JPH10156855A - Manufacture of thermoplastic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermoplastic resin foam even in the case where a foam is successively manufactured at a rapid feed speed, preceeding foaming at an end part of an expandable sheet is prevented, and foaming which produces cells having similar shapes as far as posible, can be executed. SOLUTION: In this manufacturing method, a long expandable sheet 6 containing a pyrolysis foaming agent is successively sent into a preheating oven 2. After preheating to a temperature just before decomposition start temperature of the pyrogenic foaming agent, the preheated expandable sheet 6 is successively sent into a foam oven 3, heated at a temperature or higher wherein the pyrogenic foaming agent is thoroughly decomposed to foam pyrogenic foaming agent thoroughly. In this case, for temperature at an outlet of the preheating oven 2 of the expandable sheet 6 the expandable sheet is preheated so that temperature distribution in a thickness direction becomes surface temperature-central temperature in thickness direction <=5 deg.C, temperature distribution in width direction of the expandable sheet 6 becomes temperature at end part < width direction center temperature, and temperature difference between both end parts <=3 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic resin foam.

[0002]

2. Description of the Related Art Conventionally, a sheet-shaped thermoplastic resin foam is formed by expanding a foamable thermoplastic resin sheet containing a pyrolytic foaming agent (hereinafter referred to as an “expandable sheet”). After being preheated to a temperature close to the thermal decomposition start temperature, the preheated foamable sheet is heated in a heating furnace to a temperature higher than the thermal decomposition temperature of the thermal decomposition type foaming agent to complete the foaming. I have.

[0003] However, since the foamable sheet is heated in three directions from the top and bottom and from the side, both ends thereof are more susceptible to heat from the center, and the pyrolytic foaming agent at both ends tends to pre-foam. Then, since the pre-foamed portion of the thermal decomposition type foaming agent generates huge wrinkles, foaming becomes unstable, and wrinkles may adhere to each other to impair the surface properties.

In Japanese Patent Application Laid-Open No. 57-126630, the foamable sheet is preheated in an infrared heating furnace until the start of foaming, and at the time of preheating, the infrared density at both ends of the foamable sheet is set to other values (center in the width direction). ) Suggest a way to lower it. That is, by lowering the infrared density of the foamable sheet, the heating temperature at both ends is made lower than that at the center to suppress the preceding foaming.

[0005] However, in actual foaming, it is not possible at present to suppress the preceding foaming at the end simply by lowering the temperature at the end from the center. This is because even if the temperature at the end is lower than the center in the width direction, if the sheet has a temperature distribution in the thickness direction, the foaming at the center in the thickness direction is delayed, and the unfoamed portion at the center in the thickness direction has the entire thickness direction. This is because the pre-foaming from the end of the foamable sheet, in which the temperature at the center in the thickness direction is most likely to rise most, is given priority.

[0006] If the precedent foaming from the end is extremely prioritized, a huge wrinkle is generated due to the difference in the foaming speed between the end and the center in the width direction. The parts adhere to each other, and the surface is scratched, or the foaming becomes difficult.

In view of the above, the inventor of the present invention has proposed a method for producing a stable and beautiful foam in a foaming step in which a central portion in the thickness direction and a surface portion are foamed almost uniformly, and a pyrolysis type is used. The temperature distribution in the thickness direction of the foamable sheet until the temperature immediately before the decomposition start temperature of the pyrolytic foaming agent is changed from the foamable sheet containing the foaming agent to the surface temperature−thickness center temperature ≦
After preheating in the range of 5 ° C., a production method has been proposed in which the preheated foamable sheet is heated to a temperature higher than the temperature at which the foaming agent is completely decomposed to completely foam the decomposable foaming agent. (See Japanese Patent Application No. 7-238417).

[0008] However, this production method can successfully obtain a foam when used in a batch system.
When a long foamable sheet is continuously fed from a preheating furnace to a foaming furnace to obtain a foam, and used in a continuous manner, when the feeding speed of the foamable sheet, that is, the production speed is increased, the foaming sheet is also advanced from one end in the width direction. Foaming or foaming may be unstable.

[0009] The cause is that in the continuous manufacturing method, the flow of the air stream is generated irregularly in the preheating furnace,
This is because the heat balance in the preheating furnace is easily lost, and a low-temperature part is formed in the preheating furnace, and a part that cannot be sufficiently preheated is formed.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is intended to prevent foaming at the end of a foamable sheet as much as possible even when a foam is continuously produced at a high feed rate. It is an object of the present invention to provide a method for producing a thermoplastic resin foam capable of performing similar foaming.

[0011]

In order to achieve such an object, a method for producing a thermoplastic resin foam according to the present invention comprises the steps of: forming a long foamable sheet containing a pyrolytic foaming agent; After being preliminarily heated to a temperature immediately before the decomposition start temperature of the pyrolysis type foaming agent, the preheated foamable sheet is subsequently fed into a foaming furnace to completely decompose the pyrolysis type foaming agent. A method for producing a thermoplastic resin foam in which a pyrolytic foaming agent is completely foamed by heating to a temperature or higher, wherein the temperature of the foamable sheet at the outlet of a preheating furnace is obtained by calculating the temperature distribution in the thickness direction from the surface temperature to the thickness direction. The pre-heating was performed so that the center temperature was 5 ° C. and the temperature distribution in the width direction of the foamable sheet was such that the end temperature <the center temperature in the width direction and the temperature difference between both ends ≦ 3 ° C.

In the above structure, a plurality of heating means capable of controlling the temperature are arranged side by side in the width direction inside the preheating furnace, and the temperature distribution in the width direction of the foamable sheet coming out of the preheating furnace is output to the preheating furnace outlet. It is preferable to read the data with a temperature measuring device provided and preheat the respective heating means while controlling the temperature based on the read data.

The foamable sheet of the present invention is not particularly limited, but can be obtained, for example, by the following three typical production methods. A method of mixing a thermoplastic resin, a pyrolytic foaming agent, and other fillers, shaping the sheet with an extruder or a roll and a press, and irradiating the sheet with an electron beam to crosslink the sheet.

After mixing a thermoplastic resin and a pyrolytic foaming agent, a pyrolytic crosslinker, and other fillers, form a sheet with an extruder or a roll and a press, at a temperature not lower than the temperature at which the pyrolytic crosslinker decomposes, And a method of crosslinking by heating to a temperature below the temperature at which the pyrolytic foaming agent decomposes. After mixing a thermoplastic resin grafted or copolymerized with a silicon-containing compound capable of bonding by hydrolysis and dehydration condensation, a pyrolytic foaming agent, and other fillers, the mixture is formed into a sheet by an extruder or a roll press to form a dehydration condensation crosslink. A so-called water crosslinking method.

The thermoplastic resin used in the present invention is not particularly limited. Examples thereof include olefin resins such as polyethylene, polypropylene and polybutene, copolymers of olefins, olefins such as vinyl acetate, acrylic acid and methacrylic acid and other olefin resins. Copolymers with monomers, vinyl homopolymers such as polyvinyl chloride and polyvinylidene chloride, acrylonitrile, vinyl acetate, vinylidene chloride,
Vinyl copolymer such as methyl acrylate, styrene
Diene polymers such as butadiene rubber and natural rubber; amide polymers such as nylon 6.6 and nylon 12; and thermoplastic ester polymers such as polyethylene terephthalate and polybutylene terephthalate. Of these, polyethylene and polypropylene are exemplified. Especially often used.

The pyrolytic blowing agent used in the present invention is not particularly limited, but is usually azodicarbonamide (ADCA), azobisisobutyronitrile (AIB).
N), dinitrosopentamethylenetetramine (DP
T), p-toluenesulfonyl hydrazide (TSH),
Benzenesulfonyl hydrazide (BSH) and sodium bicarbonate are utilized.

The decomposition peak temperature (temperature at which decomposition is most promoted) of each of the above pyrolytic foaming agents is as follows:
ADCA is 195 ° C, AIBN 105 ° C, DPT190
° C, TSH110 ° C, BSH110 ° C, and sodium bicarbonate 90 ° C.

The foaming agent preferably has a decomposition temperature higher than the melting temperature of the resin and is inexpensive, and is preferably made of polyethylene (melting point 105 ° C.), polypropylene (melting point 145).
C) is often used as a thermoplastic resin, and it is usually preferable to use ADCA as a foaming agent.

A foaming aid for controlling the foaming speed may be added together with these foaming agents. As foaming aids for increasing the foaming speed, metal soaps such as zinc stearate and calcium stearate, inorganic salts such as zinc white and zinc nitrate, and acids such as adipic acid and oxalic acid are used, and the foaming speed is retarded. Examples of the foaming assistant include organic acids such as maleic acid and phthalic acid, organic acid anhydrides such as maleic anhydride and phthalic anhydride, and tin compounds such as dibutyltin malate and tin chloride.

The foaming auxiliary varies depending on the type of resin, foaming agent and auxiliary used, but is usually added in an amount of about 0.1 to 2 parts by weight based on 100 parts by weight of the thermoplastic resin. preferable. That is, when the amount is 0.1 part by weight or less, the effect is small, and when the amount is 2 parts by weight or more, the state is saturated, and there is a possibility that the effect of further addition may be lost.

The crosslinking agent has a decomposition temperature equal to or higher than the softening point of the thermoplastic resin constituting the foamable sheet.
A resin suitable for crosslinking the resin may be appropriately selected, for example, dicumyl peroxide, α, α′-bis (t-butylperoxy-III-isopropyl) benzene,
5-dimethyl-2,5-di (t-butylperoxy) hexane-3, t-butylperoxybenzoate, t-
Butylcumyl peroxide, cyclohexane peroxide, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) 3,
3,5-trimethylcyclohexane, 2,2-bis (t
-Butylperoxy) octane, n-butyl-4,4-
Bis (t-butylperoxy) berrate, di-t-butylperoxide, benzoyl peroxide, cumylperoxyneodecanate, 2,5-dimethyl-2,
5-di (benzoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, di-t -Butylperoxyisophthalate, t-butylperoxymaleic acid and the like.

The kneading temperature of the thermoplastic resin varies depending on the kind, but is usually 130 ° C. or higher. Therefore, it is usually preferable to use a crosslinking agent having a decomposition temperature higher than 130 ° C., and as such a crosslinking agent, dicumyl peroxide, α, α′-bis (t-butylperoxy-
III-isopropyl) benzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and the like, and dicumyl peroxide, α, α′-bis (t -Butyl peroxy II
I-isopropyl) benzene is more preferred.

These may be used alone or in combination of two or more. In the above water crosslinking method, the use ratio of the silicon-containing compound can be appropriately determined according to a desired degree of crosslinking, but is usually 0.5 to 3 parts by weight based on 100 parts by weight of the thermoplastic resin.

As the silicon-containing compound capable of bonding to each other through the hydrolysis and dehydration bonds, a silicon-containing compound having a vinyl group capable of undergoing radical or graft or copolymerization and an alkoxy group causing hydrolysis and dehydration condensation can be used. Without limitation, for example, a compound represented by the following formula:

[0025]

Embedded image

Among these compounds, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane and the like are preferable. It is preferable that at least one organic tin compound selected from dibutyltin dilaurate and dibutyltin dimaleate is added to the above compound as a condensation crosslinking catalyst between the reactive silicon-containing groups.

The addition amount of these organotin compounds is preferably about 0.1 to 1 part by weight based on 100 parts by weight of the thermoplastic resin.

Further, in addition to the above composition, a foam nucleating agent, an antioxidant, a pigment, a flame retardant and the like may be added to the foamable sheet as required. Examples of the foam nucleating agent include calcium carbonate, talc, clay, magnesium oxide, zinc oxide, carbon black, silicon dioxide, titanium oxide, citric acid, sodium bicarbonate, orthoboric acid, talc, and alkaline earth metal salts of fatty acids. No.

The antioxidant is not particularly limited as long as it is generally used. Examples thereof include tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, dilauryl thiodipropionate, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like.

Examples of the flame retardant include brominated flame retardants such as hexabromophenyl ether and decabromodiphenyl ether, phosphoric acid-containing flame retardants such as ammonium polyphosphate, trimethyl phosphate and triethyl phosphate, melamine derivatives, inorganic flame retardants and the like. One or a mixture of two or more kinds may be mentioned.

The method for heating the foamable sheet in the preheating step is not particularly limited. For example, the foamable sheet is introduced into a heating furnace using a radiant heater, a hot air heater, a heat transfer heater, or a salt bath and heated. Method.
Further, in the preheating step, the foamable sheet may be continuously fed to a heating furnace for preheating by belt conveyance and heated by mixing, or may be heated in fixed units by a batch method.

The temperature at which the foaming agent starts to decompose is the temperature at which even a very small amount of the foaming agent starts to generate gas, and varies depending on the type, particle size and additives of the foaming agent. However, when ADCA is used as a foaming agent and no other additive is added to the foaming agent, 150 to
200 ° C. becomes the decomposition start temperature.

The heating means used in the preheating furnace is not particularly limited, and includes, for example, a radiation (radiation) heater such as a far infrared heater, a nozzle type hot air heater, and the like, and these can be used in combination. That is, after heating to about the decomposition start temperature by the radiant heater, if hot air set at a temperature slightly lower than the decomposition start temperature is blown, the surface temperature caused by heating by the radiant heater-the thickness center temperature> 5 ° C. Temperature gradient,
By using hot air, it is possible to set the surface temperature−the thickness center temperature ≦ 5 ° C.

If heating is performed while simultaneously using a radiant heater and a hot air heater set at a temperature lower than the temperature to be heated, the radiant heater having an excellent internal heating effect promotes heating of the central portion in the thickness direction while providing a hot air heater. Thereby, the surface temperature can be kept low. The temperature slightly lower than the decomposition start temperature varies depending on the heating conditions, but is preferably a temperature lower by about 5 to 10 ° C. than the normal decomposition start temperature. In other words, the effect is small at 5 ° C. or less,
Above, the sheet may be too cold.

The temperature difference between the end portion temperature and the center portion temperature is preferably up to a maximum of 10 ° C., although it depends on the composition of the foamable sheet. That is, if the temperature difference is 10
When the temperature is higher than or equal to ° C., pre-foaming from the central portion is started, and the surface is roughened due to excessive heating, and there is a possibility that a good product cannot be obtained.

As the heating means used in the foaming furnace, a radiation heater such as a far infrared heater, a hot air heater,
Examples include a heat transfer heater and a salt bath. The temperature at which the pyrolytic foaming agent is completely decomposed means a decomposition temperature at which the undecomposed foaming agent does not remain.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. 1 and 2 show an embodiment of an apparatus used for a method for producing a thermoplastic resin foam according to the present invention.

As shown in FIGS. 1 and 2, the manufacturing apparatus 1 includes a preheating furnace 2, a foaming furnace 3, a radiation thermometer 4, and a winder 5.

That is, the preheating furnace 2 is provided with a passage for the foamable sheet 6 in the center, and is divided into two heating zones A and B in the furnace as shown in FIG. In the first zone A, far-infrared heaters 21 having substantially the same width as the inner width of the preheating furnace 2 are arranged vertically as heating means. On the other hand, in the second zone B, the heating unit is divided into three in the width direction of the preheating furnace 2, and each of the divisions 22 a, 22 b, and 22 c has a far-infrared heater 22 whose temperature can be controlled and a hot air duct 23 which is vertically moved. It is provided in. Further, a glass window 20 is provided on the outlet side wall surface of the preheating furnace 2.

The foaming furnace 3 is connected to the outlet of the preheating furnace 2 so as to be orthogonal to the preheating furnace 2, and has a foaming sheet (hereinafter referred to as “preheating sheet”) 6 preheated in the center of the preheating furnace 2.
′ Are provided, and a large number of hot air ducts 31... 31 are provided inside so as to sandwich the passage from both sides. The radiation thermometer 4 measures the surface temperature of the preheating sheet 6 ′ sent to the exit side of the preheating furnace 2 from outside the furnace through the glass window 20, and controls the far infrared heater 22 (not shown).
The result is sent to. Then, the control device determines from the measurement result that each of the divided portions 22 of the far-infrared heater 22
a, 22b, and 22c are controlled.

Using the manufacturing apparatus 1 as described above, a foam sheet can be manufactured continuously as follows. First, a long foamable sheet 6 containing a pyrolytic foaming agent wound in a roll shape is prepared in advance, and a preliminary experiment shows that the preheated sheet 6 ′ has a surface temperature in the thickness direction at the outlet of the preheating furnace 2 − Two temperature distributions that can maintain the temperature in the thickness direction ≦ 5 ° C. and the surface temperature in the width direction of the preheating sheet 6 ′ such that the edge temperature <the center temperature in the width direction and the temperature difference between both ends ≦ 3 ° C. The heating conditions for the heating zones A and B are determined.

Then, the foaming sheet 6 is continuously passed through the preheating furnace 2 and the foaming furnace 3 set to the heating conditions determined in the preliminary experiment, and is preheated in the preheating furnace 2. Heat-foaming is performed to obtain a sheet-like foam 7, and the sheet-like foam 7 is continuously wound by a winder 5. Moreover, at the exit of the preheating furnace 2, the surface temperature of the preheating sheet 6 ′ is measured through the glass window 20 by the radiation thermometer 4.
As a result, the preheated sheet 6 ′ has a surface temperature in the thickness direction−a center temperature in the thickness direction ≦ 5 ° C.
When the surface temperature in the width direction is not the set temperature distribution such that the end temperature <the center temperature in the width direction and the temperature difference between both ends ≦ 3 ° C., the second zone B is set so that the set temperature distribution is obtained.
Divided portions 22a, 22b, 22c of the radiant heater 22
The heating temperature is adjusted.

As described above, according to this manufacturing method, at the outlet of the preheating furnace 2, the preheating sheet 6 ′ always has the surface temperature in the thickness direction−the center temperature in the thickness direction ≦ 5 ° C. and the surface temperature in the width direction at the end. Temperature <center temperature in the width direction, and temperature difference between both ends ≦ 3
It has been preheated to satisfy ° C. Therefore, even if the feed rate of the sheet-like foam is increased, the preceding foam at the end is always completely suppressed, and a similar foam can be obtained in which the center and the end are foamed at the same time. Can be obtained continuously.

[0044]

The present invention will be described below in more detail with reference to examples.

(Example 1, Comparative Examples 1-4) Polyethylene (YK-40 manufactured by Mitsubishi Yuka Co., Ltd.) as a thermoplastic resin 1
ADCA (manufactured by Otsuka Chemical Co., Ltd.)
AZ-40) 15 parts by weight and 1 part by weight of a white pigment were added, and the mixture was extruded with a φ120 mm single screw extruder while kneading at 100 kg / h to prepare a continuous raw sheet having a thickness of 1.5 mm and a width of 800 mm. Next, the continuous raw sheet was subjected to 600 KeV * 6 with an electron beam irradiator manufactured by Nissin High Voltage.
The foamed sheet was obtained by irradiating with an electron beam of Mrad and crosslinking.

The obtained foamable sheet is introduced into a manufacturing apparatus having a preheating furnace and a foaming furnace as shown in FIGS. 1 and 2, and the temperature distribution of the width of the preheating sheet at the outlet of the preheating furnace is measured by an infrared radiation thermometer. While measuring while scanning, each condition was changed variously, and the stability of foaming at that time was evaluated. The results are shown in Table 1. The measured temperature was defined by the following procedure.

As shown in FIG. 4, the preheated sheet 6 'is divided into nine parts in the width direction, and the temperatures of the respective parts a to i are measured. d, e,
The average value of the temperature of each part of f, the right end temperature = g, the average value of the temperature of each part of h, i are obtained, and the temperature difference between both ends = left (right) end temperature−
The right (left) end temperature was used.

[0048]

[Table 1]

It is clear from Table 1 that the production method of the present invention can always provide a good foam continuously even when the production rate is increased.

[0050]

The method for producing a thermoplastic resin foam according to the present invention is constituted as described above. Therefore, even when the foam is continuously produced at a high feed rate, the end of the foam sheet can be obtained. Pre-foaming in the part can be prevented, and foaming that is as similar as possible can be performed. That is, manufacturing costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a manufacturing apparatus used to carry out a method for manufacturing a thermoplastic foam according to the present invention.

FIG. 2 is an enlarged view of a main part of the manufacturing apparatus of FIG.

FIG. 3 is a layout view of heating means of a preheating furnace of the manufacturing apparatus of FIG.

FIG. 4 is an explanatory diagram showing measurement points of the surface temperature of a preheated sheet in Example 1 and Comparative Examples 1 to 4.

[Explanation of symbols]

2 Preheating furnace 21 Far infrared heater (heating means) 22 Far infrared heater (heating means) 22a Split body (heating means) 22b Split body (heating means) 22c Split body (heating means) 3 Heating furnace 5 Temperature measuring device 6 Foaming property Sheet (foamable thermoplastic resin sheet) 6 'Preheated sheet (preheated foamable thermoplastic resin sheet)

Claims (2)

[Claims] 1. A long foamable thermoplastic resin sheet containing a thermal decomposition type foaming agent is continuously fed into a preheating furnace and preheated to a temperature immediately before the decomposition start temperature of the thermal decomposition type foaming agent. Production of a thermoplastic resin foam in which the preheated foamable thermoplastic resin sheet is subsequently fed into a foaming furnace and heated to a temperature at which the pyrolytic foaming agent is completely decomposed to completely foam the pyrolytic foaming agent. The method, wherein the preheated foamable thermoplastic resin sheet, just before the heating furnace,
The temperature in the thickness direction is defined as the surface temperature−the center temperature in the thickness direction ≦ 5 ° C.
A method for producing a thermoplastic resin foam, comprising preheating a surface temperature in a width direction to a temperature satisfying each temperature condition of an end portion temperature <a center temperature in a width direction and a temperature difference between both end portions ≦ 3 ° C. 2. A plurality of heating means capable of controlling the temperature are arranged side by side in the width direction inside the preheating furnace, and the surface temperature distribution in the width direction of the expandable thermoplastic resin sheet coming out of the preheating furnace is output to the preheating furnace outlet. The method for producing a thermoplastic resin foam according to claim 1, wherein the heating means is read by a provided temperature measuring device, and the heating means is preheated while controlling the temperature based on the read data.