JPH0419275B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a release sheet for labels, and in particular, it is temporarily attached to the adhesive layer surface of a label to protect the adhesive layer surface from the outside at all times, and is easily peeled off when the label is used. The present invention relates to a release sheet for labels which is adapted to expose . (Problems with the Prior Art) Conventionally, release sheets for labels have a film made of thermoplastic resin or the like formed on one or both sides of a paper sheet, and a film made of a thermoplastic resin or the like formed on at least one surface of the film to facilitate peeling from the label. Those that have been subjected to peeling treatment are used. Such a release sheet for labels is temporarily attached to the adhesive layer surface of the label on the side that has been subjected to the release treatment. Thereby, the adhesive layer surface of the label is always protected from the outside, and when the label is used, by peeling off the release sheet, the adhesive layer surface of the label can be exposed and the label can be adhered to the object. Incidentally, in most cases, such labels are temporarily attached to a release sheet as described above, and printing is applied to the front surface for various display purposes. Curling and the like occur, and printing misalignment becomes a problem especially in multicolor offset printing and silk printing. The occurrence of such dimensional changes, curling, waving, etc. is thought to be mainly due to the following causes. That is, the shape of cellulose fibers constituting paper is generally approximately 3 mm long and 30 microns wide for softwood, and approximately 1 mm long and 20 microns wide for hardwood. When such cellulose fibers are immersed in water, there is almost no elongation in the length direction, but about 10 to 30% elongation occurs in the width direction. This also means that the same degree of shrinkage will occur upon drying.
Furthermore, since paper is generally stretched in the longitudinal direction during the papermaking process, the fibers tend to be aligned in the longitudinal direction, and as a result, paper expands and contracts significantly in the lateral direction. The average moisture content of paper is approximately 8% at the standard state of 65RH%, but when wetting and drying are repeated during the process, such as in multi-color offset printing or silk printing, release sheets for labels are mainly used. As a result of repeated moisture absorption and dehumidification through the cutting surface of the sheet, this water absorption rate fluctuates, causing a large dimensional change in the lateral direction (width direction) of the sheet. Furthermore, if the distribution of cellulose fibers in the paper sheet constituting the release sheet for labels is not homogeneous, water absorption and drying of the moisture-absorbed paper sheet proceed unevenly, resulting in local moisture unevenness. As a result, variations occur in the degree of expansion and contraction of the sheet, resulting in curling and waving that are undesirable in terms of handling. Curling and waviness also occur due to the way the paper is rolled when it is left in a roll before being cut, and these tend to occur in a direction perpendicular to the grain of the paper. In the process of printing, especially multicolor printing, on labels with release sheets attached, the heat cycle of heating up to a maximum of about 180°C and subsequent cooling is repeated under humid conditions, making it difficult for labels to peel off. The fibers in the sheet undergo repeated drying and moisture absorption, and as a result, the sheet becomes significantly susceptible to the aforementioned dimensional changes, curling, waving, etc., and printing misalignment occurs. (Object of the Invention) The object of the present invention is to solve the problems of the prior art, to provide excellent dimensional stability and to prevent curling, waving, etc. as much as possible, and to provide a printing method for offset printing and silk printing on labels. It is an object of the present invention to provide a release sheet for labels that can stably perform processes such as printing. (Summary of the Invention) The present inventors have focused on the fact that as the moisture content of a release sheet for labels is reduced, the above-mentioned dimensional stability etc. are improved, and thereby the printing characteristics of the label are significantly improved. As a result of repeated experiments and research, it was discovered that the above objective could be fully achieved by adding a predetermined amount of inorganic powder that is poorly soluble in water and does not adsorb water to the cellulose fibers of the sheet. did. The release sheet for labels of the present invention has been completed based on the above findings, and is made by forming a thermoplastic resin coating on one or both sides of an inorganic sheet containing 50 to 85% by weight of inorganic powder and cellulose fibers. It is characterized in that the surface of at least one of the thermoplastic resin coatings is subjected to a peeling treatment. (Structure of the Invention) The present invention will be described in more detail below. The attached drawing is an explanatory diagram showing an example of a release sheet for labels according to the present invention. In the drawing, 1 is an inorganic sheet made by adding inorganic powder to cellulose fibers, and 2 and 3 are thermoplastic resins formed on both sides of the sheet. 4 is a polyethylene coating, and 4 is a release-treated layer made of silicone resin. The inorganic sheet 1 is formed by a normal paper making method. The inorganic powder has at least one component selected from the group consisting of polyvalent metals, their hydroxides, oxides, or various salts, and mixtures thereof, which is sparingly soluble in water and does not adsorb water. Preferably, natural or artificial inorganic powders are used. Specific examples of the components include:
For example, aluminum hydroxide, calcium carbonate,
Examples include kaolin, talc, and silica sand, but aluminum hydroxide or calcium carbonate is preferred in practice. In the present invention, the content of inorganic powder in the inorganic sheet is an important factor. That is, while the average moisture content of paper is about 8% under standard conditions of 65% humidity, the above-mentioned inorganic powder used in the present invention contains almost no water. Therefore, as the content of the inorganic powder increases, the moisture content of the inorganic sheet as a whole decreases, the influence of moisture on the cellulose fibers decreases, and the dimensional stability, waving and curling tendency of the sheet, etc. are improved. Furthermore, the inorganic powder mixed in interrupts the connections between individual cellulose fibers, suppresses changes in the dimensions and shape of the sheet, and furthermore makes the distribution of the sheet constituent materials more homogeneous. It is preferable to increase the content of. In the present invention, it is necessary that the content of the inorganic powder be approximately 50% or more based on the total weight of the inorganic sheet, and if the amount is less than that, the above-described purpose due to the inclusion of the inorganic material will not be substantially achieved. is not achieved. On the other hand, if the content of inorganic powder exceeds 85%, paper making becomes difficult, and the paper sheet loses its properties such as flexibility and strength, which may cause damage to the sheet during handling. The particle size of the inorganic powder is preferably 30μ or less, more preferably 1 to 20μ. If the particle size of the inorganic powder is too large, it will be difficult to form a homogeneous sheet, and if the particle size is too small, good fixing to the sheet will not be obtained. The inorganic sheet of the present invention is composed of the inorganic powder and fibers mainly composed of cellulose fibers. Examples of fibers other than cellulose fibers include synthetic fibers such as vinylon fibers for increasing the strength of the inorganic sheet and/or inorganic fibers such as glass fibers for increasing the tear strength of the inorganic sheet. The fibers other than cellulose fibers also have the effect of inhibiting the bonding between cellulose fibers and improving the dimensional stability of the sheet. The thermoplastic resin coatings 2 and 3 formed on one or both sides of the inorganic sheet 1 may be made of the same material as the thermoplastic resin coating used in ordinary release sheets for labels. Specific examples of such thermoplastic resins include polyethylene and polypropylene. In the illustrated example, a release treatment layer 4 made of silicone resin is provided on one side of thermoplastic resin coatings 2 and 3 formed on both surfaces of an inorganic sheet 1.
The material used for the peeling treatment is appropriately selected depending on the purpose from among materials that have good adhesion to the base sheet and low surface energy to the label adhesive. Preferred materials having such properties include known mold release agents such as organic silicone resins such as polydimethylsiloxane, fluorine resins such as polytetrafluoroethylene, and various long-chain alkane compounds. It will be done. Note that the degree of releasability of the release sheet to the label varies depending on the use, and it is not always necessary to use these mold release agents in the release treatment. (Embodiments of the Invention) Example 1 Thickness 0.14 with 80 and 50% by weight of aluminum hydroxide with an average particle size of 8μ, 1% by weight of glass fibers, and the balance wood fibers based on the total weight of the inorganic sheet.
mm inorganic sheets are manufactured using normal papermaking methods,
Samples of the obtained inorganic sheets were stored overnight under conditions of relative humidity of 90, 65 and 30%, and the moisture content and dimensional change rate in the lateral direction of the sheets before and after storage were measured. For comparison, a sheet of ordinary high-quality paper not containing aluminum hydroxide was also measured in the same manner. The results are shown in Tables 1 and 2. The dimensional change rate was expressed as an increase/decrease (%) based on the humidity of 65%.

【table】

[Table] Polyethylene coatings with a thickness of 15 μm were formed on both sides of these inorganic sheets and comparative sheets by a normal extrusion molding method, and a silicone resin was applied to the surface of one of the polyethylene coatings by baking. A release sheet was formed. Samples of these release sheets with different contents of aluminum hydroxide were immersed in water tanks, and then stored overnight in an environment with relative humidity of 90%, 65%, and 30%. The lateral dimension of the sample before and after storage was measured, and the relative dimensional change rate (%) was determined. The results are shown in Table 3.

[Front] A thin aluminum film is vapor-deposited on the surface of polyethylene terephthalate film, and an acrylic adhesive (solvent type) is applied to the back side to form a label base material.
The release-treated surfaces of the respective release sheets with different aluminum hydroxide contents were temporarily attached to the back adhesive layer side of the label base material to prepare label samples with release paper. Sample A: Label base material + release paper (Al(OH) ₃ 80wt
%) Sample B: Label base material + release paper (Al(OH) ₃ 50wt
%) Sample C: Label base material + release paper (usually high-quality paper) 100 sheets each of these label samples A, B, and C were printed by an offset printing machine [Offset Ector (Kohyosha)] at room temperature. Color printing (dark blue, blue) was applied and the curl and distortion of the sample was observed. Curl is J.TAPPI paper pulp test method No.16−77
Judgment was made based on the degree of curl specified in the "Paper Curl Test Method". As a result, no curling was observed in sample A (80wt% aluminum hydroxide) after printing each color.
In sample B (aluminum hydroxide 50 wt%), the degree of curl was 10 or less in all cases. Furthermore, virtually no distortion was observed in these samples A and B. On the other hand, in Comparative Sample C, a degree of curl of 10 to 30 was observed in some samples after printing in two colors, and distortion was observed in all samples after printing in each color. Furthermore, when forced drying was performed at 60℃ (2 to 3 hours) between the printing processes for each color, no substantial curls or distortions were observed in samples A and B, as in the case of natural drying. , in comparative sample C
The number of samples showing a curl degree of 10 or higher further increased, and the degree of distortion also increased, making it difficult to perform smooth printing operations. When five-color printing (blue, black, red, yellow, and green) was performed using an offset editor using each of the above samples A, B, and C, virtually no color shift was observed for samples A and B. , for sample C about 2~
Unacceptable color shift occurred on 3% of the sheets. Example 2 An inorganic sheet with a thickness of 0.18 mm containing 75% by weight of calcium carbonate with an average particle diameter of 12 μm, 1% by weight of glass fibers, and the balance of wood fibers, based on the total weight of the inorganic sheet, was produced using a normal papermaking method. Samples of the inorganic sheets were stored day and night at relative humidity of 90, 65, and 30%, and the moisture content and lateral dimensional change of the sheets before and after storage were measured. For comparison, a sheet of ordinary high-quality paper containing no calcium carbonate was also measured in the same manner. The results are shown in Tables 1 and 2. Dimensional change rate is humidity 65
It is expressed as an increase/decrease (%) based on the case of %.

【table】

[Table] Polyethylene coatings with a thickness of 15 μm were formed on both sides of these inorganic sheets and the comparative sheet by a normal extrusion method, and a silicone resin was applied to the surface of one of the polyethylene coatings by baking. A release sheet was formed. These calcium carbonate-containing release sheet samples and comparative samples were each immersed in a water tank, and then stored overnight in an environment with relative humidity adjusted to 90%, 65%, and 30%. The lateral dimension of the sample before and after storage was measured, and the relative dimensional change rate (%) was determined. The results are shown in Table 3.

[Table] Label samples with release paper were prepared in the same manner as in Example 1 above. Sample A: Label base material + release paper (CaCO ₃ 75wt%) Sample B: Label base material + release paper (usually high-quality paper) 100 sheets each of these label samples A and B were subjected to two tests under the same conditions as in Example 1. Color printing was performed, and curling and distortion of the sample were observed using the test method of Example 1. As a result, no curling was observed in Sample A (calcium carbonate 75 wt%) after printing each color, and no substantial distortion was observed. On the other hand, in Comparative Sample B, a degree of curl of 10 to 30 was observed in some samples after printing in two colors, and distortion was observed in all samples after printing in each color. Furthermore, when forced drying at 60°C was performed between the printing processes for each color, Sample A showed no substantial curls or distortions, as was the case with natural drying, whereas Comparative Sample B showed more than 10% curl or distortion. The number of samples exhibiting a degree of curl further increased, and the degree of distortion also increased, making it difficult to perform smooth printing operations. When five-color printing (blue, black, red, yellow, green) was performed using an offset editor using each of the above samples A and B, no color shift was observed for sample A, but no color shift was observed for sample B. Approximately 2-3% of the sheets experienced unacceptable color shift. (Effects of the Invention) As described above, according to the present invention, the moisture absorption and dehumidification of the inorganic powder, which occupies most of the inorganic sheet used as a release paper, is negligible compared to that of cellulose fibers. Even in an environment where drying and wetting are repeated as in the case of a printing process, the label integrated with the release paper undergoes almost no dimensional change. In addition, in the case of a normal paper sheet, cellulose fibers tend to expand and contract due to mutual connection, but in the present invention, the inorganic powder covers the surface of the cellulose fibers and partially blocks the connections, so the cellulose fibers are connected. The dimensional changes in the sheet due to this are extremely small. Furthermore, in the case of an inorganic sheet, since particulate inorganic powder is homogeneously present in the sheet, there is little variation in the degree of expansion and contraction due to local moisture unevenness, and therefore curling and waving are less likely to occur. Therefore, the release sheet for labels of the present invention can significantly reduce printing misalignment, which has been a problem in conventional printing processes such as offset printing and silk printing for multicolor printing, and can also prevent curling, which can be a problem when handling the sheet. Does not occur.

[Brief explanation of drawings]

The drawing is a sectional view showing an example of a release sheet for labels according to the present invention. 1... Inorganic sheet, 2, 3... Thermoplastic resin coating, 4... Peeling treatment layer.

Claims (1)

[Claims] 1. A thermoplastic resin coating is formed on one or both sides of an inorganic sheet containing 50 to 85% by weight of inorganic powder and cellulose fibers, and a peeling treatment is applied to at least one surface of the thermoplastic resin coating. A release sheet for labels characterized by being subjected to. 2. The inorganic powder is a natural or artificial inorganic powder containing at least one component that is sparingly soluble in water selected from the group consisting of polyvalent metals and their hydroxides, oxides, and salts. A release sheet for labels according to claim 1. 3. The release sheet for labels according to claim 2, wherein the inorganic powder mainly consists of aluminum hydroxide. 4. The release sheet for labels according to claim 2, wherein the inorganic powder mainly consists of calcium carbonate. 5. The release sheet for labels according to claim 1, wherein the inorganic sheet contains synthetic fibers and/or inorganic fibers in addition to cellulose fibers. 6. The release sheet for labels according to claim 5, wherein the inorganic fiber is glass fiber.