JPH01254742A - Production of foamed polyethylene resin - Google Patents

Abstract

PURPOSE:To continuously produce a highly expanded foamed material containing uniform and fine cells and large thickness, by compounding a polyethylene resin with a mixture of a carbon dioxide foaming agent and an ester and extrusion-foaming the composition. CONSTITUTION:The objective foamed material can be produced by compounding (A) 1kg of a polyethylene resin with a mixture of (B) a foaming agent consisting of 0.1-0.5mol of carbon dioxide and 0.5-2.5mol of an easily volatile organic foaming agent having a saturated vapor pressure of <=30kg/cm<2> at 100 deg.C (e.g., butane or dichlorotetrafluoroethane) and (C) 0.1-2.0 pts.wt. (based on 100 pts.wt. of the resin) of a higher fatty acid ester of a polyhydric alcohol (preferably glycerol partial ester) and extruding the obtained composition with an extruder in molten state. The obtained foamed material is a closed-cell foam containing uniform and fine cells, having excellent flexibility and appearance and low heat-conductivity and moisture-permeability, useful as a cushioning material, heat-insulation material, decorative material, etc., and suitable for the production of a highly expanded material having a density of 0.1-0.02g/cm<3> or a board having a thickness of >=20mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing polyethylene resin foam,
In particular, a method of continuously producing a thick polyethylene resin foam having highly foamed uniform fine cells with a density of 0.1 to 0.01 g/cd by extruding and foaming non-crosslinked polyethylene resin. Regarding.

(Prior art) Polyethylene resin foams have been used in a variety of fields in recent years, but in general, fine cells are preferred;
In particular, foams having uniform, fine cells are strongly desired for use in cushioning materials, heat insulating materials, decorative materials, and the like. The reasons for this are that first, as a cushioning material, the finer the air bubbles, the better the cushioning properties.As for insulation materials, the finer the air bubbles, the lower the thermal conductivity and superior insulation performance. As for materials, the finer the cells, the more beautiful the appearance of the surface and cut surface.

As a method to continuously obtain highly foamed polyethylene resin having uniform and fine cells, it is possible to mix peroxide with polyethylene resin, or to perform a cross-linking reaction on polyethylene resin by irradiating it with electron beams. There is a cross-linking foaming method in which foaming is carried out after foaming. Although it is true that a foam with fine cells can be obtained, the foaming process is complicated and the equipment cost is high. can't get it.

Separately, as a method for obtaining anything from a thin sheet to a thick plate with a simple process, polyethylene resin and a foaming agent are melt-mixed in an extruder to form a fluid gel.
There is a so-called extrusion foaming method in which foaming is performed by extrusion into a low pressure region. However, although this method can efficiently produce a thick foam, it has the disadvantage that the cells are larger in size than those obtained by crosslinking and foaming.

Furthermore, attempts have been made to use carbon dioxide for extrusion foaming of polyethylene resins. One is a thermally decomposable blowing agent that reacts and decomposes to generate carbon dioxide when heated in an extruder, such as carbonates such as sodium bicarbonate, sodium carbonate, and potassium carbonate, and organic acids such as citric acid and tartaric acid. This is a method of mixing resin with resin in advance and extruding it. This is a very simple method and is suitable for producing fine-celled, low-foamed products with a product density of 0.4 g/aJ or less. However, higher foams, especially product density of 0.1g/aj! Obtaining the following products involves the following problems and is generally not possible using this method.

Firstly, if a pyrolytic blowing agent is mixed in in an amount sufficient to generate sufficient carbon dioxide to obtain a highly foamed product, it is difficult to completely decompose it in the extruder, and as a result, undecomposed residue remains. Odors and coloring may remain on the product. Secondly, the decomposition products accumulate at the tip of the extrusion mold, contaminating or damaging the product surface, which requires frequent cleaning. Thirdly, bubbles tend to burst during foaming, making it difficult to obtain a good foam.

Another method disclosed is a method in which a small amount of a substance that generates carbon dioxide is added to the polyethylene resin as a cell regulator. For example, in Japanese Patent Publication No. 46-8587, in order to make the cells of a polyethylene foam extremely fine and homogeneous, and to produce a polyethylene foam with excellent elasticity and heat insulation properties and a beautiful appearance, propane , a method using a small amount of a foam control agent consisting of a three-component mixture of an acid salt, carbonate or bicarbonate of a polyhydric carboxylic acid, and a fatty acid monoglyceride in addition to an organic foaming agent such as butane has been proposed. When using a foam regulator that generates carbon dioxide, the foam regulator decomposes due to moisture in the air and the raw material composition varies and is not constant until it is fed to the extruder. Unevenness occurs in the foam density and the size of the bubbles, and as described above, unfavorable conditions occur due to decomposition residues and decomposition products.

(Problems to be Solved) The present invention solves these drawbacks, and as a result of intensive research to obtain a highly foamed polyethylene resin material, especially a thick plate-like material, having uniform, fine cells, carbon dioxide is used as a blowing agent. The present invention was completed by discovering that even if the extrusion foaming method is used within a limited range, a foam with uniform and fine cells comparable to that of the crosslinking foaming method can be obtained. The object of the present invention is to provide a method for continuously producing a thick foam having highly foamed and uniformly fine cells by extruding and foaming a polyethylene resin.

(Means for Solving the Problems) That is, the present invention provides a method for manufacturing a foam by extrusion foam molding a polyethylene resin, in which 0.1 to 0.5 mol of carbon dioxide per 1 kg of the polyethylene resin is used. , a blowing agent consisting of 0.5 to 2.5 moles of an easily volatile organic blowing agent having a saturated vapor pressure of 30 kg/cd or less at a temperature of 100°C, and 0 higher fatty acid ester of polyhydric alcohol per 100 parts by weight of resin. .1 to 2.0 parts by weight is extruded from an extruder in a molten state to form a foam.

In the present invention, polyethylene resins include not only ethylene homopolymers, but also copolymers mainly composed of ethylene with other vinyl monomers, or polyethylene resins mixed with other thermoplastic resins, natural rubber, or synthetic rubber. In particular, the present invention is suitable for using low density polyethylene.

One key point of the present invention is to use a mixture of carbon dioxide and another easily volatile organic blowing agent as a blowing agent for polyethylene resin. A highly foamed product cannot be obtained using carbon dioxide alone, and a highly foamed product can be obtained when a readily volatile organic blowing agent such as dichlorotetrafluoroethane, which is commonly used as a foaming agent for polyethylene resins, is used alone. ,
It is not possible to obtain a product with uniform fine bubbles. The blowing agent used in combination with carbon dioxide must have a relatively low vapor pressure at the foaming temperature of the polyethylene resin. If a foaming agent with high vapor pressure is used, the cell membrane will not be able to withstand the vapor pressure during foaming, and the cells will be destroyed and become interconnected. Therefore, in order to obtain a foam with good closed cells, it is necessary to Saturated vapor pressure is 30kg/a
Equivalent organic blowing agents include butane, pentane, dichlorotetrafluoroethane, monochlorodifluoroethane, digloromonofluoromethane, trichloromonofluoromethane, etc., but particularly preferred are butane and dichlorotetrafluoroethane. By using carbon dioxide and the above blowing agent in combination, a polyethylene resin foam having extremely uniform and fine closed cells can be obtained. Although the reason for this bubble refinement is not clear, it is presumed as follows. That is, in order to obtain uniform and fine bubbles, it is necessary to generate as many bubble nuclei as possible in the resin. Carbon dioxide alone does not dissolve much in polyethylene resin, but
Butane, etc. in which carbon dioxide is dissolved dissolves well in polyethylene resin. Therefore, carbon dioxide in the extruder is dissolved in butane, etc., and dissolved in a polyethylene resin having a high resin pressure in an integrated state. The resin pressure decreases as the resin with the blowing agent dissolved advances from the extruder to the mold, and as the pressure is released, the solubility of carbon dioxide in butane etc. decreases, and eventually supersaturated carbon dioxide It is expected that carbon dioxide will dissociate from the resin, expel the molten resin, and generate bubble nuclei, but since carbon dioxide has a high solubility in butane etc., the generation of bubble nuclei occurs when the resin is discharged from the mold. This occurs just before the bubble nuclei disperse into large numbers without meeting each other.

As a result, uniform fine bubbles are formed.

In the present invention, the blowing agent used is 0.1 to 0.5 mole of carbon dioxide and 0.5 to 2.5 mole of an easily volatile organic blowing agent used in combination with respect to 1 kg of polyethylene resin. If the amount of carbon dioxide used is less than 0.1 mol, the effect of making the cells finer is weak, and if it is more than 0.5 mol, the cells of the foam tend to become interconnected, which is undesirable. In order to sufficiently dissolve carbon dioxide, it is necessary to have an amount equal to or more than 2.5 moles of carbon dioxide, and if it is more than 2.5 moles, cavities are likely to be formed in the foam, which is not preferable.

Another key point of the present invention is the use of higher fatty acid esters of polyhydric alcohols. Examples of polyhydric alcohols include glycerin, pentaerythritol, sorbitol, mannitol, mannitane, dipentaerythritol, diglycerin, and the like. Higher fatty acids include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid,
Included are saturated or unsaturated higher fatty acids having 10 to 30 carbon atoms, such as linoleic acid, or beef fatty acids containing these higher fatty acids, essential oil fatty acids, coconut oil fatty acids, and the like. In the present invention, compounds in which these polyhydric alcohols and higher fatty acids are ester bonded are used.

Partial esters in which at least one hydroxyl group remains in one molecule are preferred, and glycerin partial esters represented by the following general formula are particularly preferred.

(I) (n) (m) (IV
) (In the formula, R is a C1° to C!4 alkyl or hydroxyalkyl group) Examples of esters that can be used include lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, pentaerythritol monocaprate, and pentaerythritol monoglyceride. Slit monooleate, pentaerythrit monolaurate, dipentaerythrit distearate.

These include sorbitan monooleate, sorbitan sesqui essential oil fatty acid ester, sorbitan monopalmitate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, mannitan monolaurate, and the like. These fatty acid esters of polyhydric alcohols are used in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the polyethylene resin. The higher fatty acid ester of polyhydric alcohol has the effect of suppressing the shrinkage and expansion of the foam after extrusion molding, as well as the effect of adjusting the viscosity of the molten resin. When extrusion molding is performed using carbon dioxide, which has a small solvent capacity for polyethylene resin, it has no plasticizing effect on the resin, making it difficult to adjust the viscosity of the resin to the appropriate range for foaming in the extruder. Therefore, it becomes necessary to reduce the extrusion rate or use a special extruder.

However, when a higher fatty acid ester of a polyhydric alcohol such as stearic acid monoglyceride is added, the viscosity of the resin can be easily adjusted, and extrusion molding can be performed using an ordinary extruder without reducing the throughput. However, if it is added in excess, slippage will occur during the transfer of the resin within the extruder, making it impossible to ensure a constant extrusion amount. A suitable amount is 2.0 parts by weight.

Further, it is preferable that at least one hydroxyl group remains in the ester because it exhibits antistatic ability that is not exhibited by a complete ester. FIG. 1 shows the relationship between the surface resistivity of the foam and the amount of stearic acid monoglyceride added. In addition, the density of the foam in this case is 0.3
8 g/crl. From this figure, it is necessary to add at least 0.5 parts by weight per 100 parts by weight of resin in order to impart antistatic ability (I x 1013 Ω or less) to the polyethylene foam.

The polyethylene resin foam obtained by the method of the present invention is a closed cell foam having uniform fine cells,
Superior flexibility, aesthetics, and thermal conductivity compared to foams obtained by conventional extrusion molding methods.

It has low moisture permeability and is suitable for use as cushioning materials, heat insulating materials, decorative materials, etc. Especially the density is 0.1~0.02g/a
+? It is suitable for producing highly foamed bodies and plate-like bodies with a thickness of 20 m+a or more.

The method for producing a polyethylene resin foam according to the method of the present invention can be carried out by a conventionally known method using an ordinary extruder. That is, for example, a small amount of inorganic fine powder such as talc and higher fatty acid ester of polyhydric alcohol are added to a polyethylene resin, mixed, and fed to an extruder, and separately, carbon dioxide and a volatile blowing agent are forced into the extruder from the middle of the extruder. Then, mix these resins and additives well and add 100 to 150
A foam is obtained by extruding into the atmosphere from a mold heated to ℃. Note that the blowing agent may be carbon dioxide and a readily volatile organic blowing agent used in combination with the carbon dioxide, which may be separately pressurized.
It is preferable to mix the two in advance and dissolve them in a blowing agent that uses carbon dioxide together, and then press the mixture into an extruder.

Next, examples of the present invention and comparative examples will be shown together to further clarify the detailed description of the present invention.

(Example 1) Polyethylene (MIIO23, density 0.920 g/ad
, melting point 115° C.) and 0.3 parts by weight of finely powdered talc were mixed and fed into the first extruder from the hopper of the extruder. Starting from this supply section, the extruders are heated to a maximum of 200°C, and the resin temperature is adjusted to 110°C in the second extruder.
The mold at the tip was also set at about 110°C. On the other hand, as blowing agents, 0.18 mol of carbon dioxide and 1.04 mol of dichlorotetrafluoroethane were press-injected into the first extruder from the middle of the first extruder.

Separately, 1.0 parts by weight of stearic acid monoglyceride per 100 parts by weight of the base resin is supplied into the resin, and the mixture is melt-mixed and sent to the tip of the extruder by a screw. The mixed resin was extruded into the atmosphere through a mold having a 1.5 mm x 300 mm slit-shaped extrusion port provided at the tip of the extruder to obtain a polyethylene plate foam having an average thickness of 40 mm and a width of 550 mm.

(Examples 2 to 4) Polyethylene plate-shaped foams were manufactured using the same resin and equipment as in Example 1, and according to the primary formulation. The obtained foam was as shown in Table 1.

(Comparative Examples 1 to 4) Foamed bodies were produced in the same manner as in Example 1, except that a blowing agent having a type of blowing agent or a blowing agent having a ratio outside the range specified by the present invention was used. The results are shown in Table 1 as a comparative example.

Table 1 In the above table, O means extremely good, O means good, Δ means average, and × means not good. Also, what is open cell ratio?
It means the volume ratio occupied by communicating cells to the foam volume.

For example, the following can be well understood from Table 1 above. In the case of Comparative Example 1, in which dichlorodifluoromethane, which has a high saturated vapor pressure of 34.1 kg/cJ at a temperature of 100° C., was used as an easily volatile organic blowing agent used in combination with carbon dioxide, the bubbles were coarse and interconnected. The properties of the foam are not good. In addition, in Comparative Example 2 in which dichlorotetrafluoroethane was used alone without using carbon dioxide as the blowing agent, a closed-cell foam was obtained, but the cells were coarser than in Examples 1 and 2. Therefore, it has high thermal conductivity and moisture permeability.

Also, carbon dioxide is added to 1 kg of polyethylene resin at 0
．． In the case of Comparative Example 3 in which 5 mol or more was used, and in the case of Comparative Example 4 in which higher fatty acid ester of polyhydric alcohol was not added,
In both cases, the load during extrusion was large, the extrusion conditions were unstable, and good foams could not be obtained. In particular, in Comparative Example 3, there were many large cavities in the foam, and in Comparative Example 4, the foam contracted significantly immediately after extrusion, and even after being left for 10 days, it did not return to its original dimensions immediately after extrusion, and there were dents on the surface. 6 Also, the surface specific resistance value (Ω
) was 1.6×10”Ω.

(Example 5) Polyethylene (MIIO23, density 0.920 g/cd
, melting point 115°C) was mixed with 0.3 parts by weight of finely powdered talc, and the mixture was supplied into the extruder from the hopper of the extruder. The extruder is sequentially heated to a maximum of 200°C from this feed section, and the mold at the tip of the extruder is set at about 110°C. On the other hand, as a blowing agent, 0.89 mol of dichlorotetrafluoroethane and 0.30 mol of carbon dioxide were pressed into the extruder per 1 kg of resin, and separately, 1 mol of stearic acid monoglyceride was added to 100 parts by weight of resin. .5 parts by weight were supplied into the resin, and these were sufficiently melted and mixed in the extruder, and L, 5 mm + X 30 was provided at the tip of the extruder.
Extruded from a mold with a 0non slit-shaped extrusion port and foamed in a shaping device to an average thickness of 40 mm and a width of 550 mm.
A polyethylene plate-shaped foam having a diameter of mm was obtained.

(Example 6) The amount of stearic acid monoglyceride added was 0.6 parts by weight per 100 parts by weight of the resin, and the foaming agent was used as the resin Example 5.
An extruded polyethylene plate-shaped foam was obtained in the same manner as described above.

(Comparative Example 5) Carbon dioxide was not used as a blowing agent, and 1.
An extruded polyethylene plate foam was obtained in the same manner as in Example 5 except that only 17 mol of dichlorotetrafluoroethane was used.

(Comparative Example 6) An extruded polyethylene plate foam was obtained in the same manner as in Example 5 except that only 1.80 mol of butane was used per 1 kg of resin as a blowing agent.

The properties of the foams obtained in Examples 5 and 6 and Comparative Examples 5 and 6 are shown in Table 2. In addition, in Table 2, the foaming agent is Resin 1.
Moles per kg, stearic acid monoglyceride are parts by weight based on 100 parts by weight of resin.

Table 2 In Table 2, the amount of remaining blowing agent is determined by gas chromatography to quantify the amount of blowing agent contained in the foam resin that has been left in a constant temperature room at 20°C for 10 days after extrusion. The punching deformation amount is the value converted to the value of
The sample was punched into a size of a+m x 200 mm, and the rate of change in volume was measured 24 hours later, and expressed as an absolute value.

As seen in Table 2, in both Examples 5 and 6, foams with uniform fine cells and excellent antistatic properties and processing stability were obtained, but the foam of Comparative Example 5 was 20
Even after being left at 10°C for 10 days, the punched product showed significant shrinkage and peculiar deformation when punched. Furthermore, although the foam of Comparative Example 6 had excellent antistatic properties and processing stability, it had coarse cells, lacked cushioning properties, and had a poor appearance.

As mentioned above, the polyethylene resin plate-shaped foam obtained by using stearic acid monoglyceride does not attract dust during storage due to static electricity, or resin powder generated during processing. ,
When used as packaging material, it will not stain or damage the contents. In addition, after extrusion, it becomes a foam with excellent processing and dimensional stability in a short period of time, which reduces storage space, greatly shortens inventory periods, and has great industrial value.
Since it is a foam with uniform microcells that could not be obtained conventionally, it has excellent cushioning properties and has low thermal conductivity and moisture permeability, making it suitable for use in fields such as cushioning materials, heat insulation materials, and moisture-proofing materials. .

(Effects) As described above, in the method of manufacturing a foam by extrusion foam molding a polyethylene resin, carbon dioxide is used as a blowing agent and the saturated vapor pressure at a temperature of 100°C is 30 kg/
By using a readily volatile organic blowing agent of aJ or less in a specific ratio and adding a higher fatty acid ester of polyhydric alcohol, a thick material with uniform fine bubbles can be produced as shown in Table 1. A foam can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the relationship between the amount of stearic acid monoglyceride added to a foam and the surface resistivity value of the obtained foam. Applicant Sekisui Plastics Co., Ltd.

Claims (1)

[Claims] 1 In a method of manufacturing a foam by extrusion foam molding a polyethylene resin, 0.1 to 0.5 mol of carbon dioxide per 1 kg of polyethylene resin and a saturated vapor pressure of 30 kg/cm^2 at a temperature of 100°C. A mixture consisting of a blowing agent consisting of 0.5 to 2.5 moles of the following easily volatile organic blowing agent, and 0.1 to 2.0 parts by weight of higher fatty acid ester of a polyhydric alcohol per 100 parts by weight of the resin. A method for producing a polyethylene resin foam, which comprises extruding the polyethylene resin foam in a molten state from an extruder to obtain a foam.