JPS6011329A - Continuous manufacture of crosslinked and foamed body - Google Patents

Abstract

PURPOSE:To make it possible to extrude not only a thick-walled foamed body whose expansion ratio may range from a high expansion ratio to a low expansion ratio but also a foamed body whose cells have a fine diameter and that is high in resiliency, by giving a back pressure to the resin present in the early stage of an elongate land die. CONSTITUTION:A crosslinkable thermoplastic resin, a foaming agent and a crosslinking agent whose thermal decomposition temperature is higher than the plasticating temperature of the resin are extruded into an elongate land die. A lubricant is fed from near the inlet of the elongate land die to a sliding section between the die and the melted resin, and the resin present between the sliding sections of the die and the melted resin, the sliding sections extending from the early stage 8 of the die to the intermediate of the latter stage thereof, is removed so that a back pressure may be given to the resin present in the early stage 8 of the elongate land die. The resin is allowed to be crosslinked at the early stage and then the pressure at the latter stages 10, 11 is reduced to allow the foaming agent to volatilize or the foaming agent is heated to decompose. Then a foamed body is extruded from the die.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extrusion molding method for crosslinked foam,
More specifically, the present invention relates to an extrusion molding method that allows production of crosslinked foams, particularly plate-shaped ones, with a range of expansion ratios from low expansion ratios to high expansion ratios.

Conventionally, various methods have been known for producing crosslinked foams of thermoplastic resins. For example, after mixing a chemical blowing agent with a thermoplastic resin and molding it, irradiating it with ionizing radiation to crosslink it and heating it. After mixing a chemical foaming agent and a photosensitizer with a thermoplastic resin and molding it,
A method of irradiating ionizing radiation to cause crosslinking and heating to foam, or a method of mixing a thermoplastic resin with a chemical blowing agent and a crosslinking agent having a decomposition temperature lower than that of the foaming agent, molding the mixture, and then heating the mixture. There are methods such as decomposing a crosslinking agent to cause crosslinking, and then decomposing a chemical foaming agent to cause foaming. Although these methods differ in the crosslinking process, they all agree that they use a chemical foaming agent and are heated and foamed under regular use. A method is adopted in which the paper is heated by an infrared heater or a duck breeze while the paper is transferred by an eight-transfer device δ such as a belt.

In such foaming under normal pressure, when heated rapidly, only the surface of the resin foams, and the foamed part acts as a heat insulating layer that inhibits heat transfer to the inside of the resin (41).
Since it is difficult to thermally decompose the chemical foaming agent inside the resin, a method of gradually heating it over time is used.
Even so, when it comes to thick-walled products of 10was or more, it becomes difficult to thermally decompose the chemical foaming agent inside. Therefore, the maximum thickness of the foam is about 20 mm, and in order to obtain a crosslinked foam that is thicker than that, it is necessary to bond the foams together. In addition, when heating and foaming during transportation, the foam sticks to the wire mesh endless belt, and the belt in contact with the foam may follow the foam in the traveling direction or lateral direction due to the volumetric expansion of the foam. Because of the difficulty, there is a problem that the foam may fold over or wrinkle. Furthermore, 20
Since heating is performed in the atmosphere at a high temperature of 0° C. or higher, thermal oxidative deterioration of the resin progresses at the same time, which poses the problem of adversely affecting the surface layer of the foam.

On the other hand, the production of cross-linked foam under pressure has traditionally been a one- or two-step manufacturing process in which a compound of thermoplastic resin mixed with a cross-linking agent and a foaming agent is placed in a mold, heated, and foamed. This method has the characteristic of being able to produce thick-walled foams with uniform, fine cells, but because it is a batch system, productivity does not increase and it is difficult to produce large-sized foams. have.

The present inventors have previously proposed a method to solve these problems and continuously produce crosslinked foam ('RF Application
-52548). That is, this is a method in which the thermoplastic resin is crosslinked and the foaming agent is decomposed in a long land die equipped with a constriction section, and then foaming is performed. According to this method, it was necessary to change the structure of the constriction portion each time due to differences in the type of resin and blowing agent, the desired degree of foaming, and the like.

The present inventors have now discovered a new manufacturing method that does not require the above-mentioned constriction section.In other words, the gist of the present invention is that a crosslinkable thermoplastic resin, a blowing agent, and After uniformly mixing with a crosslinking agent having a heat content of 8 yen higher than the plasticizing temperature of the resin, the resin is extruded into a long land die, and the resin is extruded in the pre-stage of the long land die until a melt viscosity suitable for foaming is obtained. The resin pressure is reduced in order to volatilize the blowing agent at a later stage of the long land die, or the foaming agent is heated to a temperature higher than that at which the blowing agent volatilizes or decomposes, and then extruded from the long land die. In the method for producing a foam, lubricant is supplied from near the entrance of the long land die to the sliding contact area between the die and the molten resin, and lubricant is supplied from between the front and rear stages of the long land die to the die and the molten resin. Continuous production of a crosslinked foam characterized by applying back pressure to the resin at a stage before a long land die by removing lubricant present at the sliding contact portion with the molten resin. It's a method.

With this configuration, it is possible not only to obtain a thick foam with a low expansion ratio to a high expansion ratio, but also to extrude a highly elastic foam with a fine cell diameter, and to achieve high productivity. That's what I was able to get.

The present invention will be explained in detail below.

The crosslinkable thermoplastic resin used in the present invention is, for example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylon, etc., or a copolymer mainly composed of the above thermoplastic resin, such as ethylene-propylene copolymer, ethylene -Copolymers such as vinyl acetate copolymer, ethylene-vinyl chloride copolymer, vinyl chloride-vinylidene chloride copolymer, etc., and mixtures of these polymers; A mixture of thermoplastic resin and additives such as plasticizers, pigments, flame retardants, antistatic agents, fillers, and weathering agents, and crosslinking aids such as organic peroxides and polyfunctional monomers.

Furthermore, a mixture of a crosslinkable thermoplastic resin other than a thermoplastic resin, such as an ethylene-propylene copolymer elastomer, a styrene-butadiene block copolymer elastomer, and the above-mentioned additives; It also includes mixtures with

In addition, the blowing agent used in the present invention may be a volatile blowing agent or a blowing agent that is solid at room temperature and that undergoes chemical thermal decomposition to produce nitrogen.
A decomposable blowing agent that generates gases such as carbon dioxide and ammonia is used. Volatile blowing agents are usually aliphatic hydrocarbons such as butane, pentane, hexane, heftane, aliphatic norogenated hydrocarbons such as methyl chloride,
Methyl fluoride etc. are used. As a decomposable blowing agent, it is solid at room temperature and has a decomposition temperature higher than the plasticizing temperature of the resin used, and when heated above this temperature, it generates gases such as nitrogen, carbon dioxide, and ammonia. Compounds that decompose, such as azodicarbonamide, metal salts of azodicarbonamide, trihydrazinotriazine, 4
．． Examples include 4'-oxybisbenzenesulfonyl semicarbazide, 4.4'-4oxybisbenzenesulfonyl hydrazide, N,N'-simef-NN'-dinitronoterephthalamide, and the like. The amount of the blowing agent to be used is not particularly limited, and may be determined as appropriate depending on the desired expansion ratio, but it is 1 to 100 parts by weight, preferably 1 to 40 parts by weight, per 100 parts by weight of the resin. Moreover, various foaming aids and nucleating agents can be used as necessary for these foaming agents.

Further, the crosslinking agent used in the present invention has a decomposition temperature higher than the melting start temperature of the thermoplastic resin used, and a crosslinking agent suitable for crosslinking the resin may be selected as appropriate.
Typical examples include dialkyl peroxide-based ditertiarybutyl 2-oxide, tertiarybutylcumyl(-oxide, dicumyl peroxide, 2-oxide,
．． 5-dimethyl-2,5 di(tert-butylperoxy)hexane, α, α-bis(tert-butylperoxy)
It is an organic peroxide such as (oxyinopropyl)benzene or a mixture of two or more thereof, sulfur, etc., and if desired, an auxiliary agent such as a crosslinking retarder or a crosslinking accelerator is mixed therein.

Note that the decomposition temperature of the crosslinking agent herein refers to the temperature at which the half-life is 10 minutes or less.

The amount of these crosslinking agents to be used needs to be determined depending on the molecular structure of the thermoplastic resin used, such as the molecular weight, molecular weight distribution, and number of branches, the decomposition temperature of the crosslinking agent, and the degree of crosslinking required. Specifically, 1 to 5% sail weight is preferred, and more preferably 0.2 to 2 weight% is used. 0
．． If it is less than 1% by weight, especially when using a crystalline thermoplastic resin, the crosslinking will not sufficiently reduce the fluidity of the resin, resulting in a homogeneous cell structure inside the thick crosslinked foam. On the other hand, when it is more than 5% by weight,
The fluidity of the resin in the extruder is excessively reduced, and it tends to be difficult to obtain a crosslinked foam with a homogeneous cell structure.

The lubricant used in the present invention is usually chemically stable such that decomposition, boiling, etc. do not easily occur at the molding temperature of the resin, and does not dissolve in the resin and does not promote the deterioration of the resin. Preferably, the substance is

Specifically, liquid polysiloxanes (polydimethylsiloxane, polymethylsiloxane, etc.), polyhydric alcohols such as ethylene glycol and their alkyl esters and alkyl ethers, polyoxyalkylenes, and
Random, block and graft copolymers of more than one type of alkylene oxide are used. Among these, preferred are water-soluble surfactants such as polyhydric alcohols, which are easy to remove after adhering to the surface of the molded article.

Next, the method for extrusion molding the crosslinked foam of the present invention will be described in detail with reference to the process side diagram of FIG.

A crosslinking agent is added to the crosslinkable thermoplastic resin, in particular in an extruder (1
), at a temperature at which the main part of the crosslinking agent does not react, and then a volatile foaming agent is injected in the middle of the cylinder or near the outlet of this extruder (1), mixed again, and then Extrude into a land die (8). Alternatively, a crosslinking agent and a decomposable blowing agent are uniformly mixed into a crosslinkable thermoplastic resin, particularly in an extruder (1), at a temperature at which the main parts of the crosslinking agent and decomposable blowing agent do not decompose. Shakurandai (8)
Push it inside.

A lubricant supply flange (4) capable of continuously supplying lubricant is provided near the entrance of a long land die (8) connected to the extruder (1). The supply flange (4) has a structure as shown in FIG. 2, and a slit (5) is formed over the entire inner circumference of the lubricant supply flange (4) with which the resin comes into sliding contact, and a supply device (7) is formed here. ) so that the lubricant can be applied to the outer surface of the resin via the conduit (6).

The reason why the lubricant is supplied near the entrance (4) of the long land die is that as crosslinking bonds are formed in the resin due to decomposition of the crosslinking agent, the flowability of the resin decreases and the resin pressure increases. The reason for this is to allow the resin to move smoothly within the long land die using the lubricant, since this may lead to damage to the extruder.

The long land die (8) is equipped with a heater so that the thermoplastic resin can be heated to a predetermined temperature.

Here, the resin moves while sliding through the long land die (8) under pressure and temperature that do not volatilize or decompose the blowing agent, and during this time, crosslinks are generated in the resin.

The degree of crosslinking is such that the residual gel weight fraction (hereinafter referred to as gel fraction) is 5% or more after 10 hours of extraction near the boiling point of xylene, and preferably the gel fraction is 10% from the relationship between expansion ratio and gel fraction. By setting the amount to 7%, almost all of the gas generated by the blowing agent can be used for foaming and expansion.

In addition, the length of the long land die necessary to generate a crosslinking bond with a gel fraction of 5% or more in the resin is determined by the resin temperature in the long land die, the molding speed, and the thermal conductivity of the resin at the molding temperature. It can be determined based on the decomposition characteristics of the crosslinking agent used, and 100C+J1 to 3.000 cm is usually suitable.
Furthermore, 200 cm to 2,000 cm is preferable. 10
Below 0 crn, it is difficult to obtain homogeneous foam cells, while above 3,000 crn is unnecessary to obtain homogeneous cells.

A lubricant extraction flange 01 having a structure as shown in FIG. 3, for example, is provided at the position of the long land die that has reached a length sufficient to almost complete the crosslinking of the resin, and the lubricant extraction flange 01 is provided in the long land die (8). Remove the lubricant on the surface layer of the supplied resin.

The resin from which the lubricant has been removed has reduced sliding properties with the long land die (9), thereby increasing surface resistance and applying back pressure into the long land die (F+) (9).

Depending on the type of blowing agent, a portion of the blowing agent may volatilize or decompose and foam even at the temperature in the crosslinking zone, which also inhibits the crosslinking reaction. Therefore, by removing the lubricant from the vicinity of the position of the long land die where the degree of crosslinking reaches the desired gel fraction, the slipperiness between the long land die and the resin is reduced, and the resistance with the long land die wall surface is reduced. This increases the back pressure in the long land die. Even if some of the foaming agent in the long land die evaporates or decomposes due to this back pressure,
It becomes molten in the resin.

Further, if a drawing die is provided at any position of the long land dies (8) (9), further back pressure can be applied, so it is also useful to control the back pressure by using a drawing die in combination.

Furthermore, cross-linking has sufficiently progressed, and the back pressure in the long land dies (8) (9) is
(9) Apply new lubricant as necessary from the position of the long land die where sufficient back pressure has been reached to prevent gas from forming in the resin due to partial volatilization or decomposition of the blowing agent. It is also possible to reapply the slipperiness of the resin by supplying it.

In other words, if the lubricant is left drained, the back pressure will continue to rise, so when the desired back pressure is reached, the lubricant is supplied again using the lubricant supply flange (10), and the back pressure is increased. This is to prevent the formability of the cross-linked resin from deteriorating as the back pressure increases, but depending on the resin used, the lubricant may need to be supplied again. In some cases, it may not be necessary to do so.

The desired back pressure is usually about 10 Kp/- or more, preferably 30 to zooKq/d. In addition, the length of the long land die (9) required to reach the desired back pressure is
It may be determined depending on the shaped shape of the resin, the amount of lubricant extracted, and the molding speed, and is usually 30 Crn to 500 Crr1.
is suitable.

Heat to a temperature above which it evaporates and decomposes. The core resin begins to expand in volume due to the volatilization and decomposition of the foaming agent, and expands sequentially as the die cross-sectional area increases in the latter stage αI (11) of the long land die, and finally the foamed molded product is released from the long land die. (b) becomes.

Since the present invention has a diagonal structure, even if the foam is thick, it can be made into a highly foamed product that is uniform throughout the interior, and can be produced in a continuous process.

In addition, even though a long die is used, by using the diagonal configuration, the extrusion speed is increased without reducing the extrusion molding speed, and the foam can be efficiently produced. be. Furthermore, even when applied to crystalline polyolefin resins, especially high-density polyethylene resins, which have been considered difficult in the past, it has become possible to achieve high and homogeneous foaming.

The present invention will be further explained below with reference to examples. Example 1 The extrusion molding machine (1) shown in FIG. A masterbatch prepared by pre-mixing 15 parts by weight of 15 parts by weight of AC Su3) manufactured by the company and 0.8 parts by weight of a crosslinking agent (Perbutyl C manufactured by NOF Corporation) was added and supplied. The extrusion molding machine (1) uses a single screw (L/D=22) with a 1565 tone, and has a cross section of 20 m5 x 2.
It was extruded into a long land die (8) with a diameter of 0.00 mm. The resin thermometer (2) near the exit of the extrusion molding machine (1) showed 158°C. The lubricant (Nissan Unilube 75D-3800 manufactured by NOF Corporation) is supplied from the lubricant supply flange (4).
A constant amount of Z) was supplied from the entrance side wall of the front stage part (8) of the long land die through the slit (5). In the long land die (8), the temperature is 170°C in the direction of resin progression.
, 170° C., 173° C., and 175° C. Heating was performed with a temperature distribution in four stages, and the length of the front part (8) of the long land die at this time was 3 m. Next, at the outlet of the front stage part (8) of the long land die, a lubricant extraction 7 is installed.
The front part (8) of the long land die is provided with two die (2).
The lubricant interposed between the resin inside and the die wall was removed.

The length of the intermediate part (9) of the long land die was Im, and the cross section was 20 g x 200 ms, the same as the front part (8) of the long land die. At the outlet of the long land die middle part (9), there is a lubricant supply flange O1! 11 lubricant was again supplied to the interface between the resin and the die wall.

In the intermediate portion of the long land die (9), heating was performed by providing a two-stage temperature distribution of 176° C. and 178° C. in the direction of resin travel.

Further, at this time, the resin pressure gauge (3) near the outlet of the extrusion molding machine (1) showed 43 Ky/cd.

Furthermore, the gel fraction of the resin at the outlet of the intermediate portion (9) of the long land die was 41%.

Next, in the rear part of the long land die (at the temperature of 180°C, 185°C, 190°C, in order to thermally decompose the foaming agent)
Heating was performed with a temperature distribution in four stages of 190°C and 190°C, and the length of the die was 3 m.

Further, the cross sections of the long land die rear section (6) a are 30 tubes x 3.00 tubes and 50 tubes x 500 tubes, respectively, and are designed to expand as the resin foams and expands.

In this way, the resin was extruded from the long land die (B) under atmospheric pressure at a temperature of 0.degree. C., thereby making it possible to continuously extrude the foam O-bar.

The foam (b) according to this example is 63 arms x 62
It was a continuous foam board with a rectangular cross section of 0 wn, and a plate-like foam having microcells of 150 microns or less and a skin layer with a density of 0.028 t/cr/i.

Example 2 In Example 1, the amount of lubricant extracted from the lubricant extraction flange 01 was halved, the lubricant supply to the lubricant supply flange←Q was stopped, and the same molding as in Example 1 was carried out. As a result, a foam board similar to that of Example 1 was obtained.Example 3 Polypropylene (FX4 manufactured by Mitsubishi Yuka Co., Ltd.) 100
A resin prepared by mixing 18 parts by weight of a blowing agent (AC≠3 manufactured by Eiwa Kasei Co., Ltd.) into granules, 0.5 parts by weight of a crosslinking agent (Perbutyl D manufactured by NOF Corporation) and a crosslinking aid (diptylbenzene) )0.4 parts by weight were added and mixed in advance, and then molded in the same manner as in Example 1, and the cross section was 65 mm x 64 mm.
A plate-shaped foam having a density of 027 and having microscopic cells with a cell diameter of 0 mm and 300 microns or less was obtained.

Example 4 A foaming agent injection hole was provided at a length of 315 mm from the tip of the cylinder of a 50 carp C extrusion with L/D = 28 (4f AC cross source crew compression ratio 1.52) toward the die side, and a gear pump was inserted from there. Into an extruder capable of injecting a volatile blowing agent (butane), 100 parts of low-density polyethylene (Mitsubishi Yuka Co., Ltd., Yucalon LK50), 3 parts by weight of talc and a crosslinking agent (NOF Co., Ltd.) were added. Company-made, DCP)
0.6 parts by weight was added, mixed and supplied. At this time, the resin temperature measured by the resin thermometer (2) installed near the exit of the extruder (1) was 153°C, and the total length of the long land die was 6 m (front stage 4 m, middle part 1 tn, rear stage 1 m). The temperature of each part is the same as in Example 1. Also, resin pressure gauge (3
) indicated 65 Kf 7' cA.

The front part (8) and middle part (9) of the long land die have an inner diameter of 3
It is a cylindrical die with three gates, and the rear stage OI is a cylindrical die with an inner diameter of 45mm. A lubricant supply flange was installed at the entrance of the front part (8) of the long land die to supply lubricant to the sliding contact area between the die and the resin. In addition, a lubricant extraction flange a1 is provided at the entrance of the long land die intermediate part (9) to draw out the lubricant, and a lubricant supply flange aQ is provided again at the entrance of the long land die to remove the lubricant from the die. The resin was supplied to the sliding contact area.

The foam (b) extruded from the long land die (11) was a rod-shaped foam having an outer diameter of 86wIII, a density of 0.032 f/cr/4, a gel fraction of 53%, and cells with an average cell diameter of 500 microns. Ta.

FIG.

1: Extruder 2: Resin thermometer 3: Resin pressure gauge 4: Lubricant supply flange 5 Nislit part 6: Conduit 7: Lubricant supply device 8: Front part of long land die 9: Middle part 10: Rear section (1) 11:p #(2) 12: Foamed molded product +3: FFI agent removal flange 14: Conduit 15: The old lubricant receiver is a container 162 lubricant supply flange 17: +7”5 lubricant supply device 18: Conduit 4”￥Product applicant Mitsubishi Yuka Co., Ltd. Patent attorney Hidetoshi Furukawa Agent: Patent Attorney Masahisa Nagatani

Claims (1)

[Claims] After uniformly mixing a crosslinkable thermoplastic resin, a foaming agent, and a crosslinking agent having a thermal decomposition temperature higher than the plasticization temperature of the resin, extrusion is performed into a long land die, and foaming is performed at a stage before the long land die. The resin is cross-linked until a suitable melt viscosity is obtained, and the resin pressure is reduced to volatilize the blowing agent at a later stage of the long land die, or the resin is heated above a temperature that volatilizes or decomposes the blowing agent. Then, in the method of producing a foam by extrusion from the long land die, a lubricant is supplied to the sliding contact portion between the die and the molten resin from around the entrance of the long land die, and at the same time, a and a back pressure is applied to the resin at the front stage of the long two-way die by removing the lubricant present at the sliding contact between the die and the melted resin from the middle of the latter stage. A method for continuous production of crosslinked foam.