JPH0547576B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing polyethylene resin foam, in particular, using a blowing agent that does not cause environmental damage.
The present invention relates to a method for producing a polyethylene resin foam having uniform microcells. (Prior technology) The method of melting and plasticizing polyethylene resin in an extruder, mixing it with a foaming agent under high temperature and high pressure, and then extruding it from the tip of the extruder to obtain a foam is an efficient way to obtain a homogeneous product. It is widely used because it can be used. However, when polyethylene thread resin is foam-molded using an extruder in the same way as polystyrene, the foam extruded from the tip of the extruder once foams and expands, then shrinks significantly, and it takes a long time after that. The foam gradually expands and becomes a foam having a certain density. In particular, the higher the foam size, the greater the shrinkage, and it takes a long time for the dimensions to stabilize. Such shrinkage occurs because the gas permeability of most of the blowing agents commonly used in resin foam molding through the polyethylene film is much greater than that of air. That is, the vaporized foaming agent that filled the cells of the foam immediately after foaming in the can is replaced with air while the foam is placed in the atmosphere.
Since the speed at which air permeates into the foam cells is lower than the speed at which the blowing agent permeates into the atmosphere through the polyethylene resin film, the pressure inside the cells gradually decreases, and the cell membranes become distorted due to atmospheric pressure, causing the foam to deteriorate significantly. It will shrink. This shrinkage will recover as air gradually permeates into the cell, but it will take a lot of time, storage, and space, and if the initial shrinkage is large, it will not completely return to its original dimensions. Sometimes. Therefore, the selection of a blowing agent is very important for extrusion foam molding of polyethylene resin, and dichlorotetrafluoroethane (hereinafter abbreviated as F114) is a well-known blowing agent that causes relatively little shrinkage as mentioned above. F114 has been widely used as a polyethylene resin foam because it is nontoxic, nonflammable, and can produce foams with fine cells. However, in recent years, the use of F114 has come to be regulated from the perspective of protecting the natural environment. Saturated chlorofluorocarbons, including F114, are very stable compounds, and they reach the stratosphere without being decomposed in the troposphere that surrounds the earth's surface. This is because it has become known that they can destroy the atmospheric temperature (which prevents the arrival of carbon dioxide and maintains atmospheric temperature). Therefore, the present inventors used monochlorodifluoromethane (hereinafter abbreviated as F22), which is an unsaturated chlorofluorocarbon that does not decompose in the troposphere and do not destroy the ozone layer, as a blowing agent in place of F114. An attempt was made to obtain a polyethylene resin foam. However, compared to F114, F22 has a lower atmospheric pressure boiling point (approximately -41℃) and a higher saturated vapor pressure (approximately 5Kg/cm ² abs at 100℃) in the appropriate temperature range for resin foaming, so the tip of the extruder Internal foaming occurred in the die, and too rapid volume expansion occurred after exiting the die, resulting in surface roughness of the foam and communication of air bubbles, making it impossible to obtain a good foam. Further, the resulting foamed material shrank significantly immediately after extrusion, and no dimensional recovery was observed even after it was left for one month. As a method for obtaining polyethylene resin foam using F22, the technique described in Japanese Patent Publication No. 52-50220 is known. In the specification, a mixture of F22 and dichlorodifluoromethane (hereinafter abbreviated as F12) is used as a blowing agent for polyethylene resin,
A method using impact styrene, acrylic acid elastomer, sorbitan triolefiate, sorbitan monosearate, glycol monostearate, etc. as an agent to prevent foaming agent from escaping from the cells has been proposed. However, this method uses F12 as a blowing agent, whose use has come to be regulated in the same way as F114 from the perspective of environmental protection.F12 also has a low atmospheric pressure boiling point (approximately −30°C) and high saturated vapor pressure (approximately 34°C at 100°C)
Kg/cm ²・abs), so even if this
Even when used in combination with F22, it is not easy to prevent the formation of internal foaming in the die or the communication of air bubbles. In particular, when trying to obtain a foam with a large cross-sectional area, it is necessary to make the resin discharge opening of the die large, so the pressure drop inside the die accelerates the vaporization of the blowing agent, making internal foaming more likely to occur. Good foam cannot be obtained. Furthermore, it has been shown that the foaming agent dissipation prevention agent should be added in an amount of 5 to 20% by weight based on the polyethylene resin, and adding such a large amount may cause the foaming agent to be prevented from dissipating even if it has the effect of preventing dissipation. This is undesirable because it changes the original properties of the polyethylene resin. (Problems to be Solved by the Invention) As a result of intensive research into producing polyethylene resin foam using a blowing agent that is acceptable in terms of protecting the natural environment, the present inventors have discovered that the blowing agent has a low ozone depleting ability. A mixed system of F22 and other blowing agents with a relatively high boiling point, low vapor pressure, and low ozone depletion ability is used, and a limited dimensional stabilizer that suppresses the escape rate from the blowing agent when added in small amounts By using it together, internal foaming in the die during extrusion foam molding is suppressed, and rapid volumetric expansion after exiting the die is alleviated, resulting in a beautiful appearance and a closed cell structure. We also found that a foam with little dimensional shrinkage after extrusion can be obtained, and that by suppressing internal foaming, a thick foam with a large cross-sectional area can be obtained, and we proceeded with a more detailed study. This led to the completion of the present invention. (Means for Solving the Problems) The gist of the present invention is to use monochlorodifluoromethane as a blowing agent in an amount of 10 to 90 mol% and an atmospheric pressure boiling point of -
Saturated vapor pressure at 100℃ is 30Kg/at 15℃~30℃
A mixture of 90 to 10 mol % of halogenated hydrocarbons and/or aliphatic hydrocarbons of ^{cm 2} / abs or less is used as a dimensional stabilizer at 0.1 to 3 mol % per 100 parts by weight of the resin.
It is characterized by using parts by weight of higher fatty acid ester of polyhydric alcohol, and extruding a mixture formed by adding these blowing agents and dimensional stabilizers to polyethylene resin in a molten state from an extruder to form a foam. This is a method for producing polyethylene resin foam. In the present invention, polyethylene resins include not only homopolymers of ethylene monomers but also vinyl acetate, propylene, styrene, methyl methacrylate, acrylonitrile, vinyl chloride, butene, butadiene, hexene, methylpentene, etc. Also included are copolymers with octene and the like. In addition, polyethylene resin may be combined with other thermoplastic resins such as polystyrene, polyvinyl chloride, polyamide, polycarbonate, polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer resins, and other miscible thermoplastic resins or natural rubber or synthetic rubber. They can also be used in combination. As mentioned above, the blowing agent used in the present invention is monochlorodifluoromethane (F22) 10
~90 mol%, as well as atmospheric pressure boiling point -15°C to 30°C
It must be a mixture of 90 to 10 mol% of halogenated hydrocarbons and/or aliphatic hydrocarbons with a saturated vapor pressure at 100°C of 30 Kg/cm ² ·abs or less.
F22 is a blowing agent that has low ozone depletion potential and is acceptable for the protection of the natural environment, but it has a low atmospheric pressure boiling point (approximately -41℃) and a high saturated vapor pressure (approximately 50Kg/cm ² abs at 100℃). Therefore, it cannot prevent internal foaming or communication of bubbles in a diamond using this alone. Therefore, other blowing agents that have a relatively high boiling point and low vapor pressure compared to F22 are used in combination with F22.
With a blowing agent whose saturated vapor pressure exceeds 30 Kg/ ^cm2・abs, even when mixed with F22, it is not possible to completely prevent the above-mentioned internal foaming and bubble communication; If a blowing agent exceeding 10% is mixed with F22, the bubbles will become coarser, which is not preferable. 100 at atmospheric pressure boiling point -15℃ to 30℃ in the present invention
Examples of halogenated hydrocarbons and/or aliphatic hydrocarbons with a saturated vapor pressure of 30 Kg/ ^cm2・abs or less at °C include dichlorotrifluoroethane (F123), monochlorotetrafluoroethane (F124), and monochlorotrifluoroethane. (F133), monochlorodifluoroethane (F142b),
These include dichloromonofluoromethane (F21), monochloromonofluoromethane (F31), butane, and ethyl chloride, as well as trichloromonofluoromethane (F11) and dichlorotetrafluoroethane (F114), which are said to have a large ozone-depleting ability. )
Although its usage is regulated, it can be used in small quantities. Among these blowing agents to be mixed with F22, particularly preferred blowing agents are monochlorodifluoroethane (F142b), ethyl chloride and butane. The mixing ratio of F22 and other blowing agents can be arbitrarily selected within the range of 10 to 90 mol% of F22 and 90 to 10 mol% of other blowing agents, but it depends on the type of blowing agent mixed with F22. It should be determined appropriately depending on the purpose and properties of the foam to be obtained. If the proportion of F22 exceeds 90 mol%, for example, even if other blowing agents are mixed, internal foaming in the die and communication of bubbles cannot be prevented, which is undesirable. F22 if less than
In addition to making it difficult to form fine bubbles, which is the advantage of , it is not preferable to use too many of these because there is a risk of fire. In particular, when trying to obtain a highly foamed material with a density of 0.04 g/cm ³ or less, the mixing ratio of F22 is preferably 60 mol% or less, and a particularly preferable range is that F22 is
It is 20-50 mol%. Since F22 is a foaming agent whose thermal stability is not very good, it is preferable to use a phosphite ester as a thermal stabilizer by incorporating it into F22 or the polyethylene resin. Examples of phosphites include dimethyl phosphite, diethyl phosphite,
Diisopropyl phosphite, triisopropyl phosphite, dioleyl phosphite,
Examples include diphenyl phosphite, triphenyl phosphite, trisnonylphenyl phosphite, etc., and it is preferable to use one kind selected from these phosphite esters or a combination of two or more of them. The amount added is 0.01 to 1.0 parts by weight based on the resin.
Preferably it is 0.05 to 0.5 parts by weight. Generally, the amount of mixed blowing agent used is 1Kg of resin.
0.3 to 3.0 mol is added to Another key point of the present invention is that higher fatty acid ester of polyhydric alcohol is used in combination with a blowing agent as a dimensional stabilizer. Examples of polyhydric alcohols include glycerin, pentaerythritol,
Examples include sorbitol, sorbitan, mannitol, mannitan, dipentaerythritol, diglycerin, and the like. Examples of higher fatty acids include saturated or unsaturated higher fatty acids having 10 to 30 carbon atoms, such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid, and ricinoleic acid; Includes beef tallow fatty acid, cassava oil fatty acid, coconut oil fatty acid, etc. in which higher fatty acids are mixed. In the present invention, compounds in which these polyhydric alcohols and higher fatty acids are ester bonded are used, and partial esters in which one or more hydroxyl groups remain in one molecule of the ester are preferred. Examples include lauric acid mono(di)glyceride, palmitic acid mono(di)glyceride, stearic acid mono(di)glyceride, pentaerythritol monocaprate, pentaerythritol monolaurate, dipentaerythritol distearate, These include sorbitan monooleate, sorbitan sekis oil fatty acid ester, sorbitan monopalmitate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, and mannitan monolaurate, among which stearic acid is particularly preferred. It is a mono(di)glyceride. These polyhydric alcohol fatty acid esters are used in an amount of 0.1 to 3 parts by weight per 100 parts by weight of the polyethylene resin. Higher fatty acid esters of polyhydric alcohols have an extremely large effect on the shrinkage and expansion of polyethylene resin foams immediately after extrusion. However, when 0.5 parts by weight of stearic acid monoglyceride is added to the resin, extrusion Maximum contraction occurs after 30 minutes, but after that
When left in a constant temperature room at 20°C, it gradually expands and recovers to its original dimensions in 10 days. Furthermore, when 1 part by weight or more of stearic acid monoglyceride is added, the dimensions of the foam hardly change after extrusion. However, even if more than 3 parts by weight of higher fatty acid ester of polyhydric alcohol is mixed in, not only will it not be useful for stabilizing the dimensions of the foam or increasing the foaming rate, but it will also cause slippage in the transfer of the molten resin within the extruder. The resin pressure inside the extruder fluctuates, making it impossible to extrude a certain amount, and the quality of the foam varies, making it impossible to obtain a good product. Therefore, the addition of higher fatty acid ester of polyhydric alcohol is 0.1~
A suitable amount is 3 parts by weight, preferably 0.5 to 2.0 parts by weight. Further, in the present invention, in addition to the foaming agent and the dimensional stabilizer, a bubble control agent such as talc, a coloring agent such as a pigment or dye, a lubricant, a surfactant, etc. can be added. The polyethylene resin foam according to the present invention can be produced by a conventionally known method using an ordinary extruder. That is, for example, a small amount of inorganic fine powder such as talc and a higher fatty acid ester of a polyhydric alcohol such as stearic acid monoglyceride are added to a low-density polyethylene resin, and the mixture is fed to an extruder. A mixed foaming agent made by mixing F22 and other foaming agents at a predetermined ratio is injected into the extruder midway through the extruder, and after thoroughly melting and mixing them, it is extruded into the atmosphere through a die heated to 100-120°C. A foamed molded product can be obtained by shaping it into a desired shape using a sizing device or the like. (Example) Examples and comparative examples of the method of the present invention will be given below to explain in more detail. In Table 1 showing the properties of the foams of each example, the properties of the blowing agent were evaluated by the following method. (1) Density is the foam density measured within 10 minutes after extrusion, and average cell diameter is the cell size measured according to ASTM D-3576. (2) The interconnection rate indicates the volume ratio of interconnected air bubbles in the foam volume measured by the air displacement method. (3) Appearance is an evaluation of the smoothness of the surface and the beauty of the skin. ◎ is extremely good, ○ is good, △
means normal, and × means bad. (4) Dimensional stability is based on the foam volume immediately after extrusion.
Volumetric shrinkage rate after 30 minutes (initial shrinkage rate) and subsequent 20
The evaluation was based on the change in volume of the bond left in a constant temperature room for 2 weeks. VG: The initial shrinkage rate was 10% or less, the shrinkage was completely recovered after being left for one day, and there was no change thereafter. G: The initial shrinkage rate was 10 to 20%, but the shrinkage gradually recovered after being left and completely recovered within 5 days. B: The initial shrinkage rate was 20% or more, and the shrinkage gradually recovered after being left, but the shrinkage did not completely recover even after being left for 2 weeks. VB: The initial shrinkage rate was 20% or more, and there was almost no recovery from shrinkage even after leaving it for two weeks. Example 1 Low density polyethylene resin (MI value 0.3, density 0.921
0.5 part by weight of finely powdered talc was mixed with 100 parts by weight (g/cm ³ ) and fed at a rate of 8 kg per hour to two extruders each having a diameter of 40 mm connected together. As a blowing agent, a mixture of 50 mol% F22 and 50 mol% F142b was press-mixed into the resin from near the tip of the first extruder at a ratio of 1 mol per 1 kg of resin. Separately, stearic acid monoglyceride was supplied as a dimensional stabilizer into the extruder at a ratio of 1 part by weight per 100 parts by weight of the resin. A rod die having a resin discharge opening with a diameter of 4 mm was used as the die. 1st
The resin composition fed to the extruder was heated to a maximum of 200°C, melt-mixed, the resin temperature was adjusted to about 110°C in the second extruder, and then fed to the die, which was also set at 110°C. The resin discharged from the nozzle was foamed to a large extent and was a rod-shaped foam with a diameter of 30 to 40 mm. The properties of the obtained foams are shown in Table 1 together with their blending ratios. As is clear from Table 1, the obtained foam had uniform, fine cells and had a beautiful appearance. In addition, the initial shrinkage of this foam immediately after extrusion was small, and even after it was left for several days, almost no dimensional change was observed, and it had excellent cushioning properties. Examples 2 to 5 Example 1 except that the type and mixing ratio of the blowing agent in Example 1 were changed as shown in Table 1, and the amount of dimensional stabilizer added was changed as shown in Table 1. It was carried out using the same equipment and method. The obtained foam had excellent appearance and dimensional stability as in Example 1. Comparative Example 1 In order to clarify the effect of the dimensional stabilizer, a test was carried out using the same equipment and conditions as in Example 1, except that no dimensional stabilizer was added. The obtained foam shrinks significantly immediately after extrusion, and then is kept in a constant temperature room at 20℃ for 10 minutes.
It expanded slightly after being left for a day, but the dimensions did not fully recover, and the cushioning properties were poor with wrinkles on the surface. Comparative Examples 2 to 5 The experiments were carried out using the same equipment and conditions as in Example 1, except that the type and amount of the blowing agent were changed as shown in Figure 1 by a combination other than the method of the present invention. No foam was obtained. In addition, Table 1 shows Examples 1 to 5 and Comparative Examples 1 to 5.
Table 2 shows the boiling points and vapor pressures of the various blowing agents used.

【table】

【table】

[Table] As is clear from Table 1, Examples 1 to 1 of the present invention
The foam obtained in step 5 had fine bubbles, no communication between the bubbles, excellent appearance and dimensional stability, and good cushioning properties, whereas dimensional stabilization was not used at all. The product obtained by the method of Comparative Example 1, which was not used, had particularly poor appearance and dimensional stability, and the product obtained by the method of Comparative Example 2, which used F22 alone as a blowing agent, and the product obtained by the method of Comparative Example 2, which used F22 alone as a blowing agent.
The products obtained by the methods of Comparative Examples 3 and 5, which used a mixture of methyl chloride and F12, which have a high saturated vapor pressure in The cell size obtained in Comparative Example 4 in which a high amount of trichlorotrifluoroethane was used was particularly large. As described above, in all the methods of Comparative Examples 1 to 4, only inferior foams with poor cushioning properties were obtained. Example 6 According to the formulation of Example 4 in Table 1, 0.2 triphenylphosphite was added as a heat stabilizer.
parts by weight were added, and a foam was produced by continuously operating for a long time in exactly the same manner as in Example 1. The properties of the obtained foam were not much different from those of Example 4, and no inconvenience occurred even during long-term operation. (Effects) According to the present invention, a polyethylene resin foam that is socially acceptable in terms of protecting the natural environment can be continuously and efficiently produced using a blowing agent with low ozone depletion ability. In addition, F22 has conventionally been difficult to apply to polyethylene resins due to significant shrinkage of the foam, but due to its combined effect with other limited blowing agents and dimensional stabilizers, it can be used in extruded foams. There is almost no shrinkage immediately after extrusion, and therefore there is no dimensional change when left standing.
Therefore, the process of stabilizing the foam is reduced and the storage effort and space are omitted, so the method of the present invention is extremely useful as an industrial production method for polyethylene resin foam.

Claims (1)

[Claims] 1 Monochlorodifluoromethane10 as a blowing agent
~90 mol%, as well as atmospheric pressure boiling point -15°C to 30°C
A mixture of 90 to 10 mol% of a halogenated hydrocarbon and/or aliphatic hydrocarbon having a saturated vapor pressure of 30 Kg/cm ² · abs or less at 100°C is used as a dimensional stabilizer in a range of 0.1 to 100 parts by weight of the resin. It is characterized by using 3 parts by weight of higher fatty acid ester of polyhydric alcohol, and extruding a mixture formed by adding these foaming agents and dimensional stabilizers to polyethylene resin in a molten state from an extruder to form a foam. A method for producing a polyethylene resin foam.