An easy-to-stick and easy-to-tear in-mold label film and its preparation method and application

Abstract

The present invention relates to an easy-to-stick and easy-to-tear in-mold label film, a preparation method thereof, and an application thereof, and belongs to the technical field of in-mold labels. The easy-to-stick and easy-to-tear in-mold label film of the present invention comprises a first surface layer, a support layer, a second surface layer, and a roughened adhesive layer arranged in sequence; the second surface layer is composed of homopolypropylene; and the roughened adhesive layer is composed of propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer. The easy-to-stick and easy-to-tear in-mold label film prepared by the present invention using a specific method is used for in-mold labeling after being made into an in-mold label. It can effectively bond the in-mold label to the plastic part without easily generating bubbles, and can also make the in-mold label easily peelable from the plastic part, thereby achieving the technical effect of easy sticking and tearing.

Description

Technical Field

[0001] The present invention relates to the technical field of in-mold labels, and in particular to an easy-to-stick and easy-to-tear in-mold label film, a preparation method thereof, and an application thereof. Background Art

[0002] In-mold labeling (IML) technology involves forming an IML film into an IML label. The IML label is then integrated with the plastic part during IML molding, creating a secure bond between the IML label and the plastic part, resulting in a plastic part bearing the IML label (i.e., an IML-labeled product). This IML-labeled product exhibits wide temperature adaptability and weather resistance, enabling use in both high and low latitudes and at both high and low altitudes. It resists warping or detachment due to temperature fluctuations or altitude changes. IML technology has driven the rapid development of IML film, particularly in the food, cosmetic, chemical, and pharmaceutical industries.

[0003] With the development of simple recycling of plastic products, in-mold labeling technology also faces the following problems: most in-mold label films are made of polypropylene, while most plastic parts are made of polyethylene, polyester or polyamide. In addition, the in-mold label film usually needs to be printed with ink to make an in-mold label, which is then used for in-mold labeling to form a plastic part with an in-mold label. When recycling plastic parts with in-mold labels, the in-mold label and the plastic part are made of different materials, and the surface of the in-mold label has ink, which makes it difficult to recycle the plastic part with the in-mold label as pure resin. Therefore, the in-mold label needs to be separated from the plastic part and then recycled separately. However, after the in-mold label made of traditional in-mold label film is integrated with the plastic part, the in-mold label and the plastic part are extremely firmly bonded, making it difficult to separate the in-mold label from the plastic part by manual or mechanical peeling, making it difficult to achieve separate recycling of the in-mold label and plastic parts.

[0004] For traditional in-mold label films, see Figure 1, including a first surface layer 1, a support layer 2 and a laminating layer 4-2 (composed of polyolefin) arranged in sequence. The preparation method thereof is generally to realize the lamination of a three-layer structure through an integrated molding method of co-extrusion-biaxial stretching. Specifically, the raw materials of the first surface layer 1, the support layer 2 and the laminating layer 4-2 are subjected to an extrusion-sheet casting process, a longitudinal stretching process, a transverse stretching process, a traction-thickness measurement-corona-winding process, and an aging-slitting process to prepare an in-mold label film. However, in the longitudinal stretching process, since the laminating layer 4-2 needs to be in contact with the heating roller, and the polyolefin used in the laminating layer 4-2 of the current traditional in-mold label film has a low melting point, the heating roller through which the laminating layer 4-2 passes needs to be additionally provided with a Teflon coating and needs to be stretched at a low temperature. Otherwise, the laminating layer 4-2 is likely to be damaged during longitudinal stretching. However, the provision of the Teflon coating will require additional processing fees and the poor wear resistance of the Teflon coating will require frequent maintenance, thereby increasing production costs. Low-temperature stretching is prone to form longitudinal stretching stripes due to insufficient longitudinal heating and is prone to produce a high thermal shrinkage rate, affecting the subsequent processing performance of the prepared in-mold label film.

[0005] In addition, the laminating layer 4-2 of conventional in-mold label films has a room temperature adhesion phenomenon. After the in-mold labels are made, the problem of labels being connected between the stacked in-mold labels is easy to occur. This is called "connected label phenomenon" in the industry. To solve this problem, the industry generally embosses the surface of the laminating layer 4-2. The surface of the laminating layer 4-2 is given an uneven texture through the molding process. Please refer to Figure 1 This pattern helps reduce the contact area between the laminating layer 4-2 and the printed layer (printed on the first surface layer 1) between stacked in-mold labels after the in-mold label film is made into in-mold labels, thereby reducing the room temperature adhesion and preventing the occurrence of continuous labels. However, this operation will result in additional costs such as investment in embossing equipment, energy consumption, material loss, and labor investment. In addition, when traditional in-mold label film is used for in-mold labeling after being made into in-mold labels, please refer to Figure 1 and Figure 2 Although the laminating layer 4-2 has embossing on its surface, the embossing will collapse under the high temperature of in-mold labeling (the reason for the embossing collapse is that the high temperature of in-mold labeling will melt not only the raised patterns of the laminating layer 4-2, but also the non-raised parts of the laminating layer 4-2). This embossing collapse will partially block the gas flow path (i.e., the exhaust path), resulting in the laminating layer 4-2 being welded to the plastic part. Figure 2 , blocking the exhaust passage, making it difficult for gas to be discharged from between the laminating layer 4-2 and the plastic part O', causing gas accumulation and resulting in bubbles between the in-mold label and the plastic part, resulting in abnormal appearance of the bubbles in the in-mold labeling product (for example Figure 2 (the bubble anomaly point in the image). Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide an easy-to-stick and easy-to-tear in-mold label film, and its preparation method and application. The present invention is prepared by a specific method. No Teflon coating is required and no low-temperature stretching is required during the preparation process. The prepared easy-to-stick and easy-to-tear in-mold label film is made into an in-mold label and used in in-mold labeling. It can effectively bond the in-mold label to the plastic part and is not easy to generate bubbles. It can also make the in-mold label easily peeled off from the plastic part, achieving the technical effect of easy sticking and easy tearing.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A first object of the present invention is to provide a method for preparing an easy-to-stick and easy-to-tear in-mold label film, the easy-to-stick and easy-to-tear in-mold label film comprising a first surface layer, a support layer, a second surface layer, and a roughened adhesive layer arranged in sequence; the second surface layer is composed of homopolypropylene; the roughened adhesive layer is composed of a propylene-ethylene copolymer or a maleic anhydride-grafted propylene-ethylene copolymer; the method for preparing the easy-to-stick and easy-to-tear in-mold label film comprises the following steps:

[0009] The raw material of the roughening bonding layer is ground into a powder form, that is, the roughening bonding layer powder is obtained, and the surface of the roughening bonding layer powder is subjected to a high-voltage tip discharge process to obtain a static electricity of - / + (25-30) KV, and is set aside (this step can be completed before the roughening treatment process, and the order is not limited);

[0010] The raw materials of the first surface layer, the supporting layer and the second surface layer are respectively fed into the extruders of the corresponding layers, and are formed into cast sheets through the extrusion-casting process;

[0011] The cast sheet is subjected to a longitudinal stretching process to form a thick sheet;

[0012] The thick sheet undergoes a roughening treatment process: the roughening adhesive layer powder is adsorbed and welded to the second surface of the thick sheet to form a roughened thick sheet;

[0013] The roughened thick sheet undergoes a transverse stretching process, a traction-thickness measurement-corona-winding process to obtain a film semi-finished product;

[0014] The semi-finished film is subjected to an aging-slitting process to obtain a finished film, namely the easy-to-stick and easy-to-tear in-mold label film.

[0015] The present invention provides a method for preparing an easy-to-apply and easy-to-tear in-mold label film. The raw materials for a first surface layer, a support layer, and a second surface layer are melted separately through an extruder, and then co-extruded and chilled in an extrusion-sheeting step to form a cast sheet having a three-layer laminate structure (i.e., a first surface layer, a support layer, and a second surface layer). The cast sheet undergoes a longitudinal stretching step to obtain a thick sheet having a longitudinally stretched three-layer laminate structure. During the longitudinal stretching step, because the second surface layer is made of homopolypropylene, which has a higher melting point (160-168°C) than the laminating layer of conventional in-mold label films, the heated rollers on which the second surface layer passes do not require Teflon coating or low-temperature stretching. The second surface layer is less susceptible to burns and breakage during the heated rollers (heated to 138-140°C), and is also less susceptible to longitudinal streaks associated with poor longitudinal stretching. This avoids the problems of additional coating processing costs and reduced dimensional stability. The present invention pre-grinds the raw material for the roughened adhesive layer into a powdered form. Using a high-voltage tip discharge process, the surface of the roughened adhesive layer powder is subjected to a static charge of - / + (25-30) kV. During the roughening process, the static charge on the surface of the roughened adhesive layer powder is utilized to cause the roughened adhesive layer powder to adhere to the second surface layer of the slab and fuse to the slab, forming a roughened slab. The roughened adhesive layer powder on the roughened slab is densely packed. The roughened slab then undergoes a transverse stretching process, where the gaps between the roughened adhesive layer powder change from a densely packed state to a staggered arrangement. Simultaneously, the roughened adhesive layer powder further fuses to the second surface layer, further reducing the protrusion of the roughened adhesive layer powder from the second surface layer. The film is then subjected to a traction-thickness measurement-corona discharge-winding process to obtain a semi-finished film. The semi-finished film undergoes an aging-slitting process to obtain the finished film, namely the easy-to-stick and easy-to-tear in-mold label film.

[0016] The present invention employs homopolypropylene as the second surface layer, and propylene-ethylene copolymer or maleic anhydride-grafted propylene-ethylene copolymer as the roughened adhesive layer. Since propylene-ethylene copolymer or maleic anhydride-grafted propylene-ethylene copolymer are copolymers primarily composed of propylene (with a high propylene content of 85-95 wt%), this design facilitates the fusion of the roughened adhesive layer powder with the second surface layer, preventing it from falling off. A roughening treatment process allows the roughened adhesive layer powder to adsorb and densely accumulate on the surface of the second surface layer. After a transverse stretching process, the gaps between the roughened adhesive layer powders change from densely packed to a staggered arrangement, ultimately forming a roughened adhesive layer with a (ellipsoidal) concave-convex pattern on the surface of the second surface layer. This pattern of roughened adhesive layer reduces room-temperature bonding strength and prevents continuous stretching. Furthermore, the pattern of convex-concave patterns provides venting channels formed between the staggered arrangement of the roughened adhesive layer powders, facilitating subsequent degassing during in-mold labeling. Therefore, when the easy-to-stick, easy-to-tear in-mold label film of the present invention is fabricated into an in-mold label and used for in-mold labeling, the roughened adhesive layer's concave-convex texture exhibits a staggered, localized contact and adhesion with the plastic part. However, the second surface layer is composed of homopolypropylene. Due to the significant difference in solubility parameters between homopolypropylene and commonly used plastic material (such as polyethylene, polyester, or polyamide), the second surface layer does not adhere to the plastic part. Consequently, the in-mold label fabricated from the easy-to-stick, easy-to-tear in-mold label film of the present invention does not fully contact and adhere to the plastic part, but rather exhibits staggered, localized contact and adhesion. Furthermore, because the raw material of the roughened adhesive layer is propylene-based propylene-ethylene copolymer or maleic anhydride-grafted propylene-ethylene copolymer (with a propylene content of approximately 89-95 wt%), the bond strength between the roughened adhesive layer and the second surface layer is much stronger than the bond strength between the roughened adhesive layer and the plastic part. This allows the in-mold label to be easily peeled from the plastic part, facilitating the separate recycling of the in-mold label and the plastic part, thereby providing a simple solution for recycling. In addition, after the transverse stretching process, the gaps between the powders in the roughened adhesive layer change from tightly packed to staggered arrangements, forming a larger exhaust passage. Even if the roughened adhesive layer collapses during in-mold labeling, the exhaust passage will not be blocked, thereby avoiding bubble abnormalities.

[0017] In addition, the easy-to-stick and easy-to-tear in-mold label film prepared by the preparation method of the present invention has a roughened adhesive layer with a concave-convex pattern formed on the surface of the second surface layer. When the easy-to-stick and easy-to-tear in-mold label film is printed on the surface of the first surface layer and subjected to die-cutting and stacking steps to obtain a plurality of stacked in-mold labels, the roughened adhesive layer with a concave-convex pattern formed on the surface of the second surface layer prevents excessive contact area between the in-mold labels, thereby preventing the in-mold labels from being connected due to excessive contact area. During in-mold labeling, when removing a single in-mold label from the stack of multiple in-mold labels, the single in-mold label can be removed smoothly without the phenomenon of connected labels. That is, two or three in-mold labels cannot be removed, thereby preventing the placement of two or three in-mold labels in the mold from affecting in-mold labeling. When the in-mold label is applied in the mold, a roughened adhesive layer with concave and convex patterns is formed on the surface of the second surface layer, i.e., the surface topography of the in-mold label is rough, and exhaust passages are formed between the concave and convex patterns. Therefore, when the in-mold label is attached to the plastic part, gas can be exhausted in time through the exhaust passages without causing gas accumulation to form bubbles (no abnormal bubble phenomenon occurs), thereby greatly reducing the probability of bubbles forming between the in-mold label and the plastic part.

[0018] In the method for preparing an easy-to-stick, easy-to-tear in-mold label film of the present invention, a high-voltage tip discharge process is used to impart a static charge of - / + (25-30) kV to the surface of the roughened adhesive layer powder. During the roughening process, the static charge on the surface of the roughened adhesive layer powder is utilized to cause the roughened adhesive layer powder to adsorb and densely accumulate on the second surface layer of the thick sheet. This facilitates the subsequent transverse stretching process, whereby the gaps between the roughened adhesive layer powder are transformed from densely packed to staggered arrangements to form a concave-convex texture. If the static charge value on the surface of the roughened adhesive layer powder is less than 25 kV, the electrostatic adsorption force between the roughened adhesive layer powder and the second surface layer of the thick sheet is too low, resulting in insufficient adsorption and dense accumulation of the roughened adhesive layer powder on the second surface layer of the thick sheet. This results in a decrease in the roughness of the prepared easy-to-stick, easy-to-tear in-mold label film and a poor air venting effect. This, in turn, reduces the yield of in-mold labeling when used in in-mold labeling. If the static charge value on the surface of the roughened adhesive layer powder exceeds 30 kV, there is a risk of electrostatic injury during the film preparation process, posing a safety hazard.

[0019] As a preferred solution, the roughening process includes the following steps: applying a high-voltage tip discharge process to the second surface of the thick sheet so that the second surface of the thick sheet obtains + / - (25-30) KV static electricity; utilizing the mechanism of attraction between positive and negative charges to adsorb a layer of roughening adhesive layer powder on the second surface of the thick sheet, and utilizing the residual temperature of the thick sheet after the longitudinal stretching process to fuse the roughening adhesive layer powder and the second surface of the thick sheet together to form the roughened thick sheet. In the present invention, before the roughening process, the high-voltage tip discharge process is used to apply a high-voltage tip discharge process to the surface of the roughening adhesive layer powder to obtain - / + (25-30) KV static electricity, and during the roughening process, the high-voltage tip discharge process is used to apply a high-voltage tip discharge process to the second surface of the thick sheet to obtain + / - (25-30) KV static electricity. When the thick sheet passes through the roughening adhesive layer powder, the mechanism of attraction between positive and negative charges is utilized to neutralize the charges so that the second surface of the thick sheet adsorbs and densely accumulates to form a layer of roughening adhesive layer powder. At the same time, because the second surface of the thick sheet after the longitudinal stretching process has a relatively high residual temperature (in this field), the roughening process is carried out. It is well known to technicians that the second surface of the thick sheet obtained after the longitudinal stretching process will have a relatively high residual temperature, which is generally 138-140°C, and the melting point of propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer used in the roughened adhesive layer is 65-100°C). The residual temperature of the second surface of the thick sheet is used to weld the roughened adhesive layer powder to the second surface of the thick sheet, so that the roughened adhesive layer powder is difficult to fall off and prevent failure. A roughened adhesive layer with concave and convex patterns is formed on the second surface of the thick sheet, which together with the thick sheet constitutes a roughened thick sheet.

[0020] As a preferred solution, the transverse stretching ratio in the transverse stretching step is 8-10. The roughened adhesive layer powders on the roughened thick sheet obtained after the roughening step are tightly packed together. By controlling the transverse stretching to 8-10 times in the transverse stretching step, the gaps between the roughened adhesive layer powders can be changed from tightly packed to staggered arrangement, which is conducive to degassing during in-mold labeling.

[0021] As a preferred embodiment, after the longitudinal stretching process, the temperature of the second surface layer of the slab is 138-140°C. By controlling the temperature of the second surface layer of the slab to reach 138-140°C after the longitudinal stretching process, the present invention facilitates the roughening treatment process. After the roughening adhesive layer powder is adsorbed on the second surface layer of the slab, the residual heat of the second surface layer of the slab allows the roughening adhesive layer powder (melting point 65-100°C) to be fused to the second surface layer of the slab.

[0022] As a preferred embodiment, the roughened adhesive layer powder is prepared by cooling the raw material for the roughened adhesive layer (in the form of resin particles, preferably with an average particle size of 4-5 mm) with liquid nitrogen, grinding it in a grinder, and then sieving it with a sieving vibrator to obtain a powder with an average particle size of 40-60 µm, thereby obtaining the roughened adhesive layer powder. By preparing the raw material for the roughened adhesive layer into a powder with an average particle size of 40-60 µm, the roughened adhesive layer powder can be effectively adsorbed to the surface of the second surface layer due to electrostatic attraction during the roughening process. Furthermore, after the roughened thick sheet undergoes a transverse stretching process, the protrusion height of the roughened adhesive layer on the second surface layer is reduced from 40-60 µm to 4-6 µm.

[0023] As a preferred solution, after obtaining the roughened bonding layer powder, the roughened bonding layer powder is placed in a powder tank, and then the roughened bonding layer powder in the powder tank is subjected to a high-voltage tip discharge process so that the surface of the roughened bonding layer powder in the powder tank obtains a static electricity of - / + (25-30) KV.

[0024] As a preferred solution, during the roughening process, after the second surface of the slab has been subjected to a static charge of + / - (25-30) kV, the slab is passed through a powder trough, where the distance between the second surface of the slab and the roughened adhesive layer powder in the trough is 10-20 mm. By maintaining this distance of 10-20 mm, the second surface of the slab can quickly and effectively absorb a layer of roughened adhesive layer powder, resulting in a dense accumulation of the roughened adhesive layer powder on the second surface.

[0025] As a preferred solution, the ethylene content in the propylene-ethylene copolymer is 5-11 wt%.

[0026] As a preferred solution, the propylene-ethylene copolymer has a melting point of 65-100°C and a melt index of 1-8 g / 10 min (230°C, 2.16 kg).

[0027] As a preferred solution, the maleic anhydride grafting rate in the maleic anhydride grafted propylene-ethylene copolymer is 0.8-1.3 wt %, and the ethylene content in the maleic anhydride grafted propylene-ethylene copolymer is 5-11 wt %.

[0028] As a preferred solution, the maleic anhydride grafted propylene-ethylene copolymer has a melting point of 65-100°C and a melt index of 1-8 g / 10 min (230°C, 2.16 kg).

[0029] As a preferred embodiment, the first surface layer comprises homopolypropylene and 0.3-1.5 wt% of an anti-blocking agent. The first surface layer is used for surface printing. During the process of forming the easy-to-stick, easy-to-tear in-mold label film into an in-mold label, ink can be printed on the surface of the first surface layer to form a printed layer. Furthermore, by adding an anti-blocking agent to the first surface layer, the anti-blocking effect of the first surface layer can be enhanced, preventing film adhesion.

[0030] As a preferred solution, the anti-adhesion agent is at least one of silicon dioxide and polymethyl methacrylate, and the average particle size of the anti-adhesion agent is 4-5 μm.

[0031] As a preferred embodiment, the support layer comprises homopolypropylene, 0-20wt% calcium carbonate, 5-30wt% titanium dioxide, and 0.4-1.5wt% antistatic agent. Adding ≤20wt% calcium carbonate and 5-30wt% titanium dioxide to the support layer improves the hiding power of the easy-to-stick, easy-to-tear in-mold label film. After the easy-to-stick, easy-to-tear in-mold label film is fabricated into an in-mold label for in-mold labeling, consumers will not see the uneven texture (roughening) of the roughened adhesive layer. If the calcium carbonate addition exceeds 20wt%, the support layer will experience severe cavitation, prone to delamination after in-mold labeling, and some label material will remain on the surface of the plastic part, contaminating plastic recycling. If the titanium dioxide addition ratio exceeds 30wt%, the cohesive strength of the support layer will drop significantly, and it will be easy to delaminate after in-mold labeling. Part of the label material will remain on the surface of the plastic part and pollute plastic recycling. If the titanium dioxide addition ratio is less than 5wt%, the covering performance of the support layer will be insufficient, resulting in the roughened adhesive layer with staggered roughened texture, which will be observed by consumers and mistakenly believed to be a labeling defect.

[0032] As a preferred solution, in the support layer, the calcium carbonate is heavy calcium carbonate, and (after grinding) the average particle size of the calcium carbonate is 1-2 μm.

[0033] As a preferred solution, in the support layer, the titanium dioxide is rutile titanium dioxide synthesized by a chlorination method, and the average particle size of the titanium dioxide is 0.2-0.4 μm.

[0034] As a preferred solution, in the support layer, the antistatic agent is at least one of glyceryl monostearate, ethoxylated alkylamine, N,N-dihydroxyethyl lauramide, ethoxylated alcohol, alkyl sulfonate, alkyl phosphate, tetraalkyl quaternary ammonium salt, trialkylbenzyl quaternary ammonium salt, and alkyl betaine.

[0035] As a preferred solution, the homopolypropylene in the first surface layer, the support layer and the second surface layer has a melt index of 2.8-3.2 g / 10 min (230°C, 2.16 kg), an isotacticity of 95-97%, and a melting point of 160-168°C.

[0036] Another object of the present invention is to provide an easy-to-stick and easy-to-tear in-mold label film prepared by any of the above-mentioned preparation methods.

[0037] Another object of the present invention is to provide an application of an easy-to-stick and easy-to-tear in-mold label film in in-mold labeling: after the easy-to-stick and easy-to-tear in-mold label film is made into an in-mold label, the in-mold label is integrated with a plastic part through in-mold labeling to form a plastic part with an in-mold label.

[0038] As a preferred embodiment of the present invention, when the roughened adhesive layer is composed of a propylene-ethylene copolymer, the plastic part is preferably a polyethylene plastic part; when the roughened adhesive layer is composed of a maleic anhydride grafted propylene-ethylene copolymer, the plastic part is preferably a polyester plastic part (for example, a polyethylene terephthalate (PET) plastic part, a polycarbonate (PC) plastic part) or a polyamide plastic part (for example, a polyamide 6 (PA6) plastic part, a polyamide 66 (PA66) plastic part).

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The preparation method of the easy-to-stick and easy-to-tear in-mold label film of the present invention uses a specific roughening treatment process to allow the roughened adhesive layer powder to be adsorbed and densely accumulated on the second surface layer. After the transverse stretching process, the gaps between the roughened adhesive layer powder are changed from densely accumulated to staggered arrangement, so that the second surface layer of the prepared easy-to-stick and easy-to-tear in-mold label film is formed with a roughened adhesive layer with concave and convex textures. After the easy-to-stick and easy-to-tear in-mold label film is made into in-mold labels, the effective contact area between the in-mold labels can be greatly reduced, thereby avoiding the occurrence of continuous stretching.

[0041] The second surface layer of the easy-to-stick and easy-to-tear in-mold label film of the present invention is formed with a roughened adhesive layer having concave-convex patterns, and exhaust passages are formed between the concave-convex patterns. When the in-mold label is attached to the plastic part, gas can be promptly exhausted through the exhaust passages without causing gas accumulation to form bubbles (no abnormal bubble phenomenon occurs). This greatly reduces the probability of bubbles forming between the in-mold label and the plastic part, thereby improving the yield of in-mold labeling.

[0042] The present invention utilizes a specific method for preparation, and does not require a Teflon coating or low-temperature stretching during the preparation process. The prepared easy-to-stick and easy-to-tear in-mold label film can be used for in-mold labeling after being made into an in-mold label. It can effectively bond the in-mold label to the plastic part without easily generating bubbles, and can also easily peel the in-mold label from the plastic part, achieving the technical effect of easy sticking and easy tearing.

[0043] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the structure of a traditional in-mold label film;

[0045] Figure 2 Schematic diagram of the bonding between an in-mold label made of a traditional in-mold label film and a plastic part ( Figure 2 The in-mold label N in the figure only shows the laminating layer 4-2 and another layer. It should be understood that the other layer includes the printing layer, the first surface layer 1, and the support layer 2 arranged in order from top to bottom);

[0046] Figure 3 This is a schematic structural diagram of an easy-to-stick and easy-to-tear in-mold label film of the present invention;

[0047] Figure 4 Schematic diagram of the bonding between the in-mold label made of the easy-to-stick and easy-to-tear in-mold label film of the present invention and the plastic part ( Figure 4 The in-mold label N in the figure only shows the roughened adhesive layer 4-1 and another layer. It should be understood that the other layer includes a printing layer, a first surface layer 1, a support layer 2, and a second surface layer 3 arranged in order from top to bottom);

[0048] Figure 5 This is a production process flow chart of an easy-to-stick and easy-to-tear in-mold label film of the present invention;

[0049] Figure 6 This is a process flow chart for applying an easy-to-stick and easy-to-tear in-mold label film of the present invention;

[0050] Figure 7 This is a schematic diagram showing that the gaps between the powders in the roughened adhesive layer of the easy-to-stick and easy-to-tear in-mold label film of the present invention are changed from tightly packed to staggered arrangement after undergoing a transverse stretching process;

[0051] In the figure: 1. First surface layer; 2. Support layer; 3. Second surface layer; 4-1. Roughened adhesive layer; 4-2. Laminating layer; A. Raw material; B. Cast sheet; C. Thick sheet; D. Roughened thick sheet; E. Semi-finished film; F. Finished film; G. Extrusion-casting process; H. Longitudinal stretching process; I. Roughening process; J. Transverse stretching process; K. Traction-thickness measurement-corona-winding process; L. Aging-slitting process; M. Semi-finished in-mold label; N. In-mold label; O. Plastic part with in-mold label; O', plastic part; P. Printing process; Q. Die-cutting process; R. Negative pressure label feeding process; S. In-mold labeling process. DETAILED DESCRIPTION

[0052] To facilitate understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0053] The present invention provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0054] Among them, the raw material formula of each layer is as follows:

[0055] First surface layer 1: homopolymer polypropylene and anti-blocking agent;

[0056] Support layer 2: homopolymer polypropylene, calcium carbonate, titanium dioxide and antistatic agent;

[0057] Second surface layer 3: homopolymer polypropylene;

[0058] Roughened adhesive layer 4-1: propylene-ethylene copolymer or maleic anhydride-grafted propylene-ethylene copolymer.

[0059] In the easy-to-stick and easy-to-tear in-mold label film of the present invention, please refer to Figure 3 A roughened adhesive layer 4 - 1 having concave and convex patterns is formed on the surface of the second surface layer 3 .

[0060] The present invention also provides a method for preparing an easy-to-stick and easy-to-tear in-mold label film. Figure 5, comprising the following steps: premixing the screened raw materials A of the first surface layer 1, the support layer 2, and the second surface layer 3 according to the designed formula, stirring them evenly, weighing and calculating the input ratio, and feeding them into the extruders of the corresponding layers, and forming a casting sheet B after the extrusion-casting process G; the casting sheet B is formed into a thick sheet C after the longitudinal stretching process H, and after the longitudinal stretching process H, the surface temperature of the second surface layer 3 of the thick sheet C reaches 138-140°C; the thick sheet C undergoes a roughening treatment process I: a high-voltage tip discharge process is used on the surface of the second surface layer 3 of the thick sheet C, so that the surface of the second surface layer 3 of the thick sheet C obtains + / - (25-30) KV static electricity, and then the thick sheet C is passed through a powder tank containing coarse bonding layer powder (the powder tank has been subjected to a high-voltage tip discharge process in advance, so that the surface of the coarse bonding layer powder therein obtains - / + (25-30) KV static electricity, and the coarse bonding layer powder is the raw material of the coarse bonding layer (resin particles with an average particle size of 4-5 mm) cooled by liquid nitrogen and then placed in a grinder for grinding and sieving into powder with an average particle size of 40-60 nm), wherein the distance between the second surface layer of the thick sheet C and the coarse bonding layer powder in the powder tank is 10-20 mm, and after The positive and negative charges attract each other, and the charges are neutralized so that the second surface layer 3 of the thick sheet C is adsorbed and densely accumulated to form a layer of roughened adhesive layer powder. At the same time, because the surface temperature of the second surface layer 3 of the thick sheet C reaches 138-140°C after the longitudinal stretching process H, the residual heat of the second surface layer 3 of the thick sheet C is used to fuse with the roughened adhesive layer powder, so that the roughened adhesive layer powder is difficult to fall off and prevent failure, thereby obtaining a roughened thick sheet D; the roughened thick sheet D first undergoes a transverse stretching process J, and after the roughened thick sheet D undergoes the transverse stretching process J (the transverse stretching ratio is controlled at 8-10), the roughened thick sheet D is The gaps between the powders of the roughened adhesive layer are changed from tightly packed to staggered arrangement. In addition, the powders of the roughened adhesive layer will be further fused with the second surface layer 3 due to the temperature of the transverse stretching process J. At the same time, the protruding height of the powders of the roughened adhesive layer on the surface of the second surface layer 3 is reduced from 40-60µm to 4-6µm, and finally a roughened adhesive layer 4-1 with concave and convex patterns is formed on the surface of the second surface layer 3. Then, the semi-finished film E is obtained through the traction-thickness measurement-corona-winding process K. The semi-finished film E is finally subjected to the aging-slitting process L to obtain the finished film F, that is, the easy-to-stick and easy-to-tear in-mold label film.

[0061] The equipment used in the high-voltage tip discharge process is: induction discharge rod (working voltage: 0-50KV), model: SC-1, manufacturer: Jiangxi Senmu Electronics Co., Ltd.

[0062] The production equipment is a flat-film, step-by-step, biaxially oriented polypropylene production line supplied by Brückner, Germany, with a powder tank installed between the longitudinal and transverse stretching steps. The extruder, runners, piping, filters, and die heads used in this production line are controlled at temperatures between 230-260°C, with a quenching temperature between 25-40°C. The longitudinal stretching process consists of preheating, stretching, and shaping, with the process temperature (heated by heat-conducting rollers) controlled at 138-140°C. The transverse stretching process J, which consists of preheating, stretching, shaping, and cooling, is controlled at a process temperature (air-heated) between 150-180°C. The longitudinal stretch ratio is controlled between 4.0-6.0 times, and the transverse stretch ratio is controlled between 8.0-10.0 times.

[0063] The present invention also provides an easy-to-stick and easy-to-tear in-mold label film for use in in-mold labeling. Figure 6 The finished film F first undergoes a printing process P, which includes but is not limited to common processes such as rotary printing, offset printing, and flexographic printing, to obtain an in-mold label semi-finished product M. It then undergoes a die-cutting process Q to be cut into several in-mold labels N. The several in-mold labels N are stacked and placed on a label rack (the structure of each in-mold label N includes a printing layer, a first surface layer 1, a support layer 2, a second surface layer 3, and a roughened adhesive layer 4-1 arranged in sequence). The single in-mold label N is passed through a negative pressure label feeding process R and an in-mold labeling process S to finally obtain a plastic part O with an in-mold label.

[0064] In the plastic part O with an in-mold label of the present invention, please refer to Figure 4 An exhaust passage is formed between the roughened adhesive layer 4 - 1 of the in-mold label N and the plastic part O′ for gas discharge, which does not cause abnormal bubbles between the in-mold label N and the plastic part O′.

[0065] Example 1

[0066] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0067] Among them, the raw material formula of each layer is as follows:

[0068] First surface layer 1: 99.4wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg) and 0.6wt% silica (average particle size 5µm).

[0069] Support layer 2: 60wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 25wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0070] Second surface layer 3: 100wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point is 163℃, melt index is 3g / 10min, melt index test conditions: melting temperature is 230℃, load weight is 2.16kg).

[0071] Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content 9 wt%, density 0.879 g / cm 3 , melting point is 77°C, melt index is 8g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0072] This embodiment also provides a method for preparing an easy-to-stick and easy-to-tear in-mold label film, comprising the following steps:

[0073] (1) Grinding the raw material of the roughened adhesive layer 4-1 into a powder form, that is, cooling the raw material of the roughened adhesive layer 4 (resin particles, with an average particle size of 4 mm) with liquid nitrogen for 30 minutes, grinding it into powder using a grinder, and passing it through a sieving vibrator to obtain propylene-ethylene copolymer powder with an average particle size of 60 μm; placing the propylene-ethylene copolymer powder in a powder tank, and then using a high-voltage tip discharge process to make the surface of the propylene-ethylene copolymer powder in the powder tank obtain -28KV static electricity, and then set it aside;

[0074] (2) Please refer to Figure 5, the screened raw materials A of each layer of the first surface layer 1, the support layer 2, and the second surface layer 3 are premixed according to the designed formula, stirred evenly, and fed into each extruder after the input ratio is calculated by weighing, and formed into a casting sheet B after the extrusion-casting process G; the casting sheet B is formed into a thick sheet C after the longitudinal stretching process H, and the surface temperature of the second surface layer 3 of the thick sheet C reaches 138-140°C; the thick sheet C undergoes a roughening treatment process: a high-voltage tip discharge process is used on the surface of the second surface layer 3 of the thick sheet C, so that the second surface layer surface of the thick sheet C obtains +28KV static electricity, and then the above-mentioned thick sheet passes through the powder trough, wherein the distance between the second surface layer of the thick sheet and the roughened adhesive layer powder in the powder trough is 10mm, and through the positive and negative charge attraction mechanism, the second surface layer 3 of the thick sheet C is adsorbed and tightly stacked to form a layer of propylene-ethylene copolymer powder by neutralizing the charge. At the same time, due to the longitudinal stretching, the thick sheet C is subjected to a roughening treatment process. After the stretching process, the surface temperature of the second surface layer of the thick sheet reaches 138-140°C, and the residual heat of the thick sheet causes the second surface layer 3 of the thick sheet to be welded to the propylene-ethylene copolymer powder, which makes it difficult for the propylene-ethylene copolymer powder to fall off and prevent failure, thereby obtaining a roughened thick sheet D; then the roughened thick sheet D is first subjected to a transverse stretching process J, and the gaps between the propylene-ethylene copolymer powders are changed from tightly packed to staggered arrangement. In addition, due to the temperature of the transverse stretching process J, the propylene-ethylene copolymer powder will be further welded to the second surface layer 3 of the thick sheet, and the surface protrusion height is reduced from 60µm to 6µm, and finally a roughened adhesive layer 4-1 with concave and convex patterns is formed on the surface of the second surface layer 3; then the film semi-finished product E is obtained through the traction-thickness measurement-corona-winding process K; the film semi-finished product E is finally subjected to the aging-slitting process L to obtain the film finished product F.

[0075] The main production equipment is a flat-film, step-by-step, biaxially oriented polypropylene production line supplied by Brückner, Germany, located between the longitudinal and transverse stretching steps. The main extruder (for support layer 2) features a single-screw extruder with a screw diameter of 150 mm and an aspect ratio of 33:1. The two auxiliary extruders (for the first and second skin layers 1 and 3) are single-screw extruders with screw diameters of 120 mm and an aspect ratio of 30:1. The extruder temperature is 250°C in all sections except the feed section, which is 80°C. The filter, flow channel, and die sections are all set at 250°C, and the quenching (cast film) temperature is 30°C. During the longitudinal stretching step H, the preheating, stretching, and shaping zones for the first and second skin layers 1 and 3 are 140°C, 138°C, and 140°C, respectively. The longitudinal stretch ratio is 5.0. In the transverse stretching process J, the corresponding temperatures of the preheating zone, stretching zone and shaping zone are 170°C, the stretching zone is 157°C, the shaping zone is 175°C, the transverse stretching ratio is 9.0, and the production speed is 300m / min. The corona intensity of the surface of the first surface layer 1 is 30W·min / m 2.

[0076] The total thickness of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is 105 μm, the first surface layer 1 is 1 μm thick, the support layer 2 is 97 μm thick, the second surface layer 3 is 1 μm thick, and the roughened adhesive layer 4 is about 6 μm thick.

[0077] This embodiment also provides an application process for an easy-to-stick and easy-to-tear in-mold label film. Figure 6 The finished film F (i.e., an easy-to-stick and easy-to-tear in-mold label film) first undergoes a printing process P, which includes but is not limited to common processes such as flexographic printing, offset printing, and rotary printing, to obtain an in-mold label semi-finished product M. It then undergoes a die-cutting process Q to be cut into a number of in-mold labels N. The several in-mold labels N are stacked (500 sheets / stack) and placed on a label rack (the structure of each in-mold label N includes a printing layer, a first surface layer 1, a support layer 2, a second surface layer 3, and a roughened adhesive layer 4 arranged in sequence). After the negative pressure label feeding process R and the in-mold labeling process S, a high-density polyethylene plastic part O with an in-mold label is formed.

[0078] Comparative Example 1

[0079] This comparative example provides a traditional in-mold label film. Figure 1 It is a three-layer structure, including a first surface layer 1, a support layer 2 and a bonding layer 4-2 arranged in sequence.

[0080] Among them, the raw material formula of each layer is as follows:

[0081] First surface layer 1: 99.4wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg) and 0.6wt% silica (average particle size 5µm).

[0082] Support layer 2: 60wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 25wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0083] Laminating layer 4-2: 100wt% ethylene-octene copolymer (octene content is 17wt%, density is 0.905g / cm 3, melting point is 97°C, melt index is 7.5g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0084] The preparation method of the conventional in-mold label film of this comparative example is basically the same as that of Example 1, except that:

[0085] 1. Eliminate step (1), and in step (2), produce the first surface layer 1, the support layer 2, and the laminating layer 4-2 (replacing the second surface layer 3 of Example 1) using the raw materials, and simultaneously eliminate the roughening treatment process in step (2);

[0086] 2. In the longitudinal stretching process, a Teflon coating is provided on the surface of the heating roller through which the laminating layer 4-2 passes, and the heating temperature of the heating roller is 105-110°C;

[0087] 3. After the film is made, a new molding process for the laminating layer 4-2 is required to make the surface of the laminating layer 4-2 uneven.

[0088] Specifically, the preparation method of the conventional in-mold label film of this comparative example comprises the following steps:

[0089] The selected raw materials for the first surface layer 1, support layer 2, and laminating layer 4-2 are premixed according to the designed formula, stirred evenly, and weighed to calculate the input ratio before being fed into separate extruders. After the extrusion-casting process, the cast sheet is formed. The cast sheet undergoes a longitudinal stretching process to form a thick sheet. The heating rollers that the laminating layer 4-2 passes through are coated with Teflon to prevent burns and damage caused by processing temperatures exceeding the melting point of the laminating layer 4-2 material. The heating rollers are heated to 105-110°C. The thick sheet then undergoes a transverse stretching process, followed by a traction-thickness measurement-corona treatment-winding process to obtain a semi-finished film. The semi-finished film finally undergoes an aging-slitting process to obtain the finished film. The surface of the laminating layer 4-2 of the finished film is molded to give it an uneven surface.

[0090] The main production equipment is a flat-film, step-by-step, biaxially oriented polypropylene production line provided by Brückner, Germany. The main extruder (for support layer 2) has a single-screw screw diameter of 150 mm and an aspect ratio of 33:1. The two auxiliary extruders (for the first surface layer 1 and the laminating layer 4-2, respectively) are single-screw extruders with screw diameters of 120 mm and an aspect ratio of 30:1. The extruder temperature is 250°C in all sections except the feed section, which is 80°C. The filter, flow channel, and die sections are all kept at 250°C, and the quenching temperature (for cast film) is 30°C. In the longitudinal stretching process H, the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by the first surface layer 1 are 140°C, 138°C and 140°C respectively, and the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by the bonding layer 4-2 are 110°C, 105°C and 110°C respectively. The surface of the heating roller passed by the bonding layer 4-2 is treated with Teflon coating to prevent the surface of the bonding layer 4-2 from being burned or damaged. The longitudinal stretching ratio is 5.0. In the transverse stretching process J, the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by are 170°C, the stretching zone is 157°C, and the shaping zone is 175°C. The transverse stretching ratio is 9.0, and the production speed is 300m / min. The corona intensity of the surface of the first surface layer 1 is 30W·min / m 2 .

[0091] The total thickness of the conventional in-mold label film of this comparative example is 105 μm, the thickness of the first surface layer 1 is 1 μm, the thickness of the support layer 2 is 98 μm, and the thickness of the laminating layer 4-2 is 6 μm.

[0092] The application process of the conventional in-mold label film in this comparative example is the same as that in Example 1. Figure 6 The finished film F (i.e., traditional in-mold label film) first undergoes a printing process P, which includes but is not limited to common processes such as flexographic printing, offset printing, and rotary printing, to obtain an in-mold label semi-finished product M. It then undergoes a die-cutting process Q to be cut into several in-mold labels N. The several in-mold labels N are stacked (500 sheets / stack) and placed on a label rack (the structure of each in-mold label N includes a printing layer, a first surface layer 1, a support layer 2, and a laminating layer 4-2 arranged in sequence). After the negative pressure label feeding process R and the in-mold labeling process S, a high-density polyethylene plastic part O with an in-mold label is formed.

[0093] Example 2

[0094] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0095] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the proportion of calcium carbonate in the support layer 2 is 20 wt %, that is:

[0096] Support layer 2: 54.5wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 25wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 20wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0097] The preparation method of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0098] The total thickness and thickness of each layer of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1.

[0099] The application process of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides an in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0102] The formulations of the various layers of the in-mold label film of this comparative example are the same as those of Example 1, except that the proportion of calcium carbonate in the support layer 2 is 25 wt %, that is:

[0103] Support layer 2: 49.5wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 25wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 25wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0104] The preparation method of the in-mold label film of this comparative example is the same as that of Example 1.

[0105] The total thickness and thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0106] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0107] Example 3

[0108] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0109] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the proportion of titanium dioxide in the support layer 2 is 5 wt %, that is:

[0110] Support layer 2: 80wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 5wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0111] The preparation method of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0112] The total thickness and thickness of each layer of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1.

[0113] The application process of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0114] Example 4

[0115] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0116] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the proportion of titanium dioxide in the support layer 2 is 30 wt %, that is:

[0117] Support layer 2: 55wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 30wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0118] The preparation method of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0119] The total thickness and thickness of each layer of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1.

[0120] The application process of the easy-to-stick and easy-to-tear in-mold label film of this embodiment is the same as that of Example 1.

[0121] Comparative Example 3

[0122] This comparative example provides an in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0123] The formulations of the various layers of the in-mold label film of this comparative example are the same as those of Example 1, except that the proportion of titanium dioxide in the support layer 2 is 4 wt %, namely:

[0124] Support layer 2: 81wt% homopolymer polypropylene (isotacticity 95%, density 0.905g / cm 3 , melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 4wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0125] The preparation method of the in-mold label film of this comparative example is the same as that of Example 1.

[0126] The total thickness and thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0127] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0128] Comparative Example 4

[0129] This comparative example provides an in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0130] The formulations of the various layers of the in-mold label film of this comparative example are the same as those of Example 1, except that the proportion of titanium dioxide in the support layer 2 is 35 wt %, that is:

[0131] Support layer 2: 50wt% homopolymer polypropylene (isotacticity is 95%, density is 0.905g / cm 3, melting point 163 ° C, melt index 3g / 10min, melt index test conditions: melting temperature 230 ° C, load weight 2.16kg), 35wt% titanium dioxide (chloride process, rutile type, average particle size 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2µm) and 0.5wt% glyceryl monostearate.

[0132] The preparation method of the in-mold label film of this comparative example is the same as that of Example 1.

[0133] The total thickness and thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0134] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0135] Example 5

[0136] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0137] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the roughened adhesive layer 4-1 is composed of a maleic anhydride-grafted propylene-ethylene copolymer, namely:

[0138] Roughened adhesive layer 4-1: 100 wt% maleic anhydride grafted propylene-ethylene copolymer (maleic anhydride content of 1.0 wt%, ethylene content of 9 wt%, density of 0.879 g / cm 3 , melting point is 77°C, melt index is 8g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0139] The preparation method of the in-mold label film of this embodiment is basically the same as that of Example 1.

[0140] The total thickness and thickness of each layer of the in-mold label film of this embodiment are the same as those of Example 1.

[0141] The application process of the in-mold label film of this embodiment is basically the same as that of Example 1, except that the plastic part is a polyethylene terephthalate plastic part, that is, a polyethylene terephthalate plastic part O with an in-mold label is finally formed.

[0142] Example 6

[0143] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0144] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 5 wt % and the density is 0.887 g / cm 3 , the melting point is 100℃, that is:

[0145] Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content 5 wt%, density 0.887 g / cm 3 , melting point is 100℃, melt index is 8g / 10min, melt index test conditions: melting temperature is 190℃, load weight is 2.16kg).

[0146] The preparation method of the in-mold label film of this embodiment is basically the same as that of Example 1.

[0147] The total thickness and thickness of each layer of the in-mold label film of this embodiment are the same as those of Example 1.

[0148] The application process of the in-mold label film of this embodiment is the same as that of Example 1.

[0149] Comparative Example 5

[0150] This comparative example provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0151] The formulations of the easy-to-stick and easy-to-tear in-mold label film of this comparative example are the same as those of Example 1, except that the ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 4 wt %, and the density is 0.889 g / cm 3 , the melting point is 103℃, that is:

[0152] Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content is 4 wt%, density is 0.889 g / cm 3 , melting point is 103℃, melt index is 8g / 10min, melt index test conditions: melting temperature is 190℃, load weight is 2.16kg).

[0153] The preparation method of the in-mold label film of this comparative example is basically the same as that of Example 1.

[0154] The total thickness and thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0155] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0156] Example 7

[0157] This embodiment provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0158] The formulations of the layers of the easy-to-stick and easy-to-tear in-mold label film of this embodiment are the same as those of Example 1, except that the ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 11 wt %, and the density is 0.873 g / cm 3 , the melting point is 65℃, that is:

[0159] Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content 11 wt%, density 0.873 g / cm 3 , melting point is 65℃, melt index is 8g / 10min, melt index test conditions: melting temperature is 190℃, load weight is 2.16kg).

[0160] The preparation method of the in-mold label film of this embodiment is basically the same as that of Example 1.

[0161] The total thickness and thickness of each layer of the in-mold label film of this embodiment are the same as those of Example 1.

[0162] The application process of the in-mold label film of this embodiment is the same as that of Example 1.

[0163] Comparative Example 6

[0164] This comparative example provides an easy-to-stick and easy-to-tear in-mold label film. Figure 3 It is a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3 and a roughened adhesive layer 4-1 arranged in sequence.

[0165] The formulations of the easy-to-stick and easy-to-tear in-mold label film of this comparative example are the same as those of Example 1, except that the ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 16 wt %, and the density is 0.862 g / cm 3 , the melting point is 54℃, that is:

[0166] Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content 16 wt%, density 0.862 g / cm 3 , melting point is 54°C, melt index is 8g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0167] The preparation method of the in-mold label film of this comparative example is basically the same as that of Example 1.

[0168] The total thickness and thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0169] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0170] Performance evaluation

[0171] The following performance evaluations were performed on the in-mold label films, in-mold labels, and plastic parts with in-mold labels of Examples 1-7 and Comparative Examples 1-6, respectively:

[0172] Roughness: The surface roughness of the roughened adhesive layer 4-1 or laminating layer 4-2 (i.e., the surface of the in-mold label film opposite to the first surface layer 1) of the in-mold label film was tested in accordance with the national standard GB / T 14234-1993. The testing instrument was a surface roughness meter (Mitutoyo, Japan, model: SJ-210).

[0173] Room-temperature adhesion: Two sheets of in-mold label films were stacked together and pressed down with a 10kg weight. They were then placed in a 60°C oven for 30 minutes to simulate summer container transportation conditions. The bonding strength between the two sheets was then tested using a film adhesion tester (Dynisco, USA, Model: D9047).

[0174] Friction coefficient: The friction coefficient of the roughened adhesive layer 4-1 or the laminating layer 4-2 (i.e., the surface of the in-mold label film opposite to the first surface layer 1) of the in-mold label film was tested in accordance with the national standard GB / T 10006-2021. The testing instrument was a friction coefficient meter (Testing Machine, USA, model: 32-07-00-0003).

[0175] Thermal shrinkage: The thermal shrinkage of the in-mold label film was tested in accordance with the national standard GB / T 10003-2008 at a temperature of 120°C for 2 minutes using an electric blast drying oven (manufactured by Shanghai Yiheng Technology Co., Ltd., model: DHG-9075A).

[0176] Light transmittance: The light transmittance of the in-mold label film was tested in accordance with the national standard GB / T 2410-2008. The testing instrument was a direct-reading haze meter (produced by Diffusion in the UK, model: EEL 57D).

[0177] Surface resistance: The surface resistance of the roughened adhesive layer 4 or laminating layer 4-1 (i.e., the surface of the in-mold label film opposite to the first surface layer 1) of the in-mold label film was tested in accordance with the national standard GB / T 31838.3-2019. The testing instrument was a surface resistivity meter (manufactured by SIMCO, Japan, model: ST-4).

[0178] Continuous labeling: Tie a stack of 500 in-mold labels (a stack) with a rubber band, press the stacked in-mold labels with a 10kg weight, place the stacked in-mold labels in a 60℃ oven for 30 minutes, untie the rubber band, and remove the in-mold labels with a robot to observe the continuous labeling.

[0179] Heat Seal Strength: This test simulates the adhesion strength between an in-mold label and a plastic part after in-mold labeling. 100µm thick high-density polyethylene (HDPE) and polyethylene terephthalate (PET) films are first obtained through a cast film process. The in-mold label and the HDPE or PET film are then heat-sealed using a heat sealer at 135°C, 0.18 MPa, and 1 second. (The in-mold labels in Examples 1-4, 6, and 7 and Comparative Examples 1-6 correspond to HDPE film, while the in-mold label in Example 5 corresponds to PET film.) After standing for 3 minutes under the test conditions, the sample is cut into strips 15mm wide and 15cm long. The heat-sealed interface is then peeled off, and the heat seal strength is measured using a universal tensile testing machine in accordance with the national standard GB / T 10006-2021.

[0180] Surface appearance: Visually inspect the appearance of the plastic part with the in-mold label to see whether roughened lines of the roughened adhesive layer 4-1 or the lamination layer 4-2 are visible.

[0181] In-mold labeling yield rate: Count the percentage of 100 plastic parts with in-mold labels that have no air bubbles between the in-mold labels and the plastic parts.

[0182] Manual peeling performance at room temperature: Use manual peeling to separate the in-mold label from the plastic part to observe whether the in-mold label can be separated from the plastic part.

[0183] Please refer to Table 1-Table 5 for test results:

[0184] Table 1 Formulations and performance test results of each layer of the in-mold label film of Example 1 and Comparative Example 1

[0185]

[0186] Table 2 Formulations and performance test results of each layer of the in-mold label film of Example 2 and Comparative Example 2

[0187]

[0188] Table 3 Formulations and performance test results of each layer of the in-mold label film of Examples 3-4 and Comparative Examples 3-4

[0189]

[0190] Table 4 Formulation and performance test results of each layer of the in-mold label film of Example 5

[0191]

[0192] Table 5 Formulation composition and performance test results of each layer of the in-mold label film of Examples 6-7 and Comparative Examples 5-6

[0193]

[0194] In the preparation method of the easy-to-stick and easy-to-tear in-mold label film of Examples 1-7 of the present invention, a specific roughening process is adopted. Figure 3 , so that the second surface of the finally prepared easy-stick and easy-tear in-mold label film forms a roughened adhesive layer with concave and convex textures. After the easy-stick and easy-tear in-mold label film is made into an in-mold label, it can greatly reduce the effective contact area between in-mold labels, avoiding the occurrence of in-mold labels being stacked together; and during the in-mold label stacking process, the texture morphology of the roughened adhesive layer will not be transferred to the printed layer, avoiding affecting the surface appearance of the printed layer. In addition, after the easy-stick and easy-tear in-mold label film of Examples 1-7 is made into an in-mold label and used in in-mold labeling, please refer to Figure 4 , which can not only effectively bond the in-mold label N to the plastic part O' without easily generating bubbles, but also enable the in-mold label N to be easily peeled off from the plastic part O', achieving the technical effect of easy sticking and easy tearing.

[0195] The in-mold label film of comparative example 1 is prepared by using conventional components of each layer and conventional preparation method. After the in-mold label film of comparative example 1 is made into an in-mold label for in-mold labeling, please refer to Figure 2 , it is easy to have problems with abnormal bubbles, the in-mold labeling yield is relatively low, and it is difficult to peel off the in-mold label from the plastic part.

[0196] In the in-mold label film of Comparative Example 2, the amount of calcium carbonate added to the support layer 2 is too large, resulting in severe cavitation of the film. After the in-mold label film of Comparative Example 2 is made into an in-mold label for in-mold labeling, when the in-mold label is manually peeled off from the plastic part, part of the in-mold label material remains on the surface of the plastic part, affecting the recycling of the plastic part.

[0197] In the in-mold label film of Comparative Example 3, the amount of titanium dioxide added to the support layer 2 is too low, resulting in a slightly higher light transmittance of the film, which is not conducive to covering the uneven texture of the roughened adhesive layer. After the in-mold label film of Comparative Example 3 is made into an in-mold label for in-mold labeling, the staggered roughening morphology of the roughened adhesive layer can be visually observed, which can easily be mistaken for a labeling defect.

[0198] In the in-mold label film of Comparative Example 4, the amount of titanium dioxide added to the support layer 2 is too high, resulting in weak cohesive strength of the film and easy delamination between the support layer and the first surface layer / second surface layer. After the in-mold label film of Comparative Example 4 is made into an in-mold label for in-mold labeling, when the in-mold label is manually peeled off from the plastic part, some in-mold label material will remain on the surface of the plastic part, affecting the recycling of the plastic part.

[0199] The in-mold label film of Comparative Example 5 has a relatively low ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer. As a result, after the in-mold label film of Comparative Example 5 is made into an in-mold label for in-mold labeling, the in-mold label cannot effectively adhere to the plastic part, and the in-mold label can be easily peeled off from the plastic part. In addition, due to factors such as process friction and temperature / altitude fluctuations, the in-mold label is prone to partial detachment.

[0200] In the in-mold label film of Comparative Example 6, the ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer is relatively high, resulting in abnormally large adhesion and friction coefficient at room temperature. As a result, after the in-mold label film of Comparative Example 5 is made into an in-mold label, it is easy to produce a continuous phenomenon, thereby reducing the in-mold labeling yield.

[0201] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, and the present invention is intended to encompass such modifications and variations.

Claims

1. A method for preparing an easy-to-stick and easy-to-tear in-mold label film, characterized by: The easy-to-stick and easy-to-tear in-mold label film comprises a first surface layer, a support layer, a second surface layer and a roughened adhesive layer arranged in sequence; the second surface layer is composed of homopolypropylene; the roughened adhesive layer is composed of propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer; The preparation method of the easy-to-stick and easy-to-tear in-mold label film comprises the following steps: The raw material of the roughened adhesive layer is ground into a powder form, that is, the roughened adhesive layer powder is obtained, and the surface of the roughened adhesive layer powder is subjected to a high-voltage tip discharge process to obtain a static electricity of - / + (25-30) KV, and is set aside; The raw materials of the first surface layer, the supporting layer and the second surface layer are respectively fed into the extruders of the corresponding layers, and are formed into cast sheets through the extrusion-casting process; The cast sheet is subjected to a longitudinal stretching process to form a thick sheet; The slab undergoes a roughening treatment process: roughening adhesive layer powder is adsorbed and fused to the second surface of the slab to form a roughened slab; wherein the roughening treatment process includes the following steps: applying a high-voltage tip discharge process to the second surface of the slab to impart a static charge of + / - (25-30) KV to the second surface of the slab; utilizing the mechanism of attraction between positive and negative charges to adsorb a layer of roughening adhesive layer powder on the second surface of the slab; and utilizing the residual heat of the slab after the longitudinal stretching process to fuse the roughening adhesive layer powder to the second surface of the slab to form the roughened slab; The roughened thick sheet undergoes a transverse stretching process, a traction-thickness measurement-corona-winding process to obtain a film semi-finished product; The semi-finished film is subjected to an aging-slitting process to obtain a finished film, namely the easy-to-stick and easy-to-tear in-mold label film.

2. The method for preparing an easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: In the transverse stretching step, the transverse stretching ratio is 8-10.

3. The method for preparing the easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: After the longitudinal stretching process, the temperature of the second surface layer of the thick sheet is 138-140°C.

4. The method for preparing an easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: The preparation method of the roughened adhesive layer powder is as follows: the raw material of the roughened adhesive layer is cooled by liquid nitrogen and then ground in a grinder, and then sieved by a sieving vibrator into powder with an average particle size of 40-60 μm, thereby obtaining the roughened adhesive layer powder.

5. The method for preparing an easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: After obtaining the roughened bonding layer powder, the roughened bonding layer powder is placed in a powder tank, and then a high-voltage tip discharge process is performed on the roughened bonding layer powder in the powder tank; In the roughening process, the slab is passed through a powder trough, wherein the distance between the second surface layer of the slab and the roughened adhesive layer powder in the powder trough is 10-20 mm.

6. The method for preparing an easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: The ethylene content in the propylene-ethylene copolymer is 5-11 wt %; the maleic anhydride grafting rate in the maleic anhydride grafted propylene-ethylene copolymer is 0.8-1.3 wt %, and the ethylene content in the maleic anhydride grafted propylene-ethylene copolymer is 5-11 wt %.

7. The method for preparing an easy-to-stick and easy-to-tear in-mold label film according to claim 1, wherein: The first surface layer comprises homopolypropylene and 0.3-1.5 wt% of an anti-blocking agent; the support layer comprises homopolypropylene, 0-20 wt% of calcium carbonate, 5-30 wt% of titanium dioxide and 0.4-1.5 wt% of an antistatic agent.

8. An easy-to-stick and easy-to-tear in-mold label film, characterized by: The easy-to-stick and easy-to-tear in-mold label film is prepared by the preparation method of any one of claims 1 to 7.

9. Use of the easy-to-stick and easy-to-tear in-mold label film according to claim 8 in in-mold labeling, characterized in that: After the easy-to-stick and easy-to-tear in-mold label film is made into an in-mold label, the in-mold label is integrated with the plastic part through an in-mold labeling process to form a plastic part with an in-mold label; When the roughened adhesive layer is composed of propylene-ethylene copolymer, the plastic part is a polyethylene plastic part; when the roughened adhesive layer is composed of maleic anhydride grafted propylene-ethylene copolymer, the plastic part is a polyester plastic part or a polyamide plastic part.

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