003] The fruit packaging container is required to be excellent in moldability, cushioning property, flexibility and recyclability, and to be inexpensive. However, molded containers made of cross-linked expanded polyethylene (PE), cross-linked expanded polypropylene (PP), and the like have excellent buffering properties and flexibility, but have problems in moldability, recyclability, and cost. In addition, although it is excellent in flexibility, it is easily deformed, and in order to hold the fruit stably, it is necessary to increase the thickness of the container, that is, increase the weight of the container or use other materials (for example, unfoamed). Polystyrene (PS), unexpanded polyethylene terephthalate (PE
T), etc.), it is necessary to combine the sheets, for example, by laminating the sheets, and the cost is further increased in this regard.

[0004] Molded containers made of expanded polystyrene (PS) and the like are excellent in moldability and recyclability and inexpensive, but have drawbacks in that they are inferior in cushioning property and flexibility. Further, in the case of a molding container such as a pulp mold, the cost can be relatively reduced by using recycled paper, but there is a drawback that the cushioning property and the flexibility are poor.

Conventionally, soft fruits (e.g., peaches, tomatoes, strawberries, and some varieties such as pears of the twentieth century, etc.) having a soft epidermis are recyclable so that the fruit surface is not damaged and the appearance is not significantly reduced. The cost is unavoidably sacrificed, and a molded container such as cross-linked foamed polyethylene (PE), which has excellent cushioning and flexibility, is used for hard-skinned fruits (such as apples, citrus, and some kinds of pears such as Kosui). Containers are properly used depending on the type of fruit, such as using molded containers made of expanded polystyrene (PS), pulp mold, vinyl chloride (PVC), etc., which are excellent in recyclability and inexpensive.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In order to eliminate the need to use different containers according to the type of fruit, moldability, cushioning property, and flexibility are required. It is an object of the present invention to provide a foam molded article excellent in recyclability and low in cost, and a molding method thereof.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies and studies to solve the above problems, and as a result, the thermoplastic resin polymer contains 5 to 15% by weight of rubbery polymer particles. Density 0.1-0.03 g / cm ³ , closed cell rate 70%
The above-mentioned rubber-modified thermoplastic polymer foamed resin sheet is subjected to secondary foaming, formed into a shape, and then compressed and molded to a density of 0.05 to
The 0.012 g / cm ³ foam molded article was found to be excellent in moldability, cushioning property, flexibility, recyclability, and low cost, and came to the present invention.

[0008] The above-mentioned foamed molded article has a cell structure in the thickness direction in which it is mainly composed of at least one substantially polygonal cell having an interior angle exceeding 180 °, ie, a large number of cells appearing in the cross section in the thickness direction. When 50% or more, preferably 80% or more of the foam cells are substantially polygonal foam cells having at least one interior angle of more than 180 °, the above characteristics are excellent. Heading, the present invention has been reached.

Furthermore, the foamed molded article is a rubber having a density of 0.1 to 0.03 g / cm ³ and a closed cell ratio of 70% or more, containing 5 to 15% by weight of rubbery polymer particles in a thermoplastic resin polymer. Heating the denatured thermoplastic polymer foamed resin sheet to 2
Next foaming, free foam thickness X ₀ by a pair of male and female molds
Of and sandwiching a 0.7 to 2.2 times the primary molding Tokikin molding gap X _1, after shaping by vacuum suction simultaneously or alternately from each of the mold, further, male, found that can be molded by compressing to the secondary molding Tokikin molding gap X ₂ of 0.15 to 0.8 times the the female pair of molds the primary molding Tokikin molding gap X _1, the I came to the invention. The free foam thickness X ₀ is defined as a value obtained by heating the rubber-modified thermoplastic polymer foam resin sheet to cause secondary foaming.
It refers to the average thickness of the next foamed resin sheet.

Examples of the thermoplastic resin polymer containing rubber-like polymer particles include butadiene rubber, olefin rubber, styrene resin containing styrene rubber, olefin resin, and the like. Examples include high impact polystyrene, ethylene-propylene rubber, styrene butadiene rubber, and hydrogenated styrene butadiene copolymer, and among them, high impact polystyrene is preferable.

The rubbery polymer particles are preferably contained in the styrene resin, olefin resin or the like in an amount of 5 to 15% by weight, more preferably 6 to 12% by weight. If the amount is less than 5% by weight, sufficient flexibility to achieve the object of the present invention cannot be obtained. If the amount exceeds 15% by weight, the closed cell ratio of the foamed resin sheet becomes less than 70%, and sufficient cushioning property is obtained. This is because they cannot be obtained. The closed cell rate of the sheet can be determined by the following method. A true volume of about 25 cm ³ of foam is measured by an air comparison hydrometer 93 manufactured by Toshiba Beckman.
The closed cell ratio S (%) is calculated from the weight and density of the foam using the following equation. S = {Vx-W / ρ} Va-W / ρ} × 100
(%) Where Vx: true volume of foam (cm ³ ), Va: volume of foam (weight / density) (cm ³ ), W: weight of foam (g) ρ: base of foam Density of material resin (g / cm ³ )

Examples of the foaming agent used in the production of the foamed resin sheet include volatile foaming agents such as propane, n-butane, i-butane, n-pentane, and i-pentane. These may be used alone or in combination of two or more. You may. As the additive, for example, talc, perlite, calcium silicate, vermiculite, or the like is used as a cell nucleating agent in order to adjust the cell diameter of the foamed resin sheet. In addition, the cell nucleating agent has 1 carbon atom as a dispersing aid.
Metals such as lauric acid, stearic acid, and palmitic acid (Ca, Na, Zn, Al,
Mg) salt can be used in combination. Further, antistatic agents, flame retardants, pigments and the like can be added as the additives.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, specific examples of a foam molded article and a molding method of the present invention will be described with reference to the drawings.

The foamed resin sheet 1 shown in FIG. 1 contains 9% by weight of rubber-like polymer particles in a polystyrene resin, and as an additive, a cell nucleating agent, a foaming agent (content: 4.0% by weight), a coloring pigment, etc. After melt kneading in an extruder, the molten resin is extruded from a circular die connected to the tip, and the obtained foamed molded body is cut into a sheet shape. The width is 1,000 mm, the length is 200 m, Thickness 2.8mm, density 0.05g / cm ³ , expansion ratio 20
A sheet having a basis weight of 140 g / m ² was used.

As shown in FIG. 1, the foamed resin sheet 1 is placed on a transfer table 12 of a thermoforming machine (vacuum forming machine) 11 with both ends fixed with needle pins. , A heating zone 14, a forming zone 15, and a cutting zone 16 sequentially.

In the heating zone 14, as shown in FIG.
The heaters 17 are arranged above and below.
To heat the foamed resin sheet 1 to 80 to 120 ° C., which is 80 ° C. or higher, which is the softening temperature of the polystyrene rubber-containing resin.

In the following, the free foam thickness X ₀ is defined as
Heating the foamed resin sheet 1 in the heating zone 14
After the next foaming, it is cut in the cutting zone 16 without going through the shaping and compression steps in the molding zone 15 and refers to the average thickness of the obtained secondary foamed resin sheet.

In the molding zone 15, as shown in FIG.
A pair of male and female molds 2 and 3 are provided, and these molds 2 and 3 allow the container rib portion mold forming gap α and the container bottom wall when the molds are closed as shown in FIGS. 2 and 3. The mold gap .beta. And the mold gap .gamma. Of the container side wall are defined. A large number of through holes 4 are formed in the molding walls 2a, 3a of the dies 2, 3, and these through holes 4 are formed by a vacuum suction device.
The air in the mold forming gap can be sucked and removed through the opening. The dies 2 and 3 can be set at an arbitrary temperature by a temperature adjusting device, and are heated to 70 ° C. to 120 ° C., which is 10 ° C. or lower than the softening temperature of the polystyrene resin.

[0019] First, as shown in FIG. 2, sandwiching the primary molding at moving each mold 2, 3 to the stop position, a narrow molding gap δ part resin foam sheet 1 from the free foam thickness X ₀ I do. Container rib Molding gap alpha ₁ during primary molding, collectively referred to as the primary molding Tokikin molding gap X ₁ the container bottom wall Molding gap beta ₁ and the container side wall mold molding gap gamma _1, It is set to 0.7 to 2.2 times the free foaming thickness X _0.
Then, vacuum suction is performed alternately or simultaneously with the vacuum suction device from each of the molds 2 and 3 side, and the foamed resin sheet 1 is secondarily foamed and shaped to form the foamed molded body 5 as an intermediate form.

Next, as shown in FIG. 3, the molds 2 and 3 are moved to a stop position at the time of secondary molding, and the foam molded body 5 is compressed. Container rib Molding gap alpha ₂ during secondary molding, called the container bottom wall Molding gap beta ₂ and container sidewall portion Molding gap gamma ₂ overall secondary molding Tokikin molding gap X _2, set to 0.15 to 0.8 times the primary molding Tokikin molding gap X _1. Thereafter, the mold is opened to take out the foamed molded body 6 as the final form.

In the cutting zone 16, as shown in FIG.
A cutter 18 is provided, and the foam molded body 6 is cut off from the remaining portion of the foamed resin sheet 1 by the cutter 18, and as shown in FIG. 7 was produced.

The thickness of the obtained foam molded article 6 becomes slightly smaller than the set value due to compression during the secondary molding, and wrinkles are slightly observed on the surface. Wrinkles recover together, while being very lightweight, appearance,
It was suitable for a fruit packaging container having excellent strength, flexibility and cushioning properties.

The compression by the secondary molding is not necessarily performed immediately after the shaping by the primary molding. After the primary molding, the foam molding obtained through the cutting zone 16 without performing the secondary molding is performed. the body 5 may be compressed by each mold 2, 3 set to secondary molding Tokikin molding gap X ₂ later. In this case as well, a fruit packaging container having almost the same characteristics can be obtained, although the recovery of wall thickness and wrinkles is slightly reduced. In addition, by appropriately changing the container rib mold forming gap α, the container bottom wall mold forming gap β, and the container side wall mold forming gap γ, the flexibility of each part of the fruit packaging container can be increased as required. It can also be adjusted.

FIGS. 5A and 5B show the cross-sectional cell structure in the thickness direction of the foam molded article 6, and FIGS. 6A and 6B show the cross-sectional cell structure in the thickness direction of the secondary foamed resin sheet. It is shown.

In the foam molded article 6, as shown in FIG. 5, the foam cells are deformed due to the compressive stress, and the shape is slightly recovered when the compressive stress is removed, but the shape becomes partially concave. Is presented. That is, when the foam cells are regarded as substantially polygonal, they are mainly constituted by foam cells having at least one interior angle exceeding 180 °. On the other hand, in the secondary foamed resin sheet, as shown in FIG. 6, the foamed cells have a shape bulging outward due to the effect of the foaming pressure.
That is, assuming that the foam cells are substantially polygonal, each of the foam cells is mainly constituted by a foam cell whose interior angle is smaller than 180 °.

As a result of paying attention to the cell structure in the cross section in the thickness direction, 50% or more, preferably 80% or more of the large number of the foam cells appearing in the cross section in the thickness direction,
It has been found that when at least one of the foam cells has a substantially polygonal shape having an inner angle of more than 180 °, the foam molded article has excellent strength, flexibility and cushioning properties.

From the above, it is considered that the improvement in the flexibility of the foam molded article 6 is caused by the deformation of the foam cells due to the compression by the secondary molding. The improvement in flexibility by compression can be seen in a normal expanded polystyrene sheet containing no rubber component, but is more remarkable in a modified rubber expanded polystyrene sheet. this is,
It is presumed that this is because the properties of the rubber component interposed between the foam cells made of polystyrene resin are exhibited in addition to the deformation effect of the foam cells.

[0028]

EXAMPLES (Examples 1 to 5 and Comparative Examples 1 to 4) In the molding method described above, the foamed resin sheet 1 was
The temperature of the dies 2 and 3 was set to 80 ° C. in the molding zone 15 and maintained at 80 ° C.
₁ (α ₁ = β ₁ ) Mold forming gap X ₂ (α ₂
= Β ₂ ) was variously changed as shown in Table 1, and a foam molded article 6 was molded. Table 2 shows the evaluation results. In this case, the free foam thickness X ₀ was 4.0 mm.

[0029]

[Table 1]

[0030]

[Table 2]

The evaluation results in Table 2 are obtained at the time of curing one day after the secondary molding, and each characteristic was evaluated as follows.

[0032] viewing the external appearance of peach molding container 7 shown in Fukatachisei Figure 4, with the reproducibility of the mold shape was evaluated by reference to the formability below. 〇: Reproducibility of the mold shape is good in all of the container rib, bottom wall, and side wall. △: Reproducibility is slightly poor in each of the above parts, but there is no hindrance to fruit storage. ×: Poor reproducibility in each of the above parts. In this way, deformation may hinder fruit storage.

Surface hardness The hardness of the bottom wall of the peach molding container 7 was measured by a C-type hardness meter (SRIS (Japanese Rubber Association Standard) 0101) manufactured by Kobunshi Keiki Co., Ltd., and the average value was calculated. The surface hardness was evaluated according to the following criteria. 〇: 35 or less △: 36 to 40 ×: 41 or more

Scratch resistance Eighteen 280 g peaches are packed in the peach molding container 7 and about 5
kg, and transported by truck from Yamanashi to Tokyo, the state of damage to the fruits upon arrival was observed, and the scratch resistance was evaluated according to the following criteria. 〇: no damage △: slightly damaged ×: much damage

The flexibility is obtained by cutting the periphery of the fruit storage recess 8 of the peach molding container 7
Eight fruit storage containers were prepared, and the fruit storage container was compressed with the bottom wall facing upward at a compression speed of 10 mm / min according to a method according to JIS-K7220, and the compressive strength at the time of 20% strain (kgf). Was measured and the average value of 18 samples was calculated, and the flexibility was evaluated according to the following criteria. 〇: 1.5 kgf or less △: 1.6 to 2.0 kgf ×: 2.1 kgf or more

Hand holding strength The above-mentioned peach molding container 7 is filled with 18 pieces of 280 g
kg, and the container was observed for damage when the container was gripped at both ends and lifted, and the hand-held strength was evaluated according to the following criteria. 〇: Not damaged △: Damaged only at one end ×: Damaged at both ends

[0037]

According to the present invention, it has not been possible in the past to achieve high strength, high moldability, cushioning property, flexibility, recyclability and low cost while being lightweight. It is possible to provide a foam molded article having a plurality of characteristics, and it is not necessary to use a different molded container depending on the type of fruit.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a step of molding a foamed molded article of the present invention from a foamed resin sheet.

FIG. 2 is a longitudinal sectional view showing a mold molding gap at the time of primary molding.

FIG. 3 is a longitudinal sectional view showing a mold molding gap during secondary molding.

4A and 4B are a plan view and a front view, respectively, of a fruit packaging container comprising a foam molded article of the present invention.

5A is a 20-fold enlarged view and FIG. 5B is a 40-fold enlarged view showing the cell structure in the thickness direction of the foamed molded article of the present invention.

6A is a 20-fold enlarged view and FIG. 6B is a 40-fold enlarged view showing a cell structure in a thickness direction cross section of a secondary foamed resin sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Foam resin sheet 2, 3 Die 6 Foam molding 7 Molding container

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 421: 00

Claims (3)

[Claims] 1. Density of 0.1 to 0.03 g / c containing 5 to 15% by weight of rubbery polymer particles in a thermoplastic resin polymer
m ³ , a foamed molded article having a density of 0.05 to 0.012 g / cm ³ formed by subjecting a rubber-modified thermoplastic polymer foamed resin sheet having a closed cell ratio of 70% or more to secondary foaming, shaping, and compression molding. 2. A foam molded article mainly comprising a substantially polygonal foam cell having at least one internal angle exceeding 180 ° in a cell structure in a cross section in a thickness direction. 3. Density of 0.1 to 0.03 g / c containing 5 to 15% by weight of rubbery polymer particles in a thermoplastic resin polymer
m ^3, closed cell more than 70% of the rubber-modified thermoplastic polymer modulus foamed resin sheet heated to secondary foaming, male, free foaming in the thickness X ₀ by female pair of molds 0.7 to 2.2 a multiple of the primary molding Tokikin molding gap X ₁ and holding, after by vacuum suction simultaneously or alternately from each of the mold is shaped, and further,
Male, density and compression to the secondary molding Tokikin molding gap X ₂ of 0.15 to 0.8 times the primary molding Tokikin molding gap X ₁ by female pair of molds 0.05~0.012g A method for molding a foamed molded article, comprising molding a foamed molded article having a thickness of / cm ³ .