JP3932238B2 - Functional film, adhesive tape, and production method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a functional film and a pressure-sensitive adhesive tape that have a function of displaying characters, figures, etc. without printing.
[0002]
[Prior art]
Conventionally, as a film or adhesive tape having a display function, for example, characters or figures printed on the film surface or the like, or after the tape is peeled off, the printing part is cut off and the display function (hidden character function) is provided. The adhesive tape which has is known.
[Problems to be solved by the invention]
[0003]
However, any film or tape requires a printing process, leading to increased costs. In the case of a tape, an undercoat layer is also required to provide an adhesive layer on the printed surface, which has caused further cost increase.
Furthermore, there has been a problem that the printing ink component adheres to the film surface during the manufacturing process and causes contamination.
[0004]
[Means for Solving the Problems]
The present invention has been made to solve these problems, and does not require a printing process. Therefore, the present invention provides a film or an adhesive tape that is free from contamination and has a low-cost display function. Furthermore, a film or an adhesive tape having a hidden character function without printing is provided.
That is, the present invention relates to a functional film having polymer islands having relatively different crystallinity in a sea-island shape, and having a region where the number density of island-like phases is different between the display portion and other regions due to a difference in cooling rate. Is.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The functional film of the present invention is not particularly limited as long as polymer phases having relatively different crystallinities are mixed in a sea-island shape, but as a relatively highly crystalline polymer, generally a polymer having stereoregularity. Examples thereof include homopolypropylene resin. In addition, as the relatively low crystalline polymer, it is generally difficult to take stereoregularity, for example, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid copolymer, ethylene- ( Examples thereof include resins such as (meth) methyl acrylate copolymer, ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, and medium density polyethylene.
[0006]
As described above, the functional film of the present invention has a relatively different degree of crystallinity, that is, a phase of high crystallinity and low crystallinity polymer (also referred to as a domain) mixed in a sea-island shape, and a difference in cooling rate. It is necessary to have a region where the number density of the island-like phases (domains) is different between the display portion and other regions . In addition, it is not specifically limited which polymer exists in island shape or sea shape.
The size of the island-like phase (domain) is preferably about 0.1 to 1 μm, particularly about 0.4 to 0.9 μm, and within this range, a film obtained by stretching described later has a good display function. . Here, the size of the island-like phase means a width in a direction perpendicular to the stretching direction described later.
Having a region with a different number density of island-like phases means that the number of island-like phases per unit area in a certain region of the film is different from the number in other regions. It is not limited, and since the display effect by contrast is so large that the difference is large, it is preferable. For example, in one region, ² per 10 ² 1 mm, in other regions it may be 10 ⁴ to 10 ⁶ or so.
[0007]
The method for producing such a functional film is not particularly limited, but in particular, a region in which a polymer phase having a relatively different degree of crystallinity is mixed in a sea island shape and another region of the film are cooled at different cooling rates, for example. It can be obtained by forming regions having different number density of states. More specifically, it can be obtained by, for example, winding using a cooling roll having a concavo-convex surface, immediately after melting and drawing of the film, by a calendar rolling method. The reason for having regions with different number density of island-like phases by this method is not clear, but is presumed as follows. In the region where the cooling rate is low, the crystallization of the matrix component proceeds, and the size of the island-like phase tends to be finely dispersed to about 0.1 to 1 μm and its number density increases, whereas in the region where the cooling rate is high The crystallization does not progress so much, and as a result, the island-like phases are easily connected, the ratio of the size of the island-like phases increases by 1 μm or more, and the number density of the island-like phases of about 0.1 to 1 μm increases. It is thought that it does not.
[0008]
Such a functional film can be a film in which a contrast is generated between regions where the number density of island-like phases is different due to the stretching, and a display function is exhibited. In the present invention, when the functional film is stretched, stress is concentrated due to the difference in elongation at the phase boundary between the high crystalline polymer phase and the low crystalline polymer to generate a minute defect (crack). And the density of this defect | deletion part will differ in the area | region where the number density of an island-like phase differs. This difference in the density of the defect portions can be confirmed by the porosity described later.
In the present invention, the defect portion formed at the boundary of the island-like phase having a size of about 0.1 to 1 μm has a large degree of refracting (scattering) visible light transmitted through the film, and the size of the defect portion is almost the same. It is considered that the wavelength size of visible light is about 0.4 to 0.9 μm. When the number density of the 0.1 to 1 μm island-like phase is high, the density of the defect portion that scatters visible light also increases, and the region becomes whiter.
Thus, by intentionally generating a high density area and a low density area of an island-like phase of 0.1 to 1 μm in the film, the density of the defect part that scatters visible light by stretching the film differs. A region can be generated, and as a result, a function of displaying characters, figures, and the like is provided due to the contrast between the regions.
[0009]
The present invention also provides a functional pressure-sensitive adhesive tape or sheet (hereinafter referred to as a tape) formed by forming an adhesive layer on one side or both sides of the functional film. Such an adhesive layer is not particularly limited, and for example, an ordinary acrylic, rubber, silicone, polyester, or the like can be used.
[0010]
【Example】
Next, specific examples of the functional film of the present invention will be shown.
Example 1
A polypropylene resin having a sea-island structure in which a homopolypropylene and an ethylene-propylene copolymer are polymerized and blended (polymerization ratio 50/50) (island phase = homopolypropylene, sea phase = ethylene-propylene copolymer) is calendered. Immediately after melting and drawing at about 170 ° C., the character display portion was wound up through a metal cooling roll having a concave portion to produce a polypropylene film having a thickness of 80 μm.
When such a film was examined with a transmission electron microscope (TEM), the number density of the island-like phases in the region gradually cooled in contact with the concave portion of the roll was the region rapidly cooled in contact with the convex portion of the roll. It was confirmed that it was higher than the number density.
Next, the obtained film is stretched about twice in the MD direction, and the region where the number density of island-like phases is gradually cooled is rapidly cooled and whitened compared to the region where the number density of island-like phases is low. A film having a high degree of display, white characters appearing, and a display function was obtained. The haze ratio of the character part was 98%, and the haze ratio of the part other than the character part was 65%, and it was confirmed that there was a difference in optical characteristics.
When such a film was examined with a scanning electron microscope (SEM), it was confirmed that a defect (crack) was present at the boundary between the island-like phase and the sea-like phase. It was confirmed that the region having a higher number density was higher than the region having a lower number density of island-like phases after being rapidly cooled.
Moreover, the porosity of each area | region measured with the following method is 40% and 15%, respectively, and it has confirmed from now on that it has an area | region where the density of a defect part differs.
<Measurement of porosity>
The apparent specific gravity is obtained from the volume and weight of the film, and the true specific gravity is obtained from the specific gravity and blend ratio of the blend resin, and is calculated from the following formula.
Porosity (%) = (apparent specific gravity / true specific gravity) × 100
[0011]
Example 2
A polypropylene resin having a sea-island structure (island phase = homopolypropylene, sea-phase = ethylene-propylene copolymer) obtained by polymer blending of homopolypropylene and ethylene-propylene copolymer (polymerization ratio 60/40) is calendered. Immediately after melting and drawing at about 180 ° C., the character display portion was wound up through a metal cooling roll having a concave portion to produce a polypropylene film having a thickness of 100 μm. When such a film was examined with a transmission electron microscope (TEM), the number density of the island-like phases in the region gradually cooled in contact with the concave portion of the roll was the region rapidly cooled in contact with the convex portion of the roll. It was confirmed that it was higher than the number density.
An acrylic adhesive was applied to one side of the obtained film to a thickness of 15 μm to produce an adhesive tape.
Next, before sticking the obtained tape, it was possible to stick the pressure-sensitive adhesive tape on which the characters were raised on the metal plate by stretching it about twice in the MD longitudinal direction and sticking it to the adherend (metal plate). .
When such a film was examined with a scanning electron microscope (SEM), it was confirmed that a defect (crack) was present at the boundary between the island-like phase and the sea-like phase. It was confirmed that the region having a higher number density was higher than the region having a lower number density of island-like phases after being rapidly cooled.
The porosity of each region was 30% and 5%, respectively.
[0012]
【The invention's effect】
As described above, since the functional film or adhesive tape of the present invention does not require a printing process, it has the effect of being free of contamination, having a display function at low cost, and having a hidden character function even without printing.

Claims (12)

A functional film having a region in which polymer phases having relatively different crystallinities are mixed in a sea-island shape, and the number density of island-like phases is different between the display portion and other regions due to a difference in cooling rate .   The functional film according to claim 1, wherein the functional film can exhibit a display function by stretching. A polymer phase having relatively different crystallinity is mixed in a sea-island shape, and a film having a region where the number density of the island-like phase is different between the display portion and other regions due to a difference in cooling rate is stretched, A functional film having a display function between regions having different number densities.   The functional film according to claim 3, wherein the density of minute defects generated by stretching differs in regions where the number density of island phases is different, and the display function is expressed by the density difference of the defects.   The size of an island-like phase is 0.1-1 micrometer, The functional film in any one of Claims 1-4.   The functional film according to any one of claims 1 to 5, wherein the polymer is an olefin resin.   The functional film according to any one of claims 1 to 6, wherein the relatively high crystalline polymer is homopolypropylene and the relatively low crystalline polymer is an ethylene-propylene copolymer.   The adhesive tape in which the adhesion layer is formed in the at least single side | surface of the functional film in any one of Claims 1-7. The film phase and other areas where the polymer phase with relatively different crystallinity is mixed in a sea-island shape are cooled at different cooling rates , and the island-like phase is displayed in the display area and other areas depending on the cooling rate. The manufacturing method of the functional film which forms the area | region from which number density differs.   The method for producing a functional film according to claim 9, wherein the film is wound up by a calendar rolling method using a cooling roll having an uneven surface immediately after the film is melted and drawn. A polymer phase with relatively different crystallinity is mixed in a sea-island shape, and a film having a region where the number density of the island-like phase is different between the display portion and other regions due to a difference in cooling rate is stretched to form a minute defect portion. A method for producing a functional film, characterized in that the density difference of defective portions is provided between the regions.   The functional adhesive tape having an adhesive layer formed on one side of the functional film according to claim 1 or 2 is stretched before being attached to an adherend, and then a display function is exhibited by being attached. How to use the adhesive tape.