JP2002166460A - Method for manufacturing polyolefinic resin foamed sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyolefinic resin foamed sheet having a smooth surface by preventing breakage of cells in a foamed layer. SOLUTION: In the method for manufacturing the polyolefinic resin foamed sheet by laminating a polyolefinic resin non-foamed layer to at least the single surface of a polyolefinic resin foamed layer, a heated and plasticized layer, which comprises a polyolefinic resin material containing 10 wt.% or more of a polyolefinic resin which is selected from a long chain branched polyolefinic resin and a polyolefinic resin with an weight average mol.wt. of 1×105 or more and passed through a process for melting the polyolefinic resin from a solid state and subsequently re-solidifying the molten resin, is laminated on at least the single surface of a heated and plasticized layer comprising a polyolefinic resin containing a foaming agent by coextrusion, and the heated and plasticized layer comprising the polyolefinic resin containing the foaming agent is foamed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a foamed polyolefin resin sheet having excellent surface smoothness.

[0002]

2. Description of the Related Art A foamed polyolefin resin sheet in which a non-foamed polyolefin resin layer is laminated on at least one surface of a foamed polyolefin resin layer is well known, and is used as a building / civil engineering material, a container for packaging and the like. However, during the production process, a phenomenon in which bubbles in the foamed layer of the polyolefin-based resin burst, that is, a so-called foam breakage, often occurs, and as a result, a foamed polyolefin-based resin sheet having poor surface smoothness may be obtained.

[0003]

The present inventors have made intensive studies to solve this problem, and laminated a layer made of a long-chain branched polyolefin resin on a polyolefin resin layer containing a foaming agent. By extruding, a foaming agent-containing polyolefin-based resin layer effectively suppresses foam breakage on the surface of the layer when the layer is foamed, and a polyolefin-based resin foam sheet having excellent surface smoothness is obtained first. I found it.

However, according to a further study, the long-chain branched polyolefin-based resin is inferior in extrusion stability because of its high melt viscosity. As a result, in the above-mentioned improved method, the thickness of the non-foamed layer made of the long-chain branched polyolefin-based resin is reduced. It has been found that unevenness may occur, and that in a portion where the non-foamed layer is thin, foam breakage on the foamed layer surface is not always sufficiently suppressed. In particular, when a relatively thin non-foamed layer was to be formed, this tendency became remarkable, and it was found that a polyolefin-based resin foamed sheet having a portion having poor surface smoothness was easily obtained. In view of the above findings of the present inventors, an object of the present invention is a method for producing a polyolefin resin foam sheet in which a non-foam layer made of a polyolefin resin is laminated on at least one surface of a foam layer made of a polyolefin resin. Accordingly, it is an object of the present invention to provide a method for more effectively preventing foam breakage in a foam layer and stably producing a sheet having excellent surface smoothness.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, as a part or all of a resin for a non-foamed layer laminated on a foamed layer, after melting from a solid state, A long-chain branched polyolefin resin having undergone at least one resolidification step and / or a weight average molecular weight of 1 × 1
0 By using ⁵ or more polyolefin resin, a non-foamed layer occurrence of uneven thickness can be effectively prevented, and as a result, the surface smoothness by preventing the foam breaking the foam layer surface effectively It has been found that a polyolefin-based resin foam sheet having excellent heat resistance can be stably obtained, and the present invention has been completed.

That is, the present invention relates to a method for producing a foamed polyolefin resin sheet comprising a foamed polyolefin resin layer and a non-foamed polyolefin resin layer laminated on at least one side of the foamed polyolefin resin resin. On at least one side of the heat-plasticized layer, a process in which a long-chain branched polyolefin-based resin and a polyolefin-based resin having a weight average molecular weight of 1 × 10 ⁵ or more are melted from a solid state and then re-solidified. A heat-plasticized layer made of a polyolefin-based resin material containing 10% by weight or more of a polyolefin-based resin that has passed at least once is laminated and co-extruded to foam a heat-plasticized layer made of the polyolefin-based resin containing the blowing agent. A method is provided. In addition, as described above, the process of re-solidifying the resin after melting from the solid state,
Hereinafter, it may be referred to as “melting-resolidification process”. Further, a polyolefin resin selected from the group consisting of the long-chain branched polyolefin resin and a polyolefin resin having a weight average molecular weight of 1 × 10 ⁵ or more, and subjected to at least one step of melting and then re-solidifying from a solid state, Hereinafter, it may be referred to as “re-solidified polyolefin resin”.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a foamed polyolefin resin sheet, comprising a non-foamed polyolefin resin layer laminated on at least one surface of a foamed polyolefin resin layer. On at least one surface of the heat-plasticized layer made of a polyolefin resin containing a foaming agent to be formed, a heat-plasticized layer made of a polyolefin resin not containing a foaming agent to be the non-foamed layer is laminated and co-extruded, This is a method of foaming the foaming agent-containing polyolefin resin layer in a laminated state. In the method of the present invention, first, a foaming agent to be a polyolefin-based resin non-foamed layer is formed on at least one surface of a heat-plasticized layer made of a polyolefin-based resin containing a foaming agent to be a polyolefin-based resin foamed layer in a target foamed sheet. Is laminated with a heat-plasticized layer made of a polyolefin-based resin in which is not blended.

First, materials used for forming a polyolefin resin foam layer in a foam sheet to be produced will be described. The polyolefin resin foam layer is formed from a composition comprising at least a polyolefin resin and a foaming agent. The polyolefin-based resin used for the polyolefin-based resin foam layer may be any polyolefin-based resin that can be melt-extruded and form and maintain a foamed structure, for example, ethylene, propylene, butene, pentene, Examples thereof include homopolymers of olefins having 2 to 6 carbon atoms such as hexene, and olefin copolymers composed of two or more monomers selected from olefins having 2 to 10 carbon atoms. The copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer. To form a polyolefin resin foam layer,
One kind of polyolefin-based resin may be used alone, or two or more kinds of polyolefin-based resins may be blended and used. From the viewpoint of heat resistance, a polypropylene-based resin is preferable, and a small amount of a polyethylene-based resin is preferably added to the polypropylene-based resin in order to improve moldability.

Particularly preferred polypropylene resins include a propylene homopolymer and 5
Propylene copolymers containing 0 mol% or more can be mentioned. Preferred examples of the copolymer component with propylene in the propylene-based copolymer include ethylene and α-olefins having 4 to 10 carbon atoms. As the α-olefin having 4 to 10 carbon atoms, for example, 1-
Butene, 4-methylpentene-1, 1-hexene and 1-octene. The content of monomer units other than propylene in the propylene-based copolymer is preferably 10% by weight or less for ethylene and 30% by weight or less for α-olefin.

Among the polypropylene resins, (a) a long-chain branched polypropylene and (b) a polypropylene having a weight-average molecular weight of 1 × 10 ⁵ or more, because a foamed layer having a highly uniform cell structure can be formed among polypropylene resins. A system resin is preferred. These polypropylene resins have a melting point of +
Under a temperature condition of 30 ° C., the elongation strain rate is 0.1 sec.
At c ^-1 , when a uniaxial melt extensional viscosity measurement was carried out by a device such as a Meissener type extension rheometer (for example, a Merten rheometer manufactured by Toyo Seiki), 1
Uniaxial melt extensional viscosity η ₁ , η at each point of 100 seconds
Those having a ratio of ₁₀₀ (η ₁₀₀ / η ₁ ) satisfying η ₁₀₀ / η ₁ ≧ 10 are particularly preferred.

As a foaming agent used for forming the polyolefin resin foam layer, any of a so-called chemical foaming agent and a physical foaming agent can be used. As a usable chemical foaming agent, nitrogen gas is generated. Generates pyrolytic blowing agents (azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide, p, p'-oxy-bis (benzenesulfonylhydrazide), etc.) and carbon dioxide gas Pyrolytic inorganic foaming agents (sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, etc.) and the like;
Possible physical blowing agents include propane, butane,
Water, carbon dioxide and the like can be mentioned. Among these, water,
Substances that are inert to high-temperature conditions and fire, such as carbon dioxide, are preferred. In particular, when a polypropylene resin is used as the resin constituting the foam layer, the use of carbon dioxide gas is preferred.
In the present invention, the amount of the foaming agent used is not critical, and may be appropriately adjusted according to the type of the foaming agent, the type of the resin, and the like so as to obtain a desired expansion ratio.

The method of mixing the polyolefin resin with the foaming agent and the additives to be blended if necessary is not particularly limited. For example, the properties of the raw materials used in a suitable mixer such as a single-screw extruder or a twin-screw extruder may vary. A method of supplying and mixing the raw materials under appropriate conditions can be adopted.

Next, a polyolefin resin material used for forming a non-foamed polyolefin resin layer to be laminated on the foamed polyolefin resin layer in the foamed sheet to be produced will be described. The method of the present invention comprises the steps of: forming a polyolefin-based resin non-foamed layer; selecting from the group consisting of a long-chain branched polyolefin-based resin and a polyolefin-based resin having a weight average molecular weight of 1 × 10 ⁵ or more; Re-solidification process (melting-re-solidification process)
This is characterized in that a polyolefin resin material containing 10% by weight or more of a polyolefin resin (resolidified polyolefin resin) that has passed through at least once is used. By using a re-solidified polyolefin-based resin as the material of the non-foamed layer to be laminated on the foamed layer, the non-foamed layer with less thickness unevenness can be easily and reliably formed based on the fact that the melt viscosity of the resin is reduced. Can be formed. As a result, foam breakage during foam layer formation can be more reliably prevented, and a foam sheet excellent in surface appearance can be obtained more efficiently.

In the present invention, a long-chain branched polyolefin resin is defined as having a branching degree index [A] of 0.20 ≦ [A] ≦
It refers to a polyolefin-based resin that satisfies 0.98, and has a molecular structure of ethylene, propylene, butene, pentene, a homopolymer of an olefin having 2 to 6 carbon atoms such as hexene, and a polymer having 2 to 10 carbon atoms. Examples include polyolefin-based resins such as olefin copolymers composed of two or more monomers selected from olefins. The copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer. A polypropylene resin is particularly preferred from the viewpoint of heat resistance. Examples of the long-chain branched polyolefin-based resin having a branching degree index [A] satisfying 0.20 ≦ [A] ≦ 0.98 include polypropylene PF-814 manufactured by Montell.

The branching degree index indicates the degree of long-chain branching, and is a numerical value defined by the following equation. Branching degree index [A] = [η] _Br / [η] _Lin where [η] _Br is the intrinsic viscosity of the polyolefin resin having a long chain branch, and [η] _Lin is the polyolefin having a long chain branch. It is the intrinsic viscosity of linear PO having the same repeating unit as the system resin and the weight average molecular weight. Intrinsic viscosity, also called the limiting viscosity number, is a measure of the ability of a polymer molecule to enhance solution viscosity. The intrinsic viscosity depends in particular on the molecular weight of the polymer molecules and on the degree of branching. Thus, when comparing a polymer with long chain branches to a linear polymer of the same weight average molecular weight, the intrinsic viscosity is a measure of the degree of branching of the polymer, and the ratio of the intrinsic viscosity is defined as the index of branching and the index of branching. did. The method for measuring the intrinsic viscosity of polypropylene is described in Elliott et al. [J. Appl. Polym. Sci. , 14,
2947-2963 (1970)]. The intrinsic viscosity of polypropylene is, for example, 13 for samples dissolved in tetralin or orthodichlorobenzene.
It is possible to measure at 5 ° C. The weight average molecular weight (Mw) can be measured by various methods.
L. American L by McConnell
laboratory, May, 63-75 (1978)
, That is, a low-angle laser light scattering intensity measurement method is particularly preferably used.

In the present invention, the weight average molecular weight is 1 × 1
0 The ⁵ or more polyolefin resin, the weight average molecular weight of 1 × 10 ⁵ or more ethylene, propylene, butene, pentene, homopolymers of olefin having 2 to 6 carbon atoms, such as hexene, and carbon atoms 2 to 10 And polyolefin resins such as olefin copolymers composed of two or more monomers selected from olefins. The copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer. A polypropylene resin is particularly preferred from the viewpoint of heat resistance. Examples of the method of polymerizing a polypropylene resin having a weight average molecular weight of 1 × 10 ⁵ or more include the following methods. That is, the polymerization temperature is 60 ° C. and the polymerization pressure is 27 kg in the first stage.
/ Cm ² G under the conditions of liquid propylene 57kg / h,
1.3 mmol / h of triethylaluminum, 0.13 mmol / h of t-butyl-n-propyldimethoxysilane and 0.5 of the preactivated solid catalyst component.
The mixture was continuously supplied at 1 g / h to carry out propylene polymerization to obtain a polymer having an intrinsic viscosity of 7.7 dl / g. The obtained polymer was continuously transferred to the second stage without deactivating the catalyst. In the second stage, the polymerization temperature is 80 ° C. and the polymerization pressure is 18 kg.
/ Cm ² G, while supplying propylene and hydrogen so as to maintain a hydrogen concentration of 8 vol% in the gas phase, the catalyst-containing polymer and triethylaluminum transferred from the first step and 60 mmol / h, t- By continuing propylene polymerization while supplying 6 mmol / h of butyl-n-propyldimethoxysilane, the intrinsic viscosity is 7.7 dl.
/ G of polymer. The weight-average molecular weight of the polypropylene resin obtained by such a method was measured.
It was about 4 × 10 ⁵ . The weight-average molecular weight of the polypropylene-based resin can be adjusted by the amount of the monomer constituting the resin.

As an example of the process of melting and re-solidifying a polyolefin resin, a solid polyolefin resin, for example, in the form of pellets is melted by a plasticizer (eg, an extruder) and extruded into an arbitrary shape such as a strand or a sheet. ,
Cooling and re-solidification. On the other hand, a molded article such as a film or sheet produced by an appropriate molding method such as extrusion molding using a long-chain branched polyolefin-based resin and / or a polyolefin-based resin having a weight-average molecular weight of 1 × 10 ⁵ or more, or the molded article. The offcuts generated during the production of the body can be recycled and used as the resolidified polyolefin-based resin in the method of the present invention.
In the present invention, when such a molded article or scrap material is recycled, the molded article or scrap material may be a long-chain branched polyolefin-based resin and / or a weight-average molecular weight unless the effects of the present invention are remarkably performed. ^May contain 1 × 10 ⁵ or more polyolefin-based resins other than polyolefin-based resins.

The re-solidified polyolefin resin may have undergone at least one melt-re-solidification step, and the number of times of the melt-re-solidification step is not particularly limited. It is preferable to use a recycled solidified polyolefin resin.

The polyolefin resin material used for forming the non-foamed layer of the polyolefin resin contains the resolidified polyolefin resin in an amount of 10% by weight or more. If the content of the re-solidified polyolefin resin is less than 10% by weight, the non-foamed layer to be formed tends to have uneven thickness, and the effect of preventing foam breakage at the time of forming the foamed layer may not be sufficiently obtained. As a result, a foamed sheet having poor surface smoothness can be easily obtained. Considering the deterioration of the resin due to the melt-resolidification process, the content of the resolidified polyolefin resin is more preferably 20 to 80% by weight, and 30 to 50% by weight.
% By weight is particularly preferred.

The polyolefin-based resin material used for forming the non-foamed layer of the polyolefin-based resin may be composed solely of the above-mentioned resolidified polyolefin-based resin, provided that it contains at least 10% by weight of the re-solidified polyolefin-based resin. And a polyolefin resin other than the re-solidified polyolefin resin.

The polyolefin resin usable in combination with the re-solidified polyolefin resin is selected from the group consisting of a long-chain branched polyolefin resin and a polyolefin resin having a weight average molecular weight of 1 × 10 ⁵ or more. And polyolefin-based resins that have not been subjected to the above. Further, a polyolefin resin other than a long-chain branched polyolefin resin having undergone or not undergoing a melt-resolidification process or a polyolefin resin having a weight-average molecular weight of 1 × 10 ⁵ or more is also applicable. Further, a polyolefin resin modified with a carboxylic acid or a carboxylic acid anhydride is also applicable. Furthermore, a copolymer of an olefin and a monomer polymerizable with the olefin, and a modified product thereof with a carboxylic acid or a carboxylic anhydride can also be applied.

The heat plasticization of the polyolefin resin material used for forming the non-foamed layer of the polyolefin resin can be performed by melt-kneading the raw material resin using an ordinary plasticizer (eg, an extruder). . At this time, a desired additive can be blended.

The heat-plasticized foaming agent-containing polyolefin-based resin and the heat-plasticized non-foamed layer polyolefin-based resin are usually laminated by passing them through a die having a structure capable of laminating them. Coextruded as a sheet. In the method of the present invention, the plasticized layer of the blowing agent-containing polyolefin resin foams mainly after being extruded from the die, but foaming may start in the die.

In the method of the present invention, as a co-extrusion die, a flat die (for example, a T-die or a coat hanger die), a straight die, a circular die (a cross-head die, etc.) is preferably used, but not necessarily. It is not limited to these. In the case of a circular die, the diameter is preferably 50 mmφ or more, and 80 m
More preferably, it is not less than mφ.

The co-extruded polyolefin foam sheet can be stretched if necessary. As a method for stretching the polyolefin resin foam sheet, a method of drawing a foam sheet extruded by a circular die along an internal mandrel, a method of inflating a sheet extruded from a circular die by air blow, and a method of tentering a sheet extruded by a T die For example, a method of stretching in the TD direction by a stretching machine may be used. When stretching a foamed sheet extruded from a circular die, the stretching ratio is preferably 2 times or more and 10 times or less, more preferably 2.5 times or more and 10 times or less, and 3 times or more and 10 times or less. Is particularly preferred. If the stretching ratio is less than 2, wrinkles are likely to occur on the sheet surface. On the other hand, when the stretching ratio is more than 10 times, the sheet is easily broken at the time of stretching. Here, the stretching ratio means a ratio of the inner diameter of the expanded foam sheet to the inner diameter of the circular die. When the sheet extruded with the T-die is stretched in the TD direction by a tenter stretching machine, the stretching ratio is preferably 2 times or more and 4 times or less in the TD direction.

In order to increase the expansion ratio of the foam layer, it is preferable to pass the sheet extruded from the die through a vacuum chamber. The foamed layer further foams in the vacuum chamber, whereby a foamed sheet having a foamed layer with a high expansion ratio can be obtained.

In the method of the present invention, at least one surface of the heat-plasticized layer made of a polyolefin resin containing a foaming agent is heated on a heating layer made of a polyolefin resin material containing 10% by weight or more of a resolidified polyolefin resin. The plasticized underlayer can be laminated and coextruded directly, ie, without any intervening layers.

Further, in the method of the present invention, at least one surface of the heat-plasticized layer made of a polyolefin resin containing a foaming agent is heated on a heating layer made of a polyolefin resin material containing 10% by weight or more of a resolidified polyolefin resin. The plasticized layers can be laminated and coextruded indirectly, ie, through one or more heat plasticized layers.

In this case, the heat-plasticized layer provided between the layer containing the foaming agent and the layer of the polyolefin resin material containing the resolidified polyolefin resin includes:
The above-mentioned long-chain branched polyolefin resin, which is a raw material resin of the re-solidified polyolefin resin, has a weight average molecular weight of 1
A layer made of a polyolefin resin selected from the group consisting of polyolefin resins of × 10 ⁵ or more is suitable.
By laminating such a layer as an intermediate layer and co-extruding, a foamed sheet having excellent surface smoothness can be produced more stably, and the obtained foamed sheet also has excellent surface smoothness.

The method of the present invention is suitable for producing a foamed sheet in which the expansion ratio of the foamed layer is approximately 2 to 40 times.
The expansion ratio of the foam layer can be adjusted by adjusting the amount of the foaming agent used and the physical conditions at the time of molding. Also,
The method of the present invention is suitable for producing a foamed sheet having a thickness of approximately 0.1 to 3 mm. The thickness of the non-foamed layer may be appropriately set depending on the use of the sheet and the like, and is not limited.
The thickness is preferably 1 μm or more, more preferably 1 μm or more.
It is at least 0 μm, more preferably at least 50 μm.

According to the method of the present invention, a heat-plasticized layer made of a polyolefin-based resin material containing 10% by weight or more of a resolidified polyolefin-based resin is provided on at least one surface of a heat-plasticized layer made of a polyolefin-based resin containing a foaming agent. The main point is that the heat-plasticized layer made of the polyolefin resin containing the foaming agent is foamed and co-extruded while foaming the foamed layer. A foam sheet having a foam layer and a non-foam layer laminated on one side thereof can be produced. Further, in the method of the present invention, the non-foamed layer / foamed layer / non-foamed layer is formed by laminating the heat-plasticized layer for the non-foamed layer on both sides of the heat-plasticized layer for the foamed layer and co-extruding. It is also possible to obtain a foamed sheet having such a structure. Furthermore, the two heat-plasticized layers for the two foam layers are laminated through one heat-plasticized layer for the non-foam layer, and further outside the two layers for the foam layer, By laminating and co-extruding the heat-plasticized layers, a foamed sheet having a structure of non-foamed layer / foamed layer / non-foamed layer / foamed layer / non-foamed layer can also be produced. In addition, the re-solidified polyolefin resin-containing non-foamed layer / re-solidified polyolefin resin-free non-foamed layer / foamed layer / re-solidified polyolefin resin-free non-foamed layer / re-solidified polyolefin-based resin-containing non-foamed layer A foam sheet can also be obtained.

Furthermore, in the method of the present invention, unless the characteristics of the present invention are not lost, the heat-plasticized layer made of a polyolefin resin containing a foaming agent and the resolidified polyolefin resin contain at least 10% by weight. It is also possible to further laminate and co-extrude a heat-plasticized layer made of a polyolefin resin other than the heat-plasticized layer made of a polyolein resin.

In the method of the present invention, additives can be appropriately contained in each layer of the polyolefin resin foam sheet. Additives include antioxidants, light stabilizers, ultraviolet absorbers, antifoggants, antifog agents, plasticizers, antistatic agents, lubricants, colorants, dioxin inhibitors, ethylene gas absorbers, deodorants, freshness Retention agents, antibacterial agents and the like can be mentioned. These can be blended as long as the effects of the present invention are not impaired. These additives may be incorporated into the foamed layer, the non-foamed layer, or both, in the method of the present invention. In addition, the method of compounding these additives may be a method in which the components and additives of the foamed polyolefin resin sheet obtained by the method of the present invention are kneaded in advance and used as a resin composition,
In the method of the present invention, a master batch of the additives or the additives themselves can be blended by dry blending.

An example of an embodiment of the method of the present invention will be described below with reference to the drawings. In this example, carbon dioxide gas was used as a foaming agent, melted in a first extruder, and melt-extruded with a twin-screw extruder on both surfaces of a heat-plasticized layer made of a polyolefin resin mixed with carbon dioxide gas. A thermoplastic resin comprising a resin composition obtained by melt-kneading 40 parts by weight of a long-chain branched polypropylene resin cooled and then re-solidified and 60 parts by weight of a polypropylene which has not been subjected to a melt-re-solidification process in a second extruder. The formed layers are laminated in a die and co-extruded, and the intermediate layer is foamed to produce a polyolefin resin foam sheet having a three-layer structure of non-foamed layer / foamed layer / non-foamed layer.

FIG. 1 shows an example of a production apparatus used in the method for producing a foamed polyolefin resin sheet of the present invention. The manufacturing apparatus 1 includes a first extruder 3 for extruding a foam layer constituent material, a second extruder 5 for extruding a non-foamed surface layer constituent material, a die 7, a mandrel 9, and a take-up roll 1.
1 is provided.

The first extruder 3 is provided with a hopper for supplying resin and a pump 6 for supplying carbon dioxide as a foaming agent. The polypropylene resin charged into the cylinder of the extruder 3 from the hopper is melted while being sent to the die 7 by a screw. The carbon dioxide gas is supplied into the extruder at a position where the polypropylene resin in the extruder passes in a sufficiently molten state, and is uniformly dispersed in the molten polypropylene resin. The molten polypropylene resin containing the foaming agent is fed into the die 7. It is preferable that a known vent-type extruder is used as the first extruder, and carbon dioxide gas is supplied under pressure from the vent hole.

In a second extruder 5, 40 parts by weight of a long-chain branched polypropylene obtained by melt-extruding with a twin-screw extruder, cooled and re-solidified, and 60 parts by weight of a polypropylene which has not been subjected to a melt-re-solidification process are melted. The kneaded resin composition,
The extruder 5 feeds the die 7.

The foamed layer constituent material and the non-foamed layer constituent material are laminated and extruded in a molten state in the die 7, and the residence time in the die 7 after lamination is preferably 0.1 to 20 seconds. And more preferably 0.5 to 15 seconds.

The three-layer foamed sheet fed from the die 7 in the form of a tube is formed into a tube 15 having a predetermined diameter by the mandrel 9, and after cooling, folded by the take-off roller 11 and taken off. When this is cut at both folded portions, two three-layer foam sheets are obtained. When the sheet is cut open only at one of the folded portions, a three-layer foam sheet having one wide sheet is obtained.

When two of the obtained three-layer foamed sheets are laminated and bonded, a non-foamed layer / foamed layer / non-foamed layer / non-foamed layer /
A foam sheet having six layers of foam layer / non-foam layer or five layers of non-foam layer / foam layer / non-foam layer / foam layer / non-foam layer is obtained. Further, three or more three-layer foamed sheets can be laminated.

The preferred structure of the die is shown in cross section in FIG.
The die in this example is a circular die. Die 7
Has a resin flow path 23a, 23b forming a foam layer,
Flow paths 24, 24a, 24b of resin forming a non-foamed layer,
24c and 24d are formed.

The head 21 of the first extruder 3 is connected to the end of the die 7 in the direction of the resin flow path, and the head 22 of the second extruder 5 is connected to the side of the die 7 in the direction of the resin flow. . The molten resin forming the foam layer supplied from the head 21 first enters the flow path 23a and is sent toward the die exit. On the way, it is branched by passing through the path P and sent to the flow path 23b.

On the other hand, the molten resin for forming the non-foamed layer is supplied from the head 22 of the second extruder 5 and
It is divided into 4a and 24b, supplied so as to adhere to both sides of the flow path 23b so as to cover both sides of the foamed layer, and is multi-layered at 25a. The molten resin supplied to the flow paths 24a and 24b passes through a divided flow path (not shown) similar to the path P so as to cover both surfaces of the foam layer of the flow path 23a.
4c and 24d, and are multi-layered at 25b.

The molten resin having a three-layer cylindrical shape at 25a and 25b is extruded from a die outlet 26.
By opening to the atmospheric pressure, the carbon dioxide gas in the resin constituting the foam layer expands, and bubbles are formed to form a foam layer.

In the method of the present invention, the relationship between the discharge amount of molten resin (Q: kg / h · mm) and the inner diameter of the die 7 (D: mm) is such that Q / D ≧ 0.3 kg / h · mm. And Q / D ≧ 0.6 kg / hour · mm
Is more preferable. The lip clearance of the die outlet 26 is preferably 0.5 to 3 mm.
More preferably, it is 2 mm. The taper angle at the die exit is preferably from 0 ° to 5 °, more preferably from 0 ° to 1 °. The length of the tapered land is preferably 10 mm or less, more preferably 5 mm or less. The angle between the core of the die and the tapered land at the exit of the die is preferably 45 ° to 80 °, and more preferably 50 ° to 70 °.

In each of the above examples, a single screw extruder is used. However, a twin screw extruder may be used. In particular, it is preferable to use a twin-screw extruder as an extruder for extruding a foam layer constituent material. Further, in the above example, a case where a circular die is used as the die 7 has been described. However, as described above, the die used in the method of the present invention may have an internal structure that is suitable for forming a multilayer sheet. A flat die (T die, coat hanger die, etc.) and a straight die can also be applied.

Other additional layers can be laminated on the foamed sheet obtained by the method of the present invention. By laminating other additional layers on the foam sheet obtained by the method of the present invention, mechanical properties such as flexural rigidity, compressive strength, surface scratch resistance, dimensional stability, heat resistance, heat insulating property In addition, functional properties such as gas barrier properties and moldability can be improved, and properties such as gloss, surface smoothness, and appearance can be imparted.
Additional layers include layers composed of woven, non-woven, knitted, sheets, films, meshes, and the like. The polyolefin resin foam sheet obtained by the method of the present invention may have an adhesive layer for bonding the layers or a layer of an adhesive resin.

The material of the additional layer can be appropriately selected according to the purpose. Examples thereof include thermoplastic resin, thermosetting resin, rubber, thermoplastic elastomer, natural fibers such as hemp, and the like. Minerals such as calcium silicate; In addition, wood, paper, synthetic paper made of polypropylene, polystyrene, or the like, a thin metal plate or metal foil of aluminum, iron, or the like can also be used. Such an additional layer may be provided with an uneven pattern such as a grain, printing or dyeing. Such additional layers may have a single-layer configuration or a multi-layer configuration comprising two or more layers.

Examples of the thermoplastic resin constituting such an additional layer include a polyolefin resin, an ethylene-vinyl ester copolymer and a saponified product thereof, a polyester resin, a polyamide resin, and a halogen-containing resin. . When the foamed polyolefin-based resin sheet obtained by the method of the present invention is applied to a food container, the unstretched polypropylene film (CPP) or the stretched polypropylene film (OP) may be used as a layer made of the thermoplastic resin.
P), ethylene-vinyl ester copolymer film (E
It is preferable to have a layer such as VOH) as an additional layer. The polyolefin-based resin foam sheet obtained by the method of the present invention has, as an additional layer, a layer made of a thermoplastic resin film containing a dioxin inhibitor in order to suppress the load on the environment when the sheet is incinerated. Is preferred. When the polyolefin-based resin foam sheet obtained by the method of the present invention is used for packaging of easily degradable products such as fruits, vegetables and fresh flowers, an ethylene gas absorbent, a freshness preserving agent, a deodorant, an antibacterial agent and the like are used. A layer such as a contained thermoplastic resin film can be used as an additional layer. The film to be laminated on the foamed sheet may be a single-layer film composed of a single film or a multilayer film composed of two or more laminated films. The thickness of the film to be laminated on the foamed sheet is preferably from 10 to 100 μm, and in the case of a multilayer film, preferably from 50 to 200 μm. Specific examples of the film to be laminated on the foamed sheet when the foamed polyolefin resin sheet obtained by the present invention is applied to a food container include a CPP film having a thickness of 50 to 100 μm, a CPP layer /
Adhesive layer / EVOH layer / Adhesive layer 100 μm thick three-layer four-layer film, CPP layer / Adhesive layer / EVOH layer / Adhesive layer / CPP layer 100-μm-thick three-layer five-layer film, CPP layer / Adhesive layer / Nylon layer / EVOH layer /
A 100 μm-thick, three-layer, five-layer multilayer film of an adhesive layer / CPP layer may be used.

Examples of the additional layer include a method of bonding a sheet (or film) corresponding to the layer to the foamed sheet via an adhesive layer, and a method of forming the additional layer on a foamed layer or a non-foamed layer. It can be provided by a method of fusing on top.

The foamed polyolefin resin sheet obtained by the method of the present invention can be used for various applications by subjecting it to processing such as molding as required. Specifically, food containers such as microwave oven-compatible containers (HMR), heat insulating materials, cushioning materials such as sports equipment and packing materials, heat insulating materials, automobile parts such as vehicle ceiling materials, sealing materials, building materials, and aerospace industry It can be used for applications that use resins that require heat insulation. In particular, it can be suitably used as a food container such as a microwave-compatible container in which a layer made of a barrier resin is laminated. Examples of food containers include trays,
Cups, cups, boxes and the like.

[0052]

According to the method of the present invention, it is possible to effectively prevent foam breakage during foaming of the polyolefin resin foam layer, and to obtain a polyolefin resin foam sheet having excellent surface smoothness. . The surface smoothness of the polyolefin resin foam sheet can be evaluated by the following method. The surface roughness is measured at a scan speed of 0.3 mm / sec over a length of 1 cm from an arbitrary point on the test piece (foamed sheet) according to the method of measuring the center line average roughness specified in JIS B0601. This measurement is performed at three arbitrary points, and the average value of the obtained surface roughness is defined as the surface roughness Ra of the foamed sheet. The smaller the Ra value is, the more excellent the foam sheet is in the surface smoothness. In the conventional foamed polypropylene resin sheet, Ra was about 4.8 μm, but in the present invention, a sheet excellent in surface smoothness with Ra of 3.8 μm or less can be obtained.

[0053]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

Example 1 A foamed polyolefin-based resin sheet having a non-foamed layer / foamed layer / non-foamed layer was prepared in the following manner. (Foam layer constituent material) As the foam layer constituent material, polypropylene and polyethylene by the two-stage polymerization method are used in a weight ratio of 7
A mixture blended at 0/30 was used. Hereinafter, a method for producing and pelletizing the polypropylene, and a method for blending the constituent materials of the foamed layer will be described.

(1) Synthesis of solid catalyst After replacing a 200 L stainless steel reaction vessel equipped with a stirrer with nitrogen, 80 L of hexane and titanium tetrabutoxy were used.
55 mol, 2.8 mol of diisobutyl phthalate and 98.9 mol of tetraethoxysilane were added to obtain a uniform solution. Next, 51 L of a diisobutyl ether solution of butylmagnesium chloride having a concentration of 2.1 mol / L was gradually dropped over 5 hours while maintaining the temperature in the reaction vessel at 5 ° C. After completion of the dropwise addition, the mixture was further stirred at room temperature for 1 hour, then separated into solid and liquid at room temperature, and the solid phase was washed three times with 70 L of toluene. Then, toluene was added so that the slurry concentration became 0.6 kg / L, then a mixed solution of 8.9 mol of n-butyl ether and 274 mol of titanium tetrachloride was added, and 20.8 mol of phthalic chloride was further added. In addition, the reaction was performed at 110 ° C. for 3 hours. After completion of the reaction, washing was performed twice at 95 ° C. with toluene. Next, the slurry concentration was 0.6 kg / L.
Was adjusted to 3.13 mol of diisobutyl phthalate, n
8.9 mol of dibutyl ether and titanium tetrachloride 13
7 mol was added and the reaction was carried out at 105 ° C. for 1 hour. After completion of the reaction, solid-liquid separation was performed at the same temperature, and the solid phase was washed twice with 95 L of toluene at 95 ° C. twice. Next, after adjusting the slurry concentration to 0.6 kg / L, 8.9 mol of n-dibutyl ether and 137 mol of titanium tetrachloride were added, and
The reaction was carried out at a temperature of 1 hour. After completion of the reaction, solid-liquid separation was performed at the same temperature, and the solid phase was repeatedly washed with 90 L of toluene at the same temperature three times. Next, after adjusting the slurry concentration to 0.6 kg / L, 8.9 mol of n-butyl ether and 137 mol of titanium tetrachloride were added, and the mixture was reacted at 95 ° C. for 1 hour. After the completion of the reaction, solid-liquid separation was performed at the same temperature, and the solid phase was repeatedly washed with 90 L of toluene at the same temperature three times, further washed with 90 L of hexane three times, and then dried under reduced pressure to obtain 11.0 kg of a solid catalyst component. Was.

The solid catalyst component comprises 1.9% by weight of titanium atoms,
20% by weight of magnesium atom, phthalate 8.6
Weight%, ethoxy group 0.05 weight%, butoxy group 0.2
It contained 1% by weight and had good particle properties without fine powder.

(2) Pre-activation of solid catalyst component n-hexane 1.5, which was sufficiently dehydrated and degassed in a stainless steel autoclave having an internal volume of 3 L and equipped with a stirrer.
L, triethylaluminum 37.5 mmol, tert-
3.75 mmol of butyl-n-propyldimethoxysilane and 15 g of the above solid catalyst component were added, and the temperature in the vessel was adjusted to 5 to 5.
Preliminary activation was performed by continuously supplying 15 g of propylene over 30 minutes while maintaining the temperature at 15 ° C.

(3) Propylene Polymerization First Stage In a 300 L polymerization tank made of stainless steel, liquid propylene was supplied at 57 kg / h so as to maintain a polymerization temperature of 60 ° C. and a polymerization pressure of 27 kg / cm ² G. 1.3 mmol / h of triethylaluminum, 0.13 mmol / h of t-butyl-n-propyldimethoxysilane
Further, 0.51 g / h of the preactivated solid catalyst component was continuously supplied, and propylene polymerization was carried out in the substantial absence of hydrogen to obtain a polymer of 2.0 kg / h. At this time, the produced amount of the polymer was 3920 g per 1 g of the catalyst. As a result of sampling and analyzing a part of the produced polymer, the intrinsic viscosity was 7.7 dl / g. The obtained polymer was continuously transferred to the second tank without deactivating the catalyst.

Second stage In a 1 m ³ fluidized bed reactor equipped with a stirrer having an internal volume of 1 m ³ , propylene and hydrogen were added so as to maintain a polymerization temperature of 80 ° C., a polymerization pressure of 18 kg / cm ² G, and a hydrogen concentration of 8 vol% in the gas phase. While supplying, the catalyst-containing polymer transferred from the first tank and triethyl aluminum 60 mmol /
By continuing propylene polymerization while supplying 6 mmol / h of t-butyl-n-propyldimethoxysilane, 18.2 kg / h of a polymer was obtained. The intrinsic viscosity of this polymer was 1.9 dl / g.

From the above results, the amount of polymer produced in the second stage polymerization was 31760 g per 1 g of the catalyst, the polymerization weight ratio of the first polymerization tank to the second polymerization tank was 11/89,
The intrinsic viscosity of the portion of the polymer formed by the step polymerization reaction was determined to be 1.2 dL / g.

(4) Pelletization of polypropylene By kneading in an extruder, 0.1 part by weight of calcium stearate, 100 parts by weight of the polypropylene powder obtained by the above two-step reaction, and a phenolic antioxidant (commercially available) Name: Irganox 1010, 0.05 parts by weight of Ciba Specialty Chemicals) and 0.2 parts by weight of phenolic antioxidant (trade name: Sumilizer BHT, manufactured by Sumitomo Chemical Co., Ltd.) The mixture was melt-kneaded to obtain pellets having a melt flow rate (MFR) of 12 g / 10 minutes.

(5) Blend of foam layer constituent materials The polypropylene pellets obtained through the steps (1) to (4) and polyethylene (trade name: Sumikasen G)
201, manufactured by Sumitomo Chemical Co., Ltd.)
/ 30 was dry blended.

(Material for non-foamed layer) As a material for non-foamed layer, long-chain branched polypropylene (trade name: Polypropylene PF814, manufactured by Montell Co .; melting point: 159.0)
° C; crystallization temperature: 130.1 ° C; MFR: 2.2 g / 1
0 minutes) with a co-rotating twin screw extruder (trade name: PCM45; manufactured by Ikegai Co., Ltd .; screw diameter: 45 mm; screw L /
D: 30), melt-knead at a screw rotation speed of 200 rpm, extruded into a strand at a die temperature of 240 ° C., cooled in water, re-solidified, cut with a cutter, and melted with 30 parts by weight of resin pellets. A dry blend mixture with 70 parts by weight of pellets of long-chain branched polypropylene (Montell's polypropylene PF814) that had not undergone the resolidification process was used.

(Extrusion foaming) 50 mmΦ twin screw extruder and 32
An apparatus in which a 90 mmΦ circular die was attached to a mmΦ single screw extruder was used. 1 part by weight of a nucleating agent (trade name: Hydrocellol; 100 parts by weight of a 70/30 (weight ratio) mixture of polypropylene / polyethylene for the foam layer)
The mixture obtained by blending with Beilinger Ingelheim Chemicals Co., Ltd.) was charged into a 50 mmΦ twin screw extruder, and 1 part by weight of carbon dioxide gas was further injected while melting and kneading the mixture.
After sufficiently kneading the resin mixture and carbon dioxide gas,
Was sent to the temperature controlled die. On the other hand, the dry blend mixture for the non-foamed layer was charged into a 32 mmφ single screw extruder, melt-kneaded, and sent to a die adjusted to 210 ° C. The resin composition for a foaming layer from a 50 mmΦ twin screw extruder and the resin composition for a non-foaming layer from a 32 mmΦ single screw extruder are laminated in a die and then extruded into a cylindrical shape, and the extruded cylindrical sheet is placed immediately after the die. It was installed and expanded by cooling along a 210 mm outer diameter mandrel, which was cooled by circulating 6 ° C. water inside. The thus obtained cylindrical two- or three-layer foamed sheet was cut with a cutter, opened to obtain a flat two- or three-layer foamed sheet, and taken up by a take-off machine.
The physical properties of the obtained foamed sheet were evaluated. Table 1 shows the results.

Example 2 A foamed sheet was prepared in the same manner as in Example 1 except that the following resin mixture was used as the non-foamed layer constituting material, and its physical properties were evaluated. Table 1 shows the results. Incidentally, the non-foamed layer of the obtained foamed sheet contained 48% by weight of the re-solidified polyolefin-based resin. (Non-foamed layer constituent material) Foamed layer having the same composition as the foamed layer in the foamed sheet prepared in Example 1 and long-chain branched polypropylene (Montel's polypropylene PF814)
The heat-plasticized non-foamed layer-forming resin is laminated on both outer layers of the heat-plasticized foamed-layer-forming resin, and the foamed layer-forming resin is foamed.
A non-foamed layer / foamed layer / non-foamed layer formed by taking out a sheet co-extruded from a die controlled at 0 ° C. while cooling and solidifying along a cooled internal mandrel by circulating water at 6 ° C. inside. Foamed layer = 80/2200/80 μm layered two-layer, three-layer foamed sheet, unstretched polypropylene layer / maleic anhydride-modified polypropylene layer / ethylene-vinyl ester copolymer saponified layer / maleic anhydride-modified polypropylene layer / Unstretched polypropylene layer =
Heat-plasticized constituent resin of each layer is laminated so as to have a layer structure of 25/10/30/10/25 μm,
A multilayer sheet formed by laminating a multilayer film having a thickness of 100 μm produced by co-extrusion from a die and cooling and solidifying by circulating water at 10 ° C. and taking it along a cooling roll cooled therein is scrapped. Resin material 50 obtained
Parts by weight of a long-chain branched polypropylene that has not been subjected to a melt-resolidification process (Montel's polypropylene PF8
14) A resin mixture containing 50 parts by weight was used.

Example 3 A resin (A) and a resin (B) to be described later were used as non-foamed layer constituent materials, and a non-foamed layer of the resin (A) / resin ( A three-layer five-layer polyolefin-based resin foam sheet having a configuration of non-foamed layer / foamed layer / foamed layer of resin (B) / non-foamed layer of resin (A) was prepared, and its physical properties were evaluated. Table 1 shows the results.

(Non-foamed layer constituent material) Resin (A) As the non-foamed layer constituent material (A), a long-chain branched polypropylene (trade name: Polypropylene PF814; manufactured by Montell Co.) is a bidirectional twin screw extruder (trade name) : PCM45; manufactured by Ikegai Co., Ltd.), melt-kneaded at a screw rotation speed of 200 rpm, extruded into a strand at a die temperature of 240 ° C., cooled in water, re-solidified, and then cut with a cutter to obtain 30 parts by weight of resin pellets. A dry blend mixture of 70 parts by weight of pellets of long chain branched polypropylene (polypropylene PF814 manufactured by Montell Co., Ltd.) which has not been subjected to a melt-resolidification process was used. (Resin (B)) As the non-foamed layer constituent material (B), long chain branched polypropylene (trade name: polypropylene PF
814; manufactured by Montell).

(Extrusion foaming) 50 mmΦ2 for foam layer extrusion
A screw extruder, two 32 mmφ single screw extruders for non-foamed layer extrusion, and a device fitted with a 90 mmφ circular die were used. A mixture obtained by blending 1 part by weight of a nucleating agent (trade name: Hydrocellol; manufactured by Beilinger Ingelheim Chemicals) with respect to 100 parts by weight of a polypropylene / polyethylene 70/30 (weight ratio) mixture for a foam layer. Was injected into a 50 mmΦ twin screw extruder, and 1 part by weight of carbon dioxide gas was further injected while melting and kneading the mixture, and after sufficiently kneading the resin mixture and carbon dioxide gas, the mixture was fed to a die). On the other hand, the resin (A) for the non-foamed layer is
The resin (B) was charged into the other single-screw extruder into the other single-screw extruder, melt-kneaded, and fed into a die. A resin composition for a foamed layer from a 50 mmΦ twin screw extruder and a resin (A) and a resin (B) for a non-foamed layer are laminated in a die in a molten state, and then extruded into a cylindrical shape, and placed immediately after the die. Expanded while cooling along a mandrel with an outer diameter of 210 mm. The thus obtained cylindrical three-layered five-layer foamed sheet was cut with a cutter, opened to form a flat foamed sheet, and taken up by a take-off machine.

Comparative Example 1 A foamed sheet was prepared in the same manner as in Example 1 except that the following resin was used as the non-foamed surface layer constituting material, and its physical properties were evaluated. Table 1 shows the results. (Material for non-foamed surface layer) Long-chain branched polypropylene (melting point: 159.0 ° C; crystallization temperature: 130.1 ° C; MFR)
(230 ° C): 2.2 g / 10 minutes)

The surface smoothness of the foamed sheet obtained in each example was evaluated by the following method. A test piece having a predetermined shape is set on a stylus-type roughness meter (trade name: Surfcom 570A; manufactured by Tokyo Seimitsu Co., Ltd.), and the test piece in the test piece is measured according to the center line average roughness measurement method specified in JIS B0601. The surface roughness was measured at a scan speed of 0.3 mm / sec over an area of 1 cm from an arbitrary point in FIG. This measurement was performed at three arbitrary points, and the average value of the obtained surface roughness was defined as the surface roughness Ra of the foamed sheet. The smaller the Ra value is, the more excellent the foam sheet is in the surface smoothness.

[0071]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a preferred configuration of a production apparatus for a polyolefin resin foam sheet.

FIG. 2 is a cross-sectional view illustrating a preferred configuration of a head in a device for manufacturing a polyolefin resin foam sheet.

Claims (3)

[Claims] 1. A method for producing a foamed polyolefin resin sheet comprising a foamed polyolefin resin layer and a non-foamed polyolefin resin layer laminated on at least one side of the foamed polyolefin resin resin, comprising a thermoplastic resin comprising a polyolefin resin containing a foaming agent. On at least one side of the layer, is selected from the group consisting of a long-chain branched polyolefin-based resin and a polyolefin-based resin having a weight-average molecular weight of 1 × 10 ⁵ or more. A heat-plasticized layer made of a polyolefin-based resin material containing 10% by weight or more of the passed polyolefin-based resin is co-extruded to foam a heat-plasticized layer made of the polyolefin-based resin containing the blowing agent. how to. 2. The long-chain branched polyolefin resin and the polyolefin resin having a weight average molecular weight of 1 × 10 ⁵ or more contained in the non-foamed layer are each a long chain branched polypropylene resin and a 1 × 10 ⁵ weight average molecular weight. The method according to claim 1, wherein the resin is a polypropylene resin of 10 ⁵ or more. 3. A long-chain branched polyolefin resin and a weight-average molecular weight between a heat-plasticized layer made of a polyolefin resin containing the blowing agent and a heat-plasticized layer made of the polyolefin resin material. Is 1 × 10
The method according to any one of claims 1 to 2, further comprising laminating a heat-plasticized layer made of a polyolefin resin selected from the group consisting of ^five or more polyolefin resins.