In-mold label film easy to paste and tear as well as preparation method and application of in-mold label film

Abstract

The invention relates to an easy-to-paste and easy-to-tear in-mold label film as well as a preparation method and application thereof, and belongs to the technical field of in-mold labels. The easy-to-paste and easy-to-tear in-mold label film comprises a first surface layer, a supporting layer, a second surface layer and a coarsening bonding layer which are arranged in sequence, the second surface layer is made of homo-polypropylene; the coarsening bonding layer is composed of a propylene-ethylene copolymer or a maleic anhydride grafted propylene-ethylene copolymer. The in-mold label film easy to paste and tear is prepared by adopting a specific method, the in-mold label film easy to paste and tear is used for in-mold labeling after being prepared into an in-mold label, the in-mold label and a plastic part can be effectively bonded, bubbles are not prone to being generated, the in-mold label can be easily stripped from the plastic part, and the technical effect of being easy to paste and tear is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of in-mold labeling, and particularly to an easily attachable and detachable in-mold label film, a preparation method thereof, and an application thereof. Background Art

[0002] In the in-mold labeling technology, after an in-mold label film is made into an in-mold label, the in-mold label and a plastic part are integrated during in-mold label molding, so that the in-mold label and the plastic part are firmly combined to form a plastic part with an in-mold label (i.e., an in-mold labeling product). The in-mold labeling products obtained by the in-mold labeling technology have wide temperature adaptability and weather resistance, can be used in high / low latitude regions and high / low altitude regions, and will not cause the in-mold label to warp or fall off due to temperature fluctuations or altitude changes. The in-mold labeling technology has promoted the booming development of in-mold label films, especially in the food field, daily chemical field, chemical field, and pharmaceutical field.

[0003] With the development of the easy recycling of plastic products, the in-mold labeling technology also faces the following problems: Most in-mold label films are mainly made of polypropylene, while most plastic parts are made of polyethylene, polyester, or polyamide, and the in-mold label film usually needs to be printed with ink and then made into an in-mold label, and then used for in-mold labeling to form a plastic part with an in-mold label. When recycling plastic parts with in-mold labels, due to the inconsistent materials of the in-mold label and the plastic part, and the surface of the in-mold label being with ink, it is difficult to recycle the plastic parts with in-mold labels in the form of pure resin. Therefore, it is necessary to separate the in-mold label from the plastic part and then recycle them separately. However, after the in-mold label made of the traditional in-mold label film is integrated with the plastic part, the in-mold label and the plastic part are adhesively bonded extremely firmly, and it is difficult to separate the in-mold label from the plastic part by manual or mechanical peeling, thus making it difficult to achieve the classified recycling of the in-mold label and the plastic part.

[0004] For traditional in-mold label films, please refer to Figure 1, including a first surface layer 1, a support layer 2, and an adhering layer 4-2 (composed of polyolefin) arranged in sequence. Its preparation method usually realizes the lamination of the three-layer structure through an integrated co-extrusion and biaxial stretching method. Specifically, the raw materials of the first surface layer 1, the support layer 2, and the adhering layer 4-2 are processed through an extrusion-casting process, a longitudinal stretching process, a transverse stretching process, a traction-thickness measurement-corona-winding process, and an aging-slitting process to obtain the in-mold label film. However, in the longitudinal stretching process, since the adhering layer 4-2 needs to contact the heating roller, and currently the polyolefin used in the adhering layer 4-2 of the traditional in-mold label film has a relatively low melting point, a Teflon coating needs to be additionally provided on the heating roller passed by the adhering layer 4-2 and low-temperature stretching is required. Otherwise, the adhering layer 4-2 is likely to be damaged during longitudinal stretching. However, setting the Teflon coating will require additional processing costs, and the poor wear resistance of the Teflon coating leads to frequent maintenance, resulting in an increase in production costs. And low-temperature stretching is likely to cause poor longitudinal stretching stripes due to insufficient longitudinal heating and is likely to generate a relatively high thermal shrinkage rate, affecting the subsequent processing performance of the obtained in-mold label film.

[0005] In addition, the adhering layer 4-2 of the traditional in-mold label film has a phenomenon of room-temperature adhesion, and label interconnection problems are likely to occur between the stacked in-mold labels after the in-mold labels are made. The industry calls it the "interconnection phenomenon". To solve the above problems, generally, embossing treatment is carried out on the surface of the adhering layer 4-2, and through the die pressing process, the surface of the adhering layer 4-2 obtains uneven patterns. Please refer to Figure 1 , such patterns are beneficial to reducing the contact area between the adhering layer 4-2 and the printing layer (formed by printing on the first surface layer 1) between the stacked in-mold labels after the in-mold label film is made into in-mold labels, thereby reducing the room-temperature adhesion force and avoiding the occurrence of the interconnection phenomenon. However, this operation will give rise to additional costs such as the investment in new embossing equipment, energy consumption, material loss, and labor input. And when the traditional in-mold label film is made into an in-mold label and used for in-mold labeling, please refer to Figure 1 and Figure 2 , although there are embossings on the surface of the adhering layer 4-2, these embossings will cause embossing collapse at the high temperature of in-mold labeling (the reason for embossing collapse is that the high temperature of in-mold labeling will not only melt the raised patterns of the adhering layer 4-2 but also melt the non-raised parts of the adhering layer 4-2). This embossing collapse will locally block the gas flow path (i.e., the exhaust path), resulting in when the adhering layer 4-2 is welded to the plastic part, please refer to Figure 2 , the exhaust path is blocked, and it is difficult for gas to escape from between the adhering layer 4-2 and the plastic part O', causing gas accumulation and resulting in bubbles between the in-mold label and the plastic part, leading to abnormal bubble appearance of the in-mold labeling product (such as the bubble abnormal points in Figure 2 ). Summary of the Invention

[0006] Based on this, the object of the present invention is to provide an easily - attachable and easily - detachable in - mold label film, its preparation method and application. The present invention is prepared by a specific method. During the preparation process, there is no need to set a Teflon coating and no need for low - temperature stretching. The prepared easily - attachable and easily - detachable in - mold label film, when made into an in - mold label and used in in - mold labeling, can not only effectively bond the in - mold label with the plastic part and is not easy to generate bubbles, but also enable the in - mold label to be easily peeled off from the plastic part, achieving the technical effect of being easily attachable and easily detachable.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to provide a preparation method of an easily - attachable and easily - detachable in - mold label film. The easily - attachable and easily - detachable in - mold label film includes 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 an ethylene - propylene copolymer or a maleic anhydride - grafted ethylene - propylene copolymer; the preparation method of the easily - attachable and easily - detachable in - mold label film includes the following steps: Grind the raw material of the roughened adhesive layer into a powder form to obtain the roughened adhesive layer powder. Through the high - voltage tip - discharge process, make the surface of the roughened adhesive layer powder obtain an electrostatic charge of - / +(25 - 30) KV and set it aside (this step can be completed before the roughening treatment process, and there is no sequence limit); Feed the raw materials of the first surface layer, the support layer, and the second surface layer into the extruders corresponding to each layer respectively, and form a cast film through the extrusion - casting process; The cast film undergoes a longitudinal stretching process to form a thick film; The thick film undergoes a roughening treatment process: make the roughened adhesive layer powder adsorb and fuse on the surface of the second surface layer of the thick film to form a roughened - treated thick film; The roughened - treated thick film undergoes a transverse stretching process, a traction - thickness measurement - corona - winding process to obtain a film semi - finished product; The film semi - finished product undergoes an aging - slitting process to obtain a film finished product, that is, the easily - attachable and easily - detachable in - mold label film.

[0008] The preparation method of the easy-to-stick and easy-to-tear in-mold label film of the present invention is to melt the raw materials of the first surface layer, the support layer, and the second surface layer respectively through an extruder, and then co-extrude and chill-form them into a cast film with a three-layer laminated structure (i.e., the first surface layer - the support layer - the second surface layer) as a whole in the extrusion-casting process. After the longitudinal stretching process, a thick film with a longitudinally stretched three-layer laminated structure is obtained. In the longitudinal stretching process, since the second surface layer uses homopolypropylene, its melting point (reaching 160-168°C) is higher than that of the bonding layer of the traditional in-mold label film. The heating roller passed by the second surface layer does not need to be provided with a Teflon coating and does not need to be stretched at a low temperature. When the second surface layer passes through the heating roller (the heating temperature is 138-140°C), it is not easy to be scalded and damaged, nor is it easy to produce longitudinal stripes with poor longitudinal stretching, avoiding problems such as additional coating processing costs and decreased dimensional stability. In the present invention, the raw materials of the roughened adhesive layer are ground into powder form of the roughened adhesive layer powder in advance, and through the high-voltage tip discharge process, the surface of the roughened adhesive layer powder obtains an electrostatic charge of - / +(25-30) KV. In the roughening process, by using the electrostatic charge on the surface of the roughened adhesive layer powder, the roughened adhesive layer powder is adsorbed onto the surface of the second surface layer of the thick film and welded together to form a roughened thick film together with the thick film; wherein, the roughened adhesive layer powder on the roughened thick film is tightly packed together. Then, after the roughened thick film undergoes a transverse stretching process, the gaps between the roughened adhesive layer powders change from tight packing to a well-arranged state, and at the same time, the roughened adhesive layer powder is further welded to the second surface layer, so that the protruding height of the roughened adhesive layer powder on the surface of the second surface layer is further reduced. Then, through the processes of traction-thickness measurement-corona-reeling, a film semi-finished product is obtained. The film semi-finished product is obtained through the processes of aging-slitting to obtain the film finished product, that is, the easy-to-stick and easy-to-tear in-mold label film.

[0009] In the design of the present invention, the second surface layer uses homopolypropylene, and the roughened adhesive layer uses propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer. Since the propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer is a copolymer with propylene as the main body (the content of propylene is relatively high, reaching 85-95 wt%), this design is conducive to the fusion of the roughened adhesive layer powder with the second surface layer and is not prone to falling off. In the present invention, through the roughening treatment process, the roughened adhesive layer powder is adsorbed and closely packed on the surface of the second surface layer. After the transverse stretching process, the gaps between the roughened adhesive layer powders change from close packing to a well-arranged pattern, and finally a roughened adhesive layer with (ellipsoidal) concave and convex patterns is formed on the surface of the second surface layer. This roughened adhesive layer with concave and convex patterns is conducive to reducing the normal temperature bonding force and avoiding the occurrence of continuous sheet phenomenon; at the same time, there is an exhaust passage formed between the well-arranged roughened adhesive layer powders in the concave and convex patterns, which is conducive to exhaust during subsequent in-mold labeling. Therefore, when the easy-to-apply and easy-to-tear in-mold label film of the present invention is made into an in-mold label and used for in-mold labeling, the concave and convex patterns of the roughened adhesive layer will be in a well-arranged pattern and locally contact and bond with the plastic part. The second surface layer is composed of homopolypropylene. Based on the large difference in solubility parameters between homopolypropylene and the raw materials of common plastic parts (such as polyethylene, polyester, or polyamide), the second surface layer will not bond with the plastic part. Finally, the in-mold label made from the easy-to-apply and easy-to-tear in-mold label film of the present invention will not contact and bond with the plastic part comprehensively, but shows a well-arranged local contact bonding. At the same time, since the raw material of the roughened adhesive layer is a propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer with propylene as the main body (where the propylene content reaches about 89-95 wt%), the bonding strength between the roughened adhesive layer and the second surface layer is much higher than the bonding strength between the roughened adhesive layer and the plastic part, enabling the in-mold label to be easily peeled from the plastic part, which is conducive to the classification and recycling of the in-mold label and the plastic part, thus providing a simple solution for recycling. In addition, since after the transverse stretching process, the gaps between the roughened adhesive layer powders change from close packing to a well-arranged pattern, forming a larger exhaust passage, even if the roughened adhesive layer collapses during in-mold labeling, it will not block the exhaust passage, thus avoiding abnormal bubbles.

[0010] In addition, for the easy-to-apply and easy-to-remove in-mold label film prepared by the preparation method of the present invention, a roughened adhesive layer in the form of concave and convex patterns is formed on the surface of the second surface layer. When the easy-to-apply and easy-to-remove in-mold label film is printed on the surface of the first surface layer and a number of stacked in-mold labels are obtained through die-cutting and stacking processes, due to the formation of a roughened adhesive layer in the form of concave and convex patterns on the surface of the second surface layer, the contact area between the in-mold labels will not be too large, avoiding the occurrence of the phenomenon of in-mold label sticking together due to the too large contact area between the in-mold labels. When in-mold labeling, when taking out a single in-mold label from the stacked multiple in-mold labels, the single in-mold label can be taken out smoothly without the phenomenon of label sticking together, that is, 2 or 3 in-mold labels will not be taken out, avoiding putting 2 or 3 in-mold labels into the mold and affecting in-mold labeling. When the in-mold label is in-mold labeled, due to the formation of a roughened adhesive layer in the form of concave and convex patterns on the surface of the second surface layer, that is, the surface topography of the in-mold label is rough, an exhaust passage is formed between the concave and convex patterns, so that when the in-mold label is attached to the plastic part, air can be exhausted in time through the exhaust passage without the phenomenon of gas accumulation forming bubbles (no abnormal bubble phenomenon), greatly reducing the probability of bubbles appearing between the in-mold label and the plastic part.

[0011] In the preparation method of the easy-to-apply and easy-to-remove in-mold label film of the present invention, the surface of the roughened adhesive layer powder is obtained with static electricity of - / + (25 - 30) KV through a high-voltage tip discharge process. In the roughening treatment process, by using the static electricity on the surface of the roughened adhesive layer powder, the roughened adhesive layer powder can be adsorbed and closely packed on the surface of the second surface layer of the thick sheet, so that after the subsequent transverse stretching process, the gaps between the roughened adhesive layer powders change from close packing to a well-arranged pattern to form concave and convex patterns. If the static electricity value obtained on the surface of the roughened adhesive layer powder is lower 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 the roughened adhesive layer powder not being fully adsorbed and closely packed on the surface of the second surface layer of the thick sheet, resulting in a decrease in the roughness of the prepared easy-to-apply and easy-to-remove in-mold label film and a deviation in the exhaust effect. Using the in-mold label made for in-mold labeling will reduce the yield of in-mold labeling; if the static electricity value obtained on the surface of the roughened adhesive layer powder exceeds 30 KV, there will be a risk of electrostatic injury during the film preparation process, causing a safety hazard.

[0012] As a preferred solution, the roughening treatment process includes the following steps: on the surface of the second surface layer of the thick sheet, through the high-voltage tip discharge process, the second surface layer of the thick sheet obtains a static electricity of + / -(25 - 30) KV; using the mechanism of attraction between positive and negative charges, a layer of roughening adhesive layer powder is adsorbed on the second surface layer of the thick sheet, and using the remaining heat of the thick sheet after the longitudinal stretching process, the roughening adhesive layer powder is welded to the second surface layer of the thick sheet to form the roughened thick sheet. In the present invention, before the roughening treatment process, the surface of the roughening adhesive layer powder obtains a static electricity of - / +(25 - 30) KV through the high-voltage tip discharge process, and in the roughening treatment process, the second surface layer of the thick sheet obtains a static electricity of + / -(25 - 30) KV through the high-voltage tip discharge process. When the above-mentioned thick sheet passes through the above-mentioned roughening adhesive layer powder, using the mechanism of attraction between positive and negative charges, by neutralizing the charges, a layer of roughening adhesive layer powder is adsorbed and closely packed on the second surface layer of the thick sheet. At the same time, because the second surface layer of the thick sheet after the longitudinal stretching process has a relatively high remaining heat (it is well known to those skilled in the art that the second surface layer of the thick sheet obtained after the longitudinal stretching process will have a relatively high remaining heat, and the remaining heat is generally 138 - 140 °C, while the melting point of the acrylonitrile-ethylene copolymer or maleic anhydride grafted acrylonitrile-ethylene copolymer used in the roughening adhesive layer is 65 - 100 °C), using the remaining heat of the second surface layer of the thick sheet, the roughening adhesive layer powder is welded to the second surface layer of the thick sheet, so that the roughening adhesive layer powder is difficult to fall off and prevent failure, and a roughening adhesive layer manifested as concave-convex lines is formed on the second surface layer of the thick sheet, which together with the thick sheet forms a roughened thick sheet.

[0013] As a preferred solution, in the transverse stretching process, the transverse stretching ratio is 8 - 10. The roughening adhesive layer powder on the roughened thick sheet obtained after the roughening treatment process is closely packed together. By controlling the transverse stretching by 8 - 10 times in the transverse stretching process, the gap between the roughening adhesive layer powders can be changed from close packing to a well-arranged state, which is beneficial to exhaust gas during in-mold labeling.

[0014] As a preferred solution, after the longitudinal stretching process, the temperature of the second surface layer of the thick sheet is 138 - 140 °C. In the present invention, by controlling the longitudinal stretching process, the temperature of the second surface layer of the thick sheet reaches 138 - 140 °C, so that in the roughening treatment process, after the roughening adhesive layer powder is adsorbed on the second surface layer of the thick sheet, the roughening adhesive layer powder (with a melting point of 65 - 100 °C) can be welded to the second surface layer of the thick sheet through the remaining heat of the second surface layer of the thick sheet.

[0015] As a preferred solution, the method for preparing the roughened adhesive layer powder is as follows: The raw materials of the roughened adhesive layer (in the form of resin particles, with an average particle size preferably of 4 - 5 mm) are cooled with liquid nitrogen and then placed in a grinder for grinding. Then, they are sieved by a sieve shaker into powder with an average particle size of 40 - 60 µm, thus obtaining the roughened adhesive layer powder. By making the raw materials of the roughened adhesive layer into roughened adhesive layer powder with an average particle size of 40 - 60 µm, it is convenient for the roughened adhesive layer powder to be effectively adsorbed on the surface of the second surface layer under the action of electrostatic adsorption force during the roughening process. Additionally, after the thick sheet undergoes the transverse stretching process in the roughening process, the protruding height of the roughened adhesive layer on the surface of the second surface layer will decrease from 40 - 60 µm to 4 - 6 µm.

[0016] As a preferred solution, after obtaining the roughened adhesive layer powder, the roughened adhesive layer powder is placed in a powder tank, and then a high - voltage tip discharge process is performed on the roughened adhesive layer powder in the powder tank so that the surface of the roughened adhesive layer powder in the powder tank obtains an electrostatic charge of - / + (25 - 30) KV.

[0017] As a preferred solution, during the roughening process, after the second surface layer of the thick sheet obtains an electrostatic charge of + / - (25 - 30) KV, the thick sheet is passed through the powder tank, and the distance between the second surface layer of the thick sheet and the roughened adhesive layer powder in the powder tank is 10 - 20 mm. In this way, by controlling the distance between the second surface layer of the thick sheet and the roughened adhesive layer powder in the powder tank to be 10 - 20 mm, the second surface layer of the thick sheet can quickly and effectively adsorb a layer of roughened adhesive layer powder, and the roughened adhesive layer powder is closely packed on the surface of the second surface layer.

[0018] As a preferred solution, the content of ethylene in the propylene - ethylene copolymer is 5 - 11 wt%.

[0019] As a preferred solution, the melting point of the propylene - ethylene copolymer is 65 - 100 °C, and the melt index is 1 - 8 g / 10 min (230 °C, 2.16 kg).

[0020] As a preferred solution, the maleic anhydride grafting rate of the maleic anhydride - grafted propylene - ethylene copolymer is 0.8 - 1.3 wt%, and the content of ethylene in the maleic anhydride - grafted propylene - ethylene copolymer is 5 - 11 wt%.

[0021] As a preferred solution, the melting point of the maleic anhydride - grafted propylene - ethylene copolymer is 65 - 100 °C, and the melt index is 1 - 8 g / 10 min (230 °C, 2.16 kg).

[0022] As a preferred solution, 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 in-mold label film into an in-mold label, ink can be printed on the surface of the first surface layer to form a printing layer. Additionally, by adding an anti-blocking agent to the first surface layer, the anti-blocking effect of the first surface layer can be improved to prevent the film from sticking.

[0023] As a preferred solution, the anti-blocking agent is at least one of silicon dioxide and polymethyl methacrylate, and the average particle size of the anti-blocking agent is 4-5 µm.

[0024] As a preferred solution, 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. By adding ≤20 wt% of calcium carbonate and 5-30 wt% of titanium dioxide to the support layer, it is beneficial to improve the covering performance of the in-mold label film. After the in-mold label film is formed into an in-mold label for in-mold labeling, consumers will not see the uneven texture (roughened texture) of the roughened adhesive layer. If the addition ratio of calcium carbonate exceeds 20 wt%, severe cavitation occurs in the support layer, and delamination easily occurs after in-mold labeling, and some label materials will remain on the surface of the plastic part, contaminating plastic recycling. If the addition ratio of titanium dioxide exceeds 30 wt%, the cohesive strength of the support layer drops significantly, and delamination easily occurs after in-mold labeling, and some label materials will remain on the surface of the plastic part, contaminating plastic recycling; if the addition ratio of titanium dioxide is less than 5 wt%, the covering performance of the support layer is insufficient, resulting in the uneven roughened texture appearance of the roughened adhesive layer being observable by consumers, mistakenly believing it to be a labeling defect.

[0025] As a preferred solution, in the support layer, the calcium carbonate is heavy calcium carbonate, and the average particle size of the calcium carbonate (after grinding) is 1-2 µm.

[0026] As a preferred solution, in the support layer, the titanium dioxide is rutile titanium dioxide synthesized by the chloride process, and the average particle size of the titanium dioxide is 0.2-0.4 µm.

[0027] As a preferred solution, in the support layer, the antistatic agent is at least one of glycerol monostearate, ethoxylated alkylamine, N,N-dihydroxyethyl lauramide, ethoxylated alcohol, alkyl sulfonate, alkyl phosphate, tetraalkyl quaternary ammonium salt, trialkyl benzyl quaternary ammonium salt, and alkyl betaine.

[0028] As a preferred solution, the melt index of the homopolypropylene in the first surface layer, the support layer, and the second surface layer is 2.8 - 3.2 g / 10 min (230 °C, 2.16 kg), the isotacticity is 95 - 97%, and the melting point is 160 - 168 °C.

[0029] Another object of the present invention is to provide an easy-to-apply and easy-to-tear in-mold label film prepared by the preparation method described in any one of the above.

[0030] Another object of the present invention is to provide an application of the easy-to-apply and easy-to-tear in-mold label film in in-mold labeling: after the easy-to-apply 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 in-mold labeling to form a plastic part with an in-mold label.

[0031] As a preferred solution of the present invention, when the roughened adhesive layer is composed of an ethylene-propylene copolymer, the plastic part is preferably a polyethylene plastic part; when the roughened adhesive layer is composed of a maleic anhydride-grafted ethylene-propylene copolymer, the plastic part is preferably a polyester plastic part (for example, polyethylene terephthalate (PET) plastic part, polycarbonate (PC) plastic part) or a polyamide plastic part (for example, polyamide 6 (PA6) plastic part, polyamide 66 (PA66) plastic part).

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: In the preparation method of the easy-to-apply and easy-to-tear in-mold label film of the present invention, through a specific roughening treatment process, the roughened adhesive layer powder is adsorbed and tightly packed on the surface of the second surface layer. After the transverse stretching process, the gaps between the roughened adhesive layer powders change from tight packing to a well-arranged state, so that a roughened adhesive layer with concave-convex patterns is formed on the surface of the second surface layer of the prepared easy-to-apply and easy-to-tear in-mold label film. After the easy-to-apply and easy-to-tear in-mold label film is made into an in-mold label, the effective contact area between the in-mold labels can be greatly reduced, thereby avoiding the occurrence of continuous sheet phenomenon.

[0033] A roughened adhesive layer with concave-convex patterns is formed on the surface of the second surface layer of the easy-to-apply and easy-to-tear in-mold label film of the present invention, and an exhaust passage is formed between the concave-convex patterns. When the in-mold label is attached to the plastic part, gas can be exhausted in time through the exhaust passage without gas accumulation to form bubbles (no abnormal bubble phenomenon), greatly reducing the probability of bubbles appearing between the in-mold label and the plastic part, thereby improving the yield of in-mold labeling.

[0034] The present invention is prepared by a specific method. During the preparation process, there is no need to set a Teflon coating and no need for low-temperature stretching. The easily attachable and detachable in-mold label film obtained is used for in-mold labeling after being made into an in-mold label. It can not only effectively bond the in-mold label and the plastic part without generating bubbles easily, but also enable the in-mold label to be easily peeled off from the plastic part, achieving the technical effect of being easily attachable and detachable.

[0035] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0036] Figure 1 is a schematic structural diagram of a traditional in-mold label film; Figure 2 is a schematic diagram of the fitting of an in-mold label made of a traditional in-mold label film and a plastic part ( Figure 2 In the in-mold label N in, only the fitting layer 4-2 and another layer are shown. It should be understood that the other layer includes a printing layer, a first surface layer 1, and a support layer 2 arranged in sequence from top to bottom); Figure 3 is a schematic structural diagram of an easily attachable and detachable in-mold label film of the present invention; Figure 4 is a schematic diagram of the fitting of an in-mold label made of the easily attachable and detachable in-mold label film of the present invention and a plastic part ( Figure 4 In the in-mold label N in, only the roughened bonding layer 4-1 and another layer are shown. 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 sequence from top to bottom); Figure 5 is a process flow chart of the production of an easily attachable and detachable in-mold label film of the present invention; Figure 6 is a process flow chart of the application of an easily attachable and detachable in-mold label film of the present invention; Figure 7 is a schematic diagram showing that the gaps between the powders of the roughened bonding layer of an easily attachable and detachable in-mold label film of the present invention change from closely packed to scattered and orderly arrangement after the transverse stretching process; In the figure: 1, first surface layer; 2, support layer; 3, second surface layer; 4-1, roughened bonding layer; 4-2, fitting layer; A, raw material; B, cast sheet; C, thick sheet; D, thick sheet after roughening treatment; E, film semi-finished product; F, film finished product; G, extrusion-casting process; H, longitudinal stretching process; I, roughening treatment process; J, transverse stretching process; K, traction-thickness measurement-corona-reeling process; L, aging-slitting process; M, in-mold label semi-finished product; 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 Embodiments

[0037] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0038] The present invention provides an easy-to-apply and easy-to-remove in-mold label film. Please refer to Figure 3 , which has a four-layer structure and includes a first surface layer 1, a support layer 2, a second surface layer 3, and a roughened adhesive layer 4-1 arranged in sequence.

[0039] Among them, the raw material formulas of each layer are as follows: First surface layer 1: homopolypropylene and anti-blocking agent; Support layer 2: homopolypropylene, calcium carbonate, titanium dioxide, and antistatic agent; Second surface layer 3: homopolypropylene; Roughened adhesive layer 4-1: propylene-ethylene copolymer or maleic anhydride grafted propylene-ethylene copolymer.

[0040] In the easy-to-apply and easy-to-remove in-mold label film of the present invention, please refer to Figure 3 , a roughened adhesive layer 4-1 is formed on the surface of the second surface layer 3, which is manifested as concave-convex lines.

[0041] The present invention also provides a preparation method for an easy-to-apply and easy-to-remove in-mold label film. Please refer to Figure 5, including the following steps: Premix the raw materials A of the first surface layer 1, the support layer 2, and the second surface layer 3 after screening according to the design formula, stir evenly, and send them into the extruders corresponding to each layer after calculating the input ratio by weighing. After the extrusion-casting process G, a cast sheet B is formed; the cast sheet B is longitudinally stretched in the longitudinal stretching process H to form a thick sheet C, 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: on the surface of the second surface layer 3 of the thick sheet C, through a high-voltage tip discharge process, the surface of the second surface layer 3 of the thick sheet C obtains a static electricity of + / -(25 - 30) KV, and then the above-mentioned thick sheet C is passed through a powder trough containing the roughening adhesive layer powder (the powder trough has previously obtained a static electricity of - / +(25 - 30) KV on the surface of the roughening adhesive layer powder through a high-voltage tip discharge process, and the roughening adhesive layer powder is obtained by cooling the raw materials of the roughening adhesive layer (resin particles with an average particle size of 4 - 5 mm) with liquid nitrogen and then grinding and sieving them in a grinding machine into a powder with an average particle size of 40 - 60 nm). The distance between the second surface layer of the thick sheet C and the roughening adhesive layer powder in the powder trough is 10 - 20 mm. Through the mechanism of attraction between positive and negative charges, the surface of the second surface layer 3 of the thick sheet C adsorbs and tightly accumulates to form a layer of roughening adhesive layer powder. At the same time, because the surface temperature of the second surface layer 3 of the thick sheet C after the longitudinal stretching process H reaches 138 - 140 °C, the remaining temperature on the surface of the second surface layer 3 of the thick sheet C is used to fuse with the roughening adhesive layer powder, so that the roughening adhesive layer powder is difficult to fall off and prevent failure, and a roughened thick sheet D is obtained; the roughened thick sheet D first undergoes a transverse stretching process J. After the roughened thick sheet D undergoes the transverse stretching process J (the transverse stretching ratio is controlled at 8 - 10), the gaps between the roughening adhesive layer powders change from tight accumulation to a well-arranged pattern. In addition, due to the temperature of the transverse stretching process J, the roughening adhesive layer powder will further fuse with the second surface layer 3. At the same time, the protruding height of the roughening adhesive layer powder on the surface of the second surface layer 3 decreases from 40 - 60 µm to 4 - 6 µm, and finally a roughening adhesive layer 4 - 1 in the form of concave and convex patterns is formed on the surface of the second surface layer 3; then through the traction-thickness measurement-corona-winding process K, a film semi-finished product E is obtained, and the film semi-finished product E finally undergoes an aging-slitting process L to obtain a film finished product F, that is, the easy-to-stick and easy-to-tear in-mold label film.

[0042] The equipment used in the high-voltage tip discharge process is: an induction discharge rod (operating voltage: 0 - 50 KV), model: SC-1, manufacturer: Jiangxi Senmu Electronics Co., Ltd.

[0043] The production equipment is a flat film method two-step biaxially stretched polypropylene production line provided by BRUECKNER of Germany, and a powder tank is added between the longitudinal stretching process and the transverse stretching process. The temperature of the extruder, flow channel, pipeline, filter, and die head used in the above production line is controlled at 230 - 260 °C, the quenching temperature is controlled at 25 - 40 °C, the longitudinal stretching process consists of a preheating process, a stretching process, and a shaping process, and the process temperature (heating by heat conduction roller) of the longitudinal stretching process is controlled at 138 - 140 °C; the transverse stretching process J consists of a preheating process, a stretching process, a shaping process, and a cooling process, and the process temperature (heating by air) of the transverse stretching process is controlled at 150 - 180 °C; the longitudinal stretching ratio is controlled at 4.0 - 6.0 times; the transverse stretching ratio is controlled at 8.0 - 10.0 times.

[0044] The present invention also provides an application of the easy-to-stick and easy-to-tear in-mold label film in in-mold labeling. Please refer to Figure 6 , the film finished product F first goes through a printing process P, and the printing process P includes, but is not limited to, common processes such as rotary printing, offset printing, flexographic printing, etc., to obtain an in-mold label semi-finished product M. Then, it goes through 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 sent to the label by negative pressure process R and the in-mold labeling process S, and finally a plastic part O with an in-mold label is obtained.

[0045] 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', which is used for gas discharge and will not cause the problem of abnormal bubbles between the in-mold label N and the plastic part O'.

[0046] Example 1 This example provides an easy-to-stick and easy-to-tear in-mold label film. Please refer to Figure 3 , which has 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.

[0047] Among them, the raw material formulas of each layer are as follows: First surface layer 1: 99.4 wt% of homopolypropylene (isotacticity is 95%, density is 0.905 g / cm 3 , melting point is 163 °C, melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg) and 0.6 wt% of silicon dioxide (average particle size is 5 µm).

[0048] Support layer 2: 60 wt% of homopolypropylene (isotacticity is 95%, density is 0.905 g / cm 3 , melting point is 163 °C, melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg), 25 wt% of titanium dioxide (chlorination process, rutile type, average particle size is 0.3 µm), 14.5 wt% of calcium carbonate (heavy calcium carbonate, average particle size is 1.2 µm) and 0.5 wt% of glycerol monostearate.

[0049] Second surface layer 3: 100 wt% of homopolypropylene (isotacticity is 95%, density is 0.905 g / cm 3 , melting point is 163 °C, melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg).

[0050] Roughened adhesive layer 4-1: 100 wt% of propylene-ethylene copolymer (ethylene content is 9 wt%, density is 0.879 g / cm 3 , melting point is 77 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0051] This embodiment also provides a preparation method of an easy-to-stick and easy-to-tear in-mold label film, including the following steps: (1) Grind the raw materials of the roughened adhesive layer 4-1 into a powder form, that is, cool the raw materials of the roughened adhesive layer 4 (resin particles, average particle size is 4 mm) with liquid nitrogen for 30 minutes, then grind them into a powder by a grinder, and obtain propylene-ethylene copolymer powder with an average particle size of 60 µm through a sieve shaker; place the propylene-ethylene copolymer powder in a powder tank, and then through a high-voltage tip discharge process, make the surface of the propylene-ethylene copolymer powder in the powder tank obtain an electrostatic charge of -28 KV, and set aside; (2) Please refer to Figure 5, the raw materials A of each layer of the first surface layer 1, the support layer 2, and the second surface layer 3 after screening are premixed according to the designed formula respectively, stirred evenly, and after weighing and calculating the input ratio, they are sent into each extruder, and a cast sheet B is formed after the extrusion-casting process G; the cast 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: on the surface of the second surface layer 3 of the thick sheet C, through the high-voltage tip discharge process, the second surface layer of the thick sheet C obtains a static electricity of +28 KV, and then the above-mentioned thick sheet passes through a powder tank, where the distance between the second surface layer of the thick sheet and the roughening adhesive layer powder in the powder tank is 10 mm. Through the mechanism of attraction between positive and negative charges, the second surface layer 3 of the thick sheet C adsorbs and closely accumulates to form a layer of propylene-ethylene copolymer powder. At the same time, because the surface temperature of the second surface layer of the thick sheet reaches 138-140 °C after the longitudinal stretching process, the second surface layer 3 of the thick sheet and the propylene-ethylene copolymer powder are welded together through the remaining temperature of the thick sheet, so that the propylene-ethylene copolymer powder is difficult to fall off and prevent failure, and a roughened thick sheet D is obtained; then the roughened thick sheet D first passes through the transverse stretching process J, and the gaps between the propylene-ethylene copolymer powders change from close packing to a well-arranged arrangement. In addition, the propylene-ethylene copolymer powder will be further welded to the second surface layer 3 of the thick sheet due to the temperature of the transverse stretching process J, and at the same time, the surface protrusion height decreases from 60 µm to 6 µm, and finally a roughening adhesive layer 4-1 in the form of concave and convex patterns is formed on the surface of the second surface layer 3; then through the traction-thickness measurement-corona-winding process K, a film semi-finished product E is obtained; the film semi-finished product E finally passes through the aging-slitting process L to obtain a film finished product F.

[0052] Among them, the main production equipment is a flat film method biaxially oriented polypropylene production line provided by BRUECKNER of Germany. Between the longitudinal stretching process and the transverse stretching process. The screw of the main extruder (for the support layer 2) is a single-screw extruder with a diameter of 150 mm and a length-diameter ratio of 33:1. The 2 auxiliary extruders (for the first surface layer 1 and the second surface layer 3 respectively) are single-screw extruders with a screw diameter of 120 mm and a length-diameter ratio of 30:1. The temperature of the extruder is 80 °C in the feeding section, 250 °C in other sections, the temperature of the filter, the flow channel and the die head is 250 °C, and the quenching (casting film) temperature is 30 °C. In the longitudinal stretching process H, the corresponding temperatures of the preheating zone, the stretching zone and the shaping zone passed by the first surface layer 1 and the second surface layer 3 are 140 °C, 138 °C and 140 °C respectively, and the longitudinal stretching ratio is 5.0. In the transverse stretching process J, the corresponding temperatures of the preheating zone, the stretching zone and the shaping zone passed by 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 300 m / min. The corona strength on the surface of the first surface layer 1 is 30 W·min / m 2。

[0053] The total thickness of the easy - to - stick and easy - to - tear in - mold label film in this embodiment is 105μm. The thickness of the first surface layer 1 is 1μm, the thickness of the support layer 2 is 97μm, the thickness of the second surface layer 3 is 1μm, and the thickness of the roughened adhesive layer 4 is about 6μm.

[0054] This embodiment also provides an application process for the easy - to - stick and easy - to - tear in - mold label film. Please refer to Figure 6 , the film product F (i.e., the easy - to - stick and easy - to - tear in - mold label film) first goes through the printing process P. The printing process P includes, but is not limited to, common processes such as flexographic printing, offset printing, and rotary printing, to obtain the in - mold label semi - finished product M. Then, it goes through the die - cutting process Q to be cut into several in - mold labels N. The several in - mold labels N are stacked (500 pieces per stack) and placed on the label rack (the structure of each in - mold label N includes, in sequence, a printing layer, the first surface layer 1, the support layer 2, the second surface layer 3, and the roughened adhesive layer 4). Through 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.

[0055] Comparative Example 1 This comparative example provides a traditional in - mold label film. Please refer to Figure 1 , which has a three - layer structure, including, in sequence, the first surface layer 1, the support layer 2, and the bonding layer 4 - 2.

[0056] Among them, the raw material formulas of each layer are as follows: First surface layer 1: 99.4wt% homopolypropylene (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) and 0.6wt% silica (average particle size is 5μm).

[0057] Support layer 2: 60wt% homopolypropylene (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), 25wt% titanium dioxide (chlorination process, rutile type, average particle size is 0.3μm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size is 1.2μm), and 0.5wt% glycerol monostearate.

[0058] Bonding layer 4 - 2: 100wt% ethylene - octene copolymer (octene content is 17wt%, density is 0.905g / cm 3, with a melting point of 97°C and a melt index of 7.5 g / 10 min. The melt index test conditions are: a melting temperature of 190°C and a load weight of 2.16 kg).

[0059] The preparation method of the traditional in-mold label film in this comparative example is basically the same as that of Example 1, except that: 1. Step (1) is cancelled, and in step (2), production is carried out with the raw materials of the first surface layer 1, the support layer 2, and the bonding layer 4-2 (replacing the second surface layer 3 in Example 1). At the same time, the roughening treatment process in step (2) is cancelled; 2. In the longitudinal stretching process, a Teflon coating is provided on the surface of the heating roller through which the bonding layer 4-2 passes, and the heating temperature of the heating roller is 105-110°C; 3. After the film is formed, a molding process for the bonding layer 4-2 needs to be added, making the surface of the bonding layer 4-2 uneven.

[0060] Specifically, the preparation method of the traditional in-mold label film in this comparative example includes the following steps: The raw materials of each layer of the first surface layer 1, the support layer 2, and the bonding layer 4-2 that have been screened are premixed separately according to the designed formula, stirred evenly, and after calculating the input ratio by weighing, they are fed into each extruder, and a cast sheet is formed after the extrusion-casting process; the cast sheet is formed into a thick sheet after the longitudinal stretching process. Among them, a Teflon coating is provided on the surface of the heating roller through which the bonding layer 4-2 passes to avoid scalding and damage caused by the processing temperature being higher than the melting point of the material used for the bonding layer 4-2, and the heating temperature of the heating roller is 105-110°C; then the thick sheet first passes through the transverse stretching process, the traction-thickness measurement-corona-reeling process to obtain a film semi-finished product; the film semi-finished product finally passes through the aging-slitting process to obtain a film finished product. A molding process is carried out on the surface of the bonding layer 4-2 of the film finished product, making the surface of the bonding layer 4-2 uneven.

[0061] Among them, the main production equipment is a flat film method biaxially oriented polypropylene production line provided by BRUECKNER of Germany. The screw of the main extruder (for the support layer 2) is a single-screw extruder with a diameter of 150 mm and a length-diameter ratio of 33:1. The two auxiliary extruders (for the first surface layer 1 and the bonding layer 4-2 respectively) are single-screw extruders with a screw diameter of 120 mm and a length-diameter ratio of 30:1. The temperature of the extruder is 80 °C in the feeding section, and 250 °C in other sections. The temperature of the filter, the runner and the die head is 250 °C, and the quenching (casting film) temperature is 30 °C. In the longitudinal stretching process H, the corresponding temperatures of the preheating zone, the stretching zone and the shaping zone passed by the first surface layer 1 are 140 °C, 138 °C and 140 °C respectively. The corresponding temperatures of the preheating zone, the stretching zone and the shaping zone passed by the bonding layer 4-2 are 110 °C, 105 °C and 110 °C respectively. And the surfaces of the heating rollers passed by the bonding layer 4-2 are all treated with a Teflon coating to avoid scalding and damage to the surface of the bonding layer 4-2. The longitudinal stretching ratio is 5.0. In the transverse stretching process J, the corresponding temperatures of the preheating zone, the stretching zone and the 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 300 m / min. The corona strength on the surface of the first surface layer 1 is 30 W·min / m 2 .

[0062] The total thickness of the traditional 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 bonding layer 4-2 is 6 μm.

[0063] The application process of the traditional in-mold label film of this comparative example is the same as that of Example 1. Please refer to Figure 6 , the film finished product F (i.e., the traditional in-mold label film) first goes through the printing process P, which includes but is not limited to common processes such as flexographic printing, offset printing, and rotary printing, to obtain the in-mold label semi-finished product M. Then, it goes through the die-cutting process Q to be cut into several in-mold labels N. The several in-mold labels N are stacked (500 pieces per stack) and placed on the 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 bonding layer 4-2 arranged in sequence). Through 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.

[0064] Example 2 This example provides an easy-to-apply and easy-to-tear in-mold label film. Please refer to Figure 3 , which has a four-layer structure, including a first surface layer 1, a support layer 2, a second surface layer 3, and a roughened bonding layer 4-1 arranged in sequence.

[0065] The formulations of the layers of the easy-to-apply and easy-to-remove in-mold label film in this example are the same as those in Example 1, except that: the proportion of calcium carbonate in the support layer 2 is 20 wt%, that is: Support layer 2: 54.5 wt% homopolypropylene (isotacticity 95%, density 0.905 g / cm 3 , melting point 163 °C, melt index 3 g / 10 min, melt index test conditions: melting temperature 230 °C, load weight 2.16 kg), 25 wt% titanium dioxide (chlorination process, rutile type, average particle size 0.3 µm), 20 wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2 µm) and 0.5 wt% glycerol monostearate.

[0066] The preparation method of the easy-to-apply and easy-to-remove in-mold label film in this example is the same as that in Example 1.

[0067] The total thickness and the thickness of each layer of the easy-to-apply and easy-to-remove in-mold label film in this example are the same as those in Example 1.

[0068] The application process of the easy-to-apply and easy-to-remove in-mold label film in this example is the same as that in Example 1.

[0069] Comparative Example 2 This comparative example provides an in-mold label film. Please refer to Figure 3 , which 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.

[0070] The formulations of the layers of the in-mold label film in this comparative example are the same as those in Example 1, except that: the proportion of calcium carbonate in the support layer 2 is 25 wt%, that is: Support layer 2: 49.5 wt% homopolypropylene (isotacticity 95%, density 0.905 g / cm 3 , melting point 163 °C, melt index 3 g / 10 min, melt index test conditions: melting temperature 230 °C, load weight 2.16 kg), 25 wt% titanium dioxide (chlorination process, rutile type, average particle size 0.3 µm), 25 wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2 µm) and 0.5 wt% glycerol monostearate.

[0071] The preparation method of the in-mold label film in this comparative example is the same as that in Example 1.

[0072] The total thickness and the thickness of each layer of the in-mold label film in this comparative example are the same as those in Example 1.

[0073] The application process of the in-mold label film in this comparative example is the same as that in Example 1.

[0074] Example 3 This embodiment provides an easy-to-apply and easy-to-remove in-mold label film. Please refer to Figure 3 , which has 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.

[0075] The formulations of each layer of the easy-to-apply and easy-to-remove in-mold label film in this embodiment are the same as those in Embodiment 1, except that: the proportion of titanium dioxide in the support layer 2 is 5wt%, that is: Support layer 2: 80wt% homopolypropylene (isotacticity 95%, density 0.905 g / cm 3 , melting point 163 °C, melt index 3 g / 10 min, melt index test conditions: melting temperature 230 °C, load weight 2.16 kg), 5wt% titanium dioxide (chlorination process, rutile type, average particle size 0.3 µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2 µm), and 0.5wt% glycerol monostearate.

[0076] The preparation method of the easy-to-apply and easy-to-remove in-mold label film in this embodiment is the same as that in Embodiment 1.

[0077] The total thickness and the thickness of each layer of the easy-to-apply and easy-to-remove in-mold label film in this embodiment are the same as those in Embodiment 1.

[0078] The application process of the easy-to-apply and easy-to-remove in-mold label film in this embodiment is the same as that in Embodiment 1.

[0079] Embodiment 4 This embodiment provides an easy-to-apply and easy-to-remove in-mold label film. Please refer to Figure 3 , which has 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.

[0080] The formulations of each layer of the easy-to-apply and easy-to-remove in-mold label film in this embodiment are the same as those in Embodiment 1, except that: the proportion of titanium dioxide in the support layer 2 is 30wt%, that is: Support layer 2: 55wt% homopolypropylene (isotacticity 95%, density 0.905 g / cm 3 , melting point 163 °C, melt index 3 g / 10 min, melt index test conditions: melting temperature 230 °C, load weight 2.16 kg), 30wt% titanium dioxide (chlorination process, rutile type, average particle size 0.3 µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size 1.2 µm), and 0.5wt% glycerol monostearate.

[0081] The preparation method of the easy-to-apply and easy-to-remove in-mold label film in this embodiment is the same as that in Embodiment 1.

[0082] The total thickness of the easy-to-apply and easy-to-remove in-mold label film in this example and the thickness of each layer are the same as those in Example 1.

[0083] The application process of the easy-to-apply and easy-to-remove in-mold label film in this example is the same as that in Example 1.

[0084] Comparative Example 3 This comparative example provides an in-mold label film. Please refer to Figure 3 , which 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.

[0085] The formulation of each layer of the in-mold label film in this comparative example is the same as that in Example 1, except that: the proportion of titanium dioxide in the support layer 2 is 4wt%, that is: Support layer 2: 81wt% homopolypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point is 163°C, melt index is 3g / 10min, melt index test conditions: melting temperature is 230°C, load weight is 2.16kg), 4wt% titanium dioxide (chlorination process, rutile type, average particle size is 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size is 1.2µm), and 0.5wt% glycerol monostearate.

[0086] The preparation method of the in-mold label film in this comparative example is the same as that in Example 1.

[0087] The total thickness of the in-mold label film in this comparative example and the thickness of each layer are the same as those in Example 1.

[0088] The application process of the in-mold label film in this comparative example is the same as that in Example 1.

[0089] Comparative Example 4 This comparative example provides an in-mold label film. Please refer to Figure 3 , which 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.

[0090] The formulation of each layer of the in-mold label film in this comparative example is the same as that in Example 1, except that: the proportion of titanium dioxide in the support layer 2 is 35wt%, that is: Support layer 2: 50wt% homopolypropylene (isotacticity is 95%, density is 0.905g / cm 3 , melting point is 163°C, melt index is 3g / 10min, melt index test conditions: melting temperature is 230°C, load weight is 2.16kg), 35wt% titanium dioxide (chlorination process, rutile type, average particle size is 0.3µm), 14.5wt% calcium carbonate (heavy calcium carbonate, average particle size is 1.2µm), and 0.5wt% glycerol monostearate.

[0091] The preparation method of the in-mold label film of this comparative example is the same as that of Example 1.

[0092] The total thickness and the thickness of each layer of the in-mold label film of this comparative example are the same as those of Example 1.

[0093] The application process of the in-mold label film of this comparative example is the same as that of Example 1.

[0094] Example 5 This example provides an easy-to-apply and easy-to-tear in-mold label film. Please refer to Figure 3 , which has 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 formula of each layer of the easy-to-apply and easy-to-tear in-mold label film of this example is the same as that of Example 1, except that: the roughened adhesive layer 4-1 is composed of maleic anhydride grafted propylene-ethylene copolymer, that is: Roughened adhesive layer 4-1: 100 wt% maleic anhydride grafted propylene-ethylene copolymer (maleic anhydride content is 1.0 wt%, ethylene content is 9 wt%, density is 0.879 g / cm 3 , melting point is 77 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0096] The preparation method of the in-mold label film of this example is basically the same as that of Example 1.

[0097] The total thickness and the thickness of each layer of the in-mold label film of this example are the same as those of Example 1.

[0098] The application process of the in-mold label film of this example is basically the same as that of Example 1, except that: the plastic part is a polyethylene terephthalate glycol plastic part, that is, finally a polyethylene terephthalate glycol plastic part O with an in-mold label is formed.

[0099] Example 6 This example provides an easy-to-apply and easy-to-tear in-mold label film. Please refer to Figure 3 , which has 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.

[0100] The formula of each layer of the easy-to-apply and easy-to-tear in-mold label film of this example is the same as that of Example 1, except that: the content of ethylene in the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 5 wt%, and the density is 0.887 g / cm 3 , melting point is 100 °C, that is: Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content is 5 wt%, density is 0.887 g / cm 3 , melting point is 100 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0101] The preparation method of the in-mold label film in this example is basically the same as that in Example 1.

[0102] The total thickness and the thickness of each layer of the in-mold label film in this example are the same as those in Example 1.

[0103] The application process of the in-mold label film in this example is the same as that in Example 1.

[0104] Comparative Example 5 This comparative example provides an easy-to-apply and easy-to-tear in-mold label film. Please refer to Figure 3 , which 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.

[0105] The formulation of each layer of the easy-to-apply and easy-to-tear in-mold label film in this comparative example is the same as that in Example 1, except that: the ethylene content in the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 4 wt%, and the density is 0.889 g / cm 3 , melting point is 103 °C, that is:[[]] 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 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

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

[0107] The total thickness and the thickness of each layer of the in-mold label film in this comparative example are the same as those in Example 1.

[0108] The application process of the in-mold label film in this comparative example is the same as that in Example 1.

[0109] Example 7 This example provides an easy-to-apply and easy-to-tear in-mold label film. Please refer to Figure 3 , which 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.

[0110] The formulation of each layer of the easy-to-apply and easy-to-peel in-mold label film in this example is the same as that in Example 1, except that: the ethylene content in the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 11 wt%, and the density is 0.873 g / cm 3 , and the melting point is 65 °C, that is: Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content is 11 wt%, density is 0.873 g / cm 3 , melting point is 65 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0111] The preparation method of the in-mold label film in this example is basically the same as that in Example 1.

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

[0113] The application process of the in-mold label film in this example is the same as that in Example 1.

[0114] Comparative Example 6 This comparative example provides an easy-to-apply and easy-to-peel in-mold label film. Please refer to Figure 3 , which has 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.

[0115] The formulation of each layer of the easy-to-apply and easy-to-peel in-mold label film in this comparative example is the same as that in Example 1, except that: the ethylene content in the propylene-ethylene copolymer in the roughened adhesive layer 4-1 is 16 wt%, and the density is 0.862 g / cm 3 , and the melting point is 54 °C, that is: Roughened adhesive layer 4-1: 100 wt% propylene-ethylene copolymer (ethylene content is 16 wt%, density is 0.862 g / cm 3 , melting point is 54 °C, melt index is 8 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0116] The preparation method of the in-mold label film in this comparative example is basically the same as that in Example 1.

[0117] The total thickness and the thickness of each layer of the in-mold label film in this comparative example are the same as those in Example 1.

[0118] The application process of the in-mold label film in this comparative example is the same as that in Example 1.

[0119] Performance evaluation The in-mold label films, in-mold labels, and plastic parts with in-mold labels of Examples 1-7 and Comparative Examples 1-6 were respectively subjected to the following performance evaluations: Roughness: The surface roughness of the roughened adhesive layer 4-1 or the bonding layer 4-2 of the in-mold label film (i.e., the other surface of the in-mold label film opposite to the surface of the first surface layer 1) is tested in accordance with the national standard GB / T 14234-1993. The testing instrument is a surface roughness meter (manufactured by Mitutoyo Corporation, Japan, model: SJ-210).

[0120] Normal temperature bonding strength: Stack two in-mold label films together, press them with a 10 kg weight, then place them in an oven at 60 °C for 30 min to simulate the transportation conditions in a container in summer. Finally, test the bonding strength between the two in-mold label films through a film bonding strength tester (manufactured by Dynisco Corporation, USA, model: D9047).

[0121] Coefficient of friction: The coefficient of friction of the roughened adhesive layer 4-1 or the bonding layer 4-2 of the in-mold label film (i.e., the other surface of the in-mold label film opposite to the surface of the first surface layer 1) is tested in accordance with the national standard GB / T 10006-2021. The testing instrument is a coefficient of friction tester (manufactured by Testing Machine, USA, model: 32-07-00-0003).

[0122] Heat shrinkage rate: The heat shrinkage rate of the in-mold label film is tested in accordance with the national standard GB / T 10003-2008. The testing temperature is 120 °C and the time is 2 minutes. The testing instrument is an electric blast drying oven (manufactured by Shanghai Yiheng Technology Co., Ltd., model: DHG-9075A).

[0123] Light transmittance: The light transmittance of the in-mold label film is tested in accordance with the national standard GB / T 2410-2008. The testing instrument is a direct reading haze meter (manufactured by Diffusion, UK, model: EEL 57D).

[0124] Surface resistance: The surface resistance of the roughened adhesive layer 4 or the bonding layer 4-1 of the in-mold label film (i.e., the other surface of the in-mold label film opposite to the surface of the first surface layer 1) is tested in accordance with the national standard GB / T 31838.3-2019. The testing instrument is a surface resistance meter (manufactured by SIMCO, Japan, model: ST-4).

[0125] Continuous sheet phenomenon: Bind 500 stacked in-mold labels (a stack) with a rubber band, press the stacked in-mold labels with a 10 kg weight, place them in an oven at 60 °C for 30 min, untie the rubber band, take out the in-mold labels through a manipulator, and observe the continuous sheet situation.

[0126] Heat seal strength: This test simulates the adhesion strength between the in-mold label and the plastic part after in-mold labeling. First, high-density polyethylene films and polyethylene terephthalate films with a thickness of 100 µm are obtained through a casting process. Then, using a heat sealer, the in-mold label is heat-sealed with the high-density polyethylene film or the polyethylene terephthalate film at 135 °C, 0.18 MPa, and for 1 second (the in-mold labels in Examples 1-4, 6, 7 and Comparative Examples 1-6 correspond to the high-density polyethylene film, and the in-mold label in Example 5 corresponds to the polyethylene terephthalate film). After that, the samples are left standing in the test environment for 3 minutes, and then the samples are cut into strips with a width of 15 mm and a length of 15 cm. Finally, the heat-sealed interface is peeled off, and according to the national standard GB / T 10006-2021, the heat seal strength is measured using a universal tensile machine.

[0127] Surface appearance: Visually inspect the appearance of the plastic part with the in-mold label to observe whether the roughened adhesion layer 4-1 or the roughened texture of the bonding layer 4-2 can be seen.

[0128] In-mold labeling yield: Count the proportion of the in-mold labels and plastic parts without air bubble abnormalities among 100 plastic parts with in-mold labels.

[0129] Room temperature manual peeling performance: Manually peel the in-mold label from the plastic part with the in-mold label and observe whether the in-mold label can be separated from the plastic part.

[0130] Please refer to Tables 1-5 for the test results: Table 1 Composition of each layer of the in-mold label film in Example 1 and Comparative Example 1 and performance test results

[0131] Table 2 Composition of each layer of the in-mold label film in Example 2 and Comparative Example 2 and performance test results

[0132] Table 3 Composition of each layer of the in-mold label film in Examples 3-4 and Comparative Examples 3-4 and performance test results

[0133] Table 4 Composition of each layer of the in-mold label film in Example 5 and performance test results

[0134] Table 5 Composition of each layer of the in-mold label film in Examples 6-7 and Comparative Examples 5-6 and performance test results

[0135] 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 treatment process is adopted, see Figure 3 , so that the second surface of the finally prepared easy-to-stick and easy-to-tear in-mold label film forms 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 an in-mold label, it can greatly reduce the effective contact area between the in-mold labels, avoiding the occurrence of the phenomenon of in-mold labels being connected; and during the stacking process of the in-mold labels, the texture morphology of the roughened adhesive layer will not be transferred to the printing layer, avoiding affecting the surface appearance of the printing layer. In addition, the easy-to-stick and easy-to-tear in-mold label film of Examples 1-7 is used in in-mold labeling after being made into in-mold labels, please refer to Figure 4 , which can not only make the in-mold label N and the plastic part O' effectively bonded without easily generating bubbles, but also make the in-mold label N easily peeled off from the plastic part O', achieving the technical effect of easy sticking and easy tearing.

[0136] 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 abnormal bubble problems, the in-mold labeling yield is relatively low, and it is difficult to peel off the in-mold label from the plastic part.

[0137] In the in-mold label film of Comparative Example 2, the amount of calcium carbonate added in the support layer 2 is too large, resulting in serious 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.

[0138] In the in-mold label film of comparative example 3, the addition amount of titanium dioxide in the support layer 2 is too low, resulting in a slightly larger 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 roughened morphology of the roughened adhesive layer can be visually observed, which can be easily mistaken for a labeling defect.

[0139] In the in-mold label film of Comparative Example 4, the amount of titanium dioxide added in the support layer 2 is too high, resulting in weak cohesive strength of the film, and stratification is easy to occur between the support layer and the first surface layer / the 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, part of the in-mold label material will remain on the surface of the plastic part, affecting the recycling of the plastic part.

[0140] For the in-mold label film of Comparative Example 5, the low ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer results in the inability to effectively bond the in-mold label to the plastic part 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 can be easily peeled off from the plastic part, and local positions of the in-mold label are likely to fall off due to factors such as process friction, temperature / altitude fluctuations, etc.

[0141] For the in-mold label film of Comparative Example 6, the high ethylene content of the propylene-ethylene copolymer in the roughened adhesive layer causes abnormal increases in the normal-temperature bonding force and the friction coefficient. After the in-mold label film of Comparative Example 5 is made into an in-mold label, a sticking-together phenomenon is likely to occur, reducing the yield of in-mold labeling.

[0142] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and improvements.

Claims

1. A preparation method of an easy-to-stick and easy-to-tear in-mold label film, characterized in that: 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 an ethylene-propylene copolymer or a maleic anhydride grafted ethylene-propylene copolymer; The preparation method of the easy-to-stick and easy-to-tear in-mold label film comprises the following steps: Grind the raw material of the roughened adhesive layer into a powder form to obtain the roughened adhesive layer powder, and through a high-voltage tip discharge process, make the surface of the roughened adhesive layer powder obtain static electricity of - / +(25 - 30) KV for standby; Respectively feed the raw materials of the first surface layer, the support layer and the second surface layer into the extruders corresponding to each layer, and form a cast sheet through an extrusion-casting process; The cast sheet undergoes a longitudinal stretching process to form a thick sheet; The thick sheet undergoes a roughening treatment process: make the roughened adhesive layer powder adsorb and weld on the surface of the second surface layer of the thick sheet to form a roughened treatment thick sheet; The roughened treatment thick sheet undergoes a transverse stretching process and a traction-thickness measurement-corona-winding process to obtain a film semi-finished product; The film semi-finished product undergoes an aging-slitting process to obtain a film finished product, that is, the easy-to-stick and easy-to-tear in-mold label film.

2. The preparation method of the easy-to-stick and easy-to-tear in-mold label film according to claim 1, characterized in that: The roughening treatment process comprises the following steps: through a high-voltage tip discharge process on the surface of the second surface layer of the thick sheet, make the surface of the second surface layer of the thick sheet obtain static electricity of + / -(25 - 30) KV; utilize the mechanism of attraction between positive and negative charges to make a layer of roughened adhesive layer powder adsorb on the surface of the second surface layer of the thick sheet, and utilize the residual temperature of the thick sheet after the longitudinal stretching process to make the roughened adhesive layer powder weld with the second surface layer of the thick sheet together to form the roughened treatment thick sheet.

3. The preparation method of the easy-to-apply and easy-to-tear in-mold label film according to claim 1, characterized in that: In the transverse stretching process, the transverse stretching ratio is 8 - 10.

4. The preparation method of the easy-to-apply and easy-to-remove in-mold label film according to claim 1, characterized in that: After the longitudinal stretching process, the temperature on the surface of the second surface layer of the thick sheet is 138 - 140 °C.

5. The preparation method of the easy-to-stick and easy-to-tear in-mold label film according to claim 1, characterized in that: The preparation method of the roughened adhesive layer powder is: cool the raw material of the roughened adhesive layer with liquid nitrogen and then place it in a grinding machine for grinding, and then screen it through a sieve shaker into a powder with an average particle size of 40 - 60 µm, that is, obtain the roughened adhesive layer powder.

6. The preparation method of the easy-to-stick and easy-to-tear in-mold label film according to claim 1, characterized in that: After obtaining the roughened adhesive layer powder, place the roughened adhesive layer powder in a powder tank, and then perform a high-voltage tip discharge process on the roughened adhesive layer powder in the powder tank; In the roughening treatment process, make the thick sheet pass through the powder tank, wherein the distance between the second surface layer of the thick sheet and the roughened adhesive layer powder in the powder tank is 10 - 20 mm.

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

8. The preparation method of the easy-to-apply and easy-to-tear in-mold labeling 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.

9. An easily attachable and detachable in-mold label film, characterized in that: It is prepared by the preparation method of the easy-to-apply and easy-to-tear in-mold label film as described in any one of claims 1-8.

10. Use of an easily - attachable and easily - detachable in - mold label film as described in claim 9 in in - mold labeling, characterized in that: After the easy-to-apply and easy-to-tear in-mold label film is made into an in-mold label, the in-mold label and the plastic part are integrated by an in-mold labeling process to form a plastic part with an in-mold label. When the roughened adhesive layer is composed of an ethylene-propylene copolymer, the plastic part is a polyethylene plastic part; when the roughened adhesive layer is composed of a maleic anhydride-grafted ethylene-propylene copolymer, the plastic part is a polyester plastic part or a polyamide plastic part.

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