JPS6183237A - Preparation of polyolefin foam - Google Patents

Abstract

PURPOSE:To prepare the title foam with a smaller amount of undesirable large foams stably, by incorporating a particular low-molecular polyolefin with a polyolefin to make foam sizes uniform. CONSTITUTION:100pts.wt. polyolefin such as medium-density PE, PP, or ethylene/ propylene copolymer, 0.5-10pts.wt. low-molecular polyolefin having an MW of 3,000-50,000, an MI of 50-200g/10min, a density of 0.900-0.925, of the formula (wherein R1-4 is H, 1-20C alkyl; a degree of polymn. (n) of 105-1,800) as a foam stabilizer, 5-20pts.wt. org. foaming agent (e.g., azodicarbonamide) and, if necessary, 0.5-10pts.wt. crosslinker and crosslinking aid are mixed and melt-kneaded under conditions where the foaming agent does not cause expansion by decomposition for extruding into a sheet form. Next, the sheet is crosslinked so as to achieve a gel fraction of 15-60% by ionizing radiation or by heating, and then expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a polyolefin foam, and particularly to a method for regulating the foam.

[Conventional technology]

Conventionally, foam regulating methods for polyolefin foams include adding surfactants such as fatty acid esters and their metal salts, fatty acid amines, fatty acid amides, and glycols;
Alternatively, a method of adding polyethylene wax, active polypropylene, etc. is known.

[Disadvantages of conventional technology]

However, all of these conventional methods have the problem that additives separate and ooze out during the foam manufacturing process, or decompose due to lack of heat resistance, resulting in insufficient foam regulation. Needless to say, foam regulation is an essential and important technology for polyolefin foams, and all foamed parts (hereinafter referred to as "cells") must be approximately the same size and have the desired diameter. be. For example, one layer lφ in a foam with a cell diameter of 400 to 600 μφ.
If there are many large bubbles (hereinafter referred to as 1 bubble), for example, in sheet cane foam, there are 20, 150 bubbles.
If it is more than M, it becomes unusable due to quality defects. For this reason, an excellent foam regulating method for uniformly distributing cell sizes has been long-awaited in the foam manufacturing technology.

[Purpose of the invention]

In order to meet the above-mentioned needs, the present invention aims to provide a method for stably producing a polyolefin foam with few bubble defects.

[Structure of the invention]

In order to achieve the above-mentioned object, when producing a polyolefin foam, this invention uses a low-polymerized polyolefin having a molecular weight of 3,000 to 50,000 to 10% polyolefin as a foaming component.
The gist of the present invention is a method for producing a polyolefin foam, which is characterized by foam regulation by adding 0.5 to 10 parts by weight to 0 parts by weight.

The polyolefin of the polyolefin foam in the present invention includes homopolymers of α-olefin monomers such as ethylene, propylene, butene-1,4-methyl-pentene-1, and hexene-1, copolymers consisting of these monomers, and the above-mentioned. Copolymers of monomers and monomers other than these that can conduct electricity, such as vinyl compounds such as vinyl acetate and acrylic esters, conjugated diene compounds such as butadiene and isoprene, and mixtures of the above homopolymers and copolymers as main components. This is a thermoplastic resin composition.

Conventionally, polyolefins that are particularly difficult to stabilize include polyolefins with high melt viscosity, polyolefins that are difficult to knead, polyolefins with high crystallinity, polyolefins with little branching, and polyolefins with a strong linear molecular structure. This is a polyolefin typified by a polyolefin with particularly high torque. When these polyolefins are used as a mixed system, the compatibility between the polyolefins becomes particularly poor, resulting in uneven dispersibility of the blowing agent, which tends to result in large bubbles.

Therefore, this invention targets polyolefins that have hitherto been considered particularly difficult to stabilize, such as medium-density polyethylene (MDPE).
), linear low density polyethylene (L-LDPE),
Preferred targets are ethylene-pro, pyrene copolymer (RPC), polypropylene (PP), and low-Mr high-pressure low-density polyethylene (low-Ml-LDPR). Among these, L-LDPE in particular has properties such as linearity, high crystallinity, high melt viscosity, and high melt torque, so it is easy to produce large bubbles from the viewpoint of foam production.
Foam regulation is inherently difficult, especially when using other polyolefins such as EPC, MIIPE, LDPE.
It was believed that foam regulation was extremely difficult in systems where the mixture was mixed with Therefore, it can be said that L-LDPR is the most targeted polyolefin in this invention.

The low-polymerized polyolefin in this invention is represented by the following general formula.

Here, R1-R4 are H (hydrogen) or C number 1 to 20
is an alkyl group, and all of R1 to R4 may be the same or different. The degree of polymerization (n) is 10
5≦n≦1800, preferably 180≦n≦7
It is 50.

That is, specifically, it is a polyethylene-based low polymerization degree polymer, and therefore, materials such as acidic polypropylene are excluded.

The molecular weight (M-) of the low polymerized polyolefin is 3000≦
M-≦50000.

Preferably, 5000≦M tsuba≦20000. If the molecular weight is less than 3000, thermal deterioration etc. will occur during heating and foaming, or phase separation will occur during the extrusion process, and as a result, the generation of large bubbles will be promoted. If the molecular weight is greater than 50,000, the melting properties of the material will be adversely affected, making it impossible to achieve the purpose of foam regulation.

In addition, in order to stably perform foam regulation, the melt flow index (MI) of the low polymerized polyolefin is 50 to 200 g/10 minutes, and the density (ρ) is 0.900 to 0.925 g/cIA. desirable.

The amount of low polymerized polyolefin added is 100 parts by weight (hereinafter abbreviated as "parts") of polyolefin as the main foaming component.
It is necessary that the amount is 0.5 to 10 parts, preferably 0.
．． 8 to 5 parts. If the amount added is less than 95 parts of O, the foam regulating effect will be insufficient, and if it exceeds 10 parts, the difference in resin properties from the polyolefin will become significant, and the foam regulating will become unstable.

Next, the manufacturing method of the present invention will be explained in detail in the order of the process.

First, 100 parts of polyolefin as a main raw material and 0.5 to 10 parts of low polymerized polyolefin as a foam regulating side are prepared. 5 to 20 parts of a known organic blowing agent such as azodicarbonamide is added to these polymers, and if necessary, a known crosslinking agent and crosslinking agent such as divinylbenzene, trimethylpropane triacrylate or peroxide are added. Add 0.5 to 10 parts of auxiliary agent. Furthermore, if necessary, desired amounts of an antistatic agent, a flame retardant, an inorganic coloring agent, etc. are added, and the mixture is uniformly mixed using a mixer. This mixture is supplied to an extruder, melt-kneaded and extruded under conditions where the blowing agent does not decompose and foam. In this process, in order to suppress heat generation due to shearing, it is necessary to control the temperature distribution within the extruder, including the screw shape, rotation speed, and cylinder temperature.

On the other hand, it is necessary to improve the kneading properties and to uniformly and finely disperse the blowing agent and the low-polymerized polyolefin in the main raw material polyolefin and prevent them from agglomerating, and for this purpose, the shear needs to be high. Similarly, it is also important to maintain conditions such that additives other than the blowing agent, such as crosslinking agents, do not decompose or agglomerate. In this process, if the above conditions are not met, air bubbles will be generated.

The sheet-like molded product extruded as described above is crosslinked by an ionizing radiation method or a heating method. The degree of crosslinking is preferably set to a gel fraction of 15 to 60%. The degree of crosslinking, that is, the gel fraction varies depending on the expansion ratio and the purpose. If the gel fraction is too low, the gas retention force during foaming will be weak, and the cell diameter will become large. In this case, even if a low polymerization polyolefin is added, the adverse tendency cannot be stopped.

Next, this crosslinked sheet is foamed to an arbitrary foaming ratio using an infrared heater, a hot air oven, or a chemical bath. The foaming ratio varies depending on the application, but it is preferably in the range of 5 to 55 volumetric foaming ratio.

[Measurement method of physical properties, evaluation criteria]

In this invention, the measurement method and evaluation criteria for characteristics are as follows.

(2) Gel fraction measurement method: Cut the foam into pieces and weigh 0.2g. After immersing this material in tetralin heated to 135°C for 3 hours,
The insoluble portion is taken out, dried in a vacuum dryer, and then weighed.

Evaluation criteria: Gel fraction is calculated by the following formula.

(0,2-xlo, 2) X 100 (%) The number n is 10, and the thickness is an average value.

Next, a 10 cm x 100 square sample is cut out from the foamed product, and its thickness is measured in the same manner as for the sheet.

Evaluation criteria: The foaming ratio (volume foaming ratio) is calculated by the following formula.

■ Bubble measurement method: Shine white light on one side of the foam and observe the foam from the other side to observe changes in the bubbles. In advance, add 0.5 m and liter to black paper, film, etc.

Holes with diameters of 0mm, 1.5fi, 2.0m and 311 are drilled to create reference samples and checked for comparison.

Evaluation criteria: Based on the check contents obtained in the above measurement, the following ranking was given based on the number of bubbles of 1 diameter or more present in 50rrl. (Unit: 150 rrr) 20 or more
...× Less than 20 to 10 or more ...0 Less than 10 ...◎ ○ and ◎ indicate that there is no problem in practical use.

[Example, comparative example]

Examples 1 to 6 and Comparative Examples 1 to 7 are as follows.

As a polyolefin serving as a main raw material, 100 parts of raw materials for polymer composition as shown in Table 1 were prepared. To this, 10 parts of a foaming agent (azodicarbonamide) and 2 parts of a crosslinking aid (trimethylpropane triacrylate) were added, mixed, and a low polymerized polyolefin for foam stabilization was added as shown in Table 1 to form a resin composition for foam. did. Introduce this into the extruder,
It was extruded at 160 to 180°C to form a sheet. Radiation is applied to this sheet using an electron beam accelerator (Nissin High Voltage I).
R-2) was irradiated with 5 Mrad, and then introduced into a silicone bath at 240°C and heated and foamed. The foaming ratio of all these products was 30 times.

The evaluation results are also listed in Table 1. However, in the same table, 4 indicates the intrinsic viscosity, and Et indicates the ethylene content of the copolymer.

(Margins below) As is clear from Table 1, the generation of large bubbles was significantly less in all of the Examples.

On the other hand, Comparative Examples 1 to 7 did not satisfy any of the constituent requirements of the present invention, and therefore the amount of air bubbles generated was significant.

〔Effect of the invention〕

In the present invention, when producing a polyolefin foam, a low polymerized polyolefin with a molecular weight of 3,000 to 50,000 is added to 100 parts of polyolefin as a foaming component in an amount of 0.5 to 1.
Since the foam is adjusted by adding 0 parts, the obtained foam has the effect that the cell size is uniform and there are no large bubbles. To explain this in more detail,
It is as follows.

Air bubbles are thought to be created by various factors that occur during the period from when the raw material is fed into the extruder until it is discharged from the nozzle.During this time, how can each component of the raw material be uniform without agglomeration? What is important is whether fX is finely dispersed and kneaded. If fine bubbles (this is mainly caused by foaming of additives such as foaming agents and other crosslinking agents due to overheating due to excessive shearing in the extruder) are formed or misaligned in the sheet after extrusion and discharge. The fine bubbles inevitably become large bubbles in the subsequent foaming process. In addition, when two or more types of polyolefins are used as main components, if the mutual kneading properties are poor,
The foaming agent and the like aggregate at the interface between both polymers, and the aggregated portion becomes large bubbles in the subsequent foaming process.

The effects of this invention can be explained as follows based on the above circumstances.

In other words, as a result of the addition of low-polymerized polyolefin, the kneading properties are improved, and additives such as blowing agents and cross-linking agents are finely and uniformly dispersed in the polyolefin, which is the main component, and the generation of micro bubbles and agglomerations within the extruded sheet is prevented. As a result, the generation of air bubbles can be prevented. This "effect of reducing air bubbles" due to the addition of low polymerization polyolefin
can be obtained even under a wide range of extrusion conditions (temperature, screw rotation speed, etc.), and for this reason, foams without large bubbles can be stably produced.

[Usage]

Since the foam produced according to the present invention has the above-mentioned effects, it is suitable for the following uses.

■ Automotive molded ceilings, instrument panels, door panels, seat back pockets, foil house covers, center pillars, rear order trims, horn butts, and other items that require deep drawing.

■ Insulating steel plates and heat-insulating waterproof plates for building materials ■ Integral molding of pipe covers for various types of coolers for insulation ■ Packaging materials for general cushioning such as plywood and glass plates ■ Sound-absorbing applications for construction between floors of condominiums, etc. Among the above applications, automobiles In applications such as pipe covers for coolers, particularly good moldability is required, so the foam free of air bubbles produced by the production method of the present invention can serve as a useful base material.

May 5, 2015, published by Narokune City (self-proposal), Patent Application No. 204300, filed in 1982, 2, Name of the invention, Method for producing polyolefin foam 3, Relationship with the case of the person making the amendment, Patent Il. Address: Chuo-ku, Tokyo Nihonbashi Muromachi 2-2 Name Higashishi Co., Ltd.
Company Representative Representative: Director Masatoshi Ito 4, no agent 6, specification subject to amendment 7, contents of amendment (11 The text ``materials'' on page 9, line 9 of the specification 11) The sample is corrected.

(2) r(0,2-xlo) on page 9, line 13 of the specification.

2)X100(%)", I(xlo, 2)X1
00 (%)”.

(3) On page 11, line 15 of the specification, the statement ``1 all 30 times'' should be corrected to ``approximately 30 times.''

(4) The item column at the top of Table 1 on page 12 of the specification as shown in Attachment A should be corrected as shown in Attachment B.

(5) In the 7th line of page 15 of the specification, the phrase [Rear Forder Trim] is corrected to [Rear Quarter Trim].

Claims (1)

[Claims] (1) When producing a polyolefin foam, foam regulation is performed by adding 0.5 to 10 parts by weight of a low polymerized polyolefin with a molecular weight of 3,000 to 50,000 to 100 parts by weight of the polyolefin as a foaming component. Characteristic manufacturing method of polyolefin foam.