Packaging material

Abstract

To realize monomaterialization of a packaging material made of a plastic film subjected to aqueous ink jet printing.SOLUTION: In the packaging material comprising two or more layers consisting of a base material layer 1 and a sealant layer 2 using a polyolefin film, a color print 4 of CMYK is formed on the base material layer by water-based ink-jet printing, and after drying the CMYK ink, a white print 5 is formed thereon, wherein an OPP film having a heat shrinkage of ≤15% at 150°C and a heat resistance satisfying the formula (1) at 120-150°C is used as the base material layer: Log (E) ≤ 0. 0275T - 2.4839 Expression (1) (where T is temperature (°C.)) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a packaging material made of a plastic film used for packaging such as packaging bags and container lids, and in particular to a packaging material subjected to aqueous inkjet printing. [Background technology]

[0002] Inkjet printing, which does not require plate making and can generate images for printing from digital data, is a printing method that is suitable for printing on a wide variety of small-lot plastic film packaging materials. It has excellent on-demand capabilities and is useful for packaging materials that require the printing of a wide variety of designs at any time.

[0003] In the case of aqueous inkjet printing, the ink contains an aqueous solvent in addition to a colorant, and therefore the aqueous solvent must be removed by thermal drying after printing.

[0004] In relation to the above, Patent Document 1 describes an aqueous inkjet printing method in which a substrate such as paper, plastic film, or fabric passes through a print head that ejects ink and travels along a drying path, in which a first heating section and a second heating section are provided at the tip of the print head, and the set temperature of the second heating section is set higher than the set temperature of the first heating section. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2020-15588 [Patent Document 2] Patent Publication No. 2022-098422 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] However, when printing with aqueous inkjet ink on a plastic film substrate, a problem arises that is not apparent when printing on paper or fabric: distortion of the plastic film during thermal drying.

[0007] In aqueous inkjet printing, if colored inks and white inks are printed and dried at the same time, the amount of aqueous ink increases, making drying difficult. The ink used in aqueous inkjet printing contains 50-70% water, requiring a lot of drying energy.

[0008] For these reasons, it is desirable to print the colored inks and white ink separately and then dry them after printing. That is, in aqueous inkjet printing on a two-layer film consisting of at least a substrate layer and a sealant layer, the CMYK colored inks are printed using aqueous inkjet printing after an anchor coat is applied, and the white ink is printed after the colored inks have dried. In this case, high-temperature hot air drying is required to dry the water-based colored inks. However, if a typical biaxially oriented polypropylene (OPP) film is used for the substrate layer, its heat resistance is insufficient, causing the film to easily distort between the colored inks and the white ink, resulting in misregistration of the colored and white inks. Therefore, the use of a highly heat-resistant polyethylene terephthalate (PET) film is the only viable option.

[0009] On the other hand, the sealant layer must be made of a polyolefin film such as polypropylene (PP) or polyethylene (PE). As a result, the resulting packaging material is a laminate of two different resin films, polyester film and polypropylene film, which makes it difficult to separate the resin films when discarding the resulting packaging, making it unsuitable for recycling. This creates a problem of increasing environmental impact, contrary to the current trend toward mono-materials, which is strongly demanding recycling. [Means for solving the problem]

[0010] The present invention was created with the objective of providing a packaging material that can be made into a monomaterial, thereby solving the above-mentioned problems. That is, the packaging material of the present invention is A film having two or more layers, consisting of at least a base layer and a sealant layer using a polyolefin film, is used. In packaging materials where CMYK colors are printed on the base layer using aqueous inkjet printing, and white printing is performed after the CMYK ink has dried, The base layer is characterized by the use of an OPP film having heat resistance such that the thermal shrinkage at 150°C is 15% or less, and the thermal elongation E (%) in the MD direction when measured by TMA (mechanical thermal analysis) under conditions of a heating rate of 5°C / min and a load of 0.5 kg / mm2 satisfies formula (1) from 120°C to 150°C. log(E)≦0.0275T-2.4839...Equation (1) (where T is temperature (°C))

[0011] Furthermore, the invention described in claim 2 is characterized in that in the packaging material, white printing is performed using aqueous inkjet printing.

[0012] Furthermore, the invention described in claim 3 is characterized in that in the packaging material, the white printing is performed by flexographic printing.

[0013] Moreover, the invention described in claim 4 is characterized in that in the packaging material, the thickness of the base material layer is 15 to 50 μm.

[0014] Furthermore, the invention described in claim 5 is characterized in that in the packaging material, the sealant layer is made of PP or PE. [Effects of the Invention]

[0015] According to the present invention having the above-mentioned configuration, by using heat-resistant OPP, which has higher heat resistance than general OPP, it is possible to eliminate distortion of the film after color printing in aqueous inkjet printing, and to realize packaging materials made of mono-material, mono-olefin film that have a beautiful appearance and a low environmental impact. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of a packaging material according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Fig. 1 is a cross-sectional view of the packaging material of the present invention. The packaging material of the present invention uses, as base layer 1, an OPP film with a thickness of 15 to 50 µm that has heat resistance such that its thermal shrinkage at 150°C is 15% or less and its thermal elongation E (%) in the MD direction satisfies formula (1) from 120°C to 150°C when measured by TMA (mechanical thermal analysis) under conditions of a heating rate of 5°C / min and a load of 0.5 kg / mm2. log(E)≦0.0275T-2.4839...Equation (1) (where T is temperature (°C))

[0018] The sealant layer 2 uses a polyolefin film such as polypropylene (PP) or polyethylene (PE).

[0019] After applying an anchor coat 3 to the base layer 1, CMYK color printing 4 is performed by aqueous inkjet printing, and after the CMYK ink has dried, white printing 5 is performed, thereby obtaining the packaging material of the present invention.

[0020] Drying after the CMYK color printing and white printing is done with a hot air dryer, but drying after the anchor coat is done with an infrared IR heating device. The anchor coat is applied thinly to the entire surface and does not require much drying energy, so it can be achieved with infrared IR heating and does not particularly affect film shrinkage or distortion. Furthermore, even if some distortion occurs in the film, it is transparent and coated over the entire surface, so it does not affect the printing register.

[0021] White printing often requires high density, and when printing with aqueous inkjet printing, care must be taken to print twice using two heads, so flexographic printing may also be used. [Explanation of symbols]

[0022] 1 Base material layer 2 Sealant Layer 3 Anchor Court 4 color printing 5 White printing

Claims

1. A film having two or more layers, which is composed of at least a base layer and a sealant layer using a polyolefin film, is used. In a packaging material in which CMYK color printing is performed on a base layer using aqueous inkjet printing, and white printing is performed after the CMYK ink has dried, A packaging material characterized in that the base layer uses an OPP film having heat resistance such that the thermal shrinkage rate at 150°C is 15% or less, and the heat elongation E (%) in the MD direction satisfies formula (1) from 120°C to 150°C when measured by TMA (mechanical thermal analysis) under conditions of a heating rate of 5°C / min and a load of 0.5 kg / mm2. log(E)≦0.0275T-2.4839...Formula (1) (where T is the temperature (°C))

2. 2. The packaging material according to claim 1, wherein the white printing is performed by aqueous ink jet printing.

3. 2. The packaging material according to claim 1, wherein the white printing is performed by flexographic printing.

4. 4. The packaging material according to claim 1, wherein the thickness of the substrate layer is 15 to 50 μm.

5. 5. The packaging material according to claim 1, wherein the sealant layer is made of PP or PE.

Images