JP2021161236A - Method for producing polyolefin foam, method for producing packaging material for packaging, polyolefin foam, and packaging material for food product packaging - Google Patents

Abstract

To provide a method for producing a polyolefin foam which makes it easy to adopt as a packaging material for food product packaging, gives consideration to environmental measures, and avoids labor for quality management before production, a method for producing a packaging material for food product packaging, a polyolefin foam, and a packaging material for food product packaging.SOLUTION: A method for producing a polyolefin foam includes a step of heating a resin composition obtained by kneading at least a polyolefin-based resin and an inorganic filler and producing a molten material, a step of adding 0.5-3 wt.% of water to 100 wt.% of the molten material, further mixing the mixture, and producing a hydrous molten material, and a step of vaporizing moisture contained in the hydrous molten material, and producing a foam, and performs each of the steps with an extruder including a cylinder 101, a screw 111, a charging port 121, a die 131 and a water injection part 141 shown in Fig. 1, and obtains a sheet-like foam.SELECTED DRAWING: Figure 1

Description

The present invention relates to, for example, a method for producing a polyolefin foam using a resin composition suitable for the food packaging field as a raw material, a method for producing a packaging material for packaging using the produced foam, and a polyolefin foam made from the above resin composition. , And the above-mentioned foam packaging material for foods.

Conventionally, in the field of building materials, foams made from a resin composition containing a synthetic resin or the like have been used as a heat insulating material, a cushioning material, a sound insulating material, and a cold insulating material. However, for example, in the case of a heat insulating material, soot and toxic gas are likely to be generated by incineration at the time of disposal, the fuel calorie is high, the desired width cannot be formed due to insufficient foaming amount, and the heat insulating property is insufficient. I had a chilling problem.

Therefore, in Patent Document 1, when foamable polypropylene is used as the raw material of the foam, soot is generated at the time of incineration by blending a recycled resin in which a polystyrene resin and a polyolefin resin (polypropylene resin and polyethylene resin) are mixed. There are disclosed foams that are difficult to burn, have low calories burned, and have the desired foaming and heat insulating properties. Specific components of the foam are paper pellets, the recycled resin, the foamable polypropylene, and water according to a predetermined composition.

Japanese Unexamined Patent Publication No. 2011-213966

On the other hand, also in the field of packaging for foods, a resin composition containing a predetermined synthetic resin or the like is expected to alleviate the impact applied to the packaged food, suppress the misalignment due to the slipping of the food, and reduce the total weight including the food. A foam packaging made from a product is used. That is, since food is placed on the packaging, hygiene is also indispensable for the foam, and therefore it is difficult to adopt the foam of Patent Document 1 which has a poor track record in the packaging field for food.

In recent years, in foams in the field of packaging for foods, an inorganic filler is blended in a resin composition with the aim of developing strength and rigidity as a packaging body and other various resistances and reducing raw material costs. There are many types of inorganic fillers, and the types and ratios to be blended are appropriately determined according to the function and application of the package. In addition, as interest in environmental issues grows, efforts to reduce the amount of synthetic resin used are becoming more active.

Generally, a resin composition obtained by kneading a synthetic resin or an inorganic filler may be distributed as pellets. The pellets of the resin composition used as the raw material of the foam may be formed porous in order to increase the water absorption rate of the water blended at the time of formation and increase the foaming ratio of the foam. However, if the pellets are porous and have water absorption, it may take time and effort for quality control according to changes in temperature and humidity with the seasons.

Therefore, an object of the present invention is a method for producing a polyolefin foam, a method for producing a packaging material, a method for producing a polyolefin foam, which is easy to adopt as a packaging material for foods, takes environmental measures into consideration, and avoids the trouble of quality control before production. The present invention is to provide polyolefin foam and packaging materials for food packaging.

That is, the method for producing a polyolefin foam in the present invention includes a step of heating a resin composition obtained by kneading at least a polyolefin resin and an inorganic filler to produce a melt, and 0 water with respect to 100% by weight of the melt. It is characterized by including a step of adding 5% by weight to 3% by weight and further mixing to form a hydrous melt, and a step of vaporizing the water contained in the hydrous melt to form a foam. ..

It is desirable that the resin composition does not contain a chemical foaming agent and the foaming ratio of the foam to the resin composition is 4 times or more.

The weight ratio of the polyolefin resin to the inorganic filler is preferably 85: 15-30: 70.

Further, the method for producing a packaging material for packaging in the present invention includes a step of heating a resin composition obtained by kneading at least a polyolefin resin and an inorganic filler to form a melt, and water with respect to 100% by weight of the melt. A step of adding 0.5% by weight to 3% by weight and further mixing to form a hydrous melt, and vaporizing the water contained in the hydrous melt to form a sheet-like foam having a thickness of 500 μm to 3000 μm. It is characterized by including a step and a step of molding the sheet-shaped foam.

Further, the polyolefin foam in the present invention is a polyolefin foam in a state in which moisture in a hydrous melt containing at least a resin composition obtained by kneading a polyolefin resin and an inorganic filler is heated and water is vaporized. The water-containing melt contains 0.5 to 3% by weight of water with respect to 100% by weight of the melt, the polyolefin-based resin contains a polypropylene-based resin, and the inorganic filler contains talc. The weight ratio of the polypropylene-based resin to the inorganic filler is 85: 15 to 30:70.

Further, the packaging material for foods in the present invention is a packaging material for foods formed of a polyolefin foam sheet obtained by forming the polyolefin foam into a sheet, and the thickness of the polyolefin foam sheet. Is 500 μm to 3000 μm, and is characterized by including a bottom portion on which food is placed and a side wall portion provided continuously upward from the outer peripheral edge of the bottom portion.

According to the present invention, it is easy to use as a packaging material for food packaging, environmental measures are taken into consideration, and the effect of avoiding the trouble of quality control before production can be expected.

This is an example of an extruder used in the method for producing a polyolefin foam according to an embodiment of the present invention. This is an example of a foam sheet used in the method for producing a packaging material for food according to an embodiment of the present invention.

Hereinafter, a method for producing a polyolefin foam, a method for producing a packaging material for food, a polyolefin foam, and a packaging material for food packaging in one embodiment of the present invention will be described.

<Outline of method for producing polyolefin foam>
The method for producing the polyolefin foam is the first step of heating a resin composition obtained by kneading at least a polyolefin resin and an inorganic filler to produce a melt, and 0.5 to 0.5% of water based on 100% by weight of the melt. It includes a second step of adding 3% by weight and further mixing to produce a hydrous melt, and a third step of vaporizing the water contained in the hydrous melt to form a foam.

According to these steps, since the resin composition does not need to be porous (water absorption), it avoids the trouble of quality control according to the fluctuation of temperature and humidity due to the season, and it is uniform because the moisture is uniformly dispersed. By mixing an inorganic filler as a resin composition, it is expected that the amount of synthetic resin used can be reduced and the rigidity and strength of the produced foam can be improved.

The "molten product" is a state in which the resin composition is melted by heating in the first step to provide fluidity. The "hydrous melt" is a state in which the water supplied in the second step is dispersed in the melt. The "foam" means that by opening the hydrated melt under atmospheric pressure in the third step, all or part of the water content of the hydrated melt is vaporized to form bubbles, which are then cooled. It is in a solidified state. Foams are used as packaging materials for food packaging, cushioning materials, and heat insulating materials, but they can be used for any purpose as long as they can be used.

<Details of resin composition>
The resin composition is not particularly limited as long as at least a polyolefin resin and an inorganic filler as a filler are kneaded among the synthetic resins, and the synthetic resin to be kneaded is, for example, in addition to the polyolefin resin, if necessary. , Polystyrene resin may be added.

The resin composition may be supplied as a compound previously produced in a separate step. Here, the compound refers to a synthetic resin in which at least a polyolefin resin and an inorganic filler as a filler are kneaded while being heated and extruded into pellets. In the present invention, the water content of the compound is preferably 1% by weight or less, preferably 0.5% by weight or less, and more preferably 0.1% by weight or less.

The polyolefin-based resin corresponds to a polyethylene-based resin (PE) or a polypropylene-based resin (PP), and may be a mixture of a polyethylene-based resin and a polypropylene-based resin, but is preferably only a polypropylene-based resin.

The polypropylene-based resin is, for example, a homopolypropylene resin, a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, or a propylene-α-olefin copolymer.

Inorganic fillers are, for example, particles of 10 nm to 100 μm, such as talc, calcium carbonate, silica, clay, wollastonite, potassium titanate, zonotrite, gypsum fiber, aluminum borate, fibrous magnesium compound (MOS), and aramid. Fibers, carbon fibers (carbon fibers), glass fibers (glass fibers), mica, glass flakes, polyoxybenzoyl whiskers, which may be one type or a mixture of two or more types, preferably have a proven track record in the food packaging field. It is a talc, and its average particle size may be 5 μm to 15 μm, 6 μm to 10 μm, or 7 μm to 9 μm.

<Ratio of water>
The water content may be 0.5% by weight to 3% by weight, preferably 0.6% by weight to 1.5% by weight, more preferably 0.8% by weight to 1.% by weight, based on 100% by weight of the melt. It is 2% by weight, and if it is less than 0.5% by weight, it does not foam and the desired physical properties cannot be obtained, and if it is more than 3% by weight, uniform bubbles cannot be obtained and the physical properties of the foam become unstable. Is a concern.

<Another feature of the method for producing polyolefin foam>
Further, the above-mentioned resin composition does not contain a chemical foaming agent, and the expansion ratio of the above-mentioned foam with respect to the resin composition is 4 times or more.

According to this, the environmental load associated with the use of the chemical foaming agent can be avoided, and a foam having a desired foaming ratio can be obtained without kneading the chemical foaming agent into the resin composition. That is, a foam having a foaming ratio of less than 4 times is hard and does not have physical properties such as strength, rigidity, and elasticity suitable for packaging materials for foods, and therefore is not suitable as packaging materials for foods.

The chemical foaming agent includes an organic foaming agent and an inorganic foaming agent, as well as a thermally decomposable type and a reaction system, and includes, for example, dinitropentamethylenetetramine (DPT), azodicarboxylicamide (ADCA), and 4,4'-oxybis. It is a combination of benzosulfonyl hydrazide (OBSH), hydrogen carbonate, carbonate, sodium hydrogen carbonate (baking soda), sodium hydrogen carbonate and citric acid, and includes all except naturally-derived foaming agents such as water.

Further, the weight ratio of the polyolefin resin and the inorganic filler is 85: 15 to 30:70, preferably 70:30 to 35:65, and more preferably 60:40 to 40:60.

According to this, if the weight ratio of the polyolefin resin is higher than 85:15, it becomes too soft, and it is difficult for the foam to accompany physical properties such as strength, rigidity, and elasticity suitable for packaging materials for foods. If the weight ratio of the inorganic filler is higher than: 70, a sheet cannot be obtained. More preferably, the polyolefin resin is a polypropylene resin and the inorganic filler is talc.

<Outline of manufacturing method of packaging materials for food>
The method for producing the packaging material for food products includes a third step of extruding the polyolefin foam produced by the method for producing a polyolefin foam to obtain a sheet-shaped foam having a thickness of 500 μm to 3000 μm, and the above-mentioned sheet-like manufacturing method. Includes a fourth step of molding the foam.

According to these steps, it is expected that a packaging material for food packaging having desired physical properties such as strength, rigidity, and elasticity can be obtained. If the sheet is thinner than 500 μm, it is easily damaged during molding or use, and if it is thicker than 3000 μm, the manufacturing cost is high and the cost effectiveness may be lowered.

The "packaging material for food" is, for example, a packaging body including at least a bottom portion on which food is placed and a side wall portion continuously provided upward from the outer peripheral edge of the bottom portion. It is preferably provided with a flange portion that extends outward continuously from the upper end edge of the side wall portion, and more preferably the upper end of the side wall portion that extends continuously outward from the outer peripheral edge of the flange portion. It is provided with a lid covering an opening formed by an edge. The package may or may not be a so-called container, and may be rectangular or circular in a plan view, and is not limited. "Food" is, for example, all fresh products such as meat and fresh fish, as long as they are relatively dense and heavy compared to those that produce a fluffy feeling such as salads and cakes. include.

<Relationship between each process>
The first step to the fourth step are in chronological order, and from the viewpoint of improving the production efficiency, the interval between the steps may be any as long as it does not affect the production of the desired foam and packaging material for food. The next step may be started immediately after the completion of the immediately preceding step, and each step may be performed by a separate device. However, preferably, the first step to the third step are performed by one predetermined device, and the fourth step is performed. It is carried out by another device, more preferably the first step to the third step are carried out by an extruder, and the fourth step is carried out by a molding machine.

<Details of extruder>
As shown in FIG. 1, the extruder M used in the method for producing a polyolefin foam is a heating / cooling cylinder 101 having a uniaxial screw 111 inside, and a resin provided on the upstream end side of the cylinder 101. The inlet 121 into which the composition is charged, the die 131 provided on the downstream end side of the cylinder 101 to extrude the hydrous melt, and the die 131 provided between the upstream end side and the downstream end side of the cylinder 101 are provided inside. It is provided with a water injection unit 141 for injecting water.

The die 131 is a jig having a discharge hole for extruding a raw material from the outlet of the cylinder 101 to generate a foam in a desired shape. For example, a T die or a circular die, but preferably the foam S is used as a sheet. It is a T-die having a discharge hole that is easy to generate. The size and shape of the discharge hole are not particularly limited, but in the case of a T-die, for example, a rectangular shape having a thickness (clearance) of 0.01 to 0.3 mm and a width of 500 mm to 2000 mm may be used. In the case of a circular die, it may have an annular shape with a diameter of 150 to 650 mm and a thickness (clearance) of 0.01 to 0.3 mm.

The T-die 131 may have round discharge holes, and a plurality of such round holes may be provided adjacent to each other. According to such a configuration, the extruded rod-shaped foam (also referred to as rod-shaped foam) is tightly bonded to the adjacent rod-shaped foam in a molten state, and an aggregate of the rod-shaped foam can be obtained. A sheet-like aggregate can be obtained by arranging the round holes, or a cylindrical aggregate can be obtained. Here, the size of the round hole as the discharge hole may be 0.01 to 0.3 mm in diameter.

Although not shown in detail, the water injection unit 141 is provided with a check valve provided in a hole leading from the outside to the inside of the cylinder 101, and water from a metering pump, which is a separate machine, toward the vicinity of the screw 111 via the check valve. Supply. In other words, the water injection unit 141 heats the resin composition in the cylinder 101 and pushes it toward the downstream end side with the screw 111 to supply water to the melted melt to facilitate the formation of a hydrous melt. The check valve is preferably provided at a position in the cylinder 101 where the resin composition pushed toward the downstream end side by the screw 111 is completely melted into the melt.

<Details of molding machine>
The molding machine used in the method for manufacturing a packaging material for food products is, for example, a device that performs press molding, vacuum forming, hot plate pressure air forming, vacuum pressure air forming, double-sided vacuum forming, and deep drawing.

<Relationship between each process and equipment>
When the first step to the third step are performed by the extruder, in the first step, the resin composition is charged into the cylinder 101 from the charging port 121, and then the resin is heated by heating in the cylinder 101 and rotating the screw 111. Until the composition is melted to produce a melt, the second step is to supply water to the melt produced in the first step by injecting water from the water injection unit 141, and then heat the inside of the cylinder 101 and screw 111. Up to the point where the melt and water are dispersed by the rotation of the above to generate a hydrous melt, and in the third step, the hydrous melt produced in the second step is sent from the inside of the cylinder 101 to the die 131. Up to the point where foam is formed by vaporizing the water content of the hydrous melt.

A T-die having a rectangular discharge hole can also be used as the die 131 in the third step. That is, the hydrous melt sent to the die 131 in the third step passes through the discharge hole of the die 131 and is released under atmospheric pressure to obtain a sheet-like foam.

Further, in the third step, the discharge holes of the T-die 131 may be round holes, and a plurality of such round holes may be formed adjacent to each other. According to such a configuration, the extruded rod-shaped foam can be tightly bonded to the adjacent rod-shaped foam in a molten state to obtain an aggregate of the rod-shaped foam.

When the fourth step is performed by the molding machine, the fourth step is to mold the sheet-shaped foam from the place where the sheet-shaped foam obtained in the third step is supplied from the extruder to the molding machine. Up to is applicable.

<Details of sheet-shaped foam>
As shown in FIG. 2, the sheet-shaped foam S (hereinafter, also referred to as “sheet S”) is an end face sight wave type. As shown in the plan view of FIG. 2A, the linear thin line is a ridge line indicating the vertices on the wavy mountain side and the valley side, and the width between the ridge lines (distance between adjacent mountains) is irregular. However, the average is 200 μm to 500 μm, and as shown in the end view of FIG. The vertical distance from the apex of the valley) is irregular, but averages between 500 μm and 1500 μm. The thickness of the sheet S is not particularly limited, but may be 200 μm to 1500 μm or 300 μm to 800 μm. The shape of the sheet S is based on the method for producing a polyolefin foam and the method for producing a packaging material for foods, and in particular, the expansion ratio of the foam, the size and shape of the discharge hole of the die at the time of extrusion, and the inside of the hydrous melt. Based on any one or a combination of two or more of the water contents of. Since the sheet S is easily torn in the ridgeline direction due to the structure of the foam, it is easy to expand and contract in parallel with the ridgeline direction and is easily bent or rolled, in other words, it is difficult to expand and contract along the ridgeline direction and is bent. Difficult to roll.

The evaluation test of the polyolefin foam produced by the method for producing a polyolefin foam in the present invention and the packaging material for foods produced by the method for producing a packaging material for foods by the above-mentioned polyolefin foam will be described below.

<Outline of evaluation test>
The evaluation test was carried out as an example and a comparative example by changing the composition of the resin composition, the weight ratio in the above composition, and the weight% of water with respect to 100% by weight of the melt. The common conditions in the evaluation test and the evaluation method for each evaluation item are as follows.

<Common conditions for evaluation tests>
The method for producing the polyolefin foam was carried out by an extruder manufactured by Toshiba Machine Co., Ltd., the heating temperature of the cylinder was 160 to 220 ° C., the discharge hole of the T-die had a thickness (clearance) of 0.05 mm and a width of 1000 mm, and the sheet. It is assumed that a foam in the form of a foam is obtained. The resin composition contains at least a polypropylene resin as a synthetic resin and talc having an average particle size of 8 μm as an inorganic filler, and is supplied as a compound that does not contain a chemical foaming agent and does not have water absorption based on porosity or shape. Will be done.

The method for manufacturing the packaging material for food is carried out by a molding machine that performs press molding, and the packaging material for food produced is for packaging general fresh products, and at least the bottom and side walls are covered. The depth of the packaging material corresponding to the height from the opening formed at the upper end edge of the side wall portion to the bottom portion is 25 mm.

<Evaluation method of foam>
The basis weight is measured with a 100 mm × 100 mm test piece punched from a sheet with reference to JIS P8124 “Paper and paperboard-Measurement method of basis weight”. The specific gravity and foaming ratio are measured by an underwater substitution method using a hydrometer manufactured by Shimadzu Corporation with reference to JIS Z8807 "Measuring method of solid density and specific gravity".

<Evaluation method for packaging materials for sheets and food products>
The vertical width of the sheet is measured with a thickness gauge manufactured by Mitutoyo. The elastic modulus is measured using an Instron universal material tester. The orientation of the sheet for measuring the elastic modulus is based on the corrugated ridge direction, MD is the ridge direction, and TD is the direction orthogonal to the MD. The tensile elastic modulus is measured with a 140 mm × 15 mm test piece punched from a sheet by diverting JIS K7161 “Plastic-How to determine tensile properties”. The flexural modulus is measured with a 70 mm × 15 mm test piece punched from a sheet by diverting JIS K7171 “Plastic-How to determine bending characteristics”. The number of ridges is visually calculated with a 50 mm test piece with the above TD punched from the sheet.

Finally, as the state of the sheet, "○" is the case where the sheet is moldable and the unevenness of the mountain is uniform, "△" is the case where the sheet is moldable but the unevenness is uneven, and "×" is the case where the sheet cannot be molded. 』Evaluate with. In addition, as the ease of packing the packaging material by the operator, the case where there is no problem is evaluated by "○", and the case where it is too hard to be bent is evaluated by "x".

The individual conditions of Examples 1 to 4 and Comparative Examples 1 and 2 are as follows.

<Example 1>
Synthetic resin = PP, inorganic filler = talc, weight ratio = PP: talc = 45:55, water = 1% by weight

<Example 2>
Synthetic resin = PP + PE, inorganic filler = talc, weight ratio = PP: PE: talc = 35:10:55, water = 1% by weight

<Example 3>
Synthetic resin = PP, inorganic filler = talc, weight ratio = PP: talc = 85:15, water = 2% by weight

<Example 4>
Synthetic resin = PP, inorganic filler = talc, weight ratio = PP: talc = 90:10, water = 1.5% by weight

<Comparative example 1>
Synthetic resin = PP, inorganic filler = talc, weight ratio = PP: talc = 45:55, water = 0.3% by weight

<Comparative example 2>
Synthetic resin = PP, inorganic filler = talc, weight ratio = PP: talc = 45:55, water = 5% by weight

<Differences in individual conditions of Examples 1 to 4>
Example 1 is used as a reference. In Example 2, the weight ratio of the polypropylene-based resin is reduced and the polyethylene-based resin is added to Example 1. In Examples 3 and 4, the weight ratio of the polypropylene resin and the talc in the resin composition and the weight% of water in the hydrous melt were changed from those in Example 1, and the critical significance of the weight ratio was determined. It is also something to consider.

<Differences in individual conditions between Example 1 and Comparative Examples 1 and 2>
In Comparative Examples 1 and 2, the weight% of water in the hydrous melt was out of the range of 0.5% by weight to 3% by weight with respect to Example 1, and the critical significance of the above range was examined. But also.

<Evaluation result>
Table 1 shows the evaluation results of Examples 1 to 4 and Comparative Examples 1 and 2. For convenience of reference, the table also lists the individual conditions mentioned above. Each evaluation result in the above evaluation method is calculated by sampling arbitrary three points located on a predetermined straight line in the above TD and calculating the arithmetic mean value thereof.

<Discussion of Examples 1 to 4>
Comparing with reference to Example 1, in Example 2, the weight loss of the polypropylene-based resin was replaced with the polyethylene-based resin, and in Examples 3 and 4, the weight ratio of the polypropylene-based resin in the resin composition was increased. Even so, the evaluation was almost the same. On the other hand, in Example 4, when the weight ratio is out of the range of 85: 15 to 30:70, the weight% of water in the hydrous melt is in the range of 0.5 to 3% by weight with respect to Example 3. Even if there was, the formability of the sheet was evaluated as "Δ", which is formable but the unevenness of the mountain is uneven.

<Discussion of Comparative Examples 1 and 2>
The permissible range of% by weight of water in the hydrous melt is considered as 0.5% by weight to 3% by weight. In Comparative Example 1, when the weight% of water was set to be lower than the minimum value in the above allowable range, the foaming ratio of the foam was less than 4 times, and the thickness of the sheet became too thin outside the range of 500 μm to 3000 μm. Therefore, the state of the sheet was evaluated as "△", which is moldable but the above-mentioned unevenness is uneven, and "×", which is too hard to be bent as the ease of packing the packaging material for packaging. .. In Comparative Example 2, when the weight% of water was set to exceed the maximum value in the above allowable range, the foamed too much and a moldable sheet could not be obtained.

<Reference example>
For convenience of explanation, Table 2 shows the evaluation results of the tests conducted under conditions different from those of the comparative examples.

In Reference Example 1, although the composition and weight ratio of the resin composition are the same as those in Example 3, the layer structure of the sheet is 2 types and 3 layers (resin composition layer of polypropylene resin and talc / polypropylene foam layer / polypropylene). A resin composition layer of a based resin and talc) has a foaming ratio of less than 4 times, which makes it too hard for a sheet. In Reference Example 2, although the composition and weight ratio of the resin composition are the same as those in Example 1, when the foaming ratio of the foam is set to 1 (non-foaming), a hard sheet is obtained.

M extruder, S foam, 101 cylinder, 111 screw, 121 inlet, 131 die, 141 water injection part

Claims (6)

A step of heating a resin composition obtained by kneading at least a polyolefin resin and an inorganic filler to form a melt, and
A step of adding 0.5% by weight to 3% by weight of water to 100% by weight of the melt and further mixing to produce a hydrous melt.
A method for producing a polyolefin foam, which comprises a step of vaporizing the water contained in the hydrous melt to form a foam. The resin composition does not contain a chemical foaming agent and does not contain a chemical foaming agent.
The method for producing a polyolefin foam according to claim 1, wherein the foaming ratio of the foam to the resin composition is 4 times or more. The method for producing a polyolefin foam according to claim 1 or 2, wherein the weight ratio of the polyolefin resin to the inorganic filler is 85: 15 to 30:70. A step of heating a resin composition obtained by kneading at least a polyolefin resin and an inorganic filler to form a melt, and
A step of adding 0.5% by weight to 3% by weight of water to 100% by weight of the melt and further mixing to produce a hydrous melt.
A step of vaporizing the water contained in the hydrous melt to form a sheet-like foam having a thickness of 500 μm to 3000 μm, and
A method for producing a packaging material for packaging, which comprises a step of molding the sheet-shaped foam. A polyolefin foam in a state in which water in a hydrous melt containing at least a melt obtained by heating a resin composition obtained by kneading a polyolefin resin and an inorganic filler and water is vaporized.
The hydrous melt contains 0.5 to 3% by weight of the water with respect to 100% by weight of the melt.
The polyolefin-based resin contains a polypropylene-based resin and contains
The inorganic filler contains talc and contains
A polyolefin foam having a weight ratio of the polypropylene resin to the inorganic filler of 85: 15 to 30:70. A packaging material for food packaging formed of a sheet made of a polyolefin foam obtained by forming a sheet of the polyolefin foam according to claim 5.
The thickness of the polyolefin foam sheet is 500 μm to 3000 μm.
The bottom on which food is placed and
A packaging material for food products, which comprises a side wall portion provided continuously upward from the outer peripheral edge of the bottom portion.

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