JP2012067256A - Method for producing foam-molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a foam-molded body which produces a foam-molded body having low apparent density using a chemical foaming agent.SOLUTION: In the method for producing a foam-molded body, the foam-molded body is molded by extruding a mixed resin from an extruder, wherein the mixed resin is obtained by loading a sodium bicarbonate master batch, a citric acid master batch formed separately from the sodium bicarbonate master batch, and a raw material resin each into the extruder and kneading the same.

Description

  The present invention relates to a method for producing a foamed molded article using a chemical foaming agent.

  Conventionally, a method using an inorganic chemical foaming agent using sodium bicarbonate and citric acid (or citrate) is known as a method for obtaining a foamed molded product (see Patent Document 1). This chemical foaming agent generates carbon dioxide gas by a chemical reaction between an acid (citric acid) and a base (bicarbonate), and foams a thermoplastic resin with the gas. Baking soda and citric acid can be used in powder form, but from the viewpoint of handleability, baking soda and citric acid are used as one master batch, and the master batch is kneaded with the base resin and molded. It is common.

JP 2000-225638 A

  However, when a conventional chemical blowing agent masterbatch is used, an acid-base reaction between baking soda and citric acid occurs at a stage from preparation of the masterbatch to storage. For this reason, the amount of carbon dioxide generated during foam molding is reduced.

  The present invention has been made to solve the above-described problems, and provides a method for producing a foamed molded product that can produce a foamed molded product having a small apparent density using a chemical foaming agent.

  The present invention is to extrude a mixed resin obtained by charging a sodium bicarbonate master batch, a citric acid master batch formed separately from the sodium bicarbonate master batch, and a base resin into an extruder and kneading them from the extruder. Forming a foamed molded product.

  According to the present invention, it is possible to produce a foamed molded article having a small apparent density using a chemical foaming agent.

It is a figure which shows the addition weight ratio of baking soda and a citric acid. It is a figure which shows the result of having measured MT of the string-like object detected with the detector connected with the pulley for tension detection with time.

  Hereinafter, the manufacturing method of the foaming molding of this embodiment is demonstrated, referring an accompanying drawing.

  The method for producing a foamed molded product of the present embodiment is a mixing method in which a baking soda master batch, a citric acid master batch formed separately from the baking soda master batch, and a base resin are put into an extruder and kneaded. Resin is extruded from an extruder to form a foamed molded article. The powder particle size of baking soda and citric acid used as a master batch is not particularly limited, but is preferably 100 μm or less.

  Further, as shown in FIG. 1, the added weight ratio of baking soda and citric acid is preferably baking soda: citric acid = 3 or more: 1 because the apparent density is hardly lowered when citric acid becomes larger than baking soda. That is, it is desirable to add the baking soda master batch and the citric acid master batch to the raw material resin so that the added weight ratio of baking soda and citric acid is baking soda: citric acid = 3 or more: 1.

  The amount of foaming agent added (the sum of the weight of baking soda and citric acid) depends on the base resin, blow molding temperature, and the desired apparent density, but it should be added within the range of 0.2 to 3.0 wt%. Is desirable, and it is more preferably within the range of 0.8 to 1.2 wt%.

Raw material resin preferably has a product of melt tension at 200 ℃ (MT) MT and the melt flow rate at that 7gf more and 200 ° C. (MFR) is 15 g ² / 10min or more. Resins with MT smaller than 7 gf cause bubble burst (bubble breakage) from the surface of the molten resin, and it is difficult to sufficiently foam the parison. In addition, a resin having a small product of MT and MFR tends to have an adverse effect on foamability due to poor fluidity, and it may be difficult to transfer the shape when forming in a mold.

  The raw material resins may be used alone or in combination of two or more. For example, other resin components such as polypropylene resins, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and other ethylene-based resins, butene-based resins, and styrene-based resins, as long as the characteristics of the main raw material are not impaired. May be mixed as necessary.

  In addition, a bubble diameter can be adjusted using a bubble regulator as needed. Typical examples include inorganic bubble regulators such as talc, silica, zeolite, molecular sieve, zinc oxide, and calcium carbonate. These inorganic bubble regulators serve as nuclei at the time of bubble generation and can make the bubbles finer. As another bubble regulator, there is a method of using an organic acid salt of an organic acid used as a foaming aid as a bubble regulator. These can moderate acid / base reaction and suppress excessive growth of bubbles by buffering action.

(MT measurement method)
The MT of the raw material resin can be measured by, for example, a melt tension tester type II manufactured by Toyo Seiki Seisakusho Co., Ltd. Specifically, using a melt tension tester having an orifice with an orifice diameter of 2.095 mm and a length of 8 mm, the resin is extruded into a string from the orifice under the conditions of a resin temperature of 200 ° C. and an extrusion piston speed of 10 mm / min. The product is hung on a tension detection pulley having a diameter of 45 mm, and then wound with a winding roller having a diameter of 50 mm at a winding speed of 4 rpm.

  To obtain the MT, put the raw material in the piston, apply the preload after the temperature in the piston reaches 200 ± 0.2 ° C, and hold it for 4 minutes (conceivable types of raw materials include virgin raw resin, Three types are possible: a resin shredded product that has been melt-kneaded in advance, and a resin that has been cut from a molded product and shredded). The preload varies according to the MFR and is shown in Table 1. Thereafter, winding is performed at a winding speed of 5 rpm, and the MT of the string-like material detected by a detector connected to the tension detection pulley is measured over time, and MT (gf) is plotted on the vertical axis and MT (gf) on the horizontal axis. When time (seconds) is taken and shown in the chart, a graph having an amplitude as shown in FIG. 2 is obtained. In FIG. 2, MT takes the median value (X) of the amplitude where the amplitude is stable. It should be noted that a specific amplitude that occurs rarely is ignored.

(Measurement method of MFR)
The value measured at 200 ° C and a load of 2.16kgf described in JIS K7210 shall be used for MFR.

(Apparent density measurement method)
The apparent density of the foam molded article is obtained by dividing a part of the foam molded article as a test piece and dividing the weight (g) of the test piece by the volume (cm ³ ) of the test piece.
In addition, when a foaming molding is a blow molded product, the surface on which blow pressure acts is used as a test piece (the compression portion is not used).

(Production of foaming agent masterbatch / foaming aid masterbatch)
The foaming agent MB was obtained by dry blending sodium bicarbonate (having an average particle size of about 50 to 200 μm) into low density polyethylene (melting point: 106 ° C., MFR: 14 g / 10 min) and kneading with a twin screw extruder. Baking soda was mixed so as to occupy 40 wt% of the entire foaming agent MB.
Foaming aid MB was obtained by dry blending citric acid (having an average particle size of about 50 to 100 μm) into low density polyethylene (melting point: 106 ° C., MFR: 14 g / 10 min) and kneading with a twin screw extruder. Citric acid was mixed so as to occupy 40 wt% of the entire foaming agent MB.
A dry blend of foaming agent MB and foaming aid MB was used as the chemical foaming agent so that the weight ratio was foaming agent MB: foaming aid MB = 6: 1.

(Preparation of blow molded product 1)
What added 3 weight part of chemical foaming agents with respect to 100 weight part of base resin of the mixing | blending shown in Table 2 was supplied to the cylinder diameter 75mm extruder, and the foaming parison was formed through the accumulator head. When accumulating molten resin with an accumulator, it is desirable to apply pressure to the extent that the molten resin does not foam in the accumulator. Next, the obtained foamed parison was sandwiched between molds, and compressed air of 0.05 MPa was fed into the mold with a blow needle to shape a duct-shaped hollow foamed molded product. It is preferable to provide a vacuum vent such as a slit vent in the printed part of the hollow foamed molded product or a part where the blow ratio becomes high. The weight of the molded body was adjusted so that the thickness was 1.5 to 2.0 mm.

Here, the thickness of the hollow foamed molded product is calculated as follows.
The surface area S (cm ² ) and weight W (g) of the hollow foamed molded article are measured, and calculated from the following equation (1) from the apparent density.
Hollow foam molded product thickness (mm) = W / (S x ρ x 10) ··· (1)
W: Weight of hollow foam molding (g)
S: Surface area of the hollow foamed molded product (cm ² )
ρ: Apparent density of hollow foamed molded product (g / cm ³ )

Table 2 shows the evaluation results of the apparent density and the appearance. The 2MB system in Table 2 is a system that uses the foaming agent MB and the foaming aid MB as separate MBs. The 1MB system uses the same MB for the foaming agent and the foaming aid. is there. Moreover, the resin used as a raw material of base resin is as follows.
PP1: Propylene homopolymer (manufactured by Borealis, trade name: Daploy WB130), MT = 40 cN (190 ° C.), MFR = 2.1 g / 10 min (230 ° C.), density = 900 kg / m ³ .
PP2: crystalline ethylene-propylene block copolymer (manufactured by Nippon Polypro Co., Ltd., trade name: New Former FB3312), MT = 7cN (190 ° C), MFR = 3g / 10min (230 ° C), density = 900kg / m ³ .
LLDPE: ethylene-hexene-1 copolymer (Sumitomo Chemical Co., Ltd., Exelen CX2001), linear ultra-low density polyethylene polymerized by metallocene catalyst, MFR = 2g / 10min (230 ° C), density = 898kg / m ³ .
LDPE: Low density polyethylene (Sumitomo Chemical Co., Sumikasen F108), MFR = 0.42 g / 10 min (230 ° C.), density = 920 kg / m ³ .

Since Example 1 is a 2 MB system, the apparent density is smaller (the foaming ratio is higher) than Comparative Example 1 of the 1 MB system.
In Example 1, since a melt tension at 200 ° C. (MT) is at least 7 gf, is melt flow rate (MFR) and the product of MT is 15 g ² / 10min or more at 200 ° C., Example 2, Example 3 Compared to Example 4, the apparent density is small. In addition, the external appearance is also superior to that of Example 2 and Example 3.
In Example 2, since both MT and MT × MFR were too low, the apparent density was larger than that in Example 1, and the surface of the molded product was inferior.
In Example 3, bubbles were broken due to MT being too low, and the apparent density was higher than that in Example 1. Moreover, since the surface solidified in the state where the foam was broken, the surface became a skin-like shape, resulting in poor appearance.
In Example 4, since the MT was high, no bubble breakage was observed, but due to the low MT × MFR, the fluidity of the molten resin had an adverse effect on the apparent density. Also, the transferability of the mold was slightly inferior to those of Examples 1 and 3.
In Comparative Example 1, the acid-base interaction between sodium bicarbonate and citric acid had an adverse effect on foaming, and a sufficient apparent density could not be obtained.

(Production of blow molded product 2)
The raw material resin is as shown in Table 3, and 1 to 3 parts by weight of a chemical foaming agent is added to 100 parts by weight of the raw material resin in the same manner as described above (Preparation of blow molded body 1). A hollow foamed molded article was prepared. The 2MB system in Table 2 is a system that uses the foaming agent MB and the foaming aid MB as separate MBs. The 1MB system uses the same MB for the foaming agent and the foaming aid. is there. In addition to the PP1 and PP2 described above, the resin used as the raw material for the base resin is as follows.
PE: ethylene polymer (manufactured by Tosoh Corporation, 08S55A), MT = 4.19 cN, MFR = 4 g / 10 min (230 ° C.), density = 952 kg / cm ³ .

  When Examples 5 to 8 and Comparative Examples 2 to 5 were compared, it was found that in any case where the amount of addition of the foaming agent was different, the apparent density was more likely to decrease in Examples 2 to 5 using the 2MB system.

  Although the embodiments and examples of the present invention have been described above, the scope of the present invention is not limited to the above-described embodiments and examples, and various modifications are made without departing from the scope of the present invention. Implementation is possible.

Claims (2)

  Baking soda masterbatch, a citric acid masterbatch formed separately from the baking soda masterbatch, and a raw material resin are respectively introduced into an extruder and kneaded to extrude a mixed resin from the extruder to obtain a foam molded product. A method for producing a foamed molded article, comprising molding. The raw material resin is a melt tension at 200 ° C. (MT) is more than 7 gf, according to claim 1, the product of the melt flow rate (MFR) and MT at 200 ° C. is characterized in that it is 15 g ² / 10min or more A method for producing an expanded molded article.

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