JP2013142141A - Returnable box - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a returnable box which is obtained by the in-mold foam molding of polypropylene-based resin foaming particles, and from which sticking stains and molds are easily cleaned out.SOLUTION: The amount of eluted components at 40°C or less is set to be 7.5 wt.% or less, in a cross fractionation chromatography method of a returnable box foam molded article. Thereby, a returnable box from which sticking stains and molds are easily cleaned out is obtained.

Description

  The present invention relates to a returnable box formed by in-mold foam molding of polypropylene resin expanded particles.

  In-mold foam molded articles obtained using thermoplastic resin foam particles have features such as shape flexibility, cushioning, light weight, and heat insulation, which are the advantages of in-mold foam molded bodies. It is used for various applications such as materials, heat insulating materials, and automobile parts.

  As a box, it is used as a food box for transporting fish, vegetables and other foods, a tool box for transporting tools, a luggage box mounted on an automobile, and the like.

  Such a box includes a box used as a so-called “return box” used for many times, in addition to a box used for one-way transportation (only one transportation). In the case of a returnable box, since it is used multiple times, it is disliked that dirt or mold adheres to it, and if dirt or mold adheres, it must be used for transportation after washing it There is. In particular, in the case of a food transport box for transporting food, it is particularly hateful for dirt and mold, and hygiene is required.

  By the way, fish boxes, vegetable boxes, etc. formed by foaming polystyrene resin foam particles in the mold are well known, but there are strength problems that they are easy to break if dropped during transportation, and easily dent due to collision or pressure. For this reason, it cannot be transported and used repeatedly over a long period of time, and is mainly used for one-way use.

  On the other hand, a box formed by in-mold foam molding of polypropylene resin expanded particles is excellent in impact resistance and durability, so it is also marketed as a returnable box that is used multiple times instead of one-way. It is used as a food return box for transportation.

However, a box formed by in-mold foam molding of polypropylene resin foam particles has a conspicuous dent on the surface of the box (a dent / granular gap that occurs when the polypropylene resin foam particles are not completely fused together). There is a problem that dirt easily adheres to the dent, and once the dirt adheres, the dirt strongly sticks to the dent and is difficult to clean.
Particularly in food return boxes, mold may be generated due to spills and scraps of food to be transported and contents spilled from lunch boxes, and it is necessary to thoroughly clean from a hygienic point of view. However, if dirt or mold adheres to the dents on the inner surface of the food return box, it cannot be easily cleaned.

  In order to deal with such problems, a method of covering the surface of the foam container with a film has been proposed as a container that is difficult to get dirty or a foam container that is easy to clean even when it is dirty (for example, Patent Document 1). However, the provision of such a coating has a problem in that it is a manufacturing process and leads to an increase in cost.

Polypropylene resin in-mold foam moldings that have a specific value for the amount of elution components in the cross-fractionation chromatographic method are known as polypropylene foam in-mold molds that have good surface properties, excellent compressive stress, or can be molded at low temperatures. (For example, Patent Documents 2 and 3).
However, there is no clarification about the sanitary point of view when such a polypropylene resin-in-mold foam-molded product is applied to a box.

Also known is a method of providing irregularities on the surface of a molded body as a polypropylene resin-in-mold foam molded body having no turtle shell pattern on the surface of the molded body and few dents (intergranularities) between the foam particles on the surface of the molded body. (For example, Patent Documents 4 and 5).
However, the viewpoint of hygiene when such a polypropylene resin-in-mold foam-molded product is applied to a box through a box is not clarified at all.

JP 2000-355379 A JP 2011-84610 A International Publication No. 2010/087111 JP 2006-51979 A JP 2005-88442 A

  An object of the present invention is to provide a returnable box, in particular, a returnable box for foods, which is formed by in-mold foam molding of polypropylene resin foamed particles, so that attached dirt and mold can be easily washed.

  As a result of diligent research in view of the above-mentioned problems, the present invention facilitates washing of attached dirt and mold when the amount of elution component of 40 ° C. or less in the cross-fractionation chromatographic method of a returnable box foamed molded product is a specific value. The present invention has been completed by finding that it is a simple returnable box.

That is, this invention consists of the following requirements.
[1] A returnable box formed by in-mold foam molding of polypropylene resin expanded particles,
A returnable box, wherein the amount of elution components at 40 ° C. or lower in the cross-fractionation chromatography method of the returnable box foamed molded product is 7.5% by weight or lower.
[2] The returnable box according to [1], wherein an elution component amount of 40 ° C. or less in the cross-fractionation chromatographic method of the returnable box foamed molded article is 6.5% by weight or less.
[3] The returnable box according to [1] or [2], wherein the expanded polypropylene resin particles are expanded polypropylene resin particles made of a polypropylene resin polymerized with a metallocene polymerization catalyst.
[4] A plurality of concave and convex portions are provided at the same or substantially the same pitch on part or all of the inner surface of the returnable box,
The pitch is 0.1 mm or more and 5 mm or less, and the recess depth is 0.1 mm or more and 2 mm or less (however, the vertical pitch and the horizontal pitch may be the same or different). The returnable box according to any one of [1] to [3].
[5] The returnable box according to any one of [1] to [4], wherein the returnable box is colored with a natural color or a colorant other than a black colorant.
[6] The returnable box according to any one of [1] to [5], wherein the returnable box is a food returnable box used for transporting food.

  The returnable box formed by in-mold foam molding of the polypropylene resin foamed particles of the present invention has a hygienic feature that it is easy to clean attached dirt and mold in addition to the impact resistance and durability that are the characteristics of the conventional returnable box. It is an excellent returnable box. The returnable box of the present invention is particularly suitable as a food returnable box.

FIG. 1 is an example showing the main body of the returnable box of the present invention (the lid is not shown). FIG. 2 is an example of a DSC curve obtained when a polypropylene resin foamed particle according to the present invention is measured using a differential scanning calorimeter. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. In the DSC curve, there are two melting peaks, the portion surrounded by the low temperature side peak and the broken line is Ql, and the portion surrounded by the high temperature side peak and the broken line is Qh. FIG. 3 is a detailed enlarged view showing an example of a cross-section of the concavo-convex pattern forming portion when a plurality of concavo-convex portions are provided on the inner surface of the returnable box of the present invention at the same or substantially the same pitch.

The returnable box of the present invention is a returnable box used for transporting various goods. Specifically, the goods to be transported include foods, tools, electrical products, glass substrates, chemicals, cosmetics, various parts, and the like. Although it is mentioned, it is not limited to these.
However, as will be described later, the returnable box according to the present invention is a passable box that is particularly excellent in terms of hygiene that it is difficult to adhere dirt and mold and is easy to clean, so a returnable box for food, a returnable box for electrical products, and a glass substrate A returnable box, a returnable box for medicine, and a returnable box for cosmetics are preferable, and a returnable box for food is most preferable.

The shape of the return box is not particularly limited as long as it is a box shape, and an example is shown in FIG.
FIG. 1 shows an example of a rectangular shape as viewed from above, but is not limited to this, and any opening such as a rectangle other than a triangle, a rectangle, an ellipse, a polygon, etc. The shape may be sufficient, and the shape may change from the opening toward the bottom.
In addition, as an external shape viewed from above, an example of a rectangular shape is shown in FIG. 1, but the shape is not limited to this, and any external shape such as a quadrilateral other than a triangle, a circle, an ellipse, a polygon, etc. It may be a shape.

  Furthermore, although not shown in FIG. 1, a partition member for partitioning the goods to be transported is provided inside the box, a pass box is provided to fix the partition member, a groove or a mountain is provided on the standing wall portion or the bottom, etc. It does not matter if this processing is applied.

  The returnable box of the present invention may be provided with a lid corresponding to the box body. There is no restriction on how the box body and the lid are aligned, and any means such as a method of fitting the box body and the lid or a method of dropping the lid into the box body may be used.

The returnable box of the present invention is formed by in-mold foam molding of polypropylene resin foam particles, and cross-fractionation chromatography of the returnable box foam molded body (hereinafter sometimes referred to as “polypropylene resin in-mold foam molded body”). In the graph method (hereinafter, sometimes referred to as “CFC method”), the amount of eluted components at 40 ° C. or less is preferably 7.5% by weight or less, and more preferably 6.5% by weight or less. More preferably, it is 4.0% by weight or less.
If the amount of elution component at 40 ° C. or less in the cross-fractionation chromatographic method of the foamed molded product in a polypropylene resin mold exceeds 7.5% by weight, it becomes difficult to easily clean dirt and mold attached to the returnable box. There is a tendency.

  When the amount of elution components below 40 ° C in the cross-fractionation chromatographic method for polypropylene resin molds is increased, the proportion of low crystalline and low molecular weight components that tend to bleed to the surface of the returnable box increases, and these are bonded. It is presumed that it is difficult to clean dirt and mold because of its medicinal role.

  As in the present invention, when the amount of the elution component at 40 ° C. or less in the cross-fractionation chromatographic method of the polypropylene resin in-mold foam molded product is 7.5% by weight or less, the hygienic aspect that the attached dirt and mold can be easily washed. But it is an excellent returnable box.

  In the present invention, the ease of cleaning the attached dirt and mold is expressed by the phrase “hygienic”, and the fact that the attached dirt and mold is easy to wash is “improves hygiene or It may be expressed as “To be changed”. On the other hand, the fact that attached dirt and molds are difficult to clean is sometimes expressed as “hygienicity is reduced or deteriorated”.

  In addition, when the amount of the eluted component at 40 ° C. or less in the cross fractionation chromatographic method exceeds 7.5% by weight, the surface of the return box has wrinkles, sink marks, or dents or intergranular particles (hereinafter referred to as intergranular particles). In the case where a lot of voids are generated, the dirt or mold that enters the voids and adheres tends to be more difficult to clean.

  In order to make the amount of the elution component below 40 ° C. in the cross-fractionation chromatographic method of the returnable box foam molded article of the present invention 7.5% by weight or less, the polypropylene used as the base resin of the polypropylene resin in-mold foam molded article What is necessary is just to select what the amount of elution components below 40 degreeC in the cross fractionation chromatograph method of a resin is about 7.5 weight% or less.

  A polypropylene resin having an elution component amount of 40 ° C. or less in the cross fractionation chromatographic method of 7.5% by weight or less can be obtained by appropriately adjusting the polymerization catalyst selection and polymerization conditions when polymerizing the polypropylene resin. It is done.

Here, the cross-fractionation chromatographic method of the returnable box foamed molded product of the present invention or the polypropylene resin used as the base resin is measured under the following conditions.
Apparatus: manufactured by Mitsubishi Oil Chemical Co., Ltd., cross-fractionation chromatograph CFC T-150A type detector: manufactured by Miran, infrared spectrophotometer 1 ACVF type detection wavelength: 3.42 μm
GPC column: Showa Denko Co., Ltd., Shodex AT-806MS 3 column temperature: 135 ° C
Column calibration: Monodisperse polystyrene molecular weight calibration method manufactured by Tosoh Corporation: General-purpose calibration method / polyethylene equivalent eluent: o-dichlorobenzene (ODCB)
Flow rate: 1.0 mL / min.
Sample concentration: 30 mg / 10 mL
Injection volume: 500 μL
Temperature drop time: 135 minutes (135 to 0 ° C.), then hold for 60 minutes Elution category: 0, 20, 40, 50, 60, 70, 75, 80, 83, 86, 89, 92, 95, 98, 101, 104 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 130, 135 ° C (29 fractions)
The “elution component amount of 40 ° C. or less in the cross fractionation chromatographic method” refers to the ratio (%) of the integrated value of the elution amount of 40 ° C. or less to the total elution amount.

  There is no restriction | limiting in particular in the polypropylene-type resin used by this invention, The copolymer etc. which consist of a propylene homopolymer, a propylene, and a C2- or 4 or more olefin are mentioned.

Here, the olefin having 2 or 4 or more carbon atoms is not particularly limited, and specifically, ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4- Examples include α-olefins such as methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene and 1-decene. Furthermore, cyclic olefins such as cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4 -Dienes such as hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene.
These olefins having 2 or 4 carbon atoms may be used alone or in combination of two or more.

  Among these olefins having 2 or 4 or more carbon atoms, ethylene or α-olefin is more preferable, and ethylene and 1-butene are most preferable from the viewpoint of good foamability.

  In the present invention, among polypropylene resins, a propylene homopolymer, a propylene / ethylene random copolymer, and a propylene / ethylene / 1-butene random copolymer are preferable from the viewpoint of good foamability.

Furthermore, in these propylene / ethylene random copolymers and propylene / ethylene / 1-butene random copolymers, in 100% by weight of the polypropylene resin, the structural unit composed of propylene is 90% by weight to 100% by weight, ethylene and Preferably, the structural unit composed of 1-butene is from 0% by weight to 10% by weight, the structural unit composed of propylene is from 92% by weight to 99% by weight, and the structural unit composed of ethylene and / or 1-butene. Is more preferably 1% by weight or more and 8% by weight or less.
In the propylene / ethylene random copolymer and propylene / ethylene / 1-butene random copolymer, when the structural unit composed of ethylene and / or 1-butene exceeds 10% by weight, a polypropylene resin in-mold foam molded article ( There is a tendency that the dimensional stability when it is a box) decreases.

  There is no restriction | limiting in particular in the catalyst at the time of superposing | polymerizing the polypropylene resin used by this invention, A Ziegler Natta type | system | group polymerization catalyst, a metallocene type | system | group polymerization catalyst, etc. can be used.

  As a polymerization catalyst for polymerizing the polypropylene resin used in the present invention, it is easy to obtain a 2.0 wt% or less polypropylene resin with a particularly small elution component amount of 40 ° C. or less in the cross fractionation chromatography method. It is preferable to select a metallocene polymerization catalyst.

Specific examples of preferable metallocene polymerization catalysts include metallocene polymerization catalysts containing a transition metal compound described in JP-A-10-226712.
Furthermore, it is preferable to perform polymerization using a metallocene polymerization catalyst containing a metallocene compound represented by the following general formula [I] as an essential component.

（上記一般式［Ｉ］において、Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４、Ｒ_５、Ｒ_６、Ｒ_７、Ｒ_８、Ｒ_９、Ｒ_１０、Ｒ_１１、Ｒ_１２、Ｒ_１３、Ｒ_１４は水素、炭化水素基、ケイ素含有基から選ばれ、それぞれ同一でも異なっていてもよい。Ｍは第４族遷移金属であり、Ｙは炭素原子またはケイ素原子であり、Ｑはハロゲン、炭化水素基、アニオン配位子または孤立電子対で配位可能な中性配位子から同一または異なる組合せで選んでもよく、ｊは１〜４の整数である。）

(In the above general formula [I], R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ Are selected from hydrogen, a hydrocarbon group, and a silicon-containing group, and may be the same or different, M is a Group 4 transition metal, Y is a carbon atom or a silicon atom, and Q is a halogen or hydrocarbon group. A neutral ligand capable of coordinating with an anionic ligand or a lone electron pair may be selected in the same or different combination, and j is an integer of 1 to 4.)

  Specific examples of the metallocene compound represented by the general formula [I] include isopropylidene (3-tert-butyl-5-methyl-cyclopentadienyl) (fluorenyl) zirconium dichloride, isopropylidene (3-tert- Butyl-5-methyl-cyclopentadienyl) (3,6-ditert-butylfluorenyl) zirconium dichloride, diphenylmethylene (3-tert-butyl-5-methyl-cyclopentadienyl) (fluorenyl) zirconium dichloride Diphenylmethylene (3-tert-butyl-5-methyl-cyclopentadienyl) (2,7-ditert-butylfluorenyl) zirconium dichloride, diphenylmethylene (3-tert-butyl-5-methyl-cyclopenta Dienyl) (3,6-diter - and butyl fluorenyl) zirconium dichloride.

The melt flow rate of the polypropylene resin used in the present invention (hereinafter sometimes referred to as “MFR”) is not particularly limited, but is preferably 0.5 g / 10 min to 100 g / 10 min, and preferably 2 g / 10 min. 50 g / 10 min or less is more preferable, and 3 g / 10 min or more and 20 g / 10 min or less is more preferable.
When the MFR of the polypropylene resin is in the above range, it is easy to obtain polypropylene resin expanded particles having a relatively large expansion ratio, and the surface of the polypropylene resin in-mold foam molded product obtained by in-mold foam molding is beautiful. A product having excellent properties and a small dimensional shrinkage ratio can be obtained.

  Here, the MFR of the polypropylene resin is an orifice 2.0959 ± 0.005 mmφ, an orifice length 8.000 ± 0.025 mm, a load 2160 g, 230 ± 0.2 ° C. using an MFR measuring instrument described in JIS-K7210. It is the value when measured under the conditions of

As the polypropylene resin used in the present invention, the total amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units in all polypropylene insertion, as measured by ¹³ C-NMR, is 0.00. It is preferably less than 5 mol%.
Since such a polypropylene resin tends to reduce low crystalline components in the resin, hygiene of returnable boxes obtained by in-mold foam molding of polypropylene resin foam particles obtained using the polypropylene resin. The property can be further improved.

  Here, the amount of position irregular units based on 2,1-insertion and 1,3-insertion of propylene monomer units during the insertion of all polypropylene in a polypropylene resin is described in Polymer, 30, 1350 (1989) and JP-A-7-145212. It can be calculated with reference to the information disclosed in the publication.

Although there is no restriction | limiting in particular as melting | fusing point of the returnable box foaming molding of this invention, It is preferable that it is 125 to 150 degreeC.
When the melting point of the polypropylene-based in-mold foam molded product (removable box foamed molded product) is less than 125 ° C, the heat resistance tends to decrease. When the melting point exceeds 150 ° C, the molding heating vapor pressure when molding the returnable box is low. It tends to be higher.

Here, the melting point of the returnable box foam molded article (polypropylene-based resin mold foam molded article) is a value measured by the differential scanning calorimetry method (DSC method) under the following conditions.
That is, 5-6 mg of small pieces are cut out from the returnable box foamed molded article, and melted by raising the temperature from 40 ° C. to 220 ° C. at a rate of temperature increase of 10 ° C./min. In the DSC curve obtained when the temperature is increased from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min after crystallization by lowering the temperature from 220 ° C. to 40 ° C. The melting peak temperature is taken as the melting point.

  In the present invention, in order to set the melting point of the returnable box foam molding (in-molded polypropylene resin mold) to 125 ° C. or more and 150 ° C. or less, the melting point of the polypropylene resin used as the base resin is approximately 125 ° C. or more and 150 ° C. What is necessary is just to select the following.

  Here, the melting point of the polypropylene resin is also a value measured by the DSC method, and the base resin 5-6 mg is melted by heating from 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min. DSC curve obtained when the temperature is increased from 40 ° C. to 220 ° C. at a rate of 10 ° C./min after further crystallization by decreasing the temperature from 220 ° C. to 40 ° C. at a rate of 10 ° C./min. The melting peak temperature at the second temperature increase can be obtained as the melting point.

  In the present invention, the polypropylene resin is usually melted in advance using an extruder, a kneader, a Banbury mixer, a roll, etc., so that it is easy to make expanded particles, and has a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc. Molded into such a desired particle shape, it becomes polypropylene resin particles.

In the present invention, in addition to the polypropylene resin, additives such as an antioxidant, a light resistance improver, an antistatic agent, a colorant, a flame retardant improver, and a conductivity improver are added as necessary. It is good also as a particle. In particular, when carbon dioxide, air, or water is used as the foaming agent described later, it is preferable to add an inorganic nucleating agent and / or a water-absorbing substance that can improve foamability.
In that case, it is usually preferable to add these additives into the molten resin in the process of producing polypropylene resin particles.

  The inorganic nucleating agent used in the present invention promotes the formation of bubble nuclei as a starting point of foaming, contributes to the improvement of the foaming ratio, and also contributes to uniform bubble formation. Examples of the inorganic nucleating agent include talc, silica, calcium carbonate and the like.

  The amount of the inorganic nucleating agent added in the present invention is preferably 0.005 parts by weight or more and 0.5 parts by weight or less with respect to 100 parts by weight of the polypropylene resin.

  The water-absorbing substance used in the present invention means that when the substance is added to polypropylene resin particles and the polypropylene resin particles are brought into contact with water or impregnated with a foaming agent in an aqueous dispersion, A substance that can contain water.

  Specific examples of the water-absorbing substance include water-soluble inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax, and zinc borate, polyethylene glycol, and a special block polymer having a hydrophilic segment as a polyether (trade name: Perestat (manufactured by Sanyo Chemical Co., Ltd.), alkali metal salt of ethylene (meth) acrylic acid copolymer, alkali metal salt of butadiene (meth) acrylic acid copolymer, alkali metal salt of carboxylated nitrile rubber, isobutylene-anhydrous Examples include hydrophilic polymers such as alkali metal salts of maleic acid copolymers and alkali metal salts of poly (meth) acrylic acid, polyhydric alcohols such as ethylene glycol, glycerin, pentaerythritol, and isocyanuric acid, and melamine.

  The addition amount of the water-absorbing substance in the present invention varies depending on the target foaming ratio, the foaming agent to be used, and the type of the water-absorbing substance to be used, and cannot be generally described, but water-soluble inorganic substances and polyhydric alcohols are used. In this case, the amount is preferably 0.01 part by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the polypropylene resin, and when a hydrophilic polymer is used, 0.05 part by weight with respect to 100 parts by weight of the polypropylene resin. It is preferable that the amount is not less than 5 parts by weight.

In the present invention, there is no limitation on the addition of the colorant, and a natural color can be obtained without adding the colorant, or a desired color can be obtained by adding a colorant such as blue, red, or black.
Examples of such colorants include perylene organic pigments, azo organic pigments, quinacridone organic pigments, phthalocyanine organic pigments, selenium organic pigments, dioxazine organic pigments, isoindoline organic pigments, and carbon black. .

  When a colorant is not used in a conventional returnable box, or when a colorant other than black is used, stains and molds attached visually are easily noticeable. On the other hand, in the case of the returnable box of the present invention, even if dirt or mold adheres, it is easy to wash, so even when no colorant is used or when a colorant other than black is used, This is a preferable embodiment because dirt and mold are not easily noticeable.

  The returnable box of the present invention can be obtained by in-mold foam molding of polypropylene resin foam particles obtained by foaming the aforementioned polypropylene resin particles.

  The polypropylene resin foam particles used in the present invention are, for example, a polypropylene resin particle, a dispersion liquid containing water and an inorganic dispersant are accommodated in a pressure vessel and then dispersed under stirring conditions. In the presence of the above, the temperature is raised above the softening point temperature of the polypropylene resin particles, and then the dispersion in the pressure vessel is discharged into a pressure region lower than the internal pressure of the pressure vessel to produce the polypropylene resin particles by foaming. be able to.

  Here, when the temperature is raised above the softening point temperature, raising the temperature to a temperature in the range of the melting point of the polypropylene resin particles −20 ° C. or higher and the melting point of the polypropylene resin particles + 10 ° C. or lower is to ensure foamability. Is preferable.

Examples of the blowing agent used in the present invention include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane and hexane; alicyclic hydrocarbons such as cyclopentane and cyclobutane; air, nitrogen, And inorganic foaming agents such as carbon dioxide and water. These foaming agents may be used alone or in combination of two or more.
Among these, carbon dioxide gas, air, and water are preferably used.

  The amount of the foaming agent used in the present invention is not limited, and may be appropriately used according to the desired expansion ratio of the polypropylene-based resin foamed particles. The amount used is 3 weights with respect to 100 parts by weight of the polypropylene-based resin particles. It is preferable that it is 60 parts by weight or more.

  There is no particular limitation on the pressure vessel used when producing the expanded polypropylene resin particles, and any vessel that can withstand the pressure and temperature in the vessel at the time of producing the expanded polypropylene resin particles can be used. For example, an autoclave type pressure vessel can be used. It is done.

  Examples of the inorganic dispersant used in the present invention include tribasic calcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, basic zinc carbonate, aluminum oxide, iron oxide, titanium oxide, aluminosilicate, and kaolin. And barium sulfate.

In the present invention, it is preferable to use a dispersion aid in combination in order to improve dispersibility.
Examples of the dispersion aid in the present invention include sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyl ether disulfonate, sodium α-olefin sulfonate, and the like.
Among these, as a combination of the inorganic dispersant and the dispersion aid, a combination of tricalcium phosphate and sodium alkylsulfonate is preferable.

The amount of the inorganic dispersant and dispersion aid used in the present invention varies depending on the type and the type and amount of polypropylene resin used, but usually 0.2 parts by weight or more of the inorganic dispersant with respect to 100 parts by weight of water. The amount is preferably 3 parts by weight or less, more preferably 0.001 part by weight or more and 0.1 part by weight or less.
Moreover, in order to make the dispersibility in water favorable, it is usually preferable to use the polypropylene resin particles at 20 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of water.

  The amount of the inorganic dispersant adhered to the surface of the expanded polypropylene resin particles used in the present invention is preferably 2000 ppm or less, more preferably 1300 ppm or less, and even more preferably 800 ppm or less. When the amount of the inorganic dispersant adhering to the surface exceeds 2000 ppm, the fusing property at the time of in-mold foam molding tends to be lowered.

Although there is no restriction | limiting in particular in the expansion ratio of the polypropylene resin expanded particle of this invention, 3 times or more and 50 times or less are preferable, and 7 times or more and 45 times or less are more preferable.
Here, the expansion ratio of the expanded polypropylene resin particles is obtained by obtaining the weight w (g) of the expanded polypropylene resin particles and the volume of ethanol submerged volume v (cm ³ ), and the density d (= 0.9 g) of the expanded polypropylene resin before expansion. / Cm ³ ) is a value calculated by the following formula.
Foaming ratio = d × v / w

Although there is no restriction | limiting in particular in the bulk density of the polypropylene resin expanded particle of this invention, 10 g / L or more and 180 g / L or less are preferable, and 12 g / L or more and 78 g / L or less are more preferable.
Here, the bulk density of the expanded polypropylene resin particles is determined by measuring the weight of the expanded polypropylene resin particles in the container after the polypropylene expanded resin particles are gently put into the container and filling it. Divided by g / L.

The polypropylene resin expanded particles obtained as described above may be subjected to in-mold foam molding to form a returnable box.
Further, after the obtained polypropylene-based resin particles, a foaming agent, water, and a dispersion containing an inorganic dispersant are contained in a pressure resistant container, the mixture is dispersed under stirring conditions, and the mixture in the container is added in the presence of the foaming agent. The temperature is raised to a temperature in the range of the softening point temperature of the polypropylene resin particles, preferably in the range of the melting point of the polypropylene resin −20 ° C. or higher and the polypropylene resin + 10 ° C. or lower, and then the pressure range lower than the internal pressure of the pressure vessel When the polypropylene resin particles are foamed by discharging the dispersion in the pressure vessel (this process may be referred to as “one-stage foaming”), the foamed particles preferably have an expansion ratio of 3 to 35 times ( Hereinafter, sometimes referred to as “single-stage expanded particles”),
The pressure in the single-stage expanded particles is made higher than the normal pressure by pressure treatment in which the single-stage expanded particles are put in a pressure-resistant airtight container and nitrogen, air, etc. are pressure impregnated at 0.1 MPa to 0.6 MPa (gauge pressure). After that, the first-stage expanded particles are heated with steam or the like to be further expanded (this process may be referred to as “two-stage expansion”), whereby a polypropylene type having a higher expansion ratio than the expansion ratio of the first-stage expanded particles. Resin foam particles (hereinafter sometimes referred to as “two-stage foam particles”) are obtained, and this is subjected to in-mold foam molding to form a returnable box.

  The bulk density of such two-stage expanded particles is preferably 10 g / L or more and 40 g / L or less.

The expanded polypropylene resin particles used in the present invention have a melting peak ratio Qh / (Ql + Qh) × 100 (%) (hereinafter referred to as “high temperature side”) in a DSC curve obtained when calorimetric measurement is performed by a differential scanning calorimetry method. , Sometimes referred to as “DSC ratio”) is preferably 10% or more and 50% or less, and more preferably 15% or more and 40% or less.
When the DSC ratio of the polypropylene resin foamed particles is within the above range, a polypropylene resin in-mold foam-molded product having a high surface beauty is easily obtained.
If the DSC ratio of the polypropylene resin foamed particles is less than 10%, the polypropylene resin foamed particles tend to be open, and if it exceeds 50%, the fusion property when obtaining an in-mold foamed molded product tends to decrease. is there.

Here, Ql and Qh are defined as follows. As shown in FIG. 2, there are two melting peaks in the DSC curve obtained when the polypropylene resin expanded particles are heated from 40 ° C. to 200 ° C. at a temperature rising rate of 10 ° C./min.
The amount of heat surrounded by the low temperature side peak of the DSC curve and the tangent line from the maximum point between the low temperature side peak and the high temperature side peak to the melting start baseline is the low temperature side melting peak heat amount Ql,
The amount of heat surrounded by the high temperature side peak of the DSC curve and the tangent line from the maximum point between the low temperature side peak and the high temperature side peak to the melting end baseline is indicated as the high temperature side melting peak heat amount Qh.

Although there is no restriction | limiting in particular as high temperature side melting peak calorie | heat amount Qh of the polypropylene resin expanded particle used for this invention, 4J / g or more and 28J / g or less are preferable, 7J / g or more and 25J / g or less are more preferable, 10J / G or more and 22 J / g or less is more preferable.
When the high temperature side melting peak heat quantity Qh of the polypropylene resin foamed particles is less than 4 J / g, the polypropylene resin foamed particles tend to be open, and when it exceeds 28 J / g, the expansion ratio tends to be difficult to increase. .

In the present invention, the DSC ratio and the high-temperature side melting peak heat amount are, for example, the retention time from the temperature rise to the foaming in the one-stage foaming step (mainly the retention time from the foaming temperature to the foaming), the foaming It can be appropriately adjusted depending on the temperature (temperature at the time of foaming), foaming pressure (pressure at the time of foaming) and the like. In general, the DSC ratio or the high temperature side melting peak heat amount tends to increase by increasing the holding time, lowering the foaming temperature, or lowering the foaming pressure.
From the above, it is possible to easily find the conditions for the desired DSC ratio and the high-temperature side melting peak calorie by experimenting several times with systematically changing the holding time, foaming temperature, and foaming pressure appropriately. it can. The foaming pressure can be adjusted by adjusting the amount of foaming agent.

In the present invention, polypropylene resin foam particles are subjected to in-mold foam molding to form a returnable box. As the in-mold foam molding method, for example,
B) A method of in-mold foam molding of polypropylene resin expanded particles as they are,
B) A method of performing in-mold foam molding after injecting an inorganic gas such as air into the polypropylene resin expanded particles in advance and applying internal pressure (foaming ability);
C) A conventionally known method such as a method of filling polypropylene resin expanded particles into a mold in a compressed state and performing in-mold foam molding may be used.

As a specific example of a method for obtaining a returnable box (polypropylene resin-in-mold foam-molded article) using the polypropylene resin expanded particles of the present invention, for example,
Polypropylene resin foam particles are pre-air-pressurized in a pressure-resistant container and air is injected into the polypropylene resin foam particles to give internal pressure (foaming ability), which can be closed by two molds, but sealed In a molding space that cannot be filled, with water vapor as a heating medium, molding is performed at a heating water vapor pressure of about 0.1 MPa to 0.4 MPa (gauge pressure) for a heating time of about 3 seconds to 60 seconds. After fusing the resin foam particles together, by cooling the mold with water, after cooling to the extent that deformation of the expanded foam in the polypropylene resin mold after removal from the mold is suppressed, the mold is opened, Examples thereof include a method for obtaining a polypropylene resin molded in-mold foam.

  By the way, the internal pressure of the polypropylene resin expanded particles is, for example, 0.1 MPa or more and 1.0 MPa by an inorganic gas such as air or nitrogen under a temperature condition of 1 hour to 48 hours, room temperature to 80 ° C. in a pressure vessel. (Gauge pressure) It can be adjusted by applying pressure below.

Although there is no restriction | limiting in particular as a density of the returnable box foaming molding of this invention, 10 g / L or more and 180 g / L or less are preferable, and 12 g / L or more and 78 g / L or less are more preferable.
Here, the density of the returnable box foamed molded product is determined by cutting a sample into a rectangular parallelepiped from the center of each of the bottom part of the returnable box and the four standing wall parts, and taking the sample volume from the product of vertical, horizontal, and thickness dimensions for each sample. Is calculated, the sample weight is divided by the sample volume, and the density of each sample is calculated. Then, the densities of the five samples are averaged and expressed in units of g / L.

  In the returnable box of the present invention, a plurality of uneven portions are provided at the same or substantially the same pitch on a part or all of the inner surface of the returnable box. This is preferable because dirt, mold, and the like can be easily cleaned.

  FIG. 3 shows a detailed enlarged view of the cross-section of the concavo-convex pattern forming portion when a plurality of concavo-convex portions are provided on the inner surface of the returnable box of the present invention at the same or substantially the same pitch. Here, a is the width of the concave portion, b is the width of the convex portion, c is the depth of the concave portion, and a + b is the pitch of the concave and convex portions.

The pitch of the irregularities in the returnable box of the present invention is preferably 0.1 mm or more and 5 mm or less, more preferably 0.5 mm or more and 3 mm (however, the vertical pitch and the horizontal pitch are the same). Good or different.)
When the uneven pitch is less than 0.1 mm or more than 5 mm, the void reduction effect tends to be small.

The depth of the recess in the returnable box of the present invention is preferably 0.1 mm or more and 2 mm or less, and more preferably 0.1 mm or more and 1.0 mm or less.
Even if the dent depth is less than 0.1 mm, the void reducing effect tends to be small, and if the dent depth exceeds 2 mm, cleaning when dirt or mold occurs in the dent tends to be difficult.

  Although there is no restriction | limiting about the width | variety of the convex part and the width | variety of a recessed part in the returnable box of this invention, It is preferable to set a width | variety so that it may become the said pitch.

  There is no restriction | limiting in the shape of the convex part in the returnable box of this invention, Various shapes, such as column shape, cone shape, rectangular parallelepiped shape, polygonal column shape, can be used.

  In the present invention, there is no particular limitation on the method for providing the concave and convex portion on the inner surface of the returnable box, and when performing in-mold foam molding, a metal mesh or punching metal is formed on the mold portion corresponding to the portion on which the concave and convex portion is to be provided. It is possible to transfer the concavo-convex portion to the surface of the inner surface of the box by a known method such as a method of attaching a porous material such as a method of imparting a concavo-convex pattern to the mold itself, but it is limited to these methods is not.

  As described above, the returnable box formed by in-mold foam molding of the polypropylene resin foamed particles of the present invention is a returnable box that is easy to clean attached dirt and mold, and in particular, can provide a food returnable box. it can.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

  Evaluation in Examples and Comparative Examples was performed as follows.

<Foaming ratio of expanded polypropylene resin particles>
After measuring the weight w (g) of the polypropylene resin expanded particles, an increase volume (submerged volume) v (cm ³ ) when the polypropylene resin expanded particles were immersed in ethanol was determined, and the polypropylene resin expanded before expansion was measured. From the density d (= 0.9 g / cm ³ ), the expansion ratio was calculated by the following formula.
Foaming ratio = d × v / w (times)

<Bulk density of polypropylene resin expanded particles>
After the polypropylene resin foam particles are gently put into a container having a volume of about 5 L and filled, the weight of the polypropylene resin foam particles in the container is measured, and the weight is divided by the capacity of the container. Expressed density.

<DSC ratio measurement of polypropylene resin expanded particles>
Using a differential scanning calorimeter [Seiko Instruments Co., Ltd., DSC6200 type], 5-6 mg of polypropylene resin foam particles are heated from 40 ° C. to 200 ° C. at a heating rate of 10 ° C./min. For the two melting peaks in the DSC curve
As shown in FIG.
A low-temperature side peak of the DSC curve, and a low-temperature side melting peak calorie Ql that is a heat amount surrounded by a tangent to a melting start baseline from a maximum point between the low-temperature side peak and the high-temperature side peak;
The high temperature side melting peak calorie Qh, which is the amount of heat surrounded by the tangent to the melting end baseline from the maximum point between the high temperature side peak of the DSC curve and the low temperature side peak and the high temperature side peak,
The ratio of the melting peak on the high temperature side (DSC ratio) = (Qh / (Ql + Qh) × 100) (%) was calculated.

<Measurement of melting point>
Using a differential scanning calorimeter [Seiko Instruments Co., Ltd., DSC6200 type], cut out from a polypropylene resin (in the case of measuring the melting point of the base resin) as a base resin, or from an expanded foam in a polypropylene resin mold 5 to 6 mg of a small piece (when measuring the melting point of a returnable box foam molded article) is melted by raising the temperature from 40 ° C. to 220 ° C. at a heating rate of 10 ° C./min, and then the temperature is lowered by 10 ° C./min. From the DSC curve obtained when the temperature was increased from 40 ° C. to 220 ° C. at a rate of 10 ° C./min after crystallization by lowering the temperature from 220 ° C. to 40 ° C. at the second temperature increase The melting peak temperature of was taken as the melting point.

<Cross-fractionation chromatographic measurement (CFC elution measurement)>
Using a cross-fractionation chromatograph [Mitsubishi Oil Chemical Co., Ltd., CFC T-150A type], a polypropylene resin used as a base resin under the following conditions, or a foamed molded product in a polypropylene resin mold (return box foam molded product) ) Was measured at 40 ° C. or less.
Detector: Infrared spectrophotometer 1ACVF manufactured by Miran Detection wavelength: 3.42 μm
GPC column: Shodex AT-806MS manufactured by Showa Denko Co., Ltd. Three column temperature: 135 ° C
Column calibration: Monodisperse polystyrene molecular weight calibration method manufactured by Tosoh Corporation: General-purpose calibration method / polyethylene equivalent eluent: o-dichlorobenzene (ODCB)
Flow rate: 1.0 mL / min.
Sample concentration: 30 mg / 10 mL
Injection volume: 500 μL
Temperature drop time: 135 minutes (135 to 0 ° C.), then hold for 60 minutes Elution category: 0, 20, 40, 50, 60, 70, 75, 80, 83, 86, 89, 92, 95, 98, 101, 104 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 130, 135 ° C (29 fractions)

<Fusion rate evaluation of returnable box foam moldings>
After cutting about 3 mm in the thickness direction with a cutter knife into the standing wall part of the obtained returnable box foam molded article, the standing wall part was broken from the notch part by hand, and the fractured surface was observed. The ratio of the pre-expanded polypropylene resin particles to the number of pre-expanded polypropylene resin particles constituting the fracture surface was determined and used as the fusion rate.

<Void evaluation of returnable box foam moldings>
The inner bottom surface of the obtained returnable box foam molded article was visually observed and evaluated according to the following criteria.
○: No void is seen on the inner surface.
Δ: Some voids are seen on the inner surface.
X: A void is noticeable on the inner surface.

<Evaluation of detergency of returnable box foam molding>
After stirring and homogenizing a curry powder suspension prepared by mixing 0.3 g of curry powder [manufactured by House Foods Co., Ltd., curry powder granules] and 10 g of tap water, the box foamed molded product (internal volume 8 L) ) Towards the bottom of the inside. The returnable box molded body was shaken by hand, and the curry powder suspension was cast on the bottom.
The returnable foamed molded product was allowed to stand at 23 ° C. for 24 hours without being covered, and then washed as follows.
(1) The operation of pouring 8 L of 50 ° C. tap water into the box molded body and immediately releasing it was washed twice (hereinafter referred to as “washing a”).
(2) When cleaning a is performed, the inside bottom surface of the box is observed, and if the curry color remains on the inner surface, the inner surface is rubbed 10 times with a dishwashing sponge, and then 8 L of 50 ° C. tap water is added. It was poured into a returnable box molded product, immediately discharged and washed (hereinafter referred to as “washing b”).
After the washing operation as described above, the evaluation was made according to the following criteria.
A: After cleaning a, the curry color cannot be confirmed on the inside surface of the return box and the void.
○: After cleaning a, curry color cannot be confirmed on the inside surface of the return box, but a little curry color remains on the void.
Δ: After completion of cleaning a, curry color remains on the inside surface of the return box, and curry color clearly remains on the void. However, the curry color on the inside surface of the return box is eliminated by the cleaning b. X: After washing a, curry color remains on the inside surface of the return box, and curry color clearly remains on the void. Moreover, even if the cleaning b is performed, the curry color on the inner surface of the returnable box is not lost.

  Table 1 shows the properties of the polypropylene resins used in the examples and comparative examples.

Example 1
[Production of polypropylene resin particles]
After blending 0.5 parts by weight of polyethylene glycol [manufactured by Lion Corporation, PEG # 300)] and 0.1 parts by weight of talc [manufactured by Hayashi Kasei, PKS] to 100 parts by weight of polypropylene resin A, 50 mm uniaxial The mixture was melt kneaded in an extruder [Osaka Seiki Kogyo Co., Ltd., 20VSE-50-28 type]. The obtained melt-kneaded resin was extruded into a strand from a circular die, cooled with water, and cut with a pelletizer to obtain polypropylene resin particles having a weight of 1.2 mg / grain.
[Preparation of expanded polypropylene resin particles]
100 parts by weight of the obtained polypropylene resin particles, 200 parts by weight of water, 1.0 part by weight of tertiary calcium phosphate as a dispersing agent, and 0.05 part by weight of sodium alkyl sulfonate as a dispersing aid were charged into a pressure-resistant autoclave having a capacity of 10 L. Under stirring, 6.5 parts by weight of carbon dioxide gas was added as a blowing agent. The temperature of the autoclave was raised and heated to a foaming temperature of 145 ° C., and then carbon dioxide was added to make the autoclave internal pressure 3.0 MPa (gauge pressure). Then, after holding for 30 minutes, the valve | bulb of the autoclave lower part was opened, the autoclave content was discharge | released under atmospheric pressure through the 4.0 mm diameter opening orifice, and the 1st stage | paragraph expanded particle was obtained. The resulting single-stage expanded particles had an expansion ratio of 13 times and a DSC ratio of 24%.
An internal pressure was applied to the obtained single-stage expanded particles by air impregnation, and then heated with steam to obtain two-stage expanded particles having a bulk density of 26.0 g / L. The DSC ratio of the obtained two-stage expanded particles was 23%.
[Production of foamed molded product in polypropylene resin mold (return box molded product)]
Next, using a polyolefin foam molding machine P150N (manufactured by Toyo Machine Metal Co., Ltd.), the air pressure inside the polypropylene resin foamed particles is set to 0.19 MPa (absolute pressure) in advance in a mold for obtaining a box-shaped molded body. Filled with polypropylene resin resin two-stage expanded particles adjusted so as to have a molding heating vapor pressure of 0.25 MPa (gauge pressure), compressed by 10% in the thickness direction, and thermoformed to form a box-shaped [long as internal dimensions A white (natural color) polypropylene-based resin-molded in-mold foam molded article (side box foam molded article = internal volume 8 L) having a side 400 × short side 200 × height 100 mm, thickness 30 mm] was obtained.
The go-through box molding obtained was allowed to stand at 23 ° C. for 1 hour, then cured and dried in a thermostatic chamber at 75 ° C. for 3 hours, taken out again to room temperature and left at 23 ° C. for 1 hour, and then evaluated for the fusion rate. Then, void evaluation and detergency evaluation were performed. Further, the melting point and CFC elution amount of the box-shaped molded body were measured.
The evaluation results are shown in Table 2.

(Examples 2-7, Comparative Example 1)
Except for using the resins A to F, the production conditions shown in Table 2 were used, and by the same operation as in Example 1, a single-stage foamed particle and a two-stage foamed particle of a polypropylene resin were obtained, and a returnable box molded body was obtained. And evaluated.
However, in Example 2, the single-stage expanded particles were subjected to in-mold foam molding without performing two-stage foaming.
The molding heating vapor pressure at the time of in-mold foam molding is as shown in Table 2. However, the pressure is appropriately adjusted so that the fusion rate and void evaluation are equivalent to those in Example 1.
The evaluation results are shown in Table 2.

(Example 8)
After mixing 100 parts by weight of Resin A and 15 parts by weight of copper phthalocyanine blue [made by Wako Pure Chemical Industries, Ltd., chemical reagent], 220 mm using a 45 mm twin screw extruder [manufactured by OH Machinery Co., Ltd., TEK 45 mm extruder]. The mixture was melt-kneaded at 0 ° C., extruded into a strand, cooled with water, and cut with a pelletizer to obtain a blue masterbatch resin.
In [Preparation of polypropylene resin particles], the same procedure as in Example 1 was performed, except that 4 parts by weight of the blue masterbatch resin was further added to 100 parts by weight of the resin A. Corrugated foam particles were obtained, and a blue returnable box molded product was obtained.
The evaluation results are shown in Table 2.

Example 9
In [Production of foamed molded product in polypropylene resin mold], a stainless steel wire mesh (18 mesh) having a pitch of 1.41 mm and a depth of 0.68 mm is attached to the mold part corresponding to the inner surface of the bottom of the molded product. A returnable box molded body was obtained in the same manner as in Example 1 except that it was molded.
Concavities and convexities with a pitch of 1.41 mm and a recess depth of 0.68 mm were provided on the inner bottom surface of the go-through box molded body obtained.
The evaluation results are shown in Table 2.

a Width of recess b Width of protrusion c Depth of recess

Claims (6)

A returnable box formed by in-mold foam molding of polypropylene resin expanded particles,
A returnable box, wherein the amount of elution components at 40 ° C. or less in the cross fractionation chromatographic method of the returnable box foamed molded product is 7.5% by weight or less.   The returnable box according to claim 1, wherein the amount of elution component of 40 ° C or less in the cross-fractionation chromatograph method of the returnable box foamed molded product is 6.5% by weight or less.   The returnable container according to claim 1 or 2, wherein the expanded polypropylene resin particles are expanded polypropylene resin particles made of a polypropylene resin polymerized with a metallocene polymerization catalyst. A plurality of concave and convex portions are provided at the same or substantially the same pitch on part or all of the inner surface of the returnable box,
The pitch is 0.1 mm or more and 5 mm or less, and the dent depth is 0.1 mm or more and 2 mm or less (however, the vertical pitch and the horizontal pitch may be the same or different).
The returnable box according to any one of claims 1 to 3, wherein   The returnable box according to any one of claims 1 to 4, wherein the returnable box is colored with a natural color or a colorant other than a black colorant. The returnable box according to any one of claims 1 to 5, wherein the returnable box is a returnable box for food used for transporting food.

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