JP3811636B2 - Polyester laminated sheet and molded product comprising the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester laminated sheet excellent not only in heat resistance and impact resistance but also in recyclability and economy, and a molded article comprising the same.
[0002]
[Prior art]
A polyester sheet (A-PET) having excellent transparency is rapidly used as a packaging material since the packaged contents can be seen. In particular, because it is excellent in food safety and does not generate harmful gases during combustion, it is widely used in food packaging containers and blister packs such as umeboshi, tokoroten, mozuku, etc. as an alternative material to vinyl chloride that has been used in the past. ing.
[0003]
However, since A-PET made of polyethylene terephthalate has a low heat resistance temperature of about 65 ° C., it could not be used in fields requiring heat resistance. For example, when used for a lunch box lid, it cannot be used because the container is deformed when heated in a microwave oven.
[0004]
Thus, many attempts have been made to improve the heat resistance of A-PET. For example, the method of laminating a polyarylate resin having a high glass transition temperature (Japanese Patent Laid-Open No. 1-200959) has good heat resistance and mechanical properties of the sheet, but bisphenol A is used as a raw material. There is concern about elution of environmental hormones. As a countermeasure, polyester with low crystallinity is further laminated on the outermost layer, but a special extruder with three types and five layers is required, and the packaging material becomes very expensive in terms of cost. Is not generally used. Similarly, a method of laminating a PEN resin (polyethylene naphthalate) having a high glass transition temperature (Japanese Patent Laid-Open No. 9-118323) has also been studied, but the PEN resin is very brittle when not stretched and is simply laminated. The actual situation is that the impact strength is drastically reduced and the practical strength is not obtained.
[0005]
Therefore, attempts have been made to use copolymerized PEN resins in order to improve the ease of cracking, which is a drawback of PEN resins (Japanese Patent Laid-Open Nos. 10-16160 and 10-315417). However, when the copolymerization component is increased, the impact resistance is improved, but on the other hand, the high glass transition temperature (about 115 ° C.) that is characteristic of the PEN resin is lowered, and the heat resistance of the sheet and the container obtained therefrom is also improved. It will decline. In addition, the PEN resin that has undergone special copolymerization is very expensive and therefore is inferior in virginity. Therefore, at present, polyester-based heat-resistant containers having practical impact resistance strength without impairing the food safety, transparency, economy, and recyclability of A-PET have not yet been widely used.
[0006]
[Problems to be solved by the invention]
As a result of intensive investigations to solve such conventional problems, the present inventors have arrived at the present invention, and the object is not only heat resistance and impact resistance, but also recycling. It is in obtaining the polyester laminated sheet excellent also in property and economical efficiency, and a molded article consisting thereof.
[0007]
[Means for Solving the Problems]
The above-mentioned purpose is that polyethylene naphthalate (B) having an intrinsic viscosity of 0.40 to 0.70 is formed on at least one surface of a base material layer made of polyester (A) having an intrinsic viscosity of 0.50 to 1.0. The polyester laminated body is laminated, and the thickness of the (B) layer is 5 to 35 μm, and is achieved by a polyester laminated sheet and a molded article comprising the same.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The intrinsic viscosity of the polyethylene naphthalate used in the layer (B) of the polyester laminate of the present invention needs to be 0.40 or more as measured in a phenol / tetrachloroethane mixed solvent having a measurement temperature of 20 ° C. and a weight ratio of 60/40. And particularly preferably 0.45 or more. This is because if it is less than 0.40, the mechanical strength of the entire sheet is lowered due to the notch effect. On the other hand, it is necessary to be 0.70 or less, preferably 0.60 or less. This is because when the intrinsic viscosity exceeds 0.70, the melt viscosity is remarkably increased, so that the film-forming property is lowered.
[0009]
The polyethylene naphthalate used for the layer (B) is preferably homopolyethylene naphthalate from the viewpoint of economy and heat resistance. When the thickness of the (B) layer is within the specified range, the impact resistance of the sheet and the molded product is high, so that copolymerization for the purpose of improving the impact as conventionally performed is not necessary. However, dicarboxylic acid components such as isophthalic acid, adipic acid, diphenyl carboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid, naphthalenedicarboxylic acid, diethylene glycol, hexamethylene glycol, trimethylene glycol, etc. A small amount of glycol components such as propylene glycol, cyclohexanedimethanol, neopentyl glycol, butylene glycol can be copolymerized.
[0010]
About the heat resistance and impact resistance of a polyester laminated sheet and a molded product made thereof, the influence of the PEN resin laminated on the sheet surface (B) layer is large. Therefore, the polyester used in the (A) layer of the laminate of the present invention may be that used in ordinary A-PET, and it is not necessary to use a special one. From an economical point, it is preferable to use homo-PET. On the other hand, even if a resin having a high impact property is used for the (A) layer in order to improve the impact strength, if the (B) layer thickness is outside the range of the present invention, the impact strength of the sheet is extremely lowered and is not effective.
[0011]
The intrinsic viscosity of the polyester used in the layer (A) of the polyester laminated sheet of the present invention must be 0.50 or more as measured in a phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40 at 20 ° C. Yes, particularly preferably 0.60 or more. This is because if it is less than 0.50, the mechanical strength decreases. On the other hand, it is necessary to be 1.0 or less, preferably 0.80 or less. This is because even if the intrinsic viscosity exceeds 1.0, a significant improvement in mechanical strength cannot be expected, and it is necessary to use an expensive raw material with a high IV, which is not economically advantageous.
[0012]
Since the polyester laminated sheet of the present invention has a high glass transition temperature of the (B) layer, it is necessary to increase the thermoforming temperature by about 30 to 50 ° C. compared to ordinary A-PET. For this reason, when the crystallization speed of the core layer is high, the core layer may be crystallized at the time of thermoforming, and transparency may be lowered. For this reason, the one where the crystallinity of polyester used for (A) layer is low is preferable. As a guide, the peak temperature (Tc) of the crystallization temperature by DSC is preferably 130 ° C. or higher, particularly preferably 140 ° C. or higher. When the peak temperature (Tc) of the crystallization temperature is less than 130 ° C., the molded product is crystallized when the laminated sheet is thermoformed, and the transparency tends to decrease.
[0013]
In the case of producing a polyester laminated sheet only from a virgin raw material, a highly transparent thermoformed product can be obtained even with homo-PET, as with a normal A-PET sheet. However, when a large amount of recycled PET resin is blended, the crystallinity tends to be slightly high and Tc tends to decrease. In such cases, dicarboxylic acid components such as isophthalic acid, adipic acid, diphenyl carboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, sebacic acid, naphthalenedicarboxylic acid, diethylene glycol, hexamethylene glycol, trimethylene glycol, propylene glycol It can be improved by reducing the crystallinity of the polyester used in the layer (A) by copolymerizing a small amount of glycol components such as cyclohexanedimethanol, neopentyl glycol, butylene glycol and the like.
[0014]
Furthermore, a heat stabilizer, a fluidity improver, an ultraviolet absorber, an antistatic agent, an antifogging agent, and the like can be added to the polyester as long as transparency is not lowered. Further, when matting is required, a colorant such as titanium dioxide, calcium carbonate, iron oxide, carbon black, etc. can be contained.
[0015]
Impact strength of polyester laminate by laminating PEN resin to the surface layer sheet and molded article made therefrom, there are significant PEN layer thickness dependency, the PEN resin layer thickness is increased the impact strength tends to decrease. This tendency is hardly improved even if the IV of the resin used for the core layer is increased. When the thickness of at least one PEN resin layer laminated on a polyester laminated sheet and a molded product comprising the polyester exceeds 35 μm, a drop in impact strength becomes a problem, and it is difficult to maintain a practical level of impact strength when used as a container. It becomes. Further, when the thickness exceeds 50 μm, the impact strength is remarkably reduced, and the sheet breaks during film formation or cracks occur when the thermoformed container is punched, making it difficult to produce the container itself.
[0016]
On the other hand, the thickness of the PEN resin layer to be laminated to a polyester laminated sheets and moldings made of it in the case of 35μm or less, it is possible to hold the impact strength of the practical level. Particularly in the case of 25μm or less, lowering the impact strength of the polyester laminated sheets and moldings made therefrom becomes very small, the lack of impact strength is no problem as a problem in the polyester laminated sheet and molded article made therefrom were laminated PEN resin And various processes similar to A-PET can be performed.
[0017]
Although PEN resin layer stacked from the impact strength point preferably thin, PEN at least one layer thickness of the PEN resin layer to be laminated to a polyester laminated sheet and molded article made therefrom in view of heat resistance imparting are continuously above 5μm It is necessary to form a resin layer. From the standpoint of quality stability, the total thickness of the laminated PEN resin layers is preferably 10 μm or more, particularly preferably 13 μm or more.
[0018]
Specifically, the polyester laminated sheet of the present invention is obtained by laminating the (B) layer on the (A) layer, or the (B) layer, the (A) layer, the (B) layer and the three-layer structure, etc. Is mentioned.
[0019]
In any of the above laminated forms, the thickness of the (B) layer of the polyester laminated sheet and molded product of the present invention needs to be 5 to 35 μm, preferably 10 to 30 μm, particularly preferably 13 to 25 μm. It is. Even when the (B) layer is laminated on both sides of the (A) layer, excellent impact resistance can be maintained as long as the thickness of each layer is within the above range.
[0020]
Even if the PEN resin thickness of the polyester laminated sheet laminated with the PEN resin exceeds the above range and the polyester laminated sheet is inferior in impact resistance, the PEN resin layer thickness in the container is the above by performing thermoforming and receiving stretching. when entering the range, the impact resistance is improved.
[0021]
Like a jelly container that performs high-temperature filling or a lunch container body that heats in a microwave oven,
When a load is applied to the container, the total thickness of the PEN resin layer of the heat-resistant container needs to be at least 20 μm or more in total, but the container itself becomes hot like the upper lid of the lunch box, but the load is In the case where it is only necessary to maintain the shape of the container, the heat resistance can be maintained by forming a continuous PEN resin layer of 5 μm or more. In the case of a container shape in which the area of the portion without ribs is wide, the total thickness of the PEN resin layer needs to be relatively thick, but sufficient heat resistance can be imparted by laminating 10 μm or more.
[0022]
As described above, both practical heat resistance and impact resistance can be realized only in a specific lamination thickness range, but this range is constant without being influenced by the thickness of the entire sheet. As a result, the ratio of the PEN resin laminated on the surface layer to the entire sheet varies greatly depending on the thickness of the sheet. For example, when PEN resin is laminated on both sides of a 100 μm sheet (PEN resin layer 35 μm / PET resin layer 30 μm / PEN resin layer 35 μm), the proportion of PEN is 70%, but on both sides of the 1000 μm sheet When the PEN resin is laminated (PEN resin layer 15 μm / PET resin layer 970 μm / PEN resin layer 15 μm), the proportion of PEN is only 3%.
[0023]
Conventionally, in consideration of heat resistance, moldability, and economy, there are many examples in which the heat-resistant layer is preferably about 10 to 30%, but in the configuration of the present invention, the ratio of the skin layer and the impact resistance are increased. Has no correlation. For example, a 1000 μm laminated sheet in which 50 μm of PEN resin is laminated on one side has a remarkably low impact strength and is not suitable for practical use even though the heat-resistant layer is only 5%.
[0024]
From the viewpoint of thermoformability and heat resistance of the polyester laminated sheet of the present invention and a molded product made from the polyester laminated sheet , the PEN resin is preferably laminated on both sides of the polyester laminated sheet and the molded product made from the polyester laminated sheet. Particularly preferred are a polyester laminated sheet in which a layer (B) of 13 to 25 μm is laminated on both sides of the layer (A) and a molded product comprising the same.
[0025]
The total thickness of the polyester laminated sheet of the present invention and the molded product comprising the same is not particularly limited, but is usually preferably 50 to 2000 μm, particularly preferably 150 to 1000 μm. The polyester laminated sheet can be obtained by, for example, melt-extruding with an ordinary polyester extruder such as a single-screw extruder or a twin-screw vent extruder and cooling the molten resin with a cooling drum. The polyester laminated sheet is preferably cooled as quickly as possible in order to prevent deterioration of transparency and thermal adhesiveness due to crystallization, and the haze is preferably 3% or less.
[0026]
The polyester laminated sheet of the present invention can use a known coextrusion apparatus having a feed block die, a multi-manifold die and the like. Moreover, although it can manufacture by well-known techniques, such as a melt lamination and a dry lamination, co-extrusion is preferable from the quality of a polyester laminated sheet .
[0027]
In addition, as a film forming method, there are a method of sandwiching and cooling between metal rolls (touch roll method), an electrostatic application method, an air knife method, etc., but the touch roll method is used from the viewpoint of glossiness and thickness uniformity of the polyester laminated sheet. preferable.
[0028]
Moreover, there is no particular problem with applying a necessary amount of silicone or antifogging agent for preventing blocking or imparting antifogging properties.
[0029]
In-line recycling is generally used in A-PET to crush the skeleton part punched out from the ear part and thermoformed container that are cut when the polyester laminated sheet is cut into a predetermined width during film formation, In this invention, even if it mix | blends with (A) layer within the range which does not reduce the haze of a sheet | seat extremely, it is satisfactory. It is also possible to increase the compatibility of the resin and improve the transparency by copolymerizing a small amount of each of the PEN resin and the PET resin to be used. However, even if homo-PEN resin is used for the (B) layer and homo-PET resin is used for the (A) layer, there is no significant decrease in sheet haze due to the selection of the film forming temperature conditions. There is no problem in blending the skeleton obtained by punching the container into the layer (A).
[0030]
The molded product of the present invention may use any method such as vacuum molding, pressure molding, hot plate molding, plug assist molding, reverse draw molding, air slip molding, or a combination of these.
[0031]
【The invention's effect】
The polyester laminated sheet of the present invention and a molded product comprising the same maintain properties inherent to A-PET such as transparency, food safety, and recyclability, and are not only excellent in heat resistance but also economical. Ideal for heat-resistant packaging containers, especially for lunch boxes and prepared food lids.
[0032]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to this. Each characteristic value was measured according to the following method.
[0033]
(1) Intrinsic viscosity (IV of polyester laminated sheet and molded product comprising it )
The measurement was carried out using a phenol / tetrachloroethane mixed solvent having a weight ratio of 60/40 at a concentration of 1.0 g / dl at 20 ° C.
[0034]
(2) Layer thickness The layer thickness was determined by observing the cross section of a sheet and a molded product comprising the sheet with a polarizing microscope.
[0035]
(3) Haze of Sheet and Molded Product Haze meter NDH-20D manufactured by Nippon Denshoku Co., Ltd. was used, and the haze (cloudiness value) of the sheet and molded product was measured by a method according to JIS-K-7105.
[0036]
(4) Heat resistance of the container The thermoformed container is left in an oven at 100 ° C. for 10 minutes,
○ No deformation
The deformed one was evaluated as x.
[0037]
(5) Crystallization peak temperature (Tc)
Measurement was performed by a method according to JIS-K-7105 using a differential differential calorimeter (model DSC-7) manufactured by PerkinElmer. The quenched, substantially amorphous sheet was measured in a nitrogen stream at a heating rate of 10 K / min, and the crystallization peak temperature (Tc) was determined.
[0038]
(6) Impact strength of polyester laminated sheet and molded product made from it
A test piece of 90 mm in length and 90 mm in width is prepared from a polyester laminated sheet and a molded product made from the polyester sheet (the molded product is produced by cutting out the top plate portion of the container), and a surface impact tester (hydroshot) with a thermostatic bath manufactured by Shimadzu Corporation is used. The fracture energy at 20 ° C. was measured under the conditions of a punching speed of 5 m / sec, a punching punch diameter of 13 mm, and a die diameter of 3 inches.
○ with a breakdown energy of 4.0 kJ / m or more
Δ from 2.5 kJ / m to less than 4 kJ / m
Those less than 2.5 kJ / m were evaluated as x.
[0039]
The PET resin was submerged from the main extruder under the conditions of a set temperature of 295 ° C. and the vacuum of the vent part of the twin screw extruder at 667 Pa. From the extruder, melt extrusion was performed from a T die using a multilayer extruder. The ears of the sheet cut to obtain a sheet having a predetermined width were returned to the core layer. The melt-extruded resin was cooled by a touch roll method to obtain polyester laminated sheets of various configurations of 2 types and 3 layers. Further, 10 mg / m ^{2 of} silicone was applied to prevent blocking.
[0040]
For physical property evaluation, a molded product for a lid of a lunch box with a length of 135 mm × width 190 mm and a depth of 32 mm was produced using a vacuum / pneumatic molding machine with plug assist (thermoforming conditions: sheet surface temperature measured with an infrared radiation thermometer) 150 ° C., mold temperature 35 ° C., vacuum degree 8000 Pa).
[0041]
Comparative Examples 1-7
A sheet in which the PEN resin is laminated on the surface layer of the sheet tends to have a reduced impact strength. When the thickness of the PEN resin layer exceeds a specified value, the impact strength of the sheet and the molded product is remarkably low, and a practical level strength is obtained. I understand that there is no. Even if a high PIV resin is used for the PEN resin of the surface layer or a copolyester having excellent impact resistance is used for the core layer (PETG6763 1,4 cyclohexane dimethanol 33 mol% copolyester manufactured by Eastman) It is hardly seen. Further, as can be seen from Comparative Example 4, even if the ratio of the PEN resin layer to the entire sheet is low, the impact strength is extremely low when the thickness of the PEN resin layer exceeds the specified value. It can be seen that the property greatly depends on the thickness of the PEN resin laminated on the surface layer.
[0042]
Examples 1-4
It can be seen that when the thickness of the PEN resin layer on the surface layer of the sheet is within the specified range, the impact resistance is excellent, and a practical strength can be maintained without using a specially copolymerized PEN resin. It can also be seen that the heat resistance of the container is sufficient for an upper lid application where no load is applied.
[0043]
[Table 1]

Claims (2)

Polyester in which polyethylene naphthalate (B) having an intrinsic viscosity of 0.40 to 0.70 is laminated on at least one surface of a base material layer made of polyester (A) having an intrinsic viscosity of 0.50 to 1.0. the thickness of a laminated sheet, and (B) layer is a polyester laminated sheet, which is a 5 to 35 m. Polyester in which polyethylene naphthalate (B) having an intrinsic viscosity of 0.40 to 0.70 is laminated on at least one surface of a base material layer made of polyester (A) having an intrinsic viscosity of 0.50 to 1.0. a laminated sheet, and the thickness of the layer (B), the molded article comprising the polyester laminated sheet, which is a 5 to 35 m.