JPH10180886A - Manufacture of thermoplastic resin foamed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make width widening treatment unnecessary and to obtain with high productivity a foamed body of less dimensional change under heating by a method wherein after foamable thermoplastic resin particulate bodies are foamed, foamable thermoplastic resin thin films connecting them are foamed. SOLUTION: A plurality of foamable thermoplastic resin particulate bodies 2 are uniformly dispersed and arranged on a foamable thermoplastic resin sheet-like body 1 and the foamable thermoplastic resin particulate bodies 2 are connected with a foamable thermoplastic resin thin film 3. In addition, the foamable thermoplastic resin sheet 1 is arranged on a press mold 18 of a hand press 18 through a fluororesin sheet 16 and another press mold 18b is brought into contact with the foamable thermoplastic resin particulate bodies 2 through a fluororesin sheet 17. Then, foaming is performed by heating the press mold 18b at a temp. being higher than decomposition temp. of a foaming agent and the press mold 18a is heated below the decomposition temp. of the foaming agent. Then, it is transferred to another hand press 19 and the press mold 19a is heated at a temp. being higher than the decomposition temp. of the foaming agent to foam the foamable thermoplastic resin thin film 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foam made of a thermoplastic resin, and more particularly, to a method for producing a thermoplastic resin foam which enables pseudo one-dimensional foaming along a thickness direction. About the method.

[0002]

2. Description of the Related Art Thermoplastic foams are lightweight and have excellent heat insulating properties, flexibility, buoyancy, moldability, etc., so that various types of heat insulating materials such as roof heat insulating materials, vehicle ceiling materials or floor heat insulating materials are used. It is widely used in materials, cushioning materials, flotation materials or deformed shapes.

[0003] As a method for producing a thermoplastic resin foam as described above, conventionally, a foamable thermoplastic resin sheet containing a pyrolytic foaming agent is heated to a temperature higher than the decomposition temperature of the foaming agent and foamed. A method for obtaining a foam is widely used. When the foaming thermoplastic resin sheet is foamed, the foaming is performed by the pressure of the gas generated by the decomposition of the foaming agent contained therein.

[0004] Therefore, the expandable thermoplastic resin sheet usually expands and expands almost three-dimensionally and evenly. Therefore, when manufacturing a foam, especially when manufacturing a continuous long foam, It is necessary to cope with the occurrence of wrinkles due to expansion in the width direction and the longitudinal direction.

For example, in the method described in Japanese Patent Publication No. 48-9955, a foamable thermoplastic resin sheet containing a foaming agent is fed, heated and foamed to obtain a foamed sheet, and the foamed sheet is wound up. At this time, the winding speed is increased in comparison with the sheet feeding speed according to the expansion amount in the longitudinal direction due to foaming, and the sheet is widened in the width direction according to the expansion amount in the width direction, and thereby the finally obtained foamed sheet Is reduced.

However, in this method, complicated jigs and steps are required to expand a foam sheet continuously produced during heating and foaming in the width direction. in addition,
Since it is necessary to widen the foamed sheet after foaming and before cooling, the quality has to be reduced at both ends in the width direction of the obtained foamed sheet. As a result, in the obtained foamed sheet, it is necessary to remove portions in the vicinity of both ends in the width direction, so that there is a problem that productivity of the foam is reduced.

Further, in the foamed sheet obtained by the above-described production method, the expansion and expansion of the thermoplastic resin in the sheet surface direction caused by foaming are offset by stretching and widening. The force will remain as thermal stress. Therefore, there is also a problem that when a temperature change is given to the obtained foamed sheet, the dimensions of the sheet greatly change.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to perform pseudo one-dimensional foaming in the thickness direction, and to eliminate the need for a widening process. It is an object of the present invention to provide a method for producing a thermoplastic resin foam which enables a foam having a small dimensional change under heating to be produced with high productivity.

[0009]

According to a first aspect of the present invention, foamable thermoplastic resin granules are arranged substantially uniformly in a plane, and the foamable thermoplastic resin granules are foamed thermoplastic resin granules. Upon heating and foaming the foamable thermoplastic resin sheet integrally connected via the thermoplastic resin thin film, the foamable thermoplastic resin granules are foamed, and then the foamable thermoplastic resin thin film is foamed. It is characterized by making it.

According to a second aspect of the present invention, the expandable thermoplastic resin granules containing a foaming agent are arranged substantially uniformly in a plane, and the expandable thermoplastic resin granules are Supplying a foamable thermoplastic resin sheet that is integrally connected via a foamable thermoplastic resin thin film containing a sheet between a pair of endless transport belts; A step of heating the foamed thermoplastic resin sheet through the endless transport belt while heating the foamed thermoplastic resin sheet while heating the foamed thermoplastic resin at a temperature equal to or higher than the decomposition temperature of the foaming agent containing only the foamed thermoplastic resin granules. And a step of heating only the foaming thermoplastic resin thin film of the foamable thermoplastic resin granules above the decomposition temperature of the contained foaming agent, foaming, and cooling the foam. And

Hereinafter, the present invention will be described in detail. Thermoplastic Resin The thermoplastic resin for forming the foamable thermoplastic resin granules and the foamable thermoplastic resin thin film is not particularly limited as long as it is a foamable thermoplastic resin. As such a thermoplastic resin, for example, low-density polyethylene, high-density polyethylene, linear low-density polyethylene (hereinafter, “polyethylene” refers to low-density polyethylene, high-density polyethylene, linear low-density polyethylene, or Olefin resins such as random polypropylene, homopolypropylene, block polypropylene (hereinafter, “polypropylene” refers to random polypropylene, homopolypropylene, block polypropylene, or a mixture thereof); Polyvinyl chloride, chlorinated polyvinyl chloride, AB
Examples include S resin, polystyrene, polycarbonate, polyamide, polyvinylidene fluoride, polyphenylene sulfide, polysulfone, polyether ether ketone, and copolymers thereof, and these may be used alone or in combination.

Among the above thermoplastic resins, polyethylene and the like can enhance the surface properties and flexibility of the obtained foam.
An olefin resin such as polypropylene or a mixture thereof is preferable, and a high-density polyethylene, a homopolypropylene, or a mixture containing at least one of these is particularly preferable in order to enhance flexibility.

The thermoplastic resin constituting the foamable thermoplastic resin granules and the thermoplastic resin constituting the foamable thermoplastic resin thin film do not need to be the same resin. From the viewpoint of the above, it is preferable to use the same type of resin.

The above thermoplastic resin may be crosslinked as required. By using a crosslinked thermoplastic resin, it is possible to improve the expansion ratio and to reduce the weight of the obtained foam, and therefore, it is preferable to use a crosslinked thermoplastic resin.
The crosslinking method is not particularly limited.For example, after melt-kneading the silane graft polymer into a thermoplastic resin, a water treatment is performed, and a method of crosslinking, the peroxide is added to the thermoplastic resin from the decomposition temperature of the peroxide. After melt-kneading at a low temperature, a method of crosslinking by heating to a temperature not lower than the decomposition temperature of the peroxide, a method of irradiating with radiation, and the like can be mentioned.

A crosslinking method using the above silane graft polymer will be described. The silane-grafted polymer is not particularly limited, and examples thereof include silane-grafted polyethylene and silane-grafted polypropylene. The silane graft polymer can be obtained by, for example, graft-modifying the polymer with an unsaturated silane compound.

The above unsaturated silane compound is represented by the general formula R ¹
Refers to a compound represented by SiR ² _m Y _3-m . Here, m is 0, 1, or 2. Wherein R ¹ is a vinyl group,
Alkenyl groups such as allyl group, propenyl group and cyclohexenyl group; glycidyl group; amino group; methacryl group;
Organic functional groups such as halogenated alkyl groups such as -chloroethyl group and γ-bromoethyl group.

In the formula, R ² represents an aliphatic saturated hydrocarbon group or an aromatic hydrocarbon group, and examples thereof include a methyl group, an ethyl group, a propyl group, a decyl group and a phenyl group. In the formula, Y represents a hydrolyzable organic functional group, for example, a methoxy group, an ethoxy group, a formyloxy group, an acetoxy group, a propionoxyarylamino group, and the like. When m is 0 or 1, Y represents Even if they are the same,
It may be different.

In order to increase the speed of the crosslinking reaction, the above unsaturated
As the silane compound, the general formula CH _Two= CHSi (O
A)_ThreeIs preferably represented by Wherein A is preferably
Is a fatty acid having 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms.
It is an aliphatic saturated hydrocarbon group. CH_Two = CHSi (OA)
_Three Examples of preferred unsaturated silane compounds represented by
For example, vinyltrimethoxysilane, vinyltriethoxy
Examples include silane and vinyltriacetoxysilane.

As a method for producing the silane graft polymer, a general production method is used and is not particularly limited. For example, polyethylene, R ¹ SiR ² Y ₂ (wherein, R ¹ is an olefinically unsaturated monovalent hydrocarbon group or a hydrocarbonoxy group, and each Y is a hydrolyzable organic functional group. R ² is a group R ¹ or a group Y.), and an unsaturated peroxide compound and an organic peroxide are reacted to obtain a silane-modified polyethylene.

For example, when Y is a methoxy group, the silane graft polymer having a silyl group is hydrolyzed into a hydroxyl group by contact with water,
Hydroxyl groups of different molecules react with each other to form a Si—O—Si bond, and the silane graft polymers are crosslinked.

The method of mixing the silane graft polymer is as follows:
There is no particular limitation on the method as long as it can be uniformly mixed. For example, a method in which a thermoplastic resin and a silane graft polymer are supplied to a single-screw or twin-screw extruder and melt-kneaded, a method of melt-kneading using a roll, a method of melt-kneading using a kneader, and the like are exemplified.

The above-mentioned water treatment method includes a method of immersion in water and a method of exposure to water vapor.
When the treatment is performed at a temperature higher than 00 ° C., the treatment may be performed under pressure.

If the temperature of water and water vapor in the above water treatment is low, the rate of the crosslinking reaction decreases, and if the temperature is too high, the columns of the highly foamable composition coated with the low foamable composition are fused together. Therefore, 50 to 130 ° C is preferable, and 90 to 120 ° C
Is particularly preferred. Also, if the time for water treatment is short,
The water treatment time is preferably in the range of 5 minutes to 12 hours, since the crosslinking reaction may not proceed completely.

If the addition amount of the silane graft polymer is too large, crosslinking is excessively performed, and the expansion ratio of the obtained foam is reduced. If the addition amount is too small, cells are broken and uniform foamed cells are obtained. Therefore, the addition amount of the silane graft polymer is preferably 5 to 50 parts by weight, particularly preferably 20 to 35 parts by weight, based on 100 parts by weight of the thermoplastic resin.

When silane crosslinking is performed using a silane graft polymer, a silane crosslinking catalyst may be used if necessary. The silane crosslinking catalyst is not particularly limited as long as it promotes a crosslinking reaction between the silane graft polymers.For example, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, tin octoate,
Examples include tin oleate, lead octane, zinc 2-ethylhexanoate, cobalt octoate, lead naphthenate, zinc cabrate, and zinc stearate.

When the addition amount of the silane crosslinking catalyst increases, the expansion ratio of the obtained foam decreases. On the other hand, when the addition amount decreases, the crosslinking reaction speed decreases and time is required for water treatment. The amount of the silane crosslinking catalyst to be added is preferably in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 0.1 part by weight, based on parts by weight.

A method for crosslinking a thermoplastic resin with the above-mentioned peroxide will be described. The peroxide used in the present method is not particularly limited, for example, dibutyl peroxide, dicumyl peroxide, tert-butyl cumyl peroxide, diisopropyl peroxide, and the like.Since the decomposition temperature is in an appropriate temperature range, Dicumyl peroxide and tert-butyl cumyl peroxide are preferred, and dicumyl peroxide is particularly preferred.

If the amount of the peroxide is too large, the resin decomposition reaction tends to proceed, and the resulting foam is colored.
If the amount is too small, the crosslinking of the thermoplastic resin may be insufficient, so the amount of the peroxide is preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the thermoplastic resin,
1-3 parts by weight are particularly preferred.

A method for irradiating the above-mentioned radiation to crosslink the thermoplastic resin will be described. If the irradiation amount of the radiation is too large, crosslinking is excessively applied, and the expansion ratio of the obtained foam is reduced.If the irradiation amount is too small, the foamed cells are broken and a uniform foamed cell cannot be obtained. Is 1-20
Mrad is preferred, and 3-10 Mrad is particularly preferred.

The method of irradiating the radiation is not particularly limited, and includes, for example, a method of using two electron beam generators, passing a thermoplastic resin between them, and irradiating the thermoplastic resin with an electron beam. .

In the present invention, preferably, the thermoplastic resin used in the foamable thermoplastic resin comprises a mixture of a highly crosslinked thermoplastic resin composition having almost no compatibility and a low crosslinked or non-crosslinked thermoplastic resin composition. . In this case, the low cross-linked or non-cross-linked resin composition easily flows at the time of foaming, so that the surface smoothness of the obtained foam is enhanced.

The terms “highly crosslinked” and “lowly crosslinked” in the high crosslinked resin composition and the low crosslinked or non-crosslinked weight resin composition are relative expressions determined by the magnitude of the degree of crosslinkage of both. The highly crosslinked resin composition is referred to as a highly crosslinked resin composition (A), and the other is referred to as a low crosslinked or noncrosslinked resin (B).

The highly crosslinked resin composition (A) comprises a resin component (A)
′) As a main component, and the low-crosslinking or non-crosslinking resin composition (B) is a resin composition containing a resin component (B ′) as a main component. Therefore, it has almost no compatibility,
When a mixture of the highly cross-linked resin composition (A) and the low-cross-linked or non-cross-linked resin composition (B) is used as the thermoplastic resin constituting the expandable thermoplastic resin sheet, the resin component (A ′) as a main component thereof And the resin component (B ') hardly show compatibility.

As the thermoplastic resin used for the two types of resin components (A ') and (B') having almost no compatibility, the above-mentioned thermoplastic resins can be used. Resin component (A ') and resin component (B')
In order to form, the difference between the solubility parameters of the two thermoplastic resins is preferably 0.1 to 2.0,
More preferably, it is 0.2 to 1.5.

If the difference in the solubility parameter exceeds 2.0, the resin component (A ') and the resin component (B') are very coarsely dispersed, so that the expansion ratio of the obtained foam decreases.
On the other hand, if the difference between the solubility parameters is less than 0.1,
The compatibility of the two types of thermoplastic resins increases, and it becomes impossible to form the resin component (A ′) and the resin component (B ′).

The solubility parameter is σ = ρΣFi
/ M. Here, ρ is the density of the resin component, M is the molecular weight of the monomer constituting the resin component, Fi
Is the number of moles of the monomer group.

When the difference in the melt index (MI) between the above two types of thermoplastic resins increases, the resin component (A)
') And the resin component (B') are very coarsely dispersed,
When the expansion ratio of the obtained foam decreases and becomes smaller, 2
The compatibility of the various types of thermoplastic resin increases, and the resin component (A
') And the resin component (B') may not be able to be formed. Therefore, the difference in MI is preferably in the range of 3 to 15 g / 10 minutes, and the difference between the MI and the resin component (A ') is fine and uniform. In order to realize the resin component (B ′) and obtain a foam having a high expansion ratio, the difference in MI is preferably 5 to 13 g / 10 minutes,
7 to 11 g / 10 min is more preferable. Note that MI in the present specification is a value measured according to JIS K7210.

The resin component (A ') and the resin component (B') are uniformly dispersed, and a highly crosslinked resin composition (A) and a low crosslinked resin composition are required to obtain a foam molded article having a high expansion ratio and excellent surface properties. Alternatively, the mixing ratio with the non-crosslinked resin composition (B) is a weight ratio,
2: 8 to 8: 2, preferably 4: 6 to 6: 4
Is preferable, and 5: 5 is more preferable.

If the degree of crosslinking of the highly crosslinked resin composition (A) is too high, crosslinking is excessive, and the foaming ratio of the obtained foam is reduced. Conversely, if it is too low, cells are broken during foaming and uniform cells are formed. May not be obtained, so that the gel fraction as an index of the degree of crosslinking is preferably 5 to 40% by weight, more preferably 10 to 30% by weight.

If the degree of cross-linking of the low cross-linked or non-cross-linked resin composition (B) is high, the cross-linking is excessive, the fluidity of the resulting foam is reduced, the surface properties are reduced, and the surface lubricity of the foam is reduced. Since it may be low, the gel fraction as an index of the degree of crosslinking is preferably 5% by weight or less, more preferably 3% by weight or less.

The gel fraction in the present specification refers to the percentage by weight of the residue weight after immersing the crosslinked resin component in xylene at 120 ° C. for 24 hours with respect to the weight of the crosslinked resin component before immersion in xylene.

As a method of preparing a mixture of the highly crosslinked resin composition (A) and the low crosslinked or noncrosslinked resin composition (B) having almost no compatibility, the above two kinds of thermoplastic resins are mixed, and the resin component is mixed. (A ') alone or resin component (B
This is achieved by preferentially crosslinking the resin component (A ') over (1).

As a method of crosslinking the resin component (A ′) preferentially over the resin component (A ′) or the resin component (B ′), for example, only the resin component (A ′) or the resin component (A ′) is used. A method of crosslinking using a crosslinking agent that preferentially crosslinks the resin component (A ′) over the resin component (B ′). In the first step, a crosslinkable resin (C) of the same type as the resin component (A ′) having a crosslinkable functional group ) Is mixed with the resin component (A ′) and crosslinked to form a highly crosslinked resin composition (A), and then, in the second stage, the mixture is mixed with the resin component (B ′).

However, the resin components (A ') and (B') having a small particle size and uniformity can be formed;
Since the resin component (A ′) can be easily cross-linked preferentially and a thermoplastic resin can be easily prepared, it has almost the same melt index as the resin component (A ′) and has a crosslinkable functional group. The most preferable method is to mix a crosslinkable resin (C) of the same type as the resin component (A ′) with the resin components (A ′) and (B ′) and then to crosslink.

The resin component (A) having a crosslinkable functional group having almost the same melt index as the resin component (A ')
The crosslinkable resin (C) of the same type as that of ') is not particularly limited as long as it is a thermoplastic resin having a reactive functional group and capable of crosslinking the resin. As such a crosslinkable resin (C), for example, the above-mentioned thermosetting resin having an unsaturated group such as a vinyl group, an allyl group, or a propenyl group, a hydroxyl group, a carboxyl group, an epoxy group, an amino group, a silanol group, a silanate group, or the like. And a plastic resin.

Specific examples of the crosslinkable resin (C) include:
Examples include maleic acid-modified polyethylene, maleic acid-modified polypropylene, silane-modified polyethylene, and silane-modified polypropylene. Since it is easy to crosslink the resin component (A ') preferentially only to the resin component (A') or to the resin component (A ') over the resin component (B'), and it is easy to crosslink after mixing, silane-modified polyethylene, Silane-modified polypropylene is most preferred.

If the difference in the melt index between the resin component (A ′) and the crosslinkable resin (C) is large, the resin component (A ′) has priority over the resin component (A ′) alone or over the resin component (B ′). The difference in the melt index is preferably 2 g / 10 minutes or less, and 1 g / g or less.
10 minutes or less is more preferable.

The method of crosslinking the crosslinkable resin (C) includes a method of crosslinking with a peroxide, a method of crosslinking with an isocyanate, a method of crosslinking with an amine,
After the reactive functional group is hydrolyzed, a method of cross-linking with water may be used. Since crosslinking after mixing is easy, a method of hydrolyzing a reactive functional group followed by water crosslinking is most preferable.

Blowing Agent In the present invention, a pyrolytic blowing agent is used as the blowing agent contained in the expandable thermoplastic resin granules and the expandable thermoplastic resin thin film.

The pyrolytic foaming agent is not particularly limited as long as it has a decomposition temperature higher than the melting temperature of the thermoplastic resin used. Examples thereof include sodium bicarbonate, ammonium carbonate, ammonium bicarbonate and azide. Compounds, inorganic pyrolytic blowing agents such as sodium borohydride; azodicarbonamide, azobisisobutyronitrile, N, N'-dinitrosopentamethylenetetramine,
P, P'-dinitrosopentamethylenetetramine, P,
P'-oxybisbenzenesulfonyl hydrazide, barium azodicarboxylate, trihydrazinotriazine and the like can be mentioned, and azodicarbonamide which is easy to adjust the decomposition temperature and decomposition rate, generates a large amount of gas, and is excellent in hygiene is preferable.

If the amount of the thermal decomposition type foaming agent is too large, the foam breaks and uniform cells are not formed. On the other hand, if the amount is too small, the foaming may not be sufficiently performed. It is preferable that the content be contained in a proportion of 1 to 25 parts by weight based on 100 parts by weight of the thermoplastic resin.

In order to increase the strength of the component foam which can be added, the thermoplastic resin used for the foamable thermoplastic resin granules and the foamable thermoplastic resin thin film may be made of glass, if necessary. Reinforcing materials such as fibers, short carbon fibers, and short polyester fibers; fillers such as calcium carbonate, aluminum hydroxide, and glass powder may be added.

When the above-mentioned short fibers are added as a reinforcing material, if the addition ratio of the reinforcing material is too large, the cells are broken at the time of foaming, and a foam having a high expansion ratio cannot be obtained. In addition, the effect of reinforcing the obtained foam cannot be sufficiently obtained. Therefore, when the short fibers are added, the mixing ratio is preferably 1 to 2 parts by weight, particularly preferably 3 to 10 parts by weight, per 100 parts by weight of the thermoplastic resin.

If the length of the short fibers is too long, the resulting foam cannot be reduced in weight. If the length is too short, the effect of reinforcing the obtained foam may not be sufficiently obtained. The length of the short fiber is preferably 1 to 20 mm, and 3
Particularly preferred is 特 に 5 mm.

When the above-mentioned filler is added, if the amount is too large, the weight of the obtained foam cannot be reduced, and if the amount is small, the effect of reinforcing the obtained foam cannot be sufficiently obtained. There is. Therefore, the addition amount of the filler is preferably 10 to 100 parts by weight, particularly preferably 30 to 50 parts by weight, based on 100 parts by weight of the thermoplastic resin.

Foamable thermoplastic resin sheet FIGS. 1 and 2 are a cross-sectional view and a partially cutaway plan view for explaining the shape of the foamable thermoplastic resin sheet used in the present invention.

The foamable thermoplastic resin sheet 1 has a plurality of foamable thermoplastic resin granules 2 uniformly dispersed in a plane, and the foamable thermoplastic resin granules 2 are disposed at one end thereof. Has a structure connected by a foamable thermoplastic resin thin film 3.

The shape of the expandable thermoplastic resin granules 2 is not particularly limited, and may be, for example, a hexagon, a cylinder, a sphere, or the like. A columnar one is most preferable because it is easy to perform.

If the foamable thermoplastic resin granules 2 are unevenly arranged, the expansion ratio of the obtained foam will be partially non-uniform.
Preferably, they are provided in a grid pattern as shown in FIG. 2 or substantially uniformly in a staggered pattern as shown in FIG.

As shown in FIG. 2, if they are arranged in a lattice, after foaming, the foams are evenly foamed in the longitudinal direction and the width direction to fill the gaps, and the structure is a collection of squares when viewed in plan.

When the foamable thermoplastic resin granules 2 are arranged in a staggered manner, the foamable thermoplastic resin is uniformly foamed in the longitudinal direction and the width direction to fill the gap, and when viewed in plan view, the foamable thermoplastic resin particles 6 are formed. Because it becomes a pseudo honeycomb structure in which polygons are gathered,
The expansion ratio of the obtained foam becomes uniform throughout,
preferable.

The thickness of the foamable thermoplastic resin thin film 3 is not particularly limited, but if it is too thick, it takes a long time to foam, and the foamable thermoplastic resin particles may shrink, and if it is too thin, it may be thinned. When the foamable thermoplastic resin particles are foamed, the foamable thermoplastic resin thin film sometimes foams at the same time. Therefore, the thickness of the foamable thermoplastic resin thin film,
0.1 to 3 mm is preferable, and 0.2 to 1 mm is particularly preferable.

Production of Expandable Thermoplastic Resin Sheet The method for producing the expandable thermoplastic resin sheet used in the present invention is not particularly limited. For example, 1)
The thermoplastic resin constituting the foamable thermoplastic resin sheet, the pyrolytic foaming agent, etc. are supplied to the extruder, melt-kneaded at a temperature lower than the decomposition temperature of the pyrolytic foaming agent, and extruded into a sheet form. A method of forming a foamable thermoplastic resin sheet by cooling while shaping with a roll having concave portions corresponding to the foamable thermoplastic resin granules, 2) thermoplasticity constituting the foamable thermoplastic resin sheet After supplying the resin or the pyrolytic foaming agent to the extruder, melt-kneading at a temperature lower than the decomposition temperature of the pyrolytic foaming agent, and then injecting it into a mold having recesses corresponding to the foamable thermoplastic resin granules A method of cooling and obtaining a foamable thermoplastic resin sheet can be used.

An example of a method for producing a foamable thermoplastic resin sheet will be described with reference to FIG. In FIG. 4A, a foamable thermoplastic resin composition is supplied to a twin-screw extruder 11, melt-kneaded, extruded into a sheet form by a die 12, passed through rolls 13 and 14, and shaped. By cooling, the foamable thermoplastic resin sheet 1 can be obtained. As shown in FIG. 4 (b) in an enlarged manner, one of the rolls 13 and 14 has a recess 13a corresponding to the shape of the foamable thermoplastic resin granule 2 uniformly in the circumferential direction. Are located. The shape and arrangement of the expandable thermoplastic resin particles 2 can be adjusted by adjusting the size and position of the recess 13 a provided on the roll 13.

[0065] In the invention described in the foamed claim 1, heating the foamable thermoplastic resin sheet product obtained as described above, when foaming and after foaming the expandable thermoplastic resin granular materials,
The foamable thermoplastic resin thin film is foamed.

The above foaming step will be described more specifically with reference to FIGS. First, as shown in FIG. 5 (a), the foamable thermoplastic resin sheet 1 is placed on one press die 18a of the hand press 18 via the fluororesin sheet 16 so that the foamable thermoplastic resin thin film 3 is
Place in the direction to contact The other pressing die 18 b of the hand press 18 is brought into contact with the upper surface of the expandable thermoplastic resin sheet 1 via the fluororesin sheet 17, that is, the upper surface of the expandable thermoplastic resin granule 2. In this state, the press die 18b is heated to a temperature about 30 ° C. higher than the decomposition temperature of the blowing agent, and the press die 18a is heated to a temperature lower than the decomposition temperature of the blowing agent. As a result, the foamable thermoplastic resin particles 2 are foamed, and the foaming proceeds from the state shown in FIG. 6A as shown in FIG. 6B.

Next, after the foaming of the foamable thermoplastic resin particles 2 is completed, the foamable thermoplastic resin sheet 1 is moved to the state shown in FIG.
As shown in (b), it is transferred to another hand press 19. The press mold 19a of the hand press 19 is a fluororesin sheet 2
Thus, the press mold 19b is brought into contact with the foamable thermoplastic resin granule 2 'having completed foaming. In addition, 21 shows a fluororesin sheet.

After the arrangement as shown in FIG. 5 (b), if the press mold 19a is heated to a temperature about 30 ° C. higher than the decomposition temperature of the foaming agent, the foaming of the foamable thermoplastic resin thin film proceeds. As shown in FIG. 6 (c), the foamable thermoplastic resin sheet 1 is deformed, and finally a thermoplastic resin foam 22 shown in FIGS. 7 (a) and 7 (b) can be obtained.

When foaming the foamable thermoplastic resin thin film 3, the press mold 19b may be heated in the same manner as the press mold 19a, or may be heated to a temperature lower than the decomposition temperature of the foaming agent. .

According to the second aspect of the present invention, the foamable thermoplastic resin sheet is supplied between a pair of endless transport belts, and the foamable thermoplastic resin sheet is transported together with the endless transport belt. First, only the foamable thermoplastic resin granular material is heated through the endless conveyor belt to a temperature higher than the decomposition temperature of the foaming agent to cause foaming, and then only the foamable thermoplastic resin thin film is heated to a temperature higher than the decomposition temperature of the foaming agent. To foam and cool the foam.

Referring to FIG. 8, the manufacturing method according to the second aspect of the present invention will be described more specifically. Supply roll 31
Endless conveyor belt 3 from foamable thermoplastic resin sheet 1
Supply between 2 and 33. As the supply roll 31, for example, a roll obtained by winding a foamable thermoplastic resin sheet around a paper tube can be used, and the foamable thermoplastic resin sheet 1 is fed by rotating the paper tube. be able to. The endless transport belts 32 and 33 are respectively stretched over rolls 34a to 34g and rolls 35a to 35g, and are transported in the direction of the arrow shown in the figure.
Accordingly, the foamable thermoplastic resin sheet 1 is transported together with the endless transport belts 32, 33.

The heating furnaces 36 and 37 are arranged in a conveying area where the endless conveying belt 32 and the endless conveying belt 33 face each other, and a cooling device 38 is further arranged on the downstream side. As described above, for the heating furnaces 36 and 37, any heating device such as far infrared heating, hot air heating, and a plate heater can be used.

In the heating furnace 36, the endless conveyor belt 32 which is in contact with the foamable thermoplastic resin granules 2 is heated to a temperature about 30 ° C. higher than the decomposition temperature of the foaming agent. In this case, the endless conveyor belt 33, that is, the side that comes into contact with the foamable thermoplastic resin thin film 3 is configured to be heated to a temperature lower than the decomposition temperature of the foaming agent. Therefore, in the heating furnace 36, the foamable thermoplastic resin particles 2 foam, and the foaming proceeds.

On the other hand, in the heating furnace 37, the foamable thermoplastic resin thin film 3 side is heated to a temperature higher by about 30 ° C. than the decomposition temperature of the foaming agent, so that the foamable thermoplastic resin thin film 3 also foams, Thereafter, the mixture is cooled in the cooling device 38 to obtain the thermoplastic resin foam 22 (see FIG. 7).

Since the endless conveyor belts 32 and 33 are exposed to high temperatures, they are preferably made of a material having excellent heat resistance, and are preferably excellent in releasing properties from a thermoplastic resin foam. Therefore, the endless transport belts 32, 3
3 is, for example, a belt reinforced with fiber of polytetrafluoroethylene, a belt made of cloth or a belt made of inorganic fiber, which has been subjected to a polytetrafluoroethylene treatment on the entire surface.

Further, more preferably, in order to enhance the releasability of the foamed thermoplastic resin foam, inorganic fibers impregnated and coated with polytetrafluoroethylene, fired at a high temperature, and processed into a belt shape. Used.

The direction in which the foamable thermoplastic resin sheet 1 is supplied between the endless conveyor belts 32 and 33 may be upside down from the example shown in FIG. That is, the foamable thermoplastic resin sheet is heated as long as the foamable thermoplastic resin particles 2 are heated so as to foam first, and then the foamable thermoplastic resin thin film 3 is heated and foamed. The vertical direction at the time of supplying the state body 1 may be reversed.

In the heating furnace 37, it is desirable to heat the foamable thermoplastic resin thin film 3 to a temperature lower than the melting point of the thermoplastic resin used. By setting the temperature to be equal to or lower than the melting point of the thermoplastic resin, it is possible to prevent the foam from shrinking due to heat.

When the upper and lower temperatures are the same in the heating furnaces 36 and 37, the foaming starts from the foamable thermoplastic resin thin film 3 having a small heat capacity. When the body 2 is supplied so as to be located above, only the upper part of the heating furnace 36 is
It is desirable to set the temperature in a range from the decomposition temperature of the foaming agent to a temperature 30 ° C. higher than the decomposition temperature. With such a temperature, disturbance of the cell structure of the foam due to rapid foaming can be suppressed.

The cooling in the cooling device 38 can be performed from the outside of the conveyor belts 32 and 33 by any method such as air cooling, water cooling, or contact with a cooling plate. By the foam 2
2 can be obtained. However, it is preferable to cool to around normal temperature, so that the endless transport belt 32,
Separation from 33 is facilitated.

[0081] act in the method for producing a thermoplastic resin foam of the invention according to claim 1, for initially heating foaming a foamable thermoplastic resin granular materials, because the expandable thermoplastic resin film is in the unfoamed state Without causing expansion in the in-plane direction of the foamable thermoplastic resin thin film, the foamable thermoplastic resin particles are foamed so that their height is reduced, and the interval between the foamable thermoplastic resin particles is narrow. Become. Next, the expandable thermoplastic resin particles foam and the expandable thermoplastic resin particles are thermally fused to each other, and then the expandable thermoplastic resin thin film is expanded. In this case, since the foaming of the foamable thermoplastic resin particles is almost completed, the foamable thermoplastic resin thin film foams only in the thickness direction. Therefore, it is possible to reliably obtain a thermoplastic resin foam which is pseudo-one-dimensionally foamed as a whole in the thickness direction.

According to the second aspect of the present invention, when the foamable thermoplastic resin sheet is foamed, the foamable thermoplastic resin sheet is supplied between a pair of endless conveyor belts, and the foamed thermoplastic resin sheet is transported and conveyed. Since the foaming process over is carried out,
A long-sized thermoplastic resin foam can be continuously produced.

[0083]

The present invention will be clarified by the following non-limiting examples.

Example 1 30 parts by weight of polypropylene (manufactured by Mitsubishi Chemical Corporation, trade name: MA3, MI = 11 g / 10 min), cross-linked silane-modified polypropylene (manufactured by Mitsubishi Chemical Corporation)
Trade name: XPM800H, MI = 11 g / 10 min, gel fraction after crosslinking 80% by weight) 20 parts by weight, high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, trade name: HY340, MI = 1.
5 g / 10 min) 50 parts by weight, 0.1 part by weight of dibutyltin laurate as a crosslinking catalyst, and 10 parts by weight of azodicarbonamide (manufactured by Otsuka Chemical Co., trade name: SO-20, decomposition temperature 210 ° C.) as a foaming agent. The thermoplastic resin composition is supplied to a twin screw extruder 11 (see FIG. 4) having a diameter of 44 mm, melt-kneaded at 180 ° C., extruded into a sheet shape with a die 12 having a surface length of 300 mm and a lip of 1.5 mm, and rolled. 1
As 3, foaming is performed by cooling while shaping using a roll having a diameter of 250 mm and a surface length of 300 mm in which the recesses 13 b having a diameter of 250 mm are arranged in a zigzag pattern, immersing in 98 ° C. water for 2 hours, and then drying. A thermoplastic resin sheet was obtained. Table 1 below shows the shape, height, diameter, interval, and thickness of the foamable thermoplastic resin thin film of the foamable thermoplastic resin granules of the obtained foamable thermoplastic resin sheet.

The above-mentioned foamable thermoplastic resin sheet is wound around a roll, and a pair of endless conveyor belts 3 shown in FIG.
Foaming was performed by feeding between 2 and 33. That is, the foamable thermoplastic resin sheet 1 is continuously supplied between the endless transport belts 32 and 33 from the supply roll 31, the speed of the endless transport belts 32 and 33 is set to 0.5 m / min, and the heating furnace 36.
In, the upper side is heated to 230 ° C, the lower side is heated to 170 ° C,
After the expandable thermoplastic resin particles 2 are expanded, the heating furnace 3
7, the upper part was heated to 150 ° C. and the lower part was heated to 230 ° C. to foam the foamable thermoplastic resin thin film 3. Next, in the cooling device 38, the foam is pressed and cooled by allowing the thermoplastic resin foam 22 to pass through a pair of cooling plates (the temperature is 25 ° C.) having a vertical interval set to 20 mm while being rubbed. Obtained.

Comparative Example 1 The foaming thermoplastic resin sheet prepared in Example 1 was supplied to the endless conveyor belts 32 and 33 shown in FIG.
6 and 37, the upper and lower temperatures were set to 23
A foam was obtained in the same manner as in Example 1, except that the foaming was carried out by heating at 0 ° C.

(Comparative Example 2) In order to obtain a foamable thermoplastic resin sheet in Example 1, the roll 13 was not used.
The foamable thermoplastic resin sheet extruded into a sheet from the die 12 is cooled between a pair of rolls having a diameter of 250 mm and a surface length of 300 mm, immersed in water at 98 ° C. for 2 hours, and then dried to obtain a thickness of 1. A foamable thermoplastic resin sheet of 0 mm was obtained. That is, in Comparative Example 2, a foamable thermoplastic resin sheet having a uniform thickness was prepared. Except that the foamable thermoplastic resin sheet was used, foaming was performed in the same manner as in Example 1 to obtain a foam.

(Comparative Example 3) The foaming thermoplastic resin sheet prepared in Comparative Example 2 was used, and the heating temperature in the heating furnaces 36 and 37 was set to 230 ° C. for both the upper and lower portions during the heating and foaming. Except for the above, foaming was carried out in the same manner as in Example 1 to obtain a foam.

(Evaluation of Examples and Comparative Examples) The expansion ratio, thickness, and pseudo one-dimensional expandability of the thermoplastic resin foams obtained in Example 1 and Comparative Examples 1 to 3 were measured in the following manner.
The results are shown in Table 1 below.

Expansion ratio: Measured in accordance with JIS K6767. Thickness of foam: Measured with a caliper. Pseudo one-dimensional foaming: Measures the area of the foaming thermoplastic resin sheet before foaming or the area of the foaming thermoplastic resin sheet and the area of the foam obtained, finds the ratio of the two areas, and performs pseudo one-dimensional foaming. Gender.
The closer this ratio is to 1, the higher the pseudo one-dimensional foamability.

[0091]

[Table 1]

In Table 1, PP is polypropylene, silane-modified PP is crosslinkable silane-modified polypropylene, and HDPE is high-density polyethylene.

As apparent from Table 1, in Comparative Example 1,
Although an expandable thermoplastic resin sheet-like material in which expandable thermoplastic resin particles are connected by an expandable thermoplastic resin thin film is used, it is uniformly heated to 230 ° C. in heating furnaces 36 and 37 to cause foaming. Therefore, the thickness of the obtained foam was 15 mm, and the value of the ratio showing the pseudo one-dimensional foamability was 1.33, which was larger than 1, probably because the foamable thermoplastic resin thin film also foamed from the beginning. That is, since the foamable thermoplastic resin thin film foams from the beginning, it is considered that the foamable thermoplastic resin thin film also foams in the in-plane direction and the pseudo one-dimensional foamability is reduced.

In Comparative Examples 2 and 3, regardless of the temperature distribution of the heating furnace, the value of the ratio indicating the pseudo one-dimensional foaming property was 2.5.
It was very large at 0 and 2.71. This is presumably because foaming proceeded three-dimensionally because a foamable thermoplastic resin sheet having a uniform thickness was used.

On the other hand, according to Example 1, the foamed thermoplastic resin thin film was foamed after foaming the foamable thermoplastic resin particles, and the value of the ratio showing pseudo one-dimensional foamability was probably caused by foaming. Was 1.00.

[0096]

According to the first aspect of the present invention, the foamable thermoplastic resin granules are foamed first, and foaming is started without causing foaming in the thickness direction of the foamable thermoplastic resin thin film. After the thermoplastic resin particles are foamed, the foamable thermoplastic resin thin film is foamed, so that the foaming proceeds while maintaining the area at the time of foaming, and thus the area of the entire foamable thermoplastic resin sheet material. Foaming proceeds without much change. Therefore, it is possible to obtain a thermoplastic resin foam that is pseudo-one-dimensionally foamed in the thickness direction using relatively simple equipment.

Since the obtained thermoplastic resin foam is foamed in a pseudo-one-dimensional manner, it is not necessary to expand the resin in the width direction or stretch it by applying tension in the length direction. This can simplify the manufacturing process of the body and reduce the cost. In addition, since it is not necessary to perform stretching after foaming, a thermoplastic resin foam having excellent thermal dimensional stability can be provided.

Further, in the method in which the foamable thermoplastic resin pellets are sprayed and then foamed, the thickness accuracy, weight accuracy and surface property tend to vary due to the dispersion of the foamable thermoplastic resin pellets. According to the invention described in Item 1, since the foamable thermoplastic resin particles are connected in advance by the foamable thermoplastic resin thin film, the thickness accuracy,
A foam having excellent weight accuracy and excellent surface properties can be provided.

According to the second aspect of the present invention, the foamable thermoplastic resin sheet is supplied between a pair of endless transport belts and transported together with the endless transport belt. Foaming takes place. Therefore, it is possible to continuously produce a long thermoplastic resin foam with high productivity.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view for explaining a foamable thermoplastic resin sheet used in the present invention.

FIG. 2 is a plan view of an example of a foamable thermoplastic resin sheet used in the present invention.

FIG. 3 is a plan view of another example of a foamable thermoplastic resin sheet used in the present invention.

FIGS. 4 (a) and 4 (b) are schematic structural views for explaining an apparatus for producing a foamable thermoplastic resin sheet used in the present invention, and FIGS. FIG. 5 is a partially cutaway sectional view for explaining a step of molding the expandable thermoplastic resin granules.

FIGS. 5A and 5B are cross-sectional views for explaining a step of foaming a foamable thermoplastic resin sheet according to the present invention.

FIGS. 6A to 6C are cross-sectional views illustrating a process in which foaming proceeds in the method for producing a thermoplastic resin foam of the present invention.

FIGS. 7A and 7B are a cross-sectional view and a plan view, respectively, of a thermoplastic resin foam obtained by the method for producing a thermoplastic resin foam according to the present invention.

FIG. 8 is a schematic configuration diagram for explaining a manufacturing apparatus used in the method for manufacturing a thermoplastic resin foam according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Foamable thermoplastic resin sheet 2 ... Foamable thermoplastic resin granule 3 ... Foamable thermoplastic resin thin film 22 ... Thermoplastic resin foam 32, 33 ... Endless transport belt 36, 37 ... Heating furnace 38 ... Cooling apparatus

Claims (2)

[Claims] 1. The foamable thermoplastic resin particles are arranged substantially uniformly in a plane, and the foamable thermoplastic resin particles are integrally connected via a foamable thermoplastic resin thin film. A method for producing a thermoplastic resin foam characterized in that, upon heating and foaming the foamable thermoplastic resin sheet, the foamable thermoplastic resin granules are foamed and then the foamable thermoplastic resin thin film is foamed. Method. 2. The foamable thermoplastic resin granules containing a foaming agent are arranged substantially uniformly in a plane, and the foamable thermoplastic resin granules contain a foaming agent. A step of supplying a foamable thermoplastic resin sheet integrally connected via a thermoplastic resin thin film between a pair of endless transport belts, and transporting the foamable thermoplastic resin sheet together with the endless transport belt A step of heating and foaming the foaming thermoplastic resin sheet containing the foaming thermoplastic resin particles only through the endless conveyor belt at a temperature not lower than the decomposition temperature of the foaming agent containing only the foaming thermoplastic resin granules; Heating only the foamable thermoplastic resin thin film of the granular material above the decomposition temperature of the contained foaming agent,
A method for producing a thermoplastic resin foam, comprising: a step of foaming; and a step of cooling the foam.