Transfer foil with relief structure

Abstract

The transfer foil, which is separably supported on a support, has a first resin layer, a second resin layer, and a relief-forming layer in the indicated sequence from the support side. The first resin layer is composed of an acrylic resin having a glass transition temperature Tg of at least 95°C. The second resin layer and the relief-forming layer are composed of mixtures of an acrylic resin with a cellulose ester resin in which a portion of the hydroxyl groups are urethane crosslinked. The melting point of the second resin layer is higher than the melting point of the relief-forming layer.

Description

Technical Field

[0001] The present invention relates to a transfer foil. In particular, the present invention relates to a transfer foil having a relief structure that exhibits an optical effect such as diffraction and requiring high durability. This application claims priority to Japanese Patent Application No. 2021-133833, filed in Japan on August 19, 2021, the content of which is incorporated herein by reference.

Background Art

[0002] As a means for transferring and adhering a relief structure such as a hologram or a diffraction grating to an article, a method of attaching in the form of a transfer foil is known. A transfer foil having a relief structure is configured by sequentially laminating a release layer, a relief forming layer having a relief structure such as a hologram or a diffraction grating, a reflective layer, and an adhesive layer on a support. As a method of attaching the transfer foil, thermal pressure transfer by hot stamping or thermal transfer by a thermal head roll is common.

[0003] First, in thermal pressure transfer and thermal transfer, the transfer foil is placed between a heated metal stamp or a thermal head roll and the transfer object. Next, after applying instantaneous (about 0.1 second to 1 second) pressing or heating by the stamp or the roll, the transfer foil is peeled off from the support. Generally, thermal pressure transfer is a transfer method mainly using pressure, with a heating temperature of 100°C to 120°C and an applied pressure of 300 Kg / cm 2 or so. Thermal transfer is a transfer method mainly using heat, with a heating temperature of 100°C to 120°C and an applied pressure of 100 Kg / cm 2 or so. Thermal pressure transfer has a higher applied pressure than thermal transfer and is a transfer method suitable when the surface of a transfer medium such as paper is not smooth.

[0004] Therefore, the transfer foil is made of a material having heat resistance and impact resistance so that the transfer foil itself is not damaged due to heat or pressure shock during transfer and attachment, or the attached transfer foil is not damaged by external heat or shock. In particular, heat resistance and impact resistance are important for the material of the relief structure forming layer in order to prevent damage to the relief structure, which has the function of producing optical effects. One problem with the material of the relief structure forming layer is that extremely high temperatures and high pressures are required when forming the irregularities of the relief structure. As a result, the forming process becomes difficult, and the accuracy of the relief structure formation decreases. Furthermore, imparting such heat resistance and impact resistance to the transfer foil comes with deterioration of transferability such as burrs and chips, so it is extremely difficult to achieve high levels of relief structure formation accuracy, durability against heat and pressure, and transferability all at the same time.

[0005] Patent Document 1 describes a method for using cellulose-based materials to improve the heat resistance and pressure resistance of transfer foils. Patent Document 1 also presents a method for incorporating a cellulose-based material with a high melting point into the release layer to prevent cracking of the relief structure caused by thermal transfer using a thermal head. However, the above method is not sufficiently effective in the case of hot stamping, where high pressure is applied instantaneously. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2016-60046 [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to achieve a high level of three things in transfer foil: precision in forming the relief structure, durability against heat and pressure, and transferability. [Means for solving the problem]

[0008] The present invention is a transfer foil that is detachably supported on a support. This transfer foil has, in order from the support side, a first resin layer, a second resin layer, and a relief-forming layer. The first resin layer is made of acrylic resin with a glass transition temperature (Tg) of 95°C or higher. The second resin layer and relief-forming layer are composed of a mixture of acrylic resin and cellulose ester resin in which some of the hydroxyl groups are crosslinked with urethane. The melting point of the second resin layer is higher than that of the relief-forming layer. [Effects of the Invention]

[0009] This invention achieves high levels of three aspects in transfer foil: precision in forming the relief structure, durability against heat and pressure, and transferability. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing a transfer foil according to an embodiment of the present invention. [Figure 2] This figure schematically shows the relationship between temperature and elastic modulus of the second resin layer and relief-forming layer in the present invention. [Figure 3] This table shows the evaluation results when the Tg of the acrylic resin in the first resin layer and the presence or absence of urethane crosslinking are changed. [Figure 4] This table shows the evaluation results when the mixing ratio of cellulose ester resin in the second resin layer is changed. [Figure 5] This shows the evaluation results when the mixing ratio of cellulose ester resin in the relief formation layer is changed. [Figure 6] This table shows the relationship between the mixing ratio of cellulose ester resin in the second resin layer and the relief-forming layer. [Figure 7] Figure 6 shows a list of detailed defects in each region and their suspected causes. [Modes for carrying out the invention]

[0011] The material composition described in the present invention brings an improvement effect in terms of three aspects: the shaping accuracy of the relief structure, the durability against heat and pressure, and the transferability. In the present invention, in view of the problem of achieving both contradictory physical properties of the relief structure shaping accuracy, the durability against heat and pressure, and the transferability in the transfer foil, a layer obtained by mixing an acrylic resin and a cellulose ester resin in which a part of the hydroxyl groups is urethane-crosslinked is devised, and attention is paid to the arrangement of a plurality of layers with different mixing ratios, leading to the solution of the problem.

[0012] The acrylic resin used for the first resin layer is selected such that its glass transition temperature Tg is 95°C or higher. The reason is to impart heat resistance to prevent the first resin layer from unintentionally melting during transfer to the transfer foil, which would increase the adhesiveness to the support surface side and cause transfer defects, and also to enhance the compatibility with the second resin layer to be laminated next. Such an acrylic resin, among the acrylic resins produced by the polymerization of methyl methacrylate (MMA), particularly has a structure in which there is no copolymerization or addition of butyl methacrylate (BMA), styrene, or other monomers in its functional group structure, or the amount is extremely small. Such an acrylic resin has particularly excellent transparency and dimensional stability, is very hard, has a high melting point, and protects the relief structure provided in the transfer foil from external physical elements.

[0013] In addition, the acrylic resin without copolymerization of other monomers as described above has very good compatibility with the cellulose ester resin. Furthermore, the acrylic resin (refractive index of about 1.49) and the cellulose ester (refractive index of about 1.46 - 1.50) have very close refractive indices. Therefore, the interface reflection between the first resin layer and the second resin layer in contact with it, and the light intensity attenuation due to intra-layer scattering inside the second resin layer are minimized. Moreover, the mixing of the cellulose ester and the acrylic resin reduces the adverse effects caused by the birefringence of the cellulose ester. The reduction of the above interface reflection, light intensity attenuation, or birefringence is very effective in the sense that it enables the optical effects brought about by the relief structure to be externally manifested without attenuation. The second resin layer and the relief forming layer are both a mixture of the above acrylic resin and a cellulose ester resin in which a part of the hydroxyl groups is urethane-crosslinked, and the melting point of the second resin layer is higher than that of the relief forming layer. By adopting such a layer structure, the following two effects can be obtained.

[0014] First, such a layer structure can improve the processing and shaping accuracy of the relief structure and impart very high heat resistance and pressure resistance to the transfer foil. The presence of the second resin layer, which has a higher melting point than the relief forming layer, which is a feature of the present invention, brings about a very effective durability effect. The second resin layer with a high melting point is in contact with the relief forming layer and is located between the relief forming layer and the first resin layer. Part of the external heat and pressure applied to the relief forming layer diffuses into the second resin layer with a high melting point, thereby reducing the thermal burden on the relief forming layer and imparting an effect that makes it difficult for the uneven relief structure to be destroyed by external heat and pressure. As a result, the heat resistance of the transfer foil against external factors during heat and pressure transfer or after pasting is significantly improved. Utilizing this, by increasing the melting point of the second resin layer, an effect can be obtained that the heat resistance of the transfer foil can be sufficiently maintained even if the melting point of the material constituting the relief forming layer is lowered. The relief forming layer using a material with a low melting point leads to a reduction in the processing temperature required for forming the relief structure, that is, ease of relief shaping processing, and it becomes easy to stably and favorably maintain the accuracy of the relief structure.

[0015] Second, such a layer structure can improve the heat resistance and pressure resistance of the transfer foil without deterioration of transfer suitability. The second effect is particularly realized by mixing an acrylic resin and a cellulose ester resin in which a part of the hydroxyl groups is urethane-crosslinked. Cellulose ester resin is produced by esterifying some of the hydroxyl groups in the glucose units, which are the repeating units that make up cellulose. It contains approximately 1-5% of hydroxyl groups that have not undergone esterification. Furthermore, cellulose ester resin generally forms a strong hydrogen bond network within and between molecular chains, resulting in a higher glass transition temperature (Tg: approximately 130-160°C) than acrylic resin (Tg: 95-105°C), and excellent heat resistance and impact resistance. On the other hand, it has poor thermoplasticity around the transfer temperature conditions (approximately 100-150°C for 0.1-1 seconds). This poor thermoplasticity can cause cracking of the transfer surface and transfer burrs in processes that involve instantaneous application of heat and pressure, such as the transfer of transfer foil. More specifically, when a transfer foil with a layer composed solely of cellulose ester resin is heat-pressurized, the temperature range during transfer (100-120°C) is lower than the Tg of cellulose ester resin (approximately 130-160°C). In other words, the cellulose ester resin layer is not partially melted and broken by heat, but rather the foil is transferred by the resin layer cracking and breaking due to pressure. Therefore, it is thought that defects such as cracks on the transfer surface and transfer burrs are likely to occur.

[0016] One feature of this invention is that by mixing with an acrylic resin and crosslinking the hydroxyl groups with urethane, thermoplasticity is imparted to the cellulose ester resin (Tg: approximately 130°C to 160°C) at a transfer temperature of around 100°C to 120°C. Imparting thermoplasticity at or near the transfer temperature suppresses the occurrence of cracks and transfer burrs during hot-press transfer, thereby improving transferability.

[0017] The effects of urethane conversion of hydroxyl groups will be explained in detail. One feature of this invention is that some of the hydroxyl groups in the cellulose ester resin are crosslinked with urethane. Cellulose ester that is not crosslinked with urethane is not easily entangled and is prone to softening. On the other hand, crosslinking with urethane allows the cellulose ester to obtain the necessary rigidity. The advantages of urethane crosslinking include, as mentioned above, the improvement of thermoplasticity in the transfer temperature range of the cellulose ester resin, which prevents cracking during transfer, and the reduction of burrs and chips during application due to resin shrinkage caused by urethane crosslinking. When the hydroxyl groups of cellulose ester resin are crosslinked with a suitable isocyanate, a urethane crosslinked network is formed within the rigid molecular network of the cellulose ester, consisting of approximately 1-5% by mass of hydroxyl groups. Changes in crosslink density and volume shrinkage due to this urethane crosslinking reaction result in residual stress and residual strain within the material after curing. As a result, the transfer foil is more easily separated from the support in accordance with the engraved shape during hot-press transfer. This effect is particularly effective in reducing transfer burrs.

[0018] Preferred isocyanates include toluene diisocyanate (TDI) systems having a benzene ring structure. TDI systems tend to generate internal residual stress and residual strain in the material after curing. Furthermore, it is desirable that the formed urethane groups have thermoplasticity (peak of decrease in flexural modulus) at a transfer temperature of around 100°C to 120°C.

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings as appropriate. Components that perform similar or equivalent functions are denoted by the same reference numerals throughout all drawings, and redundant descriptions are omitted.

[0020] Figure 1 is a schematic cross-sectional view showing a transfer foil according to an embodiment of the present invention. The transfer foil 2 shown in Figure 1 is provided on one side of the support 1 in a removable manner. The transfer foil 2 comprises, in order from the side closest to the support 1, a first resin layer 3, a second resin layer 4, a relief-forming layer 5, and an adhesive layer 7. Furthermore, a relief structure 6 and a reflective layer 8 are located between the relief-forming layer 5 and the adhesive layer 7.

[0021] [Support] Support 1 supports the transfer foil 2 until it is transferred to the transfer target. A plastic film can be used for support 1. Polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polypropylene (PP) can be used as the material forming the plastic film. Preferably, the film forming material is one that is resistant to deformation and deterioration due to the heat and pressure applied to support 1 during the formation of the transfer foil 2. In addition to plastic film, paper, synthetic paper, plastic multilayer paper, and resin-impregnated paper can also be used for support 1.

[0022] [First resin layer] The first resin layer 3 holds the transfer foil 2 from the support 1 until it is transferred to the transfer target. During transfer, heat, pressure, or a force that separates the transfer foil from the support 1 generated when the adhesive layer 7 adheres to the transfer target is applied to the first resin layer 3. This serves to separate the transfer foil 2 from the support 1. Furthermore, after transfer, it has the function of protecting the surface of the transfer foil 2 from damage caused by external heat or impact. In this embodiment, the material constituting the first resin layer 3 is an acrylic resin with a glass transition temperature Tg of 95°C or higher. Such an acrylic resin is one of the acrylic resins produced by polymerization of methyl methacrylate (MMA), and in particular, has a functional group structure in which butyl methacrylate (BMA), styrene, or other monomers are not present or are present in very small amounts. Acrylic resins having such a structure have particularly excellent transparency, are very hard, and have a high melting point, so they do not interfere with the optical effect of the relief structure. Furthermore, they provide durability to the transfer foil 2 against external physical elements. An example of a specific material is Dianaal BR-84 (Dianal is a registered trademark) manufactured by Mitsubishi Rayon Co., Ltd. (glass transition temperature 105°C, weight-average molecular weight Mw 120,000).

[0023] The first resin layer 3 may contain additives such as lubricants. Lubricants can include polyethylene powder, paraffin wax, silicone, waxes such as carnauba wax, or inorganic particles such as silica, or material degradation inhibitors. The amount of additive is preferably about 0.1 to 10 units, where the total weight solids content of the materials constituting the first resin layer 3 is 100 units. Furthermore, the first resin layer 3 and the support 1 do not necessarily have to be in direct contact. A new layer may be added between them to assist the function of the first resin layer 3. Specific examples of such additional layers include transferability-improving layers using wax, resin, or a sea-island structure of inorganic particles. The thickness of the first resin layer 3 is preferably about 0.2 μm to 3 μm.

[0024] [Second resin layer] The second resin layer 4 is located between the first resin layer 3 and the relief-forming layer 5, and imparts high heat resistance and pressure resistance to the transfer foil 2. The second resin layer 4 is composed of a mixture of an acrylic resin with a glass transition temperature Tg of 95°C or higher and a cellulose ester resin in which some of the hydroxyl groups are crosslinked with urethane, and the melting point of the second resin layer 4 is set to be higher than that of the relief-forming layer 5. In other words, when the second resin layer 4 and the relief-forming layer 5 use cellulose ester resins having the same glass transition temperature Tg, it can also be said that the proportion of cellulose ester resin in the second resin layer 4 is set to be higher than that of the relief-forming layer 5. This is because the glass transition temperature of cellulose ester resin (Tg: approximately 130°C to 160°C) is higher than that of acrylic resin (Tg: 95°C to 105°C). Therefore, the higher the mixing ratio of cellulose ester resin in the second resin layer 4, the closer the material composition of the second resin layer 4 becomes to that of cellulose ester resin, and the higher its melting point.

[0025] Examples of cellulose ester resins used in the second resin layer 4 include cellulose acetate resin, cellulose acetate butyrate resin, cellulose acetate propionate resin, and cellulose nitrate. Cellulose ester resin has hydroxyl groups at a weight ratio of 1-5%. In the present invention, crosslinking these hydroxyl groups with urethane improves transferability. This is thought to be because changes in the resin density and volume shrinkage within the layer due to the urethane crosslinking reaction result in residual stress and residual strain within the material, making it easier for the transfer foil to separate from the support according to the engraved shape during hot-press transfer. Cellulose ester resin with a high proportion of hydroxyl groups exhibits a high improvement in transferability, but at the same time, it leads to a deterioration in the resistance of the transfer foil 2 to organic solvents. Therefore, it is preferable to select an appropriate proportion of hydroxyl groups. In the present invention, the proportion of hydroxyl groups in the cellulose ester resin is about 1-3%. An example of a specific material is CAB-381-2 (glass transition temperature 133°C, weight-average molecular weight Mw 40000, hydroxyl group content 1.3%) manufactured by Eastman Chemical Co., Ltd. The hydroxyl group content mentioned above refers to the ratio of the amount of hydroxyl groups to the average molecular weight of the resin, and the unit is mass%. Examples of isocyanate compounds used for urethane crosslinking of hydroxyl groups include diisocyanates. Examples of diisocyanates include toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI). An example of a toluene diisocyanate product is Coronate 2030 (Coronate is a registered trademark) manufactured by Nippon Polyurethane Industries Co., Ltd. An example of a hexamethylene diisocyanate product is Takenate D-160N (Takenate is a registered trademark) manufactured by Mitsui Chemicals, Inc. From the viewpoint of facilitating the generation of residual stress and residual strain within the layer after the crosslinking reaction, diisocyanates having a benzene ring structure are preferred. Furthermore, toluene diisocyanate having a benzene ring structure may also be used. Since the amount of hydroxyl groups contained in the second resin layer 4 is very small, less than 5% by weight of the cellulose ester resin contained, in reality, many isocyanates react with other functional groups and become inactive before reacting with the target hydroxyl groups. Considering this, the amount of isocyanate required for urethane crosslinking to a sufficient degree to confirm the effect in the present invention is preferably such that the molar ratio of isocyanate to hydroxyl groups (NCO / OH ratio) is 1.5 (the amount of isocyanate is 1.5 times more than the amount of hydroxyl groups). This molar ratio can also be between 1.0 and 3.0. As an example of a specific material, Coronate 2030 (Coronate is a registered trademark) (quick-drying type, NCO content 8%, solids content 50%) manufactured by Nippon Polyurethane Industry Co., Ltd. can be cited. The number of functional groups in the urethane is preferably 2 to 10, more preferably 1 to 5. Particularly preferably 2 or 3.

[0026] [Relief cambium] The relief-forming layer 5 is provided so as to be in contact with the second resin layer 4. In this embodiment, the materials of the second resin layer 4 and the relief-forming layer 5 are the same, and the melting point of the relief-forming layer 5 is lower than that of the second resin layer 4. This configuration maintains the heat resistance of the transfer foil 2 and reduces the processing temperature required to form the relief structure 6, which will be described later, thus facilitating the relief shaping process. This makes it easier to maintain a stable and good accuracy of the relief structure 6. The acrylic resin and cellulose ester resin used in the relief-forming layer 5 and the second resin layer 4 must meet the conditions of the present invention, namely, the acrylic resin's Tg must be 95°C or higher. It is sufficient to use a cellulose ester resin in which some of the hydroxyl groups are crosslinked with urethane, and to ensure that the melting point of the relief-forming layer 5 is lower than that of the second resin layer 4; it is not necessary to use exactly the same materials. Therefore, for example, cellulose ester resins with different glass transition temperatures, molecular weights, or hydroxyl group amounts may be used in the second resin layer 4 and the relief-forming layer 5. However, in this case, it is necessary to select materials with care regarding compatibility to prevent clouding due to the mixing of each resin. The relief-forming layer 5 may contain additives such as lubricants to facilitate the shaping of the relief structure 6. Silicone-based or fluorine-based lubricants can be used. The amount of additive is preferably about 0.1 to 10 units, where the total weight solids content of the material constituting the relief-forming layer 5 is 100 units.

[0027] [Relief structure] The relief structure 6 is composed of fine irregularities. It has optical effects such as optical diffraction, selective reflection or anti-reflection, isotropic or anisotropic scattering, light focusing, and polarized reflection. As a result, it provides effects such as preventing counterfeiting and tampering and improving design aesthetics through visual inspection or mechanical detection. The relief structure 6 can be composed of one or more reliefs having different optical effects. The relief structure 6 is typically formed with a thickness-direction unevenness difference of 0.01 μm to 10 μm and a surface-extension period of 0.01 μm to 10 μm, either with a specific period or a random pattern.

[0028] [Reflective layer] The reflective layer 8 is a layer provided to allow easy observation of the optical effect of the relief structure 6. Suitable materials for the reflective layer 8 include aluminum and transparent ceramic materials such as zinc sulfide and titanium dioxide. Aluminum is inexpensive, yields a highly glossy and opaque film, and is easy to handle. Transparent ceramic materials have a high refractive index in visible light and are easy to process. The thickness of the reflective layer 8 is preferably 100 to 800 nm. The reflective layer 8 can be formed by methods such as vacuum deposition or sputtering.

[0029] [Adhesive layer] The adhesive layer 7 is provided to allow the transfer foil 2 to be attached to the object to be transferred. The adhesive layer 7 is inert at room temperature, but is activated by external factors such as heat and pressure, and exhibits an adhesive effect to the object to be transferred. As materials for the adhesive layer 7, thermoplastic resins, thermosetting resins, ultraviolet curable resins, and electron beam curable resins can be used. More specifically, modified acrylic resins, polyester resins, and urethane resins can be given as examples. Known printing methods such as gravure printing, flexographic printing, screen printing, and offset printing can be used to form the adhesive layer 7, the first resin layer 3, the second resin layer 4, and the relief-forming layer 5, but are not limited to the methods exemplified. The film thickness of each of the above-mentioned layers can be approximately 0.2 to 5 μm.

[0030] Figure 2 is a schematic diagram showing the relationship between temperature and elastic modulus of the second resin layer 4 and the relief-forming layer 5 in the present invention. Figure 2 shows the bending modulus (Kgf / cm²) on the vertical axis. 2Figure 2 schematically shows the temperature dependence of the flexural modulus of the second resin layer 4 and relief-forming layer 5, which are composed of a cellulose ester resin single layer, an acrylic resin single layer, and a mixture thereof, with the horizontal axis representing temperature (°C). Furthermore, the transfer condition region (the region with good transferability) and the heat-resistant region required for the transfer foil 2 are shown as rectangular regions specified by the temperature range and the range of flexural modulus. The present invention aims to realize a transfer foil having a temperature dependence of flexural modulus that includes both of these regions. In Figure 2, for clarity, the flexural modulus of the second resin layer 4 and relief-forming layer 5, which are composed of the material with the highest melting point in each layer of the transfer foil 2, are shown.

[0031] As shown in Figure 2, the flexural modulus of a single layer of cellulose ester resin and a single layer of acrylic resin decreases sharply due to thermal softening after the temperature approaches the glass transition temperature (Tg). In a comparison of the two, the cellulose ester resin has a generally higher flexural modulus than the acrylic resin. Furthermore, because its Tg is higher than that of the acrylic resin, it can be seen that the decrease in flexural modulus occurs in the high-temperature range compared to the acrylic resin.

[0032] The behavior of a single layer of cellulose ester resin overlaps with a portion of the required heat resistance range, thus possessing sufficient heat resistance. However, it does not overlap with the transfer condition range. This indicates that because the elastic modulus of cellulose ester resin hardly decreases at the transfer condition temperature, the layer is less likely to break apart during transfer. In other words, the transfer foil is less likely to be transferred in its original shape. On the other hand, the behavior of the acrylic resin single layer, contrary to that of the cellulose ester resin single layer, overlaps with the transfer condition region but does not overlap with the required heat resistance region. This indicates that while the transferability is good, it does not possess the heat resistance necessary for a transfer foil.

[0033] Based on the above findings, the inventors configured the second resin layer 4 and the relief-forming layer 5 with a mixture of acrylic resin and cellulose ester resin. As a result, they succeeded in creating a behavior for the second resin layer 4 and the relief-forming layer 5 that combines the advantages of both a single layer of acrylic resin and a single layer of cellulose ester resin. This made it possible to overlap the behavior of the second resin layer 4 and the relief-forming layer 5 with both the transfer condition region and the required heat-resistant region, as shown in Figure 2. In this embodiment, the second resin layer 4 and the relief-forming layer 5 exhibit good transferability because, in the transfer temperature range, the acrylic resin contained within the layers softens with heat, leading to a decrease in elastic modulus. Furthermore, at higher temperatures, the cellulose ester resin contained within the layers does not soften excessively, maintaining a constant elastic modulus, thus realizing a transfer foil with good heat resistance.

[0034] The present invention will be described in detail below with reference to specific examples. In the following examples, "parts" means parts by mass, and "ratio" means mass ratio.

[0035] Multiple samples with a layer structure similar to transfer foil 2 were prepared and evaluated, while changing some of the materials constituting the first resin layer 3, the second resin layer 4, and the relief-forming layer 5. Figures 3 to 5 show the contents of the prepared samples in a table. For the sample corresponding to transfer foil 2 in this embodiment, the label "Example" is added in addition to the sample number.

[0036] Figure 3 shows the materials and preparation procedure for sample number 1. (material) <Support 1> Lumirror 25T60 (Toray Industries, Inc.) <Acrylic resin used in the first resin layer 3> Mitsubishi Rayon Co., Ltd. Dianaal BR-84 (Tg=105℃) MMA copolymerization (multiple types of MMA monomers copolymerized) <Acrylic resin used for the second resin layer 4 and the relief-forming layer 5> Mitsubishi Rayon Co., Ltd. Dianaal BR-84 (Tg=105℃) MMA copolymerization <Cellulose ester resin used in the second resin layer 4 and the relief-forming layer 5> CAB-381-2 (Tg=133℃), manufactured by Eastman Chemical Co., Ltd. <Isocyanate used for hydroxyl group crosslinking of cellulose ester resin contained in the second resin layer 4 and relief-forming layer 5> Coronate 2030, manufactured by Nippon Polyurethane Industries Co., Ltd. <Reflection layer 8> aluminum <Adhesive layer 7> Modified olefin resin, 30 parts Urethane resin, 60 units Silica particles (longest diameter 10 μm) 10 parts Organic solvents, 900 copies

[0037] (Manufacturing procedure) <Method for providing a first resin layer 3, a second resin layer 4, a relief-forming layer 5, and an adhesive layer 7> Each material was dissolved or dispersed in an organic solvent to form an ink, which was then coated using gravure printing. <Method for providing the relief structure 6> A metal cylindrical plate is provided with a relief structure consisting of uneven shapes having a predetermined height and pitch, and the press pressure is 2 kgf / cm². 2 Then, the relief forming layer 5 was shaped by pressing it at a press temperature of 220°C and a press speed of 10 m / min to form the relief structure 6. <Method for providing a reflective layer 8> A reflective layer 8 was formed on the relief structure 6 using a vacuum deposition method. <Method for crosslinking hydroxyl groups of cellulose ester resin contained in the second resin layer 4 and the relief-forming layer 5 with urethane> After coating each layer, the samples were stored in a 60°C oven for 10 days to accelerate the urethane crosslinking reaction.

[0038] Samples 2 through 5, shown in Figure 3, differ from sample 1 in that the Tg of the acrylic resin in the first resin layer 3 is changed. The acrylic resins used are listed below. <Sample Number 2> Mitsubishi Rayon Co., Ltd. Dianaal BR-82 (Tg=95℃) MMA copolymerization <Sample number 3> Mitsubishi Rayon Co., Ltd. Dianaal BR-95 (Tg=80℃) MMA copolymerization with other monomers <Sample No. 4> Mitsubishi Rayon Co., Ltd. Dianaal BR-101 (Tg=50℃) MMA copolymerization with other monomers <Sample No. 5> Mitsubishi Rayon Co., Ltd. Dianaal BR-1122 (Tg=20℃) MMA copolymerization with other monomers Sample No. 6 was prepared in the same manner as Sample No. 1, except that it did not contain isocyanate (i.e., no urethane crosslinking).

[0039] Samples 7 through 14, shown in Figure 4, differ from sample 1 in that the mixing ratio of cellulose ester resin in the second resin layer 4 was changed. Samples 15 to 22, shown in Figure 5, are variations of sample 1 in which the mixing ratio of cellulose ester resin in the relief-forming layer 5 has been changed.

[0040] The evaluation items and methods used for each sample are described below. <Exterior> The appearance of the transfer foil 2 was observed visually from the support 1 side, and the transparency of the lamination of the first resin layer 3, the second resin layer 4, and the relief forming layer 5 was evaluated. If it was transparent, it was marked as ○ (good), and if it was cloudy or otherwise opaque, it was marked as × (poor). <Pressure resistance> An evaluation sample was prepared by transferring transfer foil 2 onto the transfer target (paper) using a hot stamping transfer machine. The transferred transfer foil 2 was visually inspected to evaluate whether or not cracks had formed. The transfer conditions were a transfer temperature of 110°C and a pressure of 300 kg / cm².2 The transfer time is 1 second. A score of ○ (good) was used if no cracks were observed, and a score of × (poor) was used if cracks were observed. <Heat resistance> After transferring the design onto the foil 2, an iron heated to 170°C was pressed against the surface of the foil 2 for 10 seconds, and the foil 2 was then visually inspected. The surface condition of the foil (the surface of the first resin layer 3) or the relief structure 6 was evaluated for any damage. A "good" (○) rating was given if there was no change compared to before the iron was applied. Specific examples of defects (×) are described in the table. Note that when the iron is heated to 170°C for about 10 seconds, the foil temperature is heated to around 130°C. In other words, the foil temperature does not reach the embossing temperature, thus preventing damage to the surface condition of the transfer foil or the relief structure 6. <Relief structure precision> The relief structure of the metal cylinder used for processing and the relief structure 6 formed on the relief-forming layer 5 were compared in terms of unevenness height, pitch, and shape. A result of 90% or more (a difference of less than 10% relative to the metal cylinder) was considered good (○). <Transferability> An evaluation sample was prepared by transferring transfer foil 2 onto a transfer target (paper) using a hot stamping transfer machine with a circular imprint shape. The transferred transfer foil 2 was visually observed, and the maximum length of the portion that differed from the circular shape (transfer burr) was evaluated. The measurement was taken from the point of contact of the circular contour to the point furthest from the transfer burr. The vertical transfer conditions were a transfer temperature of 110°C and a pressure of 300 kg / cm². 2 The transcription time was 1 second. Five samples were evaluated for each sample number and rated on a three-point scale as follows. ○ (good): Maximum transfer burr length is less than 1 mm in all samples. △ (fair): Transfer burrs of 1 mm or more are observed in some samples. × (bad): Transfer burrs of 1 mm or more are observed in all samples.

[0041] In Figure 3, samples 1 and 2 showed good results in all evaluation items, while samples 3 through 5 showed inferior results in appearance and heat resistance. Regarding appearance, it is thought that the presence of copolymers of other monomers in the acrylic resin worsened the resin compatibility and caused clouding. The poor heat resistance was thought to be due to the acrylic resin having too low a Tg (temperature). In samples 4-5, the transfer burrs were large. This is thought to be because the acrylic resin's Tg was too low, causing the first resin to melt due to the heat generated during the transfer process.

[0042] In Figure 3, comparing the evaluation results of sample numbers 1 and 6, transfer cracks occurred in sample number 6 during the pressure resistance evaluation. Furthermore, the transferability evaluation results for sample number 6 were poor.

[0043] In Figure 4, with the exception of samples 11-13, poor results were obtained in one of the following items: pressure resistance, heat resistance, relief structure accuracy, or transferability. When the cellulose ester resin mixing ratio of the second resin layer 4 was small (samples 7-9), it is thought that the second resin layer 4 had insufficient heat resistance due to the small proportion of cellulose ester resin. In the case of sample 10, since the proportion of cellulose ester resin in the second resin layer 4 and the relief forming layer 5 was the same, there was no difference in melting point (or difference in the temperature dependence of the elastic modulus) between the two layers. It is thought that the fact that these two layers essentially became one thick layer is the reason why the size of the transfer burr increased. On the other hand, in the case of sample 14, it can be estimated that the deterioration of pressure resistance and transferability was caused by the cellulose ester resin mixing ratio of the second resin layer 4 being too large.

[0044] In Figure 5, with the exception of samples 16-19, poor results were obtained in either heat resistance, relief structure accuracy, or transferability. When the cellulose ester resin mixing ratio of the relief-forming layer 5 was small (sample number 15), it is thought that the heat resistance of the relief-forming layer 5 was insufficient due to the small proportion of cellulose ester resin. In the case of samples 20-22, it is thought that the deterioration of relief structure accuracy and transferability was caused by either the same proportion of cellulose ester resin in the second resin layer 4 and the relief-forming layer 5 (sample number 20), or by the proportion of cellulose ester resin being too high (sample numbers 21-22).

[0045] Figure 6 is a matrix table summarizing the results shown in Figures 3 to 5 based on the cellulose ester resin mixing ratios of the second resin layer 4 and the relief-forming layer 5, respectively. For areas with poor evaluation results, regions that are thought to be due to similar causes are grouped as A to F, and the estimated causes for each region are summarized in Figure 7. According to Figure 6, the mixing ratio of cellulose ester resin in the second resin layer 4 is 40% to 90%, and the mixing ratio in the relief-forming layer 5 is 10% to 60%. Furthermore, the mixing ratio of cellulose ester resin in the second resin layer 4 is greater than the mixing ratio of cellulose ester resin in the relief-forming layer 5. The above conditions are considered to be the conditions for obtaining the best evaluation results.

[0046] (Invention 1) A transfer foil that is detachably supported on a support, The transfer foil has, in order from the support side, a first resin layer, a second resin layer, and a relief-forming layer. The first resin layer is composed of an acrylic resin having a glass transition temperature Tg of 95°C or higher. The second resin layer and the relief-forming layer are composed of a mixture of the acrylic resin and a cellulose ester resin in which some of the hydroxyl groups are crosslinked with urethane. The melting point of the second resin layer is higher than the melting point of the relief-forming layer. Transfer foil.

[0047] (Invention 2) The aforementioned acrylic resin is a polymer in which only methyl methacrylate (MMA) monomers are polymerized. The transfer foil described in Invention 1.

[0048] (Invention 3) The mixing ratio of the cellulose ester resin in the second resin layer is greater than the mixing ratio of the cellulose ester resin in the relief forming layer. A transfer foil according to Invention 1 or Invention 2.

[0049] (Invention 4) The cellulose ester resin comprises at least one of cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate. A transfer foil according to any one of Inventions 1 to 3.

[0050] (Invention 5) The mixing ratio of the cellulose ester resin is 40% to 90% in the second resin layer and 10% to 60% in the relief-forming layer. A transfer foil according to any one of Inventions 1 to 4.

[0051] (Invention 6) The urethane crosslink has a benzene ring, A transfer foil according to any one of Inventions 1 to 5. [Industrial applicability]

[0052] The transfer foil according to the present invention, taking advantage of its characteristics, can be used in transfer foils that have a relief structure and require high durability, such as securities, banknotes, ID cards, and passports. [Explanation of Symbols]

[0053] 1 Support 2 Transfer foil 3. First resin layer 4. Second resin layer 5. Relief-forming layer

Claims

1. A transfer foil that is detachably supported on a support, The transfer foil has, in order from the support side, a first resin layer, a second resin layer, and a relief-forming layer. The first resin layer is composed of an acrylic resin having a glass transition temperature Tg of 95°C or higher. The second resin layer and the relief-forming layer are composed of a mixture of the acrylic resin and a cellulose ester resin in which some of the hydroxyl groups are crosslinked with urethane. The melting point of the second resin layer is higher than the melting point of the relief-forming layer. Transfer foil.

2. The aforementioned acrylic resin is a polymer in which only methyl methacrylate (MMA) monomers are polymerized. The transfer foil according to claim 1.

3. The mixing ratio of the cellulose ester resin in the second resin layer is greater than the mixing ratio of the cellulose ester resin in the relief forming layer. The transfer foil according to claim 1 or 2.

4. The cellulose ester resin comprises at least one of cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate. The transfer foil according to claim 1 or 2.

5. The mixing ratio of the cellulose ester resin is 40% to 90% in the second resin layer and 10% to 60% in the relief forming layer. The transfer foil according to claim 1 or 2.

6. The urethane crosslink has a benzene ring, The transfer foil according to claim 1 or 2.

Images