JPH0647810A - Manufacture of heat-shrinkable film - Google Patents

Abstract

PURPOSE:To prevent troubles such as running out of a raw material, variation of extrusion and cut of a film, eliminate the generation of heat deterioration as in the case of melt re-pelletizing and make use of a biaxial extruder by improving the mixture of a scrap recovered raw material with a pellet-like new raw material for a heat-shrinkable film. CONSTITUTION:In a method for manufacturing a heat-shrinkable film F2, in which the film F1 is extruded out of an extruder 1, and the film is stretched by a tenter stretching machine 6 to impart heat shrinkability to the film F2, and trimmings S are heated upto the temperature higher than the heat shrinkage beginning temperature and lower than the flowing beginning temperature by blowing hot air while being passed through a heating zone 15, and then crushed by a crusher 9, mixed with a pellet-like new raw material V and fed to the extruder 1.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to a method for producing a heat-shrinkable film.

[0001]

2. Description of the Related Art A heat-shrinkable film used for shrink wrapping, labels and the like has conventionally been manufactured by the following method using an apparatus as shown in FIG.
That is, the resin melt-kneaded by the extruder 1 is guided to the mold 2 attached to the tip of the extruder 1, discharged from the discharge port of the mold 2 in a film shape, and taken by the take-up machine 3 to obtain the unstretched film F. _1, and the unstretched film F ₁ is reheated by the heating device 4 to a temperature not lower than the heat contraction start temperature and not higher than the flow start temperature,
Uniaxial stretching is carried out in the machine direction (traveling direction) by the roll stretching machine 5 through the process indicated by the arrow A, or in the transverse direction (width direction) by the tenter stretching machine 6 through the process indicated by the arrow B.
Alternatively, biaxial stretching is sequentially performed in the roll stretching machine 5 in the longitudinal direction and then in the tenter stretching machine 6 in the transverse direction. Although not shown in FIG. 6, stretching is performed by a method such as simultaneous biaxial stretching in both longitudinal and transverse directions with a tenter stretching machine for simultaneous biaxial stretching to impart heat shrinkability, and then the ears at both ends in the width direction are trimmed. After being cut off by a cutter 7 and trimmed, and if necessary, the product is cut into a predetermined width by a slitter and wound into a roll by a winder 8 to obtain a heat-shrinkable film F ₂ .

In the manufacturing process of the heat shrinkable film as described above, scrap S (hereinafter collectively referred to as "ear scrap") generated in the trimming process and the slitter process after stretching, defective products, and used products Since the amount of scraps generated such as reaches 15 to 30% of the input raw material, it is extremely important in terms of cost to collect and reuse scraps such as ear scraps S.

The generated ear scrap S is usually crushed by a pinch roll or a blower while being continuously continuous in a ribbon shape.
Sent to and crushed into small pieces, and the scrap crushed product obtained is melted and re-pelletized alone or mixed with a new raw material (pellet form) and reused by an offline method, or the scrap crushed product R obtained Extruder 1 as it is
The cyclone type hopper loader 10 installed above is pneumatically transported, and the cyclone type hopper loader 1 is installed side by side.
1 and the new raw material V sent to the extruder 1 are fed into the extruder hopper 14 by the quantitative feeders 12 and 13, respectively.
It is collected and reused by the in-line method that is reused in.

However, most of the crushed scraps of heat-shrinkable film are flakes having a thickness of 100 μm or less, and the apparent specific gravity is, for example, in the case of polyethylene heat-shrinkable film, about 0 of a new raw material in pellet form. Since it is remarkably small, about 0.1 compared to 0.8, it is difficult to mix with the pellet-shaped new raw material, and even once mixed, it is easy to separate in the hopper. Then, a bridge is formed in the vicinity of the outlet of the hopper, making it extremely difficult to fall. Then, there is a problem in that an accident such as running out of raw materials is caused.

In order to solve such a problem, recently, recovery and reuse are performed by the following improved method. A method in which the extruder hopper is divided into two parts, the scrap crushed product is supplied to the front side of the extruder and the new raw material is supplied to the rear side, and mixed in the barrel. The extruder hopper has a double structure inside and outside, the pelletized new raw material is put in the outer lower hopper, the scrap crushed product is put in the inner upper hopper, and it is pushed into the extruder by the vertical special screw feeder provided in the center of the inner upper hopper. , A method of forcibly mixing with a new raw material just before it gets into the extrusion screw. ("ASR System": See "Plastic Molding Factory Automation Technology", page 74, issued by Plastic Age Co., Ltd.).

[0006]

However, even in the above method, the difference in shape and apparent specific gravity between the scrap crushed product and the pellet-like new raw material is large, and therefore the recovered raw material mixing ratio is 10% or less, and scrap is generated. Since only a small amount can be collected and used for the rate, and a bridge may form near the outlet of the hopper loader or extruder hopper, scrap crushed product stays in the hopper loader and blows out from the cyclone, or the extrusion amount. Problems such as film breakage may occur due to fluctuations.

Further, the above method is problematic in the case of a single-screw extruder because the raw material is pushed in by a special screw feeder in the extruder hopper and the barrel is full in the feed zone of the extruder. However, in the case of a twin-screw (or multi-screw) extruder, it may be overloaded due to the structure of the extruder. This means that the scrap crushed product and the new raw material need to be supplied in a fixed amount in a constant amount by a feeder until just before cutting into the extrusion screw, which is difficult to carry out in the case of the above method. There is also a problem that a special hopper is required as equipment.

The present invention has been made in view of the above problems, and by improving the mixing of the scrap of the heat-shrinkable film and the new raw material in pellet form,
Prevents problems such as raw material breakage, extrusion fluctuation, film breakage, etc. without the deterioration of the film due to heat history as in the case of melt re-pelleting, and it can also be applied to a twin-screw extruder, heat shrinkage It aims at providing the manufacturing method of a flexible film.

[0009]

In order to achieve the above object, the present invention heats a scrap of a film stretched to provide heat shrinkability to a temperature not lower than the heat shrinkage start temperature and not higher than the flow start temperature. This is because the shrinkage and the increase in the apparent specific gravity facilitate mixing with a new raw material in the form of pellets, dropping from the hopper, and biting by the extrusion screw.

That is, according to the present invention, the heat-shrinkable film scrap is heated to a temperature not lower than the heat-shrinking start temperature and not higher than the flow start temperature to shrink and then crushed, mixed with a new raw material in pellet form, and put into an extruder. The gist is to supply and extrude and stretch into a film.

According to the second aspect of the present invention, the scrap of the heat-shrinkable film is crushed and then heated to a temperature not lower than the heat-shrinking start temperature and not higher than the flow start temperature to shrink, and mixed with the new raw material in pellet form. Then, the main point is to supply it to an extruder and extrude and stretch it into a film.

Here, the heat shrinkage start temperature refers to JIS Z
The minimum temperature at which the shrinkage ratio measured by 1709 shows 10% or more is set. (However, the temperature of the heat transfer liquid is 30 ° C. and is increased by 5 ° C., and the heat transfer liquid is immersed in the heat transfer liquid for 20 seconds to complete the measurement at a temperature at which the shrinkage ratio is 10% or more. ) In addition, the flow starting temperature is JIS K 7199.
The minimum temperature at which the viscosity measured by the method is 4,000 poise or less. (However, the radius of the capillary is 0.5.
mm, capillary length 20 mm, shear rate 100
Set to ⁰ sec ^-1 . )

Resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyester, polyamide, polyethylene terephthalate, and polysulfone are used as the material of the heat-shrinkable film produced by the method of the present invention.

[0014]

The scrap of the heat-shrinkable film is crushed (invention of claim 1) or crushed (claim 2).
Invention), the thickness is increased and the apparent specific gravity is increased by heating at a temperature not lower than the thermal contraction start temperature and not higher than the flow start temperature and contracting in the stretched direction. Therefore, the scrap crushed product has a small difference in apparent specific gravity from the new raw material in pellet form, is easy to mix with the new raw material in pellet form, is difficult to separate, and has a shape that is difficult to form a bridge,
Even if it is mixed with the new raw material in pellet form and supplied to the extruder, it easily falls and is easily bited into the extrusion screw.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is an explanatory view of a manufacturing apparatus used in the method of the present invention according to claim 1. In FIG. 1, a hopper loader 11 stores a pelletized new raw material V of a copolyester resin. In this new raw material V, the dicarboxylic acid component is 100 mol% of terephthalic acid, the diol component is 70 mol% of ethylene glycol, and 30 mol% of 1,4-cyclohexanedimethanol. Also,
The hopper loader 10 stores the recovered raw material R of the recovered crushed ear scrap.

80% by weight of the pelletized new raw material V from the hopper loader 11 by the screw feeder 13
Further, the recovered raw material R is weighed by the screw feeder 12 from the hopper loader 10 so as to be 20% by weight and sent to the extruder hopper 14 to be mixed, and the mixed raw materials are twin-screw having a screw diameter of 57 mm and rotating in the same direction. The mixture was supplied to the extruder 1, melt-kneaded, and extruded into a film form from a mold 2 having a lip length of 400 mm and a lip gap of 0.8 mm at an extrusion rate of 80 kg / hour. Then, the unrolled film F ₁ having a thickness of 120 μm was molded by a roll-type take-off machine 3 having a roll surface temperature of 50 ° C. at a take-up speed of 20 m / min. Subsequently, it is reheated to 85 ° C. by the heating device 4, and uniaxially stretched 3.0 times in the transverse direction (width direction) by the tenter stretching machine 6.
A heat-shrinkable film having a thickness of 40 μm was obtained as F ₂ . The heat shrinkable film F ₂ thus obtained had a heat shrinkage start temperature of 75 ° C. and a flow start temperature of 240 ° C.

The ears at both ends of this heat-shrinkable film F ₂ are each trimmed with a trimming cutter 7 to a width of 100 mm, and the resulting ribbon-shaped ears scrap S is heated to a heating zone having a length of 2,000 mm as shown in FIG. Line speed 20 in 15
As a result of heating by blowing hot air at 170 ° C. while passing at m / min (passing time 6 seconds), the width contracted to 42 mm.

Next, the contracted ear scrap S
₁ is a crusher BO-210A for exclusive use of film and sheet manufactured by Horai Co., Ltd., which has a screen with an opening hole diameter of 5 mm.
It was crushed by RFT to obtain a recovered raw material R having an apparent specific gravity of 0.43. (Note that the apparent specific gravity of the scrap crushed product before heating and shrinking was 0.12.) Obtained recovered raw material R
_As described above, ₁ was refluxed to the hopper loader 10 and mixed with the pellet-shaped new raw material V for use.

In the production of the heat-shrinkable film F ₂ , the unstretched film F ₁ is cut accurately every 6 seconds for 50 times, the weight of each cut piece is measured, and the extrusion rate variation rate is 4σ.
(Σ is the standard deviation), and the tensile strength of the heat-shrinkable film F _{2 in} the stretching direction and the direction orthogonal thereto are
It was measured according to the method specified in JIS C 2318.
Moreover, the presence or absence of abnormality in the manufacturing process was observed.

As a result, the variation rate of the extrusion rate was 3.0%, and the tensile strength of the obtained heat-shrinkable film was 5.
4 kg / 10 mm, 2.2 kg in the direction orthogonal to the stretching direction
Was / 10 mm. In addition, no abnormalities such as raw material breakage and film breakage due to stretching were observed, and the manufacturing process was stable.

In the present embodiment, a method of blowing hot air was used to heat and shrink the ear scrap S, but irradiation with the infrared heater 16 as shown in FIG. 3 is shown in FIG. A method of allowing the heating roll 17 to pass while contacting the heating roll 17 may be used.

The scrap to be used is not limited to the ear scrap, and may be, for example, a defective product of the obtained films or a recovered product of the used film.

When the heat-shrinkable film F ₂ is stretched only in the transverse direction as in the above embodiment, the feed rates on the inlet side and the outlet side of the heating zone 15 should be substantially the same. However, in the case where the heat-shrinkable film F ₂ is stretched in the machine direction, the stretch in the machine direction is removed by heating and the film tends to shrink in the machine direction. It is preferable to adjust the feed rate on the outlet side of the heating zone 15 to be slower than the feed rate on the inlet side.

(Example 2) 60% of new raw material in pellet form,
A heat-shrinkable film was produced by using the recovered raw material obtained from the ear scrap in the same manner as in Example 1 except that the recovered raw material was 40%. The tensile strength of the obtained heat-shrinkable film was measured.
(The heat shrinkable film had a heat shrinkage starting temperature of 75 ° C. and a flow starting temperature of 240 ° C.)

As a result, the variation rate of extrusion amount was 3.1%, and the tensile strength of the obtained heat-shrinkable film was 5.3 in the stretching direction.
kg / 10 mm, 2.3 kg / in the direction orthogonal to the stretching direction
It was 10 mm. Further, the raw material was not cut, the film was not broken due to stretching, and the manufacturing process was stable.

(Example 3) A pelletized new raw material of the same copolyester resin as in Example 1 was used in an amount of 60% by weight and a recovered raw material in an amount of 40% by weight, and extruded in the same manner as in Example 1 What was uniaxially stretched 3.0 times in the transverse direction was once wound on a winder to obtain a heat-shrinkable film having a thickness of 40 μm. The heat shrinkage initiation temperature of the obtained heat shrinkable film was 75 ° C, and the flow initiation temperature was 240 ° C.

This heat-shrinkable film is slit by a slitter in an off-line batch system to have a width of 650 m.
m, the other part is ear scrap S, and the length of the heat generating part as shown in FIG. 3 is 1,050 m.
m, infrared heater 16 (heater capacity 1.5k
w) An infrared heater 16 is provided in the heating type heating zone 15.
100m away from the line speed 3m / min (passing time 21 seconds)
As a result, it contracted to a width of 210 mm.

Next, the contracted ear scrap S
₂ was crushed with the same crusher for film and sheet as in Example 1 to obtain a recovered raw material having an apparent specific gravity of 0.42. The obtained recovered raw material was used as a mixture with a pellet-shaped new raw material.

Then, in the same manner as in Example 1, the extrusion rate variation rate and the tensile strength of the heat shrinkable film obtained were measured, and the presence or absence of abnormality in each step was observed. Is 3.1%, the tensile strength of the obtained heat-shrinkable film is 5.4 kg / 10 mm in the stretching direction,
It was 2.3 kg / 10 mm in the direction orthogonal to the stretching direction. Further, the raw material was not cut, the film was not broken due to stretching, and the manufacturing process was stable.

Example 4 The same pelletized new raw material V of copolyester resin as in Example 1 was mixed in an amount of 60% by weight and the recovered raw material R ₂ was mixed in an amount of 40% by weight, and the same extruder as in Example 1 was used. , Lip length 900mm, lip gap 0.8mm
After being extruded from the mold at an extrusion rate of 80 kg / hour, the roll surface temperature is 50 ° C. and the take-up speed is 15
It is taken up at m / min to form an unstretched film having a thickness of 120 μm, subsequently reheated to 83 ° C. by a heating device, and uniaxially stretched 3.0 times in the longitudinal direction (traveling direction) using a roll stretching machine, A heat-shrinkable film having a thickness of 40 μm was obtained. The heat shrinkage initiation temperature of the obtained heat shrinkable film was 75 ° C, and the flow initiation temperature was 240 ° C.

The ears at both ends of this heat-shrinkable film are respectively 70
After trimming the width by mm, the generated ear scrap S was crushed by the same crusher for film and sheet as in Example 1 to obtain a crushed scrap having an apparent specific gravity of 0.12.

As shown in FIG. 5, the air sent from the blower 18 is supplied to the air heater 1 for the scrap crushed product.
9 was heated and shrunk while being pneumatically transported to the hopper loader 10 on the extruder by hot air passing through 9 and heated to 200 ° C. to obtain a recovered raw material R ₂ having an apparent specific gravity of 0.40. The recovered raw material R ₂ thus obtained was used as a mixture with the new pellet-shaped raw material V as described above. Since the recovered raw material R ₂ transported by air is still quite high in temperature and may be fused with each other to form a lump, the hopper loader 10 should be equipped with a stirrer so that the scrap crushed product is constantly stirred. did.

Then, in the same manner as in Example 1, the extrusion rate variation rate, the tensile strength of the heat shrinkable film obtained were measured, and the presence or absence of abnormality in each step was observed.
The extrusion rate variation rate was 3.3%, and the tensile strength of the obtained heat-shrinkable film was 5.3 kg / 10 mm in the stretching direction and 2.1 kg / 10 mm in the direction orthogonal to the stretching direction. Also, raw material cut, film break due to stretching, etc. does not occur,
The manufacturing process was stable.

(Comparative Example 1) An ear scrap obtained by the same method as in Example 1 was crushed without heating and shrinking, and the recovered raw material having an apparent specific gravity of 0.12 was used. A heat shrinkable film was produced in the same manner as in Example 1.

As a result, the variation rate of the extrusion rate was 4.8%, and the tensile strength of the obtained heat-shrinkable film was 4.
7 kg / 10 mm, 1.9 kg in the direction orthogonal to the stretching direction
Was / 10 mm. Further, due to fluctuations in the extrusion rate, raw material breakage and film breakage due to stretching often occurred, and stable production was not possible.

(Comparative Example 2) The same procedure as in Example 2 was carried out except that the selvage scrap obtained in the same manner as in Example 2 was crushed without heating and shrinking, and the recovered raw material having an apparent specific gravity of 0.12 was used. A heat shrinkable film was produced in the same manner as in Example 2.

As a result, it was impossible to continue the production due to the fact that the raw material of the ear scraps could not be supplied due to the formation of a bridge in the hopper loader or the extruder hopper, or the extrusion amount fluctuated drastically.

The results of Examples 1 to 4 and Comparative Examples 1 and 2 are summarized in Table 1 above.

[0039]

[Table 1]

[0040]

EFFECT OF THE INVENTION According to the method for producing a heat-shrinkable film of the present invention, poor mixing and separation with the new pellet-shaped raw material, poor falling due to the formation of bridges in the hopper, and variation in extrusion amount due to these It is possible to collect and use a maximum of 40% by weight of the recovered scrap by mixing with the new pellet-shaped raw material without causing troubles such as running out of the raw material and without lowering the strength of the heat-shrinkable film.

In addition, there is no large energy loss for scrap recycling as in the case of melting and re-pelletizing, and it is possible to collect in an in-line system in production by a twin-screw (multi-screw) extruder.

[0042]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing apparatus used in the method of the present invention according to claim 1.

FIG. 2 is an explanatory view showing an example of an ear scrap heating device used in the method of the present invention according to claim 1.

FIG. 3 is an explanatory diagram showing another example of the ear scrap heating device used in the method of the present invention according to claim 1.

FIG. 4 is an explanatory view showing another example of the ear scrap heating device used in the method of the present invention according to claim 1.

5 is an explanatory diagram showing an example of an ear scrap heating device used in the method of the present invention according to claim 2. FIG.

FIG. 6 is an explanatory diagram of a manufacturing apparatus used in a conventional heat-shrinkable film manufacturing method.

[Explanation of symbols]

 1 Extruder 3 Take-up machine 4 Heating device 5 Roll drawing machine 6 Tenter drawing machine 9 Crusher 10,11 Hopper loader 15 Heating zone 16 Infrared heater 17 Heating roll 19 Air heater S, Ear scrap V Pelletized new raw material

Claims (2)

[Claims] 1. A film of heat-shrinkable film is heated to a temperature not lower than the heat-shrinking start temperature and not higher than the flow start temperature to shrink and then crushed, mixed with new raw material in pellet form and supplied to an extruder, A method for producing a heat-shrinkable film, which comprises extruding and stretching the film into a shape. 2. A heat-shrinkable film scrap is crushed, and then heated to a temperature not lower than the heat shrinkage start temperature and not higher than the flow start temperature to shrink, and is mixed with a new raw material in pellet form and supplied to an extruder to obtain a film form. A method for producing a heat-shrinkable film, which comprises extruding and stretching.