JP2623136B2 - 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.

(Prior art and its problems) Conventionally, in order to obtain a mixed resin foam of a polyolefin-based resin and a polystyrene-based resin, a polystyrene-based resin and a high-density polyethylene resin are mixed with 100 parts by weight of a low-density polyethylene resin. The total amount is 10 to 60 parts by weight, and the polystyrene resin is 6 to 40% by weight based on the total amount of the polystyrene resin and the high-density polyethylene resin.
A method is known in which the mixture is melt-kneaded together with a foaming agent under pressure at a ratio of as follows, and then transferred to a low-pressure zone to form a foam (JP-B-51-41149).

The mixed resin foam obtained by this method has the advantage that there is no shrinkage after molding, and it is flexible and highly elastic. However, in the case of this conventional method, it is difficult to obtain a low-density foam, and even the lowest-density foam has a density of about 0.03 g / cm ³ .

According to the present inventors, 0.03 g /
It has been found that the foam shrinks significantly when trying to obtain a foam having a density less than cm ³ .

On the other hand, in order to obtain a low-density foam mainly composed of a polyolefin-based resin, a method is known in which high-density polyethylene and freon gas as a foaming agent are melt-kneaded and then transferred to a low-pressure zone. However, in this conventional method, in order to obtain a low-density foam, 1,2-dichloro-1,1,1 is used as a blowing agent.
It is necessary to use 2,2-tetrafluoroethane or / and 1,1,2-trichloro-1,2,2-trifluoroethane (because other foaming agents result in a foam having a large shrinkage). ), The problem of chlorofluorocarbon pollution was inevitable.

(Problems to be Solved by the Invention) The present invention overcomes the above-mentioned drawbacks of the conventional foam, enables the use of various foaming agents, and has a low density, a small shrinkage, and an excellent rebound resilience. An object of the present invention is to provide a foam and a method for producing the foam.

(Means for Solving the Problems) The present inventors have conducted intensive studies to solve the above problems, and as a result, when using a mixed resin in which high-density polyethylene, low-density polyethylene and polystyrene-based resin are blended in a specific ratio, It was found that a low-density, high-foamed product with very high expansion ratio, very small shrinkage, and excellent rebound resilience can be obtained without using a fluorocarbon gas having a high ozone layer destruction ability as a foaming agent. The invention has been completed.

That is, according to the present invention, high density polyethylene 40 ~
A mixed resin foam comprising 85% by weight, 5 to 30% by weight of low density polyethylene and 5 to 40% by weight of a polystyrene resin, having a density of less than 0.03 g / cm ^3. A foam is provided.

Further, according to the present invention, high-density polyethylene, low-density polyethylene and polystyrene-based resin, each 45 ~
85 wt%, in a proportion of 5 to 30 wt% and 5 to 40 wt%, was melt-kneaded under pressure with a low-boiling blowing agent, transferred to a low pressure zone to obtain a foam density of less than 0.03 g / cm ³ A method for producing a mixed resin low-density foam 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 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 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, which is preferable.

As the blowing agent used in the present invention, an aliphatic hydrocarbon, a halogenated hydrocarbon, or a Freon gas having one or more hydrogen atoms in a molecule is used alone or in combination. Specific examples of the aliphatic hydrocarbon, for example, propane, butane,
Examples include isobutane, pentane, and isopentane. Examples of the halogenated hydrocarbon include a chlorine- or bromine-substituted aliphatic hydrocarbon. In addition, chlorodifluoromethane, trifluoromethane, 1,2,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane include chlorodifluoromethane, trifluoromethane, 1-chlorofluoromethane having one or more hydrogen atoms in the molecule. And 1-chloro-1,2,2,2-tetrafluoroethane. It is desirable to select a foaming agent having a boiling point range of −20 to 20 ° C. as a main component. Particularly, in the present invention, isobutane is preferably used. Isobutane has a low gas permeation rate to the resin and is suitable as a foaming agent for obtaining a foam having a high expansion ratio. Of course, as the blowing agent in the present invention, if the social environment allows, for example, trichlorochloromethane, dichlorodifluoromethane, 1,2-dichloro-1,
Although it is possible to use Freon gas such as 2,2,2-tetrafluoroethane, in the case of the present invention, even without using the expensive and highly polluting Freon gas, the extremely low-density foam as described above can be used. Obtainable. However, as a blowing agent, a small amount (40%) is added to aliphatic hydrocarbons and halogenated hydrocarbons.
Mixing the CFC gas (by weight% or less) 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 40 to 85% by weight, preferably 50 to 70% by weight, and the proportion of low-density polyethylene is 5 to 30% by weight, preferably 15 to 25% by weight.
% By weight and the proportion of polystyrene resin is 5 to 40% by weight,
Preferably it is 15 to 25% by weight. If the proportion of the high-density polyethylene is less than the above range, it is difficult to obtain a low-density foam, and if it exceeds 85% by weight, a large shrinkage is observed in the obtained foam and rebound resilience is obtained. Will also be spoiled. If the proportion of the low-density polyethylene is less than the above range, the rebound resilience of the obtained foam will be impaired, while if it exceeds the above range, a surging phenomenon will occur and the resin and the foaming agent will not mix well, It becomes difficult to obtain a low density foam. When the proportion of the polystyrene resin is less than the above range, the shrinkage of the foam becomes large, while when it exceeds the above range, the compatibility with the polyethylene resin is inferior at the time of melt-kneading, and the rigidity of the obtained foam is too high. It becomes brittle and has poor rebound resilience.

The proportion of the foaming agent used in the present invention is a mixed resin.
The amount is 7 to 40 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight, and is appropriately determined depending on the desired density of the foam. When using those composed mainly of isobutane as the blowing agent, mixing amount required to obtain a foam density of less than 0.03 g / cm ³ is 10 to 20 parts by weight based on the mixed resin 100 parts by weight Good.

In the present invention, a commonly used bubble nucleating agent may be used, if necessary. As the cell nucleating agent, for example, an inorganic substance such as talc, a chemical foaming agent which decomposes at a temperature in the extruder to generate gas, or an acid-alkali which reacts at the temperature to generate carbon dioxide gas Combinations, such as citric acid and sodium bicarbonate, alkali salts of citric acid and sodium bicarbonate. By adding these cell nucleating agents, the size of the cells of the foam obtained 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. Such things include, for example,
Polyoxyethylene monomyristate, polyoxypropylene monomyristate, polyoxyethylene monopalmitate, polyoxypropylene monopalmitate, polyoxyethylene monostearate, polyoxypropylene monostearate, polyoxyethylene distearate, monourarin Acid glyceride, monominostinic acid glyceride, monopalmitic acid glyceride, monostearic acid glyceride, monoarachiic acid glyceride, dilauric acid glyceride, dipalmitic acid glyceride, distearic acid glyceride, 1-palmito-
Various aliphatic esters such as 2-stearic acid glyceride, 1-stearo-2-myristic acid glyceride, and tristearic acid glyceride 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 or a foaming apparatus having a structure in which an accumulator is connected to the extruder. That is, the mixed resin and the foaming agent are melt-kneaded in a pressure cylinder of an extruder, and the kneaded product is extruded from a die of the extruder to an atmospheric pressure to obtain a foam. Alternatively, the melt-kneaded material in the pressurized cylinder may be once extruded into an accumulator under pressurized conditions, and then extruded to atmospheric pressure through a die by a piston. The shape of the foam can be any shape such as a sheet, a block, a column, and a tube.

Foams of the present invention are those having a density less than 0.03 g / cm ^3, preferably foam having 0.02~0.01g / cm ³ density. Expressed in terms of expansion ratio, the foam of the present invention shows a high expansion ratio of at least 40 times or more.

(Effect of the Invention) The foam of the present invention has very low density, very low shrinkage (10% or less), and is flexible and excellent in rebound resilience.

The foam of the present invention takes advantage of such properties to provide a heat insulating material for buildings (particularly one used by pressing between pillars), and a cushioning or cushioning material for packaging or transporting home appliances, glass, pottery, and the like. It is advantageously used as such.

(Example) Next, the present invention will be described in more detail with reference to examples.

Examples 1-4, Comparative Examples 1-4 Density 0.958 g / cm ³ High density polyethylene (HDPE), density 0.
Low density polyethylene 923g / cm ³ (LEPE) and density 1.05 g /
A polystyrene resin (PS) of cm ³ was used in the proportions shown in Table 1, and 100 parts by weight of these resins were mixed with 1.0 part by weight of glyceride monostearate as an anti-shrinkage agent. The amount of blowing agent shown
After melt-kneading at a pressure of 170 kg / cm ² G in a 10 kg / hr extruder, the mixture was once extruded into an accumulator. Next, this accumulator (from a pressure of 40 kg / cm ² G, the melt-kneaded product was passed through a die provided in the accumulator at a temperature (foaming temperature) shown in Table 1 at a discharge speed of 620 kg / hr, and the pressure was reduced to atmospheric pressure. After discharging, a plate-like foam was obtained.

The density and thickness of the foam thus obtained at room temperature after 7 days were measured, and the shrinkage of the foam was calculated by the following equation. Table-
It is shown in FIG.

A: Volume of foam immediately after discharge B: Volume of foam after 7 days Examples 5, 6 and Comparative Example 5 HDPE, LDPE and PS shown in Examples 1 to 4 are used in proportions shown in Table 1. With 100 parts by weight of these resins, 1.0 part by weight of monostearic acid glyceride was added as a shrinkage-preventing agent.
After melt-kneading at a pressure of 200 kg / cm ² G in an extruder with a discharge rate of 150 kg / hr, it was extruded to atmospheric pressure at the temperature (foaming temperature) shown in Table 1 from an annular die provided at the tip of the extruder. Next, the tubular foam was cut out from one end in the extrusion direction to obtain a sheet-like foam.

The density and thickness of the foam thus obtained at room temperature after 7 days were measured, and the shrinkage of the foam was determined by the above equation. Table 1 shows the results.

In addition, the code | symbol shown about the foaming agent in a table | surface means the following content.

CFC114: 1,2-Dichloro-1,1,2,2-tetrafluoroethane CFC22: Chlorodifluoromethane CFC142b: 1-Chloro-1,1-difluoroethane (Effects of the Invention) As can be seen from the results shown in Table 1, the foam of the present invention has an extremely low density (low density) but a very low shrinkage. Further, the foam of the present invention shows excellent rebound resilience, which is 0.5 to 1 kg / c.
Even if the load is removed after pressing with a load of m ^2, the residual strain is extremely small.

On the other hand, when the amount of the high-density polyethylene in the foam of the comparative example is too small (Comparative Examples 1 and 2)
, A surging phenomenon is observed during the production thereof, the resin and the foaming agent are separated, and the foam cannot be uniformly mixed into the resin. In addition, when the blending of the high-density polyethylene resin is too large (Comparative Example 3) and when the polystyrene resin is not blended (Comparative Example 4), the shrinkage of the foam is large in each case, and the foam having practical utility is obtained. I can't get it. Furthermore, even when the blending amount of the low-density polyethylene resin is too large (Comparative Example 5), a surging phenomenon is observed at the time of production, and a practical foam cannot be obtained.

Claims (3)

(57) [Claims] 1. A high-density polyethylene of 40 to 85% by weight, a low-density polyethylene of 5 to 30% by weight, and a polystyrene resin of 5 to 30% by weight.
40% by weight of a mixed resin foam, 0.03 g / cm ³
A mixed resin low-density foam characterized by having a density of less than or equal to. 2. A high-density polyethylene, a low-density polyethylene and a polystyrene-based resin, each containing 45 to 85% by weight,
In a proportion of 30 wt% and 5 to 40 wt%, it was melt-kneaded under pressure with a low-boiling blowing agent, transferred to a low pressure zone, characterized in that to obtain a foam density of less than 0.03 g / cm ³ A method for producing a mixed resin low-density foam. 3. The method according to claim 2, wherein said foaming agent contains isobutane as a main component.