JP2000211018A - Container and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To obtain a styrene-based resin sheet useful for obtaining a container excellent in low thickness unevenness and deep drawability. SOLUTION: The temperature is 130 ° C., and the elongation speed is 0.0025-
In the measurement of elongational viscosity in the range of 0.0035 sec ^-1 ,
Equations (1) to (3) below: Δlnλ _n / Δε = (lnλ _n2 −lnλ _n1 ) / (ε ₂ −
ε ₁ ) ≧ 0.15 (1) λ _n = λ / λ _l (2) ε = ln (l / l ₀ ) (3) (where λ _n is a nonlinear parameter, λ is the elongational viscosity in the nonlinear region, lambda _l represents an extensional viscosity in the linear region, epsilon consisted of styrene-based resin to satisfy.) indicating the length of the sample in the elongation strain amount, l ₀ and l each extension time 0 and t the Hencky two The axially stretched sheet is vacuum-pneumatic-formed at a sheet temperature of 120 ° C. or more and a pneumatic pressure of 3 kg / cm ² or less to produce a container. The orientation relaxation stress of the biaxially stretched sheet is 3 to 6 kg / in both longitudinal and transverse directions.
It may be about cm ² .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a container excellent in deep drawability and low thickness unevenness and a method for producing the same.

[0002]

2. Description of the Related Art A biaxially stretched styrene resin sheet is inexpensive in addition to its various properties such as transparency, stiffness and hygiene (it is tasteless and odorless).
It is widely used in various applications, especially in the field of food packaging (such as food containers).

In general, a biaxially stretched sheet is biaxially stretched so that the orientation relaxation stress in the sheet increases.
For this reason, when deep drawing is performed, the thickness of the container is extremely uneven, and the strength is reduced. In addition, the sheet is broken due to the formation of the container, which is not suitable for forming a deep container.

[0004] In order to improve the container moldability of a biaxially stretched styrene resin sheet (such as low thickness unevenness and deep drawability), a biaxially stretched sheet obtained by adding a rubber component to a styrene resin is used.

JP-A-55-23123 discloses that 0.2 to 5 parts by weight of a low-molecular-weight liquid rubber is added to 100 parts by weight of a resin composition obtained by mixing and polymerizing a monovinyl aromatic compound and a rubber elastic material. It is disclosed that 5 to 3 parts by weight of an internal lubricant is added to obtain a styrene resin composition suitable for vacuum forming. In this resin composition, when a specific amount of the liquid rubber and the internal lubricant are added, the sheet is formed, and the secondary processing is performed by vacuum forming, a molded article with less uneven thickness and less uneven thickness can be obtained. As described above, when the rubber component is added, it is possible to obtain a styrene-based resin sheet and a molded article having low uneven thickness, but the transparency of the sheet and the molded article cannot be maintained. Further, if the amount of rubber added is such that the transparency of the sheet and the molded article can be maintained, sufficient deep drawability and low unevenness in thickness cannot be imparted to the sheet.

When a biaxially stretched sheet is subjected to secondary processing without adding a rubber component or the like, molding is performed under high temperature or high pressure conditions in order to obtain a container corresponding to the shape of the mold with good reproducibility. Advantageously. However, when the sheet is formed into a container or the like under such high temperature or high pressure, the container has a non-uniform thickness (a wide thickness distribution) and poor unevenness in thickness. It breaks (low deep drawability), making even container molding difficult. Such molding problems result in a reduction in product yield and a decrease in the moldability of the biaxially stretched sheet into a container.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a container excellent in low thickness deviation and deep drawability even when molded using a biaxially stretched sheet, and a method for producing the same. is there.

Another object of the present invention is to provide a container which can be molded with a relatively low pressure and has a high reproducibility in accordance with the shape of a mold and a method for producing the same.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and have found that a biaxially stretched sheet composed of a styrene-based resin exhibiting a specific elongational viscosity behavior can be obtained under a specific condition. It was found that forming into a container by using the method can improve uneven thickness and deep drawability of the container, and completed the present invention.

[0010] That is, in the present invention, the temperature 130 ° C., in measurement of extensional viscosity in the range of elongation rate 0.0025～0.0035Sec ^-1, the following equation (1) ~ (3) Δlnλ n / Δε = (lnλ n2 −lnλ _n1 ) / (ε ₂ −ε ₁ ) ≧ 0.15 (1) λ _n = λ / λ _l (2) ε = ln (l / l ₀ ) (3) (where λ _n is a nonlinear parameter , lambda is extensional viscosity in the non-linear region, lambda _l represents an extensional viscosity in the linear region, epsilon elongation strain amount of Hencky, represented by l ₀ and l represents the length of the sample at each extension time 0 and t.) A biaxially stretched sheet composed of a styrene-based resin satisfying the following relationship is applied at a sheet temperature of 120 ° C. or more and a compressed air pressure of 3 k.
The container is manufactured by vacuum-pressure forming at a pressure of g / cm ² or less.
The orientation relaxation stress of the biaxially stretched sheet may be about 3 to 6 kg / cm ² in both the vertical and horizontal directions.

In the container of the present invention, the biaxially stretched sheet is formed by the following formula (4) H / (2 (A / π) ^1/2 ) (4) (where H is the height (mm) of the container) , A represents the area (mm ² ) of the opening of the container, and π represents the circumferential ratio).

In the present specification, acrylic monomers and methacrylic monomers are collectively referred to as (meth) acrylic monomers.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION [Styrene Resin] The container of the present invention comprises a biaxially stretched sheet made of a specific styrene resin.

The styrene resin constituting the sheet is as follows:
Temperature 130 ° C, elongation rate 0.0025-0.0035se
In the measurement of elongational viscosity in the range of c- ^1, the following formula (1)
Satisfies the relationship expressed by (3). Δlnλ _n / Δε = (lnλ _n2 −lnλ _n1 ) / (ε ₂ −ε ₁ ) ≧ 0.15 (1) λ _n = λ / λ _l (2) ε = ln (l / l ₀ ) (3) ( wherein, lambda _n nonlinear parameter, lambda any elongation viscosity at an elongation time, lambda _l is .ε showing the elongation viscosity in a linear region extending strain amount of Hencky under constant temperature and constant strain rate, l ₀ and l are the extension times 0 and t, respectively.
Shows the length of the sample at. The linear region refers to a region in which the extensional viscosity does not depend on various strain rates and shows the same time dependency (see Kiyoto Koyama, Osamu Ishizuka, Journal of the Rheological Society of Japan, 13 , 93 (1985)). ). When measuring the extensional viscosity, some resins have a property that the extensional viscosity in the high strain region deviates from the linear region and rises sharply (that is, the strain hardening property) depending on the type of the resin. In such resins, the logarithm of λ _n (lnλ _n) is Henc
It is known that it increases linearly with the elongation strain ε of ky (Kiyoto Koyama, Osamu Ishizuka, Journal of the Textile Society of Japan, 37 , T
-258 (1981)).

In the case of a resin having no strain hardening property, λ _n is 1 for an arbitrary amount of elongational strain, and a logarithm of λ _n (lnλ _n ) is plotted against Hencky's elongational strain ε. Is 0 (= Δlnλ _n / Δε). In the case of a resin having a strain hardening property, the slope α of the straight line plot does not become zero particularly in a high strain region.

In this specification, the slope α of a straight line plotting the logarithm (lnλ _n ) of the nonlinear parameter λ _n with respect to the amount of elongation strain ε is defined as a parameter representing the degree of strain hardening.

The inclination α of the straight line is an index indicating the fluidity and moldability of the resin. For a styrene resin, the temperature is 130 ° C. and the elongation speed is 0.0025 to 0.0035 sec.
The slope α of the straight line measured by the elongational viscosity in the range of ^-1 is 0.1
In the case of 5 or more, the container is excellent in deep drawability and low thickness unevenness,
Even if the container is molded under relatively low pressure, the mold shape can be reproduced with high accuracy and can be molded at high speed. Slope α (= Δlnλ)
_n / Δε) is preferably 0.2 to 2, more preferably 0.2 to 1.5 (for example, 0.3 to 1.5), and particularly about 0.35 to 1.0. When the inclination α of the straight line is 0.
If it is less than 15, low unevenness in thickness, deep drawability and the like may be reduced,
The sheet breaks during container molding.

The strain hardening property is usually exhibited by the presence of a molecular chain having a long relaxation time in the polymer. Therefore, the method for increasing the slope α of the straight line (for example, to 0.15 or more) is not particularly limited.
As a polymer chain having a long relaxation time, a method of blending a linear ultrahigh molecular weight component, a method of using a branched polymer, and the like can be given. In a preferred embodiment, by using a styrene resin containing a branched styrene polymer,
Strain hardening can be exhibited.

In the styrenic resin, the branching parameter (shrinkage factor) g indicating the degree of branching is not particularly limited, and may be about 0.5 to 1.0.
0.5 or more and less than 0.99 (for example, 0.5 to 0.9
8), preferably about 0.6 to 0.98, and more preferably about 0.7 to 0.97.

The shrinkage factor g is determined by gel permeation chromatography (GPC) for a branched styrene polymer and a linear styrene polymer synthesized by thermal polymerization.
It is the ratio of the respective intrinsic viscosities measured by the method and is represented by the following formula in this specification.

The branch parameter g (= [η] _branch / [η] _linear ) (where [η] _branch is the intrinsic viscosity of the branched polymer at 40 ° C. in chloroform, and [η] _linear is the weight of the branched polymer and weight The intrinsic viscosity of the linear polymer having the same average molecular weight in chloroform at 40 ° C. is shown.) [Η] _linear is Schultz's viscosity equation [η] = 4.
The molecular weight distribution was calculated based on 9 × 10 ⁻³ Mw ^0.794 (where Mw represents a weight average molecular weight) according to the Schultz-Zimm exponential function.

The branching parameter g, which is an index indicating the degree of branching of the styrenic resin, is also called a shrinkage factor (Kyoritsu Shuppan, edited by The Society of Polymer Science, New Polymer Experiment 1, Basic Polymer Experiment, Molecular Characteristic Analysis) , 295 (1994)), at a certain temperature, in a dilute solution of a polymer dissolved in a good solvent or a θ solvent, based on the fact that the molecular spread differs depending on the structure of the polymer molecule (BH
Zimm and WHStockmayer, J. Chem. Phys., 17,1301
(1949)). For example, when comparing a linear polymer and a branched polymer having the same molecular weight, the spread of the polymer molecule having a branched structure is smaller than that of the linear polymer molecule.
As a result, the mean square turning radius representing the intrinsic viscosity or molecular size of the branched polymer is observed to be smaller than that of the linear polymer.

The measurement of the contraction factor can be performed by using the light scattering method.
The measurement can also be performed by measuring the intrinsic viscosity. The styrene-based resin is a styrene-based monomer homopolymer or copolymer,
It can be composed of a copolymer of a styrene monomer and a copolymerizable vinyl monomer.

Examples of the styrene monomer include styrene, alkylstyrene (for example, vinyltoluenes such as o-, m-, p-methylstyrene and 2,4-dimethylstyrene, ethylstyrene, p-isopropylstyrene). , Alkyl-substituted styrenes such as butylstyrene and pt-butylstyrene), α-alkyl-substituted styrenes (eg, α-methylstyrene and α-methyl-p-
Methylstyrene), halogen-substituted styrene (eg, o-, m- and p-chlorostyrene, p-bromostyrene, etc.), 1,1-diphenylethylene, p-
(N, N-diethylaminoethyl) styrene, p-
(N, N-diethylaminomethyl) styrene and the like can be exemplified. These styrene monomers can be used alone or in combination of two or more. Preferred styrene monomers include styrene, vinyltoluene, α-methylstyrene and the like, and styrene is particularly preferred.

As the copolymerizable vinyl monomer, for example,
(Meth) acrylonitrile, alkyl (meth) acrylate, vinyl ester-based monomer (eg, vinyl acetate), hydroxyl group-containing monomer [hydroxy C ₁ such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc. _-4 alkyl (meth) acrylate, etc.], glycidyl group-containing monomer [glycidyl (meth) acrylate, etc.], carboxyl group-containing monomer [(meth) acrylic acid, maleic anhydride, fumaric acid, etc.], imide monomer Monomers (maleimide, N-methylmaleimide, N-phenylmaleimide, etc.). The alkyl (meth) acrylate includes methyl (meth) acrylate, ethyl (meth) acrylate,
Butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
_C1-20 alkyl (meth) acrylates such as lauryl (meth) acrylate are included. These vinyl monomers can be used alone or in combination of two or more. The ratio between the styrene monomer and the copolymerizable monomer is, for example, 10
0/0 to 50/50 (weight ratio), preferably 100/0
３０30/70 (weight ratio).

The styrenic resin may be modified with a rubber component in order to improve moldability, impact resistance, flexibility, anti-blocking property and the like. When a rubber-modified styrene resin is used, drawdown can be suppressed without impairing rigidity and impact strength, and moldability can be improved.

In the rubber-modified styrene resin, the rubber component may be, for example, a conjugated diene rubber [polybutadiene, polyisoprene, poly (2-chloro-1-1,3-
Butadiene), poly (1-chloro-1,3-butadiene), butadiene-styrene copolymer, etc.], ethylene-propylene rubber (EPDM rubber), acrylic rubber, ethylene-vinyl acetate copolymer, chlorinated polyethylene, etc. Can be illustrated. These rubber components can be used alone or in combination of two or more. As a preferable rubber component, a conjugated diene rubber is often used.

The rubber-modified styrenic resin comprises a rubber component,
An impact-resistant styrene resin composed of an admixture with a styrene resin that is not rubber-modified may be an impact-resistant styrene resin. It is a graft copolymer (impact styrene resin) obtained by polymerizing a monomer (styrene monomer).

In the graft polymer, the aromatic vinyl monomer may be used in combination with a vinyl cyanide monomer, and if necessary, the copolymerizable vinyl monomer may be used in combination. The ratio between the aromatic vinyl monomer and the vinyl cyanide monomer is, for example, the former / the latter = 10/90 to 9
0/10 (% by weight), preferably 20/80 to 80/2
0 (% by weight), more preferably 30/70 to 70/3
0 (% by weight). The ratio between the aromatic vinyl monomer and the copolymerizable vinyl monomer is, for example, the former / the latter = 10/90 to 100/0 (% by weight), particularly 30/70.
About 70/30 (% by weight).

The styrene resins can be used alone or as a mixture of two or more. The branched polymer can be prepared by using at least one selected from a polyfunctional vinyl compound, a polyfunctional chain transfer agent, and a polyfunctional polymerization initiator.

The polyfunctional vinyl compound is not particularly limited as long as it has a plurality of unsaturated bonds, and various compounds can be used. Examples of the polyfunctional vinyl compound include aromatic compounds having a vinyl group or an allyl group (divinylbenzene,
-Allyl-3-vinylbenzene, etc.), alkenyl (meth) acrylates (such as allyl (meth) acrylate), di (meth) acrylate compounds of polyhydric alcohols [for example, ethylene glycol di (meth) acrylate, propylene glycol di (meth) ) Acrylate,
1,4-butanediol di (meth) acrylate, 1,
Diol (meta) such as 6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate ) Acrylate, dipropylene glycol di (meth)
Polyoxyalkylene glycol di () such as acrylate, tripropylene glycol di (meth) acrylate, and tetrapropylene glycol di (meth) acrylate
Bifunctional vinyl compounds such as meth) acrylates;
Trifunctional vinyl compounds such as tri (meth) acrylate (trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, etc.); tetra (meth) acrylate (tetramethylolmethane tetraacrylate, pentaerythritol tetra (meth) acrylate Etc.) and the like. These polyfunctional vinyl compounds can be used alone or in combination of two or more. Particularly, a 2- to 4-functional vinyl compound (such as divinylbenzene) is preferable.

The proportion of the polyfunctional vinyl compound is from 0 to 700 ppm, preferably from 30 to 700 ppm, based on the styrene monomer.
550 ppm, more preferably 50 to 400 ppm
(Weight basis).

When a polyfunctional vinyl compound is used, the ratio between the initiator and the polyfunctional vinyl compound is the former / the latter = 100
/ 20-20 / 100 (weight ratio), preferably 100 /
30 to 30/100 (weight ratio), for example, 1
It may be about 00/50 to 50/100 (weight ratio).

In order to control the molecular weight of the polymer, a chain transfer agent may be added, if necessary, as long as the drawdown property, heat resistance and oil resistance are not impaired. The type of the chain transfer agent is not particularly limited, and a conventional chain transfer agent can be used. For example, mercaptans (for example, polyfunctional mercaptans such as ethylene glycol bisthioglycolate, trimethylolpropane tristhioglycolate, and pentaerythritol tetrakisthioglycolate), styrene dimers (such as α-methylstyrene dimer), terpenes ( It is preferable to use terpinolene or the like.
As the terpene, for example, “NOFMER TP” (manufactured by NOF Corporation) or the like can be used. The chain transfer agents can be used alone or in combination of two or more.

The ratio of the chain transfer agent is about 10 to 2000 ppm (weight basis), preferably 50 to 1000 ppm (weight basis), more preferably about 100 to 800 ppm (weight basis), based on the styrene monomer. .

In the production of the styrenic resin, a polymerization initiator is not always necessary and may be thermally polymerized.
A polymerization initiator is used. As the polymerization initiator, a monofunctional or polyfunctional initiator can be used, and a peroxide, an azo compound or the like may be used.

Among the peroxides, examples of the monofunctional or bifunctional peroxide include ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide and methylcyclohexanone peroxide; -Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane,
Peroxyketals such as 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valate, cumene hydroperoxide, diisopropylbenzene hydroperoxide, , 5-dimethylhexane-2,5-
Hydroperoxides such as dihydroperoxide, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α, α ′
Dialkyl peroxides such as -bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, benzoyl peroxide, decanoylperoxide Diacyl peroxides such as oxide, lauroyl peroxide and 2,4-dichlorobenzoyl peroxide; peroxycarbonates such as bis (4-t-butylcyclohexyl) peroxydicarbonate; t
-Butyl peroxybenzoate, 2,5-dimethyl-
Peroxyesters such as 2,5-di (benzoylperoxy) hexane; triazines [bis (t-alkylperoxy) triazines such as bis (t-butylperoxy) triazine; bis (di-t-butylperoxy) triazine Bistris (di-t) such as oxycyclohexyl) triazine
-Alkylperoxycycloalkyl) triazine; bis (di-t-aralkylperoxycycloalkyl) triazine such as bis (di-2-phenylpropylperoxycyclohexyl) triazine, and the like.

Examples of the polyfunctional peroxides having three or more functional groups include compounds represented by the following formulas (5) to (7).

[0039]

Embedded image

Wherein R ¹ is the same or different and represents a hydrogen atom or an alkyl group; R ² is the same or different and represents a hydrogen atom, an alkyl group or an aralkyl group;
³ is the same or different and represents an alkyl group or an aralkyl group. R ⁴ is the same or different and represents a hydrogen atom, an alkyl group or an aralkyl group. In the formulas (5) to (7), R ¹ is preferably an alkyl group, and is usually a tertiary alkyl group (t-butyl group, t-butyl group).
-Amyl group, t-hexyl group and t-C _4-10 alkyl group such as t-octyl group). Particularly, a C _4-8 alkyl group such as a t-butyl group is preferable. R ² and R
⁴ is preferably a hydrogen atom, an alkyl group (particularly, C _1-4 alkyl group such as methyl group, ethyl group), R ³
Is usually the same tertiary alkyl group or tertiary aralkyl group (such as a C _9-14 aralkyl group such as a 2-phenylpropyl group) as described above. Particularly, R ² is preferably a hydrogen atom, a methyl group or an ethyl group, and R ³ is preferably a C _4-8 alkyl group such as a t-butyl group. R ⁴ is preferably a C _4-8 alkyl group such as a t-butyl group or a C _9-14 aralkyl group such as a 2-phenylpropyl group.

Examples of the trifunctional peroxide represented by the formula (5) include, for example, tris (t-alkylperoxy) triazine such as tris (t-butylperoxy) triazine and tris (t-amylperoxy) triazine. And the like. Also, tris (di-t-alkylperoxycycloalkyl) triazine such as tris (di-t-butylperoxycyclohexyl) triazine, tris (di-2-phenylpropylperoxycyclohexyl)
Tris (di-t-aralkylperoxycycloalkyl) triazines such as triazine can also be used.

Examples of the tetrafunctional peroxide of the formula (6) include 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane and 2,2-bis (4,4-di -T-amylperoxycyclohexyl) propane,
2,2-bis (4,4-di-t-hexylperoxycyclohexyl) propane, 2,2-bis (4,4-di-
bis (4,4-di-t-alkylperoxycyclohexyl) alkanes such as t-octylperoxycyclohexyl) propane and bis such as 2,2-bis (4,4-di-2-phenylpropylperoxycyclohexyl) propane (4,4-Di-t-aralkyl peroxycyclohexyl) C _2-8 alkane and the like can be exemplified. Preferred tetrafunctional peroxide (6) is 2,2-bis (4,4-di-
bis (4,4-di-t-C _4-10 alkylperoxycyclohexyl) alkanes such as t-butylperoxycyclohexyl) propane;

Examples of the tetrafunctional peroxide represented by the formula (7) include 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 3,3',
4,4'-tetra (t-amyl peroxycarbonyl)
Benzophenone, tetra (t-alkylperoxycarbonyl) benzophenone such as 3,3 ′, 4,4′-tetra (t-hexylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra (t-2) Examples thereof include tetra (t-aralkylperoxycarbonyl) benzophenone such as -phenylpropylperoxycarbonyl) benzophenone.

These organic peroxides can be used alone or in combination of two or more. Further, an inorganic peroxide such as hydrogen peroxide or a persulfate (such as potassium persulfate or ammonium persulfate) may be used in combination.

As the azo compound, azobisnitrile [for example, 2,2'-azobisisobutyronitrile (A
2,2′-azobisbutyronitriles such as IBN) and 2,2′-azobis (2-methylbutyronitrile);
2,2′-azobisvaleronitriles such as 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) and 2,2′-azobis (2,4-dimethylvaleronitrile); 2,2'-azobispropionitrile such as 2'-azobis (2-hydroxymethylpropionitrile); 1,1'-azobiscyclohexane-1
1,1′-azobis-1-alkanenitrile such as carbonitrile, especially 1,1′-azobis-1-cycloalkanenitrile (for example, 1,1′-azobis-1)
-C _5-8 cycloalkane carbonitrile), 4,4'-azobis (4-cyanovaleric acid) and azo bis cyano carboxylic acids, such as, azonitrile [2- (carbamoylazo) Azobuchiro such isobutyronitrile Nitriles; azovaleronitriles such as 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, etc.], azobisalkanes [eg, 2,2′-azobis (2-methylpropane), 2,2 ′ - azobis (2,4,4-trimethylpentane), such as 2,2'-azobis C _3-10 alkanes, etc.], dimethyl-2,2'-azo-bis-isobutyrate and the like.

The polyfunctional organic peroxide (for example, the compound represented by the formula (6)
Has a plurality of (for example, four) functional groups in one molecule, so that the molecular weight of the polymer can be increased and the polymer has a partially branched structure. It appears to improve the flowability of the resulting polymer.

The polymerization initiators can be used alone or in combination of two or more. The ratio of the polymerization initiator is 2 to the polymerizable monomer containing at least the styrene monomer.
000 ppm or less (0-2000 ppm), preferably 50-1000 ppm (for example, 100-700 pp)
m) (weight basis).
It is about 0 to 500 ppm.

The ratio between the initiator and the chain transfer agent is 100 /
20-20 / 100 (weight ratio), preferably 100/3
0 to 30/100 (weight ratio), more preferably 100
/ 50 to 50/100 (weight ratio).

In order to obtain the styrenic resin, it is advantageous to carry out polymerization using at least a polyfunctional vinyl compound and a chain transfer agent, and furthermore, a polyfunctional polymerization initiator (polyfunctional organic compound represented by the formula (6)). It is preferable to carry out the polymerization in combination with a peroxide.

The method for producing the styrene-based resin is not particularly limited, and a conventional polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, or bulk-suspension polymerization can be employed.
In the bulk polymerization method (bulk polymerization method) advantageous for industrial production, a solvent may be added. The solvent is not particularly limited, and a conventional solvent such as an aromatic hydrocarbon (benzene, toluene, ethylbenzene, xylene, etc.), an alicyclic hydrocarbon (cyclohexane, etc.), an aliphatic hydrocarbon (hexane, octane, etc.) Etc.) can be exemplified.

The amount of the solvent (solvent) used is, for example, from 0 to 30% by weight, preferably from 5 to 2% by weight, based on the whole reaction mixture.
It can be selected from a range of about 0% by weight. Solvent ratio is 30
If the content exceeds% by weight, economic efficiency such as solvent recovery may be reduced.

The polymerization can be carried out under normal pressure or under pressure. The polymerization temperature depends on the type of polymerization method, the composition of the polymerization initiator system,
80 to 180 ° C., preferably 9 to 80 ° C., depending on the polymerization rate and the like.
It can be selected from the range of about 0 to 150 ° C. Polymerization temperature is 8
If the temperature is lower than 0 ° C., the productivity is reduced. If the temperature is higher than 180 ° C., the molecular weight of the resin is reduced, and the impact strength is lowered.

The polymerization may be carried out usually in an atmosphere of an inert gas such as nitrogen, helium, argon or the like, for example, under a flow of an inert gas. The polymer may be separated and purified, for example, after the polymerization reaction, if necessary, by diluting with a solvent and precipitating in a poor solvent, or removing volatile components such as monomers and solvents.

The weight average molecular weight Mw of the styrene resin is
It is about 150,000 to 700,000, preferably about 200,000 to 500,000, and more preferably about 250,000 to 350,000. If the weight-average molecular weight is less than 150,000, the impact resistance of the obtained sheet and container is remarkably reduced, and if it exceeds 700,000, the viscosity at the time of melting is increased, the moldability is significantly reduced, and the sheet is broken during stretching. Or

In the styrenic resin, the molecular weight distribution Mw / Mn (where Mw is the weight average molecular weight of the styrenic resin, Mn
Represents the number average molecular weight of the styrene resin. ) Is 10 or less (about 1 to 10), preferably 5 or less (about 1.5 to 5). If the molecular weight distribution exceeds 10, physical properties such as mechanical strength and moldability deteriorate.

The styrene-based resin may be another styrene-based resin not exhibiting the above-mentioned properties, for example, a styrene-based monomer alone or a copolymer, or a copolymer of a styrene-based monomer and a copolymerizable vinyl monomer. It may be used in combination with two or more resins selected from a polymer and a rubber-modified styrenic resin. Further, it may include a block copolymer of a rubber block and an aromatic vinyl polymer block (such as an ABA type block copolymer). Block copolymers often form thermoplastic elastomers. The structure of the block copolymer may be linear or star (star).

If necessary, the styrene resin may be another thermoplastic resin such as an olefin resin, crystalline polystyrene (isotactic or syndiotactic),
Polyester resin, polyamide resin, polycarbonate resin, polysulfone resin, polyphenylene ether resin, polyphenylene sulfide resin, polyether ether ketone resin, polyacetal resin (homopolymer or copolymer polyacetal), thermoplastic elastomer (thermoplastic) (Polyurethane elastomer, polyester elastomer, etc.) and the like.

In order to improve the miscibility and wettability of the styrene resin with other resins, a compatibilizer may be added. The styrene-based resin may contain various additives as necessary, for example, stabilizers (such as ultraviolet absorbers, antioxidants, and heat stabilizers), lubricants, release agents (such as silicone oil), plasticizers ( Mineral oil, etc.), dispersant (higher fatty acid salt, etc.), reinforcing agent, filler (inorganic filler such as talc), slip agent, anti-blocking agent, nucleating agent, cross-linking agent, conductivity imparting agent, antistatic agent, Anti-fogging agents, flame retardants, light-shielding agents such as titanium oxide, coloring agents (pigments, dyes, etc.) may be added. [Biaxially stretched sheet] The biaxially stretched sheet used for molding the container of the present invention is obtained by forming a sheet of the resin composition containing at least the styrene-based resin and biaxially stretching the obtained sheet (biaxially in the vertical and horizontal directions). It can be obtained by:

The following formula of such a biaxially stretched sheet: Substantial stretching ratio = 100 / (100−L) (wherein L is a temperature of 30 ° C. higher than the Vicat softening point of the styrene resin and the resin is treated for 20 minutes) The actual stretching ratio represented by the formula (1) is not particularly limited, and is, for example, 1.5 to 3.
It is about 5 times (for example, 1.8 to 3 times), preferably about 2 to 3 times (for example, 2 to 2.8 times). In the present invention, the Vicat softening point temperature of the styrene resin is AS AS
The value is measured according to TM D1524.

The mechanical stretching ratio of the resin sheet, including the stretching component and the reorientation component caused by stretching in the other axis direction, is not particularly limited.
It is about 0 times, preferably about 1.5 to 5 times. The correlation between the mechanical stretching ratio and the substantial stretching ratio changes depending on stretching factors such as a roll or a tenter, stretching conditions such as a stretching temperature, or various factors such as mechanical stretching ratios in other axial directions. I do.

[0061] The biaxially stretched sheet is an ASTM
The orientation relaxation stress measured according to D1504 is 3 to 7 kg / cm ² in both the vertical and horizontal directions (for example, 3 to 6 kg / cm ² ).
5kg / cm ^2), preferably 3~6kg / cm ^2, more preferably 4~6kg / cm ² approximately. Orientation relaxation stress is less than 3 kg / cm ^2, the impact resistance of the sheet is insufficient, there is a possibility that the strength of the container resulting drops, also exceeds 7 kg / cm ^2, at the time of sheet formation There is a possibility that the sheet may be broken, and a sufficient elongation may not be ensured during the molding of the container.

The biaxially stretched sheet can be formed by a conventional molding method,
For example, a resin composition is melt-kneaded and a die (flat,
A sheet is formed by an extrusion method of extruding a sheet from a T-shape (T-die) or a cylindrical shape (circular die) or the like, and a conventional stretching method, for example, a tenter method, a tube method, or the like is performed using a stretching machine. It is obtained by biaxial stretching (in the longitudinal and transverse biaxial directions) by a biaxial stretching method and usually cooling. In the case where a circular die is used, the sheet is obtained by folding the cylindrical sheet with a pinch roll and cutting open the sheet by trimming. The extruder in the extrusion molding and the stretching machine used for stretching are not particularly limited, and conventional ones can be used.

The thickness of the biaxially stretched sheet is in a range that does not impair the moldability of the container, for example, 0.05 to 1 mm (for example, 0.08 to 0.8 mm), preferably 0.1 to 0.
It is about 5 mm, more preferably about 0.12 to 0.4 mm. If the thickness is small, the mechanical strength, stiffness and heat retention of the container are reduced, and if it is too large, the moldability is reduced and the thickness of the container is liable to be uneven.

The biaxially stretched sheet may be used as a single layer sheet or as a laminated sheet having a surface layer formed on at least one surface of the sheet.
This surface layer may be a skin layer, and may be a coating layer (for example, an olefin-based resin such as polypropylene, polystyrene, polyester, or the like) laminated with or without an adhesive layer by coextrusion lamination or dry lamination. Or a stretched or unstretched film or sheet of polyamide or the like.

The biaxially stretched sheet is further coated with a surface modifier, an antifogging agent, a conductivity-imparting agent, an antistatic agent, a release agent (polysiloxane in the form of an emulsion or the like, silicone oil, etc.). May be.

The biaxially stretched styrene resin sheet thus obtained is usually wound up by a winding roll or the like. In the molding step, the sheet is heated (heated to a temperature equal to or higher than the softening point of the base resin) and subjected to molding processing such as container molding. [Container molding] The container of the present invention is obtained by molding the biaxially stretched sheet into a desired container shape.

The means for heating the sheet at the time of molding the container is not particularly limited as long as it is suitable for molding the container. For example, the sheet may be directly heated using a hot plate contact heating molding machine, etc. (Indirect heating with a heating heater, infrared heater, etc.). In particular, heating by a hot plate contact heating method or the like is preferable. In the hot plate contact heating method,
Usually, the sheet is brought into contact with a heated hot plate in a compressed air or vacuum state and heated to a temperature suitable for molding.

The temperature of the sheet in the forming process (for example, when directly heated by a hot plate, the temperature of the hot plate) is 120 ° C. or more, preferably 120 to 160 ° C., and more preferably 1 to 160 ° C.
It is about 20 to 145 ° C.

The container is molded by a conventional molding method, for example,
It can be performed by pressure forming, vacuum forming, vacuum pressure forming, or the like. In the present invention, in particular, molding is performed by air pressure molding or vacuum pressure molding. In such a method, a heated sheet is pressed against a container mold by compressed air to form a container. When the sheet is pressed against the mold, it is advantageous to draw the sheet by vacuum from the mold side in an auxiliary manner. In addition,
Vacuum pressure forming is usually performed by vacuum from the mold side and by pneumatic pressure from the opposite side of the mold. In this method, for example, the sheet is brought into contact with a heated hot plate by pressurized air from the mold and vacuum from the hot plate side, heated to a temperature suitable for molding, and then heated to the hot plate side (the opposite side of the mold). The container is formed by pressing the sheet against the container mold by the compressed air from the step (1). When the sheet is pressed against the mold, vacuum drawing from the mold side may be used as an auxiliary.

The mold temperature is, for example, about 20 to 100 ° C., preferably about 30 to 80 ° C. Even if it is as low as about 30 to 75 ° C., it is possible to mold a container which follows the mold shape with high accuracy.

When the container is formed under the pneumatic condition, the pneumatic pressure is 3 kg / cm ² or less (particularly less than 3 kg / cm ² ,
For example, 0.1~2.8kg / cm ^2), preferably 0.1~2.5kg / cm ² approximately. Also, 0.1
The mold shape can be satisfactorily reproduced even under a low pressure condition of about 5 to 1.5 kg / cm ² . If the air pressure is too high, the speed at which the sheet is stretched into a container shape is too fast,
In particular, when the amount of elongation of the sheet is large as in a deep container, the strain hardening property of the sheet cannot be sufficiently exhibited.

In the present invention, the biaxially stretched sheet is subjected to the above-mentioned compressed air pressure of 3 kg / cm ² or less and a sheet temperature of 120 ° C. or more.
By molding into the shape of a container, the strain hardening properties of the styrene-based resin can be maximized, and even when molded from a biaxially stretched sheet, the uneven thickness and deep drawability of the container can be improved. Can be reproduced in detail.

The shape of the container is not particularly limited as long as it has an opening for accommodating contents, and may be a square, an ellipse, a circle, or the like, or may be a bottomed cylindrical shape. . Also, the size is not particularly limited. The container is
What is necessary is just to provide the container main body which has an accommodation recessed part, and a flange part may be extended from the upper end part of the side wall of a container main body. For example, in the case of a cylindrical container with a bottom, the opening diameter is
It may be larger or smaller than the bottom diameter, or may be the same.

When the container has a bottomed cylindrical shape, the degree of deep drawing can be represented by a drawing ratio represented by the following equation (4). H / (2 (A / π) ^1/2 ) (4) (where H represents the height (mm) of the container, A represents the area (mm ² ) of the opening of the container, and π represents a circle. In the container of the present invention, the drawing ratio is not particularly limited, but is, for example, 0.2 to 1.2, preferably 0.3 to 1.
It is about 2 and even in a deep container of about 0.4 to 1.2, it has low uneven thickness and excellent deep drawability.

According to the present invention, even if the container has a bottomed cylindrical shape, in which uneven thickness is liable to occur, the biaxially stretched sheet made of a specific styrene resin is used under specific molding conditions to reduce the uneven thickness. Thus, a container having excellent deep drawability can be obtained.

[0076]

According to the present invention, a biaxially stretched sheet is formed using a specific styrene-based resin and further molded into a container. Therefore, even if a biaxially stretched sheet is used, it is excellent in low thickness unevenness and deep drawability. Container can be obtained. Further, even if the container is molded at a relatively low pressure, a container corresponding to the shape of the mold can be obtained with high reproducibility.

[0077]

EXAMPLES The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to these Examples.

The physical properties of the styrene resin were measured by the following methods. [Inclination of straight line α] Under the following conditions, both ends of a cylindrical sample are supported by a pinch roller or a caterpillar, and the sample is rotated at a constant strain rate to apply elongation deformation to the sample, and the cross-sectional area and pinch of the sample being deformed Elongational viscosity was determined by detecting the torque applied to the roller or track. A nonlinear parameter was calculated from the obtained extensional viscosity and the extensional viscosity in a nonlinear region having the same extensional time as the extensional viscosity in accordance with the above equation (2). Further, the strain amount is calculated from the lengths of the samples at the elongation times 0 and t according to the formula (3), and the logarithm of the nonlinear parameter and the strain amount are plotted for a plurality of points having different elongation times. The slope α was calculated according to 1).

Measuring temperature: 130 ° C. Strain rate: 0.0005 to 0.1 sec ^-1 Measuring equipment: MELTEN RHEOMETER (manufactured by Toyo Seiki Co., Ltd.) [Measurement of molecular weight and branching parameter g] Chloroform at a temperature of 40 ° C. Is used as an eluent, and the polymer solution eluted by gel permeation chromatography (GPC) is detected by a differential refractive index detector and a differential pressure viscosity detector, and the molecular weight is determined from a universal calibration curve and intrinsic viscosity calibrated with standard polystyrene. Calculated. The intrinsic viscosity of the linear and branched polymers can be determined by dividing the obtained viscosity chromatogram by the polymer concentration, and by dividing the intrinsic viscosity of the branched polymer by the intrinsic viscosity of the linear polymer. The branch parameter g was calculated.

Preparation Example 1 In a reaction vessel (20 liters), an initiator [2,2-bis (4,4-di-t-butylperoxycyclohexyl)] was added.
Propane, manufactured by NOF Corporation, Pertetra A] 300p
pm, a polyfunctional vinyl compound [divinylbenzene, 100 ppm, manufactured by Wako Pure Chemical Industries, Ltd.] and a chain transfer agent [pentaerythritol tetrakisthiopropionate (HS)
CH ₂ CH ₂ COOCH ₂ ) ₄ C, manufactured by Aldrich]
After purging with nitrogen, the mixture was heated to 110 ° C. for polymerization (2 hours), and then heated to 125 ° C. for polymerization (2 hours).
The mixture was further heated to 140 ° C. and polymerized for 2 hours, and polymerized until the amount of styrene monomer in the polymerization solution became 15% by weight or less. The styrene resin A was recovered by devolatilization of the unreacted monomer and the solvent in the reaction solution. Styrene resin A obtained
Is that the slope α of the straight line measured at a weight average molecular weight Mw of 320,000 and a strain rate of 0.00283 sec ⁻¹ is 0.4
7. A resin having a shrinkage factor g of 0.95.

Preparation Example 2 A styrene resin B was prepared in the same manner as in Preparation Example 1, except that the initiator and the polyfunctional vinyl compound were not added. The obtained styrene resin B has a weight average molecular weight Mw of 310,
000, the resin had a slope α of 0.09 and a shrinkage factor g of 1.00 measured at a strain rate of 0.00276 sec ⁻¹ .

Examples 1 to 5 and Comparative Examples 1 to 5 (Sheet molding) A styrene resin A or B
Was extruded, heated by an extruder, melt-kneaded, and extruded into a sheet from a T-die (temperature: 230 ° C.) at the tip of the extruder to produce an unstretched sheet having a thickness of 1.56 mm. Next, this unstretched sheet is 24 cm long and 24 c wide.
m, and the sample was stretched by a biaxial stretching tester [manufactured by Iwamoto Seisakusho] at a stretching ratio shown in Table 1 in the longitudinal and transverse directions at a stretching temperature of 118 to 130 ° C.
A biaxially stretched sheet having a thickness of 250 μm and a length of 60 cm × width of 60 cm was obtained. In the comparative example, an unstretched sheet was prepared in the same manner as described above, except that the thickness of the unstretched sheet was set to 250 μm, cut into a size of 60 cm (length) × 60 cm (width), and used as a container without being stretched. . (Container molding) The obtained styrene-based resin sheet was molded into a container (opening φ200 mm, bottom φ180 mm, deep) under the following molding conditions by using a hot plate pressure molding machine [manufactured by Asano Research Institute Co., Ltd.] of a direct heating system. (Height H) 90 mm, drawing ratio 0.45).

Molding conditions Upper air pressure: 0.2 to 5 kg / cm ² Hot plate temperature: 115 to 140 ° C. Mold temperature: 70 ° C. The actual stretching ratio and orientation relaxation stress were calculated according to the following criteria. And about the container obtained by the comparative example, the uneven thickness at the time of container molding, sheet breakage, and deep drawability were evaluated as follows. [Actual stretching ratio] The substantial stretching ratio of the biaxially stretched styrene-based resin sheet is represented by the following formula: substantial stretching ratio = 100 / (100-L) (where L is a temperature 30 ° C. higher than the Vicat softening point temperature of the styrene-based resin). Indicates the shrinkage after treating the resin for 20 minutes.) In addition, the Vicat softening point temperature of the styrene resin indicates a value measured according to ASTM D1524. [Orientation Relaxation Stress] The orientation relaxation stress of the biaxially stretched styrene resin sheet was measured in accordance with ASTM D1504. From the middle of the [polarization receptivity] opening of the container and the bottom, the side walls of the over the bottom, thickest part of the thickness T _max, the thickness of the thinnest portion and T _min, uneven thickness index T _max / T
It was calculated _{mi n.} The thickness unevenness of the container was evaluated according to the following standard using the above thickness unevenness index.

：: T _max / T _min is less than 2 ×: T _max / T _min is 2 or more −: Measurement was not possible because the sheet was broken [Deep drawability] And used as an index for deep drawability evaluation.

：: No break Δ: Crack or whitening occurs ×: Break [Reproducibility of mold shape] The reproducibility of the shape of the mold in the container was visually evaluated for the corner portion of the container according to the following criteria. .

：: The shape of the mold was sufficiently reproduced. ：: The corner portion was slightly rounded. ×: The corner portion was rounded. .

[0087]

[Table 1]

As is clear from the table, the results obtained using the resin A were as follows.
In the embodiment, the compressed air pressure is 3 kg / cm ^TwoLess and relatively low pressure
Excellent mold unevenness and deep drawability even under molding conditions, mold shape
Is reproducible. On the other hand, using resin A
Also, the compressed air pressure is 5kg / cm^TwoIn Comparative Example 1, the sheet
In Comparative Example 2 where the hot plate temperature was 115 ° C.
And good deep drawability, but good mold shape reproducibility
Inferior. In Comparative Examples 3 to 5 using resin B, Comparative Example 3
In Examples 4 and 4, the sheet was broken.
Since it is molded at a higher temperature (140 ° C.) than in Comparative Example 3,
Improved deep drawability and mold shape reproducibility
Is inferior in uneven thickness.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29L 22:00

Claims (4)

[Claims] 1. A temperature of 130 ° C. and an elongation rate of 0.0025 to
In the measurement of elongational viscosity in the range of 0.0035 sec ^-1 ,
Equations (1) to (3) Δlnλ _n / Δε = (lnλ _n2 −lnλ _n1 ) / (ε ₂ −ε ₁ ) ≧ 0.15 (1) λ _n = λ / λ _l (2) ε = ln ( l / l ₀ ) (3) (where, λ _n is a nonlinear parameter, λ is the elongational viscosity in the non-linear region, λ _l is the elongational viscosity in the linear region, ε is the Hencky elongation strain amount, and l ₀ and l are This is a method for producing a container for vacuum-pressure-forming a biaxially stretched sheet made of a styrene-based resin satisfying the relationship represented by the following expressions: ℃ or higher, compressed air pressure 3kg / cm ²
A method for producing a container to be molded below. 2. The method for producing a container according to claim 1, wherein the orientation relaxation stress of the biaxially stretched sheet is 3 to 6 kg / cm ² in both the longitudinal and transverse directions. 3. The following formula (4) H / (2 (A / π) ^1/2 ) (4) (where H represents the height (mm) of the container, and A represents the area of the opening of the container. (mm ²⁾ .π showing a is the circular constant.) a method of manufacturing a container according to claim 1, wherein a drawing ratio of the container is 0.4 to 1.2 represented by. 4. A container obtained by molding the biaxially stretched sheet according to claim 1, wherein the following formula (4) H / (2 (A / π) ^1/2 ) (4) H indicates the height (mm) of the container, A indicates the area (mm ² ) of the opening of the container, and π is the circular constant. container.