JP3351967B2 - Non-crosslinked polypropylene resin foam sheet for thermoforming - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-crosslinked polypropylene resin foam sheet for thermoforming .

[0002]

2. Description of the Related Art Hitherto, foams of high density to low density using a specific polypropylene resin have been obtained. Among them, density 0.0
A foamed sheet of 9 g / cm ³ or more is mainly used as a foamed sheet for molding, and such a foamed sheet for molding is required to have printability and a beautiful appearance of a molded article obtained.

[0003] However, the known foamed polypropylene resin sheet has a drawback that the foam is somewhat coarser and has a poor appearance in comparison with a foamed sheet made of a polystyrene resin or the like, which occupies most of the foamed sheet for molding. was there. Moreover, polypropylene-based resin has a lower melt viscosity at the time of foaming than polystyrene-based resin and the like. Although the bubble diameter in the thickness direction becomes small, the bubble shape becomes short and flat elliptical in the thickness direction of the sheet, resulting in a problem that the sheet has insufficient rigidity.

Further, in obtaining a foamed sheet using a polypropylene-based resin, the foamed sheet is extruded and foamed into a cylindrical shape from an annular die, passed through a cylindrical side surface of a cylindrical cooling device called a mandrel, and then subjected to a cylindrical process. Is generally manufactured by cutting a foamed sheet into a sheet shape.At this time, when trying to reduce the bubbles of the foamed sheet, the foaming speed increases and the resin extruded from the annular die rapidly decreases. Foaming occurs three-dimensionally, resulting in a cylindrical foam having a diameter larger than the die diameter. Therefore, due to the difference between the diameter of the die and the diameter of the cylindrical foam, a large number of wrinkles flowing in the foam extrusion direction as if the cylindrical foam were squeezed by the dice as in a gather skirt were formed in the cylindrical foam. There is also a problem that the wrinkles are generated on the peripheral surface (this wrinkle is referred to as a corrugate), which causes unevenness in the thickness of the sheet and non-uniformity of bubbles in the width direction of the sheet. Also, the pillar of the secondary breaker that supports the annular die of the extruder is located in the resin flow path, and the resin is blocked in the extruder by this secondary breaker. There is also a problem that unevenness occurs (this thickness unevenness is referred to as a breaker mark), and this has also been a factor that hinders the uniformity of the thickness of the foam sheet in the width direction. When a foamed sheet having non-uniform properties in the width direction of the sheet is thermoformed by such a corrugate or a breaker mark, a thin portion is particularly stretched and formed, so that the obtained molded product has an appearance and rigidity. Was lacking.

By the way, in order to solve the breaker mark as described above, the present applicant has disclosed Japanese Patent Application Laid-Open No. Hei 5-33855 / 1993.
No. 2, a method was adopted in which a throttle was provided in a part of the die downstream of the secondary breaker. However, such a restriction in the die raises the pressure of the die part, so that it is necessary to limit the discharge amount of the resin from the extruder to a certain range. For this reason, in order to obtain a foamed sheet using a polypropylene-based resin, it is necessary to keep the discharge amount of the resin from the extruder within a certain range, and because measures for corrugation are insufficient, the bubbles are reduced. It is difficult, and the polypropylene-based resin foam sheet obtained under such restrictions is still not sufficiently satisfactory in printability and appearance aesthetics as compared with a widely used molding foam sheet, There was also room for improvement in productivity.

[0006] The inventors of the present invention have conducted intensive studies and have obtained a polypropylene resin foam sheet having fine bubbles and excellent appearance and rigidity by employing a specific extrusion condition and a die having a specific structure. In particular, in such a polypropylene-based resin foam sheet, the density, thickness, and closed cell rate are specified, and the physical properties such as the rigidity of the foam sheet are improved by setting the cell shape to a specific shape. Then, it was found that the moldability and the appearance of the foamed sheet itself, and further the appearance of the obtained molded product were also better than conventionally known polypropylene-based resin foamed sheets. It was completed.

[0007]

Means for Solving the Problems That is, the present invention relates to a density
0.09-0.4g / cm^Three , Thickness 0.5-8mm, Germany
Non-crosslinked polypropylene-based tree for molding with a bubble ratio of 70% or more
It is a fat foam sheet, and the cell shape is the following formula (1)-(3)
Non-crosslinked polypropylene for thermoforming characterized by satisfying
Len resinExtrusionFoam sheet. 0.35 <A / B <0.65 (1) 0.35 <A / C <0.65 (2) 0.10 <A ≦ 0.4 (3) [ However, each of A, B, and C in the formula is the thickness of the foam sheet.
Direction, extrusion direction (MD direction), width direction (TD direction)
Average cell diameter in mm. ]
 Polypropylene tree with drawdown performance of 60m / min or less
Non-crosslinked polypropylene for thermoforming as described above, comprising a fat
Extruded resin foam sheet. 30m / min drawdown
The thermoforming described above comprising the following polypropylene resin
Non-crosslinked polypropylene resin extruded foam sheet for forming.  
Within 25% of the total thickness of the sheet from the surface of the foam sheet
Regarding bubbles existing in the surface layer, the thickness of the foam sheet
Direction, extrusion direction (MD direction), width direction (TD direction)
The average bubble diameters are A1, B1, and C1, respectively.
More than 25% of the total thickness of the foam sheet from the surface of the sheet
Regarding the bubbles existing in the inner layer, the thickness of the foam sheet
Direction, extrusion direction (MD direction), width direction (TD direction)
When the average bubble diameters are A2, B2, and C2, respectively.
The above that satisfies the following equations (4) to (6)No
RekaniNon-crosslinked polypropylene resin for thermoforming as describedExtrusion
Foam sheet. 0.8 <A1 / A2 ≦ 1.2 (4) 0.8 <B1 / B2 ≦ 1.2 (5) 0.8 <C1 / C2 ≦ 1.2 (6) )  Measure thickness along the width direction (TD direction) of the foam sheet
When set, one piece in the width direction (TD direction)
Partitioned from the side edge to the other side edge at 100mm intervals
The maximum thickness (T_m ) And minimum thickness
(T_l ) And the ratio (T_l / T_m ) Is 0.90 or more
RecordTo any ofNon-crosslinked polypropylene for thermoforming as described
Len resinExtrusionFoam sheet.  Thick on at least one side
Inorganic filler content of 200 μm or less 5 to 70% by weight
The above resin sheet is laminatedTo any ofRecord
Non-crosslinked polypropylene resin for thermoformingExtrusionFoam sea
G. Is the gist.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 (a) is a cross-section in the thickness direction along the extrusion direction (hereinafter referred to as the MD direction) of the non-crosslinked polypropylene resin foam sheet for molding according to the present invention, and FIG. It is a schematic diagram based on a microscope enlarged photograph which expresses the cross section in the thickness direction along the width direction (henceforth TD direction) of a resin foam sheet, and is a figure for explaining the cell shape of the foam sheet of the present invention.

[0010] In the figures, 1 indicates the foam sheet of the present invention, and 2 indicates air bubbles. A (a ₁ , a ₂ , a ₃ ,..., A _n ) are the diameters of the cells 2 in the thickness direction of the foam sheet 1, b (b ₁ ,
b ₂ , b ₃ ,..., b _n ) are the diameters of the bubbles 2 in the MD direction of the foam sheet 1 and c (c ₁ , c ₂ , c ₃ ,.
_n ) respectively represents the diameter of the foam 2 in the TD direction of the foam sheet 1.

In the present invention, the MD direction refers to a direction in which the resin is extruded when the foamed sheet 1 is obtained using an extruder, and the TD direction refers to a direction wider than the extrusion direction. Further, the thickness direction of the foam sheet 1, the MD direction,
The TD directions are orthogonal to each other.

In the foam sheet 1 of the present invention, the average of a is replaced by A, and the average of b is [(a ₁ + a ₂ + a ₃ +... + A _n ) / n], and the average of b is [(b ₁ + b ₂ + b). ₃ ＋ ・ ・ ・
+ B _n ) / n] is replaced by B, and the average of c [(c
₁ + c ₂ + c ₃ +... + C _n ) / n] is replaced with C (where the average bubble diameters A, B, and C are the averages for any bubble of 50 or more (n ≧ 50)). Value
The unit of A, B, and C is mm), and A, B, and C have bubble shapes that satisfy the following expressions (1) to (3). 0.35 <A / B <0.65 (1) 0.35 <A / C <0.65 (2) 0.10 <A ≦ 0.40 (3)

At this time, if at least one of A / B and A / C is 0.35 or less, the rigidity of the foamed sheet 1 becomes insufficient, and at least one of A / B and A / C is obtained. For a foamed sheet having one side of 0.65 or more, a foam having a cross section close to a circle can be expected to have ideal and balanced mechanical properties as a bubble,
When it is desired to obtain a foamed sheet having an average cell diameter A within the range of the above formula (3) and a cell cross-sectional shape close to a circle, by adjusting the foaming temperature of the resin and the amount of the cell adjuster added, corrugation and thickness unevenness may occur. Occurs, resulting in poor moldability.
When A is 0.1 or less, it is difficult to maintain the closed cell ratio of the foamed sheet 1 at 70% or more, the secondary foaming property of the foamed sheet is reduced, and the moldability is deteriorated. Mechanical properties such as When A exceeds 0.4, there is a problem that the bubbles are coarse and the appearance of the foamed sheet 1 is deteriorated. In the present invention, each preferable range of A / B and A / C is 0.45 <A / B <0.5.
5, 0.45 <A / C <0.55. A preferred range of A is 0.15 <A <0.3.

In the present invention, each of the bubbles 2 does not necessarily have to satisfy the above conditional expression. That is, for example, 0.35 <a ₁ / b ₁ <0.65, 0.
35 <a ₁ / c ₁ <0.65, 0.10 <a ₁ ≦ 0.4
It need not be zero. Further, in the present invention, the average value of all the bubbles of the value of [(diameter in the thickness direction of foam sheet 1) / (diameter in the MD direction of foam sheet 1)] for each bubble 2 is 0.35. Is not larger than 0.65 and smaller than 0.65, and for each bubble 2, [(foam sheet 1
Diameter in the thickness direction) / (diameter in the TD direction of the foamed sheet 1)]
Of the average value of all the bubbles is larger than 0.35 and 0.1.
Nor is it smaller than 65. That is, 0.35
<[(A ₁ / b ₁ ) + (a ₂ / b ₂ ) + (a ₃ / b ₃ )
+ ... + (a _n / b _n )] / n <0.65,
Also, 0.35 <[(a ₁ / c ₁ ) + (a ₂ / c ₂ ) +
(A ₃ / c ₃ ) +... + (A _n / c _n )] / n <0.
Not 65.

Note that a ₁ , a ₂ , a _3, ...
a _n , b ₁ , b ₂ , b ₃ ... b _n , c ₁ , c ₂ ,
The value of c ₃ ····· c _n (n is 50 or more) adopts the maximum tangent interval of the tangent to each bubble in the thickness direction, MD direction or TD direction as shown in FIG. I do.
The diameter of each of the bubbles 2 in the thickness direction, the MD direction, and the TD direction is, for example, the microscope of the thickness direction cross section of the foam sheet 1 along the MD direction and the thickness direction cross section of the foam sheet 1 along the TD direction. An enlarged photograph can be obtained and it can be determined based on the obtained photograph.

Further, in the present invention, as shown in FIG. 1, the total thickness T of the sheet 1 is measured from both surfaces S, S of the foam sheet 1.
The portion having a thickness of 0.25T within 25% of the surface layer portion Ts,
Ts, when a portion having a thickness of 0.5 T exceeding 25% of the total thickness T of the sheet 1 from both surfaces S, S of the foam sheet 1 is defined as the inner layer portion Ti, the surface layer portions Ts, Ts and the inner layer The average cell diameter is determined separately for the bubbles present in each of the portions Ti in the same manner as described above, and the average cell diameter in the thickness direction, MD direction, and TD direction of the foamed sheet 1 is determined for the bubbles existing in the surface layer portion Ts. To A1, B respectively
A1, B1, C1, A2 when the average cell diameter in the thickness direction, MD direction, and TD direction of the foamed sheet 1 is A2, B2, and C2, respectively, for bubbles existing in the inner layer portion Ti. , B2 and C2 preferably have a bubble shape satisfying the following equations (4) to (6). 0.8 <A1 / A2 ≦ 1.2 (4) 0.8 <B1 / B2 ≦ 1.2 (5) 0.8 <C1 / C2 ≦ 1.2 (6) )

In the present invention, the bubble 2 in FIG.
_{As shown in FIG. 0} , air bubbles are present on both sides S of the foam sheet 1, at positions 25% of the total thickness T of the foam sheet 1, that is, over the surface layer portion Ts and the inner layer portion Ti. If
If the position is the portion exceeding 50% in a surface portion Ts side of the cross-sectional area of the bubble 2 _0, the bubbles and those present in the surface layer portion Ts, the portion exceeding 50% inner layer portion of the cross-sectional area of the bubble 2 ₀ T
If it is located on the i side, it is assumed that this bubble exists in the inner layer portion Ti.

In the foamed sheet 1 having the cell shape satisfying the above formulas (4) to (6), there is little variation in the cell shape between the surface layer portion Ts and the inner layer portion Ti of the foamed sheet 1 and the thickness direction of the foamed sheet 1 The air bubbles become more uniform and the moldability becomes more excellent. In addition, if the cells are uniform in the thickness direction of the foam sheet 1, the rigidity of the foam sheet 1 is further improved. On the other hand, those not satisfying the above equations (4) to (6) indicate that the bubbles existing in the surface layer portion Ts are laterally flatter than the bubbles existing in the inner layer portion Ti, or irregularly. There are many variations in the bubble shape between the surface layer portion Ts and the inner layer portion Ti such that many small bubbles are mixed.
The uniformity of bubbles in the thickness direction of the foamed sheet 1 is impaired, and such a foamed sheet is likely to be burnt on the surface of the sheet during thermoforming. In the present invention, A1 / A
2, B1 / B2 and C1 / C2 are 0.82 <
A1 / A2 ≦ 1.10, 0.82 <B1 / B2 ≦ 1.1
0, 0.82 <C1 / C2 ≦ 1.10, more preferably 0.84 <A1 / A2 ≦
1.05, 0.84 <B1 / B2 ≦ 1.05, 0.84
<C1 / C2 ≦ 1.05.

The foamed polypropylene resin sheet 1 of the present invention has a density of 0.09 to 0.4 g / cm ³ , a thickness of 0.5 to 8 mm, and a closed cell ratio of 70% or more. In the present invention, if the density of the foam sheet 1 is less than 0.09 g / cm ³ , sufficient rigidity cannot be obtained because of poor shape retention and easy bending. On the other hand, if the density exceeds 0.4 g / cm ³ , the rigidity is too high, resulting in poor cushioning properties and poor heat insulation properties.

In particular, in the present invention, the density of the foam sheet 1 is preferably 0.11 to 0.3 g / cm ³ .
Within this range, a balance between rigidity and cushioning can be achieved,
A foam sheet having both sufficient rigidity suitable for use as a foam sheet and good secondary workability such as appropriate cushioning property and moldability can be obtained.

In the present invention, if the thickness of the foam sheet 1 is less than 0.5 mm, it is not preferable in terms of heat insulation, and if it exceeds 8 mm, it is not preferable in terms of moldability. If the closed cell ratio is less than 70%, sufficient sheet rigidity cannot be obtained. In the present invention, the foam sheet 1 preferably has a thickness of 1.5 to 3.0 mm and a closed cell rate of 75% or more.

The foam sheet 1 of the present invention has a specific density, thickness and closed cell ratio, and the cell shape satisfies the above-mentioned conditions. Since it has a shape, it not only has excellent moldability, but also has high rigidity and excellent cushioning properties, and also has excellent appearance, compressive strength, and bending strength.

When the thickness of the foamed sheet 1 of the present invention is measured along the TD direction, it is sectioned from one end to the other end at an interval of 100 mm as shown in FIG. The foamed sheet 1 is divided into the respective ranges α, β, γ,... In the TD direction (however, as shown in FIG.
A portion η less than 00 mm is neglected), the maximum thickness (T _m ) of the foamed sheet 1 and the minimum thickness (T _m ) of the foamed sheet 1 in each of the above ranges α, β, γ,. _It is preferable that the thickness unevenness is small so that the ratio (T ₁ / T _m ) with respect to _l ) is 0.90 or more, preferably 0.92 or more.

Each of the ranges α, β,
The ratio (T ₁ / T _m ) between the maximum thickness (T _m ) of the foam sheet 1 and the minimum thickness (T _l ) of the foam sheet 1 at γ,.
Is less than 0.90, the thin part of the sheet is weaker than the thick part of the sheet during thermoforming, so it is locally stretched, and in extreme cases there is a hole in the molded product. Inconveniences such as breakage and cracking are likely to occur, resulting in poor moldability.

As the base resin of the foam sheet 1 of the present invention, a non-crosslinked polypropylene resin is used. Examples of the polypropylene resin include a propylene homopolymer or a copolymer of propylene and another olefin. Other olefins copolymerizable with propylene include ethylene, 1-butene, isobutylene, 1-pentene, and 3-olefin.
Α-olefins having 4 to 10 carbon atoms, such as methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, and 3-methyl-1-hexene.
The 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 can be used alone or in combination of two or more.

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

In the present invention, the term "non-crosslinked" refers to a peroxide,
It also includes micro-crosslinking due to radiation and has a gel fraction of 10
Less than 5% by weight, preferably less than 5% by weight, particularly preferably substantially 0% by weight. Further, the gel fraction is obtained by performing an extraction operation in boiling xylene for 15 hours, and is obtained as a 100-percentage of the resin extraction remaining amount relative to the weight before resin extraction. The closer the gel fraction is to 0, the less foaming of the resin occurs in the obtained foamed sheet during extrusion foaming from the annular die, leading to an improved appearance.

Further, the polypropylene resin includes a) 1 as described in JP-A-7-53797.
Has a branching index of less than and a significant strain hardening elongation viscosity, or b) has a z-average molecular weight of 1.0 × 10 ⁶ or more, a z-average molecular weight (Mz) and a weight-average molecular weight (Mw)
(Mz / Mw) is not less than 3.0 and the equilibrium compliance J ₀ is not less than 1.2 × 10 ⁻⁴ cm ² / dyn, or the recovery of shear strain per unit stress Sr / S is 5 per second. × is 10 ^-5 cm ² / dyn or more, usually above a) or b) can also be used propylene polymer material without a high molecular weight of the gel is a solid.

Further, as the polypropylene resin used in the present invention, c) those exhibiting physical properties such that the drawdown property is 60 m / min or less can be mentioned. A more preferred drawdown property is 30 m / min or less, particularly preferably 15 m / min or less.

The drawdown property means that a molten propylene resin heated to 230 ° C. is melted with a nozzle 21 of a melt tension tester using a device shown in FIG.
m, length 8 mm) at a piston pressing speed of 10 mm / min, extruding in a string form in the direction of the arrow in the drawing, and then pulling the string-like material in a tension detection pulley 22 located below the nozzle, and a feed roll located above it After passing through 23, 24 and 24, the winding speed of the winding roll is gradually increased while winding by the winding roll 25 to cut the string, and the string at the time of this cutting is cut. It refers to the winding speed. Incidentally, in the apparatus shown, the distance L ₁ between the nozzle 21 and the pulley 22 is 250 mm, the diameter R of the pulley 22 is 45 mm, the distance L ₂ between the pulleys 22 and the feed roll 23 is 90 mm, the feed rolls 23 and 24 of the distance between L ₃ is 45 mm, the angle θ relative to the tangent of the horizontal plane extending on the upper surface of the feed roll 23 from the contact surface of the feed roll 24, 24 is 40 °.

The propylene-based resin having a drawdown property of 60 m / min or less is a normal crystalline linear propylene-based resin (usually, a weight average molecular weight of 100,000 or more) and further contains an atactic component and / or Resins containing components that are isotactic but not crystallized (hereinafter referred to as
This resin is referred to as “normal propylene-based resin” and a low-temperature decomposition type peroxide (decomposition temperature: room temperature to 120 ° C.)
About 5 to 50 mmol per 1 kg of resin, and heated to about 120 ° C., preferably about 70 to 105 ° C. to cause a reaction (usually for 30 to 120 minutes). It can be obtained by a method in which an atactic or / and non-crystallized isotactic component is bonded to a chain as a branched chain.

The low-temperature decomposable peroxides include di (s-butyl) peroxydicarbonate and bis (2-
Ethoxy) peroxydicarbonate, dicyclohexylperoxydicarbonate, di-n-propylperoxydicarbonate, di-n-butylperoxydicarbonate, diisopropylperoxydicarbonate,
Examples include t-butyl peroxy neodecanoate, t-amyl peroxy neodecanoate, t-butyl peroxy pivalate, and the like.

The drawdown property of the propylene resin can be adjusted by the number and length of long chain branches. The propylene resin having a drawdown property of 60 m / min or less obtained as described above is mainly It is considered to have a branched structure having a long-chain branch at the end of the main chain. Generally speaking, as the number of long-chain branches increases and as the length of the branches increases, the value showing the drawdown property tends to decrease.
Therefore, in order to obtain a desired drawdown polypropylene-based resin, it is necessary to set reaction conditions in consideration of these points. In the case of a resin having no long-chain branch, or having a branch that is too short, or a normal propylene-based resin, the drawdown property exceeds 60 m / min.

Extrusion foaming is performed using a resin having a drawdown property of more than 60 m / min to obtain a resin having a density of 0.09 to 0.4.
In order to obtain a sheet-like foam of g / cm ³ , the resulting foamed sheet has a large number of surface irregularities, so that the appearance as a product is poor, and the smoothness of the foamed sheet is impaired. It is a cause of obstruction, and it has no commercial value. This means that the drawdown property is 60
In the case of a propylene-based resin or the like exceeding m / min, it is difficult to reduce the density to 0.45 g / cm ³ or less even if the amount of the foaming agent is increased. Since the strength of the bubble film cannot withstand the tension, the sheet is torn in the TD direction on the mandrel.
If the temperature of the resin is lowered in order to prevent this, crystallization of the resin starts, and the foam sheet surface becomes scale-like irregularities.

Alternatively, the propylene-based resin used in the present invention comprises: d) an angular frequency: ω (rad / sec.) Obtained by measuring the dynamic viscoelasticity of the resin at 230 ° C .; and a storage modulus: G ′ (dyn / cm ² ), the relationship shown in the following approximate expression (7) holds in the range of ω = 0.1 to 1, and α and β in the expression are each 0 <α ≦ 1.00, preferably Is 0.70 ≦ α ≦ 1.00 and 3.65 ≦ β ≦ 4.
It may exhibit a dynamic viscoelastic behavior of 50, preferably 3.85 ≦ β ≦ 4.35. logG ′ = α · logω + β (7)

In the above equation (1), α is expressed by a coordinate having logG ′ on the vertical axis and logω on the horizontal axis, and logω = −1.
And the value of logG ′ at that time and the value of logω ′ and the value of logG ′ at that time are plotted, and are the slopes of a straight line represented by equation (7). Β is expressed by equation (7). The intercept where the indicated straight line intersects the vertical axis of logω = 0. FIG. 5 shows that in the above equation (7), α is 1.
A straight line with β being 3.65 at 00 (indicated by the symbol a),
α represents 1.00 and β represents 4.50 (represented by a symbol b).

In FIG. 5, when the value of log ω is large, the dynamic viscoelastic behavior represented by log G ′ represents the elastic modulus of the resin in a state where the properties of the elastic body are strong, and the bubble formation immediately after extrusion foaming during the foaming process. It is considered to correspond to the behavior of the resin at the time. On the other hand, when the value of logω is small, the dynamic viscoelastic behavior represented by logG ′ represents the elastic modulus of the resin in a strong state of the viscous material, and is used to maintain the bubbles after the bubble formation during the foaming step. It is considered to correspond to the behavior of the resin.
In the foaming of the polypropylene resin, an angular frequency: ω is used in order to maintain the foam after foaming in the extrusion foaming.
Storage modulus when the value changes from 1 to 0.1 (rad / sec.):
By adopting and specifying the value of G ′ and the numerical value of the rate of change, an excellent foamed sheet 1 can be obtained.

The angular frequency and the storage modulus are expressed by the above equation (7).
Even if the resin has the relationship shown in
Is 0 or less, and when α is less than 0.7,
As α approaches 0, bubble formation during foaming becomes more difficult. On the other hand, in the case of a resin in which α exceeds 1.00, only a foam having a low expansion ratio can be obtained. When the β is less than 3.65, the obtained foam has a low closed cell rate,
In the case of a resin having only a low expansion ratio and a resin having β of more than 4.50, the resulting foam has too high a melt tension to eliminate surface irregularities. It is also difficult to maintain air bubbles, resulting in poor surface condition.

It is considered that the behavior of resin formation and maintenance represented by the storage elastic modulus: G 'can be more reliably grasped by the loss elastic modulus: G''measured simultaneously with G'. That is, even if the values of G ′ are the same, the behavior of bubble formation / maintenance in the foaming process may be different from each other. The properties of the resin can be considered as a combination of the properties of the elastic body (corresponding to G ′) and the properties of the viscous body (corresponding to G ″). For this reason, it is considered that the difference in the behavior of bubble formation / maintenance even though G ′ is the same resin as described above is due to the difference in the loss elastic modulus: G ″, and G ″ / G As a result of focusing on the value of tan δ represented by ', the angular frequency: ω is 0.1 to 1 (rad / se
c.), the value of tan δ is 1.25 to 3.
When it is 50, more preferably between 1.30 and 2.70, the appearance, expansion ratio, and closed cell rate can be more easily controlled, and an excellent extruded foam sheet can be produced more easily.

The dynamic viscoelasticity of the resin is measured in a linear range by a dynamic viscoelasticity tester (for example, a dynamic viscoelasticity tester manufactured by Rheometrics Far East Co., Ltd .: SR200 type) by a stress control method. Measured. For example, measurements in the linear region have a stress of 5000 dyn / cm ² .
In the measurement by the stress control method, when the polypropylene resin is measured up to a maximum frequency of 100 rad / sec.
If the stress is 2000 to 50000 dyn / cm ² , the value falls within the linear region. Needless to say, the linear region is a region in which the strain rate and the stress are in a proportional relationship, that is, a range in which the measured value of the viscoelasticity such as the storage elastic modulus is not affected by the stress. In the dynamic viscoelasticity test, a measurement sample resin plate having a thickness of about 2 mm was sandwiched between parallel plates having a diameter of 25 mm, and allowed to stand for about 10 minutes until the temperature reached 230 ° C. And the parallel plate is improved, and the overflowed resin is further scraped off, and then the angular frequency: ω is changed, and the storage elastic modulus: G ′ and the loss elastic modulus: G ″ corresponding to the angular frequency are measured.

The selection of the measurement temperature of the dynamic viscoelasticity of 230 ° C. is accompanied by a decrease in the temperature until the molten resin to be extruded and foamed is extruded from the extruder die at the foaming temperature and bubbles are formed and solidified. Viscoelastic body (polypropylene resin)
This is because when the change in the elastic modulus of the viscoelastic body is determined in correspondence with the change in the elastic modulus due to the decrease in the angular frequency, the temperature is such that the behavior of the change in the elastic modulus due to the decrease in the temperature of the viscoelastic body can be remarkably expressed.

The polypropylene resin having the above-mentioned specific relationship between the angular frequency, the storage elastic modulus, and the tan δ is, for example, a metallocene catalyst used as a polymerization catalyst when polymerizing the polypropylene resin, or a low molecular weight polymer. It can be suitably prepared by irradiating a linear polypropylene resin containing polypropylene with radiation.

In the present invention, a) those having a branching index of less than 1 and a remarkable strain hardening elongation viscosity as described above, b) those having a specific molecular weight distribution and specific equilibrium compliance or shear strain recovery, c) And / or d) a specific drawdown property, or d) a specific relationship between the angular frequency and the storage elastic modulus obtained by dynamic viscoelasticity measurement in the linear region. Polypropylene resin having the following physical properties is preferably used.

In the present invention, not only the above-mentioned propylene-based resin can be used alone, but also if necessary, another resin can be mixed and used. Examples of the resin used as a mixture include propylene resins other than those described above, or high-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-butene copolymer, and ethylene-anhydrous. Examples include ethylene resins such as maleic acid copolymers, butene resins, polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride-vinyl acetate copolymer, and styrene resins.

When other resins are mixed as described above, the amount of the resin to be mixed is limited to 40% by weight of the total weight of the polymer after mixing.

In the foam sheet 1 of the present invention, for example, after the above-mentioned polypropylene resin and a foaming agent are melt-kneaded in an extruder, the melt-kneaded product is attached to the tip of the extruder as shown in FIG. Further, it is easily manufactured by using an annular die having an annular lip, extruding and foaming from the lip of the die to obtain a cylindrical foam, and then cutting out the cylindrical foam to form a sheet. .

The step of obtaining a cylindrical foam will be described in more detail with reference to FIG. 6. An annular die 5 having an annular lip 4 is attached to the tip of an extruder 3 and extruded from the lip 4 of the die. Thus, a cylindrical foam body 6 as shown in FIG. 1 is obtained, and then the cylindrical foam body 6 is cooled from the inside of the foam body 6 by a mandrel 7 arranged inside the cylindrical foam body 6 and Then, cooling is performed by blowing cooling air onto the outer surface of the foam 6, and thereafter, the cylindrical foam 6 is cut into a sheet by the rotary blade 8 to form a foam sheet. In the figure, reference numeral 9 denotes a mandrel support.

In the above description, the diameter of the mandrel 7 can be appropriately selected according to the width of the foam sheet 1 to be obtained.
The length of the mandrel 7 is arbitrary as long as it is long enough to cool the cylindrical foam 6. Extrusion speed (line speed)
Although it depends on the discharge amount, the target thickness of the foam sheet 1, and the like, it is preferably about 3 to 15 m / min. The cooling temperature of the cylindrical foam 6 varies depending on the extrusion speed and the like.
~ 80 ° C is preferred. The cooling means is not limited to the above-mentioned method, but is optional.

In obtaining the foamed sheet 1 of the present invention, in order to make the cell shape specified in the present invention,
For example, at the stage of manufacturing the cylindrical foam 6, a die having specific extrusion conditions and a specific structure may be employed.

The specific extrusion conditions include, for example, the temperature of an annular die attached to the extruder tip is accurately controlled by oil temperature control, the temperature of the resin is reduced to a limit temperature at which crystallization does not occur, and a high viscosity is maintained. This is to pass through an annular die as it is.

A die having a specific structure means that, for example, when the resin passes through a secondary breaker that supports a shaft of an annular die, the flow of the resin is not interrupted, and a state close to a piston flow can be maintained. A die is formed using a secondary breaker having a shape, and the inside of the die is rapidly compressed at the tip of the lip.
The structure is set to be less than cm ² .

By producing the cylindrical foam 6 under the specific conditions as described above, a foam sheet having air bubbles substantially in the specific shape according to the present invention can be obtained.

In obtaining the foam sheet 1 of the present invention as described above, as the foaming agent, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent, or the like can be 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 include halogenated hydrocarbons such as 1,1,2-tetrafluoroethane, 1,1-difluoroethane, methyl chloride, ethyl chloride, and methylene chloride.

Further, examples of the decomposition type foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like. These foaming agents can be used by being appropriately mixed.

The amount of the foaming agent varies depending on the type of the foaming agent, the desired expansion ratio, and the like.
The standard of the amount of the foaming agent used to obtain a foamed sheet of 9 to 0.4 g / cm ³ is about 0.05 to 0.5 mol of a volatile foaming agent per 1 kg of resin, and 0.03 to 0.5 mol of an inorganic foaming agent.
About 0.45 mol, 0.03 to 0.45
It is about a mole.

In obtaining the foamed sheet 1 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, as a foam control agent
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 the foam control agent in an amount of about 0.2 part by weight or less per 100 parts by weight of the resin (except when a large amount of an inorganic filler is contained in the resin, as described later). Also, if necessary, further a heat stabilizer,
Additives such as an ultraviolet absorber, an antioxidant, and a coloring agent can also be added.

Further, the resin is previously added to the resin in an amount of 40% by weight based on the total weight.
The inorganic filler may be contained as much as possible. As the inorganic filler, for example, talc, silica, calcium carbonate,
Examples include clay, zeolite, alumina, barium sulfate, and magnesium hydroxide. Their average particle size is 1 to
It is preferably 70 μm. When a large amount of such an inorganic filler is contained, the resulting foamed sheet has improved heat resistance and can reduce calorie burned during incineration.

In the present invention, printability and surface hardness are improved.
In order to further improve rigidity such as bending strength, a resin sheet containing an inorganic filler can be laminated on at least one surface of the foam sheet 1. By laminating such resin sheets, the rigidity of the foamed sheet can be further increased, the lip strength of the molded article can be increased, and the shape retention and productivity can be improved.

The resin sheet contains the inorganic filler in an amount of 5 to 70%, preferably 15 to 50% by weight based on the total weight, and the inorganic filler greatly contributes to improving the rigidity of the foam sheet. In particular, a remarkable effect is observed when a deep drawn container is formed using the foamed sheet 1 of the present invention. When the content of the inorganic filler is less than 5% by weight, the effect of improving rigidity is poor,
If it exceeds 70% by weight, moldability is adversely affected. As the inorganic filler, talc, silica, calcium carbonate,
Examples include clay, zeolite, alumina, barium sulfate, and glass.

When such a resin sheet is laminated on the foam sheet 1, the thickness of the resin sheet is 200 μm or less, preferably 180 μm or less. As a result, sufficient rigidity can be obtained. Further, since the resin sheet contains an inorganic filler, heat resistance is improved. When the thickness of the resin sheet exceeds 200 μm, the heating temperature at the time of molding must be increased, and not only the moldability is impaired, but also the density of the molded article may increase due to the heat compression at the time of molding, and In addition, when storing the obtained molded products, the height when the molded products are stacked (stack height) also increases.

As the base resin of the resin sheet, a polyethylene resin, a polypropylene resin, a polyester resin, an acrylic resin, a polyvinyl chloride resin, a polycarbonate resin or the like can be used. In particular, a polypropylene-based resin is preferable in terms of recyclability, adhesiveness, heat resistance, oil resistance, rigidity, and the like, and is more preferably the same as the resin constituting the foam sheet 1. That is, the foam sheet 1
If the base resin is a propylene-ethylene block copolymer, the base resin of the resin sheet is also preferably a propylene-ethylene block copolymer.

In laminating the resin sheet on the foam sheet 1, as the laminating method, a general method such as an extrusion laminating method, a thermal laminating method, or a laminating method using an adhesive such as hot melt can be adopted.

The foamed sheet 1 of the present invention can be formed by vacuum forming, air pressure forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air drawing, and the like. Slip molding, plug-assist molding, plug-assist reverse draw molding, or the like, or a combination thereof can be used to form a desired molded product.

[0065]

Next, the present invention will be described in more detail with reference to specific examples.

Examples 1 to 5 After the base resin, the foaming agent and the foam control agent were melted and kneaded in the extruder, the shapes of the secondary breaker and the annular die to be attached to the tip of the extruder were appropriately selected, and the pressure in the die portion was adjusted. 8
The melt-kneaded product was extruded from a circular lip onto a mandrel at a discharge rate shown in Table 1 at 0 kg / cm ³ or less to obtain a cylindrical foam. Next, the cylindrical foam was passed through the mandrel as it was and cut into a sheet to obtain a foam sheet. At this time, an oil temperature controller is provided in the die section to adjust the temperature of the melt-kneaded product to 160 to 170.
It was precisely controlled to a specific temperature in the range of ° C. still,
Details are as follows (common to Examples 1 to 5).

[Base resin]-Ethylene-propylene block copolymer MI: 2.0 g / 10 min. Crystallization temperature: 126 ° C Melting point: 158 ° C Draw Down property: 5 m / min Melt tension: 23 g Dynamic viscoelasticity: α = 0.8, β = 4.2 tan δ = 2.1 to 1.5 (Ω = 0.1-1 rad / sec) Equilibrium compliance: 1.5 × 10 ⁻⁴ cm / dyn (210 ° C., 100 N / m ² constant, time: 1-300 sec) Shear strain recovery ··· 6.2 × 10 ⁻⁵ cm / dyn (210 ° C., shear rate 1 / sec) Weight average molecular weight (Mw) ··· 3.7 × 10 ⁵ (* 1) Z average molecular weight ( Mz)... 1.2 × 10 ⁶ (* 1) * 1: 13 using Waters 150CV GPC
Column Water using 5 ° C trichlorobenzene as solvent
s μ-Styrogel HT (10 ³ , 10 ⁴ , 1
0 ⁵ , 10 ⁶ Å), solution concentration 0.2% by weight, flow rate 1 ml
/ Min. [Blowing agent]-Butane [Bubble regulator]-Monosodium citrate [Extruder]-Tandem extruder [Blending and temperature conditions] The blending amount of butane and monosodium citrate with respect to 100 parts by weight of the base resin is determined. The results are shown in Table 1. Table 1 also shows the temperature conditions of the primary breaker part during extrusion foaming.

COMPARATIVE EXAMPLE 1 Using the same base resin, foaming agent and cell regulator as in the example,
Extrusion foaming was carried out under the mixing and temperature conditions for 100 parts by weight of the base resin shown in Table 1. In the extruder, an ordinary secondary breaker was used, and a squeeze was attached to a part of the die. Then, at a discharge rate of 30 kg / h, a cylindrical foam obtained by extrusion foaming was cut open to obtain a foam sheet. In Comparative Example 1, the oil temperature of the die was not adjusted.

COMPARATIVE EXAMPLES 2 AND 3 Using the same base resin, foaming agent and cell regulator as in the Examples,
Extrusion foaming was carried out under the mixing and temperature conditions for 100 parts by weight of the base resin shown in Table 1. In the extruder, a normal secondary breaker and a die are used, and the discharge amount is set to 8 as usual.
The test was performed at 0 kg / h. In Comparative Examples 2 and 3, the oil temperature of the die was not adjusted.

[0070]

[Table 1]

With respect to the foamed sheets obtained in Examples 1 to 5 and Comparative Examples 1 to 3, the thickness, density, cell shape, cell uniformity, closed cell ratio, thickness unevenness were measured, and the moldability and The appearance of the foam sheet was evaluated. Table 2 shows the results. The schematic diagram shown in FIG. 1 is based on a microscope enlarged photograph of a cross section of the foam sheet obtained in Example 2, and FIG. 10 is a microscope enlarged photograph of a cross section of the foam sheet obtained in Comparative Example 3. FIG. Note that FIG.
(A) is a cross-section in the thickness direction along the MD direction, FIG. 10 (b) is a cross-section in the thickness direction along the TD direction, and in the figure, 2 ′ represents bubbles.

[0072]

[Table 2]

The cell shape was determined by observing each of the cross sections in the MD and TD directions, and determining 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 of each of the cross sections. The measurement was performed to determine the ratio of A to each of B and C (A / B, A / C). When each cross section was observed, the cells of the foamed sheets of Examples 1 to 5 satisfied the requirements of the present invention in their shapes. The cells of the foamed sheets of Comparative Examples 1 to 3 had a flat shape that was short, long and long, and did not satisfy the requirements of the present invention.

Further, [average bubble diameter A in thickness direction] / [M
The value of the average cell diameter B in the D direction exists in a width five times the thickness of the foamed sheet based on the microscopic enlarged photograph of the cross section in the thickness direction along the MD direction of the foam sheet. As shown in FIG. 2, the values of a and b of each bubble were measured with calipers for each bubble as shown in FIG. 2 for all the bubbles (n ≧ 50), and the a ₁ , a ₂ , a ₃ ,
··· a _n and b ₁ , b ₂ , b ₃ ,... B _n are arithmetically averaged, and the average cell diameter A in the thickness direction and the average cell diameter B in the MD direction are obtained from the magnification of the enlarged photograph of the microscope. Then, the ratio A / B was determined.

The value of [average cell diameter A in the thickness direction] / [average cell diameter C in the TD direction] is a value obtained by obtaining an enlarged microscopic photograph of a cross section in the thickness direction of the foamed sheet along the TD direction. Based on the above, the values of a and c of each bubble are measured for each bubble in the same manner as described above, and a ₁ , a
₂ , a ₃ ,... _An , and c ₁ , c ₂ , c ₃ ,.
· The c _n and the arithmetic mean, and the thickness direction average cell diameter A than the magnification of the microscope magnified photograph, the average cell diameter C in the TD direction and, to obtain the A / C is the ratio.

Regarding the uniformity of the cells, the M
In each of the direction along the direction D and the direction along the TD direction, a microscopic enlarged photograph of a cross section in the thickness direction is obtained, and based on the obtained photograph, a position 25% of the thickness from both surfaces of the foam is obtained. A line is drawn to separate the bubbles in the surface layer and the inner layer. Then, the air bubbles existing in the surface layer portion and the air bubbles existing in the inner layer portion are separately separately averaged in the sheet thickness direction of the air bubbles existing in the surface layer portion in the same manner as described above. Average cell diameter C1 in the TD direction, average cell diameter A in the thickness direction of the sheet of each cell present in the inner layer portion
2. The average cell diameter B2 in the MD direction and the average cell diameter C2 in the TD direction are obtained by arithmetic averaging, and A1 / A2, B1 / B2,
The value of C1 / C2 was calculated.

At the time of performing this measurement, all air bubbles having a width (T × 5) that is five times the thickness T shown in the enlarged photograph of the microscope (all air bubbles existing in the hatched portions in FIG. 7;
FIG. 7 shows a cross section in the thickness direction of the foam sheet, but illustration of bubbles is omitted). In addition, as for the bubble overlapping the line at the position of 25% of the total thickness of the foam sheet, if a portion exceeding 50% of the cross-sectional area of the bubble is located on the surface layer portion Ts side, the bubble exists in the surface layer portion Ts. and things, the portion exceeding 50% inner layer portion of the cross-sectional area of the bubble 2 ₀ T
If it is located on the i side, the measurement was performed assuming that this bubble exists in the inner layer portion Ti.

The closed cell rate of the foamed sheet was determined by the following equation (8) using an air-comparison hydrometer. Closed cell ratio (%) = [Vx−Va (ρf / ρs)] / [Va−Va (ρf / ρs)] (8) [Vx: actual volume of foam sheet sample (c)
m ³ ), Va: Apparent volume of foam sheet sample (c)
m ³ ), ρf: Apparent density (g /
cm ³ ), ρs: density of resin (g / cm ³ ). ]

Regarding the thickness unevenness, as shown in FIG.
Along the direction D from one end to the other end
The foamed sheet 1 is sectioned in the TD direction into ranges α, β, γ,... Sectioned every 00 mm (however, as shown in FIG. 3, a portion η less than 100 mm is ignored). The thickness was measured at a pitch of 5 mm over the range.
Then, the ratio (T ₁ / T _m ) between the minimum thickness (T _l ) and the maximum thickness (T _m ) was determined from the measured values. Table 2 shows the smallest value of T ₁ / T _m in each range as a representative value of thickness unevenness. That is, for example, T _l / T _m in the range α is α ₀ , T _l / T _m in the range β is β ₀ ,
T ₁ / T _m in the range γ is γ ₀ , α ₀ , β ₀ ,
the α ₀ smaller α ₀ is the best of the γ ₀ was the representative value.

Regarding the moldability, a multi-cavity molding test was continuously performed by plug-assist vacuum molding using a continuous molding machine. As shown in FIG. 8, the target tray-shaped container is a dish-shaped container 30 having storage portions 32 and 33 on both sides of a partition 31. In FIG. 8, each dimension of k to r is k: 175 mm, l: 112 mm, m: 63 mm,
n: 110 mm, o: 90 mm, p: 40 mm, q: 4
0 mm, r: 35 mm. The evaluation criteria for the moldability and the evaluation criteria for the appearance of the obtained molded article are as follows.
8A is a plan view of the molded product, and FIG. 8B is a side view of the molded product.

Evaluation criteria for moldability A: No streak cracks or surface burns due to poor thickness in all molded products.・ ········································································································································ · △ ・ ・ ・ Some of the molded products have slight stripe cracks and surface burns. × ・ ・ ・ ・ Streak cracks have occurred in many molded products.

Evaluation Criteria for Appearance A: The texture is fine, the bubbles are tight, and the gloss is high. ○ ・ ・ ・ ・ ・ ・ Texture is fine, but there are some wrinkles on the surface. Δ: Texture is slightly rough and the surface has some wrinkles. C: The texture was rough, the surface was wrinkled, and the surface was uneven in the width direction.

Example 1 and Comparative Example 2, and Example 2 and Comparative Example 3 having substantially the same density and thickness were compared, and the bending strength was measured. Table 3 shows the results. The bending strength of the foamed sheet was determined by cutting a test piece from each of the foamed sheets of the above Examples and Comparative Examples at a length of 25 mm and a width of 150 mm, and using a universal testing machine (Tensilon manufactured by Orientic Co., Ltd.). Distance 30mm, support base radius 2.5
mm and a head speed of 10 mm / min, JIS-K7203 in the MD and TD directions at n = 3, respectively.
The arithmetic mean value of the average value of the bending strength in the MD direction and the average value of the bending strength in the TD direction was defined as the bending strength of the foamed sheet.

[0084]

[Table 3]

As shown in Table 3, although the densities and thicknesses were substantially the same, Examples 1 and 2 exhibited bending strength approximately twice that of Comparative Examples 2 and 3, respectively.

Examples 5 to 8 and Comparative Examples 4 to 6 The sheet-like foams obtained in Examples 2 to 4 and Comparative Examples 1 to 3 were extruded with an inorganic filler-containing resin sheet having the structure shown in Table 4 by lamination. And a molded article was obtained using the laminated sheet. As a base resin of the inorganic filler-containing resin sheet, a 30% talc-containing PP-based master batch (KS3268-6, manufactured by JPO) was used.

[0087]

[Table 4]

The obtained molded product was excellent in both moldability and rigidity, though the thickness of the resin sheet containing the inorganic filler was as thin as less than 200 μm. The evaluation of the moldability was performed according to the same evaluation criteria as described above, by molding a tray-like container so that at least the surface of the resin sheet containing the inorganic filler became the inner surface.

In order to determine whether or not the molded product has practical strength, the lip strength was measured by the following method. The results are shown in Table 4.

Method of Measuring Lip Strength A test sample was prepared from a molded product 40 having the shape shown in FIGS. 9A and 9B by a single-shot molding machine, and the edge portion was formed as shown in FIG. 9B. (Indicated by oblique lines) was cut by 5 mm. Next, as shown in FIG. 9 (c), the sample was sandwiched between the load cell 41 and the support 42 with the cut edge portion up and down, and the distance between the load cell 41 and the support 42 became 150 mm. The compression strength at the time was measured as lip strength. In FIG. 9, each dimension of sw is:
s: 180 mm, t: 160 mm, u: 120 m, v:
30 mm: w: 170 mm. 9A is a cross-sectional view of the molded product, FIG. 9B is a plan view of the molded product, and FIG.
(C) is an explanatory view showing a method for measuring the lip strength.

[0091]

As described above, the non-crosslinked polypropylene resin foam sheet for thermoforming of the present invention has a density of 0.0
9 to 0.4 g / cm3, thickness 0.5 to 8 mm, closed cell ratio of 70% or more, and in the thickness direction of the foam sheet,
When the average bubble diameter in the extrusion direction (MD direction) and the width direction (TD direction) are A, B, and C, respectively, the bubble shape satisfies the following formulas (1) to (3), and is compared with the conventional shape. It is longer in the thickness direction and has a more spherical shape, so it is not only excellent in moldability, but also has high rigidity and excellent cushioning property, as well as compressive strength, bending Since it is excellent in strength, practical strength is not impaired even when the density is lowered, and the foamed sheet for thermoforming has sufficient rigidity required. In addition, the appearance is good because the bubbles are fine. 0.35 <A / B <0.65 (1) 0.35 <A / C <0.65 (2) 0.10 <A ≦ 0.4 (3)

In the present invention, in addition to the above conditions, the average cell diameter of the foam present in the surface layer portion in the thickness direction, extrusion direction (MD direction) and width direction (TD direction) of the foamed sheet is A1, B1, respectively. Assuming that the average cell diameter in the thickness direction, the extrusion direction (MD direction), and the width direction (TD direction) of the foam sheet is A2, B2, and C2, respectively, assuming that C1 is the cell present in the inner layer portion, the following (4) )
By specifying the cell shape so as to satisfy the expressions (6) to (6), there is little variation in the cell shape between the surface layer portion and the inner layer portion of the foam sheet, the cells are uniform in the thickness direction of the foam sheet, and the formability is improved. It will be excellent. If the cells are uniform in the thickness direction of the foam sheet, the rigidity of the foam sheet is further improved. 0.8 <A1 / A2 ≦ 1.2 (4) 0.8 <B1 / B2 ≦ 1.2 (5) 0.8 <C1 / C2 ≦ 1.2 (6) )

Further, in the present invention, when the thickness is measured along the TD direction, when the thickness of the foamed sheet is divided at intervals of 100 mm from one end to the other end in the TD direction, maximum thickness (T _m) and the minimum thickness (T _l) and the ratio of (T _l / T _m) that is 0.90 or higher, a thin portion of the sheet during thermoforming and the like are locally stretched, There is no such thing as inferior moldability.

Further, when a resin sheet having a thickness of 200 μm or less and an inorganic filler content of 5 to 70% by weight is laminated on at least one surface of the non-crosslinked polypropylene resin foam sheet of the present invention, the rigidity of the foam sheet can be further increased. Can be
By increasing the lip strength of the molded product, it is possible to improve the shape retention, the moldability, and the productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a longitudinal section of a foamed polypropylene resin sheet (Example 2) of the present invention.

FIG. 2 is a diagram for explaining the meaning of a bubble diameter in the present invention.

FIG. 3 is a diagram illustrating partitioning of a foam sheet in the TD direction in the present invention.

FIG. 4 is an explanatory view of an apparatus for measuring a drawdown property.

FIG. 5 shows an example of the dynamic viscoelasticity of a polypropylene resin which can be suitably used in the present invention, and the storage elastic modulus G corresponding to each frequency ω obtained by dynamic viscoelasticity measurement in a linear region at 230 ° C. ′ And logω as the horizontal axis,
This is a straight line approximating a curve plotted on coordinates with logG 'as the vertical axis.

FIG. 6 is a conceptual diagram showing a part of a production process of a foamed polypropylene resin sheet of the present invention.

FIG. 7 is an explanatory view showing a bubble portion to be measured in Examples and Comparative Examples.

FIG. 8 is an explanatory view showing molded products obtained for evaluating moldability in Examples and Comparative Examples.

FIG. 9 is an explanatory view showing a molded article obtained for measuring the lip strength of the molded article in Examples and Comparative Examples, and an explanatory view showing a method for measuring the lip strength.

FIG. 10 is a schematic view showing a longitudinal sectional view of a conventional polypropylene resin foam sheet (Comparative Example 3).

[Explanation of symbols]

 1 Non-crosslinked polypropylene resin foam sheet 2 Bubble

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akinori Taira 1078-4 Komaocho, Utsunomiya City, Tochigi Prefecture Casa Eye Room 202 (56) References JP-A 8-231745 (JP, A) JP-A 5- 338055 (JP, A) JP-A-5-293903 (JP, A) JP-A-58-213028 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 47/00-47 / 96 C08J 9/00-9/42

Claims (6)

(57) [Claims] 1. A non-crosslinked polypropylene resin foam sheet for molding having a density of 0.09 to 0.4 g / cm ³ , a thickness of 0.5 to 8 mm, and a closed cell ratio of 70% or more. A non-crosslinked polypropylene resin extruded foam sheet for thermoforming, characterized by satisfying formulas (1) to (3). 0.35 <A / B <0.65 (1) 0.35 <A / C <0.65 (2) 0.10 <A ≦ 0.4 (3) [ However, each of A, B, and C in the formula is an average cell diameter in the thickness direction, the extrusion direction (MD direction), and the width direction (TD direction) of the foamed sheet, and the unit thereof is mm. ] 2. Polypropylene having a drawdown property of 60 m / min or less.
The non-crosslinked polymer for thermoforming according to claim 1, comprising a pyrene-based resin.
Extruded propylene resin foam sheet. 3. Polypropylene having a drawdown property of 30 m / min or less.
The non-crosslinked polymer for thermoforming according to claim 1, comprising a pyrene-based resin.
Extruded propylene resin foam sheet. 4. An average cell in a thickness direction, an extrusion direction (MD direction), and a width direction (TD direction) of a foam sheet, which is present in a surface layer portion within 25% of a total thickness of the foam sheet from the surface thereof. The diameters are A1, B1, and C1, respectively, and the total thickness of the sheet is 25 from the surface of the foamed sheet.
%, The average cell diameter in the thickness direction, the extrusion direction (MD direction), and the width direction (TD direction) of the foamed sheet is A2, B2, and C2, respectively. claim 1 which satisfies - (6)
4. The non-crosslinked polypropylene resin extruded foam sheet for thermoforming according to any one of items 1 to 3 . 0.8 <A1 / A2 ≦ 1.2 (4) 0.8 <B1 / B2 ≦ 1.2 (5) 0.8 <C1 / C2 ≦ 1.2 (6) ) 5. When the thickness of the foamed sheet is measured along the width direction (TD direction), the foam sheet is partitioned from one end to the other end at an interval of 100 mm in the width direction (TD direction). the ratio of the maximum thickness in the respective ranges (T _m) and the minimum thickness _{(T l) (T l /} T m) is for thermoforming according to any one of claims 1 to 4 is 0.90 or more Non-crosslinked polypropylene resin extruded foam sheet. 6. The non-crosslinked polypropylene resin for thermoforming according to claim 1, wherein a resin sheet having a thickness of 200 μm or less and an inorganic filler content of 5 to 70% by weight is laminated on at least one surface. Extruded foam sheet.