JPS6141749B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermoplastic resin sheet for vacuum forming. More specifically, the present invention relates to a sheet with improved vacuum forming properties, which is made by laminating a stretched thermoplastic resin film to an unstretched thermoplastic resin sheet. Thermoplastic resin sheets are used as materials for manufacturing food containers, other containers, or other molded products by forming methods such as vacuum forming or pressure forming. Among thermoplastic resin sheets, sheets made of polyolefin resins, especially polypropylene resins, are suitable for so-called secondary processing methods such as vacuum forming or pressure forming (hereinafter referred to as "vacuum forming, etc."). It is inferior to thermoplastic resin sheets made of hard vinyl chloride resin or polystyrene in terms of physical properties. In order to improve this drawback caused by polypropylene resin (hereinafter referred to as polypropylene), the following improvement methods are known. In other words, when manufacturing the sheet, MFR
(melt flow rate) is used,
Alternatively, low density polyethylene (hereinafter referred to as LDPE) or high density polyethylene (hereinafter referred to as HDPE) may be mixed with polypropylene. However, when such improvements are implemented, although the processability for vacuum forming etc. (hereinafter referred to as "vacuum formability") is improved to some extent, another drawback is that the transparency, rigidity and other physical properties of the molded product are reduced. invite. On the other hand, it is widely practiced to bond thermoplastic resin films (of the same or different types) to each other. Examples of practical use include cellophane and
LDPE film (hereinafter referred to as "cellophane/LDPE film"), biaxially oriented polypropylene film (hereinafter referred to as OPP)/LDPE film, OPP/
The main material is unstretched polypropylene film (hereinafter referred to as CPP), and the purpose of lamination is to improve the properties of such films, such as heat sealability, moisture resistance, and air resistance. As is obvious from these purposes, these bonded films are used as packaging materials or similar uses.
Further, the thickness of these laminated films is that each film of about 30 μm or less is laminated together, and is different from the sheet of the present invention described later in terms of thickness. The present inventors have made extensive research in order to solve the above-mentioned drawbacks when using thermoplastic resin sheets, particularly polyolefin resin sheets, especially polypropylene resin sheets, for vacuum forming by a method different from the known methods described above. As a result, it was discovered that the above-mentioned drawbacks (including new drawbacks associated with known methods) can be overcome by laminating a thermoplastic resin film that has been stretched to a certain extent to an unstretched thermoplastic resin sheet, and the present invention has been developed. completed. As is clear from the above description, an object of the present invention is to provide a new use for a thermoplastic resin laminated sheet. Another object of the present invention is to provide a vacuum-formed product with good physical properties obtained by secondary processing the sheet. Other objectives will become clear from the description below. The present invention provides the following features: (1) An unstretched thermoplastic resin sheet and a stretched thermoplastic resin film are bonded together, and the ratio of the thickness of the stretched thermoplastic resin film to the bonded product is 20% or less 1.0 % or more thermoplastic resin sheet for vacuum forming. (2) The sheet according to item (1) above, wherein the unstretched thermoplastic resin sheet is made of polyolefin resin. (3) The sheet according to item (1) above, wherein the stretched thermoplastic resin film is made of polyolefin resin, and the stretching ratio is 4 times or more. It is. The configuration and effects of the present invention will be explained in detail below. B. Unstretched thermoplastic resin sheet; The thermoplastic resin to be used may be one that can be processed into a sheet and used for secondary processing, such as LDPE, HDPE, polypropylene, polybutene-1, poly-4-methylpentene. In addition to polyolefin resins such as -1, vinyl chloride resins, polystyrene, polyester resins, etc. can be used. These resins include not only homopolymers but also copolymers with monomers of the same or different types (random copolymers, block copolymers, and graft copolymers). Moreover, not only one type of polymer but also a mixture of two or more types of these polymers can be used. Of course, various fillers, pigments, and other additives can be mixed with the above resin in addition to necessary stabilizers. The method for manufacturing the sheet follows a known method. That is, both the calendar method and the T-die method can be used. The thickness of the sheet is 100-2000μ, preferably 200-1000μ. If it is less than 100μ, it is unsuitable as a material for vacuum forming, and if it exceeds 2000μ, other processing methods such as press molding are more appropriate. (b) Stretched thermoplastic film; The thermoplastic resin used is the same as in the case of the thermoplastic resin sheet in (a) above. The method for producing the film is the same as that for the sheet described above, but the thickness after stretching is different. That is, the thickness of the film is 5 to 50μ, preferably 10
~30μ and has been stretched 4 times or more (area magnification). If the stretching ratio is less than 4 times, the effects of the present invention described below will be extremely insufficient. Furthermore, although there is no upper limit to the magnification, the current limit is about 60 times due to processing methods, and even if stretched beyond this, the effects of the present invention will not particularly increase. Any known stretching method can be used. That is, the tenter biaxial stretching method, the inflation multiaxial stretching method, the roll method uniaxial stretching method, and the like. Moreover, it goes without saying that both uniaxially stretched products and multiaxially stretched products can be used. C. Bonding of sheet and film; The sheet and film produced as described above are bonded together by a known method. As the bonding method, any of known extrusion lamination methods, dry lamination methods, and others may be used. However, extrusion lamination is preferred from the viewpoint of manufacturing efficiency and quality of the sheet of the present invention obtained. When the thermoplastic resins constituting the sheet and film according to the present invention are of the same type, they are generally easily fused together, but when they are of different types, they do not necessarily fused together, so in such a case, The sheet and film are bonded together using an adhesive. D. Thickness ratio of the stretched thermoplastic resin film to the bonded product; The thickness of the film constituting the bonded sheet according to the present invention is 20% or less and 1.0% or more, preferably 15% or more relative to the sheet. % or less 3
Must be greater than or equal to %. If it exceeds 20%, vacuum molding becomes impossible because the sheet will be cut due to the reorientation of the stretched film bonded during the molding. Also,
If it is less than 1.0%, the various effects resulting from the bonding of stretched films (improvements in vacuum forming, rigidity, and impact strength) will be drastically reduced, making it virtually impossible to achieve the object of the present invention. As detailed above, by performing vacuum molding using the bonded sheet of the present invention, the following effects can be achieved. There is no need to use a thermoplastic resin with a particularly low MFR as a raw material thermoplastic resin. In the case of polypropylene resin, it is not necessary to mix other resins. Vacuum formability as expressed by heating behavior (see Examples) is improved. The transparency of molded products is greatly improved. The rigidity (Young's modulus) and impact strength of the molded product are improved. The heating behavior is measured as follows. That is, a sample sheet is fixed in a frame with an opening size of 300 x 300 mm, and the fixed sheet is held horizontally for a certain period of time in a heating furnace maintained at 180°C. Due to this heating, the central part of the sheet first sag, and then the sagging partially returns, and this returned state continues for a certain period of time. The "sagging amount" in each of the examples described below refers to the amount of drooping (mm) before the start of the partial return described above, and the "return amount" is
It refers to the return rate (%) in a state where the maximum return occurs, and similarly, "retention time" refers to the time (sec) during which the maximum return amount is maintained. The above-mentioned returned state is lost by sagging again after the retention time has elapsed, and no return phenomenon occurs thereafter. The present invention will be explained below with reference to Examples. Examples 1 to 14, Comparative Examples 1 and 2 Commercially available polypropylene resin with MFR3.3 (trade name,
Chitso Polypro A5014) set at 250℃ 75
Extruded from φT die, thickness separately prepared at that time
12, 18, 20, 30 μ OPP (stretching ratio: 40 times; Examples 1 to 12), inflation method multiaxially stretched polypropylene film with a thickness of 20 μ (hereinafter referred to as
IOPP, stretching ratio 36 times; Example 13) and a uniaxially stretched polypropylene film with a thickness of 20 μm (stretching ratio 8 times; Example 14) were laminated, respectively, and the thickness of the non-stretched portion during extrusion was adjusted. , sheet thickness after lamination 250μ (Examples 1 to 4),
350μ (Examples 5-8, 13, 14) and 500μ (Examples 9-12) were obtained. Also, as a comparative example, 20μ
A sheet having a total thickness of 350 μm was obtained by laminating or not laminating (Comparative Example 2) CPP (Comparative Example 1). The structure and physical properties of these sheets are shown in Table 1, and the heating behavior is shown in Figures 1 and 2, showing the relationship between various physical properties and the thickness ratio of the stretched film bonded together. The relationship between the heating behavior (sagging amount, return amount, and holding time) shown in FIG. 1 and vacuum formability will be explained. FIGS. 1A, B, and C each show the relationship between the amount of drooping during heating, the amount of return, and the holding time of the laminated sheet according to the present invention, and the thickness ratio of the stretched film. The curves in each figure are obtained by plotting samples of the same thickness according to the thickness ratio. △ in the figure,
● and Γ are the thicknesses of OPP laminated together.
500μ, 350μ, and 250μ sheets of the present invention are shown, and × and □ represent measurement results for sheets laminated with IOPP and uniaxially stretched polypropylene films, respectively. As is clear from Figure 1A, the drooping amount is better when the overall sheet thickness is thicker when the thickness ratio is the same, but when the sheet thickness is the same, the thickness ratio is 2% or more, especially about 4%. With the above steps, favorable results can be obtained. Figure 1B
As is clear, the return amount is 2% for sheets with the same thickness ratio regardless of the overall sheet thickness.
More than 3% is particularly preferable (note: close to 100%)
Get results. As is clear from Figure 1C, the retention time is better for sheets with a thicker overall sheet thickness when the thickness ratio is the same;
% or more, preferable results are obtained. As is clear from the above explanation of the measurement items of heating behavior,
For sheets for vacuum forming, the smaller the amount of droop, the larger the amount of return, and the longer the holding time, the better the vacuum formability. It goes without saying that the physical properties of the sheet directly indicate the moldability or the physical properties after molding. Next, Figures 2 A, B, and C show the transparency (haze %), stiffness (Young's modulus Kg/mm ² ), and impact strength of the same samples as in Figure 1, respectively, and the sheet of the present invention. The relationship between the ratio of the stretched film to the thickness is plotted for each sample. In the figure, △, ●, and Γ indicate sheets of the present invention with thicknesses of 500μ, 350μ, and 250μ, respectively, which are laminated with OPP, and × and □ indicate IOPP (inflation method multiaxially stretched film) and uniaxially stretched polypropylene film, respectively. The measurement results for the bonded sheets are shown. As is clear from Figure 2A, haze is better for sheets with a thinner overall sheet thickness when the thickness ratio is the same;
% or more, especially 3% or more, preferable results are obtained.
On the other hand, when uniaxially oriented polypropylene or IOPP is laminated to a thickness ratio of 5.7% instead of OPP, a haze value that is almost the same as that of the OPP laminated product is obtained, and the haze value as a whole is better than that without lamination (0%). The improvement is about 1/2 or less than 2/3 of the case.
As is clear from FIG. 2B, the Young's modulus is better when the total sheet thickness is thicker when the thickness ratio is the same. As for the same sheet thickness, preferable results can be obtained when the thickness of the stretched film portion is 2% or more, particularly about 5% or more. On the other hand,
Uniaxially oriented polypropylene or
Unlike the case of haze (Fig. 2 A), the product with IOPP laminated to a thickness ratio of 5.7% is considerably inferior to the corresponding OPP laminated product, but it is better than the product without lamination (0%). showed excellent results. Furthermore, as is clear from Figure 2C, the impact strength is as follows for those with the same thickness ratio:
Naturally, the thicker the overall sheet thickness is, the better. As for the same thickness, preferable results can be obtained when the thickness of the stretched film portion is 2% or more, particularly about 4% or more. On the other hand, for products in which uniaxially oriented polypropylene or IOPP is laminated with a thickness ratio of 5.7% instead of OPP, it is considerably inferior to the corresponding OPP laminated product, as in the case of Young's modulus, but it is not laminated. showed better results. In addition, the CPP laminated product of Comparative Example 1 is
It has no effect on anything other than improving transparency.

【table】

[Table] Examples 15-16, Comparative Examples 3-6 Commercially available polypropylene resin with MFR0.5 (trade name,
Chitsuso Polypro K4011), (commercially available) ethylene propylene block copolymer resin with 8% ethylene content (trade name, Chituso Polypro K7011) and
Using ethylene propylene random copolymer resin (trade name, Chitsuso Polypro
A sheet of 350 μm was obtained by laminating the OPPs together (Examples 15 and 16). OPP respectively as comparison
For comparison with sheets that are not laminated (Comparative Examples 3 to 5) and each example, polypropylene resin
LDPE 10% by weight with MI (melt index) 2.0
and 5% by weight of ethylene propylene rubber (Comparative Example 6) to obtain sheets of 350μ. The composition and physical properties of these sheets are
Shown in the table. Compare the example and the corresponding comparative example (Note 15 comparison 3, Actual 16 comparison 4, Actual 17 comparison 5, Actual 15
-17 Comparison 6) It is clear that the laminated sheets of each example are superior to the sheets of each comparative example in terms of heating behavior, transparency, rigidity, and impact strength.

【table】

[Table] Examples 18, 19, Comparative Examples 7, 8 In the same manner as in Examples 1 to 14 using MI1.0 HDPE and LDPE, uniaxially stretched HDPE films of 30 μm (stretching ratio 6 times) to obtain a sheet with a thickness of 350 μm. (Examples 18 and 19). For comparison, a 350μ sheet was obtained without laminating a uniaxially stretched film to each. (Comparative Examples 7 and 8). Table 3 shows the composition and physical properties of these sheets. It is clear from a comparison between each of the Examples and the corresponding Comparative Example that the sheet of each Example is superior to that of the Comparative Example in terms of heating behavior, transparency, and Young's modulus. Also, Example 19
HDPE made of heterogeneous resin on LDPE sheet like
Even when stretched films are bonded together, the effects of the present invention remain the same.

【table】

【table】 [Brief explanation of the drawing]

FIGS. 1A, B, and C show the relationship between the heating behavior (sagging amount, return amount, holding time) of the laminated sheet of the present invention and the stretched film thickness ratio. Moreover, FIGS. 2A, B, and C show the relationship between the physical properties (haze, Young's modulus, and impact strength) of the laminated sheet of the present invention and the thickness ratio.

Claims (1)

[Claims] 1. An unstretched thermoplastic resin sheet and a stretched thermoplastic resin film are bonded together, and the ratio of the thickness of the stretched thermoplastic resin film to the bonded product is 20% or less 1.0 % or more thermoplastic resin sheet for vacuum forming. 2. The sheet according to claim 1, wherein the unstretched thermoplastic resin sheet is made of a polyolefin resin. 3. The sheet according to claim 1, wherein the stretched thermoplastic resin film is made of polyolefin resin, and the stretching ratio is 4 times or more.