JPS6055290B2 - Method for manufacturing polyethylene foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing polyethylene foam.

Conventionally, as a method for foaming a thermoplastic resin, a method is known in which a thermoplastic resin and a volatile liquid are mixed under high pressure and extruded into a low pressure zone to foam.

However, in this method, when polyethylene is foamed, most of the cells in the foam are independent, and they are completely impermeable to applications that require air permeability, such as filters. The inventor is
As a result of intensive research into ways to improve these shortcomings,
By specifying the melt index, mixing ratio, and extrusion temperature of low-density polyethylene and high-density polyethylene, we have discovered a method that can produce polyethylene foam in which most of the cells are connected.

That is, the gist of the present invention is to combine high-density polyethylene with a melt index of 10 or more and low-density polyethylene with a melt index of 1 or less, with a content of high-density polyethylene of 1.9.
53.5 p-O,, amount % or more, p-O, 'amount % or less (
A volatile organic liquid with a boiling point of 100°C or less under normal pressure is mixed with a mixed resin so that ρ is the density of high-density polyethylene), and the mixture is heated to a temperature higher than the melting point of low-density polyethylene. The present invention relates to a method for producing polyethylene foam, which comprises cooling to a temperature 10° C. lower than the melting point of high-density polyethylene, and then extruding it into a low-pressure zone.

High-density polyethylene (hereinafter referred to as HDPE) used in the present invention
) refers to polyethylene that is an ethylene homopolymer or a copolymer of ethylene and a small amount of other monomers, and has a density of O, 940y/cc or more as measured according to JIS 6760.

In the present invention, among the HDPEs, those having a melt index (hereinafter referred to as ?1) of 10 or more are selectively used. Furthermore, the low-density polyethylene (hereinafter referred to as LDPE) used in the present invention is an ethylene homopolymer or a copolymer of ethylene and a small amount of other monomers, and has a density of 0.930 Da as measured by JIS 6760. /
Refers to polyethylene of cc or less.

In the present invention, among the LDPEs, those having an MI of 1 or less are selectively used. Further, the volatile organic liquid used in the present invention is an organic liquid having a boiling point of 100°C or less under normal pressure, and examples thereof include aliphatic hydrocarbons such as propane, butane, and pentane, dichlorodifluoromethane, and dichlorotetrafluoroethane. , halogenated hydrocarbons such as trichloromonofluoromethane, and the like.

In order to produce a polyethylene foam in which most of the cells are connected by the method of the present invention, first, I-[DP
The volatile organic liquid is mixed under high temperature and high pressure into a mixed resin in which E and LDPE of less than MII are mixed such that the content of HDPE is greater than T% and less than H%.

As mentioned above, in the present invention, HDPE and LDPE (7
) MI is specified because HDPE (7) When the MI is less than 1 or when the MI of LDPE is larger than 1, the MI is specified so that 50% or more of the cells in the obtained foam are connected.
U) This is based on the fact that it has been found through various experiments that increasing the mixing ratio of PE causes non-uniformity of cells and makes it impossible to obtain a good foam. The reason for this is not clear, but
At the resin temperature when extruded to the low pressure zone, HDPE is in a solid state, and in FIDPE with an MI of less than 1, the strength of the bubble membrane was too large to be sufficiently foamed under the vaporization pressure of a volatile liquid, resulting in a high degree of foaming. If a foam cannot be obtained, and if LDPE with an MI of more than 1 is used, the resin composition in the foam film will become non-uniform during foaming, resulting in minute racks from which the foaming agent will escape, resulting in high This is thought to be due to the fact that a foamed product cannot be obtained. Regarding the mixing ratio of HDPE and LDPE, if the content of HDPE is less than the above content, the cell structure will not be sufficiently open, whereas if the content of HDPE is more than the above content, the foam will not have a uniform cell structure. I can't get it. Note that in the present invention, the order in which the volatile organic liquid is mixed is not limited to the case where the volatile organic liquid is mixed with the mixed resin; This may be done in the order of mixing one with the other.

Next, in the present invention, the mixture of HDPE, LDPE and volatile organic liquid mixed above is heated to a temperature higher than the melting point of LDPE.
It is cooled to a temperature 10°C lower than the melting point of DPE, and then extruded into a low-pressure zone, thereby creating a polyethylene foam with a cell structure in which most of the cells are continuous and a high expansion ratio. is obtained.
Since the cooling of the mixture in the present invention is as described above, the melting point of HDPE used in the present invention and the LDP
It is necessary that the difference between the melting point of E and the melting point of
If the extrusion temperature is below the melting point of LDPE, part or all of the mixture will solidify and will not form a uniform foam or will be impossible to extrude, and if the mixture is 10°C lower than the melting point of HDPE. This is based on the fact that it has been found that if extrusion is carried out at a temperature higher than this temperature, the blowing agent escapes from the resin at the same time as it is extruded, and a highly foamed foam cannot be obtained.

In addition, one method for carrying out the present invention industrially and continuously is to supply a premix of LDPE and HDPE from an extruder hopper, melt and knead it to a temperature higher than the melting point of HDPE, and then add it to the middle of the extruder barrel. A volatile organic liquid is injected through the injection hole provided, mixed with the resin, cooled to a temperature higher than the melting point of the LDPE used and 10°C lower than the melting point of HDPE, and then extruded into the atmosphere through a mouthpiece of the desired shape. There is a way to make it foam.

At this time, commonly used additives such as a bubble control agent, colorant, antiaging agent, and antistatic agent may be kneaded into the resin in advance, or they may be added from the middle of the hopper or barrel. Since the method for manufacturing the polyethylene foam of the present invention is as described above, it is possible to easily obtain a high-quality polyethylene foam that has a majority of open cells and has a high expansion ratio. The resulting foam can be used in various applications such as filters where open cells are required.

Examples of the present invention will be described below.

Example 1 and Comparative Example 1 M113, density 0.965y/Cc melting point 135°C E)
PE and MIO. 3. Density 0.923y/Ccl melting point 11
A mixture of LDPE at 0°C in the proportions shown in Table 1 was supplied to an extruder with a diameter of 50Tn1L/D=30, and 10kg/
Dichlorotetrafluoroethane was injected at a rate of 2.5k9/H through a blowing agent injection hole provided in the middle of the barrel, kneaded with the resin, and the resin temperature was lowered to the temperature shown in Table 1. After adjustment, it was extruded into the atmosphere through a circular hole nozzle with a diameter of 4T1 m.

Fine talc powder was used as a foam regulator by mixing with the resin at a ratio of 0.5 parts by weight per 1 (4) parts by weight of the resin. The open cell ratio of the obtained foam was measured using an air comparison hydrometer. The results are shown in Table 1. Example 2 and Comparative Example 2 M112, HD with density 0.94y/Ccl melting point 124°C
PE and MIO. 3. Density 0.923y/Ccl melting point 11
A mixture of LDPE at 0°C in the proportions shown in Table 2 was extruded at a rate of 10kg/H using the extruder used in Example 1, and dichlorodifluoromethane was added at 2k9/H through the blowing agent injection hole.
Inject at a ratio of 112, mix with resin, lower the resin temperature
After adjusting the temperature to .degree. C., it was extruded into the atmosphere through a circular hole nozzle with a diameter of 47WL.

A cell control agent was used in the same manner as in Example 1. The results obtained are shown in Table 2. Comparative example 3M15, density 0.957
y/Ccl melting point 128°C (7) parts by weight of HDPE4O and MIO. L with density 0.923y/Ccl melting point 110℃
Using the same extruder as in Example 1, 1 part by weight of DPE6O was added.
Extrude at a rate of 0k9/(I, inject dichlorotetrafluoroethane at a rate of 2.5kg/H from the blowing agent injection hole, knead the resin and blowing agent, cool the mixture to 115°C, and make a caliber of 477 It was extruded into the atmosphere through the circular hole nozzle of !77!.

Claims (1)

[Claims] 1 High-density polyethylene with a melt index of 10 or more and low-density polyethylene with a melt index of 1 or less,
Always use a mixed resin mixed so that the content of high-density polyethylene is 1.95/ρ-0.9% by weight or more and 3.5/ρ-0.9% by weight or less (ρ is the density of high-density polyethylene). Volatile organic liquids with a boiling point under pressure of 100°C or less are mixed under high temperature and high pressure, and the mixture is cooled to a temperature equal to or higher than the melting point of low-density polyethylene and 10°C lower than the melting point of high-density polyethylene, A method for producing polyethylene foam, characterized in that it is then extruded into a low pressure zone.