JP4735271B2 - Light-transmitting paper and release paper - Google Patents

Description

The present invention relates to a paper having light transmissivity above a certain level, and in particular to light transmissivity suitable for a base material of release paper, and a release paper.

  Conventionally, pressure-sensitive adhesive sheets are generally composed of surface base materials, pressure-sensitive adhesives, and release paper, and can be used in a wide range of applications such as commercial, office, and home use, in the form of labels, seals, stickers, and emblems. Processed and used.

  The release paper can be classified into a polyethylene laminate type, a glassine type, a clay coat type, an aqueous resin coat type, a film base type, and the like. Among these, a polyethylene laminate type and a glassine type are widely used.

  The polyethylene laminate type is made by laminating polyethylene on the surface of the base paper for the purpose of preventing the penetration of release agents such as silicone into the base paper such as high-quality paper and kraft paper, or for the purpose of demonstrating the peeling performance effectively. , And a release agent layer provided thereon. The polyethylene laminate type has an advantage that the silicone (release agent) is completely retained on the polyethylene layer formed, and thus effectively exhibits the release performance. However, since polyethylene is laminated, it cannot be re-disaggregated and has the disadvantage that it cannot be recycled as a raw paper raw material.

  On the other hand, for the glassine type, raw materials such as softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), etc. are beaten and processed so as to be in the range of Canadian Standard Freeness (hereinafter referred to as CSF) 150 to 350 ml CSF. Further, a glassine paper obtained by densification with finishing equipment such as a super calender is provided with a release agent layer such as silicone. Therefore, the glassine type does not have a laminate layer, and thus has an advantage that it can be recycled as a raw paper raw material.

Furthermore, highly refined glassine paper is characterized by high light transmission. Due to such characteristics, glassine paper is particularly suitable for a release paper substrate.
As described above, the release paper becomes a pressure-sensitive adhesive sheet in combination with a surface base material and a pressure-sensitive adhesive, and is further processed into a label or the like. These labels and the like are often automatically affixed to the product and its outer container by a labeler in a product packaging process or the like, and a transmissive position detector is often used as a position detection means at that time. Therefore, if the release paper has a high light transmittance, the label position can be easily detected, and the working efficiency is good.

  In order to impart high light transparency to paper such as glassine paper, a lot of softwood bleached kraft pulp (NBKP), which has a characteristic that light transmittance is easily expressed by beating, is used as a raw material, or the beating degree is made higher. The method is taken.

However, the method using a lot of softwood bleached kraft pulp (NBKP) has a disadvantage that the formation of paper becomes worse.
Further, the method of increasing the beating degree has various drawbacks. In other words, large beating power is required and power costs are incurred, drainage is inferior, papermaking speed is not increased, productivity is inferior, dimensional change due to humidity change is large, disaggregation is inferior and recycled as waste paper pulp It is difficult to do so.

  Therefore, a method for obtaining high light transmittance without performing advanced beating processing has been proposed. For example, Patent Document 1 proposes improving light transmittance by applying a clarifying agent.

JP 2003-340976 A

  However, in the above proposal, there are drawbacks in that a lot of chemicals are used to develop transparency, so that costs and extra work steps are required. Furthermore, depending on the chemicals used, it is difficult to use as waste paper pulp. There are drawbacks such as those showing disaggregation and generating dirt in the paper making process.

  As a result of intensive studies to solve the above problems, the present inventors have a low α cellulose content as a raw material, that is, when using hardwood bleached kraft pulp with a large amount of hemicellulose or cellulose having a relatively low molecular weight, the swelling In addition, the fiber is easily crushed by the wet press due to the sticking action, and at the same time, the bonding area between the fibers is increased, the sheet density is increased, and as a result, the same effect as in the case of advanced beating is obtained, and the light transmittance is increased. The present invention has been found to be excellent, and the present invention has been completed. That is, the present invention adopts the following configuration.

The first of the present invention is bleached hardwood unbleached kraft pulp having a kappa number of 20 to 24, and is made of raw pulp containing 20% by weight or more of hardwood bleached kraft pulp having an α cellulose content of 90% or less, and has an opacity. It is a paper having light transmittance of 70% or less.

^2nd of this invention is the paper which has the light transmittance of 1st this invention whose basic weight is 20-100 g / m < ² >.

  3rd of this invention is the release paper which used the paper which has the light transmittance as described in any one of 1-2 of this invention as the base material.

  According to the present invention, it can be reused as waste paper pulp, has good formation, has light transmittance, and is particularly suitable as a base material for release paper, and has light transmittance excellent in productivity. It became possible to provide paper.

The light-transmitting paper of the present invention is made from a raw material containing 20% by mass or more, preferably 50% or more of hardwood bleached kraft pulp having an α-cellulose content of 90% or less in the total pulp.
As the raw material pulp other than the hardwood bleached kraft pulp having an α cellulose content of 90% or less, any pulp can be used as needed. For example, various chemical pulps such as softwood kraft pulp, or mechanical pulp In addition, waste paper pulp and the like can be appropriately mixed and used.
When the hardwood bleached kraft pulp having an α cellulose content of 90% or less is less than 20% by mass, it is difficult to obtain desired light transmittance.

In addition, as a method of making alpha cellulose content rate 90% or less, the method of selecting a kind with much hemicellulose, for example, acacia, is mentioned. Moreover, there exists a method of making the kappa number of the kraft pulp (LUKP) before bleaching high, specifically making it the range of 20-24. As a method of increasing the kappa number, specifically, a method of decreasing the cooking temperature is used.
By the way, in the case of softwood bleached kraft pulp, the effect of the fiber form on the light transmission was larger than the effect of the α cellulose content, and the effect of hardwood bleached kraft pulp was not observed.

Next, the pulp raw material is beaten. The beating is performed using a beater such as a beater, a Jordan, a conical refiner, a single disc refiner, a double disc refiner, a deluxe refiner, or the like. It is known that paper made from highly beaten pulp (small CSF) has higher light transmittance.
In the production of glassine paper used as a base material for release paper, the pulp is usually beaten in the range of 150 to 350 ml CSF, and sufficient light transmission cannot be obtained unless beaten to about 350 ml CSF. However, if the raw pulp of the present invention is used, the light transmittance of the paper is greatly improved even if the beating degree is the same. Therefore, if the beating is performed to a freeness of about 500 ml CSF, a sufficient effect can be obtained.
In this way, a paper with improved light transmission can be obtained with the same beating degree under the same conditions as in the prior art. On the other hand, if the light transmittance is comparable, it is possible to increase the freeness. As a result, reduction of beating power, improvement of papermaking speed by improvement of drainage, improvement of dimensional stability against humidity change, disaggregation It is possible to obtain effects such as improvement of

  It should be noted that the paper material used in the present invention may contain an internal additive such as a filler, a sizing agent, a yield improver, a drainage improver, a paper strength enhancer, and a dye depending on the desired paper quality. Can be added and mixed to prepare. The paper stock obtained as described above is further guided to a wire part through a screening process such as a screen and finished as paper through a dehydration process and a drying process.

  The paper obtained above can be further coated with other chemicals such as polyvinyl alcohol, starch, casein, and surface sizing agent on the surface as necessary. The method is not particularly limited. For example, there are various methods such as two-roll or metering blade type size press, gate roll, bill blade, short dwell coater, roll coater, air knife coater, blade coater, etc. It can be used as appropriate.

The paper-making method of the light-transmitting paper of the present invention is not particularly limited. For example, an acidic paper-making method in which the paper-making pH is around 4.5, a neutral paper-making method in which the paper-making pH is about 6 to 9 or the like is used. be able to. As the paper machine, known apparatuses such as a long net paper machine, a twin wire paper machine, a circular net paper machine, and a Yankee paper machine can be used as appropriate.
Further, the light transmission can be further increased by increasing the tension with a press or a machine calendar. Similarly, applying a pressure finish with an on-machine or off-machine super calender, soft calender or the like is extremely effective in improving the light transmittance. It should be noted that the pressure finishing is more effective when the moisture of the paper is raised by means such as humidification.

  The paper having optical transparency obtained by the present invention has excellent optical transparency, good formation, and good re-disaggregation that can be used as a raw material for recycled paper. Its application is optimal as a base paper for release paper used in adhesive sheets, but there are many other applications such as food packaging, pharmaceutical packaging, cups for cakes and chocolates, transparent windows for envelopes, etc. Can be used in the field of

When a release agent such as silicone is applied to the light-transmitting paper of the present invention and used as a base paper for release paper, a known resin such as polyethylene is laminated in advance to prevent the release agent from penetrating into the base paper. It is also possible to do it. However, since re-disaggregation cannot be performed by laminating, it is more preferable to prevent penetration by providing an undercoat layer mainly composed of polyvinyl alcohol, starch, casein or the like. It is also possible to apply the release agent directly on the paper surface.
The release paper obtained above can be processed into a pressure-sensitive adhesive sheet in combination with any surface base material and pressure-sensitive adhesive.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition,% in an Example and a comparative example shows the mass% unless there is particular notice.

Moreover, the measuring method used in the Example and the comparative example is as follows.
[Α-cellulose] Measured according to JIS P8101.
[Kappa Number] Measured according to JIS P 8211.
[Opacity] Based on JIS P 8149-2000, it was measured with a C / 2 light source using a spectral whiteness meter (manufactured by Suga Test Instruments Co., Ltd.).
[Formation] Visual evaluation was performed.

<Example 1>
Hardwood unbleached pulp obtained by digesting hardwood raw materials (eucalyptus 20%, acacia 80%) to a kappa number of 22.0 is ECF-bleached to a whiteness of 84.0%, and the α cellulose content is 88. 7% hardwood bleached kraft pulp was obtained. 50 parts of this pulp and 50 parts of softwood bleached kraft pulp are mixed to make a pulp slurry, beaten with a double disc refiner to 200 ml CSF, and further 1 part of cationic starch (trade name: P3Y, PIRAAB STARCH Co., Ltd.), 0.5 parts of rosin emulsion sizing agent (trade name: N-776, manufactured by Arakawa Chemical Co., Ltd.) and 2 parts of a sulfuric acid band were used as a stock.
This stock was made with a long mesh multi-cylinder paper machine and dried to obtain a base paper having a rice basis weight of 60 g / m ² . A 7% strength aqueous solution of polyvinyl alcohol resin (trade name: RS-2817SB, manufactured by Kuraray Co., Ltd.) was applied to the base paper with a size press device and dried again. The coating amount at this time was 1.2 g / m ² . Subsequently, the above-mentioned base paper was finished with a super calendar facility to obtain a paper having light transmittance according to the present invention.

<Example 2>
In Example 1, a paper having optical transparency was obtained in the same manner as in Example 1 except that the pulp slurry was beaten to be 410 ml CSF.

<Example 3>
Except that 100 parts of hardwood bleached kraft pulp used in Example 1 was made into a pulp slurry alone and beaten to become 203 ml CSF, paper having optical transparency was obtained in the same manner as Example 1.

<Example 4>
Example 1 except that 80 parts of hardwood bleached kraft pulp used in Example 1 and 20 parts of softwood bleached kraft pulp used in Example 1 were mixed to obtain a pulp slurry and beaten to become 203 ml CSF. Similarly, a paper having optical transparency was obtained.

<Example 5>
Example 1 except that 20 parts of hardwood bleached kraft pulp used in Example 1 and 80 parts of softwood bleached kraft pulp used in Example 1 were mixed to form a pulp slurry and beaten to become 202 ml CSF. Similarly, a paper having optical transparency was obtained.

<Comparative Example 1>
Hardwood unbleached pulp digested to a Kappa number of 18.5 (the same tree species used in Example 1) was ECF-bleached to a whiteness of 84.0%, and the α cellulose content was 91.8% hardwood bleached kraft pulp was obtained. A paper was prepared in the same manner as in Example 1 except that 50 parts of the pulp and 50 parts of the bleached kraft pulp used in Example 1 were mixed to obtain a pulp slurry, and the pulp slurry was beaten to become 201 ml CSF. Got.

<Comparative example 2>
Paper was obtained in the same manner as in Example 1 except that 100 parts of softwood bleached kraft pulp used in Example 1 was made into a pulp slurry and beaten to become 204 ml CSF.

As is clear from Table 1, the paper of the present invention exhibits good light transmission when subjected to high level beating, and also exhibits sufficient light transmission without high level beating. It is.
In addition, when only softwood bleached kraft pulp was used as the raw material, the light transmission was sufficient, but the formation was poor.

Claims (3)

Bleaching unbleached kraft pulp with a copper number of 20 to 24, consisting of raw material pulp containing 20% by mass or more of hardwood bleached kraft pulp with an α cellulose content of 90% or less, and having an opacity of 70% or less Characteristic light transmissive paper. The paper having light transmittance according to claim 1, wherein the basis weight is 20 to 100 g / m ² . A release paper, characterized in that the light-transmitting paper according to claim 1 is used as a base material.