JPH0211621B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an ionically crosslinked resin foam. More specifically, the present invention relates to an economical method for producing an ionically crosslinked resin foam, which comprises performing an ionically crosslinking step and a foam molding step in one step. Foams made of ionically crosslinked resins such as ionomer resins, which have a structure in which molecular chains are crosslinked with metal cations, have higher tensile strength, tear strength, and rigidity than foams made of polyolefin resins. It has excellent physical properties such as elasticity, and also has a suitable degree of flexibility, so it is effectively used for various purposes. However, in order to mold a foam from an ionically crosslinked resin, it is not only necessary to perform an ionically crosslinked process and a foam molding process separately, but also because of the ionic crosslinked structure, it is difficult to mold it using an extruder or the like. There are disadvantages in the molding process, such as increased pressure, the need for a lot of energy for molding, and the need to use molding equipment equipped with a large-capacity motor. Furthermore, ionic crosslinked resins are often used in the production of foams in a blended form with other olefinic resins, but the compatibility between the two resins is generally poor, so it is necessary to improve the mixing. Depending on the processing conditions and equipment contents,
It will be even more limited. Moreover, many foaming agents that have coloring properties and odor are used. The present inventors have conducted various studies on a method for producing an ionically crosslinked resin foam that can perform the ionic crosslinking process and the foam molding process in one step and does not cause the drawbacks in the molding process described above. It has been found that the use of specific metal crosslinking agents, namely metal carbonates, is extremely effective under operating conditions, leading to the completion of the present invention. Therefore, the present invention relates to a method for producing an ionically crosslinked resin foam, in which the ionically crosslinked resin foam contains a comonomer containing a carboxylic acid group or a carboxylic acid anhydride group by 0.5%.
~25 mol% copolymerized ethylene copolymer and metal carbonate powder masterbatch pellets, 130%
Under melting temperature conditions between ~290°C and approximately 5Kg/cm ²
The mixture is kneaded under the above pressure conditions to crosslink some or all of the carboxylic acid groups or carboxylic acid anhydride groups in the copolymer with metal ions, and then the kneaded product is extruded into a low pressure zone. It is produced by foaming with carbon dioxide gas, which is a byproduct of the reaction. In the method for producing an ionically crosslinked resin foam of the present invention, which is carried out in this way, the ionic crosslinking step and the foam molding step can be performed in one step, and therefore it is not only economical, but also The back pressure of the extruder is lower than during foam molding, so less energy is required during molding, there is no need for special equipment such as a blowing agent injection device, and compatibility with other olefin resins is improved. It has many advantages, including no coloration or odor caused by foaming agents. As the ionic crosslinkable resin used for producing the crosslinked foam, an ethylene copolymer copolymerized with a comonomer containing a carboxylic acid group or a carboxylic acid anhydride group is used. Suitable copolymers include copolymers of ethylene and α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms or acid anhydrides thereof. Preferred α,β-unsaturated carboxylic acids or acid anhydrides thereof include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, monoethyl fumarate, and maleic anhydride. In the copolymer of ethylene and α,β-unsaturated carboxylic acid or its acid anhydride, each of which is used at least one type, for example, a vinyl ester such as vinyl acetate, an unsaturated carboxylic acid such as methyl methacrylate, etc. Ethylenically unsaturated compounds such as esters, vinyl chloride and acrylonitrile can also be copolymerized. Such copolymers are preferably produced by direct copolymerization between these comonomers. The copolymerization reaction takes place in the presence of a free radical type polymerization catalyst, with approximately
It is generally carried out under high pressure and high temperature conditions of 50 to 3000 Kg/cm ² and approximately 150 to 300°C. The copolymer also has α, β
- It can also be obtained by graft copolymerization of unsaturated carboxylic acids, or by saponification reaction of a copolymer obtained by copolymerizing a comonomer containing a carboxylic acid forming group. Regardless of which method is used, the copolymer contains approximately 0.5
~25 mole % carboxylic acid groups or carboxylic acid anhydride groups must be contained. If the content is less than this, the resin will lack characteristics as an ionically crosslinked resin, and the amount of carbon dioxide gas produced as a by-product during the ionically crosslinked reaction with the metal carbonate will be small, making it impossible to achieve sufficient foaming. On the other hand, if the content is higher than this, the resin will have poor thermoplasticity and it will be difficult to mold it into a foam. The ethylene copolymer can be used alone, but it can also be used in a blend with other olefin resins. Examples of other olefin resins include polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-propylene copolymer, polystyrene, etc.
About 10 to 400 parts by weight per 100 parts by weight, preferably about 20 parts by weight
~200 parts by weight. Metal carbonates used as ionic crosslinking agents and blowing agents include those in the periodic table of elements, -a
and group metals having a valence of 1 to 3, specifically monovalent metals such as sodium, potassium, lithium, cesium, silver, mercury, copper, calcium, magnesium, beryllium, strontium, barium, copper, cadmium, mercury, tin,
One or two types of carbonates, including bicarbonates, hydroxy carbonates, and hydrated carbonates of divalent metals such as lead, iron, cobalt, nickel, and zinc, or trivalent metals such as aluminum, scandium, iron, and yttrium. A mixture of the above is used. Preferably, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, calcium carbonate, magnesium carbonate, zinc carbonate, lead carbonate, etc. are used. Note that other metal compounds such as metal oxides may be mixed and used as long as there are no problems with ionic crosslinking, foaming, odor, corrosion, etc. When metal compounds other than these metal carbonates are used without metal carbonates, (a) the ionic crosslinking reaction does not proceed sufficiently with the commonly used foam molding equipment and processing conditions; (b) It is difficult to add the metal compound into the resin using the foam molding equipment; (c) the molding equipment is severely corroded by the metal compound or the acid that is produced as a by-product during the ionic crosslinking reaction; (d) ) The odor of the by-products during the ionic crosslinking reaction is significant. (e) The reaction by-products such as acid, water, and alcohol have poor volatility at room temperature, so when they are used as blowing agents, the resulting Foams are not suitable for use as the crosslinkable metal ion source of the present invention because they undergo significant post-shrinkage upon cooling and are useless as foams. On the other hand, when the metal carbonate is used, ionic crosslinking proceeds smoothly even with commonly used foam molding processing equipment, and addition to the resin can be achieved by simply blending a commercially available powdered metal carbonate. It is sufficient to produce a foam with fine cells without corrosion of the equipment, no odor during reaction, and no discoloration that occurs when other thermally decomposed foaming agents are used. The metal carbonate is preferably used in powder form in order to facilitate the ionic crosslinking reaction.
This is supplied in the form of masterbatch pellets which are melt-kneaded in advance with the ethylene copolymer or a suitable resin compatible therewith in an appropriate ratio. Note that it is permissible to use other solid, liquid or gaseous blowing agents or cell control agents in combination with the metal carbonate, as long as the properties of the foam do not deteriorate. The addition ratio of metal carbonate as a source of crosslinked metal ions depends on the degree of ionic crosslinking, which affects the degree of change in solid properties and melting properties as an ionically crosslinked resin, the degree of foaming as a foamed resin, etc. The amount must be sufficient to neutralize at least 10 mole percent of the carboxylic acid or anhydride groups in the copolymer. The method according to the present invention is carried out using a resin melt-kneading device that is heated and pressurized, preferably a screw extruder or an injection molding device equipped with a screw extruder, which is commonly used as a foam manufacturing device. This is done using The melt-kneading process of the copolymer resin and metal carbonate, which is necessary to carry out the ionic crosslinking reaction (neutralization reaction) and foaming by by-product carbon dioxide, is performed at a temperature of about 130 to 290 ml at a temperature above the melting point of the copolymer.
C., preferably between about 150 and 270.degree. C., and under pressure conditions of about 5 Kg/cm2 ^or more, preferably about 20 Kg/cm2 ^{or more} . At temperatures below about 130°C, the ionic crosslinking reaction does not proceed sufficiently in ordinary foam molding processing equipment, and at temperatures above about 290°C, the resin tends to deteriorate. Further, if it is less than about 5 kg/cm ² , the progress of the ionic crosslinking reaction is slow and the foaming becomes non-uniform, which is not preferable. By melt-kneading, some or all of the carboxylic acid groups or carboxylic acid anhydride groups in the copolymer are cross-linked with metal ions, and the kneaded product of the ionic cross-linked copolymer, which contains carbon dioxide gas by-produced therein, is produced under low pressure. The carbon dioxide gas expands due to the release of pressure and the ionic crosslinked copolymer foams. Examples of foam molding methods include foam molding into a predetermined shape such as a sheet, rod, or pipe through a die of an extruder in the air or water, or by injecting the foam into a cooling mold from a screw extruder for injection molding. A method of molding it into a predetermined shape is used. The method of the present invention, in which an ionically crosslinked resin foam is produced in this way, has many advantages as described above compared to the conventional method of foaming a copolymer that has already been ionically crosslinked. It can be said that its industrial significance is extremely large. Next, the present invention will be explained with reference to examples. Note that the melt index is measured at 190°C according to JIS K-6760. Examples 1 to 4 Ethylene-methacrylic acid copolymer (methacrylic acid content 10% by weight, melt index 500g/10
) 40 parts by weight of pellets and sodium carbonate powder
After kneading 60 parts by weight with a Banbury mixer, a pellet-shaped sodium carbonate masterbatch was prepared. 5 parts by weight of this sodium carbonate masterbatch was dry blended with 100 parts by weight of various methacrylic acid copolymers (compositions are in weight %) listed in Table 1 below. The mixed resin pellets are heated to 140℃, 180℃, 230℃, 230℃ and 180℃ from the resin supply port side, respectively.
Diameter 65mm with temperature of 1st to 5th zone adjusted to °C
After being melted and kneaded, the extruder (L/D-26) is supplied with a gap of 1.0 mm and a width of 63 mm installed at the tip of the extruder.
It was extruded into the atmosphere through a slit (150°C) and formed into a sheet-like foam. The obtained foam is a nearly closed-cell foam that is colorless and odorless, and has properties such as good tensile strength and tear strength that are characteristic of ionically crosslinked resin foams. The ^infrared absorption spectrum of this foam has −
Absorption of COO ^- Na ⁺ was observed, confirming that ionic crosslinking had occurred. A summary of these Examples is shown in Table 1 below. Comparative Example 1 100 parts by weight of ionically crosslinked resin pellets (Himilan 1601 manufactured by Mitsui Polychemicals, Na ⁺ ion crosslinked, melt index 1.3g/10 minutes) were added with a chemical blowing agent powder (azodicarbonamide, Uniform AZ- manufactured by Otsuka Chemical Industries). S) 3 parts by weight were dry blended, kneaded using the same equipment, temperature conditions, and operating method as in Example 1, and foam-molded into a sheet. The obtained foam was colored yellow and had an odor. In addition, the pressure of the extruder was higher and the motor load was 20 to 30% higher than in each of the above examples. The summary of this comparative example is shown in Table 1 below.

[Table] Examples 5 to 7 To 70 parts by weight of the ethylene-methacrylic acid copolymer used in Example 1 and 3.5 parts by weight of the sodium carbonate masterbatch, 30 parts by weight of the olefinic polymer listed in Table 2 below was added. was further dry-bred. The mixed resin pellets were kneaded using the same equipment, temperature conditions, and operating method as in Example 1, and foam-molded into a sheet. The obtained foam is uncolored,
It is odorless and has closed cells. A summary of these examples is shown in Table 2 below.

[Table] Examples 8 to 11 Ethylene-methacrylic acid copolymer (methacrylic acid content 10% by weight, melt index 500g/10
55 parts by weight of pellets and 45 parts by weight of various metal carbonate powders listed in Table 3 below were kneaded in a Banbury mixer to prepare a pellet-shaped metal carbonate masterbatch. Five parts by weight of this metal carbonate masterbatch were dry blended with 100 parts by weight of ethylene-methacrylic acid copolymer (methacrylic acid content 12% by weight, melt index 13.5 g/10 minutes) pellets. The mixed resin pellets were kneaded using the same equipment, temperature conditions, and operating method as in Example 1, and foam-molded into a sheet. The resulting foam was uncolored and odorless, and had the characteristics of the ionically crosslinked resin foam described above. A summary of these examples is shown in Table 3 below.

[Table] Examples 12 to 17 An in-line screw type injection molding machine (L/D-18) with a screw diameter of 55 mm, a length of 140 mm, a width of 70 mm,
A mold with a square plate type cavity with a thickness of 10 mm is installed, and the temperature of each part is set from the resin supply side of the injection molding machine to 150℃ in the first zone, 180℃ in the second zone, 200℃ in the third zone,
The temperature was adjusted to 200°C in the nozzle and 27°C in the mold. 100 parts by weight of various methacrylic acid copolymer pellets listed in Table 4 below and a predetermined amount of dry blend pellets of the sodium carbonate masterbatch used in Example 1 were supplied to this injection molding machine, and the screw was rotated. Several 100rpm, injection pressure 100Kg/
cm ² and a molding cycle of 3 minutes and 15 seconds, a square plate-shaped foam was obtained. This foam is an uncolored, odorless foam that has fine closed cells inside and an unfoamed, hard skin layer about 1 mm thick on its surface. A summary of these examples is shown in Table 4 below.

【table】

[Table] Examples 18 to 19 In Example 13, 70 parts by weight of an ethylene-methacrylic acid copolymer was blended with 30 parts by weight of various olefinic polymers listed in Table 5 below. In each case, foams exhibiting the same properties as the foam obtained in Example 13 were obtained. A summary of these examples is shown in Table 5 below.

【table】

Claims (1)

[Claims] 1. Ethylene copolymer copolymerized with 0.5 to 25 mol% of a comonomer containing a carboxylic acid group or a carboxylic acid anhydride group and metal carbonate powder masterbatch pellets at a melting temperature between 130 and 290°C. and a pressure of 5 kg/cm ² or more to crosslink some or all of the carboxylic acid groups or carboxylic acid anhydride groups in the copolymer with metal ions, and then knead the kneaded product under low pressure. 1. A method for producing an ionically crosslinked resin foam, characterized by extrusion molding into a zone and generating foaming with carbon dioxide gas as a reaction by-product.