JPS62285930A - Production of closed-cell crosslinked polyolefin resin foam - Google Patents

Abstract

PURPOSE:To obtain the title foam having fine cells and excellent surface chromaticity and surface smoothness, by introducing a crosslinkage into a polyolefin resin mixed with a heat-decomposable blowing agent and a polysiloxane oil and expanding the resin by heating. CONSTITUTION:A crosslinkage is introduced into an expandable resin formed by mixing a polyolefin resin with a heat-decomposable blowing agent and a polysiloxane oil, and the resin is expanded by heating. The polysiloxane oil which can be used include those which become oily and show fluidity at the processing temperature in the production of an expandable composition or an expandable molding and those which are oily (liquid) at normal temperature. Especially, when a modified polysiloxane formed by modifying a siloxane with a glycol is used, a closed-cell crosslinked polyolefin resin foam having fine cells and an improved surface whiteness can be produced in a suitable expansion efficiency.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field] The present invention relates to an improvement in a method for producing a closed-cell crosslinked polyolefin resin foam.

[Prior art]

Generally, the following methods are known as methods for producing crosslinked polyolefin resin foams using thermally decomposable blowing agents.

(1) Atmospheric pressure chemical crosslinking foaming method A pyrolyzable blowing agent and a crosslinking agent are added to a polyolefin resin to obtain a foamable molded product without decomposing the blowing agent and the crosslinking agent. Heating the foamable molded product under normal pressure,
After or while introducing a crosslinking structure into a polyolefin resin by decomposing a crosslinking agent, a foaming agent is thermally decomposed and foamed.

(2) Atmospheric pressure electron beam crosslinking foaming method Add a thermally decomposable blowing agent to a polyolefin resin to obtain a foamable molded product without decomposing the foaming agent, and then irradiate the polyolefin resin with an electron beam to obtain a foamable molded product. A method in which a crosslinked structure is introduced into the resin, and the foaming agent is thermally decomposed under normal pressure to foam.

(3) Pressure chemical crosslinking foaming method (batch method) After adding a thermally decomposable blowing agent and a crosslinking agent to a polyolefin resin to obtain a foamable composition without decomposing the blowing agent and the crosslinking agent. , a method in which the composition is introduced into a mold, heated under pressure to decompose the crosslinking agent and foaming agent, and then expanded (foamed) by reducing the pressure (opening the mold) or crosslinking. A method (two-step method) in which after the agent and foaming agent are thermally decomposed under pressure, the molded product is cooled, taken out from the mold, and reheated to expand (foam).

However, the atmospheric pressure chemical crosslinking foaming method (1).

Although it is possible to continuously obtain a crosslinked foam with excellent mechanical strength at a relatively low equipment cost, the foam has large bubbles and a large amount of surface discoloration due to undecomposed blowing agent. There is. In addition, as a method to prevent this surface coloration, several methods have been proposed to add various foaming aids, but all of these methods reduce the decomposition temperature of the blowing agent and promote the decomposition of the blowing agent. Therefore, it is not appropriate to apply it to the atmospheric pressure chemical crosslinking and foaming method, which requires crosslinking by thermal decomposition of a crosslinking agent prior to thermal decomposition of the blowing agent. In addition, these foaming aids lower the decomposition temperature of the foaming agent, so crosslinking does not precede foaming.
When foaming, the air bubbles become open.

The resulting foam is an open-cell foam.

It has the disadvantage that mechanical properties such as compression hardness are extremely reduced.

In addition, in the normal pressure chemical crosslinking foaming method, in order to maintain the low temperature, the processing speed (for example, the discharge amount in molding processing using an extruder) is reduced, and the low temperature and high viscosity polyolefin composition is processed at high speed or under high pressure (high shear rate or Because the composition is extruded under high shear stress (high shear stress), the composition causes melt fracture, resulting in surface roughness of the resulting foamable molded product. This creates the problem that the product value decreases.

In addition, in the normal pressure electron beam crosslinking and foaming method (2), since the polyolefin resin composition does not contain a crosslinking agent, the normal pressure chemical crosslinking and foaming method (1) is carried out during the production of the foamable molded product. Although there are no restrictions on the processing temperature, in order to make the bubbles smaller and reduce surface coloration, metal oxides such as zinc white, metal soaps such as zinc stearate, and higher fatty acid ethanolamines such as stearic acid are used. It is necessary to add a blowing aid such as an amine compound such as amine compound to extremely lower the decomposition temperature of the blowing agent and shorten the decomposition time. A drawback is that melt roughing causes surface roughness.

In addition, although the pressurized chemical cross-linking foaming method (3) can produce cross-linked foams with fine bubbles and good surface whiteness at low equipment costs, it is a batch method, It has the disadvantage that it is not possible to obtain the desired results, and the productivity is also low. In addition, similar to the atmospheric pressure chemical crosslinking foaming method in (1),
Because a crosslinking agent is used, it is necessary to lower the processing temperature (kneading temperature) during manufacturing of the foamable composition to be filled into the mold, which causes surface roughness problems due to decomposition of the foaming agent and melt fracture. .

In addition, recently, 100 parts by weight of ethylene resin, 1 to 100 parts of blowing agent,
20 parts by weight of a crosslinking agent, 0.3 to 10 parts by weight of an organic peroxide as a crosslinking agent, and 0.1 to 1 part of a trifunctional monomer.
0 parts by weight, 0.1 to 5 parts by weight of silicone oil or its derivative, and the 10-minute half-life temperature (Tρ) of the organic peroxide is 100 to 170°C, and the foaming temperature (Tf) of the blowing agent is is 90 to 160°C and satisfies the following formula %.
A method has been proposed in which open-cell crosslinked ethylene resin foam is produced by forming sheets or other molded products and heating them (Japanese Patent Laid-Open No. 58-67734).
However, this method has the disadvantage that the manufacturing conditions are complicated, and since foaming is performed before crosslinking, the resulting foam has open cells and cannot be a closed cell foam.

〔the purpose〕

An object of the present invention is to provide a method for efficiently producing a closed-cell crosslinked polyolefin resin foam having fine cells and excellent surface whiteness and surface smoothness.

〔composition〕

According to the present invention, closed-cell crosslinked polyolefin resin foaming is performed by introducing a crosslinked structure into a foamable resin obtained by mixing a polyolefin resin with a pyrolytic blowing agent and a polysiloxane oil, and then heating and foaming the foamable resin. A method of manufacturing a body is provided.

In the present invention, a polyolefin resin, a thermally decomposable blowing agent, and a polysiloxane oil are used as the foamable resin, and a method of crosslinking these and then heating and foaming is adopted. Closed-cell crosslinked polyolefin resin foams with fine surface chromaticity and surface smoothness can be advantageously produced industrially.

Next, the present invention will be explained in more detail.

The polysiloxane oil used in the present invention includes those that are oily (liquid) at room temperature, and those that become oily and exhibit fluidity at processing temperatures during the production of foamable compositions or foamable molded articles. . As polysiloxane oils that are oily (liquid) at room temperature, ordinary siloxane oils such as dimethylpolysiloxane oil and methylphenylpolysiloxane oil, or modified polysiloxane oils obtained by modifying siloxane with glycol, can be used. Examples of polysiloxanes that become oily at the processing temperature during production include polysiloxanes having a pour point of 210° C. or lower, such as silicone compounds or silicone greases.

Pour point means the lowest temperature at which the oil will flow when the oil is cooled in the specified manner without stirring.

In the present invention, as described above, various polysiloxane oils are used, but especially when a modified polysiloxane in which siloxane is modified with glycol is used,
A closed-cell crosslinked polyolefin resin foam with finer cells and improved surface whitening can be produced with suitable foaming efficiency.

The reason for this is not necessarily clear, but the surfactant action of the modified polysiloxane increases the flexibility of the foamed membrane produced during foaming, lowers its surface tension, and further stabilizes the foamed membrane at an early stage. It is thought that this is because the destruction of the bubble membrane is prevented and the growth of bubbles due to bubble fusion can be suppressed, resulting in the bubbles becoming finer.

In addition, according to the results of the weight measurement (TG), etc., even when the modified polysiloxane is added, there is no decrease in the decomposition temperature of the blowing agent. It is believed that a foam is obtained.

In the present invention, the amount of the modified polysiloxane oil used is 0.00 parts by weight per 100 parts by weight of the polyolefin resin.
A suitable amount is 0.01 to 1.0 parts by weight, preferably 0.02 to 0.5 parts by weight. If the amount is less than 0.01 part by weight, the various effects of the modified polysiloxane, such as frictional heat suppression effect, melt structure prevention effect 1, improvement in foaming efficiency, cell refinement, and surface whiteness improvement, will not be fully exhibited. . Moreover, if it exceeds 1.0 parts by weight, excessive slip phenomenon occurs due to over-blending, which causes poor conveyance and cross-talk of the expandable/foaming composition, reducing its productivity, which is not preferable.

In the present invention, there is no particular restriction on the method of introducing a crosslinked structure into the foamable resin. For example, after incorporating various organic peroxides into the polyolefin resin by kneading, etc.,
Chemical crosslinking method that crosslinks by heating, electron beam crosslinking method that crosslinks polyolefin resin molded bodies by irradiating them with electron beams, and silane crosslinking method that involves modifying polyolefin resin with silane and then exposing it to moisture in the presence of a silanol condensation catalyst for crosslinking. Any method such as a crosslinking method (water crosslinking method) may be used.

Organic peroxides used in chemical crosslinking methods include:
For example, 2,2-bis(t-butylperoxy)octane 1, n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butylperoxide, t
-Butylcumyl peroxide, dicumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5- dimethyl-2,5-
Examples include di(t-butylperoxy)hexyne-3.

In addition, examples of the polyolefin resin used in the present invention include low density polyethylene, linear low density polyethylene, medium and high density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer,
Ethylene-propylene copolymer, chlorinated polyethylene,
Examples include polypropylene, polybutyne, etc., and two or more of these can be used as a mixture, if necessary.

Examples of the thermally decomposable blowing agent include azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybisbenzenesulfonyl hydrazide.

Further, as the heating foaming method in the present invention, any known foaming method such as hot air heating, infrared heater heating, heating on or in a heat medium bath such as a salt bath, etc., can be arbitrarily applied.

〔effect〕

The method for producing a closed-cell crosslinked polyolefin resin foam of the present invention has the above-described structure, and contains a polysiloxane oil, particularly a modified polysiloxane oil obtained by modifying siloxane with glycol, as a foamable composition. By adopting a method of heating and foaming after introducing a crosslinked structure, it has the following advantages compared to the conventionally known manufacturing method mentioned above, and is an extremely advantageous manufacturing method from an industrial perspective. Can be done.

(1) Without decomposing the crosslinking agent and foaming agent and without causing surface roughness of the foamable molded product due to melt fracture, the production rate of the foamable molded product can be increased to approximately 55% by the normal pressure chemical crosslinking foaming method. %, and in the normal pressure electron beam crosslinking foaming method, it can be improved by up to about 60%. Furthermore, in the pressurized chemical crosslinking foaming method, the production rate of the foamable composition can be increased by 30%.

(2) The blowing agent efficiency can be improved by about 20% regardless of the crosslinking and foaming method.

(3) The uniformity of the cells increases, and the average cell diameter can be reduced by up to about 40% in the normal pressure chemical crosslinking foaming method, and by about 30% in the normal pressure electron beam crosslinking foaming method.

(4) YI (yellowness), which is a measure of surface whiteness, is up to 40% by normal pressure chemical crosslinking foaming method and normal pressure electron beam crosslinking foaming method.
In the pressure chemical crosslinking foaming method, the size is reduced by about 15%, and the surface whiteness is therefore greatly improved.

〔Example〕

Examples are shown below to explain the present invention in more detail.

Example 1 Density 0.92g/-Melt index Ig/10m1
n low density polyethylene (hereinafter referred to as LDPE) 100
Azodicarbonamide (hereinafter referred to as AD) is added to the weight part as a blowing agent.
15 parts by weight of dicumyl peroxide (hereinafter referred to as DCP) as a crosslinking agent, and 15 parts by weight of dicumyl peroxide (hereinafter referred to as DCP) as a crosslinking agent, and dimethyl polysiloxane oil (Toray Silicone 5RX3).
10) After adding and mixing 0.1 part by weight, DCP, AD
φ90mm at extrusion temperature of 130℃ without decomposition of CA
A good foamable sheet having a thickness of 2 mm and a width of 400 mm was extruded by the extruder at a discharge rate of 65 kg/Hr without causing surface roughness due to remelt fracture. The foamable sheet was introduced into a heating furnace at a maximum temperature of 250° C. and crosslinked and foamed.

Example 2 A mixture of Example 1 and 0.1 part by weight of siloxane glycol copolymer-modified polysiloxane oil (Toray Silicone SH193) was added in place of the dimethylpolysiloxane oil (Toray Silicone SRX 310) of Example 1. Expandable sheets of the same size were extruded using the same extruder at the same extrusion temperature and at a discharge rate of 63 kg/Hr without causing melt fracture. Next, the foamable sheet was foamed under the same conditions as in Example 1.

Comparative Example 1 In Example 1, a foamable sheet of the same size was extruded using the same extruder as in Example 1 without adding dimethylpolysiloxane oil. Same discharge amount as Example 1: 65
kg/)Ir, the extrusion temperature rose to 140°C. In order to set the extrusion temperature to 130'C, the screw rotation speed and the set temperatures of the cylinder, etc. were lowered, and the discharge amount was 52 kg/Hr. The foamable sheet extruded under these conditions had surface roughness due to melt fracture. Next, the foamable sheet was foamed under the same conditions as in Example 1.

Comparative Example 2 Melt fracture was eliminated by further lowering the screw rotation speed and extrusion pressure than the foamable sheet manufacturing conditions of Comparative Example 1, and the discharge amount was 42 kg/
It decreased to Hr. Next, the foamable sheet was prepared in Example 1.
It was foamed under the same conditions.

Example 3 Density 0.918g/cm, melt index 4.5g
/10w1n LDPE 100 parts by weight ADCA 1
After adding and mixing 5 parts by weight and 0.1 part by weight of siloxane glycol copolymer-modified polysiloxane (Toray Silicone 5H193), the surface was roughened by melt fracture using a φ90ffin extruder at an extrusion temperature of 160°C without decomposing ADCA. 2mm thick without causing
Discharge rate of 95% of good foamable sheet with width of 400mm
It was extruded at kg/Hr. The sheet was supplied to an electron beam accelerator, and the upper and lower surfaces of the sheet were irradiated with 58 rad of ionizing radiation to form a foamable crosslinked sheet, which was then introduced into a heating furnace at a maximum temperature of 250° C. and foamed.

Comparative Example 3 In Example 3, without adding any Toray Silicone 5H193, a foamable uncrosslinked sheet of the same size was produced in the same extruder as in Example 3 at the same extrusion temperature under conditions that no surface roughness due to melt fracture occurred. Extruded. The discharge amount at this time was 63 kg/Hr.

Next, the sheet was crosslinked under the same conditions as in Example 3, and then introduced into a heating furnace and foamed.

Comparative Example 4 In place of 1 part by weight of Toray Silicone 5H1930 in Example 3, 2 parts of zinc white (zinc stearate = 1 = 1 mixture) was added.
．． A foamable uncrosslinked sheet of the same size was extruded from the mixture containing 0 parts by weight using the same extruder as in Example 3. Since the decomposition temperature of ADCA was extremely lowered by the addition of zinc white and zinc stearate, it became necessary to lower the extrusion temperature to 125° C. or lower. Furthermore, at this temperature, in order to prevent surface roughness due to melt fracture, the discharge rate had to be lowered to 59 kg/l (r). After crosslinking under the same conditions as above, it was introduced into a heating furnace and foamed.

Example 4 A mixture with the same blending ratio as in Example 1 was put into a small twin-screw extruder (rotating in different directions), and a foamable composition in a molten state was produced at an extrusion temperature of 130°C without decomposing DCP and ADCA. Obtained. The discharge amount at this time was 54. kg/l (r).

Next, the composition immediately after extrusion was heated at 30°C set at 150°C.
After putting it into a 0W x 600 Q x 20tmm mold and repeating pressurization and depressurization several times to bleed out the air,
Pressure is increased to 200 kg/d, and the heating rate is 6°C/1Ili.
The mixture was heated to 200° C. and then the mold was opened for foaming.

Comparative Example 5 A mixture having the same blending ratio as Comparative Example 1 was put into the same twin-screw extruder as in Example 4 to obtain a foamable composition in a molten state. However, unlike Example 4, in order to maintain the extrusion temperature g of 130° C., the discharge rate had to be reduced to 42 kg/Hr. The foamable composition was foamed under the same conditions as in Example 4.

The foamable sheets of Examples 1 to 4 and Comparative Examples 1 to 5 obtained above were examined for expansion ratio, average cell diameter, cell uniformity, surface coloration, surface smoothness, and blowing agent efficiency. The results are shown in Table-1.

(1) The method of determination is as follows.

Foaming ratio: In-house method (foam density/resin density) Average cell diameter: Uniformity of bubbles using in-house method in accordance with ASTM-D3576: Visual surface coloring with expansion measures Degree: JIS K 7103 Surface smoothness: In-house method (by visual inspection and touch) Foaming agent efficiency: Expansion ratio/ACOA parts by weight 1 Delicate foam efficiency index, This means that the smaller this value is, the lower the density of the foam can be obtained with a smaller amount of blowing agent.

(2) The meanings of the abbreviations are as follows.

ADCA...Azodicarbonamide DCP...Dicumyl peroxide ◎・・・Good Good 0...Slightly bad Δ...bad ×...very bad

Claims (3)

[Claims] (1) Production of a closed-cell crosslinked polyolefin resin foam characterized by introducing a crosslinked structure into a foamable resin obtained by mixing a polyolefin resin with a pyrolytic blowing agent and a polysiloxane oil, and then heating and foaming the foam. Method. (2) The method for producing a closed-cell crosslinked polyolefin resin foam according to claim 1, wherein the polysiloxane oil is a modified polysiloxane obtained by modifying siloxane with glycol. (3) Production of a closed-cell crosslinked polyolefin resin foam according to claim 2, wherein the amount of modified polysiloxane used is 0.01 to 1.0 parts by weight per 100 parts by weight of the polyolefin resin. Method.