JPH0811149A - Heterogenous foamed sheet, production thereof and container - Google Patents

Abstract

PURPOSE:To newly impart high rigidity, printability, beautifulness or the like while holding conventional characteristics, in a thermoplastic resin foamed sheet of which the foaming magnification is specific times or more and the density is a specific value or less, by differentiating the foaming state on one surface side of the sheet from that on the other surfaces side thereof. CONSTITUTION:A heterogenous foamed sheet S is characterized by that foaming magnification is 1.1 times or more and density is 0.8 or less and the foaming magnification on one surface side B of the sheet S is high while that on the other surface side A of the sheet is low or substantially zero. A foamed state is coarse on one surface side B of the sheet S and successively becomes dense toward the other surface side B thereof. By this constitution, the sheet S holds conventional characteristics such as lightweight properties, heat insulating properties or buffering properties on one surface side B thereof and can satisfy various physical properties such as rigidity, printability or beautifulness on the other surface side A thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a special thermoplastic resin foam sheet having different foaming on one side and the other side, a method for producing the same, and a container using the same, preferably used for containers such as food trays. The present invention relates to a foamed sheet, a method of manufacturing the same, and a container, which are also applied to applications such as automobile members, building members, interior members and other general industrial members.

[0002]

2. Description of the Related Art Conventionally, as a foamed sheet for a food tray container such as a side dish tray and a lunch box container or a foamed sheet used as an interior material for an automobile, the cross section is generally foamed uniformly. Foamed sheets and the like are used, and JP-A-4-364930 and JP-A-1-50583 have been proposed as methods for producing these foamed sheets. The foamed state of these sheets is that the entire sheet is foamed uniformly,
Various physical properties such as heat retention, cushioning, and lightness are satisfied.
However, with the recent diversification of uses and the like, various properties such as high rigidity, printability, and beauty (surface smoothness) have been newly demanded in addition to the above-mentioned physical properties in containers and building members. There is.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to solve these problems of the prior art and to reduce the weight, the heat retaining property, the cushioning property,
To provide an inhomogeneous foamed sheet which retains the conventional properties such as heat insulating property and which is newly imparted with high rigidity, printability, beauty (surface smoothness), etc., a manufacturing method thereof, and a container using the sheet. With the goal.

[0004]

Means for Solving the Problems In developing a special foamed sheet satisfying the above various properties,
As a result of diligent study, a heterogeneous foamed sheet that retains the conventional properties such as light weight, heat retention, cushioning, and heat insulation properties, as well as newly added high rigidity, printability, beauty (surface smoothness), etc. And its manufacturing method and the development of a container using the sheet.

That is, the present invention is a thermoplastic resin foam sheet having a foaming ratio of 1.1 times or more and a specific gravity of 0.8 or less, and the foaming state is different between one side and the other side of the sheet. A heterogeneous foam sheet characterized by the above. In this heterogeneous foamed sheet, it is desirable that the expansion ratio is 1.1 to 40 times and the foamed cell diameter ratio B / A on the one surface side B and the other surface side A is 1.2 to 250 times. . Further, polyolefin or a composition thereof is desirable as the thermoplastic resin, and it is desirable to use an inert gas as the foaming agent. Further, the present invention includes a means for supplying a thermoplastic resin sheet having a foaming ability, a means for heating the sheet to form an inhomogeneous foamed sheet, and a means for winding up the foamed sheet, which is characterized by being non-homogeneous. It is a method of manufacturing a foamed sheet. Furthermore, the present invention is a container characterized by using the above-mentioned heterogeneous foamed sheet.

The present invention will be described in detail below. The thermoplastic resin used in the present invention is not particularly limited, but is generally an olefin resin, an ethylene-vinyl acetate copolymer saponified product, a polyamide resin, a polyester resin, a polycarbonate resin, a polyvinyl chloride resin. resin,
Examples thereof include polystyrene resins and mixtures thereof.

Of these, olefin resins are preferable, and specifically, high / medium density polyethylene, high pressure radical method low density polyethylene, linear low density polyethylene,
Ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid alkyl ester copolymer such as ethylene- (meth) acrylic acid alkyl ester copolymer, polypropylene, propylene-α-olefin copolymer, etc. Is mentioned. Particularly preferable examples from the viewpoint of heat resistance and economy are polyethylene resins and polypropylene resins.

Examples of the polyethylene resin include (A) low-density polyethylene or ethylene-α-olefin copolymer by a high-pressure radical polymerization method having a density of 0.86 to 0.94 g / cm ³ , and (B) ethylene-vinyl ester copolymer. At least one selected from a polymer and (C) ethylene-α, β-unsaturated carboxylic acid alkyl ester copolymer, or a mixture thereof can be mentioned.

More specifically, (A) density 0.86-0.
The low density polyethylene or ethylene-α-olefin copolymer produced by the high pressure radical polymerization method of 94 g / cm ³ has a density of 0.91 to 0.94 obtained by the radical polymerization method.
Low density polyethylene (hereinafter abbreviated as LDPE) of g / cm ³ and ethylene and carbon number 3 to 12 by the medium and low pressure method using Ziegler catalyst and other known methods
Of α-olefin and a density of 0.86 to
An ethylene-α-olefin copolymer having a density of less than 0.91 g / cm ³ (ultra-low density polyethylene, hereinafter abbreviated as VLDPE) and an ethylene-α-olefin copolymer having a density of 0.91 to 0.94 g / cm ³ ( Linear low-density polyethylene (hereinafter abbreviated as LLDPE).

Examples of polypropylene resins include propylene homopolymers, random copolymers of propylene and other α-olefins, and block copolymers. Further, in order to obtain an elastic body or a rigid body of foam, it is desirable to appropriately select these resins. For example, when high rigidity is required, a propylene homopolymer is selected, and the isotacticity (P ₀ ) is preferably 0.94 or more. Further, when the elasticity of the foam is maintained, it is preferable to add a polyethylene resin to the polypropylene resin.

Specific α-olefins include propylene having 1 to 3 carbon atoms, 1-butene, and 4-methyl-1-.
Pentene, 1-hexene, 1-octene, 1-dodecene and the like can be mentioned. Of these, 1 is preferred
-Butene, 4-methyl-1-pentene, 1-hexene,
1-octene. The content of α-olefin in ethylene and other α-olefin copolymer or propylene and other α-olefin copolymer is preferably 5 to 40 mol%.

The polyolefin composition in the present invention means a mixture of the above resins, a resin and an inorganic or organic filler such as silica, talc or calcium carbonate, a cell regulator,
It includes a mixture of additives such as a lubricant, a phosphorus-based antioxidant, a phenol-based antioxidant, a UV inhibitor, a crosslinking agent, a nucleating agent, a flame retardant, a pigment and a dye.

As the foaming agent used in the present invention, azodicarbonamide, dinitrosopentamethylenetetramine, paratoluenesulfonyl semicarbazide, 4,
Chemical decomposition type foaming agents such as 4'-oxybisbenzenesulfonyl hydrazide and azobisisobutyronitrile, volatile foaming agents such as trifluoromethane, monochlorotrifluoromethane, methyl chloride, pentane and hexane,
Gas type blowing agents such as water (H ₂ O), carbon dioxide, carbon monoxide, helium, argon, nitrogen, oxygen, air, freon, propane and butane are not particularly limited.
When used as a container for food trays, etc., nitrogen,
Inert gas type blowing agents such as oxygen, carbon dioxide and air are suitable.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of the heterogeneous foamed sheet of the present invention. In the figure, the heterogeneous foamed sheet S has a foaming ratio of 1.1 times or more, a specific gravity of 0.8 or less, and one surface side B It is important that the expansion sheet has a high expansion ratio and the other surface side A has a low expansion ratio or is a substantially non-foamed state, and the foaming state is sequentially from the one surface side B to the other surface side A. It is desirable that the is coarse to dense. However, as shown in FIG. 2, depending on the purpose of use, the foamed state may be substantially uniform from one side B'of the sheet S to about 1/5, preferably about 1/4 of the other side A '. . Further, although depending on the type of resin, in a food tray or the like, the expansion ratio is 1.1 to 40 times, preferably 1.1 to 30 times,
It is more preferably 1.1 to 20 times.
With such a configuration, the one side B retains the conventional characteristics such as light weight, heat retention, cushioning, and heat insulation,
The other surface A can satisfy various physical properties such as rigidity, printability, and beauty (surface smoothness).

The thickness of the heterogeneous foamed sheet of the present invention varies depending on the application and purpose of use of building civil engineering materials, automobile parts, food materials, etc., and is not particularly limited. For example, for containers for food trays such as side dish trays, It is desirable to make a thin sheet of about several millimeters using an inert gas.

The size of the foamed cell of the present invention is 20% of the total thickness of the sheet from the one side B where foaming is high.
Is in the range of 10 to 500 μm, and it is desirable that 20% of the total thickness of the sheet from the other side A having a low foaming state to the solid state is 200 μm. In particular, the ratio between the one side B and the other side A is B / A = 1.2 to 250, preferably 2
It is preferably in the range of 0 to 100. The ratio is 1.
If it is less than 2, the characteristics of the foamed sheet of the present invention are not exhibited, and 2
When it exceeds 50, there is a possibility that the rigidity is lowered.

The manufacturing method of the heterogeneous foam sheet of the present invention is
A method for producing a heterogeneous foamed sheet, comprising: a means for supplying a thermoplastic resin sheet having foaming ability; a means for heating the sheet to form an inhomogeneous foamed sheet; and a means for winding the foamed sheet. is there. The thermoplastic resin sheet having a foaming ability of the present invention means a sheet in which the foaming agent still has a foaming ability by heating.

An example of the method for producing the heterogeneous foamed sheet of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows a schematic process diagram of the method for producing a heterogeneous foamed sheet of the present invention. In the figure, the supplying means of the thermoplastic resin sheet having the foaming ability is as follows: 1 is a hopper for supplying a resin raw material, 2 is an extruder, 3 is a vent port for introducing an inert gas or exhausting unnecessary gas, 4 is a A step of supplying a thermoplastic resin raw material and / or a step of supplying a foaming agent, such as a T-die, 5 is a pressing roll, 6 is a refrigerant liquid tank, 7 is a refrigerant liquid using water, oil, polyethylene glycol, or the like, 8 , 8'is a turn roll, 9 is a cooling mechanism of a molten thermoplastic resin including a hydraulic mechanism, a mechanism by a rack and pinion, a vertical adjustment drive mechanism that can be driven by a screw mechanism, etc. The means for heating to make an inhomogeneous foamed sheet includes an oven device 12 equipped with an infrared heater 11 and the like, cooling rolls 15 and 15 ', and a cooling step of a cooling water tank or the like (not shown). , Place (Not shown) annealing step to eliminate such warpage of the foam sheet is intended to encompass rolling step (not shown) or the like. Further, the foaming sheet winding means 18 is a winding means provided with a winding roll or the like, and a surface to which a corona discharge treatment device 17 or the like is preliminarily applied to the surface of the foamed sheet before winding if desired. Processing steps,
Printing process (not shown), adhesive coating process (not shown)
Etc. are included.

An example of the present invention will be shown below. In the case of a decomposable foaming agent as the foaming agent, the thermoplastic resin supplying step and / or the foaming agent supplying step means dry blending the thermoplastic resin pellets and the chemically decomposable foaming agent and supplying them to the hopper 1. Then, in the extruder 2, it is melted and melted uniformly at a temperature not lower than the melting point of the resin and at which the foaming agent is not substantially decomposed. When an inert gas or the like is used as the foaming agent, the gas is introduced from the vent port 3 of the extruder to uniformly melt and sorb the gas in the extruder at a temperature not lower than the melting point of the resin and at which the foaming agent is not substantially decomposed. Then, the molten resin sheet that is not substantially foamed is extruded from the T die 4 at the tip of the extruder, and then the extruded molten resin sheet is rapidly cooled at the outlet of the T die 4 in the cooling step to suppress foaming of the foaming agent. It is controlled and made into a sheet.

In the cooling step, the molten resin sheet discharged from the T die 4 is introduced into a pair of pinching rolls 5 installed immediately below the die. The pinching roll is installed in the coolant liquid tank 6 and is equipped so that the roll 5 is wholly or partially immersed in the coolant liquid 7. The whole or part of the pinching roll is immersed in the refrigerant liquid in order to prevent the roll from being heated by the molten resin.

In order to bring the outlet of the T die 4 and the pinching roll 5 as close to each other as possible, the refrigerant liquid tank 6 is adjusted between the outlet of the T die 4 and the pinching roll 5 by the vertical adjustment drive mechanism 9. In addition, when the molding speed is increased, the refrigerant liquid may be entangled in the pinching roll to cause uneven cooling of the sheet,
At this time, it is effective to combine with several stages of draining rolls (not shown). By doing so, the high temperature sheet discharged from the T-die 4 is in a molten state in the pressing roller 5
Of the non-foamed resin sheet 10 (a sheet having a foaming ability) in which the surface is smoothed and then cooled in the refrigerant liquid 7, and the warp and strain of the entire sheet are corrected by passing through the roll group. ) Can be efficiently molded.

The sheet 1 having the foaming ability manufactured as described above
0 is an oven device 12 equipped with an infrared heater 11.
It is introduced into the inside and the one side B is heated and foamed. It is desirable to foam so that the foaming state becomes denser from the one surface side B to the other surface side A sequentially, but depending on the purpose of use, about 1/4 of the one surface side B to the other surface side A of the sheet 10 Alternatively, the foaming may be performed until the foaming state becomes uniform up to about 1/3. Further, the heating means is not particularly limited, and varies depending on the type, composition, blending, or purpose of use, application of the resin, but in order to appropriately select the heating temperature and the heating time, instead of the infrared heater 12,
A burner, hot plate, hot roll, hot belt, heated steam, hot air, etc. may be used alone or in combination.

After leaving the oven device 12, an annealing process (not shown) is performed to finally correct the warp of the sheet while cooling it with a pair of cooling rolls 15 and 15 '.
Then, if desired, the product is wound up through a corona discharge treatment, an adhesive coating process, etc. to obtain a product.

The container of the present invention is a container using the above-mentioned heterogeneous sheet, and is preferably made of a polyolefin resin or its composition. Particularly, in the case of food containers, heat retention, heat resistance, rigidity, etc. From this point, it is preferable to use a polypropylene resin and use an inert gas as the foaming agent.

The containers of the present invention include trays such as fresh food trays, side dish trays, lunch boxes, and trays for mushrooms, food containers such as cups such as ramen cups, heat-insulating containers, and fish boxes. And is formed by thermoforming, drawing, press forming, or the like. Further, the sheet having the foaming ability may be directly foamed at the time of molding a container such as thermoforming.

In the container of the present invention, the inner surface may have a foamed state and the outer surface may have a dense structure, or the inner surface may have a dense structure and the outer surface may have a rough structure. The structure in which the outer surface is dense is preferable because printing can be performed on the outer surface and the outer surface has beauty (smoothness).

In the present invention, additives such as a crosslinking agent, an antioxidant, an ultraviolet absorber and a pigment may be blended within the range not departing from the gist of the present invention.

[0028]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Using the apparatus of FIG. 3, polypropylene resin (MFR = 0.5 g / 10 min, density = 0.90 g / cm) was used as the resin.
³ , product name: Nisseki Polypro E610G, manufactured by Nippon Petrochemical Co., Ltd.) was introduced into the extruder from the hopper 1, N ₂ gas as a foaming agent was fed through the vent port 3, and the molding speed was 5
The sheet was extruded at a temperature of 27 ° C. at a temperature of 27 ° C. to obtain a substantially unfoamed sheet. Next, the sheet was foamed on one side with an oven equipped with a special gas burner and an infrared heater (1.9 kW, 280 mm × 3) to produce the heterogeneous foamed sheet of the present invention, and the evaluation revealed that the average foaming ratio was 1 .8 times, 2 from side A
Cell diameter up to 0% thickness (reflection electron microscope SEM J
Is 5 μm on average, measured by ESM JSM-T20,
The cell diameter from the B surface to the thickness of 20% was 150 μm, and B / A = 30. When a tray was formed using this sheet with the side B as the inside, the outside was very smooth and the printing characteristics were good.

Example 2 Using the apparatus of FIG. 3, polypropylene resin (MFR = 0.5 g / 10 min, density = 0.90 g / cm) was used as the resin.
³ , the product name: Nisseki Polypro E610G, manufactured by Nippon Petrochemical Co., Ltd.) was introduced into the extruder from the hopper 1, N ₂ gas as a foaming agent was fed through the vent port 3, and the molding speed was 3
The sheet was extruded at a temperature of 27 ° C. at a temperature of 27 ° C. to obtain a substantially unfoamed sheet. Then, the sheet was foamed on one side in an oven equipped with a special gas burner and an infrared heater (1.9 kW, 280 mm × 3) to produce a heterogeneous foamed sheet of the present invention, which was evaluated. 20 times from side A
% Cell diameter (reflection electron microscope SEM JE
(Measured by JEM-T20 manufactured by OL) is 5 μm on average, and B
The cell diameter from the surface to the thickness of 20% is 210 μm,
B / A = 42. When a tray was formed using this sheet with the B side as the inner side, the outer surface was very smooth and
The printing characteristics were also good.

[0030]

EFFECTS OF THE INVENTION According to the present invention, the one side B is lightweight because the one side B having a high degree of foaming and the other side A having a low degree of foaming have different foaming states made of a special thermoplastic resin. , Other properties such as rigidity, printability, beauty (surface smoothness), etc. can be satisfied on the other side A while maintaining the conventional characteristics such as heat retention, cushioning and heat insulation. It is also applied to applications such as containers, automobile parts, building parts / interior parts, and other general industrial parts.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of a heterogeneous foam sheet of the present invention.

FIG. 2 is a schematic sectional view of another example of the heterogeneous foamed sheet of the present invention.

FIG. 3 is a schematic process diagram of a method for producing a heterogeneous foam sheet of the present invention.

[Explanation of symbols]

S: Heterogeneous foamed sheet, A, A ': other side, B, B':
One side, 1: Hopper, 2: Extruder, 3: Vent port,
4: T die, 5: pinching roll, 6: cooling liquid tank, 7: cooling liquid, 8, 8 ': turn roll, 9: vertical adjustment drive mechanism,
10: Foaming ability sheet, 11: Infrared heater, 12: Oven device, 13, 13 ': Roll, 14, 14': Roll, 15, 15 ': Cooling roll, 16: Roll, 1
7: Corona discharge device, 18: winding roll.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29L 7:00 C08L 23:02

Claims (6)

[Claims] 1. A thermoplastic resin foam sheet having a foaming ratio of 1.1 times or more and a specific gravity of 0.8 or less, wherein one surface side and the other surface side of the sheet have different foaming states. Inhomogeneous foam sheet. 2. The expansion ratio of the heterogeneous foam sheet is
It is 1.1 to 40 times, and the foam cell diameter ratio (B / A) of the one surface side B and the other surface side A is 1.2 to 250 times, and the heterogeneous foaming according to claim 1. Sheet. 3. The thermoplastic resin according to claim 1, wherein the thermoplastic resin is a polyolefin or a composition thereof.
The heterogeneous foamed sheet described. 4. The heterogeneous foamed sheet according to claim 1, wherein an inert gas is used as the foaming agent. 5. A non-homogeneous foam comprising: a means for supplying a thermoplastic resin sheet having foaming ability; a means for heating the sheet to form a non-homogeneous foam sheet; and a means for winding the foam sheet. How to make a sheet. 6. A container using the heterogeneous foamed sheet according to claim 1.