JP2001287262A - Non-crosslinked polypropylene resin foamed sheet for molding and non-crosslinked polypropylene resin multilayered foamed sheet for molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sagging properties at the time of thermal molding and mold reproduciblity. SOLUTION: In a non-crosslinked polypropylene resin foamed sheet 1, the shape of cells 2 satisfy formulae 0.3<=A/B<=0.7 and 0.3<=A/C <=0.7 [wherein, A is an average cell size in a thickness direction; B is an average cell size in an extrusion (MD) direction; and C is an average cell size in a lateral (TD) direction]. A non-crosslinked polypropylene resin foamed multilayered foamed sheet is obtained by providing a polypropylene resin layer on at least the single surface of the sheet 1 and the shrinkage factor (at the time of heating at 190 deg.C for one min) thereof is 25-60% in the extrusion direction and 5-30% in the lateral direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-crosslinked polypropylene resin foam sheet for molding and a non-crosslinked polypropylene resin multilayer foam sheet for molding having improved sag during thermoforming.

[0002]

2. Description of the Related Art Foamed polypropylene resin sheets have been widely used for thermoforming for producing various containers and trays. As a method for producing a polypropylene resin foam sheet, there is an extrusion foaming method in which a polypropylene resin is melt-kneaded with a foaming agent in an extruder, and a foamable melt-kneaded product is extruded from a die attached to the extruder tip and foamed. Are known.

[0003] The present applicant has previously made a laminated foam sheet in which a stretched film is laminated on at least one side of a propylene-based resin foam sheet, thereby making it possible to utilize a conventional molding apparatus without improving production facilities. We have proposed a propylene-based resin foam sheet for molding that prevents corrugation (undulation phenomenon due to thermal expansion) during molding, eliminates uneven heating and bridges, and enables to obtain molded articles with excellent physical properties and appearance. (Japanese Patent Laid-Open No. 8-318602)
issue).

Further, in the foamed propylene-based resin sheet, the density, thickness and closed cell ratio are specified, and the foamed sheet is made to have a specific shape, thereby improving the physical properties such as the rigidity of the foamed sheet. It has been proposed that a molded article having excellent moldability, appearance of the foam sheet itself, and appearance of the obtained molded article can be obtained (JP-A-10-1304).
No. 12).

[0005]

The former laminated foam sheet described above has a problem that the large sagging of the foam sheet during thermoforming is improved, but the resulting molded article has a problem in mold reproducibility. Also, the latter foam sheet has room for improvement, for example, the foam sheet easily sags during thermoforming. This sagging can easily cause defects such as wrinkles and overlap between sheets called bridges in the thermoformed product, and in some cases, the foamed sheet may come into contact with the heater, scorch, shrink, or open a hole. Cause.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is intended to provide a molded non-crosslinked polypropylene resin foam sheet having improved mold reproducibility during thermoforming and a sagging property of a foam sheet, and a mold for molding. An object is to provide a non-crosslinked polypropylene resin multilayer foam sheet.

[0007]

Means for Solving the Problems The present inventors heat-stretch a foamed sheet, and set a specific cell diameter and a shrinkage ratio in a foaming sheet extrusion direction and a width direction when heated under a specific atmosphere to a specific value. By doing so, mold reproducibility during heat molding,
It has been found that the sagging property of the foam sheet is improved.

That is, the present invention provides an apparent density of 90 to 4
It is a non-crosslinked polypropylene resin foam sheet having a thickness of 0.5 g / L, a thickness of 0.5 to 2.5 mm, and a cell shape satisfying the following formulas (1) and (2).
Shrinkage in the extrusion direction of the foamed sheet when heated for 25 minutes
収縮 60%, and the shrinkage ratio in the foam sheet width direction is 5-30.
% Of a non-crosslinked polypropylene resin foam sheet for molding.

[0009]

(3) 0.3 ≦ A / B ≦ 0.7 (1) 0.3 ≦ A / C ≦ 0.7 (2) [where A is the thickness of the foam sheet] Average bubble diameter in the direction,
B is the average cell diameter in the foam sheet extrusion direction (MD direction), C
Is the average cell diameter in the foam sheet width direction (TD direction),
The unit is mm]

[0010] The present invention also provides an apparent density of 90 to 400.
g / L, thickness of less than 0.5 to 2.0 mm, multi-layer having a foamed non-crosslinked polypropylene resin sheet satisfying the following formulas (3) and (4) and having a polypropylene resin layer on at least one surface. The shrinkage rate in the extrusion direction of the multilayer foam sheet when heated for 1 minute in an atmosphere of 190 ° C. is 25 to 60%, and the shrinkage rate in the width direction of the multilayer foam sheet is 5 to 30%. The present invention relates to a non-crosslinked polypropylene resin multilayer foam sheet for molding.

[0011]

(4) 0.3 ≦ A / B ≦ 0.7 (3) 0.3 ≦ A / C ≦ 0.7 (4) [where A is the thickness of the foam sheet] Average bubble diameter in the direction,
B is the average cell diameter in the foam sheet extrusion direction (MD direction), C
Is the average cell diameter in the foam sheet width direction (TD direction), and the unit is mm.]

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram based on a microscope enlarged photograph showing a cross-sectional view of the polypropylene resin foam sheet of the present invention, and FIG. 2 is a schematic diagram illustrating the cell shape of the polypropylene resin foam sheet. FIG. 1A is a cross-sectional view in the thickness direction along an extrusion direction (hereinafter, referred to as an MD direction) of a foamed polypropylene resin sheet (hereinafter, sometimes simply referred to as a “foamed sheet”) of the present invention, and FIG. The thickness direction sectional drawing along the width direction (henceforth TD direction) of the polypropylene resin foam sheet of this invention is each represented.

In the figures, 1 is a foamed sheet of the polypropylene resin of the present invention, and 2 is a cell. Also, a (a1, a2,
a3... an) are the diameters of the cells 2 in the thickness direction of the foam sheet, b (b1, b2, b3... bn) are the diameters of the cells 2 in the foam sheet MD direction, and c (c1, c2, c2). c3 ...
* Cn) represents the diameter of each of the bubbles 2 in the foam sheet TD direction. The extrusion direction (MD) in the foam sheet 1
"Direction" means the direction in which the resin is extruded when the foamed sheet 1 is manufactured using an extruder. The TD direction is a width direction with respect to the extrusion direction. The thickness direction, MD direction, and TD direction of the foam sheet are orthogonal to each other.

The foamed polypropylene resin sheet 1 of the present invention has an average cell diameter a in the thickness direction [(a1,
a2, a3... an) / n] with A
[(B1, b2, b3,...)
[Bn) / n] is replaced with B, and the average of the bubble diameter c in the TD direction is [(c1, c2, c3... Cn) / n].
(Where A, B, and C are average values of arbitrary 20 or more bubbles (n ≧ 20), and the unit is mm). Has a bubble shape that satisfies both the conditions of the following equations (1) and (2).

[0015]

(5) 0.3 ≦ A / B ≦ 0.7 (1) 0.3 ≦ A / C ≦ 0.7 (2)

The foamed sheet and the multilayered foamed sheet satisfying the above formulas (1) and (2) are excellent in rigidity and have little sag of the sheet.

In the present invention, in each of the bubbles 2, it is necessary that 0.3 ≦ [(diameter in the thickness direction of the foamed sheet 1) / (diameter in the MD direction of the foamed sheet 1)] ≦ 0.7. And 0.3 ≦ [(diameter of foam sheet 1 in thickness direction) / (diameter of foam sheet 1 in TD direction)] ≦ 0.7
Need not be. That is, for example, 0.3 ≦
a1 / b1 ≦ 0.7 or 0.3 ≦ a1 / c1 ≦
That is, it need not be 0.7.

In the present invention, the preferred ranges of A / B and A / C are 0.3 ≦ A / B ≦ 0.6 and 0.3 ≦ A from the viewpoint of the balance between rigidity and sag. / C ≦
0.6, and a more preferred range is 0.4 ≦ A / B ≦
0.6, 0.4 ≦ A / C ≦ 0.6.

In the present invention, the average cell diameter in the thickness direction is 100 to 300 μm, and the average cell diameter is 100 to 2
50 μm is preferred.

In the present invention, the value of [((diameter of foam sheet 1 in thickness direction) / (diameter of foam sheet 1 in MD direction)]] of all cells is 0.3 or more. 0.7
The value of [(diameter of foam sheet 1 in thickness direction) / (diameter of foam sheet 1 in TD direction)] of all cells is not less than 0.3. 0.7
Neither is it. That is, 0.3 ≦
[(A1 / b1) + (a2 / b2) + (a3 / b3) +
... + (An / bn)] / n ≦ 0.7 and 0.3 ≦ [(a1 / c1) + (a2 / c2) + (a3
/ C3) +... + (An / cn)] / n ≦ 0.7.

Incidentally, a1, a2, a3,...
an, b1, b2, b3, ..., bn, c1, c
, Cn (n is 20 or more)
As shown in FIG. 2, a maximum tangent interval of tangents to bubbles in the thickness direction, the MD direction, or the TD direction is adopted. The diameter of each of the bubbles 2 in the thickness direction, the MD direction, or the TD direction is, for example, a microscope enlarged photograph of a cross section in the thickness direction along the MD direction of the foam sheet 1 and a cross section in the thickness direction along the TD direction of the foam sheet 1. Can be obtained from the obtained photograph.

The foamed sheet of the present invention has a thickness of 0.5-2.
5 mm. If the thickness is less than 0.5 mm, the resulting molded article may have low rigidity and poor heat insulating properties. On the other hand, if it exceeds 2.5 mm, uneven heating may occur during molding. In addition, there is a possibility that a good molded product cannot be obtained, for example, when the molded products are piled up. In particular, the thickness of the foam sheet is preferably 0.5 mm or more and less than 2.0 mm for the above reason. In the case of a non-crosslinked polypropylene resin multilayer foam sheet for molding in which a polypropylene resin layer is laminated on at least one side of a foam sheet (hereinafter, sometimes simply referred to as a “multilayer foam sheet”), the thickness is 0.5 mm or more. The same phenomenon as described above may occur in a foamed sheet having a thickness of less than 0 mm, and a good molded product cannot be obtained.

The apparent density of the foam sheet of the present invention is 90
４００400 g / L. If it is less than 90 g / L, there is a possibility that rigidity as a container may not be obtained.
If it exceeds L, the heat insulating property and economic efficiency may be deteriorated, which is not preferable. Preferably, it is 150 to 400 g / L to obtain a foamed sheet having a good balance of rigidity and cushioning property and good secondary workability such as cushioning property and moldability suitable for use as a foamed sheet for thermoforming. it can.

The foamed sheet of the present invention has a shrinkage ratio in the extrusion direction (MD direction) of the foamed sheet of 25 to 60% when heated in an atmosphere of 190 ° C., preferably 30 to 60%.
55%, shrinkage rate in the foam sheet width direction (TD direction) is 5
30%, preferably 10-25%. In the present invention, when the shrinkage rate in the foam sheet extrusion direction is less than 25% or when the shrinkage rate in the foam sheet width direction is less than 5%, the mold reproducibility and sagging property during thermoforming are improved. No, and each shrinkage rate is 60% or 30%
When the shrinkage ratio is more than 1.2, the stretching ratio becomes 1.2 times or more, the foam sheet is excessively stretched, the internal bubbles are broken, and there is a possibility that sufficient rigidity to withstand use as a foam sheet may not be obtained. is there.

In the present invention, the measurement of the shrinkage rate is performed by using "Perfect Oven PH" manufactured by Tabai Espec Corporation.
200 ". Measurement is 100mm × TD in MD direction
The heat shrinkage in the MD and TD directions when the foamed sheet cut to a size of 100 mm in the direction is left for 1 minute in an oven set at an ambient temperature of 190 ° C. is determined. At this time, the foamed sheet is sprayed with talc on a flat metal plate in an oven, and left horizontally on it. As the heat shrinkage, a value calculated by the following equation is adopted, where the dimension before the measurement is 100 mm and the dimension after the heat shrink is a (mm).

[0026]

(6) Heat shrinkage (%) = {(100−a) / 100} × 100 (5)

A non-crosslinked polypropylene resin is used as the base resin of the foamed sheet of the present invention. Examples of the polypropylene resin include a propylene homopolymer and a copolymer of propylene and another olefin. Other olefins copolymerizable with propylene include ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-
Α-olefins having 4 to 10 carbon atoms such as 1-butene, 3-methyl-1-hexene and 1-heptene are exemplified. The above copolymer may be a random copolymer or a block copolymer, and may be not only a binary copolymer but also a ternary copolymer. These polypropylene resins may be used alone or in combination of two or more.

The term "non-crosslinked" as used in the present invention means that a foamed sheet is used as a sample, about 1 g of the sample is put in 100 g of xylene, boiled for 8 hours, quickly filtered through a 100-mesh wire mesh, and then left on the wire mesh. Boiled xylene insolubles
After drying at 0 ° C. for 24 hours, the weight: G (g) is measured, and as determined by the following equation, it means that the proportion of the insoluble component after drying is 0 to 10% by weight. 5% by weight
g, more preferably 0 to 2% by weight. It is preferable that the ratio of the insoluble component is lower, since the recyclability and cost reduction are more excellent.

[0029]

(7) Ratio of insoluble components after drying (% by weight) = [G (g) / sample weight (g)] × 100 (6)

When a copolymer of propylene and another olefin is used as the base resin, the olefin in the copolymer is preferably contained in a proportion of 25% by weight or less, particularly preferably 15% by weight or less. The preferred lower limit of the olefin content in the copolymer is 1% by weight.

The polypropylene resin used in the present invention may have a) a branching index of less than 1 and a remarkable strain hardening elongation viscosity as described in JP-A-7-53797, or b) z-average molecular weight (Mz) of 1.0
× 10 ⁶ or more, or the ratio (Mz / Mw) of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) is 3.0 or more, and the equilibrium compliance J ₀ is 1.2 × 10 ⁻³ m ^Two
/ N or more, recovery of shear strain per unit stress Sr
A) or b) above, wherein / S is 5 m ² / N or more per second.
The normally solid, high molecular weight, gel-free propylene polymer material can also be used.

Further, as the polypropylene resin used in the present invention, there are also those which exhibit physical properties such as c) a drawdown property of 60 m / min or less as described in JP-A-10-130412. No. A more preferred drawdown property is 30 m / min or less, particularly preferably 15 m / min or less.

Extrusion foaming is performed using a resin having a drawdown property of more than 60 m / min, and the apparent density is 90 to 400.
When trying to obtain a foamed sheet of g / L, the resulting foamed sheet has a large number of surface irregularities, so that the appearance is poor as a product, and the smoothness of the foamed sheet is impaired, which is a factor inhibiting secondary workability and moldability. As a result, the commercial value is reduced.
This is because it is difficult to reduce the apparent density to 400 g / L or less even if the amount of the foaming agent is increased in a polypropylene resin or the like having a downloadability exceeding 60 m / min. TD of the sheet on the mandrel because the strength of the bubble film cannot withstand the tension of
Tears in the direction. If the temperature of the resin is lowered to prevent this, crystallization of the resin starts, and the surface of the foamed sheet becomes uneven in the shape of scale.

Further, the polypropylene resin used in the present invention is d) an angular frequency given by the dynamic viscoelasticity measurement of the resin at 230 ° C .: ω (as described in JP-A-10-130412). rad / se
c) and the storage elastic modulus: G ′ (10 μN / cm ² ), in the range of ω = 0.1 to 1, the following approximate expression (7)
Holds, and each of α and β in the equation is 0
<Α ≦ 1.00, preferably 0.70 <α ≦ 1.00
And 3.65 ≦ β ≦ 4.5, preferably 3.85 ≦
It may exhibit a dynamic viscoelastic behavior in which β ≦ 4.35.

[0035]

(8) logG ′ = α · logω + β (7) (where G ′ is the storage modulus and ω is the angular frequency)

Even if the resin whose angular frequency and storage modulus have the relationship shown in the above equation (7), the resin in which α in equation (7) is 0 or less cannot be confirmed, and α is 0.7 If α is less than 0, it becomes difficult to form bubbles during foaming as α approaches 0. On the other hand, when the resin has an α exceeding 1.00, only a foamed sheet having a low expansion ratio can be obtained. Β is 3.6
When the resin is less than 5, the foamed sheet obtained has a low closed cell ratio and only a foamed sheet having a low expansion ratio can be obtained.
Is more than 4.50, the resulting foamed sheet has too high a melt tension, so that surface irregularities are not eliminated,
Even if the foaming temperature is increased, it is difficult to maintain the bubbles, resulting in a poor surface condition.

Further, in the present invention, e) a compound containing a radical polymerizable monomer, a radical polymerization initiator and an additive is melted at a temperature at which the polyolefin resin melts and the radical polymerization initiator decomposes. It may be a polypropylene resin modified by kneading, or f) a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer and a radical polymerization initiator.

In the present invention, a) those having a branching index of less than 1 and a remarkable strain hardening elongation viscosity as described above, and b) those having a specific molecular weight distribution and a specific equilibrium compliance J ₀ or shear strain recovery. , C) a specific drawdown property, or d) a specific relationship between angular frequency and storage modulus obtained by dynamic viscoelasticity measurements in the linear region, e)
A polypropylene resin showing at least one of these physical properties, such as a modified polypropylene resin obtained by radical polymerization or f) a modified polypropylene resin obtained by polymerizing isoprene, is suitably used.

In the present invention, not only the above-mentioned polypropylene resin can be used alone, but also other resins can be mixed and used if necessary. Examples of the resin that can be used as a mixture include, for example, polypropylene resins other than those described above, or high-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, and ethylene-butene copolymer. , Ethylene-based resin such as ethylene-maleic acid copolymer, butene-based resin,
Examples thereof include polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride-vinyl acetate copolymer, and styrene resins. When such another resin is mixed, the amount of the resin to be mixed is limited to 40% by weight of the total amount of the polymer after mixing.

As the foaming agent used for producing the foamed sheet of the present invention, a foaming agent which has been used conventionally, such as an inorganic foaming agent, a volatile foaming agent, or a decomposable foaming agent, is used.
Examples of the inorganic foaming agent include carbon dioxide, air, and nitrogen.

Examples of the volatile foaming agent include propane, n-butane, i-butane, a mixture of n-butane and i-butane, chain aliphatic hydrocarbons such as pentane and hexane, and cyclic hydrocarbons such as cyclobutane and cyclopentane. Aliphatic hydrocarbons, trichlorofluoromethane, dichlorofluoromethane,
1,1-dichloro-1,1,1,2-tetrafluoroethane, 1,1, -difluoro-1-chloroethane, 1,
Examples thereof include halogenated hydrocarbons such as 1,1,2-tetrafluoroethane, 1,1-difluoroethane, methyl chloride, ethyl chloride, and methylene chloride.

Examples of the decomposition type foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like. These foaming agents can be mixed and used as desired.

The amount of the foaming agent used varies depending on the type of the foaming agent, the desired expansion ratio, and the like. However, in order to finally obtain a foamed sheet having an apparent density of 90 to 400 g / L, the amount of the foaming agent per 1 kg of the resin used is required. 0.05 to 0.
About 5 mol, about 0.03 to 0.45 mol of an inorganic foaming agent, and about 0.03 to 0.45 mol of a decomposition type foaming agent are used.

In obtaining the foamed sheet of the present invention, a foam regulator can be added to the melt-kneaded product of the resin and the foaming agent, if necessary. Talc,
Examples include inorganic powders such as silica, acidic salts of polyvalent carboxylic acids, and reaction mixtures of polyvalent carboxylic acids with sodium carbonate or sodium bicarbonate. It is preferable to add about 0.2 parts by weight or less of these foam adjusters per 100 parts by weight of the resin. If necessary, additives such as a heat stabilizer, an ultraviolet ray inhibitor, and a coloring agent can be further added.

In addition, the resin may contain an inorganic filler up to 5% by weight based on the total weight. Examples of the inorganic filler include talc, silica, calcium carbonate, clay, zeolite, alumina, barium sulfate, and magnesium hydroxide. These have an average particle size of 1
It is preferably from 70 to 70 μm. When such an inorganic filler is contained, the resulting foamed sheet has improved heat resistance and can reduce calorie burned during incineration.

Next, a method for producing the foamed sheet of the present invention will be described. FIG. 3 is a conceptual diagram showing an example of the production process of the foam sheet of the present invention. The foamed sheet of the present invention is, for example, a melt-kneaded polypropylene-based resin and a foaming agent in an extruder, and then, as shown in FIG. The foam is extruded and foamed from the die lip to obtain a tubular foam, and then the tubular foam is cut open to form a sheet, and then easily heated and stretched as shown in FIG. Alternatively, the sheet-like foam obtained by cutting and opening the tubular foam may be once wound into a roll, and the sheet-like foam may be drawn from the roll and stretched by heating.

The step of cutting and opening the above-mentioned tubular foam to obtain a sheet-like foam and subjecting it to heat stretching will be described with reference to FIG. The tubular foam 13 was obtained by extrusion foaming from the die lip 12 of the annular die 11 attached to the tip of the extruder 10, and then the inner surface of the tubular foam was disposed inside the tubular foam 13. While cooling from the inside of the mandrel 14, the tubular foam 1
3 is cooled by means such as blowing cooling air onto the outer surface thereof, passed through a mandrel 14, cut into a sheet-like foam 16 with a rotary blade 15, and then fed into the rolls 20, 20 and a heating furnace. After passing through the rollers 18 and 18 in sequence and being stretched by stretching rolls 19 and 19, they are wound into a roll (not shown).

In the above, the diameter of the mandrel 14 can be appropriately selected according to the width of the foam sheet to be obtained. The length of the mandrel 14 is arbitrary as long as it is long enough to cool and cut the tubular foam 13.
The extrusion speed (line speed) varies somewhat depending on the length and diameter of the mandrel 14, but is generally about 3 to 20 mm /
Minutes are preferred. The cooling temperature of the tubular foam 13 varies depending on the extrusion speed, but is preferably about 5 to 50C. The cooling means is not limited to the above-mentioned method, but is optional. The thickness of the tubular foam 13 is preferably 80 to 95% of the target thickness. Within this range, the production is easy and the thickness of the finally obtained foamed sheet can be easily adjusted to a preferable range of 0.5 to 2.5 mm.

The stretching rolls 19, 19 and the feed roll 20,
Between 20, the sheet-like foam 16 is heated by, for example, being passed through a heating furnace 18. During this heating, the bubbles inside the foam expand further, especially in the thickness direction, thereby increasing the thickness. Since the sheet-like foam was passed through the mandrel as described above and was obtained by the slitting method, the difference in orientation between the front and back surfaces of the sheet-like foam due to the difference in cooling, and the thickness of the tubular foam , Distortion remains due to the difference between the inner circumference and the outer circumference, and the sheet-like foam has a tendency to bend. In order to completely eliminate the problems caused by these distortions, make the temperature difference between the heating of the front side and the back side of the sheet-like foam, such as by increasing the heating of the sheet-like foam side corresponding to the outer peripheral surface of the tubular foam. Is preferred.

The stretching rolls 19, 19 and the feed roll 20,
The feed speed of the stretching rolls 19 is different from the feed speed of the feed rolls 20 by 20.
The sheet-like foam 16 is stretched between the stretching rolls 19, 19 and the feed rolls 20, 5 to 1.2 times faster (stretching ratio: 1.05 to 1.2 times). It is assumed that each roll does not slip between the roll and the sheet-like foam. At this time, the film may be slightly stretched in the width direction so as to prevent the end portion in the width direction from waving. At the time of stretching, since the sheet-like foam 16 is heated, it is thermally stretched. Since the sheet-like foam is manufactured using a method in which a tubular foam is cut open on a mandrel, the sheet-like foam has a wide width (a width of 10 mm).
(Ex. 00 mm or more) can be manufactured using the conventional apparatus, so that no equipment cost is required, and since there is no need to drastically change the extrusion molding conditions, the manufacturing cost does not increase and the cost is low. Provided and advantageous.

The ambient temperature of the heating furnace 18 is usually 150 to
230 ° C. The heating means is not limited to radiant heating using a heating furnace or the like as described above, and various means such as contact heating using a heat roll or the like can be used.

In the present invention, a multi-layer foamed sheet obtained by laminating a polyolefin resin layer on at least one surface of a foamed sheet can be produced by a method known per se.
A typical method is, for example, a method of manufacturing a foamed sheet in advance, and then laminating a polypropylene-based resin layer on the foamed sheet by supplying a molten resin of a polypropylene-based resin on a production line or a separate line, or foaming. A sheet is manufactured, a polypropylene resin film is introduced on a production line or another line, and bonded by a hot roll, or a method of bonding by supplying an adhesive from another extruder, or a method of co-extrusion to form a foam. A method of forming a polypropylene-based resin layer on at least one surface is exemplified. The method for obtaining a multilayer foamed sheet by the above-mentioned coextrusion method will be described in further detail. A method of obtaining a multi-layered foamed sheet, and then cutting out this to form a multi-layered foamed sheet. Above all, the method of manufacturing by a co-extrusion method is a preferable method because the steps are simpler and lower in cost than other methods, and the adhesive strength between the foamed sheet and the laminated resin layer is high. Among them, a method of co-extrusion using an annular die is preferable because a wide product (having a width of 1000 mm or more) can be easily obtained.

After obtaining the multilayer foam sheet by the above method,
The multilayer foamed sheet of the present invention is obtained by heating and stretching. Alternatively, a foamed sheet may be prepared in advance, and then heated and stretched, and then the above-described polypropylene-based resin may be laminated to form a multilayer foamed sheet.

The thickness of the polypropylene resin layer laminated on the foamed sheet is preferably 10 to 250 μm, and 20 to 250 μm.
200 μm is preferred in that the rigidity of the multilayer foam sheet is improved and the appearance of the surface is improved. The foam sheet and the multilayer foam sheet are obtained by the method as described above, and are wound into a roll.

The foamed sheet and the multilayer foamed sheet of the present invention can be formed by vacuum forming, pressure forming, free drawing forming, plug and ridge forming, plug and ridge forming, ridge forming, matched mold forming, straight forming,
By drape molding, reverse draw molding, air slip molding, plug assist molding, plug assist reverse draw molding, etc., or a method combining these,
A desired molded article can be formed.

[0056]

Next, the present invention will be described with reference to examples and comparative examples.

Examples 1-4 A tandem extruder was used to melt-knead a base resin, a foaming agent and a cell regulator in an extruder, and the melt-kneaded product and a polypropylene resin melt were attached to the extruder tip. Co-extruded foam from the die lip of the annular die having a special structure to obtain a tubular foam having a polypropylene-based resin layer laminated thereon. After cooling this tubular foam over a mandrel, it is cut open to form a sheet having a width of 1040 mm. Then, it was stretched to a predetermined stretching ratio by a heating stretching apparatus capable of sandwiching the sheet end to produce a multilayer foam sheet having a width of 1080 mm. In Example 1, a stretched foamed sheet was manufactured in the same manner except that the polypropylene resin was not laminated.

Comparative Examples 1-4 Foamed sheets were obtained in the same manner as in the above Examples, except that the heat stretching was not performed. However, in Comparative Example 4, the stretched film was thermally bonded to the foam sheet using a hot roll.

The details of the base resin, the foaming agent, and the type of the foam controlling agent used in the examples and comparative examples, the composition, and the heating and stretching conditions are as follows.・ Base resin: Propylene homopolymer (MI; 2.0 g)
/ 10 min, crystallization temperature; 131 ° C., melting point: 159 ° C., melt tension; 20 g, drawdown; 5 m / min) ・ Blowing agent: butane ・ Bubble regulator: monosodium citrate Also, the foaming agent and foam control The agents were mixed at the ratios shown in Table 1 below with respect to 100 parts by weight of the base resin.

[0060]

[Table 1]

The heating and stretching conditions are as follows. Sheet take-up speed: 5 to 7 m / min Heating furnace feed speed: Same as sheet take-up speed Stretching roll feed speed: 5 to 20% of heating furnace feed speed Roll interval between drawing rolls 19, 19: (sheet thickness ×
0.7) mm Distance between the stretching rolls 19, 19 and the feed rolls 20, 20: 2 to 6 m Heating means: heating furnace Length of heating furnace: 2.5 m Distance from heat source to sheet surface: 200 mm Heating furnace Immediately after sheet surface temperature: upper 140 ° C, lower 12
0 ° C

Next, the thickness of the obtained foamed sheet was determined.
The apparent density and shrinkage were measured, respectively, and the sagging property, moldability and mold reproducibility of the foam sheet during thermoforming were evaluated. The results are shown in Table 2. In addition, while observing each cut surface in the MD direction and the TD direction of the foamed sheet, the average cell diameter A in the thickness direction, the average cell diameter B in the MD direction, and the average cell diameter C in the TD direction at the center in the thickness direction of each cross section. , Respectively, and the ratio (A / B, A / C) to each of A, B and C was determined. (However, A, B, and C were determined excluding the bubbles that were open cells.) The values are shown in Table 2. In Table 2, the polypropylene-based resin is referred to as “PP resin”.

Thickness of foamed sheet, multilayer foamed sheet and polypropylene-based resin layer: The thickness was measured from any 20 points of the cross section in the thickness direction of the foamed sheet or multilayer foamed sheet, and the average value was adopted. In the measurement of the thickness, each thickness was obtained by converting the magnification using a micrograph.

The apparent density of the foam sheet in the foam sheet and the multilayer foam sheet: The sample weight (g) cut out from the foam sheet or the multilayer foam sheet into a size of 20 cm × 20 cm × (thickness (cm) of the foam sheet). It was measured in advance and determined by dividing the weight (g) of the foamed sheet by a value obtained by converting the volume (cm ³ ) of the sample foamed sheet into units (g / L). In the case of a multilayer foam sheet, the weight of the foam sheet was the weight excluding the weight of the polypropylene resin layer. As the weight of the polypropylene-based resin layer, the weight calculated from the volume determined using the thickness determined from the micrograph and the density of the resin was employed.

The value of A / B was determined by obtaining an enlarged microscopic photograph of a cross-sectional view in the thickness direction along the MD direction of the foamed sheet. Based on the obtained photograph, all the air bubbles (n ≧ 20) were determined in the above-mentioned directions. The diameter was measured with a caliper as shown in FIG. 2, and the values of a and b for each bubble were obtained for each bubble. The obtained a
1, a2, a3,..., An, and b1, b2
, bn, the arithmetic average values of A and B were obtained, and the value of A / B was obtained.

The value of A / C was determined by obtaining an enlarged microscopic photograph of a cross-section in the thickness direction along the TD direction of the foamed sheet. As shown in FIG. 2, the diameter of a was measured with a caliper, and the values of a and c of each bubble were obtained for each bubble. The obtained a1, a2, a3,..., An, and c1, c
, Cn, the arithmetic average values A and C were obtained, and the value of A / C was obtained. A, B, C above
Is a width (T) that is five times the thickness (T) in each microscope enlarged photograph.
× 5) All the bubbles present in the region were measured.

As described above, the measurement of the shrinkage rate was performed using “Perfect Oven P” manufactured by Tabai Espec Corporation.
H20 "was used. Measurement is 100mm × TD in MD direction
The heat shrinkage in the MD and TD directions when the foamed sheet cut to a size of 100 mm in the direction was allowed to stand for 1 minute in an oven set at an ambient temperature of 190 ° C. was determined from the above equation (5).

The sagging property of the foam sheet during thermoforming is as follows:
Single-shot molding machine (manufactured by Sanwa Kogyo Co., Ltd., “PLAVAC-F
E36HP type ”), 600mm in MD direction x 3 in TD direction
A foam sheet cut to a size of 00 mm was attached, heated under molding conditions under which the sheet surface temperature immediately before molding was 175 ° C., the position of the sheet immediately after was measured, and the difference from the position of the sheet before heating was adopted. .

Regarding the moldability, the mold for pasta tray was attached by plug-assist vacuum molding in the above single-shot molding machine, and the sheet was heated so that the sheet surface temperature immediately before molding was 175 ° C. Each dimension of the tray container has an inner diameter of the opening surface of 200 mm and a depth of 35 mm. The evaluation criteria for moldability and mold reproducibility were as follows.

Evaluation criteria for moldability: The molded articles obtained by thermoforming were visually evaluated for wrinkles and bridges.・: No wrinkles or bridges are formed in the molded product. ×: Wrinkles and bridges occurred in molded products. As shown in Table 2, the foamed sheet of the present invention has a large shrinkage, particularly in the MD direction, as compared with the conventional foamed sheet, has improved sagging during molding, and is excellent in moldability.

Evaluation criteria for mold reproducibility: It was visually evaluated whether or not the molded product obtained by thermoforming had the same shape as the mold.・ · The shape of the corner of the molded product is the same as the mold shape. ×: The shape of the mold, especially the shape of the corner of the molded product, is not found.

[0072]

[Table 2]

[0073]

As described above, the apparent density is 90 to 40.
0 g / L, a thickness of 0.5 to 2.5 mm, a bubble shape satisfying the above formulas (1) and (2), and a foam sheet extrusion direction when heated for 1 minute in an atmosphere at 190 ° C. The shrinkage rate in the foam sheet width direction is 25 to 60%,
A non-crosslinked polypropylene resin foam sheet for molding of 30%, an apparent density of 90 to 400 g / L, and a thickness of 0.1%;
A multilayer foamed sheet having a polypropylene resin layer laminated on at least one side of a non-crosslinked polypropylene resin foamed sheet having a diameter of less than 5 to 2.0 mm and having a cell shape satisfying the above formulas (3) and (4); The shrinkage rate in the multilayer foam sheet extrusion direction and the multilayer foam sheet width direction when heated for 1 minute in an atmosphere are 25 to 60% and 5 to 30%, respectively.
The non-crosslinked polypropylene resin multilayer foam sheet for molding is improved in sagging during thermoforming compared to conventional foam sheets, wrinkles and bridges are less likely to occur during molding, and the foam sheet contacts the heater. As a result, no deterioration such as scorching, shrinkage, or perforation occurs, and the thermoformability is excellent. Further, when thermoformed, the mold reproducibility is excellent.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of a non-crosslinked polypropylene resin foam sheet of the present invention.

FIG. 2 is a diagram illustrating an average cell diameter of a foam sheet according to the present invention.

FIG. 3 is a conceptual diagram illustrating an example of a production process of a non-crosslinked polypropylene resin foam sheet of the present invention.

[Explanation of symbols]

1: Non-crosslinked polypropylene resin foam sheet for molding 2: Foam 10: Extruder 11: Annular die 12: Die lip 13: Tubular foam 14: Mandrel 15: Rotating blade 16: Sheet foam 17: Mandrel support 18 : Heating furnace 19: stretching roll 20: feed roll a in Fig. 1: bubble diameter in thickness direction, b: bubble diameter in MD direction, c: bubble diameter in TD direction

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) B29L 7:00 B29L 7:00 9:00 9:00 (72) Inventor Yoshiaki Momose Tsuruta-cho, Utsunomiya City, Tochigi Prefecture 3282-5 F-term (reference) 4F100 AK07A AK07B AK07C BA03 BA06 BA10B BA10C DJ01A EH17A GB16 JA13A JA20A JK01 JK11 JL01 YY00A 4F210 AA11 AB02 AG01 AG03 AG20 AM32 AR12 AR15 QA03 QC05 QD13 QDQ1

Claims (3)

[Claims] An apparent density of 90 to 400 g / L and a thickness of 0.1 g / L.
A non-crosslinked polypropylene resin foam sheet having a size of 5 to 2.5 mm and having a cell shape satisfying the following formulas (1) and (2), and is heated in a 190 ° C. atmosphere for 1 minute in the foam sheet extrusion direction. A non-crosslinked polypropylene resin foam sheet for molding, wherein a shrinkage rate is 25 to 60% and a shrinkage rate in a foam sheet width direction is 5 to 30%. (1) 0.3 ≦ A / B ≦ 0.7 (1) 0.3 ≦ A / C ≦ 0.7 (2) [where A is the thickness of the foam sheet] Average bubble diameter in the direction,
B is the average cell diameter in the foam sheet extrusion direction (MD direction), C
Is the average cell diameter in the foam sheet width direction (TD direction),
The unit is mm] 2. The non-crosslinked polypropylene resin foam sheet for molding according to claim 1, wherein the thickness is 0.5 mm or more and less than 2.0 mm. 3. An apparent density of 90 to 400 g / L and a thickness of 0.1 g / L.
A multilayer foamed sheet having a polypropylene resin layer on at least one side of a non-crosslinked polypropylene resin foam sheet having a cell shape satisfying the following formulas (3) and (4) and having a foam shape satisfying the following formulas (3) and (4). The shrinkage ratio in the extrusion direction of the multilayer foam sheet when heated for 1 minute in an atmosphere is 2
5 to 60%, and the shrinkage ratio in the width direction of the multilayer foam sheet is 5
A non-crosslinked polypropylene resin multilayer foam sheet for molding, characterized in that the content is from 30% to 30%. (2) 0.3 ≦ A / B ≦ 0.7 (3) 0.3 ≦ A / C ≦ 0.7 (4) [where A is the thickness of the foam sheet] Average bubble diameter in the direction,
B is the average cell diameter in the foam sheet extrusion direction (MD direction), C
Is the average cell diameter in the foam sheet width direction (TD direction),
The unit is mm]