JP2717579B2 - Mixed resin low density foam and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mixed resin low-density foam comprising a polyolefin-based resin and a polystyrene-based resin and a method for producing the same, and in particular, a buffer packaging material for easily damaged fruits and the like. And a method for producing the same.

[Prior art and its problems]

2. Description of the Related Art Conventionally, low-density polyethylene foams produced by extruding from a circular die with a foaming agent have been widely used as buffer packaging materials for easily scratched fruits and the like.
However, this kind of low-density polyethylene foam has a drawback that it is difficult to handle at the time of packaging work because of its low bending rigidity and poor shape retention. This is due to the maximum thickness in the manufacturing process.
It can be manufactured only about 6 mm and has a low flexural modulus.

As a method of obtaining a thick sheet, a foam extruded with a blowing agent from a circular die is formed into a balloon,
A common method is to press the inner surface of the balloon between the rolls. Since the low-density polyethylene foam has a low crystallization speed, the inner surface of the balloon is press-bonded according to the above method, and although a thick sheet is obtained temporarily, the thickness unevenness and corrugation easily occur, and the thick sheet having a uniform thickness is Could not be obtained.

Therefore, as a cushioning wrapping material having excellent cushioning property and bending rigidity, a low-density foam was bonded to a low-density polyethylene foam or a material having high bending rigidity such as a corrugated cardboard or expanded polystyrene sheet by secondary processing. Packaging materials are used. However, such packaging materials
Since it is manufactured by secondary processing, there is a disadvantage that the cost is high.

Although a foam made of high-density polyethylene alone is also known, a good foam cannot be obtained unless freon gas is used as a foaming agent, and thus has a problem of ozone layer destruction by freon gas.

The total amount of polystyrene resin and high-density polyethylene is 100 parts by weight of low-density polyethylene.
At a ratio of 10 to 60 parts by weight, and at a ratio of 6 to 40% by weight of the polystyrene-based resin with respect to the total amount of the polystyrene-based resin and the high-density polyethylene, after melt-kneading with a foaming agent under pressure, A method in which the foam is transferred to a low pressure zone to form a foam is also known (JP-B-51-41149).

Since the high-density polyethylene and the polystyrene-based resin are mixed in the mixed resin foam obtained by this method, the mixed resin foam exhibits a better flexural modulus than the low-density polyethylene foam. However, even with the above composition, thick unevenness, corrugation, etc. also occur, and a thick sheet having a uniform thickness cannot be obtained, so that a cushioning packaging material having sufficient bending rigidity cannot be obtained.

[Problem of the Invention]

The present invention overcomes the drawbacks of the conventional cushioning packaging material, and provides a foam suitable for an inexpensive cushioning packaging material having good bending rigidity and a method for producing the same, by suitable thickness and flexural modulus. Is the task.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a high-density polyethylene, a low-density polyethylene, and a polystyrene-based resin having a specific melt flow rate (hereinafter abbreviated as MFR) in a specific ratio. When using the mixed resin blended in the above, after melt-kneading under pressure with a low-boiling blowing agent, a balloon is formed from a circular die, transferred to a low-pressure zone, and the inner surface of the balloon is press-bonded between rolls to obtain a suitable thickness. (6 mm or more), it was found that a foam having a suitable flexural modulus and suitable as a cushioning packaging material could be obtained, and the present invention was completed.

That is, according to the present invention, there is provided a mixed resin foam comprising 20 to 60% by weight of high-density polyethylene, 20 to 40% by weight of low-density polyethylene and 20 to 40% by weight of a polystyrene resin. A mixed resin low-density foam characterized by having a density of less than 0.05 g / cm ^3, which is obtained by pressing a foam in an inner surface thereof.

According to the present invention, the high-density polyethylene, the low-density polyethylene and the polystyrene-based resin having an MFR of 5 g / 10 minutes or more are respectively 20 to 60% by weight, 20 to 40% by weight and 20 to 40% by weight.
At a rate of, was melt-kneaded with a low-boiling blowing agent under pressure, and transferred to a low pressure zone to form a balloon from a circular die, by crimping a balloon inner surface through between the rolls, a density of less than 0.05 g / cm ³ foam A method for producing a mixed resin low-density foam characterized by obtaining a body is provided.

The high-density polyethylene in the present invention, a polymer having a density in the normal temperature and pressure are mainly ethylene is 0.941~0.970g / cm ^3, a vinyl acetate, methacrylate, copolymerized with acrylates or propylene and other ethylene And a copolymer with a vinyl monomer. The high-density polyethylene used in the present invention preferably has an MFR in the range of 0.03 to 10 g / 10 minutes.

The low density polyethylene in the present invention, a polymer having a density in the normal temperature and pressure are mainly ethylene is 0.910~0.930g / cm ^3, a vinyl monomer of various copolymerizable with such and the ethylene Copolymers with the body are also included.
The low-density polyethylene used in the present invention preferably has an MFR in the range of 0.1 to 10 g / 10 minutes.

The polystyrene-based resin in the present invention is a polymer mainly composed of styrene, a copolymer of a styrene homopolymer and another vinyl-based monomer copolymerizable with styrene,
Furthermore, copolymers or mixtures with rubber-based polymers mainly composed of polystyrene, which are generally called impact-resistant polystyrene resins, or copolymers with diene-based monomers are also within the scope of the polystyrene-based resins of the present invention. It is included in. In the present invention, when an impact-resistant polystyrene resin is used as the polystyrene resin, the flexibility and elasticity of the obtained foam can be improved. In the present invention, polystyrene resins having an MFR of 5 g / 10 minutes or more are used. MFR is 5g / 10
If less than one minute is used, it becomes difficult to press the inner surface of the balloon-like foam.

The MFR referred to in this specification is measured by the method described in JIS K7210, and the condition 8 is used for a polystyrene resin and the condition 4 is used for a polyethylene resin.
Is adopted.

As the foaming agent used in the present invention, an aliphatic hydrocarbon, a halogenated hydrocarbon or Freon gas is used alone or in combination. Specific examples of the aliphatic hydrocarbon include, for example, propane, butane, isobutane, pentane, isopentane and the like, and examples of the halogenated hydrocarbon include chlorine- or bromine-substituted aliphatic hydrocarbons. In addition, chlorodifluoromethane, trifluoromethane, 1,2,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1,2,2 , 2-tetrafluoroethane, trichlorofluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,2,2,2-tetrafluoroethane and the like. In using the above foaming agent,
It is desirable to select a blowing agent having a boiling point range of −20 to 20 ° C. as a main component. In addition, as a foaming agent, a small amount (40% by weight or less) in aliphatic hydrocarbons and halogenated hydrocarbons
Is an effective method from the viewpoint of obtaining a low-density foam.

In the mixed resin of the present invention, the proportion of high-density polyethylene is 20 to 60% by weight, preferably 25 to 40% by weight, and the proportion of low-density polyethylene is 20 to 40% by weight, preferably 25 to 40% by weight.
% By weight and the proportion of polystyrene resin is 20-40% by weight,
Preferably it is 25 to 40% by weight. When the proportion of the high-density polyethylene is less than the above range, the mixing with the low-density polyethylene and the polystyrene-based resin becomes worse, and when the proportion is more than the above-mentioned range, a large shrinkage is observed in the obtained foam and repulsion occurs. The elasticity will also be impaired.

When the proportion of the low-density polyethylene is less than the above range, the recoverability of the obtained foam after compression becomes impaired.On the other hand, when the proportion is more than the above range, a surging phenomenon occurs, and the resin and the foaming agent mix well. No mixing occurs, making it difficult to obtain a low-density foam. If the proportion of the polystyrene resin is less than the above range, the shrinkage of the foam increases, and it becomes difficult to press the inner surface of the balloon-like foam. Conversely, if it is more than the above range, the compatibility with the polyethylene resin at the time of melt-kneading is poor, and the rigidity of the obtained foam is too high to be brittle, and the recovery after compression is also poor.

The proportion of the foaming agent used in the present invention is a mixed resin.
The amount is 1 to 40 parts by weight, preferably 10 to 25 parts by weight based on 100 parts by weight, and is appropriately determined depending on the desired density of the foam. When a foaming agent containing butane (normal: iso = 7: 3) as a main component is used, the mixing amount required to obtain a foam having a density of less than 0.05 g / cm ³ is usually 10
It may be 10 to 20 parts by weight with respect to 0 parts by weight.

In the present invention, a commonly used bubble nucleating agent may be used, if necessary. As the bubble nucleating agent, for example, an inorganic substance such as talc, or a chemical foaming agent such as decomposing at a temperature in an extruder to generate a gas,
Alternatively, an acid-alkali combination that reacts at the temperature to generate carbon dioxide gas, such as citric acid and sodium bicarbonate, or an alkali salt of citric acid and sodium bicarbonate. By adding these cell nucleating agents, the size of the cells of the obtained foam can be arbitrarily adjusted, and the flexibility and feel of the foam can be improved. Further, in the present invention, an anti-shrinkage agent may be added to the mixed resin, if necessary, in order to prevent the foaming agent from permeating the resin during foaming and to suppress shrinkage of the foam. As such, for example, polyoxyethylene monomyristate, polyoxypropylene monomyristate, polyoxyethylene monopalmitate, polyoxypropylene monopalmitate, polyoxyethylene monostearate, polyoxypropylene monostearate , Polyoxyethylene distearate,
Glyceride monolaurate, glyceryl monomyristate, glyceride monopalmitate, glyceride monostearate, glyceride monoarachiate, glyceryl dilaurate, glyceride dipalmitate,
Various aliphatic esters such as glyceride distearate, glyceride 1-palmit-2-stearate, glyceride 1-stearo-2-myristate, and glyceride tristearate are exemplified. In addition, a foam nucleating agent, an inorganic filler and the like can also be used.

The foam of the present invention can be produced using a conventional extrusion foam molding machine. That is, the mixed resin and the foaming agent are melt-kneaded in the pressurized cylinder of the extruder, the kneaded material is formed into a balloon from a circular die of the extruder, extruded into the atmosphere, and the inner surface of the balloon is compressed by passing between rolls. Thus, a plate-like foam can be obtained.

The foams of the present invention have a density of less than 0.05 g / cm ³ , with preferred foams having a density of 0.015 to 0.025 g / cm ³ . Expressed in terms of expansion ratio, the foam of the present invention exhibits an expansion ratio of at least 18 times.

〔The invention's effect〕

The foam of the present invention has a suitable thickness and flexural modulus,
It is preferable as an inexpensive cushioning packaging material having good bending rigidity.

By utilizing such properties, the foam of the present invention is advantageously used as a cushioning or cushioning material for packaging or transporting agricultural products, home appliances, glass and the like.

〔Example〕

 Next, the present invention will be described in more detail by way of examples.

Examples 1-3, Comparative Examples 1-6 High density polyethylene having a density of 0.958 g / cm ³ and MFR 0.3 (HDP
E), density of 0.923 g / cm ^3, low density polyethylene MFR0.26 (LDPE) and density 1.05g / cm ^3, MFR of polystyrene resin of the values shown in Table 1. The (PS), are shown in Table 1 In addition to using at a ratio, about 100 parts by weight of these resins were mixed with 1.0 part by weight of glyceryl monostearate as an anti-shrinkage agent,
A foaming agent butane (normal: iso = 7: 3) was added to this composition at a ratio shown in Table 1, and the mixture was melt-kneaded at a pressure of 200 kg / cm ² G in an extruder having a discharge rate of 18 kg / hr. The balloon was extruded from the circular die provided at the tip of the extruder at the temperature (foaming temperature) shown in Table 1 under atmospheric pressure to form a balloon, and the inner surface of the balloon was pressed between rolls to obtain a plate-like foam. .

With respect to the foam thus obtained, the density and thickness at room temperature after 7 days were measured, and the flexural modulus and compression residual strain were measured. Table 1 shows the results.

In addition, the measurement of the bending elastic modulus and the compression residual strain was performed according to the following method.

(1) Flexural modulus According to JIS K2703, test speed 10mm / min, sample shape
The test was performed at 150 × 25 mm, span 100 mm, and jig radius 5 mm.

(2) 50% compression residual strain After compressing a sample (size 50 × 50 mm) to 50% of the total thickness (A) (compression speed 10 mm / min), immediately remove the compression at the same speed as the compression, and reduce the stress to 0. It was calculated from the resulting thickness (B) and the original thickness (A).

From the results in Table 1, it can be seen that the foam of the present invention has excellent bending elasticity and recoverability after compression while having a very low density (low density) and a suitable thickness. I understand.

Claims (2)

(57) [Claims] 1. A high-density polyethylene of 20 to 60% by weight, a low-density polyethylene of 20 to 40% by weight and a polystyrene resin of 20 to 60% by weight.
A mixed resin foam consisting of 40% by weight, and the foam is obtained by compressing a balloon-like foam on the inner surface at 0.05 g / cm.
A mixed resin low-density foam having a density of less than ³ . 2. A high-density polyethylene, a low-density polyethylene and a polystyrene resin having a melt flow rate of 5 g / 10 minutes or more, respectively, in an amount of 20 to 60% by weight, 20 to 40% by weight and 20 to 40% by weight, respectively. was melt-kneaded under pressure with a blowing agent having a boiling point, was transferred to a low pressure zone to form a balloon from a circular die, by crimping a balloon inner surface through between the rolls, to obtain a foam density of less than 0.05 g / cm ³ A method for producing a mixed resin low-density foam.