JP3742550B2 - Resin composition for thermoforming sheet and thermoforming sheet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a resin composition for a thermoforming sheet, a thermoforming sheet comprising the same, and a container. More specifically, the present invention relates to a thermoforming sheet resin composition used for applications requiring heat resistance and transparency, and a thermoforming sheet and a container comprising the same.
[0002]
[Prior art]
In the field of food packaging, safety is strictly required, and for example, it is required not to contain environmental hormones. In recent years, bisphenol A has been suspected of acting as an environmental hormone, but thermoplastic polyesters do not contain bisphenol A, are excellent in safety, and are widely used as packaging containers for beverages. For example, hollow containers obtained by thermoforming a sheet made of polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) are widely used. However, thermoformed products made of PET are inferior in heat resistance and have problems such as deformation or shrinkage of the molded product with hot water at 80 ° C., and cannot be used for food packaging applications that require heat treatment. Therefore, in this application, PET called C-PET which has improved heat resistance by crystallizing PET in a thermoforming process is used. However, when this C-PET is obtained by thermoforming, the obtained molded product becomes cloudy due to crystallization, and only a molded product with low transparency can be obtained.
[0003]
In food packaging applications, the contents are required to look beautiful, and transparency is required. Under such circumstances, a copolymer of polytetramethylene terephthalate (hereinafter sometimes abbreviated as “PBT”) is used in Japanese Patent Application Laid-Open No. 04-7119 in order to exhibit transparency and heat resistance at the same time. Thus, a method of heat treatment under special conditions has been proposed. However, this method is difficult to put into practical use because of high material costs and low productivity.
[0004]
[Problems to be solved by the invention]
This invention makes it a subject to provide the resin composition for thermoforming sheets which can shape | mold the container provided with outstanding transparency and heat resistance by thermoforming, the sheet | seat for thermoforming, and a container consisting thereof. It is another object of the present invention to provide a food packaging container having heat resistance that does not cause deformation even by heat treatment in a microwave oven or the like.
[0005]
[Means for Solving the Problems]
As a result of intensive studies, the inventors have found that a thermoforming sheet excellent in transparency and heat resistance can be obtained by blending PBT into PET and adjusting it to a specific melting point range. It was.
[0006]
That is, the present invention
Item 1) With respect to 100 parts by weight of a resin composition containing 83 to 100% by weight of a polyester component having a weight ratio of polyethylene terephthalate and polytetramethylene terephthalate of 10 to 50:90 to 50 per total resin component, inorganic and / Or a thermoforming sheet resin composition comprising 0.001 to 0.5 parts by weight of an organic phosphoric acid compound, wherein the melting point due to polyethylene terephthalate satisfies the following conditions: Resin composition for thermoforming sheet,
0 ≦ (Tm−Tm1) <12 ° C.
(However, Tm represents the melting point of polyethylene terephthalate, and Tm1 represents the melting point resulting from the polyethylene terephthalate of the resin composition.)
Item 2) The resin composition contains 1 to 17% by weight of a polyethylene terephthalate copolymer per total resin component in addition to the polyester component, and the polyethylene terephthalate copolymer is 1 to 30 mol% per total diol component. Item 2. The resin composition for thermoforming sheets according to Item 1, which is a polyethylene terephthalate copolymer containing cyclohexanedimethanol as a copolymerization component,
Item 3) It has a core layer (A) and a surface layer (B) that is in contact with both surfaces of the core layer (A), and the core layer (A) and the surface layer (B) are B layer / A layer / B A thermoforming sheet having a laminated structure in the order of the layers, wherein the core layer (A) is made of the resin composition for thermoforming sheets of Item 1 or 2, and the surface layer (B) is made of polyethylene terephthalate. Thermoforming sheet and Item 4) Container (Tic1-20 ° C) <T1 <(Tic1 + 30 ° C) obtained by thermoforming the thermoforming sheet of Item 3 under the following conditions:
T2> Tic1
T3 <Tic1
T1: Sheet heating temperature during thermoforming Tic1: Crystallization temperature caused by PBT crystallization during temperature rise by DSC method T2: Mold temperature during thermoforming T3: Cooling roll temperature during film formation.
[0007]
Hereinafter, the present invention will be described in detail.
[0008]
[Resin composition for thermoforming sheet]
Polyethylene terephthalate is a polyester having terephthalic acid as a dicarboxylic acid component of 90 mol% or more of all dicarboxylic acid components and ethylene glycol as a glycol component of 90 mol% or more of all glycol components, and is a total dicarboxylic acid component or total dicarboxylic acid. You may copolymerize a copolymerization component in 10 mol% or less of a component, Preferably it is 5 mol% or less of range.
[0009]
Polytetramethylene terephthalate is a polyester having terephthalic acid as a dicarboxylic acid component of 90 mol% or more of all dicarboxylic acid components and tetramethylene glycol as a glycol component of 90 mol% or more of all glycol components, You may copolymerize a copolymerization component in 10 mol% or less of all the dicarboxylic acid components, Preferably it is 5 mol% or less.
[0010]
The resin composition for thermoforming sheets of the present invention comprises a polyester component (P) in which the weight ratio of polyethylene terephthalate and polytetramethylene terephthalate is 10 to 50:90 to 50, preferably 20 to 40:80 to 60. The resin composition contains 83 to 100% by weight per total resin component. When the weight ratio of PET of the polyester component (P) is less than 10 and the weight ratio of PBT exceeds 90, the crystallinity is high and thermoforming cannot be performed. If the weight ratio of PET exceeds 50 and the PBT is less than 50, a transparent molded product cannot be obtained after thermoforming.
[0011]
When the polyester component (P) is less than 83% by weight based on the total resin components, the heat resistance is not exhibited due to the decrease in crystallinity, and a transparent molded product cannot be obtained after thermoforming.
[0012]
And in this invention, melting | fusing point resulting from the polyethylene terephthalate of the polyester component (P) of the said resin composition needs to satisfy the following conditions.
0 ≦ (Tm−Tm1) <12 ° C.
(However, Tm represents the melting point of polyethylene terephthalate, and Tm1 represents the melting point resulting from the polyethylene terephthalate of the resin composition.)
[0013]
In order to obtain a container having excellent transparency and heat resistance, it is necessary to satisfy the above-mentioned conditions for the melting point. If this condition is not satisfied, a thermoforming sheet excellent in transparency and heat resistance and a container made thereof cannot be obtained.
[0014]
Generally, when PET and PBT are melt-kneaded, a copolymer of-[PET]-[PBT]-is generated by transesterification. Since this copolymer has no crystallinity, sufficient heat resistance cannot be obtained when formed into a molded body.
[0015]
However, if the resin composition obtained by melt-kneading PET and PBT has a difference between the melting point due to PET and the melting point of PET alone of less than 12 ° C, preferably less than 8 ° C, the sheet for thermoforming and Furthermore, when a container is formed by thermoforming, a thermoforming sheet and container having sufficient crystallinity and high heat resistance can be obtained.
[0016]
If the melting point difference is 12 ° C. or more or the kneading is continued until the melting point is not observed and the transesterification reaction proceeds, the crystallinity of the resin composition is impaired, and sufficient heat resistance cannot be obtained.
[0017]
The melting point difference (Tm−Tm1) is preferably 3 ° C. or more. When the melting point difference is 3 ° C. or more, particularly good compatibility between PET and PBT can be obtained, and a sheet with further excellent transparency can be obtained.
[0018]
Therefore, the present invention satisfies the following conditions as a preferred embodiment.
3 ° C. ≦ (Tm−Tm1)
[0019]
[Inorganic and / or organic phosphoric acid compounds]
In the resin composition for thermoforming sheets of the present invention, a resin composition comprising 83 to 100% by weight of a polyester component having a weight ratio of polyethylene terephthalate and polytetramethylene terephthalate of 10 to 50:90 to 50 per total resin component. 0.001 to 0.5 parts by weight of an inorganic and / or organic phosphoric acid compound is blended with respect to 100 parts by weight. When the blending amount of the inorganic and / or organic phosphoric acid compound is less than 0.001 part by weight, the transesterification reaction is promoted during film formation, and transparency and heat resistance cannot be achieved at the same time. If it exceeds 0.5 parts by weight, the mechanical properties of the sheet may be impaired, and the sheet may become cloudy.
[0020]
Examples of the inorganic and / or organic phosphoric acid compounds include the following compounds. An example of the inorganic phosphoric acid compound is sodium dihydrogen phosphate dihydrate. Examples of the organic phosphate compound include triphenyl phosphite, trioctadecyl phosphite, trisnonylphenyl phosphite, triuraryl trithiophosphite, bis (2,4-di-t-butylphenyl) pentaerythritol-diphosphite, bis ( Examples thereof include 3-methyl-1,5-di-t-butylphenyl) pentaerythritol-diphosphite, tris (2,4-di-t-butylphenyl) phosphite, and trimethylphosphite.
[0021]
As the inorganic phosphate compound, sodium dihydrogen phosphate is particularly preferable. As the organic phosphate compound, trimethyl phosphite, triphenyl phosphite, and bis (2,4-di-t-butylphenyl) pentaerythritol-diphosphite are particularly preferable. As the inorganic and / or organic phosphate compound, sodium dihydrogen phosphate dihydrate is particularly preferable.
[0022]
[Polyethylene terephthalate copolymer]
In a preferred embodiment, the resin composition for a thermoforming sheet of the present invention comprises 1 to 17% by weight of a polyethylene terephthalate copolymer (Q) per total resin component in addition to the polyester component (P). And the polyethylene terephthalate copolymer is a polyethylene terephthalate copolymer containing 1 to 30 mol% of cyclohexanedimethanol as a copolymer component for all diol components. By containing 1 to 17% by weight of the polyethylene terephthalate copolymer (Q), a thermoforming sheet and a container having even better impact resistance can be obtained.
[0023]
[Additives, etc.]
You may mix | blend a coloring agent etc. including various stabilizers with the resin composition in the range which does not impair the effect of this invention.
[0024]
[Multilayer sheet]
The resin composition for thermoforming sheets of the present invention can be used as a thermoforming sheet. The thermoforming sheet may be a multilayer sheet or a single layer sheet, but is preferably a multilayer sheet from the viewpoint of cost and formability.
[0025]
When it is set as a multilayer sheet, the preferable aspect of the sheet | seat for thermoforming has a core layer (A) and the surface layer (B) which exists in contact with both surfaces of a core layer (A), a core layer (A) and The surface layer (B) is a thermoforming sheet having a laminated structure in the order of B layer / A layer / B layer, and the core layer (A) uses the resin composition for thermoforming sheet of the present invention, and the surface layer In (B), polyethylene terephthalate is used. On the other hand, when polyethylene terephthalate is used for the core layer (A) and the resin composition for thermoforming sheet of the present invention is used for the surface layer (B), the surface layer is formed by a temperature gradient in the thickness direction when heated to the moldable temperature. Tends to crystallize, and as a result, it may become difficult to form, and is not very preferable as a multilayer sheet.
[0026]
[Production method]
The polyester component (P) PET and PBT and the polyethylene terephthalate copolymer (Q) used in the present invention can be produced using a known polyester polymerization process.
[0027]
A single-layer or multilayer sheet for thermoforming can be produced by applying a known sheet production method to a composition obtained by mixing the above polyester by a known method.
[0028]
In order to produce the thermoforming sheet of the present invention, it is necessary to form an amorphous sheet. For this reason, when forming a sheet, it is preferable to rapidly cool the resin composition melted and discharged from the die part to form a sheet, and a cooling roll for cooling the resin discharged from the die. It is preferable to set the temperature to Tic1 or lower. By using a cooling roll having a temperature in this range, white turbidity due to crystallization of PBT can be suppressed.
[0029]
The thermoforming sheet of the present invention can be thermoformed by known vacuum forming, plug-assisted vacuum forming, vacuum / pressure forming, etc. to form a thermoformed product such as a container.
[0030]
Thermoforming for obtaining a thermoformed product is performed by heating within a range where PBT does not crystallize during thermoforming heating, tracing the mold, and then crystallizing PBT at the mold temperature. Therefore, it is preferable that the mold temperature at the time of thermoforming is Tic1 or more.
[0031]
When PBT is crystallized during heating, the thermoforming sheet becomes cloudy and the thermoformability is extremely reduced. Therefore, heating during thermoforming heating is performed within a range in which PBT does not crystallize. For this reason, it is preferable that the heating temperature of the sheet | seat at the time of thermoforming shall be Tic1 + 30 degreeC or less.
[0032]
In order to obtain a container excellent in transparency and heat resistance, it is preferable to promote crystallization after mold tracing. For this reason, the mold temperature is preferably Tic1 or more, and is lower than the crystallization temperature when the PET alone is heated. By setting the mold temperature within this range, a molded product having excellent transparency and heat resistance can be obtained.
[0033]
Therefore, the present invention is also a container obtained by thermoforming a thermoforming sheet under the following conditions.
(Tic1-20 ° C) <T1 <(Tic1 + 30 ° C)
T2> Tic1
T3 <Tic1
T1: Sheet heating temperature during thermoforming Tic1: Crystallization temperature caused by PBT crystallization during temperature rise by DSC method T2: Mold temperature during thermoforming T3: Cooling roll temperature during film formation
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[resin]
The following resins were used as the resin.
Resin 1: Polyethylene terephthalate having an intrinsic viscosity of 0.75 measured at 35 ° C. in orthochlorophenol, wherein the acid component constituting the polyethylene terephthalate polyester is terephthalic acid and the glycol component is ethylene glycol.
Resin 2: Polytetramethylene terephthalate whose polytetramethylene terephthalate polyester is composed of terephthalic acid as the acid component and 1,4-butanediol as the glycol component and has an intrinsic viscosity of 1.02 measured at 35 ° C. in orthochlorophenol .
Resin 3: Cyclohexanedimethanol copolymer Polyethylene terephthalate polyester is a copolymer obtained by copolymerizing 4 mol% of cyclohexanedimethanol with terephthalic acid as the main component and glycol component as the main component of glycol, and the total mol amount of glycol component. Polymerized polyethylene terephthalate.
[0035]
[DSC measurement]
DSC measurement was performed as follows.
The sheet was subjected to transition temperature measurement by DSC method according to JIS K-7121. Regarding the crystallization temperature at the time of temperature increase, the crystallization exothermic peak measured at the lowest temperature when the sheet was measured as it was was defined as the PBT Tic peak.
Regarding the melting point, when two melting endothermic peaks are observed in the resin composition, the peak appearing on the high temperature side (usually around 240 ° C.) is taken as the melting point peak due to PET, and it appears on the low temperature side (usually around 220 ° C.) This peak was taken as the melting point peak due to PBT. The measurement was performed at a heating rate of 20 ° C./min.
[0036]
[Sheet Formation]
The sheet was formed as follows.
The raw material polyester was extruded from a T die connected to a single-shaft 40 mmΦ extruder, and contacted by a cooling roll to obtain a 0.3 mm unstretched sheet. A temperature regulator is connected to the cooling roll, and the cooling temperature can be freely controlled.
Tm was appropriately changed by using a polyester that was pre-kneaded and partially transesterified before the sheet was produced.
[0037]
[Thermoforming]
A box-shaped product having a length of 21 cm, a width of 15 cm, and a depth of 4 cm was formed by vacuum forming. The sheet heating temperature was changed, the traceability to the mold was visually confirmed, and the moldability was evaluated.
[0038]
[Haze]
The haze (haze) according to JIS K-7361 was determined.
[0039]
[Heat resistance evaluation]
A box-shaped container-shaped molded product obtained by thermoforming was charged with water at a volume ratio of 30%, heated at an output of 500 W for 6 minutes in a household microwave oven, and the degree of deformation was visually evaluated.
[0040]
[Example 1]
A resin composition for thermoforming sheets, in which 0.2 parts by weight of sodium dihydrogen phosphate was blended with 100 parts by weight of a resin composition composed of 30% by weight of PET and 70% by weight of PBT, was formed into a sheet at a cooling roll of 20 ° C. The obtained sheet had a haze of 1.9%, Tic1 of 63 ° C., a melting point Tm2 attributed to PBT of 218 ° C., and a melting point Tm1 attributed to PET of 247 ° C.
[0041]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to obtain a thermoformed product. The obtained molded article had a haze of 4.1%, had transparency, and had good mold traceability, that is, moldability. When the heat resistance of the molded product was evaluated, no deformation due to heating was observed.
[0042]
[Example 2]
In the same manner as in Example 1, a resin composition for thermoforming sheet, in which 0.2 parts by weight of sodium dihydrogen phosphate was blended with 100 parts by weight of a resin composition consisting of 40 wt% of PET and 60 wt% of PBT, was cooled at 20 ° C. To form a film. The obtained sheet had a haze of 1.5%, Tic1 was 64 ° C., the melting point Tm2 attributed to PBT was 217 ° C., and the melting point Tm1 attributed to PET was 245 ° C.
[0043]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to obtain a molded product. The obtained molded product had a haze of 3.7%, had transparency, and had good mold traceability, that is, moldability. When the heat resistance of the molded product was evaluated, no deformation due to heating was observed.
[0044]
[Example 3]
A resin composition for thermoforming sheets, in which 10 parts by weight of copolymerized PET of the above resin 3 is blended with 100 parts by weight of a resin composition comprising 30% by weight of PET and 70% by weight of PBT, and further 0.2 part by weight of sodium dihydrogen phosphate is blended. The product was formed into a sheet at 20 ° C. on a cooling roll.
[0045]
The obtained sheet had a haze of 1.6%, Tic1 of 65 ° C., a melting point Tm2 attributed to PBT of 218 ° C., and a melting point Tm1 attributed to PET of 246 ° C.
[0046]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to produce a molded product. The obtained molded article had a haze of 3.6%, had transparency, and had good mold traceability, that is, moldability. When the heat resistance of the molded product was evaluated, no deformation due to heating was observed.
[0047]
[Example 4]
A resin composition for thermoforming sheets in which 0.2 parts by weight of sodium dihydrogen phosphate is blended with 100 parts by weight of a resin composition consisting of 30 wt% PET and 70 wt% PBT as a core layer, and a resin composition consisting of 100 wt% PET as a surface layer, Using a multilayer coextrusion die, a two-type three-layer sheet having a core layer thickness of 80% of the total thickness was formed at a cooling roll of 20 ° C. The obtained sheet had a haze of 2.2%, Tic1 of 64 ° C., a melting point Tm2 attributed to PBT of 218 ° C., and a melting point Tm1 attributed to PET of 245 ° C.
[0048]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to obtain a molded product. The obtained molded product had a haze of 1.2%, good transparency, and good mold traceability, that is, good moldability. When the heat resistance of the molded product was evaluated, no deformation due to heating was observed.
[0049]
[Comparative Example 1]
A sheet was formed from a resin composition comprising 100 wt% of PET at a cooling roll of 20 ° C. The obtained sheet had a haze of 1.1%, no Tic1 was observed, and the melting point Tm1 attributed to PET was 249 ° C. Tm1 at this time is the melting point of PET alone.
[0050]
The obtained sheet was thermoformed at a heating temperature of 100 ° C. and a mold temperature of 20 ° C. to obtain a molded product. The haze of the obtained molded product was 1.2%, the transparency was good, and the mold traceability, that is, the moldability was also good. When the heat resistance of this molded product was evaluated, the contents were spilled because it was significantly deformed by heating and thermally contracted.
[0051]
[Comparative Example 2]
In the same manner as in Example 1, a sheet of a resin composition composed of PET 30 wt% and PBT 70 wt% was formed on a cooling roll 20 ° C. and thermoformed at a mold temperature 20 ° C.
[0052]
The haze of the obtained molded product was 2.1%, had transparency, and had good mold traceability, that is, moldability. When the heat resistance of this molded product was evaluated, it was deformed until the softening progressed and the contents spilled.
[0053]
[Comparative Example 3]
Pellets preliminarily kneaded with a resin composition consisting of 30 wt% PET and 70 wt% PBT were again put into an extruder, and a sheet was formed at a cooling roll of 20 ° C.
The obtained sheet had a haze of 1.7%, Tic1 was 62 ° C., the melting point Tm2 attributed to PBT was 218 ° C., and the melting point Tm1 attributed to PET was 228 ° C.
[0054]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to obtain a molded product. This molded article had a haze of 1.8%, good transparency, and good mold traceability, that is, moldability. When the heat resistance of this molded product was evaluated, the contents were spilled because it was significantly deformed by heating and thermally contracted.
[0055]
[Comparative Example 4]
A sheet of a resin composition composed of 30 wt% PET and 70 wt% PBT was formed on a cooling roll at 80 ° C. The obtained sheet had a haze of 16.2%, became cloudy, Tic1 was not observed, the melting point Tm2 attributed to PBT was 221 ° C., and the melting point Tm1 attributed to PET was 246 ° C.
[0056]
The obtained sheet was thermoformed at a heating temperature of 75 ° C. and a mold temperature of 100 ° C. to obtain a molded product, but it was difficult to form because of poor traceability.
[0057]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the resin composition for thermoforming sheets which can shape | mold the container provided with the outstanding transparency and heat resistance by thermoforming, the sheet | seat for thermoforming, and a container which consist thereof can be provided. Furthermore, it is possible to provide a food packaging container having heat resistance that does not cause deformation even by heat treatment in a microwave oven or the like.

Claims (4)

Inorganic and / or organic with respect to 100 parts by weight of the resin composition containing 83 to 100% by weight of the polyester component having a weight ratio of polyethylene terephthalate and polytetramethylene terephthalate of 10 to 50:90 to 50 per total resin component A thermoforming sheet resin composition comprising 0.001 to 0.5 parts by weight of a phosphoric acid compound, wherein the melting point resulting from polyethylene terephthalate satisfies the following conditions: Resin composition for sheet.
0 ≦ (Tm−Tm1) <12 ° C.
(However, Tm represents the melting point of polyethylene terephthalate, and Tm1 represents the melting point resulting from the polyethylene terephthalate of the resin composition.) The resin composition contains 1 to 17% by weight of a polyethylene terephthalate copolymer per total resin component in addition to the polyester component, and the polyethylene terephthalate copolymer is 1 to 30 mol% of cyclohexane di per total diol component. The resin composition for thermoforming sheets according to claim 1, which is a polyethylene terephthalate copolymer containing methanol as a copolymerization component. It has a core layer (A) and a surface layer (B) existing in contact with both surfaces of the core layer (A), and the core layer (A) and the surface layer (B) are in the order of B layer / A layer / B layer. A thermoforming sheet having a laminated structure in which the core layer (A) comprises the resin composition for thermoforming sheets according to claim 1 or 2 and the surface layer (B) comprises polyethylene terephthalate. Sheet. A container formed by thermoforming the thermoforming sheet according to claim 3 under the following conditions.
(Tic1-20 ° C) <T1 <(Tic1 + 30 ° C)
T2> Tic1
T3 <Tic1
T1: Sheet heating temperature during thermoforming Tic1: Crystallization temperature caused by PBT crystallization during temperature rise by DSC method T2: Mold temperature during thermoforming T3: Cooling roll temperature during film formation